Hydroelectric Power Station Questions

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DHAYANANDHAN.S.,

india

1. Check; is the station at or near a stream of water sufficient enough to operate the station.

2. Measure electrical continuitly between the generator and transformer.

3. The load is thrown off under certain conditions.

4. Y is better TAN delta

My backgraound includes start-up engineer for Allis-Chalmers Hydro-Turbine Div for 5 years and started about 15 hydro plants in the US and Canada.

1. There are regular tests carried out in a hydro station daily, weekly, monthly, annually and during dewatered outage, and during rebuilds. There are electrical, mechanical, hydraulic, and visual inspections. These tests are too numerous to detail here.

2. First safety precautions are taken to insure no headgates or tailgates can be opened, the testing begins with the unit in the dewatered condition.

Pre-commissioning would start when all of the systems are installed and connected electrically and mechanically. Then control checks begin, sequentially ringing out electrical circuits, checking PT's and CT's polarity, calibrating protective relays, testing all sub-systems. At this time also clean and flush hydraulics, lube oil, cooling water, etc. using safety precautions and experience. The hydraulic system must be flushed to remove all debri from the hydraulic piping by achieving a minimum 4,000 Reynolds number to create turbulent flow, using finer and finer filters and heat until the control hydraulics are filtered to 3 micron if using proportional valves or 10 micron with sliding spool. The lube oil system is looped and flushed also to achieve turbulent flow, but limit the filtration to about 15 micron so additives are not removed from the oil.

Commissioning tests are the procedure of operating the equipment using the manual control mode first to verify positive and correct operation of circuits, then beginning to test control in of the hydraulics, cooling water, lube oil systems. Then start doing automatic circuit checks.

When all is in order, water up the turbine and begin doing slow speed start and stop, then build speed and observe vibration and run-out of rotating components, when normal operating speed is reached close the generator breaker and observe at "No Load" for excitiation stability and watch generator winding temps, bearing temps, and this would be the first time an electrical center could "push" the generator rotor and shafting system. After a half hour of observing bearing temps if all is OK, do a first load rejection, and watch all systems automatically safely shutdown and the unit stop rotation.

3. Then repeat this procedure until full load is reached, always stop at each 1/4 load to allow bearing temps and generator winding temps to stabilize and record readings. Adjust cooling water as necessary or if you have thermostatic cooling water control for heat exchangers observe temps and water strainers for plugging, watch flow and adjust to maintain temps and packing box cooling.

After the unit has passed all load rejection tests (maximum speed can be 2.5 times normal speed during a load rejection, this is seen within seconds after the breaker opens.

4. Tan-Delta is a testing method for generator windings, by applying a high voltage (10kV) and observing current readings over time. The comparision of the numerous windings that go into a hydro generator. (You can do a tan delta on a wooden hammer handle, any insulating material, and compare readings.) There is a better explanation but I am done writing now.