unit protection scheme for a thermal power plant,master fuel relay,turbine trip,generator trip ,GT trip ,UAT trip

1. SHIVAJI CHOUDHURY

2.  Safe operation of plant
 Lowest cost of generation
 Long equipment life
 Minimum environmental effects

3.  The basic requirements of an interlock
system for a unit shall accomplish the following:
 (1) Protect personnel from injury.
 (2) Protect equipment from damage.
 (3) Protect boiler/turbine/generator operation by
limiting actions to a prescribed operating
sequence or by initiating trip devices when
approaching an out-of-range or unstable operating
condition.

4.  Boiler tripping -Master fuel relay ( MFR )
 Turbine( Steam) tripping
 Generator tripping

5.  Operating safety ,
 To prevent uncontrolled fire ,
 To prevent implosions and explosions in the
boiler.

6.  Less than fireball and loss of 240 V AC any elevation in service.
 Drum level very low
 Drum level very high
 Both ID fan off
 Both FD fan off
 Air flow is less than 30%
 Furnace press VLO
 Furnace press VHI
 Loss of all fuel trip
 Unit flame failure trip
 Both emergency PB trip
 Reheater protection trip
 Loss of 220 V DC more than 2 sec

7.  Shut/close main fuel valve (LDO)
 Shut/close main fuel valve (HFO)
 Trip all running mills
 Trip all running P A fans
 Trip all running SA fans
 Close HPLP bypass( if open)
 Turbine trip
 Shut/close SH attemp block valve
 Shut/close RH attemp block valve
 Trip Electrostatic Precipitators (ESP)
Boiler
Fuel
trip

8. 1. Drum boilers, a MFR trip on low drum level
is required by ASME Boiler Code to
prevent loss of natural circulation and
to protect the drum against thermal shock.
2. Turbine trip on high drum level of boiler to prevent
water carryover to Turbine.
3. For controlled circulation boilers, pumps are
utilized to ensure circulation.
Adequate circulation is determined by
differential pressure measurements,
and tripping of the boiler fuel(MFR) is required
when adequate circulation is not verified.

9.  When spray attemperators are used for
regulating superheat and reheat
temperatures, the spray control valves
and block valves should be automatically
closed when the MFR is tripped to prevent
spray water from entering the turbine
through the Main Steam /cold reheat line.

10.  Excessive negative pressure (draft) can
produce implosions of the boiler
walls, precipitator, or the ducts
connected to them.
 The most likely time for a furnace implosion is at t
he time of a boiler-fuel trip (MFR).
This causes a sudden
drop in temperature, which in turn causes a
sudden negative pressure within the furnace.


11. MFR optd
BOILER
TRIP
Turbine
trip
Reverse
Power
Prot
2 sec
Generator
C B trip
UAT
C B trip
Field
C B trip

12.  Low condenser vacuum
 Low lube oil press
 Hi axial shift
 HPSU emergency OFF
 Bearing temperature protection optd
 Main steam temp VLO
 Elect generator protection optd class A
 Elect generator protection optd class B
 Fire protection optd
 MFR optd
 Turbine emergency PB optd
 Trip command initiated from ATRS
 Overspeed of turbine

13.  Loss of vacuum in the condenser is
detected and initiates a turbine trip to
prevent over heating damage to the low
pressure turbine section .
 Overspeed detection is a basic turbine
protection to prevent damage from high
centrifugal .
 An excessive axial motion of the rotor spindle at th
e thrust bearing initiates a turbine trip
to prevent or reduce mechanical damage .

14.  Turbine trip results in the closing of the main and r
eheat stop valves.
 The generator should not be tripped until the
turbine-generator unit reaches a no load
or negative load condition.
 A reverse power relay (short timer) is used in
the sequential trip logic scheme where motoring is
allowed for a short time to ensure the prime mover
has lost sufficient energy to prevent overspeed
following a turbine trip .

15.  Turbine vacuum breaker will open to reduce coasting down
time of turbine :
If Turbine tripped on
1. axial shift tripped,
2. Lube oil press VLO,
3. Fire protection operated,

16. Turbine
trip
HPLP
Bypass
Not
opened
MFR
OPTD
Boiler
trip
Open
HPLP
bypass
Reheater
Protection
optd
Gen
Reverse
Power
Prot
2 sec Field
C B trip
UAT
C B trip
Generator
C B trip

17.  Class A tripping• This trip will operate
when the fault needs to isolate the generator
immediately. • This gives the command to trip
turbine and generator.
 Class B tripping – • This trip will operate when
the fault is not serious view of generator or it is
not directly harmful to generator • This gives the
command to trip turbine.

18.  Generator protection
 Generator transformer protection
 Unit auxiliary transformer protection

19.  Under voltage relay -27G
 Generator overvoltage protection-59G
 Generator negative sequence protection 46G
 Generator out of step (pole slipping)-98G
 Generator backup impedance prot -21G
 Generator field failure prot -40G
 Dead machine protection -50GDM
 95 % gen stator earth fault protection-64G2
 Generator difrential relay 87 G
 100% generator stator earth fault-64G
 Generator rotor earth fault-64R
 GT overfluxing 99G
 Generator interturn fault protection 64GIT
 Generator stator backup earth fault 51NG
 Bus bar protection
 Reverse power relay for anti-motoring 32G Long timer

20.  Differential protection -87GT
 REF protection -64RGT
 GT Overcurrent protection 50/51GT
 GT backup earth fault protection 51NGT
 GT buchholz relay
 GT PRV trip
 GT SPRV trip
 GT oil temp HI
 GT winding temp HI

21.  Differential protection-87
 UT LV side ref protection -64UAT
 Overcurrent protection-50/51UAT
 Earth fault protection-51NUAT
 UAT buchholz relay
 UAT PRV trip
 UAT oil temp HI
 UAT winding temp HI

22.  Liquid main leads top max
 Cold gas cooler temp A+B more than 55 c deg
 Cold gas cooler temp C+D more than 55 c deg
 Hot air main exciter more than 85 c deg

23.  When generator is connected to the grid system and
power input to turbine is insufficient to drive
generator ,motoring will occur.
 Motoring is harmfull to turbine blades if it sustained
for extended period.
 This is due to loss of the cooling effect of steam flow
which can result in overheating the last stage blading.
 Anti motoring detection include exhaust hood
temperature monitoring and reverse power relay(32G)
with long timer.

24. 1. Reverse power relay ( long timer eg 30 sec ) logic for
anti motoring
( it is a protection of turbine )
2.Reverse power relay (short timer eg 3 sec ) logic for turbine trip to
Generator trip to prevent overspeed of Turbine
Reverse
power relay
32-1
Long
Timer
30 sec
Trip generator and
Field breaker

25. Generator
C B trip
Turbine
trip
HPLP
bypass
Not
open
Open
HPLP
Bypass
MFR
Boiler
trip
Generator
GT,UAT
Protection
Optd
Class A
Generator ,GT,UAT protection : class A
Reheater
Prot
optd
UAT
C B trip
Field
C B trip
C B- circuit breaker

26. 1. NFPA 85 -Boiler and Combustion Systems
Hazards.
2. IEEE Guide for Protective relay applications to
Power Transformer (IEEE Std C37.91) .
3. IEEE Guide for AC Generator Protection (IEEE Std
C37.102).

27. BOILER TRIP Conditions ,FSSS, master fuel
relay( MFR)
BHEL (T) Boiler ,500 MW
 1• Less than fire ball and loss of +24V DC(N) at any elevation in service.
 2• Drum level very low for more than 5 seconds.
 3• Drum level very high for more than 10 seconds.
 4• Both FD Fans off.
 5• Both ID Fans off.
 6• Air flow is less than 30%
 7• Furnace pressure very low.
 8• Furnace pressure very high.
 9• Loss of all fuel trip
 10• Unit flame failure trip
 11• Both emergency trip Push Buttons pressed (Operator initiated boiler trip)
12• Loss of reheater protection.
 13• Loss of +24V DC(T) for more than 2 seconds
 14• All Secondary Air Heaters off.
 15• Water wall circulation not correct for more than 5 seconds
 16• Boiler feed pumps tripped for more than 10 seconds

28. Turbine Trip
KWU Steam Turbine – 500 MW
1. Turbine overspeed ( hyraulic)
2. Manual trip device (hydrualic)
3. Turbine overspeed (electronic)
4. Axial shift
5. Trip switch optd (Desk)
6. HP exh temp high
7. TG brg temp high
8. Condenser press trip
9. Fire protection trip
10. MOT Level VLO
11. Low MS temp trip
12. Trip command from ATRS
13. Gen electrical protection
14. Gen protection (mech)
15. MFT Relay optd
16. HP casing top-bot diff HI
17. IP Casing top-bot diff HI
18. LP casing top bot diff HI

29. Turbine emergency trip conditions (Electrical )
LMZ Russia ,Steam Turbine -660 MW

30. BOILER TRIP Conditions ,FSSS, master fuel relay( MFR)
Doosan Boiler ,660 MW ,Supercritical boiler
1.Both ID Fans Off
 2.Both FD Fans Off
 3.Unit Air Flow < 30 % TMCR
 4.All Feed Water Pumps Are Off For More Than 40 Sec
 5. the furnace pressure High / Low for more than 8 sec ( 150 mmwc / -180
mmwc))
 6. the furnace pressure High – High / Low - Low ( 250 mmwc / - 250 mmwc)
 7.Loss Of Re-heater Protection
 8.EPB Pressed
 9.All SAPH Off
 10.Economizer Inlet Flow Low For More Than 10 Sec
 11.Furnace Vertical Wall Temperature High For more than 3 Sec (479 C)
 12.SH Pressure High On Both Side
 13.SH Temperature High For More Than 20 Sec ( 590 C)
 14.RH O/L Temperature High For More Than 20 Sec ( 590 C)
 15.Separator Level Low-Low During Wet Mode
 16.Separator Level High-High During Wet Mode
 17. MFT Relay Tripped
 18.Loss Of Fuel Trip
 19.Unit Flame Failure Trip

31. Boiler trip -FSSS MFR conditions
-Shanghai electric co ,China- boiler 600 MW
 (1) Manually operate MFR
 (2) IDF trip
 (3) FDF trip
 (4) All preheater trip
 (5) MCS power loss
 (6) Drum water over max.
 (7) Boiler light-up failed
 (8) Drum water below min.
 (9) Boiler pressure excess max limitation (choose two from the three)
 (10) Boiler pressure below min limitation (choose two from the three)
 (11) Whole furnace loses fuel
 (12) Whole furnace loses flame
 (13) Loss flame test cooling air (delayed) (choose two from the three)
 (14) Air flow below min. value (choose two from the three)
 （ 15 ） All boiler water recycle pump trip
 （ 16 ） Reheater loses protection.
 （ 17 ） All water feed pump trip
 （ 18 ） Air flow of economizer inlet is lower than min set value (choose two from the three)

32. Steam Turbine emergency trip conditions ( electric)
Harbin Power Engg Co Ltd –China ;turbine- 600 MW
1. When turbine is over speeding to 3300rpm.
 2 .When condenser pressure VHIGH
 3 .When axial displacement is more than +1.0mm or less than -1.0mm.
 4. When lube oil pressure is as Vlow
 5 .HP /LP casing expansion difference reachs to +11.1mm or -5.1mm.
 6 .LP casing expansion difference reachs to +27.8mm or -4.3mm.
 7. When generator trips.
 8. When boiler MFT.
 9 .When EH oil pressure is as low
 10. DEH is in fault (power off).
 11. ETS is in fault (power off).
 12 .X or Y bearing vibration of any bearing of #1 ～ 8 is HIGH
 13. Stop unit manually by button on standby manual operation panel.
 14 .Stop turbine remotely.
 15. Local STOP button in turbine hall.

33. This ppt is only for education purpose