AC BRIDGE CIRCUITS

AC Bridge Circuits

Bridge circuit
As we saw with DC measurement circuits, the circuit configuration known as a bridge can be a very useful way to measure unknown values of resistance. This is true with AC as well, and we can apply the very same principle to the accurate measurement of unknown impedances.
Detector, null Null detector Null meter
To review, the bridge circuit works as a pair of two-component voltage dividers connected across the same source voltage, with a null-detector meter movement connected between them to indicate a condition of "balance" at zero volts:

Any one of the four resistors in the above bridge can be the resistor of unknown value, and its value can be determined by a ratio of the other three, which are "calibrated," or whose resistances are known to a precise degree. When the bridge is in a balanced condition (zero voltage as indicated by the null detector), the ratio works out to be this:

One of the advantages of using a bridge circuit to measure resistance is that the voltage of the power source is irrelevant. Practically speaking, the higher the supply voltage, the easier it is to detect a condition of imbalance between the four resistors with the null detector, and thus the more sensitive it will be. A greater supply voltage leads to the possibility of increased measurement precision. However, there will be no fundamental error introduced as a result of a lesser or greater power supply voltage unlike other types of resistance measurement schemes.
Null detector, AC bridge
Impedance bridges work the same, only the balance equation is with complex quantities, as both magnitude and phase across the components of the two dividers must be equal in order for the null detector to indicate "zero." The null detector, of course, must be a device capable of detecting very small AC voltages. An oscilloscope is often used for this, although very sensitive electromechanical meter movements and even headphones (small speakers) may be used if the source frequency is within audio range.
Headphones, as sensitive null detector
One way to maximize the effectiveness of audio headphones as a null detector is to connect them to the signal source through an impedance-matching transformer. Headphone speakers are typically low-impedance units (8 W), requiring substantial current to drive, and so a step-down transformer helps "match" low-current signals to the impedance of the headphone speakers. An audio output transformer works well for this purpose:

Using a pair of headphones that completely surround the ears (the "closed-cup" type), I've been able to detect currents of less than 0.1 mA with this simple detector circuit. Roughly equal performance was obtained using two different step-down transformers: a small power transformer (120/6 volt ratio), and an audio output transformer (1000:8 ohm impedance ratio). With the pushbutton switch in place to interrupt current, this circuit is usable for detecting signals from DC to over 2 MHz: even if the frequency is far above or below the audio range, a "click" will be heard from the headphones each time the switch is pressed and released.
Connected to a resistive bridge, the whole circuit looks like this:

Listening to the headphones as one or more of the resistor "arms" of the bridge is adjusted, a condition of balance will be realized when the headphones fail to produce "clicks" (or tones, if the bridge's power source frequency is within audio range) as the switch is actuated.
When describing general AC bridges, where impedances and not just resistances must be in proper ratio for balance, it is sometimes helpful to draw the respective bridge legs in the form of box-shaped components, each one with a certain impedance:

Again, it must be stressed that the impedance quantities in the above equation must be complex, accounting for both magnitude and phase angle. It is insufficient that the impedance magnitudes alone be balanced; without phase angles in balance as well, there will still be voltage across the terminals of the null detector and the bridge will not be balanced.
Bridge circuits can be constructed to measure just about any device value desired, be it capacitance, inductance, resistance, or even "Q." As always in bridge measurement circuits, the unknown quantity is always "balanced" against a known standard, obtained from a high-quality, calibrated component that can be adjusted in value until the null detector device indicates a condition of balance. Depending on how the bridge is set up, the unknown component's value may be determined directly from the setting of the calibrated standard, or derived from that standard through a mathematical formula.
A couple of simple bridge circuits are shown below, one for inductance and one for capacitance:

Bridge, symmetrical
Simple "symmetrical" bridges such as these are so named because they exhibit symmetry (mirror-image similarity) from left to right. The two bridge circuits shown above are balanced by adjusting the calibrated reactive component (Ls or Cs). They are a bit simplified from their real-life counterparts, as practical symmetrical bridge circuits often have a calibrated, variable resistor in series or parallel with the reactive component to balance out stray resistance in the unknown component. But, in the hypothetical world of perfect components, these simple bridge circuits do just fine to illustrate the basic concept.
Wien bridge circuit Bridge, Wien
An example of a little extra complexity added to compensate for real-world effects can be found in the so-called Wien bridge, which uses a parallel capacitor-resistor standard impedance to balance out an unknown series capacitor-resistor combination. All capacitors have some amount of internal resistance, be it literal or equivalent (in the form of dielectric heating losses) which tend to spoil their otherwise perfectly reactive natures. This internal resistance may be of interest to measure, and so the Wien bridge attempts to do so by providing a balancing impedance that isn't "pure" either:

Being that there are two standard components to be adjusted (a resistor and a capacitor) this bridge will take a little more time to balance than the others we've seen so far. The combined effect of Rs and Cs is to alter the magnitude and phase angle until the bridge achieves a condition of balance. Once that balance is achieved, the settings of Rs and Cs can be read from their calibrated knobs, the parallel impedance of the two determined mathematically, and the unknown capacitance and resistance determined mathematically from the balance equation (Z1/Z2 = Z3/Z4).
It is assumed in the operation of the Wien bridge that the standard capacitor has negligible internal resistance, or at least that resistance is already known so that it can be factored into the balance equation. Wien bridges are useful for determining the values of "lossy" capacitor designs like electrolytics, where the internal resistance is relatively high. They are also used as frequency meters, because the balance of the bridge is frequency-dependent. When used in this fashion, the capacitors are made fixed (and usually of equal value) and the top two resistors are made variable and are adjusted by means of the same knob.
An interesting variation on this theme is found in the next bridge circuit, used to precisely measure inductances.

Maxwell-Wien bridge circuit Bridge, Maxwell-Wien
This ingenious bridge circuit is known as the Maxwell-Wien bridge (sometimes known plainly as the Maxwell bridge), and is used to measure unknown inductances in terms of calibrated resistance and capacitance. Calibration-grade inductors are more difficult to manufacture than capacitors of similar precision, and so the use of a simple "symmetrical" inductance bridge is not always practical. Because the phase shifts of inductors and capacitors are exactly opposite each other, a capacitive impedance can balance out an inductive impedance if they are located in opposite legs of a bridge, as they are here.
Another advantage of using a Maxwell bridge to measure inductance rather than a symmetrical inductance bridge is the elimination of measurement error due to mutual inductance between two inductors. Magnetic fields can be difficult to shield, and even a small amount of coupling between coils in a bridge can introduce substantial errors in certain conditions. With no second inductor to react with in the Maxwell bridge, this problem is eliminated.
For easiest operation, the standard capacitor (Cs) and the resistor in parallel with it (Rs) are made variable, and both must be adjusted to achieve balance. However, the bridge can be made to work if the capacitor is fixed (non-variable) and more than one resistor made variable (at least the resistor in parallel with the capacitor, and one of the other two). However, in the latter configuration it takes more trial-and-error adjustment to achieve balance, as the different variable resistors interact in balancing magnitude and phase.
Unlike the plain Wien bridge, the balance of the Maxwell-Wien bridge is independent of source frequency, and in some cases this bridge can be made to balance in the presence of mixed frequencies from the AC voltage source, the limiting factor being the inductor's stability over a wide frequency range.
There are more variations beyond these designs, but a full discussion is not warranted here. General-purpose impedance bridge circuits are manufactured which can be switched into more than one configuration for maximum flexibility of use.
A potential problem in sensitive AC bridge circuits is that of stray capacitance between either end of the null detector unit and ground (earth) potential. Because capacitances can "conduct" alternating current by charging and discharging, they form stray current paths to the AC voltage source which may affect bridge balance:

The problem is worsened if the AC voltage source is firmly grounded at one end, the total stray impedance for leakage currents made far less and any leakage currents through these stray capacitances made greater as a result:

Wagner earth
One way of greatly reducing this effect is to keep the null detector at ground potential, so there will be no AC voltage between it and the ground, and thus no current through stray capacitances. However, directly connecting the null detector to ground is not an option, as it would create a direct current path for stray currents, which would be worse than any capacitive path. Instead, a special voltage divider circuit called a Wagner ground or Wagner earth may be used to maintain the null detector at ground potential without the need for a direct connection to the null detector.

The Wagner earth circuit is nothing more than a voltage divider, designed to have the voltage ratio and phase shift as each side of the bridge. Because the midpoint of the Wagner divider is directly grounded, any other divider circuit (including either side of the bridge) having the same voltage proportions and phases as the Wagner divider, and powered by the same AC voltage source, will be at ground potential as well. Thus, the Wagner earth divider forces the null detector to be at ground potential, without a direct connection between the detector and ground.
There is often a provision made in the null detector connection to confirm proper setting of the Wagner earth divider circuit: a two-position switch, so that one end of the null detector may be connected to either the bridge or the Wagner earth. When the null detector registers zero signal in both switch positions, the bridge is not only guaranteed to be balanced, but the null detector is also guaranteed to be at zero potential with respect to ground, thus eliminating any errors due to leakage currents through stray detector-to-ground capacitances:

REVIEW:
AC bridge circuits work on the same basic principle as DC bridge circuits: that a balanced ratio of impedances (rather than resistances) will result in a "balanced" condition as indicated by the null-detector device.
Null detectors for AC bridges may be sensitive electromechanical meter movements, oscilloscopes (CRT's), headphones (amplified or unamplified), or any other device capable of registering very small AC voltage levels. Like DC null detectors, its only required point of calibration accuracy is at zero.
AC bridge circuits can be of the "symmetrical" type where an unknown impedance is balanced by a standard impedance of similar type on the same side (top or bottom) of the bridge. Or, they can be "nonsymmetrical," using parallel impedances to balance series impedances, or even capacitances balancing out inductances.
AC bridge circuits often have more than one adjustment, since both impedance magnitude and phase angle must be properly matched to balance.
Some impedance bridge circuits are frequency-sensitive while others are not. The frequency-sensitive types may be used as frequency measurement devices if all component values are accurately known.
A Wagner earth or Wagner ground is a voltage divider circuit added to AC bridges to help reduce errors due to stray capacitance coupling the null detector to ground.

SINGLE PHASE

Single-phase

Depicted above is a very simple AC circuit. If the load resistor's power dissipation were substantial, we might call this a "power circuit" or "power system" instead of regarding it as just a regular circuit. The distinction between a "power circuit" and a "regular circuit" may seem arbitrary, but the practical concerns are definitely not.
One such concern is the size and cost of wiring necessary to deliver power from the AC source to the load. Normally, we do not give much thought to this type of concern if we're merely analyzing a circuit for the sake of learning about the laws of electricity. However, in the real world it can be a major concern. If we give the source in the above circuit a voltage value and also give power dissipation values to the two load resistors, we can determine the wiring needs for this particular circuit:

83.33 amps for each load resistor adds up to 166.66 amps total circuit current. This is no small amount of current, and would necessitate copper wire conductors of at least 1/0 gage. Such wire is well over 1/4 inch in diameter, weighing over 300 pounds per thousand feet. Bear in mind that copper is not cheap either! It would be in our best interest to find ways to minimize such costs if we were designing a power system with long conductor lengths.
One way to do this would be to increase the voltage of the power source and use loads built to dissipate 10 kW each at this higher voltage. The loads, of course, would have to have greater resistance values to dissipate the same power as before (10 kW each) at a greater voltage than before. The advantage would be less current required, permitting the use of smaller, lighter, and cheaper wire:

Now our total circuit current is 83.33 amps, half of what it was before. We can now use number 4 gage wire, which weighs less than half of what 1/0 gage wire does per unit length. This is a considerable reduction in system cost with no degradation in performance. This is why power distribution system designers elect to transmit electric power using very high voltages (many thousands of volts): to capitalize on the savings realized by the use of smaller, lighter, cheaper wire.
However, this solution is not without disadvantages. Another practical concern with power circuits is the danger of electric shock from high voltages. Again, this is not usually the sort of thing we concentrate on while learning about the laws of electricity, but it is a very valid concern in the real world, especially when large amounts of power are being dealt with. The gain in efficiency realized by stepping up the circuit voltage presents us with increased danger of electric shock. Power distribution companies tackle this problem by stringing their power lines along high poles or towers, and insulating the lines from the supporting structures with large, porcelain insulators.
At the point of use (the electric power customer), there is still the issue of what voltage to use for powering loads. High voltage gives greater system efficiency by means of reduced conductor current, but it might not always be practical to keep power wiring out of reach at the point of use the way it can be elevated out of reach in distribution systems. This tradeoff between efficiency and danger is one that European power system designers have decided to risk, all their households and appliances operating at a nominal voltage of 240 volts instead of 120 volts as it is in North America. That is why tourists from America visiting Europe must carry small step-down transformers for their portable appliances, to step the 240 VAC (volts AC) power down to a more suitable 120 VAC.
Is there any way to realize the advantages of both increased efficiency and reduced safety hazard at the same time? One solution would be to install step-down transformers at the end-point of power use, just as the American tourist must do while in Europe. However, this would be expensive and inconvenient for anything but very small loads (where the transformers can be built cheaply) or very large loads (where the expense of thick copper wires would exceed the expense of a transformer).
An alternative solution would be to use a higher voltage supply to provide power to two lower voltage loads in series. This approach combines the efficiency of a high-voltage system with the safety of a low-voltage system:

Voltage "polarity," AC Polarity, AC Polarity, AC
Notice the polarity markings (+ and -) for each voltage shown, as well as the unidirectional arrows for current. For the most part, I've avoided labeling "polarities" in the AC circuits we've been analyzing, even though the notation is valid to provide a frame of reference for phase. In later sections of this chapter, phase relationships will become very important, so I'm introducing this notation early on in the chapter for your familiarity.
The current through each load is the same as it was in the simple 120 volt circuit, but the currents are not additive because the loads are in series rather than parallel. The voltage across each load is only 120 volts, not 240, so the safety factor is better. Mind you, we still have a full 240 volts across the power system wires, but each load is operating at a reduced voltage. If anyone is going to get shocked, the odds are that it will be from coming into contact with the conductors of a particular load rather than from contact across the main wires of a power system.
There's only one disadvantage to this design: the consequences of one load failing open, or being turned off (assuming each load has a series on/off switch to interrupt current) are not good. Being a series circuit, if either load were to open, current would stop in the other load as well. For this reason, we need to modify the design a bit:
Hot conductor Neutral conductor

Split-phase
Instead of a single 240 volt power supply, we use two 120 volt supplies (in phase with each other!) in series to produce 240 volts, then run a third wire to the connection point between the loads to handle the eventuality of one load opening. This is called a split-phase power system. Three smaller wires are still cheaper than the two wires needed with the simple parallel design, so we're still ahead on efficiency. The astute observer will note that the neutral wire only has to carry the difference of current between the two loads back to the source. In the above case, with perfectly "balanced" loads consuming equal amounts of power, the neutral wire carries zero current.
Notice how the neutral wire is connected to earth ground at the power supply end. This is a common feature in power systems containing "neutral" wires, since grounding the neutral wire ensures the least possible voltage at any given time between any "hot" wire and earth ground.
An essential component to a split-phase power system is the dual AC voltage source. Fortunately, designing and building one is not difficult. Since most AC systems receive their power from a step-down transformer anyway (stepping voltage down from high distribution levels to a user-level voltage like 120 or 240), that transformer can be built with a center-tapped secondary winding:

If the AC power comes directly from a generator (alternator), the coils can be similarly center-tapped for the same effect. The extra expense to include a center-tap connection in a transformer or alternator winding is minimal.
Boosting, AC voltage sources Bucking, AC voltage sources Here is where the (+) and (-) polarity markings really become important. This notation is often used to reference the phasings of multiple AC voltage sources, so it is clear whether they are aiding ("boosting") each other or opposing ("bucking") each other. If not for these polarity markings, phase relations between multiple AC sources might be very confusing. Note that the split-phase sources in the schematic (each one 120 volts with polarity marks (+) to (-) just like series-aiding batteries can alternatively be represented as such:

If we mark the two sources' common connection point (the neutral wire) with the same polarity mark (-), we must express their relative phase shifts as being 180o apart. Otherwise, we'd be denoting two voltage sources in direct opposition with each other, which would give 0 volts between the two "hot" conductors. Why am I taking the time to elaborate on polarity marks and phase angles? It will make more sense in the next section!
Single-phase
Power systems in American households and light industry are most often of the split-phase variety, providing so-called 120/240 VAC power. The term "split-phase" merely refers to the split-voltage supply in such a system. In a more general sense, this kind of AC power supply is called single phase because both voltage waveforms are in phase, or in step, with each other.
The term "single phase" is a counterpoint to another kind of power system called "polyphase" which we are about to investigate in detail. Apologies for the long introduction leading up to the title-topic of this chapter. The advantages of polyphase power systems are more obvious if one first has a good understanding of single phase systems.
REVIEW:
Single phase power systems are defined by having an AC source with only one voltage waveform.
A split-phase power system is one with multiple (in-phase) AC voltage sources connected in series, delivering power to loads at more than one voltage, with more than two wires. They are used primarily to achieve balance between system efficiency (low conductor currents) and safety (low load voltages).
Split-phase AC sources can be easily created by center-tapping the coil windings of transformers or alternators.

ELECTRIC POWER

ELECTRIC POWER

electric power energy dissipated in an electrical or electronic circuit or device per unit of time. The electrical energy supplied by a current to an appliance enables it to do work or provide some other form of energy such as light or heat. Electric power is usually measured in watts, kilowatts (1,000 watts), and megawatts (1,000,000 watts). The amount of electrical energy used by an appliance is found by multiplying its consumed power by the length of time of operation. The units of electrical energy are usually watt-seconds (joules), watt-hours, or kilowatt-hours. For commercial purposes the kilowatt-hour is the unit of choice.

Sources of Electrical Energy

Electrical energy occurs naturally, but seldom in forms that can be used. For example, although the energy dissipated as lightning exceeds the world's demand for electricity by a large factor, lightning has not been put to practical use because of its unpredictability and other problems. Generally, practical electric-power-generating systems convert the mechanical energy of moving parts into electrical energy. While systems that operate without a mechanical step do exist, they are at present either excessively inefficient or expensive because of a dependence on elaborate technology. While some electric plants derive mechanical energy from moving water (hydroelectric power), the vast majority derive it from heat engines in which the working substance is steam. Roughly 89% of power in the United States is generated this way. The steam is generated with heat from combustion of fossil fuels or from nuclear fission.

Steam as an Energy Source

The conversion of mechanical energy to electrical energy can be accomplished with an efficiency of about 80%. In a hydroelectric plant, the losses occur in the turbines, bearings, penstocks, and generators. The basic limitations of thermodynamics fix the maximum efficiency obtainable in converting heat to electrical energy. The necessity of limiting the temperature to safe levels also helps to keep the efficiency down to about 41% for a fossil-fuel plant. Most nuclear plants use low-pressure, low-temperature steam operation, and have an even lower efficiency of about 30%. Nuclear plants have been able to achieve efficiency up to 40% with liquid-metal cooling. It is thought that by using magnetohydrodynamic "topping" generators in conjunction with normal steam turbines, the efficiency of conventional plants can be raised to close to 50%. These devices remove the restrictions imposed by the blade structure of turbines by using the steam or gasses produced by combustion as the working fluid.

Environmental Concerns

The heat generated by an electric-power plant that is not ultimately converted into electrical energy is called waste heat. The environmental impact of this waste is potentially catastrophic, especially when, as is often the case, the heat is absorbed by streams or other bodies of water. Cooling towers help to dispose waste heat into the atmosphere. Associated with nuclear plants, in addition to the problem of waste heat, are difficulties attending the disposal and confinement of reaction products that remain dangerously radioactive for many thousands of years and the adjustment of such plants to variable demands for power. Public concern about such issues—fueled in part by the accidents at the Three Mile Island nuclear plant in Harrisburg Pennsylvania in 1979, and the nuclear plant explosion in the Soviet Union at Chernobyl in 1986—forced the U.S. government to introduce extensive safety regulations for nuclear plants. Partly because of those regulations, nuclear plants are proving to be une- conomical. Several are being shut down and replaced by conventionally fueled plants.

Alternative Energy Sources

Fuel cells develop electricity by direct conversion of hydrogen, hydrocarbons, alcohol, or other fuels, with an efficiency of 50% to 60%. Although they have been used to produce electric power in space vehicles and some terrestrial locations, several problems have kept them from being widely used. Most important, the catalyst, which is an important component of a fuel cell, especially one that is operating at around room temperature, is very expensive. Controlled nuclear fusion could provide a virtually unlimited source of heat energy to produce steam in generating plants; however, many problems surround its development, and no appreciable contribution is expected from this source in the near future.

Solar energy has been recognized as a feasible alternative. It has been suggested that efficient collection of the solar energy incident on 14% of the western desert areas of the United States would provide enough electricity to satisfy current demands. Two main solar processes could be used. Photovoltaic cells convert sunlight directly into electrical energy. Another method would use special coatings that absorb sunlight readily and emit infrared radiation slowly, making it possible to heat fluids to 1,000°F (540°C) by solar radiation. The heat in turn can be converted to electricity. Some of this heat would be stored to allow operation at night and during periods of heavy cloud cover. The projected efficiency of such a plant would be about 30%, but this fairly low efficiency must be balanced against the facts that energy from the sun costs nothing and that the waste heat from such a plant places virtually no additional burden on the environment. The principal problem with this and other exotic systems for generating electricity is that the time needed for their implementation may be considerable.

Windmills, once widely used for pumping water, have become viable for electric-power generation because of advances in their design and the development of increasingly efficient generators. Windmill "farms," at which rows of windmills are joined together as the source of electrical energy, serve as a significant, though minor, source of electrical energy in coastal and plains areas. However, the vagaries of the wind make this a difficult solution to implement on a large scale.

Transmission of Electrical Energy

Electrical energy is of little use unless it can be made available at the place where it is to be used. To minimize energy losses from heating of conductors and to economize on the material needed for conductors, electricity is usually transmitted at the highest voltages possible. As modern Transformers are virtually loss free, the necessary steps upward or downward in voltage are easily accomplished. Transmission lines for alternating current using voltages as high as 765,000 volts are not uncommon. For voltages higher than this it is advantageous to transmit direct current rather than alternating current. Recent advances in rectifiers, which turn alternating current into direct current, and inverters, which convert direct into alternating, have made possible transmission lines that operate at 800,000 volts and above. Such lines are still very expensive, however.

Electric utilities are tied together by transmission lines into large systems called power grids. They are thus able to exchange power so that a utility with a low demand can assist another with a high demand to help prevent a blackout, which involves the partial or total shutdown of a utility. Under such a system a utility experiencing too great a load, as when peak demand coincides with equipment failure, must remove itself from the grid or endanger other utilities. During periods in which demand exceeds supply a utility can reduce the power drawn from it by lowering its voltage. These voltage reductions, which are normally of 3%, 5%, or 8%, result in power reductions, or brownouts, of about 6%, 10%, or 15%, causing inefficient operation of some electrical devices. The power distribution system, because of its generation of low-frequency electromagnetic fields, has been suggested as a possible source of health problems.

Reactive Power

Reactive power is a concept used by engineers to describe the loss of power in a system arising from the production of electric and magnetic fields. Although reactive loads such as inductors and capacitors dissipate no power, they drop voltage and draw current, which creates the impression that they actually do. This "imaginary power" or "phantom power" is called reactive power. It is measured in a unit called Volt-Amps-Reactive (VAR). The actual amount of power being used, or dissipated, is called true power, and is measured in the unit of watts. The combination of reactive power and true power is called apparent power, and it is the product of a circuit's voltage and current. Apparent power is measured in the unit of Volt-Amps (VA). Devices which store energy by virtue of a magnetic field produced by a flow of current are said to absorb reactive power; those which store energy by virtue of electric fields are said to generate reactive power. Reactive power is significant because it must be provided and maintained to insure continuous, steady voltage on transmission networks. Reactive power thus is produced for maintenance of the system and not for end-use consumption. Power losses incurred in transmission from heat and electromagnetic emissions are included in the total reactive power requirement as are the needs of power hungry devices, such as electric motors, electromagnetic generators, and alternators. This power is supplied for many purposes by condensers, capacitors, and similar devices, which can react to changes in current flow by releasing energy to normalize the flow. If elements of the power grid cannot get the reactive power they need from nearby sources, they will pull it across transmission lines and destabilize the grid. In this way, poor management of reactive power can cause major blackouts.

Bibliography

See K. W. Li and A. P. Priddy, Power Plant System Design (1985); L. F. Drbal et al., Power Plant Engineering (1996).

Voltage regulation

Voltage regulation

Voltage regulation

As we saw in a few SPICE analyses earlier in this chapter, the output voltage of a transformer varies some with varying load resistances, even with a constant voltage input. The degree of variance is affected by the primary and secondary winding inductances, among other factors, not the least of which includes winding resistance and the degree of mutual inductance (magnetic coupling) between the primary and secondary windings. For power transformer applications, where the transformer is seen by the load (ideally) as a constant source of voltage, it is good to have the secondary voltage vary as little as possible for wide variances in load current.

The measure of how well a power transformer maintains constant secondary voltage over a range of load currents is called the transformer's voltage regulation. It can be calculated from the following formula:

"Full-load" means the point at which the transformer is operating at maximum permissible secondary current. This operating point will be determined primarily by the winding wire size (ampacity) and the method of transformer cooling. Taking our first SPICE transformer simulation as an example, let's compare the output voltage with a 1 kW load versus a 200 W load (assuming that the 200 W load will be our "full load" condition). Recall if you will that our constant primary voltage was 10.00 volts AC:

freq          v(3,5)      i(vi1)

6.000E+01     9.962E+00   9.962E-03    Output with 1k ohm load

freq          v(3,5)      i(vi1)

6.000E+01     9.348E+00   4.674E-02    Output with 200 ohm load

Notice how the output voltage decreases as the load gets heavier (more current). Now let's take that same transformer circuit and place a load resistance of extremely high magnitude across the secondary winding to simulate a "no-load" condition:

transformer

v1 1 0 ac 10 sin

rbogus1 1 2 1e-12

rbogus2 5 0 9e12

l1 2 0 100

l2 3 5 100

k l1 l2 0.999

vi1 3 4 ac 0

rload 4 5 9e12

.ac lin 1 60 60

.print ac v(2,0) i(v1)

.print ac v(3,5) i(vi1)

.end

freq          v(2)        i(v1)

6.000E+01     1.000E+01   2.653E-04

freq          v(3,5)      i(vi1)

6.000E+01     9.990E+00   1.110E-12   Output with (almost) no load

So, we see that our output (secondary) voltage spans a range of 9.990 volts at (virtually) no load and 9.348 volts at the point we decided to call "full load." Calculating voltage regulation with these figures, we get:

Incidentally, this would be considered rather poor (or "loose") regulation for a power transformer. Powering a simple resistive load like this, a good power transformer should exhibit a regulation percentage of less than 3%. Inductive loads tend to create a condition of worse voltage regulation, so this analysis with purely resistive loads was a "best-case" condition.

There are some applications, however, where poor regulation is actually desired. One such case is in discharge lighting, where a step-up transformer is required to initially generate a high voltage (necessary to "ignite" the lamps), then the voltage is expected to drop off once the lamp begins to draw current. This is because discharge lamps' voltage requirements tend to be much lower after a current has been established through the arc path. In this case, a step-up transformer with poor voltage regulation suffices nicely for the task of conditioning power to the lamp.

Another application is in current control for AC arc welders, which are nothing more than step-down transformers supplying low-voltage, high-current power for the welding process. A high voltage is desired to assist in "striking" the arc (getting it started), but like the discharge lamp, an arc doesn't require as much voltage to sustain itself once the air has been heated to the point of ionization. Thus, a decrease of secondary voltage under high load current would be a good thing. Some arc welder designs provide arc current adjustment by means of a movable iron core in the transformer, cranked in or out of the winding assembly by the operator. Moving the iron slug away from the windings reduces the strength of magnetic coupling between the windings, which diminishes no-load secondary voltage and makes for poorer voltage regulation.

Ferroresonant transformer Transformer, ferroresonant

No exposition on transformer regulation could be called complete without mention of an unusual device called a ferroresonant transformer. "Ferroresonance" is a phenomenon associated with the behavior of iron cores while operating near a point of magnetic saturation (where the core is so strongly magnetized that further increases in winding current results in little or no increase in magnetic flux).

Tank circuit

While being somewhat difficult to describe without going deep into electromagnetic theory, the ferroresonant transformer is a power transformer engineered to operate in a condition of persistent core saturation. That is, its iron core is "stuffed full" of magnetic lines of flux for a large portion of the AC cycle so that variations in supply voltage (primary winding current) have little effect on the core's magnetic flux density, which means the secondary winding outputs a nearly constant voltage despite significant variations in supply (primary winding) voltage. Normally, core saturation in a transformer results in distortion of the sinewave shape, and the ferroresonant transformer is no exception. To combat this side effect, ferroresonant transformers have an auxiliary secondary winding paralleled with one or more capacitors, forming a resonant circuit tuned to the power supply frequency. This "tank circuit" serves as a filter to reject harmonics created by the core saturation, and provides the added benefit of storing energy in the form of AC oscillations, which is available for sustaining output winding voltage for brief periods of input voltage loss (milliseconds' worth of time, but certainly better than nothing).

In addition to blocking harmonics created by the saturated core, this resonant circuit also "filters out" harmonic frequencies generated by nonlinear (switching) loads in the secondary winding circuit and any harmonics present in the source voltage, providing "clean" power to the load.

Ferroresonant transformers offer several features useful in AC power conditioning: constant output voltage given substantial variations in input voltage, harmonic filtering between the power source and the load, and the ability to "ride through" brief losses in power by keeping a reserve of energy in its resonant tank circuit. These transformers are also highly tolerant of excessive loading and transient (momentary) voltage surges. They are so tolerant, in fact, that some may be briefly paralleled with unsynchronized AC power sources, allowing a load to be switched from one source of power to another in a "make-before-break" fashion with no interruption of power on the secondary side!

Unfortunately, these devices have equally noteworthy disadvantages: they waste a lot of energy (due to hysteresis losses in the saturated core), generating significant heat in the process, and are intolerant of frequency variations, which means they don't work very well when powered by small engine-driven generators having poor speed regulation. Voltages produced in the resonant winding/capacitor circuit tend to be very high, necessitating expensive capacitors and presenting the service technician with very dangerous working voltages. Some applications, though, may prioritize the ferroresonant transformer's advantages over its disadvantages. Semiconductor circuits exist to "condition" AC power as an alternative to ferroresonant devices, but none can compete with this transformer in terms of sheer simplicity.

• REVIEW:
• Voltage regulation is the measure of how well a power transformer can maintain constant secondary voltage given a constant primary voltage and wide variance in load current. The lower the percentage (closer to zero), the more stable the secondary voltage and the better the regulation it will provide.
• A ferroresonant transformer is a special transformer designed to regulate voltage at a stable level despite wide variation in input voltage.

AC Phase

AC Phase

Phase

Things start to get complicated when we need to relate two or more AC voltages or currents that are out of step with each other. By "out of step," I mean that the two waveforms are not synchronized: that their peaks and zero points do not match up at the same points in time. The following graph illustrates an example of this:

Phase shift

The two waves shown above (A versus B) are of the same amplitude and frequency, but they are out of step with each other. In technical terms, this is called a phase shift. Earlier we saw how we could plot a "sine wave" by calculating the trigonometric sine function for angles ranging from 0 to 360 degrees, a full circle. The starting point of a sine wave was zero amplitude at zero degrees, progressing to full positive amplitude at 90 degrees, zero at 180 degrees, full negative at 270 degrees, and back to the starting point of zero at 360 degrees. We can use this angle scale along the horizontal axis of our waveform plot to express just how far out of step one wave is with another:

The shift between these two waveforms is about 45 degrees, the "A" wave being ahead of the "B" wave. A sampling of different phase shifts is given in the following graphs to better illustrate this concept:

Lagging phase shift Leading phase shift

Because the waveforms in the above examples are at the same frequency, they will be out of step by the same angular amount at every point in time. For this reason, we can express phase shift for two or more waveforms of the same frequency as a constant quantity for the entire wave, and not just an expression of shift between any two particular points along the waves. That is, it is safe to say something like, "voltage 'A' is 45 degrees out of phase with voltage 'B'." Whichever waveform is ahead in its evolution is said to be leading and the one behind is said to be lagging.

Phase shift, like voltage, is always a measurement relative between two things. There's really no such thing as a waveform with an absolute phase measurement because there's no known universal reference for phase. Typically in the analysis of AC circuits, the voltage waveform of the power supply is used as a reference for phase, that voltage stated as "xxx volts at 0 degrees." Any other AC voltage or current in that circuit will have its phase shift expressed in terms relative to that source voltage.

Number, complex Complex number

This is what makes AC circuit calculations more complicated than DC. When applying Ohm's Law and Kirchhoff's Laws, quantities of AC voltage and current must reflect phase shift as well as amplitude. Mathematical operations of addition, subtraction, multiplication, and division must operate on these quantities of phase shift as well as amplitude. Fortunately, there is a mathematical system of quantities called complex numbers ideally suited for this task of representing amplitude and phase.

Because the subject of complex numbers is so essential to the understanding of AC circuits, the next chapter will be devoted to that subject alone.

• REVIEW:
• Phase shift is where two or more waveforms are out of step with each other.
• The amount of phase shift between two waves can be expressed in terms of degrees, as defined by the degree units on the horizontal axis of the waveform graph used in plotting the trigonometric sine function.

Shidqul Intima (Menjadi Anggota Jamaah Yang Sebenarnya)

Shidqul Intima (Menjadi Anggota Jamaah Yang Sebenarnya)

Shidqul intima sama dengan menolong dakwah dan menjaga fikrah sama dengan menjadi anggota jamaah yang sebenarnya

Oleh: Isma’il Hamid

Perkumpulan ataukah Jamaah?

“Sesungguhnya tidak ada Islam tanpa jamaah, tidak ada jamaah tanpa kepemimpinan dan tidak ada kepemimpinan tanpa ketaatan”. Sebuah hakikat abadi yang dikumandangkan dan digemakan oleh Umar Al-Faruq RA semenjak 1400 tahun yang lalu. Melalui hakikat ini beliau menetapkan bahwa Islam tidak dapat tegak kecuali melalui sebuah jamaah yang memikulnya, menyeru kepadanya, membelanya dan berjihad di jalannya.

Dengan pernyataan ini al-Faruq mengukuhkan –tanpa ada ruang keraguan sedikit pun- bahwa terdapat perbedaan besar antara tajammu’ (perkumpulan) dan jama’ah. Perbedaan di antara keduanya sangatlah jauh. Tajammu’ :

• Berdiri dan bubar berdasarkan pendapat, kesenangan dan keinginan personal,

• Tidak ada nizham yang mengikatnya,

• Tidak ada pula kaidah-kaidah yang mengatur pergerakannya.

• Setiap orang memiliki pendapat dan kepribadiannya secara mandiri.

Sedangkan jama’ah memiliki:

• Nizham dan manhaj hayah,

• Rencana strategis, sasaran taktis,

• Nizham idari, jenjang organisasi, dan jalur komando,

• Laihah, dan qanun,

• Program dan instrumen kerja

Sangat teringat kalimat-kalimat ini dengan seluruh makna dan konotasi tarbawinya saat saya mengikuti berbagai hal yang diucapkan dan ditulis di sana sini, ini dan itu tentang program Partai Ikhwanul Muslimin, serta buntut dari semua ini yang berupa berbagai pernyataan. Sikap-sikap dan peristiwa-peristiwa ini serta hal-hal lainnya termasuk sarana tarbiyah bagi Ikhwan yang sangat kuat, sebab tarbiyah mempergunakan mawaqif (sikap) merupakan pelindung dari berbagai kehancuran. Tarbiyah seperti ini dapat memberikan tsabat terhadap hati yang faham (sadar), meluruskan jalan bagi yang guncang, dan menegakkan hujjah bagi yang meragukan.

Syahwat ataukah Syubhat?

Tahapan dakwah pada marhalah manapun tidak pernah kosong dari dualisme permusuhan abadi terhadap berbagai rencana musuh-musuh Islam. Catatan sejarah penuh dengan berbagai konspirasi mereka, adakalanya dalam bentuk upaya melakukan pengrusakan dengan menebar berbagai syahwat di satu sisi, atau terkadang pula dengan cara menebar berbagai syubhat di saat yang lain. Akibat dari hal ini, tahapan dakwah yang manapun tidak pernah sepi dari musyakkikin (para penebar keraguan), mutsabbithin (para penggembos semangat dan pembongkar ketegaran), dan mudzabdzibin (penebar sikap bermuka dua) terhadap barisan muslim dari dalamnya. Hakikat Al-Qur’an pun menegaskan hal ini, sebagaimana firman Allah SWT: “Dan di antara kamu terdapat ‘telinga-telinga’ bagi mereka” (At-Taubah: 41). Hakikat Al-Qur’an ini memberi peringatan kepada barisan muslin agar tidak merespon rencana-rencana para musuh. Bahkan Al-Qur’an mengingatkan bahwa urusan ini bisa sampai ke tingkat terjerumus kepada hal yang dilarang, sebagaimana firman Allah SWT: “Sesungguhnya orang-orang yang datang membawa berita bohong adalab kelompok dari kamu sendiri” (An-Nur: 11). Dan sangat mungkin masalahnya bisa berkembang sampai ke tingkat melupakan al-ghayah (tujuan). Allah SWT berfirman: “Di antara kamu ada orang-orang yang menginginkan dunia dan di antara kamu ada yang menginginkan akhirat” (Ali Imran: 152)

Imam Al-Banna sangat memahami hakikat ini, karenanya beliau berkata: “Betapa banyak orang-orang yang ada di dalam (organisasi) kita, padahal mereka bukan bagian dari kita, dan betapa banyak orang-orang kita yang tidak ada bersama kita”!! Beliau pun meminta Ikhwan untuk memperhatikan bahaya urusan ini dan akibatnya yang sangat fatal. Beliau juga menekankan pentingnya melakukan pengawasan terhadap barisan serta membersihkannya dari orang-orang lemah. Beliau berkata: “Jika ada di tengah-tengah kamu orang yang sakit hatinya, cacat tujuannya, tersembunyi keinginannya, dan cacat masa lalunya, maka keluarkanlah mereka dari dalam barisan kalian, sebab orang seperti ini menjadi penghalang rahmat dan penutup taufiq Allah SWT”.

Emosi ataukah Akal

“Kekanglah lompatan-lompatan emosi dengan nalar akal, dan terangi cahaya akal dengan bara emosi, kekang khayalan yang ada dengan kebenaran hakikat dan realita, ungkap berbagai hakikat dalam sorotan khayalan yang memukau dan berkilau, dan janganlah seluruh kecenderungan diikuti, sebab ia akan menjadikannya seperti tergantung (tidak membumi dan tidak pula melangit”.

Ini adalah kata-kata abadi yang ditaujihkan oleh Imam Al-Banna rahimahullah kepada para ikhwan. Taujih ini dimaksudkan untuk:

• Mendisiplinkan barisan muslim agar tidak terjadi inhiraf dalam pemahaman, pemikiran ataupun perilaku.

• Merealisasikan fokus tawazun dan i’tidal (moderasi) dalam manhajiyyatut-tafkir al-ikhwani (metodologi berfikir Ikhwan).

• Menjaga barisan agar tidak dipermainkan oleh berbagai emosi yang meluap nan membara atau akal pikiran yang bernalar dengan gaya para filosof.

Jadi, jangan ada dominasi akal atas emosi dan jangan ada permainan perasaan yang mendominasi pemikiran. Jadi, taujih ini adalah pandangan yang obyektif, berimbang, moderat, dan bimbingan dari seorang panglima yang menjadi muassis, semoga Allah SWT merahmatinya.

Hawa Nafsu ataukah Prinsip?

“Hati-hati terhadap segala bentuk hawa yang diberi nama dengan selain Islam”. Sebuah isyarat peringatan yang ditaujihkan oleh Maemun bin Muhran rahimahullah kepada semua orang yang tertarik oleh manisnya hawa dan enaknya pendapat, dan kita dapati pemandu perjalanan mengingatkan kita dengan kekhasan ini, kenapa Imam Al-Banna menulis Ushul ‘Isyrin?! Dan untuk siapa beliau menulisnya? Dan begitu pentingkah sehingga beliau menempatkannya sebagai rukun pertama dari rukun-rukun bai’at?!

Dan datangnya jawaban dari seorang pemberi nasihat yang terpercaya: Sungguh, Ushul ‘Isyrin telah menjadi –dan akan terus menjadi-

• Benang tenun yang menjaga jamaah dan para anggotanya dari inhiraf,

• Bendungan yang kokoh dalam menghadapi berbagai pen-takwil-an yang salah dalam memahami Islam,

• Penjaga barisan supaya tidak mengikuti zhan (persangkaan, dugaan) dan segala yang disenangi oleh jiwa,

• Patokan bagi setiap pergerakan, perbuatan dan pernyataan Ikhwan di sana sini.

Imam Al-Banna menulis Ushul ‘Isyrin ini ini:

1. Dalam rangka kesatuan pemikiran, gerakan dan manhaj tarbawi bagi Jama’ah di tengan berbagai badai,

2. Agar tidak muncul berbagai madrasah pemikiran atau “jama’ah-jama’ah” yang menyusup ke tengah-tengah Jamaah,

3. Untuk tidak memberi toleransi terhadap adanya pemikiran yang menyusup atau gagasan yang kontradiksi –dikarenakan adanya emosi yang meluap atau penggampangan yang tendensius- yang bermaksud meng-infiltrasi barisan,

4. Untuk menjaga jama’ah agar tetap berada di atas garis tarbawi dan da’awi yang orisinil, menepis berbagai kotoran dan upaya-upaya penumpangan terhadapnya,

5. Dan pada akhirnya agar menjadi rujukan saat terjadi ikhtilaf (perbedaan) atau saat munculnya satu bentuk inhiraf, sebab Ushul ‘Isyrin dapat membantu penyelamatan amal, dan implementasi yang baik yang akan menjaga Jama’ah dan anggotanya dari berbagai keterplesetan

Orang-Orang yang Muncul di Permukaan ataukah Tersembunyi

Sepanjang sejarah Jama’ah seluruhnya, belum pernah terjadi perpecahan barisan atau inhiraf dari tujuan dan orientasi dikarenakan adanya suara yang tinggi, dan belum pernah pula terjadi berbagai macam move dan ketokohan di dalam Jama’ah kecuali bagi mereka yang terdepan dan bersifat shidq, serta terealisir untuk mereka, dengan mereka dan pada mereka shidqul wala’ wal intima’ (loyalitas dan merasa menjadi bagian yang benar) dari Dakwah yang diberkahi ini, semua tokoh Dakwah ini, marhalah ini dan seluruh marhalah yang ada adalah Ikhwan yang shadiqun dari Ikhwan al-Muslimin, yang:

• Mengimani ketinggian Dakwah mereka, kesucian fikrahi mereka,

• Bertekad dengan sebenarnya untuk hidup dengan Dakwah ini atau mati di jalannya.

Kepada Ikhwan yang seperti itulah yang mulia Mursyid ‘Am Syeikh Mahdi ‘Akif mengarahkan taujih-nya dalam risalahnya yang terakhir “Dan bagi mereka yang melihat bahwa dalam menjalani jalan dakwah ini terdapat peluang popularitas publik dan gemerlapnya para bintang, sungguh ia telah benar-benar merugi, sebab, para pelaku dakwah tidak melihat adanya balasan selain pahala Allah SWT jika mereka ikhlas, dan surga jika Allah SWT mengetahui bahwa dalam dirinya terdapat kebaikan, dan mereka itu beginilah adanya, orang-orang yang tersembunyi dari sisi tampilan publik, dan miskin dari sisi materi, kondisi mereka adalah men-tadh-hiyah-kan apa yang mereka miliki, dan memberikan apa yang ada di tangan mereka, harapan mereka adalah ridha Allah, dan Dia-lah sebaik-baik pelindung dan sebaik-baik penolong”.

Untuk lebih memperjelas urusan ini, beliau berkata: “dan supaya Ikhwan mengetahui bahwa tantangan terbesar yang menghadang mereka adalah:

• Adanya upaya-upaya untuk memperlemah tekad kalian,

• Adanya tasykik (pemunculan keraguan) terhadap manhaj dan keagungan risalah kalian

• Supaya para musuh kalian mendorong kalian pada posisi:

• Putus asa yang menyebabkan duduk tidak mau bekerja, atau

• Keraguan yang mencerai beraikan, atau

• Dorongan emosi yang tanpa kendali”.

Tsawabit ataukah Mutaghayyirat?

Allah SWT telah menjadikan dakwah Ikhwan berbeda dengan yang lainnya dalam hal adanya:

• Ru’yah wadhihah (visi yang jelas), yang memungkinkannya untuk menyatukan Jamaah, baik sebagai qiyadah maupun individu dalam hal persepsi dan mafahim.

• Ketegasan dalam berbagai posisi sulit dan pemilihan manhaj taghyir yang paling benar yang tegak di atas minhaj nubuwwah, serta

• Pemahaman terhadap perbedaan antara tsawabit dan mutaghayyirat dalam perjalanan amal Islami.

Shidqul Intima (Menjadi Anggota Jamaah Yang Sebenarnya)

Shidqul intima sama dengan menolong dakwah dan menjaga fikrah sama dengan menjadi anggota jamaah yang sebenarnya

Oleh: Isma’il Hamid

Perkumpulan ataukah Jamaah?

“Sesungguhnya tidak ada Islam tanpa jamaah, tidak ada jamaah tanpa kepemimpinan dan tidak ada kepemimpinan tanpa ketaatan”. Sebuah hakikat abadi yang dikumandangkan dan digemakan oleh Umar Al-Faruq RA semenjak 1400 tahun yang lalu. Melalui hakikat ini beliau menetapkan bahwa Islam tidak dapat tegak kecuali melalui sebuah jamaah yang memikulnya, menyeru kepadanya, membelanya dan berjihad di jalannya.

Dengan pernyataan ini al-Faruq mengukuhkan –tanpa ada ruang keraguan sedikit pun- bahwa terdapat perbedaan besar antara tajammu’ (perkumpulan) dan jama’ah. Perbedaan di antara keduanya sangatlah jauh. Tajammu’ :

• Berdiri dan bubar berdasarkan pendapat, kesenangan dan keinginan personal,

• Tidak ada nizham yang mengikatnya,

• Tidak ada pula kaidah-kaidah yang mengatur pergerakannya.

• Setiap orang memiliki pendapat dan kepribadiannya secara mandiri.

Sedangkan jama’ah memiliki:

• Nizham dan manhaj hayah,

• Rencana strategis, sasaran taktis,

• Nizham idari, jenjang organisasi, dan jalur komando,

• Laihah, dan qanun,

• Program dan instrumen kerja

Sangat teringat kalimat-kalimat ini dengan seluruh makna dan konotasi tarbawinya saat saya mengikuti berbagai hal yang diucapkan dan ditulis di sana sini, ini dan itu tentang program Partai Ikhwanul Muslimin, serta buntut dari semua ini yang berupa berbagai pernyataan. Sikap-sikap dan peristiwa-peristiwa ini serta hal-hal lainnya termasuk sarana tarbiyah bagi Ikhwan yang sangat kuat, sebab tarbiyah mempergunakan mawaqif (sikap) merupakan pelindung dari berbagai kehancuran. Tarbiyah seperti ini dapat memberikan tsabat terhadap hati yang faham (sadar), meluruskan jalan bagi yang guncang, dan menegakkan hujjah bagi yang meragukan.

Syahwat ataukah Syubhat?

Tahapan dakwah pada marhalah manapun tidak pernah kosong dari dualisme permusuhan abadi terhadap berbagai rencana musuh-musuh Islam. Catatan sejarah penuh dengan berbagai konspirasi mereka, adakalanya dalam bentuk upaya melakukan pengrusakan dengan menebar berbagai syahwat di satu sisi, atau terkadang pula dengan cara menebar berbagai syubhat di saat yang lain. Akibat dari hal ini, tahapan dakwah yang manapun tidak pernah sepi dari musyakkikin (para penebar keraguan), mutsabbithin (para penggembos semangat dan pembongkar ketegaran), dan mudzabdzibin (penebar sikap bermuka dua) terhadap barisan muslim dari dalamnya. Hakikat Al-Qur’an pun menegaskan hal ini, sebagaimana firman Allah SWT: “Dan di antara kamu terdapat ‘telinga-telinga’ bagi mereka” (At-Taubah: 41). Hakikat Al-Qur’an ini memberi peringatan kepada barisan muslin agar tidak merespon rencana-rencana para musuh. Bahkan Al-Qur’an mengingatkan bahwa urusan ini bisa sampai ke tingkat terjerumus kepada hal yang dilarang, sebagaimana firman Allah SWT: “Sesungguhnya orang-orang yang datang membawa berita bohong adalab kelompok dari kamu sendiri” (An-Nur: 11). Dan sangat mungkin masalahnya bisa berkembang sampai ke tingkat melupakan al-ghayah (tujuan). Allah SWT berfirman: “Di antara kamu ada orang-orang yang menginginkan dunia dan di antara kamu ada yang menginginkan akhirat” (Ali Imran: 152)

Imam Al-Banna sangat memahami hakikat ini, karenanya beliau berkata: “Betapa banyak orang-orang yang ada di dalam (organisasi) kita, padahal mereka bukan bagian dari kita, dan betapa banyak orang-orang kita yang tidak ada bersama kita”!! Beliau pun meminta Ikhwan untuk memperhatikan bahaya urusan ini dan akibatnya yang sangat fatal. Beliau juga menekankan pentingnya melakukan pengawasan terhadap barisan serta membersihkannya dari orang-orang lemah. Beliau berkata: “Jika ada di tengah-tengah kamu orang yang sakit hatinya, cacat tujuannya, tersembunyi keinginannya, dan cacat masa lalunya, maka keluarkanlah mereka dari dalam barisan kalian, sebab orang seperti ini menjadi penghalang rahmat dan penutup taufiq Allah SWT”.

Emosi ataukah Akal

“Kekanglah lompatan-lompatan emosi dengan nalar akal, dan terangi cahaya akal dengan bara emosi, kekang khayalan yang ada dengan kebenaran hakikat dan realita, ungkap berbagai hakikat dalam sorotan khayalan yang memukau dan berkilau, dan janganlah seluruh kecenderungan diikuti, sebab ia akan menjadikannya seperti tergantung (tidak membumi dan tidak pula melangit”.

Ini adalah kata-kata abadi yang ditaujihkan oleh Imam Al-Banna rahimahullah kepada para ikhwan. Taujih ini dimaksudkan untuk:

• Mendisiplinkan barisan muslim agar tidak terjadi inhiraf dalam pemahaman, pemikiran ataupun perilaku.

• Merealisasikan fokus tawazun dan i’tidal (moderasi) dalam manhajiyyatut-tafkir al-ikhwani (metodologi berfikir Ikhwan).

• Menjaga barisan agar tidak dipermainkan oleh berbagai emosi yang meluap nan membara atau akal pikiran yang bernalar dengan gaya para filosof.

Jadi, jangan ada dominasi akal atas emosi dan jangan ada permainan perasaan yang mendominasi pemikiran. Jadi, taujih ini adalah pandangan yang obyektif, berimbang, moderat, dan bimbingan dari seorang panglima yang menjadi muassis, semoga Allah SWT merahmatinya.

Hawa Nafsu ataukah Prinsip?

“Hati-hati terhadap segala bentuk hawa yang diberi nama dengan selain Islam”. Sebuah isyarat peringatan yang ditaujihkan oleh Maemun bin Muhran rahimahullah kepada semua orang yang tertarik oleh manisnya hawa dan enaknya pendapat, dan kita dapati pemandu perjalanan mengingatkan kita dengan kekhasan ini, kenapa Imam Al-Banna menulis Ushul ‘Isyrin?! Dan untuk siapa beliau menulisnya? Dan begitu pentingkah sehingga beliau menempatkannya sebagai rukun pertama dari rukun-rukun bai’at?!

Dan datangnya jawaban dari seorang pemberi nasihat yang terpercaya: Sungguh, Ushul ‘Isyrin telah menjadi –dan akan terus menjadi-

• Benang tenun yang menjaga jamaah dan para anggotanya dari inhiraf,

• Bendungan yang kokoh dalam menghadapi berbagai pen-takwil-an yang salah dalam memahami Islam,

• Penjaga barisan supaya tidak mengikuti zhan (persangkaan, dugaan) dan segala yang disenangi oleh jiwa,

• Patokan bagi setiap pergerakan, perbuatan dan pernyataan Ikhwan di sana sini.

Imam Al-Banna menulis Ushul ‘Isyrin ini ini:

1. Dalam rangka kesatuan pemikiran, gerakan dan manhaj tarbawi bagi Jama’ah di tengan berbagai badai,

2. Agar tidak muncul berbagai madrasah pemikiran atau “jama’ah-jama’ah” yang menyusup ke tengah-tengah Jamaah,

3. Untuk tidak memberi toleransi terhadap adanya pemikiran yang menyusup atau gagasan yang kontradiksi –dikarenakan adanya emosi yang meluap atau penggampangan yang tendensius- yang bermaksud meng-infiltrasi barisan,

4. Untuk menjaga jama’ah agar tetap berada di atas garis tarbawi dan da’awi yang orisinil, menepis berbagai kotoran dan upaya-upaya penumpangan terhadapnya,

5. Dan pada akhirnya agar menjadi rujukan saat terjadi ikhtilaf (perbedaan) atau saat munculnya satu bentuk inhiraf, sebab Ushul ‘Isyrin dapat membantu penyelamatan amal, dan implementasi yang baik yang akan menjaga Jama’ah dan anggotanya dari berbagai keterplesetan

Orang-Orang yang Muncul di Permukaan ataukah Tersembunyi

Sepanjang sejarah Jama’ah seluruhnya, belum pernah terjadi perpecahan barisan atau inhiraf dari tujuan dan orientasi dikarenakan adanya suara yang tinggi, dan belum pernah pula terjadi berbagai macam move dan ketokohan di dalam Jama’ah kecuali bagi mereka yang terdepan dan bersifat shidq, serta terealisir untuk mereka, dengan mereka dan pada mereka shidqul wala’ wal intima’ (loyalitas dan merasa menjadi bagian yang benar) dari Dakwah yang diberkahi ini, semua tokoh Dakwah ini, marhalah ini dan seluruh marhalah yang ada adalah Ikhwan yang shadiqun dari Ikhwan al-Muslimin, yang:

• Mengimani ketinggian Dakwah mereka, kesucian fikrahi mereka,

• Bertekad dengan sebenarnya untuk hidup dengan Dakwah ini atau mati di jalannya.

Kepada Ikhwan yang seperti itulah yang mulia Mursyid ‘Am Syeikh Mahdi ‘Akif mengarahkan taujih-nya dalam risalahnya yang terakhir “Dan bagi mereka yang melihat bahwa dalam menjalani jalan dakwah ini terdapat peluang popularitas publik dan gemerlapnya para bintang, sungguh ia telah benar-benar merugi, sebab, para pelaku dakwah tidak melihat adanya balasan selain pahala Allah SWT jika mereka ikhlas, dan surga jika Allah SWT mengetahui bahwa dalam dirinya terdapat kebaikan, dan mereka itu beginilah adanya, orang-orang yang tersembunyi dari sisi tampilan publik, dan miskin dari sisi materi, kondisi mereka adalah men-tadh-hiyah-kan apa yang mereka miliki, dan memberikan apa yang ada di tangan mereka, harapan mereka adalah ridha Allah, dan Dia-lah sebaik-baik pelindung dan sebaik-baik penolong”.

Untuk lebih memperjelas urusan ini, beliau berkata: “dan supaya Ikhwan mengetahui bahwa tantangan terbesar yang menghadang mereka adalah:

• Adanya upaya-upaya untuk memperlemah tekad kalian,

• Adanya tasykik (pemunculan keraguan) terhadap manhaj dan keagungan risalah kalian

• Supaya para musuh kalian mendorong kalian pada posisi:

• Putus asa yang menyebabkan duduk tidak mau bekerja, atau

• Keraguan yang mencerai beraikan, atau

• Dorongan emosi yang tanpa kendali”.

Tsawabit ataukah Mutaghayyirat?

Allah SWT telah menjadikan dakwah Ikhwan berbeda dengan yang lainnya dalam hal adanya:

• Ru’yah wadhihah (visi yang jelas), yang memungkinkannya untuk menyatukan Jamaah, baik sebagai qiyadah maupun individu dalam hal persepsi dan mafahim.

• Ketegasan dalam berbagai posisi sulit dan pemilihan manhaj taghyir yang paling benar yang tegak di atas minhaj nubuwwah, serta

• Pemahaman terhadap perbedaan antara tsawabit dan mutaghayyirat dalam perjalanan amal Islami.

Jadi, ada perbedaan jelas:

• Antara yang dini (agama) yang tsabit dan tsaqafi (wawasan, budaya) yang mutaghayyir

• Antara tsawabit al-harakah dan mutaghayyirat al-siyasah

Ia merupakan tsawabit al-’amal dalam dakwah kita. Darinya menjadi jelas sebagian dari kaidah-kaidah tanzhimi kita:

• Siapa menyalahkan siapa?

• Siapa meng-audit siapa?

• Adakah anggota (person) hak menyalahkan Jamaah? Ataukah sebaliknya?!

Perbedaan antara nasihat, tidak mendiamkan kesalahan dan kritik membangun yang diletakkan pada tempatnya yang benar di satu sisi dan antara memaksakan pendapat. Di manakah nasihat? Kapan diberikan? Dan apakah ia bersifat mulzimah (mengikat)?

Instrumen pengambilan kebijakan; antara lingkaran syura dan lingkaran pengambilan keputusan, perbedaan antara syura dan istisyarah, perbedaan antara syura terorganisir yang mulzimah dan istisyarah yang afawiyyah (tidak terorganisir), antara marhalah syura dan marhalah tanfidz, keseimbangan antara syura mulzimah dan qarar yang mulzim, dan perilaku minoritas terhadap qarar yang mulzim

Membela ataukah Menjaga

Shidqul intima’ wal wala’ (keanggotaan dan loyalitas yang benar) terhadap dakwah yang diberkahi ini, yang ada di dalam jiwa seorang akh yang shadiq, dikukur berdasarkan tingkat pelaksanaannya terhadap tugas yang diminta darinya untuk dakwahnya, dalam berbagai kondisi, dalam zhuruf apapun, dan sejauh mana ketetapan dia dalam hal ini dengan penuh tsabat yang mengharap pahala dari Allah SWT, di mana hal ini tercermin pada:

1. Membela dakwah. Dengan cara menyebarluaskannya, membelanya dan ber-tadh-hiyah di jalannya. Sebab, sebuah fikrah menjadi sukses “jika

   1. Menguat keimanan kepadanya

   2. Terpenuhi ikhlas di jalannya

   3. Bertambah semangat untuknya

   4. Ditemukan adanya persiapan yang mendorongnya untuk tadh-hiyah dan kerja untuk merealisasikannya”.

2. Menjaga fikrah. Terhadap pemikiran-pemikiran dan klausul-klausulnya, pokok-pokok dan tsawabit-nya, rukun-rukun dan tiang-tiangnya, karakteristik dan kekhasannya. Serta menjaganya agar tidak ada infiltrasi pemikiran yang menimpanya. Penjagaan seperti ini menuntut adanya empat pilar:

   1. Kehendak kuat yang tidak terdampak oleh kelemahan.

   2. Kesetiaan kokoh yang tidak terkontaminasi bunglonisme dan pengkhianatan

   3. Tadh-hiyah langka yang tidak terhambat ketamakan dan kepelitan

   4. Pengenalan terhadap prinsip, keyakinan kepadanya dan penghargaan terhadapnya, yang akan melindunginya dari kesalahan, inhiraf, tawar menawar dan tergoda oleh yang lainnya.

Di atas rukun-rukun dasar yang merupakan kekhasan jiwa satu-satunya ini, dan di atas kekuatan ruhani yang besar seperti inilah berbagai prinsip dibangun, berbagai bangsa yang bangkit di-tarbiyah, dan berbagai masyarakat baru dibentuk serta kehidupan diperbaharui dari mereka-mereka yang sudah lama tidak dapat menikmati kehidupan dalam tempo yang lama”.

Detik Kejujuran

Ini merupakan detik-detik kebeningan jiwa. Di dalamnya kita saling mengingat hal-hal yang mengikatkan kita dengan dakwah mubarakah dan Jama’ah yang kekal ini. Ini merupakan waqfah shadiqah (perenungan yang jujur) bersama jiwa. Di dalam detik-detik ini kita perbaharui janji kita dengan Allah SWT, dengan dakwah kita dan dengan Jama’ah kita:

Hendaklah kita tetap tsiqah terhadap Jama’ah, sebab, ia adalah benteng yang aman bagi kita semua. Ia adalah rahasia keberlangsungan dakwah, betatapun ia diterpa berbagai syubhat, ittihamat (tuduhan) serta pendapat yang ini itu sepanjang sejarahnya.

Hendaklah kita menjaga faktor-faktor kekuatan di dalam Jama’ah, yang terwujud dalam:

• Kesatuan pemikiran, keanggotaan dan tanzhimi

• Keterikatan barisan yang tegak di atas ukhuwwah,

• Pelaksanaan hak-hak ukhuwwah secara sempurna yang berupa: cinta, penghargaan, bantuan dan itsar

• Menghadiri berbagai pertemuan jama’ah dan jangan menyelisihinya kecuali karena adanya alasan yang “memaksa”.

• Selalu mendahulukan ber-mu’amalah dengan ikhwah

• Menerima pendapat internal yang berbeda

• Saling memberi nasihat, tidak mendiamkan kesalahan dan berterus terang dalam memberikan mauizhah, akan tetapi pada tempatnya yang wajar.

• Bekerja untuk menyebarluaskan dakwah kita di semua tempat.

• Memberitahukan kepada qiyadah tentang berbagai situasi dan kondisi kita secara utuh.

• Tidak melakukan suatu pekerjaan yang memiliki pengaruh secara mendasar kecuali dengan ijin.

• Selalu connect secara ruhi dan amali dengan dakwah

• Selalu memandang diri sendiri sebagai prajurit di barak yang menunggu segala perintah

• Melepaskan diri dengan berbagai hubungan dengan lembaga atau jama’ah apapun yang tidak membawa maslahat bagi fikrah kita, khususnya jika hal ini diperintahkan

Penutup

Kalimat berikut diucapkan oleh Imam Asy-Syahid: “Wahai al-akh ash-shadiq! Ini adalah global dakwah kamu, penjelasan singkat terhadap fikrahmu, kamu dapat menghimpunnya dalam lima kosa kata: Allah ghoyatuna, Ar-Rasul Qudwatuna, Al-Qur’an syir’atuna (Al-Qur’an undang-undang kami), al-Jihad sabiluna, asy-syahadah umniyyatuna (syahid cita-cita kami), tampilan dakwah kamu dapat dihimpun dalam lima kosa kata yang lain: al-basathah (simpel), tilawah (baca Al-Qur’an), shalat, jundiyah (keprajuritan), khuluq (akhlaq), maka, berpeganglah kepada ajaran ini dengan kuat, jika tidak, pada barisan para pengangguran masih ada tempat bagi mereka yang malas dan suka main-main.

Saya yaki bahwa jika kamu mengamalkannya, dan menjadikannya sebagai cita-cita dan akhir dari segala tujuanmu, maka balasannya adalah kemuliaan di dunia, kebaikan dan ridha Allah di akhirat, sementara kamu adalah bagian dari kami dan kami bagian dari kamu, dan jika kamu berpaling darinya, dan duduk tidak mau bekerja untuknya, maka tidak ada hubungan antara kami dan kamu, walaupun kamu berada pada posisi terdepan dalam majelis kami, dan kamu pun membawa gelar paling agung yang ada serta tampil di antara kami dengan tampilan terbesar, dan Allah SWT akan meng-hisab kamu atas duduk-duduk kamu dengan hisab terberat, maka, pilihlah untuk dirimu pilihan yang tepat, dan kami memohon taufiq dan hidayah kepada Allah SWT untuk kebaikan kami dan kamu”.

duk kamu dengan hisab terberat, maka, pilihlah untuk dirimu pilihan yang tepat, dan kami memohon taufiq dan hidayah kepada Allah SWT untuk kebaikan kami dan kamu”

CAHAYA DI WAJAH UMAT

Oleh : KH. Rahmat Abdullah

Dalam satu kesatuan amal jamai ada orang yang mendapatkan nilai tinggi karena ia betul-betul sesuai dengan tuntutan dan adab amal jamai. Kejujuran, kesuburan, kejernihan dan kehangatan ukhuwahnya betul-betuk terasa. Keberadaannya menggairahkan dan menentramkan. Namun perlu diingat, walaupun telah bekerja dalam jaringan amal jamai, namun pertanggungjawaban amal kita akan dilakukan dihadapan Allah SWT secara sendiri-sendiri.

Karenanya jangan ada kader yang mengandalakan kumpulan-kumpulan besar tanpa berusaha meningkatkan kualitas dirinya. Ingat suatu pesan Rasulullah SAW : Man abtha a bihi amaluhu lam yusri bihi nasabuhu (Siapa yang lamban beramal tidak akan dipercepat oleh nasabnya).


Makna Tarbiyah itu sendiri adalah mengharuskan seseorang lebih berdaya, bukan terus-menerus menempel dan tergantung pada orang lain. Meskipun kebersamaan itu merupakan sesuatu yang baik tapi ada saatnya kita tidak dapat bersama, demikian sunnahnya. Sebab kalau mau, para Sahabat Rasulullah SAW bisa saja menetap dan wafat di Madinah, atau terus-menerus tinggal ber-mulazamah tinggal di Masjidil Haram yang nilainya sekian ratus ribu atau di Masjid Nabawi yang pahalanya sekian ribu kali. Tapi mengapa makam para Sahabat tidak banyak berada di Baqi atau di Mala, tetapi makam mereka banyak bertebaran jauh, beribu-ribu mil dari negeri mereka.

Sesungguhnya mereka mengutamakan adanya makna diri mereka sebagai perwujudan firman-Nya : Wal takum minkum ummatuy yad'una ilal khair. Atau dalam firman-Nya : Kuntum khaira ummatin ukhrijat linnaas (QS : Ali imran : 110). Ummat yang baik tidak untuk disembunyikan tetapi untuk ditampilkan kepada seluruh ummat manusia. Inilah sesuatu yang perlu kita jaga dan perhatikan. Kita semua beramal tapi tidak larut dalam kesendirian. Hendaklah ketika sendiri kita selalu mendapat cahaya dan menjadi cahaya yang menyinari lingkungan sekitarnya.

Jangan lagi ada kader yang mengatakan, saya jadi buruk begini karena lingkungan. Mengapa tidak berkata sebaliknya, karena lingkungan seperti itu, saya harus mempengaruhi lingkungan itu dengan pengaruh yang ada pada diri saya. Seharusnya dimanapun dia berada ia harus berusaha membuat kawasan-kawasan kebaikan, kawasan cahaya, kawasan ilmu, kawasan akhlaq, kawasan taqwa, kawasan al haq, setelah kawasan-kawasan tadi menjadi sempit dan gelap oleh kawasan-kawasan jahiliyah, kezhaliman, kebodohan dan hawa nafsu. Demikianlah ciri kader PKS (tulisan aslinya PK), dimanapun dia berada terus-menerus memberi makna kehidupan. Seperti sejarah da'wah ini, tumbuh dari seseorang, dua orang kemudian menjadi beribu-ribu atau berjuta-juta orang.

Sangat indah ungkapan Imam Syahid Hasan Al Banna,Antum ruhun jadidah tasri fi jasadil ummah. Kamu adalah ruh baru, kamu adalah jiwa baru yang mengalir di tubuh ummat, yang menghidupkan tubuh yang mati itu dengan Al Qur'an. Jangan ada sesudah ini, kader yang hanya mengandalkan kerumunan besar untuk merasakan eksistensi dirinya. Tapi, dimanapun dia berada ia tetap merasakan sebagai hamba Allah SWT., ia harus memiliki kesadaran untuk menjaga dirinya dan taqwanya kepada Allah SWT., baik dalam keadaan sendiri maupun dalam keadaan terlihat orang. Kemanapun pergi, ia tak merasa kesunyian, tersudut atau terasing karena Allah senantiasa bersamanya. Bahkan ia dapatkan kebersamaan Rasul-Nya, ummat dan alam semesta senantiasa.

Kehebatan Namrud bagi nabi Ibrahim AS tidak ada artinya, tidaklah sendirian. Allah bersamanya dan alam semesta selalu bersamanya. Api yang berkobar-kobar yang dinyalakan Namrud untuk membinasakan dirinya, ternyata satu korps denganya dalam menunaikan tugas pengabdian kepada Allah. Alih-alih dari menghanguskanya, justeru malah menjadi bardan wa salaman (penyejuk dan penyelamat). Karena itu, kader sejati yakni bahwa Allah SWT akan senantiasa membuka jalan bagi pejuang da'wah sesuai denga janji-Nya, intanshurullah yan shurkum wa yutsabbit aqdamakum (jika kamu menolong Allah, Ia pasti menolongmu dan mengokohkan langkahmu).

Semoga para kader mendapatkan perlindungan dan bimbingan dari Allah SWT di tengah derasnya arus dan badai perusakan ummat. Kita harus yakin sepenuhnya akan pertolongan Allah SWT dan bukan yakin dan percaya pada diri sendiri. Masukkan diri dalam benteng-benteng kekuatan usrah atau halaqah tempat junud da'wah melingkar dalam satu benteng perlindungan, menghimpun bekal dan amunisi untuk terjun ke arena pertarungan haq dan bathil yang berat dan menuntut pengorbanan. Disanalah kita mentarbiyah diri sendiri dan generasi mendatang. Inilah sebagian pelipur kesediahan ummat yang berkepanjangan, dengan munculnya generasi baru. Generasi yang siap memikul beban da'wah dan menegakkan islam. Inilah harapan baru bagi masa depan yang lebih gemilang, dibawah naungan Al Qur'an dan cahaya islam rahmatan lil alamin.