VI Discuss with your partner if the sentences are true or false.

1 A voltage regulator controls the magnetic field strength.

2 Current generating the magnetic field is known as excitation engine

3 The exciter is on the different shaft as the ac generator to make it an integral part

of the generator.

4 The chief disadvantage of exciter units is that each generator has its own

independent source of excitation.

5 Some external source of electric power is necessary for generator operation.

6 In a multi-generator installation, failure of one generator exciter makes the

complete system inoperative.

7 This would happen if a generator system had a common external excitation

system.

8 Internal excitation does not make it unnecessary to transmit excitation power.

9. In contrast to dc generators, the magnetic field coils in most aircraft ac

generators rotate.

10.One type of voltage regulator that has a mechanical moving partsis the solid-

state regulator.

11. The ac generator output flows to the engine regulator, which compares it to a reference voltage.

12 The difference supplies the control amplifier section of the regulator.

13 If the output is too low, regulator circuitry decreases the field strength of the ac

exciter.

14 If the output is too high, it doesn`t reduce the field strength.

15 The power supply for the bridge circuit is R1.

16 CR1 provides full-wave rectification of the three-phase output from transformer

T1.

17 The negative anode of CR1 supplies power through point C, R2, point B, Zener

diode CR1,point R, and to parallel-connected V1 and R1.

18 Takeoff point C of the bridge is located between resistor B2 and the Zener

diode.

19 The other leg of the reference bridge (resistors R9, R7, and temperature

compensating resistor RT1) connects in series with V1 and R1 through points

B, A, and D.

20 The output of this leg of the bridge is at point B.

21 As voltage changes occur, voltage across R2 and B1 remains constant, leaving

the total voltage change occurring across the bridge.

22 Since voltage across the Zener diode remains constant,the total voltage change

occurring in that leg of the bridge is across resistor R2.

23 In the other leg of the bridge, the voltage change across the resistors is

proportional to their resistance values.

24 For this reason, the voltage change across B2 is greater than the voltage change

at point E. If the generator output voltage drops, point C is negative with

respect to point Zener diode.

25 Conversely, if the generator voltage output increases, the voltage between the

two points reverses polarity.

26 The bridge output taken between points R and B connects between the emitter

and the base of transistor Q1.

27 With the generator output voltage low, the voltage from the bridge is postive to

the emitter and positive to the base.

28 With the increase of current, the voltage across emitter resistor B11 increases.

29 This increase, in turn, applies a negative signal to the base of transistor Q4,

which decreases emitter to collector current and decreases the voltage drop

across emitter resistor R10.

30 This gives a negative bias on the base of Q2, which increases its emitter to

collector current and increases the voltage drop across its emitter resistor, R4.

31 This positive signal controls output transistor Q2.

32 The positive signal on the base of Q3 increases the emitter to collector current.

33 The control field of the exciter generator is in the collector circuit.

34 Decreasing the output of the exciter generator increases the field strength of the

ac generator, which decreases the generator output.

35 An underspeed switch located near the F+ terminal prevents generator

excitation when thefrequency is at a low value.

36 When the generator reaches a suitable operating frequency, the switch closes

and allows the generator excitation.

37 Resistors R27, R28, and R29 connect in series with the normally closed

contacts of relay K1. 38 The coil of relay K1 connects across the power supply

(CR4) for the transistor amplifier.

39Another type of solid-state voltage regulator operates by sensing the voltage

existing on the lines.

40 The voltage regulator consists of a sensing circuit with input rectifiers, a

temperature compensated Zener diode.