3 Unit operation and maintenance
3.6 Unit interlock protection and test
3.6.1 Turbine interlock protection 3.6.1.1 Turbine main protection 1）Over speed mechanical trip
When turbine running speed reaches to 110％～111％ of rated running speed, mechanical emergency governor actuates; LP protection oil is discharged through sliding valve of mechanical emergency governor, diaphragm valve opens to make AST oil head pipe discharge oil, to close HP & IP main steam valves and governor valves and to close all stages steam extraction check valves and HP steam discharging check valves, and then the turbine stops.
2） Local manual mechanical trip
This trip device lies in front of turbine front box. During operation, turn it for 90°PPand then pull it out; LP protection oil is discharged through sliding valve of mechanical emergency governor, diaphragm valve opens to make AST oil head pipe discharge oil, to close HP & IP main steam valves and governor valves and to close all stages steam extraction check valves and HP steam discharging check valves, and then the turbine stops.
3） Remote manual trip
Two buttons are installed on DEH panel in main control room. During operation, press the two buttons at the same time, then four automatic stop emergency governor protecting solenoid valves （AST-1.2.3.4）actuate to make AST oil head pipe discharge oil, to close HP & IP main steam valves and governor valves and to close all stages steam extraction check valves and HP steam discharging check valves, and then the turbine stops.
4) Any of the following abnormities occurs, automatic stop emergency governor protecting solenoid valves （AST-1.2.3.4）actuate, and then turbine trips:
a. Unit bearing vibration reaches to 0.25mm;
b. Turbine lubricate oil pressure is low as 0.049MPa;
c. Thrust bearing abrasion is high and axial displacement reaches to ±1.0 mm;
d. EH oil pressure is low ≤8.5MPa;
e. Condenser vacuum is ≥65KPa(absolute value);
f. HP IP differential expansion reaches to 11.1mm (Rotor extends) or —5.1mm (rotor shortens);
g. LP differential expansion reaches to 27.8mm (Rotor extends) or —4.3 mm (rotor shortens);
h. Turbine generator unit supporting bearing metal temperature reaches to 113℃;
i. Turbine thrust bearing metal temperature reaches to 107℃;
j. DEH TSI over speed ≥3300r/min;
k. Generator main protection actuates (turbine trips after generator trips);
l. Boiler MFT (turbine trips after boiler MFT);
m. DEH loses power.
5） Stop the turbine manually if any of the following happens:
a. Reach over speed protection value, but turbine over speed protection device does not actuate;
b. Protection device does not actuate when unit vibrates heavily;
c. Turbine impeller blade breaks or there is obvious metal friction sound in cylinder;
d. There is water impact in turbine;
e. There is friction sound or spark at turbine gland sealing;
f. Any bearing of turbine is in short of oil or in smoke;
g. Oil system is on fire or there is fire around turbine generator unit, which can not be extinguished and threatens safety operation;
h. Smoke comes out from generator or hydrogen explodes;
i. LP cylinder steam exhausting temperature is within 80～120℃ and running exceeds 15min or the temperature is higher than 120℃;
j. HP & IP up and down cylinder metal temperature difference reaches to 56℃;
k. Main steam temperature exceeds 565℃;
l. Reheating temperature exceeds 565℃;
m. Main steam, reheating steam temperature decreases to 454℃;
n. Bearing returning oil temperature is higher than 82℃;
o. Turbine lubricate oil tank level is lower than normal level 300mm;
p. Control value reaches to protection device actuation value, but protection refuses to actuate.
3.6.1.2 OPC interlock protection
1) When load is ≥30% rated load, generator overrides, over speed limit solenoid valve actuates to discharge over speed limit oil (OPC), all steam regulating valves close quickly under forces of valve operation seat spring and steam pressure. When running speed decreases to 3090r/min, over speed limit solenoid valve recovers and opens all the steam regulating valves again to keep turbine running speed of 3000r/min.
2) When running speed reaches to 103% rated running speed, over speed limit solenoid valve actuates to discharge over speed limit oil (OPC), all steam regulating valves close quickly under forces of valve operation seat spring and steam pressure. When running speed decreases to 3090r/min, over speed limit solenoid valve recovers and opens all the steam regulating valves again to keep turbine running speed of 3000r/min.
3.6.1.3 Turbine oil system interlock protection
1) When bearing lubricate oil is lower than 0.083MPa, #1 AC lubricate oil pump starts automatically and alarm;
2) When bearing lubricate oil is lower than 0.076MPa, #2 AC lubricate oil pump starts automatically and alarm;
3) When bearing lubricate oil is lower to 0.06MPa, start DC lube oil pump and stop unit put turning gear into operation;
4) When bearing lubricate oil is lower to 0.03MPa, switch to auto turning gear and interrupt turning gearing manually.
5) When jacking oil pump inlet oil pressure is lower than 0.0823MPa, AC lubricate oil pump starts automatically;
6) When turbine running speed increase more than 200 r/min, jacking oil pump stops automatically; running speed decrease to 200 r/min , jacking oil pump starts automatically;
7) When turbine oil tank oil temperature is lower than 25℃, electric heaters put into operation automatically; when the temperature is higher than 30℃, electric heaters stop automatically;
8) When EH oil pressure is lower than 11.2MPa, standby EH oil pump starts automatically;
9) When EH oil temperature is lower than 15℃, electric heaters put into operation; when it is higher than 25℃, heaters stop;
10) When EH oil temperature is higher than 55℃, put cooling water solenoid valve into operation and circulating water pump starts automatically; when the temperature is lower than 40℃, close cooling water solenoid valve and circulating water pump stops automatically;
11) EH oil tank level is lower than 370mm, it alarms;
3.6.1.4 LP steam exhausting cylinder water spraying protection interlock
1) LP steam exhausting cylinder water spraying is under automatic control, when running speed reaches to 600r/min, it starts to spray water until unit is running with 15% load.
2) When LP cylinder steam exhausting temperature reaches to 70℃, LP steam exhausting cylinder water spraying system puts into operation automatically; When LP cylinder steam exhausting temperature reaches to 80℃, alarm, and if reach to 120℃, stop unit at once.
3.6.1.5 Bypass system protection
1) Conditions for automatic open of HP bypass control valve
a. Main steam pressure exceed regulating value when pressure recover to rated value and lower than it, HP bypass close automatically;
b. When turbine trip, auto main steam valve close;
c. When outlet switch of generator trip;
d. When generator reject 60% load or more than 60%.
2) Conditions for automatic close of LP bypass control valve:
a. HP & LP condenser vacuum is low to 60KPa.
b. HP & LP condenser steam exhausting temperature ≥120℃.
c. Condenser hot well water level is high to 1300mm.
d. LP bypass outlet temperature is high to 160℃.
e. LP bypass attemperating water pressure is low to 1.5MPa.
3.6.1.6 Turbine turning gear device interlock protection 1) Automatic start conditions for turning gear motor:
a. Turning gear motor interlock switch is at „Automatic‟;
b. Bearing lubricate oil pressure ＞0.028MPa;
c. All jacking oil pressures are not low;
d. Turning gear motor has no electric fault;
e. Turning gear device is at „Automatic‟;
f. Turbine tripped;
g. Turbine running speed is zero (0).
2) Turning gear motor trips when any of the following conditions occurs:
a. Any jacking oil pressure ＜ 6MPa;
b. Bearing lubricate oil pressure ＜ 0.028MPa;
c. Turning gear motor has electric fault;
d. Shaft protection is in fault.
3.6.1.7 Turbine water entering proof protection
1) When turbine load is lower than 20％, following drainage valves start automatically:
a. Drainage valves after first extraction motorized valve and before check valve;
b. Drainage valves after second extraction motorized valve and before check valve;
c. Drainage valves after third extraction motorized valve and before check valve;
d. Drainage valves before and after fourth extraction motorized valve, before first check valve and after second check valve;
e. Drainage valve of fifth extraction motorized valve;
f. Drainage valves before and after fifth extraction check valve;
g. Drainage valves before and after sixth extraction check valve;
h. Main steam head pipe drainage valve;
i. Drainage valve after main steam governor valve;
j. Drainage valve at hot section head pipe;
k. Drainage valves before and after HP steam exhausting check valve.
2) After boiler ignition, check and make sure that condensing water system, circulating water system, vacuum system run normally; all drainage valves at turbine side should be opened according to actual situation. When load is higher than 20％, close all the drainage valves (following drainage valve are closed automatically); during stopping the unit, when load is lower than 20%, unit drainage water valves should be opened manually:
a. HP & IP cylinder inner cylinder drainage water;
b. HP & IP cylinder outer cylinder drainage water;
c. HP governor valve guiding pipe drainage water;
d. IP governor valve guiding pipe drainage water.
3.6.1.8 HP heater water level protection
1) HP heater water level high Ⅰvalue, alarm;
2) HP heater water level highⅡ value, HP heater emergency drainage water opens by interlock;
3) HP heater water level high Ⅲ value, any two of switch value, high Ⅲ value simulation value and high Ⅱ value switch value reach to actuation value, HP heater overrides and HP heater water side bypass works, HP heater steam extraction motorized isolation valve and check valve close and steam extraction pipeline drainage water open at the same time.
4) HP heater water level low Ⅰvalue, alarm;
3.6.1.9 LP heater water level protection
1) LP heater water level high Ⅰvalue, alarm;
2) LP heater water level highⅡ value, LP heater emergency drainage water opens by interlock;
3) LP heater water level high Ⅲ value, any two of switch value, high Ⅲ value simulation value and high Ⅱ value switch value reach to actuation value, LP heater overrides and LP heater water side bypass works, LP heater steam extraction motorized isolation valve and check valve close and steam extraction pipeline drainage water open at the same time.
4) LP heater water level low Ⅰvalue, alarm.
3.6.1.10 Deaerator water level and pressure protection
1) When deaerator pressure is lower than 0.15MPa, motorized isolation valve from fourth section steam extraction to deaerator closes by interlock, motorized valve of standby steam source opens by interlock, standby steam source puts into operation (transferred to be fourth section steam extraction before putting HP heater into operation);
2) When deaerator pressure is higher than 0.15MPa, standby air source motorized valve close by interlock; motorized isolation valve from fourth section steam extraction to deaerator opens by interlock.
3) Deaerator water level high Ⅰvalue, open deaerator overflow valve by interlock.
4) Deaerator water level highⅡ value, deaerator emergency water discharging valve opens by interlock.
5) Deaerator water level high Ⅲ value, close water level main governor front and back motorized valve of deaerator and motorized valve of bypass by interlock.
6) Deaerator water level low Ⅰvalue, alarm.
7) When deaerator water level low value and deaerator low Ⅰ value hydraulic level acts (or soft act produced by deaerator water level transmitter), booster pump of steam driven pump and motorized pump trip by interlock.
8) When feeding water flow is higher than 30%, deaerator water level is allowed to be transferred from single impulse to three pulses.
3.6.1.11 Steam extraction check valve interlock:
1) When all steam extraction check valves, HP cylinder steam discharging check valves are at „Automation‟ position and turbine main steam valve trip device closes, all above valves close by interlock.
2) When all steam extraction check valves, HP cylinder steam discharging check valves are at „Manual‟ position, all above valves can be opened or closed individually.
3.6.1.12 Pump equipment interlock
1) Condensing water pump trips or outlet head pipe pressure is lower than 2.5MPa, standby pump puts into operation by interlock.
2) Circulating water pump trips, standby pump puts into operation by interlock.
3) Vacuum pump trips, standby pump puts into operation by interlock.
4) When open cooling circulating water pump trips or outlet head pipe pressure is lower than 0.20MPa, standby pump puts into operation by interlock.
5) When closed cooling circulating water pump trips or outlet head pipe pressure is lower than 0.35MPa, standby pump puts into operation by interlock.
6) When stator cooling water pump trips or outlet head pipe pressure is lower than 0.40MPa, standby pump puts into operation by interlock.
7) When turbine oil tank discharging air fan trips, standby discharging air fan puts into operation by interlock.
3.6.1.13 Steam driven feed water pump main protection 1) Local stop button
a. Press „Emergency stop‟ button on front bearing box of feed water pump turbine, stop solenoid valve actuates to discharge control oil and close HP & LP main steam valve and governor valve, the turbine stops.
b. Press „Emergency stop‟ button on operation panel in earth room, stop solenoid valve actuates to discharge control oil and close HP & LP main steam valve and governor valve, the turbine stops.
c. Press „Emergency stop‟ button DSC-CRT, stop solenoid valve actuates to discharge control oil and close HP & LP main steam valve and governor valve, the turbine stops.
2) Remote stop button
3) Protection actuates to stop the turbine if any of following abnormities occurs in steam driven feed water group:
a. Feed water pump turbine bearing vibration is high to 0.125mm;
b. Rotor axial displacement is high to ±0.25mm;
c. Lubricate oil pressure is low to 0.07MPa;
d. Steam exhausting pressure reach to 30KPa;
e. Feed water pump turbine is in over speed to 6050r/min;
f. Feed water pump turbine steam discharging temperature is 120℃;
g. Booster pump stops;
h. MEH loses power;
i. LP safety oil pressure is low to 0.25MPa;
j. Oil tank level low to 400mm;
k. Bearing metal temperature at water inlet & outlet side of steam driven pump
≥100℃;
l. Steam driven feed water pump thrust bearing temperature ≥100℃;
m. Mechanical sealing water temperature at water inlet & outlet side of steam driven pump ≥90℃;
n. Steam driven feed water pump inlet flow low, overtime 90s and recirculating valve is not open.
o. Steam driven feed water pump inlet pressure is low, overtime 3s;
p. Deaerator level low II, overtime 3s;
q. Turbine trip.
r. Local emergency button is pressed down.
3.6.1.14 Steam driven pump booster pump trip protection 1) Deaerator level low II, overtime 3s;
2) Booster pump drive end, non-drive end bearing temperature ≥100℃;
3) Booster pump inlet valve is closed;
4) Steam driven feed water pump inlet flow low, overtime 90s and recirculating valve is not open.
5) Steam-drive feed water pump trip, overtime 3s.
6) Booster pump inlet pressure low, overtime 30s.
7) Local emergency button is pressed down.
3.6.1.15 Motorized feed water pump trip protection
1) Motorized pump inlet flow is low, and minimum flow valve position<30%.
2) Deaerator low, overtime 3s;
3) Motorized pump inlet pressure is low, overtime 3s.
4) Oil pressure after lubricate oil filter of motorized pump ≤0.08 MPa, the pump trips.
5) Motorized pump operated 30s and outlet valve closed.
6) Motorized pump inlet, outlet end radial bearing temperature ≥90℃, alarms;
≥110℃, the pump trips.
7) Motorized thrust bearing temperature ≥90℃, alarms; ≥110℃, the pump trips.
8) Motorized pump motor coupler end bearing temperature ≥80℃, alarms; ≥90℃, the pump trips.
9) Motorized pump booster pump drive end and non-drive end radial bearing temperature ≥90℃, alarms; ≥100℃, the pump trips.
10) Motorized pump motor non-drive end thrust bearing temperature ≥90℃, alarms;
≥100℃, the pump trips.
11) Motorized pump inlet & outlet end sealing water temperature ≥80℃, alarms;
≥90℃, the pump trips.
12) Motorized pump motor drive end and non-drive end radial bearing temperature
≥80℃, alarms; ≥90℃, the pump trips.
13) Motorized pump hydraulic coupler radial bearing & thrust bearing temperature
≥90℃, alarms; ≥95℃, the pump trips.
14) Motorized pump lubricate oil cooler inlet oil temperature ≥65℃, alarms; ≥70℃, the pump trips.
15) Motorized pump lubricate oil cooler outlet oil temperature ≥55℃, alarms; ≥60℃, the pump trips.
16) Motorized coupler working oil cooler inlet oil temperature ≥110℃, alarms; ≥130℃, the pump trips.
17) Motorized pump coupler working oil cooler outlet oil temperature ≥75℃, alarms;
≥85℃, the pump trips.
18) Local emergency stop button is pressed down.
3.6.1.16 Motorized feed water pump system interlock protection
1) During motorized pump running, lubricate oil pressure after lubricate oil filter ≥0.22 MPa, the auxiliary oil pump stops in interlock.
2) During motorized pump running, lubricate oil pressure after lubricate oil filter≤0.15 MPa, the auxiliary oil pump stops in interlock.
3) Oil pressure after motorized pump working oil 0.3 MPa＜p＜0.4 MPa.
4) Motorized pump working oil pressure is normally ≥0.17 MPa.
5) Working oil pressure before motorized working oil control valve ＞0.1 MPa.
6) Working oil pressure after motorized pump spoon pipe ＞0.15 MPa.
3.6.1.17 Condensing water pump
1) Condensing water pump up & down bearing temperature ≥95℃.
2) Condensing water pump motor thrust bearing ≥80℃.
3) Inlet valve of condenser water pump is confirmed to be closed.
4) Condensing water flow ≤380t/h and condensing water re-circulating valve does not open with a timely of 15s.
5) Hot well water level low II value ≤100mm and water level low I value ≤250mm.
6) Press emergency stop button locally.
3.6.1.18 Generator hydrogen, oil and water system interlock protection
1) Front and rear differential pressure of AC sealing oil pump at air side is less than 0.035MPa, DC sealing oil pump starts by interlock.
2) Main oil pump is working and AC oil pump at air side is in operation; when hydrogen-oil differential pressure decreases to 0.056MPa, standby differential pressure valve actuates and first standby oil source puts into operation controlled by standby differential pressure valve automatically.
3) Main pump does not work normally and AC oil pump at air side is in operation;
when hydrogen-oil differential pressure decreases to 0.056MPa, HP sealing oil standby pump starts automatically, standby differential pressure valve actuates and second standby oil source puts into operation automatically.
4) AC oil pump at air side is in operation; when hydrogen-oil differential pressure decreases to 0.035MPa, third standby oil source of DC standby oil pump at air side starts automatically.
5) Stator water pump out and inlet differential pressure ＜0.14MPa, standby pump starts with a time delay of 3－5s.
6) When stator water tank level is low than 450mm, make up water solenoid valve opens.
7) When generator stator winding inlet water conductivity is >9.5μs/cm, reject load or stop the unit.
8) When stator water flow is <52% rated flow, generator trips with a time delay of 30s.
3.6.1.19 Other interlock protections of the turbine
1) When condensing water pump outlet head pipe pressure is lower than 2.5MPa, standby condensing water pump starts by interlock.
2) 300mP3P water tank level ≤1.2m, condensing water transportation pump trips.
3) When open circulating water pump outlet head pipe pressure is lower than 0.20MPa, standby open circulating water pump starts by interlock.
4) When closed circulating water pump outlet head pipe pressure is lower than 0.35MPa, standby closed circulating water pump starts by interlock.
5) When closed circulating water tank level is lower than 700mm, closed circulating water pump trips.
6) When condenser vacuum is lower than 75KPa, standby vacuum pump starts by
interlock.
7) When condenser hot well water level is high to 710mm, it alarms.
8) When condenser hot well water level is low to 250mm, it alarms.
9) When condensing water pump motor winding temperature is high to 105℃, it alarms.
10) When boiler circulating water pump cooling water booster pump returning pipe pressure is lower than 0.45MPa, the pumps run together.
11) When boiler circulating water pump cooling returning pipe pressure is lower than 0.45MPa, emergency cooling water pump starts.
3.6.2 Unit test
3.6.2.1 Unit interlock protection test
Equipments and systems interlock protection test should be simulated by I&C personnel after all the test conditions are satisfied (unsatisfied conditions should be forced by I&C personnel) to check whether actions and alarms are normal or not.
3.6.2.2 Motorized valve (damper) and pneumatic valve (damper) test
Before test, make sure that motorized valves (damper) turning directions are right, pneumatic valve (damper) switches are right and light signal status indications are right.
Before test, make sure that motorized valves (damper) turning directions are right, pneumatic valve (damper) switches are right and light signal status indications are right.