Generator & Switchyard system operation Presentation outline
SEAL OIL SYSTEM CHARGING
• Commissioning of seal oil system will be required when the
1) generator to be filled with hydrogen or air.
2) machine to be put on barring gear
• Prior to commissioning make sure that all instruments and devices are ready for operation after calibration, overhauling and trial.
SEAL OIL SYSTEM CHARGING
• Seal oil system has to be filled with oil
• Prerequisite for oil filling
1) set all level switches
2) close all stop and non-return shut off valves
3) open all pressure gauge and pressure switches isolating valves
4) open pressure transducer isolating valves
5) open isolating valves of impulse lines of differential pressure regulator
6) bearing lube oil system is in service

SEAL OIL SYSTEM CHARGING
• Open isolating valve of seal oil storage tank to seal oil system. Oil will start filling the seal oil system
• Open valves in oil flow path
• Take coolers and filters into service
• After oil is filled up into the system level will be visible in the gauge glass of the SOT
• Take governing oil system into service
• Start AC seal oil pump
• To clear air locking seal oil pump should be switched on and off till its discharge pressure gauges shows a constant pressure
• Vent DPRV-A and DPRV-B

SEAL OIL SYSTEM CHARGING
• Vent both the coolers one by one
• Vent filters
• Vent pressure gauges, pressure switches and transmitters
• Set seal oil pressure by DPRV-A
• Stop AC seal oil pump and set DPRV-B (<0.3Kg/cm2 from DPRV-A)
• Set thrust oil pressure (0.5 Kg/cm2 more than seal oil pressure)
• Take vacuum pump into service and adjust SOT vacuum as recommended

SEAL OIL SYSTEM CHARGING
• Check all the meter readings are within limit
• Check seal oil flow is as per system requirement.
• Check automatic starting of stand by DC seal oil pump by different interlocks including alarm
• Check function of level switch of SOT, seal oil storage tank and pre-chambers
• After seal oil temperature reaches 300C start cooling water flow to seal oil cooler and adjust the flow in such a way so that the seal oil temperature is maintained at 400C



HYDROGEN COOLING SYSTEM
• PRE CHECHS
• Overhauling of gas drier has been carried and the drier is boxed up
• Check all instruments are in position after calibration
• Functionally check the gas drier system
• Check the availability of adequate no of CO2 filling point and adequate no of co2 cylinders.
• Check availability of adequate no of Hydrogen filling points and cylinders.
• Check whether the relief valves in the high pressure valves are alright.
• Check the generator is completely boxed up & it’s air tightness test is successfully completed.
• Check the seal oil system is in service.

Purging of Air By CO2
• CO2 is admitted from CO2 manifold to generator casing at bottom by opening the valves on cylinder and regulator.
• Rate of admission is being controlled normally by regulating the valves on the manifold.
• To avoid excessive frosting, the CO2 flow rate should be carefully regulated.
• When CO2 percentage reaches 98%, the filling of CO2 can be stopped and preparation for filling hydrogen can be made.
• After achieving 98% CO2 concentration and a pressure of 0.15 to 0.2 Kg/cm2 inside the machine, filling of hydrogen in machine can be started.
H2 FILLING
• Hydrogen is admitted into the generator through hydrogen feed pipe which is connected to perforated pipe header inside the generator extending along the length of the cooling at the top.
• During process of filling with H2 the CO 2 air mixture is discharged through CO2 feed pipe from bottom.
• During H2 filling, continuously analyze the concentration of H2 in gas mixture inside the machine.
• Continue purging till hydrogen purity reaches above 98% and H2 pressure attains rated value.
• Take drier into service.
• Take gas coolers into service.
• Vent the coolers and establish flow.


Stator Water System
• For commissioning the system the system has to be filled up first
• Prerequisites for filling the cooling circuits
– Circuit should be flushed
– Installation of pump and motors after O/H
– Filters cleaned and boxed up
– Coolers and all other components are boxed up
– Ion exchanger is ready and is in service
– All instruments and measuring devices are in position after their calibration

Stator Water System
• System should be lined up for filling.
• Complete stator water system should be filled with DM water having required quality.
• All air should be vented from the system before starting of the pump.
• Take trial of the water pumps.
• Check the stand by pump for automatic starting
• Adjust level regulator in the expansion tank.
• Check all the instruments and meters for their proper functioning.

Stator Water System
• Adjust make up water pressure around 2.0Kg/cm2
• Adjust small water flow through the gas trap
• Check there is no leakage of water in the system
• Take ejector into service
• Take one cooler into service
• Check emergency switching in circuit of the stand by water pump
• Check high and low alarm of the expansion tank
• Check high conductivity alarm and tripping
• Check pump discharge pr., filter diff. pr., conductivity, flow, inlet winding pr., winding diff. pr., vacuum in expansion tank, motors current

CHECKS before Rolling
• Ensure the availability and completeness of all the equipment and circuits. Take clearance from Electrical Division for starting the set.

• Ensure that the insulation resistance of the system is within permissible limits especially if the generator is being synchronized after a long time or in rainy season. If the insulation resistance of the system is low, dry out of stator winding and associated bus duct should be carried out.

PRE-SYNCHRONISING CHECKS
Before Synchronization check and ensure:

• Protection and metering circuits are healthy.
• All the flags on relays are reset and annunciation circuit is healthy.
• Supply of oil to generator bearings is normal.
• Check seal oil system for seal oil pressure, flow and temperature. If the oil pressure is not proper, adjust differential pressure regulator. In case of temperature, adjust cooling water flow.
PRE-SYNCHRONISING CHECKS
Before Synchronization check and ensure:

• Check H2 cooling system for H2 pressure, purity and gas leakage. If the H2 pressure and purity are low, fill more H2 cylinders for increasing the pressure and purity.
• Charge stator winding coolers with distillate and ensure quality, pressure, flow and temperature of the distillate.
SYNCHRONISING PROCESS
Before Synchronization check and ensure:
• Check that generator breaker and Generator field breaker are open. If not, open Generator breaker or field breaker as the case may be.
• Advice rolling of turbine to rated full speed (3000 rpm).
• Check bearing Vibrations If the vibrations on the generator bearings exceed the permissible limits (60-micron) shut down the machine and check the bearings. In case of rubbing abnormal sound, shut down TG set and check clearance between stator and rotor.
SYNCHRONISING PROCESS
• Check temperature of bearing, seal babbitt and drain oil. If the babbitt temperature of bearing or seal is high, check oil flow and vibration on that bearing. If the temperature goes beyond 80°c shut down the T.G. set and check the bearing.
• Ensure that the machine has attained the rated speed of 3000 r.p.m. Obtain a go forward signal from boiler and turbine operator to synchronize the machine.
• Enquire from the switchyard control room about synchronising of machine to the required bus.
• Close the isolator for bus.
SYNCHRONISING PROCESS
• Ask switchyard control room operator to close transformer side isolator and report back to UCB about proper closing of the isolators after physically verifying the same.
• Switch on the synchroscope.

SYNCHRONISING PROCESS
• Close exciter field breaker. Give closing impulse for about 5-sec., and release the switch when Red lamp glows indicating the closing of breaker.
• Voltage will start building up due to residual magnetism. Check that the voltage is equal in all three phases. If voltage on the phases is not equal, check PT fuse and replace the blown one, if any. If the difference is more than 1KV, inform EM Divn., for thorough check up. Open the exciter field breaker and isolators. Check insulation resistance of all the three phases and take necessary action.
SYNCHRONISING PROCESS
• Put Auto/Manual excitation mode selector switch on "Auto" position voltage will start building up. Check that the rate of building up is normal. If the rate of voltage build up is more than the permissible limits, switch over to "Manual" mode and build up voltage manually.
• When the voltage has built up approx., upto 10 KV, check that the voltage and frequency of the incoming machine and that of the system and approximately equal. If the frequency is not approx., equal, give impulse to the load changer to bring the frequency approx. equal. If the excitation mode is on "Auto" it will automatically match the voltage; otherwise in "Manual" mode, give impulse to field rheostat switch to match the voltage.
SYNCHRONISING PROCESS
• Switch on the synchroscope. If the frequency of the incoming m/c is higher than the system frequency, the synchroscope pointer will move in the clockwise director, and if the frequency is lower, it will move in anti-clockwise direction. Speed of rotation of the pointer will depend upon the difference in frequencies. Give impulse by load change switch to have very slow clockwise rotation.
SYNCHRONISING PROCESS
When the voltage and frequency match, the synchroscope will move very slowly in the clockwise direction. This position shows that:
i) Phase sequence of generated voltage and system voltage is same.
ii) Effective values of both the voltage are same.
iii) Frequency of both the system and the incoming m/c is same.
STEPS FOR GENERATOR SYNCHRONISING
• Give closing impulse to Gen. breaker the instance when the synchroscope pointer is in between 11 and 12 ° Clock position which indicates synchronism by the glowing of lamp at the Gen. annunciation panel.
• Take 10-20 MW load on the machine. Ask boiler operator to carry out necessary operations on boiler side to raise the steam pressure and temperature, so that load can be raised.
• Put synchroscope switch to "OFF" position. Return synchronising switch to "OFF" position and lock it. Ask turbine operators to carry out necessary operations on turbine side required for raising the load.
• Put "antimotoring" protection switch on "ON" position after taking some load on the machine (say 20 MW).
• Gen. voltage and P.F., will be maintained by AVR if the excitation mode is on "Auto", otherwise, maintain Gen. voltage and PF by varying the field rheostat from the Gen. control desk. If excitation mode is on manual, then change over to "Auto" mode after matching the parameters.
STEPS FOR GENERATOR SYNCHRONISING
• Slowly raise the load on Generator upto 80 MW (Follow the guide lines given for loading the machine). Now the voltage and power factor will be maintained by the automatic voltage regulator (AVR). However, the level can be changed by varying the rheostat resistance.
• Changeover 6.6 KV auxiliary bus from station supply to unit auxiliary supply taking both the unit auxiliary transformer into circuit. Check that the unit auxiliary supply incoming breakers are racked in service position, springs are charged and "Local/Remote" switches are on "Remote" position.
• Keeping Gen. winding & core temperature, Gen. transformer winding temperature H2 gas temperature generator seals and bearing metal temperature in limits by adjusting cooling water flow to Generator gas coolers and oil coolers. Load the generator upto 150 MW as per guide lines available.
• At this load, check Gen. bearing and seals temp. Gen. Wdg./Core temperature Gen. T/F Wdg. temperature H2 gas temperature performance of automatic voltage regulator and cooling water flow to R.C.U. If Gen. Wdg/Core temperature is higher adjust distillate flow and cooling water flow to gas coolers. If Gen. T/F wdg. temp. is high, check that all the cooling fans and pumps of cooler banks are in service. If the AVR is not functioning properly take the voltage control on "manual" mode.
STEPS FOR GENERATOR SYNCHRONISING
• Check exciter winding temperature & slip ring sparking. Ensure that the exciter voltage and current are within permissible limits.
• Check H2 pressure, purity and temperature performance of seal oil system and stator water cooling system. Fill more H2 gas cylinders if pressure and purity are low. If the performance of seal oil system is not satisfactory take corrective measures.
• Increase Load on the Gen. as per loading guide lines upto full rated load 21n MW). Check Gen. wdg/core temp. Gen. T/F wdg. temp. and vibrations. If Gen. wdg./core temp., cannot be controlled by increasing cooling water flow to gas coolers and distillate to stator water coolers. Reduce load.
• If all parameters are within limits, maintain load on the Generator according to boiler and Turbine parameters and conditions.
• If the vibrations increase beyond limits, reduce load and investigate cause.
• Check that all the cooler bank fans and pumps are running if not start them. Even then if the temperature of T/F wdg, does not come down, reduce load.
STEPS FOR GENERATOR SYNCHRONISING
• IMPORTANT FACTORS TO BE CONSIDERED WHILE LOADING
• During loading of the turbo generator, the turbine expansion should be smooth and always on increasing trend.
• Gen. winding temperature and Gen. T/F wdg. temperature should be kept under permissible limits by regulating cooling water flow to gas coolers and running the transformer cooler fans and pumps according to the winding temperature.

Critical Parameters
• MW
• MS Pressure
• external parameter is frequency of the network
Response Time

• Response of the Turbine is fast
• Response of the Boiler is slow due to transport lag and Thermal inertia.
• Turbine will be able to maintain only one unit parameter MW or main steam pressure. The other is to be controlled, naturally by the boiler.
Modes of Operation
• turbine follow mode
• boiler follow mode.
Turbine follow mode
• Turbine maintains throttle steam pressure. The MW depends on the steam output from the Boiler. The variations in the Boiler steam output will be resulting variations in MW output.
• Turbine follow mode gives more stability to unit by controlling main steam pressure perfectly and fastly which is a very important unit parameter.
Boiler follow mode
• Turbine maintains MW demands and Boiler maintains main steam pressure. Turbine will be responding to grid requirement fastly because of droop characteristic set in EHC and Boiler will be following to maintain main steam pressure if combustion controls are in Auto.
coordinated mode of operation
• unit/master control station sets MW set point
• Turbine will be controlling the MW
• Boiler will be trying to control main steam pressure

Sliding Pressure Operation

• MS Pressures varies according to generator output.
• turbine governing valves kept wide open.
• Utilizing sliding pressure, the thermal efficiency of the steam turbine is improved at partial operating loads through decreasing thermodynamic efficiency as follows, by comparison with constant pressure type operation:
(1) A smaller governing value loss enables improvement of high pressure turbine internal efficiency
(2) Decrease of feed water pump throughput
(3) Boiler reheat steam temperature can be maintained at higher levels because of higher temperatures in high-pressure turbine exhaust steam.