SYNCHRONOUS GENERATOR

J.Majumder MIE Senior Faculty

SYNCHRONOUS GENERATOR

Brushless Generator Rotor

PARTS OF THE ROTOR

Brushless Generator Excitation

ROTARY EXCITER BRUSHLESS SYSTEM

CT

G

K L

K L

SPACE HEATER

A.C. GENERATOR

F1S1

Sil

Ex

FzJK

Rc

Sz

Siz

RT

H1

H2

H1

H2

R

S

T

R

S

T

3A

4A

3A

4A

T1S1R1A

BAVR

123

CW

RISE

VR

CCRACB

AUX. CONT

DCT

k l

k l k l

K LCCT

l1k1 l2k2

kl

R

S

T

AC 1

SWITCH BOARD

VOLTAGE BUILD UP IN BRUSHLESS GENERATOR

An unloaded generator builds up voltage due to residual voltage in the winding .Star connected Reactor coil L2 is only the load of the generator. The inductivecurrent which appears in the reactor coil will appear in primary winding P1.

This current willinduce current

In secondarywinding S

Field

Connection diagram of Generator

AVR

The actual function of the

voltage regulator is to provide

a bypass for a variable portion

of the current supplied by the

excitation equipment for

controlling the generator

voltage.

The thyristor regulator module

consists of two assemblies:

the regulator module and the

firing module with thyristor in buck circuit.

AVR

The three-phase generator voltage, having been reduced to 24V by the

measuring-circuit transformers, is applied to terminals 17,18 and 19.

A direct voltage of approx. 30 V (terminal 20 to terminal 13 or 14) is produced at

the output of the rectifier bridge under the rated voltage of the generator.

This rectified voltage provides the actual pulse signal and the supply voltage the

control amplifier.

The regulator module supplies output terminal 15 with a control voltage of approx. 1 to 10 V, which is proportional to the control deviation.

AVR

In the control circuit of the firing module, a time adjustable firing impulse for the

thyristor is formed from the control voltage of terminal 15 in comparison with a

saw tooth voltage. The overvoltage protector operates at voltages over

600 V between terminals 1 and 5, then switches the thyristor through.

The excitation current is normally bucked with a single pulse.

If higher excitation is required, two firing modules for two pulse "buck" operation will be provided.

Mode of operation of regulatorThe generator voltage is fed to the regulator via plug connector X1 in a

single-phase, two-circuit arrangement. Transformer T1 steps down the

generator voltage which is then rectified by the load-side rectifier bridge V1,

V4. This rectified voltage provides the actual pulse signal "Uist“ the setpoint

voltage Usoll and the supply voltage ① for the regulator.

If the system uses a reactive current compensator, Current transformer T15

or interposing transformer T4 of the excitation unit is connected to load

resistor R1 via plug-in contacts X2/5 and X2/9.

In this operating mode the actual voltage is composed of the secondary

voltage of transformer T1 and the voltage of load resistor R1.

The magnitude of the resulting reduction in generator

voltage can be set with potentiometer S.

If an external set point selector is used, this is connected

by contacts X2/1 (A1) and X2/3 (A3). In this case micro switch S1/3 of the regulator must be opened.

A DC voltage of 0 to 10 V can be fed in via plug-in contacts X2/6 and

X2/2. This voltage acts on the comparator point of the control

amplifier. The set point can thus, for instance, be preset by higher-levelequipment.

Control amplifier ② (proportional again adjustable by potentiometer K and

reset time by potentiometer T) outputs a DC voltage which is converted into a

time adjustable firing pulse for thyristor V18 or V28 via the load side pulse

unit ③ .The generator excitation circuit is fed from rectifier

bridge V29. Resistor R48 and thyristor V28 form a parallel bypass circuit to

the field winding through which part of the current supplied by the excitation

unit flows. This method provides for generator voltage control.

In order to optimize the correcting action, a disturbance variable is injected

into the control amplifier via resistor R47.

Regulator gain, set point voltage integral action

The control module comprises potentiometers U, K, T, R 47 and S.

The rated generator voltage has been adjusted by potentiometer U, and the dynamic behaviour of the regulator on potentiometers K, T and R 47.

Potentiometer K is used to adjust the controller gain and potentiometer T is

used to adjust the integral action time, whereas potentiometer R 47 is used

to inject a disturbance variable into the comparator point of the control

amplifier in order to adjust dynamic behaviour.

Turning the knob of K and R 47 in the direction of descending numerals and

that of T in the direction of ascending numerals normally stabilizes the

control circuit and reduces the control rate.

Voltage Droop

When the generator is operating by itself, the thyristor

voltage regulator controls the generator voltage to the

preset reference value.

Frequency changes due to the droop characteristics of the

prime mover do not influence the accuracy of the generator output voltage.

Parallel operation by droop compensation equipment

Droop compensating equipment ensures uniform distribution of the reactive

power and reduces the generator output voltage in linear with the increase in

reactive current.

Regarding generators with current transformer for droop compensation,

potentiometer S in the regulator is adjusted so that there is no reduction in the generator voltage at unity p.f. but a 4% reduction at zero p.f.