Synchronous Generator Part 3

EET 306
Electrical Machine

Synchronous Generator

Part 3

School of Electrical System Engineering
DR. MOHAMAD NUR KHAIRUL HAFIZI BIN ROHANI

Blok 3, Cubicle 2
016-7425020

1

Chapter 4:
Synchronous Machine

4.1 SyncG : Constructional features & operation theory
4.1.1 Introduction
4.1.2 Salient pole rotor generators
4.1.3 Non-salient pole rotor generators
4.1.4 Different between Salient and Non-Salient pole generator
4.1.5 Principle Operation

4.2 SyncG : Basic parameter
4.2.1 Speed of rotation
4.2.2 Internal generated voltage
4.2.3 Equivalent circuit
4.2.4 Voltage regulation & Phasor diagram
4.2.5 Measuring model parameters

4.3 SyncG : Parallel operation of AC Generators

2

Chapter 4:
Synchronous Machine

4.1 SyncG : Constructional features & operation theory
4.2 SyncG : Basic parameter
4.3 SyncG : Parallel operation of AC Generators

4.3.1 Synchronization
4.3.2 Active and reactive power sharing between parallel

generator.
4.4 SyncM : Principle operation

4.4.1 Basic Principle.
4.4.2 Method of starting.
4.4.3 V-curve Characteristic..

3

RE-CALL

Salient?

RAM & RFM? Non-salient?

Alternator?

S.G Principle operation?

Common approach to supply DC Supply?

How to create AC Supply? Equivalent Circuit?
DC Test?

4

4.3 SyncG : Parallel operation of AC Generators

4.3.1 SYNCHRONIZATION
• Why in parallel? Advantages :

i. Can supply a bigger load than one machine by it self.
ii. To increase the reliability of the power system, since the failure of any one of

them does not cause a total power loss to the load.
iii. To allow one or more of them to be removed for shutdown and preventive

maintenance.
iv. If only one generator is used and it is not operating near full-load, then it will

be relatively inefficient. With several smaller machines in parallel, it is possible
to operate only a fraction of them.

5

Paralleling of a Generator Set System

6

4.3 SyncG : Parallel operation of AC Generators`

4.3.1 SYNCHRONIZATION
• The Conditions Required for Paralleling:

FoTrhe2 rsmets loinfevovlotaltgaegsestoobf e2 igdeennetricaatol,rrsmmsumstabgenietuqduealo. f
The 2 generators mvoultsatgheasvme tuhset ssaammee phase sequence.
Huge currents would flo(aw→ibn→otch)er two phases that not

sequence and damaging both machines.
ThTehephvaoslteaagneginlebooft‘hph‘pahsaesae’ afo’ rwbilol tbhemidaecnhtiincaelmatuasltl btiemeeqsuiaf l.

The frequenmcaygonfittuhdeenaenwdgaenngelreaatorer, scaamlleed oncoming
Thgeenpehraasteora,nmgulesst obfeosnlicgohmtlyinhgigmhaecrhtihnaenwthillecfhreaqnugesncslyoowfly

to be equal as runnriunngnsiynsgtesmys,tesmo t.he voltages can be
observed.

7

4.3 SyncG : Parallel operation of AC Generators

4.3.1 SYNCHRONIZATION

• The following steps describe the actual process of synchronizing two three-
phase alternator:

i. Assume that alternator 1 is iv. The three voltages of the incoming
supplying energy to the bus bas
of the station at rated voltage generator must be in phase with the
and frequency.
respective voltages of generator 1. To
ii. An incoming machine, alternator
2, is to be synchronized with accomplish this, the phase sequence of
alternator 1 for the first time.
the two alternators and their
iii. The speed of alternator 2 is
increased until it turns at the frequencies must be the same. The use
value required to give the
desired frequency. The voltage of synchronizing lamps is a simple way to
of generator 2 is adjusted by
means of its field rheostat until
it is equal to that of generator 1.

check these relationships. 8

Chapter 4:
Synchronous Machine

4.1 SyncG : Constructional features & operation theory
4.2 SyncG : Basic parameter
4.3 SyncG : Parallel operation of AC Generators

4.3.1 Synchronization
4.3.2 Active and reactive power sharing between parallel

generator.
4.4 SyncM : Principle operation

4.4.1 Basic Principle.
4.4.2 Method of starting.
4.4.3 V-curve Characteristic.

9

4.3 SyncG : Parallel operation of AC Generators

4.3.2 ACTIVE AND REACTIVE POWER SHARING BETWEEN
PARALLEL GENERATOR.

❑Introduction as Stand Alone:

• When the generator is loaded

• power is drawn from the mechanical system
• the generator applies a torque which opposes the direction of motion of the

mechanical system
• As a result, the generator tends to slow down the mechanical system.

• Changing mechanical speed is undesirable, as it results in a change in the
frequency of the induced voltages.

• For this reason, a "governor" is applied to the mechanical system to make the
change in speed predictable with power changes.

10

4.3 SyncG : Parallel operation of AC Generators

4.3.2 ACTIVE AND REACTIVE POWER SHARING BETWEEN
PARALLEL GENERATOR.

❑Introduction as Stand Alone (Cont’d):

• The governor or speed limiter sets the no-load speed and controls the
reduction in speed so that the frequency-power relationship is linear:

Figure : The plots show the
linear reduction in speed as the
power drawn from the
mechanical system increases.

• If the frequency of the generated voltages is too low, the frequency can be
increased by increasing the no-load speed of the mechanical governor.

11

4.3 SyncG : Parallel operation of AC Generators

4.3.2 ACTIVE AND REACTIVE POWER SHARING BETWEEN
PARALLEL GENERATOR.

❑Introduction as Stand Alone (Cont’d):

• Mathematically, the changes in frequency with load are described using two
quantities, the Speed Droop, SD and the slope of the power-frequency plot, Sp.

• Speed Droop, SD is defined as

n −n f −f
SD = NL FL x100% = NL FL x100%

nf
FL FL

• Typical values for speed droop are in the range 2% - 4%

12

4.3 SyncG : Parallel operation of AC Generators

4.3.2 ACTIVE AND REACTIVE POWER SHARING BETWEEN
PARALLEL GENERATOR.

❑Introduction as Stand Alone (Cont’d):

• The power from the generator can be found using:

Pgen = S ( f − f ) where;
p NL sys
fNL = no load frequency
fsys = operating system frequency

• The slope Sp is often quoted in kW/Hz or MW/Hz.

P P
S = f = FL
p
f −f
NL FL

13

4.3 SyncG : Parallel operation of AC Generators

4.3.2 ACTIVE AND REACTIVE POWER SHARING BETWEEN
PARALLEL GENERATOR.

❑Introduction as Stand Alone (Cont’d):

• The effect of changes to terminal voltage with reactive load can be plotted on
a diagram similar to the f-P plot;

Figure : The plots show the
linear reduction in voltage as
the reactive-power drawn from
the mechanical system
increases.

• Increasing the inductive load on the generator reduces the terminal voltage,
adding capacitance increases the terminal voltage. Reductions to the terminal
voltage can be compensated by increasing the no load voltage (|E|).

14

4.3 SyncG : Parallel operation of AC Generators

4.3.2 ACTIVE AND REACTIVE POWER SHARING BETWEEN
PARALLEL GENERATOR.

❑Introduction as Stand Alone (Cont’d):
• In a stand-alone system, Power and Reactive Power drawn from a

generator are determined by the load.
• We will see with parallel operation that the demand on a

generator in a parallel system can be controlled independently of
the load requirements by adjusting the mechanical governor and
excitation voltage.

15

4.3 SyncG : Parallel operation of AC Generators

4.3.2 ACTIVE AND REACTIVE POWER SHARING BETWEEN
PARALLEL GENERATOR.

❑Frequency-Real Power Characteristics:

• Consider the case where 2 generators (G1 & G2) are connected to supply all
the power requirements for a load. In this case the frequency-power plots:

• The total power to the load, Pload is the sum of the power from each generator,
PG1 + PG2.
16

4.3 SyncG : Parallel operation of AC Generators

4.3.2 ACTIVE AND REACTIVE POWER SHARING BETWEEN
PARALLEL GENERATOR.

❑Frequency-Real Power Characteristics (Cont’d):

• Substituting to find the power from each generator in terms of the system
frequency:

Pgen = S ( f − f )
p NL sys

17

4.3 SyncG : Parallel operation of AC Generators

4.3.2 ACTIVE AND REACTIVE POWER SHARING BETWEEN
PARALLEL GENERATOR.

❑Frequency-Real Power Characteristics (Cont’d):

• From the equation above it is clear that the system frequency is a function of
both generator mechanical governors and no-load frequencies.

• In addition, the power drawn from one generator is dependent on how the
other generator is operated.

18

4.3 SyncG : Parallel operation of AC Generators

4.3.2 ACTIVE AND REACTIVE POWER SHARING BETWEEN
PARALLEL GENERATOR.

❑Frequency-Real Power Characteristics (Cont’d):

➢Changing Load Power, Pload
• With constant generator no-load speeds or frequencies, fNL1 & fNL2 ;
• Changing load effects the system frequency, fsys.

19

4.3 SyncG : Parallel operation of AC Generators

4.3.2 ACTIVE AND REACTIVE POWER SHARING BETWEEN
PARALLEL GENERATOR.

❑Frequency-Real Power Characteristics (Cont’d):

➢Changing Load Power, Pload
• With constant generator no-load speeds or frequencies, fNL1 & fNL2 ;
• Changing load → effects the system frequency, fsys.

20

4.3 SyncG : Parallel operation of AC Generators

4.3.2 ACTIVE AND REACTIVE POWER SHARING BETWEEN
PARALLEL GENERATOR.

❑Frequency-Real Power Characteristics (Cont’d):

➢Changing Load Power, Pload
• With constant system frequency, fsys;
• The generator set points can be adjusted. Both fNL1 & fNL2 must be adjusted in

order to maintain the balance of power between Generators 1 & 2.

21

4.3 SyncG : Parallel operation of AC Generators

4.3.2 ACTIVE AND REACTIVE POWER SHARING BETWEEN
PARALLEL GENERATOR.

❑Frequency-Real Power Characteristics (Cont’d):

➢Changing Load Power, Pload
• With constant system frequency, fsys;
• The generator set points can be adjusted. Both fNL1 & fNL2 must be adjusted in order to maintain

the balance of power between Generators 1 & 2.

22

4.3 SyncG : Parallel operation of AC Generators

4.3.2 ACTIVE AND REACTIVE POWER SHARING BETWEEN
PARALLEL GENERATOR.

❑Frequency-Real Power Characteristics (Cont’d):

➢Constant Load Power, Pload
• The system frequency fsys can still be adjusted by controlling both generators

or one of the generators alone,;
• Both fNL1 & fNL2 are adjusted to control the system frequency and to maintain

the power balance between the generators.

23

4.3 SyncG : Parallel operation of AC Generators

4.3.2 ACTIVE AND REACTIVE POWER SHARING BETWEEN
PARALLEL GENERATOR.

❑Frequency-Real Power Characteristics (Cont’d):

➢Constant Load Power, Pload
• The system frequency fsys can still be adjusted by controlling both generators or one of the

generators alone,
• Both fNL1 & fNL2 are adjusted to control the system frequency and to maintain the power balance

between the generators.

24

4.3 SyncG : Parallel operation of AC Generators

4.3.2 ACTIVE AND REACTIVE POWER SHARING BETWEEN
PARALLEL GENERATOR.

❑Frequency-Real Power Characteristics (Cont’d):

➢Constant Load Power, Pload
• The system frequency fsys can still be adjusted by controlling only one

generator fNL2, with constant fNL1.
• Changes both the power balance, PG1 & PG2 and fsys .

25

4.3 SyncG : Parallel operation of AC Generators

4.3.2 ACTIVE AND REACTIVE POWER SHARING BETWEEN
PARALLEL GENERATOR.

❑Frequency-Real Power Characteristics (Cont’d):

➢Constant Load Power, Pload
• The system frequency fsys can still be adjusted by controlling only one generator fNL2, with constant

fNL1.
• Changes both the power balance, PG1 & PG2 and fsys .

26

4.3 SyncG : Parallel operation of AC Generators

4.3.2 ACTIVE AND REACTIVE POWER SHARING BETWEEN
PARALLEL GENERATOR.

❑Voltage-Reactive Power Characteristics:
• The house diagram and relationship for voltage variation with

reactive power supply is constructed in a similar manner to the
frequency-power characteristic.

27

28

4.2 SyncG : Basic Parameter

EXAMPLE 4.3
A 480-V, 250-kVA, 0.8-PF-lagging, two-pole, three-phase, 60-Hz synchronous
generator’s prime mover has a no-load speed of 3650 r/min and a full-load

speed of 3570 r/min. It is operating in parallel with a 480-V, 250-kVA, 0.85-PF-

lagging, four-pole 60-Hz synchronous generator whose prime mover has a no-

load speed of 1800 r/min and a full-load speed of 1780 r/min. The loads supplied

by the two generators consist of 300 kW at 0.8 PF lagging.

(a) Calculate the speed droops of generator 1 and generator 2. [2.24%,
1.12%]

(b) Find the operating frequency of the power system. . [59.627 Hz]

(c) Find the power being supplied by each of the generators in this system. .
[181 kW, 119 kW]

(d) What must the generator’s operators do to adjust the operating
frequency to 60 Hz?

(e) If the current line voltage is 460 V, what must the generator’s operators

do to correct for the low terminal voltage? 29

EXAMPLE 4.3

Solution

30

EXAMPLE 4.3

Solution (cont’d)

(e) If the terminal voltage is 460 V, the operators of the generators must increase the field
currents on both generators simultaneously. That action will increase the terminal voltages
of the system without changing the reactive power sharing between the generators.

31