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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?