Design Voltage Regulator for Synchronous Generator

As the loud on an alternator is varied, its terminal voltage is also found to vary. This variation terminal voltage is due to voltage drop in armature (resistance, leakage reactance) and armature reaction, therefore this research aim to design voltage regulator to maintain the terminal voltage of alternator at constant value at load condition. By making the compensation time of voltage drop approach to zero at load condition.


Introduction
A synchronous machine rotates at constant speed in the steady state.Un like induction machines.The rotating air gap field and the rotor in the synchronous machine rotate at the same speed, called the synchronous speed.Synchronous machine are used primarily as generators or alternator.They are usually large machines generating electrical power at hydro.Nuclear or thermal power stations synchronous generators with power ratings will be used before the end of the twentieth century.Synchronous generators are the primary energy conversion devices of the word's electric power systems today.In spit of continuing research for more direct energy conversion techniques.It is conceded that synchronous generators will continue to be used well into the next century.
Like most rotating machines, asynchronous machine can also operate as both a generator and motor.

Simple regulation
Figure (1) illustrates the idea of voltage regulation, line voltage, normally 120v rms.Drives an unregulated power supply like a fullwave rectifier with capacitor-input filter .The voltage from this unregulated supply varies directly with line voltage .For instance a 10 percent in line voltage results in approximately a 10 percent increase in the un regulated voltage .furthermoreany changes in load current produce changes bin unregulated voltage because of supply impedance, filter-capacitor discharge, etc.

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This is where the voltage regulation comes in as shown in Fig.
(1) the voltage of the unregulated supply drives a voltage regulator, which produces the final output voltage .This output is ideally constant, varying neither with changes in line voltage nor in load current .In a practical regulator, The output voltage is almost constant and the ripple is greatly reduced.

Zener-diode regulator
A zener diode can be used voltage regulator.

Figure
(2) shown abridge peak rectifier driving a zener diode regulator .asyou recall ,the average voltage and ripple across the filter capacitor depend on the source resistance ,the filter capacitance ,and the load resistance ,but as long as V in is greater than V z , the zener diode regulates in the breakdown region .Ideally ,this means the final output voltage is constant .To a second approximation, however the zener impedance cause the final output to changes in line voltage and load current.
The limitation on the zener diode regulator is this .Changes in load current produce equal and opposite changes in zener current: The changes in zener current following through the zener impedance produce changes in the final output voltage: The larger the changes in zener ,the larger the changes in output voltage if the changes in zener current are only a few milliamperes, the changes in load voltage may be accepted ,but when the changes are tens of milliamperes or more ,the changes in load voltage become too large for most applications.

Zener Diode and Emitter Follower
What do we if the changes in zener current are too large ?the simplest approach is to add an emitter followers ,as shown in fig.
(3) the load voltage still equal the zener voltage (less than V BE drop of the transistor, but the changes in zener current are reduced by factor of ß. When necessary, we can use a Darlington pairs to get a larger ß this circuit is an example of a series voltage regulator the collector emitter terminals are in series with the load because of this, the load current must pass through the transistor, and this is the reason the transistor is often called a pass transistor .thevoltage across the pass transistor equals 4) And its power dissipation is (5) Series regulator are the most widely used type.

Sp regulation
In critical application, zener voltages near 6V are used because the temperature coefficient approaches zero.The highly stable zener voltage, sometime called the reference voltage, can be amplified with an SP negativefeedback amplifier to get higher voltages with essentially the some temperature stability as the reference voltage.

A Discrete SP Regulator
Figure (4a) shows a discrete SP regulator.Transistor Q 2 acts like an emitter follower as before.
Transistor Q 1 provides voltage gain in a negative-feedback loop.Here is the basic idea behind circuit operation.Suppose the load voltage tries to Eng.&Tech.Vol.26.No.11,2008Design Voltage Regulator for Synchronous Generator 1357 increase.The feedback voltage V F will increase.Since the emitter voltage of Q 1 is held constant by the zener diode, more collector current flows throws Q 1 ; most of it flows through R 3 and causes the base voltage of Q 2 to decrease.In response, the emitter voltage of Q 2 decreases, offsetting almost all the original increase in load voltage.Figure (4b) shows the circuit redrawn so can recognize the amplifier and feedback section.The output voltage is Fed back to the input side.Because of the SP negative feedback, the dosed-loop gain is Including the V BE drop of Q 1 .The final regulated load voltage equals ( ) This means we can use a low zener voltage where the temperature coefficient approaches zero and still have a higher output voltage with an equally good temperature coefficient.
The potentiometer of fig ( 4a) allows us to adjust the output voltage to the exact value required in a particular application.In this way, we can adjust for the tolerance in zener voltages, V BE drops, and feedback resistors.

Current limiting
The SP cottage regulator of Fig. (3a) is a series regulator.As it now stands, it has no short-circuit protection.If we accidentally place a short across the load terminals, we get an enormous current through a 2 .
Either a 1 will be destroyed or a diode in the unregulated supply will burn out, or both.To avoid this possibility, regulated supplies often include current limiting.Figure (5) shows one way to limit load current to safe values even though the output terminals are shorted.For normal load currents, the voltage drop across R 4 is small and a 3 is off; under this condition.The regulator works as previously described.If excessive load current flows, however, the voltage across R 4 becomes large enough to turn on a 3 .The collector current of a 3 flows through R 3 ; this decreases the base voltage of a 2 and reduces the output voltage to prevent damage.
In fig.
(5) current limiting starts when the voltage across R 4 is around 0.6 to 0.7 V.At this point, a 3 turns on and decreases the base drive for a 2 .Since R 4 is 1Ω, Current limiting begins when load current is the vicinity of 600 to 700 mA.By selecting other values of R 4 , we can change the level oh current limiting.
The current limiting of fig ( 5) is a simple example of how it is done.In more advanced approaches, a 3 may be replaced by an op amp to increase the sharpness of the current limiting.

An op-amp regulator
In fig ( 5) a 1 provides the open-loop gain.As discussed earlier.
The greater the open-loop gain, the more precise the closed-loop gain.Because of this, we can improve performance by using an op amp in the place of a 1 .
Figure ( 6)show an op-amp regulator.Zener voltage V z drives the noninverting input, and feedback voltage V F drives the inverting input.Because we have eliminated the V BE drop of Q 1 the regulated output voltage is Where This means the regulated output is as constant ai the zener voltage, with temperaturecompensated Zener diodes.Therefore we can build extremely good voltage regulation.As before, we can use a Darlington pair in the place of Q 2 to increase current-handling capability.
A final point, to reduce the changes in zener voltage caused big changes in un regulated voltage, we can use the regulated output to drive the zener series limiting resistor R s as shown in fig.( 6).In this ray, we get an almost rock-solid regulated output.

The main generator
The stator of main generator which used in this design shown in fig ( 7(a, b)) The rotor of this generator consists of magnetic poles the rate of (pole to pole path) must be (0.707) to give us pure out put sin wave.The fig ( 8 a The values on this relation are practically taken from station generator its output rate is 1 MVA.And the range of d.c current from 0A to8A, in this station generator two exciting winding used and one rotor and assistant generator be using voltage regulator the compensation time is approach to zero to load condition.

References
) show the rotor.The fig (8b) shows the magnetic char.Of the generator machine The Excitation generator The stator of generator excitation consist of two different group of coils, group one produce ¢ Ex1 is inverse the ¢Ex2) Fig (8) shows the stator and its coils connection.The rotor of this generator shown in fig (9) The assistant generator The generator produce IEx1 which produce ¢Ex1, This current must be constant in no load and in full load and fig (10) show the circuit of assistant generator.Conclusions Fig. (12)shown the connected of the three generators with voltage regulator.Fig. (13) shown the relation between flux density (B) and field intensity (H), this relation for main generator which connected with load this relation on the size of generator.Fig. (14) shown the relation between e.m.f and the result submersion of(¢ Ex1)and(¢ Ex2) which gave us out put voltage equal to (400V) and value constant between no load and full load.Fig. (15) shown that the field current (I f ) is proportional to the load current (I L ), and (I f ) equal to the different between (¢ Ex1) and (¢ Ex2).Fig. (16) shown the relation between load current and flux of main generator.Fig. (17) shown that the field current is proportional to different between(¢ Ex1) and (¢ Ex1).Fig. (18) shown the relation between (I L ) and result of the different between (¢ Ex1) and (¢ Ex2).Fig. (19) shown that (I L ) is proportional to different between (I Ex 1 ) and (I Ex 2 ).Fig. (20) shown the relation between (I L ) and(I Ex 2 ) , from this figure appear that (I L ) is inverse proportional with (I Ex 2 ), which mean that (I Ex 2 ) is inverse to the (I Ex 1 ).

Fig
Fig. (1)Basic idea of voltage regulation