GENERATOR PROTECTION

SYSTEM t.· . _.·,, __ ·-

~· .... .. . '.

44311 TICHNICAL TRAINING SQUADRON

44311 MILITARY a•LIFI W•G, lNG (MAC)

ALTUS AIR FORCE BASI, OKLAHOMA 19 OCT 77 GPO 500

.,

FOR TRAINING PURPOSES ONLY

NOT NECISSARIL Y CURRENT AFTER DISTRIBUTION

Page A

GENERATOR PROTECTION SYSTEM

~ When you have finished this program you will be able to state:

1. The location of the generator protection panels.

2. The purpose of the autoparalleling circuit.

3. The indication of an unbalanced current.

4. The indications of an undervoltage caused by a bus fault that is:

a. Cleared by opening the BUS TIE CONTACTOR.

b. NOT cleared by opening the BUS TIE CONTACTOR.

5. The indication of an undervoltage caused by a generator fault.

6. The indication of an overvoltage.

7. The indications of neutral current.

8. The indication of a differential fault.

9. The action to take when:

a. GENERATOR OUT light illuminates then extinguishes when the generator

switch is turned off.

b. GENERATOR OUT light illuminates and remains illuminated when the

generator switch is turned off.

c. BUS TIE OPEN light illuminates.

d. BUS TIE OPEN, GENERATOR OUT and MAIN BUS OFF lights illuminat~.

e. All four BUS TIE OPEN lights illuminated.

Page 1

A generator protection panel, for each MAIN generator, provides pro-

tection and control of the generating system. The protection provided is

~ automatic; therefore, your primary responsibility is to analyze the indica-

tions received, and determine the corrective action to take.

We will discuss each of the possible malfunctions, their indications and

then, later in the book, the corrective action to take.

First, let's determine the LOCATION of the generator protection panels.

Look at the illustration below.

MAIN GENERATOR PROTECTION PANELS

The generator protection panels are located on the Lt~~R

5L6CI Fill in the blanks then turn to Page 2 and

check your answers.

Page 2

UNDER DECK ELECTRICAL EQUIPMENT RACK.

Yes, the generator protection panels are located on the Under Deck

Electrical Equipment Rack, to the right of the crew latrine.

The first protective circuit we will discuss is the AUTOPARALLELING

CIRCUIT. The PURPOSE of the autoparalleling circuit is to prevent or allow

initial placement of the generators on the tie bus. The tie bus is energized

by the first generator connected to it. The autoparalleling circuit compares

the frequency of each generator, being added to the bus, to ~he frequency of

the tie bus. The circuit will PREVENT a generator from being connected to

the tie bus if it is out of phase. When the generator is in phase with the

tie bus, the circuit will ALLOW it to connect to the tie bus.

What is the purpose of the autoparalleling circuit?

( ) a. Keep the generators in parallel.

( ~ b. Prevent or allow initial placement of the generators on the tie bus.

Page 3

( ) b. Prevent or allow initial placement of the generators on the tie bus • •

Yes, the purpose of the autoparalleling circuit is to prevent or allow

~initial placement of the generators on the tie bue. After the generators

are connected to the tie bus the autoparalleling circuit is NOT used.

During parallel operation, if unbalanced loads occur between generators,

the system is protected by an UNBALANCED CURRENT circuit. If a generator

gets more than 10% out of parallel, either high or low, the unbalanced current

circuit will disaonneat it from the Tie Bus.

Study the picture.

NO. 1 NO. 2 NO. 3 NO. 4 With the above condition, would you expect the No. 2 BUS TIE OPEN

light to illuminate?

( ) No

( vY Yes

Page 4

(~ Yes .

Right, the indication you will receive from an unbalanced current is a

BUS TIE OPEN l ight.

If a generator gets more than 10% higher or lower than the others, it is

automatically disconnected ·from the Tie Bus by the

(~a . Unbalanced current circuit.

( ) b . Autoparalleling circuit .

s.

7 .

Page 5

f~) a. Unbalanced current circuit .

Yes, if a generator gets more than 10% out of parallel it is automatically

disconnected from the tic bus by the unbalanced current circuit.

Remember now, the generator is still operating and supplying po,.;er to

its main bus . The unbalanced current circuit ONLY disconnects it from the

tie bus . The only indication of UNBALANCED CURRENT is the BUS TIE OPEN light.

UNBALANCED CURRENT -~ ~ -~::~

The next protective circuit \ve will discuss is for UNDERVOLTAGE. An

undervoltage can be caused by a BUS fault (excessive amperage draw) or by a

GENERATOR fault (internal malfunction of a generator or its voltage regulator).

First, l et ' s discuss undcrvoltage caused by a bus fault.

Should an undervoltage condition occur, caused by a BUS FAULT, two time

delay relays are energized. 1nc first relay causes the Bus Tic Contactor to

open . If this decrease in load corrects the condition, the second relay is

de-energized .

\'/hat indication will you receive for an undervoltage , caused by a bus

fault, that is isolated by opening the Bus Tie Contactor?

( ) a . GENERATOR OUT light .

( v1 b . BUS TIE OPEN light.

Page 6

(wf) b. BUS TIE OPEN light.

Yes, the indication for an undervoltage, caused by a bus fault and

isolated by opening the Bus Tie Contactor, is the BUS TIE OPEN light.

If the undervoltage condition is NOT cleared by opening the Bus Tie

Contactor, the second relay will open the Generator Line Contactor. The

generator is de-energized and the voltage output drops to zero.

See if you can list~the indications you will receive from this under­

voltage condition.

1. {)US \\E

2. Gt:N ou-r

3. ~u~ oFt=

Did you lis t these?

GENERA TOR OUT light .

NAIN BUS OFF l ight .

BUS TIE OPEN l ight.

Page 7

You will receive these indications because the Bus Tie Contactor is

open , the Generator Line Contact or is open and the generator is de-energized .

Should an undervoltage occur , caused by a GENERATOR FAULT, the generator

line contactor will open and the generator will be de-energized. The Bus Tie

Contactor will NOT open and the remai ni ng generators will pick up the load of

the faulty generator.

What indication \"ill you receive for an undervoltage caused by a generat or

fault?

a. GEU OvT

Page 8

a. GENERATOR OUT light.

Yes, the only indication is the GENERATOR OUT light. The generator is

de-energized but its main bus receives power from the tie bus.

GENERATOR FAULT is a malfunction of the_ generator., therefore, the

generator is de-energized. The ONLY indication of UNDERVOLTAGE caused by a

GENERATOR FAULT is the GENERATOR OUT light.

OK, let's see if you remember the indications.

1. What indications will you receive from an undervoltage caused by a BUS fault that is:

cleared by opening the Bus Tie Contactor?

NOT cleared by opening the Bus Tie Contactor?

a. GE.t-J OUT

b. Bus oFF

c. {3us. opel\/

2. What indication will you receive from an undervoltage caused by a GENERATOR fault?

a. Gf,.J ou_,-

Answers to review questions.

1. cleared by opening the Bus Tie Contactor.

a. BUS TIE OPEN light.

NOT cleared by opening the Bus Tie Contactor.

a. GENERATOR OUT light.

b. MAIN BUS OFF light.

c. BUS TIE OPEN light.

2. a. GENERATOR OUT light.

Wonderful, but, ever onward.

Page 9

Protection is also provided for OVERVOLTAGE. In the event of an over­

voltage, the overvoltage circuit will OPEN the Generator Line Contactor and

de-energize the generator. The time required to open the Generator Line

Contactor depends on the amount of overvoltage. The higher the voltage, the

shorter the time required to open the Generator Line Contactor.

What indication will you receive from an overvoltage condition?

( ) a. MAIN BUS OFF light.

( ~ b. GENERATOR OUT light.

Page 10

(V ) b. GENERATOR OUT light.

Yes, the GENERATOR OUT light is the indication of an ovcrvoltage . The

overvoltage circuit will open the Generator Line Contactor and de-energize

the generator' so the GENERATOR OUT light \"ill illuminate . ,, GEN our II \\'hen a generator is kicked off the line, because of ovcrvoltage, its

main bus is powered from the tie bus . The only indication of OVERVOLTAGE

is the GENERATOR OUT light.

Now, it ' s review time. Answer the following questions, then check your

answers on the next page.

1. lfuere are the generator protection panels located?

2. What is t he purpose of the autoparalleling circuit? lo ~[ - J~ tJ"T' Of. / ll')( 6 -,l ""f.;) C,o\"'-L 0.._1 LIIV._

,:, . lfuat is the indication of an unbalanced current?

,J I L

4 . lfuat are t he indications of an undervoltage caused by a bus fault if openi ng t he Bus Tic Contactor will:

a . clear the fault? '&.;.,~ \\ ~ o, "'

b . ~OTclearthefault? E1l ov\ j ~

5. M1at is the indication of an undervoltagc caused by a generator fault ?

6 . What is the indication of an overvoltage?

u c· , ..)CT

Page 11

1. On the Under Deck Electrical Equipment Rack.

2. To prevent or allow initial placement of the generators on the tie bus.

3. BUS TIE OPEN light.

4. Opening the Bus Tie Contactor will:

a. clear the fault. BUS TIE OPEN light.

b. NOT clear the fault. BUS TIE OPEN light.

5. GENERATOR OUT light.

6. GENERATOR OUT light.

GENERATOR OUT light_.

MAIN BUS OFF light.

OK, let's see what the other protective circuits do.

The next circuit protects the system in the event of a DIFFERENTIAL FAULT.

Differential fault is a short in the main power leads. See the illustration

below.

TIE BUS

·Jit-1 ----c0t----J;""T"""'t' ~~Gr;---....(1

DIFFERENTIAL FAULT/

This is a simplified diagram showing only one phase of one generator.

Page 12

The protection circuit consists of a current sensing loop, current

sensing transformers (CT) and a differential protection relay (DPR). See

the illustration below.

GLC

~ ~ -------·CURRENT SENSING

TB

BTC

~ !

LOOP--------J

uuring normal operation, each CT has the same amount of current flowing

through it. Since the CT's are connected 180° out of phase, their voltages

cancel. So, in normal operation NO current flows through the current sensing

loop. See the illustration below. TB

GLC BTC CT

EQUAL OPPOSING VOLTAGES

Page 39

Answers to review questions. ~

l. Disconnect the CSD.

~. Test the voltage and frequency of the affected generator. Return it to the

line if they are within limits.

3. Observe the voltage and frequency of the affected generator. Reset the Bus

Tie Contactor if the voltage and frequency are within limits.

4. Turn the generator switch off. Observe that the generator out light

extinguishes. Reset the Bus Tie Contactor.

5. None.

This completes the Generator Protection System program.

Ii you want to review the booklet, or portions of it, feel free to do so.

INDEX

PAGE

Objectives .......................... A

Autoparalleling Circuit • • • • • • • • • • • • • • • • • • • 2

Unbalanced Current . . . . 3-4-5

Undervoltage • . . . . . . . . . . . . . . . • . 5-6-7

Overvoltage. • 9-10

Differential Fault • • • • • 11 thru 16

Neutral Current .•• . . . . . . . . . . . . . . . • • 17 thru 22

'tru,S.COVERNMENT PRINTING OFFICE: 1977·771·018/40·77

Page 38

None.

Right, there is no action you can take. Just continue operating in

isolated operation.

It's review time again. Answer the following questions.

1. What action should you take when the "GENERATOR OUT" light illuminates

and REMAINS ILLUMINATED when the generator control switch is turned OFF?

'\)\3c_ CsD

2. lfuat action should you take when the "GENERATOR OUT" light illundnates

then EXTINGUISHES when the generator control switch is turned OFF? IE'.sr G;;;,J

3. What action should you take when the "BUS TIE OPEN" light illuminates?

TE3T G~JJ

4. What action should you take when the "BUS TIE OPEN", "GENERATOR OUT",

and "MAIN BUS OFF" lights illuminate?

kv..'fe OFF

5. What action should you take when all four "BUS TIE OPEN" lights illuminate?

No we:

Page 37

Make NO further attempt to reset it.

IMPORTANT:

Anytime the GENERATOR OUT light, MAIN BUS OFF light and BUS TIE OPEN

light all illuminate, DO NOT reset the Bus Tie Contactor until you have

turned the generator control switch OFF.

Now the indication of all four BUS TIE OPEN lights. This is an indi­

cation of a fault on the tie bus.

What action should you take if all four BUS TIE OPEN lights illuminate

at the same time?

Page 36

Turn the control switch off and make no further attempt to return it to the

line.

Yes, turn the generator off and RESET the Bus Tie Contactor.

What should you do if the BUS TIE OPEN light illuminates again?

~~vc. Op-q-""

,,

(

Page 35

voltage and frequency

If the voltage and frequency are within limits, return the generator to

the line.

What should you do ~f the generator trips off of the line again?

Lt:AIJ~ 01'P

Page 34

( v') a. Leave the system off.

Yes, if the GENERATOR OUT light remains illuminated with the control

switch off, and the BUS TIE OPEN and MAIN BUS OFF lights are on, you have a

differential fault some place.between the GLC and BTC. You should not reset

the Bus Tie Contactor because it would connect the differential fault to the

Tie Bus, and could put the system in isolated operation.

If the GENERATOR OUT light EXTINGUISHES when the control switch is

turned off, reset the Bus Tie Contactor, then place the control switch to

the "TEST" position and test the generator as previously outlined.

With the control switch in the "TEST" position, you should observe the

Va--tS and ~e of that generator.

Page 33

The Bus Tie Contactor is reset to restore power to the main bus.

Remember now, if the BUS TIE OPEN light illuminates, the FIRST thing

to do is observe the voltage and frequency of that generator.

Now, let's see what to do if you receive these indications: GENERATOR

OUT light, MAIN BUS OFF light, BUS TIE OPEN light.

The first thing you should do is turn the generator switch OFF.

What should you do if the GENERATOR OUT light remains illuminated?

( ) a. Leave the system off.

( ) b. Leave the generator off and reset the Bus Tie Contactor.

Page 32

Cv1 b. Place the bus tie switch to OPEN and then to NORMAL.

Yes, you reset the Bus Tie Contactor by placing the bus tie switch to

OPEN and then to NORMAL. If the BUS TIE OPEN light illuminates again, do NOT

attempt to reset.

If the voltage and frequency are NOT within limits, turn the generator

off and reset the Bus Tie Contactor.

Why do you reset the Bus Tie Contactor after the generator is turned off?

Page 31

(V ) i\o .

That • s right, l t ls NOT necessary to place the generator control Slvi tch

in the 11TEST" position. Just turn the voltage and frequency selector to the

generator you want to observe .

lf the vol tagc is in the green range and the frequency i s 1vi thin eight

cycles of system frequency, reset the Bus Tie Contactor.

llow do you reset the Bus Tie Contactor?

( ) a . Turn the generator control switch OFF and then back ON .

( t)/b . Place the bus tie switch to OPEN and then to NORNAL.

Page 30

Approximately one minute .

Yes, hold the control switch in the "TEST" position approximately one

minute to see if the frequency returns within limits.

If the frequency comes back within limits, return the generator to the

line. However, if it does NOT or if the generator trips off the line again,

you should leave that generator off.

The next trouble \ve \vill discuss is the BUS TIE OPEN light .

If this light illuminates, you should observe the voltage and frequency

of that generator .

Is it necessary to place the generator control S\vitch in the "TEST" position

to observe the voltage and frequency when the BUS TIE OPEN light illuminates?

( ) Yes.

(~No.

Page 29

(~ c. Within eight cycles of system frequency and within the green range

on the Voltmeter.

Yes, you should return the generator to the line if each phase is stabilized

within eight cycles of system frequency and within the green range on the Volt-

meter. However, if the generator trips off the line again, turn the control

switch off and make NO further attempt to return it to the line.

If a generator test reveals that the voltage is within limits but the

frequency is not, hold the generator control switch in the "TEST" position

for approximately one minute. If the frequency returns within limits, return

the generator to the line.

When testing a generator, if the voltage is within limits but the frequency

is not, how long should you hold the control switch in the "TEST" position?

Af?MX., l W\ \ J

Page 28

"A" Phase.

Yes, the phase selector is set to test "A" Phase.

After you have tested all three phases, if the frequency is stabilized

and within EIGHT cycles of system frequency and if the voltage is within the

GREEN range on the meter, return the generator to the line.

( )

You should return the generator to the line if each phase

a. Within eight cycles of system frequency.

is:

( ) b.

(~.

Within the green range on the Voltmeter.

Wi~hin eight cycles of system frequency and within the green range

on the Voltmeter.

Page 27

( ~ a. Voltage and Frequency output.

Yes, you should observe the Voltage and Frequency output of all three

phases of the affected generator.

You can test each phase of the generator by holding the generator control

switch to the "TEST" position, and turning the phase selector to each phase.

See the illustration below.

Which phase would be tested when the phase selector is in the position

shown above? ~A''

Page 26

Cv0 b. Turn the Voltage and Frequency selector to the affected generator.

Rog, you must first turn the Voltage and Frequency selector to the

affected generator before testing.

Then test the generator by holding the generator control switch in the

"TEST" position. See the illustration below.

With the generator control switch in this position, you should observe

the:

( ~. Voltage and Frequency output.

( ) b. GENERATOR OUT light.

Page 25

disconnect the CSD.

Yes, disconnect the CSD because a differential fault has occured.

If the GENERATOR OUT light illuminates, but EXTINGUISHES when the generator

control switch is turned off, as in an overvoltage condition. You should first

turn the "Voltage and Frequency Selector" to the affected generator. This wi.ll

.allow the Voltmeter and Frequency meter to indicate the output of that gener­

ator. See the illustration below.

Before testing a generator, you must first:

( ) a. Adjust the Voltmeter and Frequency meter.

( ~. Turn the Voltage and Frequency selector to the affected generator.

Page 24

(~ b. Disconnect the CSD.

That's right, baby, don't fool around. Disconnect the CSD. This will

prevent possible damage to the generator and unnecessary operation of the

CSD.

Any time the GENERATOR OUT light illuminates and remains illuminated

after the generator switch has been turned off, you should:

(

Page 23

Answers to review questions.

1. The GENERATOR OUT light will remain illuminated with the generator control

switch OFF.

2. GENERATOR OUT light, MAIN BUS OFF light, BUS TIE OPEN light.

3. All four BUS TIE OPEN lights.

OK, now that you know the indications of the troubles, let's see what to

do about them.

First the DIFFERENTIAL FAULT. When a differential fault occurs you

should make no attempt to return that generator to the line.

l~at action should you take if a differential fault occurs in flight?

( ) a. Test the generator.

( w-- b. Disconnect the CSD.

Page 22

All four BUS TIE OPEN lights .

Yes, if you have a neutral current on the tie bus, all four BUS TIE

OPEN lights will illuminate .

It ' s r eview time again . Answer the following questions .

1 . What is the indication of a diffe r ential fault? _;.__ -, J )£ L crE. ...--q-~ _ .Jt

2 . What are the i ndications of a neu tral current that is NOT on the tie bus? ,. .f u ::>« .. iT ( p ._)- orr ( ..1 1J ~ I

3 . \fuat are the indications of a neutral current on the tie bus?

4 ~~LIs opOI...J Lt I c~

. Page_ 2_1

Put the system in isolated operation.

Yes, a neutral current on t}l.e tie bus will· op~J)· ai(._-fol!:r Bus Tie·

Contactors, and put the system· ~n isolated- -op~rati'on~_ ·

What inC,.ication will'you receive from ~- ~eutr.a:l: curren'l;. on the tie bus?

.· .. ·

. · :

...... . . '

.. ..

L .

Page 20

GENERATOR OUT light. MAIN BUS OFF light. BUS TIE OPEN light.

Did you list all three· of. these lights? It's true that the neutral

current circuit only causes the BUS TIE OPEN light to illuminate, but the

undervoltage relay will cause the other lights to illuminate. The indication

of neutral current is all three lights, GENERATOR OUT, MAIN BUS OFF and BUS

TIE OPEN.

Should a neutral current occur on the tie bus, or a line attached directly

to it, the neutral current circuit will open.all four Bus Tie Contactors.

NEUTRAL CURRENT

DPR

What effect will this ·have .on the generating system?

\TB

MAIN BUS

Opens the BTC . . Yes, the neutral current circuit opens the BTC, in the event of a shorted

phase, which occurs outside the differential fault-protected zone.

\~at are the indications of a neutral current?

Page 18

Opens the BTC.

Yes, the neutral current will open the BTC and the undervoltage

circuit trips the generator and GLC.

The neutral current circuit provides protection from a shorted phase,

when the short is OUTSIDE the differential fault protected zone. See the

illustration below.

NEUTRAL CURRENT

MAIN BUS

If the neutral current should occur, as in the illustration above, the

neutral current relay will cause the BTC to open, then the undervoltage circui

will cause the GLC to open and de-energize the generator.

What protection does the neutral current circuit provide for a shorted

phase, which occurs outside the differential fault protected zone?

Page 17

(~ b. Neutral current circuit.

YES. The electrical system is protected from an open or shorted phase

by the neutral current circuit.

Neutral current is a cousin to "differential fault" and the same current

sensing loop is us~d to provide protection from it. See the illustration

below.

TB

NCR= NEUTRAL CURRENT RELAY MAIN BUS

In the event of an OPEN PHASE, the neutral current circuit will open the

Bus Tie Contactor, then the undervoltage relay will de-energize the generator

and the Generator Line Contactor.

What protection does the NEUTRAL CURRENT circuit provide for an open

phase?

Page 16

a. 1he GENERATOR OUT light remains i lluminated \vith the generator control

Slvi tch OFF .

DIFFERENTIAL FAULT INDICATIO~

TI1e next circuit is for NEUTRAL CURRENT .

TI1e NEUTRAL CURRENT circuit protects the system i~ the event of an open

or shorted phase.

TI1e e lectrical system is protected from an open or shorted phase by the:

( ) a . Overvoltage circuit.

( v5 b. Neutral current circuit .

Page 15

(/) Yes. TB

GLC

l= I BTC CT

~

Yes, the differential fault circuit will cause the, BTC to open, because

the fault was not cleared by opening the GLC.

When a GENERATOR OUT light illuminates and remains illuminated after the

Generator Control Switch is placed in the OFF position, a Differential Fault

has occurred.

How can you tell if a differential fault has occurred?

Ge1v -0\..11 ON

I

Page 14

De-energizes the generator and opens the GLC.

TB . DIFFERENTIAL FAULT -- GLC

~ Yes, in the event of a differential fault the differential protection

cir~uit will de-energize the generator and open the GLC.

If opening the GLC isolates the fault, the DPR will de-energize. However,

if the fault is NOT cleared by opening the GLC, the DPR will remain energized

and cause the BTC to open.

GLC

~ With the above condition, will the DPR cause the BTC to open?

( \)( Yes.

( ) No.

TB

Page 13

Should a differential fault occur in the protected zone, one CT receives

a higher current flow. See the illustration below.

l_--- - - -- - -PROTECTED ZONE - - - - - - - +

This unbalances the circuit and energizes the differential protection

relay, which causes the generator and GLC to be de-energized.

How does the differential protection circuit protect the system from a

differential fault?