GENERATOR TESTING.pptx, Turbo generator stator and rotor mechanical and electrical testing

The document talks about static and dynamic testing of turbo generators

1. GENERATOR STATIC TESTING Dr. Pradip Chanda

2. Insulation Testing The insulation resistance test consists of a measurement of the dc resistance between the winding and ground, or between two windings. The test voltage on rotors is typically 500 V dc (the diodes should be disconnected) The test voltage for stators up to 6.6 kV is 1 kV dc. It is 5 kV dc for higher stator voltages. The IR test results should be corrected to a standard temperature of 20°C. Dry air should be blown through water-cooled windings following draining to remove the water from all the hoses.

3. Polarization Index Test The dc voltage is applied across the insulation for 10 min. The PI is the ratio of the insulation resistance reading obtained after 10 min to the reading obtained after 1 min. The insulation condition is considered acceptable if the PI is greater than 2

4. Loss Angle Test. The loss angle (or tan delta) test is used to determine the condition of the insulation. Voids develop in the insulation as it deteriorates, resulting in a change in capacitance of the winding.

5. Loss Angle Test. Apply ac voltage (60 or 50 Hz) to the winding. Increase the voltage from 20 to 100 percent of the line voltage V1 in increments of 0.2V1. Record the capacitance and tangent of the insulation loss angle at each step, using an ac bridge. Discharge the winding following completion of the test. This step is necessary to ensure the safety of personnel working with this equipment.

6. Loss Angle Test.

7. Testing the Stator Core Ring Flux Test. A flux is induced in the core by using several turns of heavy high- voltage (HV) cable wound toroidally around the core and supplied from a voltage source of 3 to 14 kV. Hot spots will appear in the core due to the induced eddy currents in the regions where the interlaminar insulation (between the core laminations) is damaged. An infrared camera is used to detect these regions.

8. Testing the Stator Core The Electromagnetic Core Imperfection Detector (ELCID) Test. One turn of a light conductor is wound in a similar fashion as above around the core to generate a small flux in the core. The conductor is normally supplied from 120 or 240 V ac. The EL-CID detector contains a pickup coil detects the magnetic flux induced in the air by the small fault currents flowing in the damaged region. detector is scanned along the conductor slots inside the stator

9. Testing the Stator Core

10. Stator Coolant Circuit Testing It consists of drawing a 700-mbar vacuum in the winding and observing the change in pressure over a 12-h period. A typical 660-MW stator should drop around 10 mbar within 12 h. If the vacuum test results are unsatisfactory, a mixture of air and 20 per- cent (by volume) of a tracer gas should be pressurized in the winding. A leak search should then be performed, using an electronic gas detector.

11. Hydrogen Loss Test A pressure drop test should be performed using air, nitrogen, or CO2 to ensure that the frame is gas-tight. The pressure drop test is performed normally over a 12-h period. The volume of gas lost during the test, at normal temperature and pressure (NTP), can be found using the following expression:

12. Hydrogen Loss Test

13. Rotor Winding Tests The installed rotor ground fault detection equipment can be used to detect and measure rotor ground faults onload . The recurrent surge test is used to identify ground and interturn faults.

14. Rotor Winding Tests A 12-V dc square wave is injected through a matching resistor at each end of the rotor winding in turn. The input and output waveforms of both waves are stored and viewed on an oscilloscope. If there is fault in the winding, a reflected wave will travel back to the input, causing a change in the input voltage. The time of this change is proportional to the distance of the fault from the input.

15. Rotor Winding Tests

16. DYNAMIC TESTING OF 210 MW GENERATOR

17. 17 PURPOSE OF DYNAMIC TESTING OF THE GENERATOR To ensure the healthiness and operation/Stability of Generator differential protection under actual fault conditions. Over all differential protection under actual fault conditions. Generator back up impedance protection under actual fault conditions. Generator earth fault protection under actual fault conditions. Generator differential protection while supplying through currents. Over all differential protection while supplying through currents. To obtain and check the Short circuit characteristic of the generator Open circuit characteristic of the generator To ensure the healthiness of all the CTs and its associated circuits .

18. 18 TA set is running at 3000 rpm. Faults created at different locations (as per the diagram) Controlled excitation for controlling the fault current. Set up required for measurements while test. Requirements of Dynamic Testing

19. 19 ROUTINE PROCEDURE OF DYNAMIC TESTING Modifications Require to facilitate controlled Excitation Faults to be created in power circuit Different Tests to be Carried out by feeding the faults

20. 20 Modifications carried out. Replace existing manual pot with Spare digital pot already prepared for dynamic testing Remove Excitation Transformer HV links and Extend 6.6KV supply to Excitation Transformer HV side Extend Excitation protection tripping to 6.6 KV Bkr Inhibit FFB closing to bypass the FF disturb proton. Tier fan supply: Extend the 230V ac supply to tier fan from station supply Thyrister Fan Supply: Extend 415 V 3phase supply to thyrister fans through FF supply Bypass Generator to Turbine Tripping.

21. 21 DETAILED PROCEDURE Operation of generator differential protection Roll the TA set to 3000 RPM Establish Generator Cooling System Close the Field Breaker and go on increasing excitation current till operation of Gen diff proton. & master trip relay 86G1/86G2 along with FB tripping. 5 min

22. 22 Short metro-sils of generator differential relay. Close the Field Breaker Go on increasing excitation current till operation of relay. Observe operation of Master trip & FB 10 min(15) DETAILED PROCEDURE Operation of Over All Differential Protection

23. 23 Remove shorting from point A when TA set is at bar 60 min(120) Trip the TA set & Bring to Barring speed 45 min(60) DETAILED PROCEDURE Removal of shorting from Point A

24. 24 Roll the TA set to 3000rpm, Create single phase to earth fault with the help of Earth Rod at point B 30 min(150) Close the Field Breaker go on increasing excitation current till operation of master trip relay 86G1/86G2 along with FB Tripping. Remove the earth rod 10 min (160) DETAILED PROCEDURE Operation of Stator Earth Fault Relay

25. 25 DETAILED PROCEDURE Generator short Circuit Charectristic Close the isolator to connect Three phase shorting at point "C“ Bypass the 220KV Bus-Bar diff. Protn . Bypass the tripping of 50LBB protection 10 min(170) Close the field breaker, increase excitation and record the short circuit characteristics 15 min(185)

26. 26 Open the isolator to remove the shortings 10 min (195) Close the field breaker and increase excitation record the Open circuit characteristics 15 min(210) DETAILED PROCEDURE Open Circuit Charectristic

27. 27 NORMLIZATION 1. Trip the TA set and bring to barring. 45 min(255) 2. Remove shorting from point C. 3. Normalize the excitation transformer HV links 4. Normalize the modifications done for slow built up in excitation. 45 min(300)

28. 28 Hand over the machine back to operation staff Roll the TA set to 3000RPM Synchronize as per normal procedure. Total time estimated 30 min(330 min) Synchronization

29. 29 The Proposed New Procedure scheme Proposed by Testing Section PTPS Parli

30. 30 Excitation System Modifications: Same as Conventional Modifications Excitation Transformer Modification: Same as Conventional Modifications Create Three Phase Short at Point D instead of A & C Modifications for Dynamic Testing

31. 31 Operation of generator differential protection Short phase side CT for Generator Diff and 220KV for Over All Diff Protection Close the Transfer Bus Isolator to Connect Three Phase Short to GT HV Side Bypass the 220KV Bus-Bar diff. Protection. Bypass the tripping of 50LBB protection Roll the TA set to 3000 RPM Establish Generator Cooling System Close the Field Breaker and go on increasing excitation current till operation of Gen diff protection & FB tripping. 10min The Proposed New Procedure

32. 32 Operation of over all differential protection The Proposed New Procedure Normalize the CT circuit of Generator diff protection Close the Field Breaker and go on increasing excitation current till operation of relay. Take the readings. Observe operation of Master trip with FB tripping. Normalize the CT circuit of over all diff Protection. 10min (20)

33. 33 short circuit characteristic The Proposed New Procedure Close the field breaker, increase excitation gradually & record the short circuit characteristics Make the FB OFF Open the isolator to isolate three phase shorting from point D Give clearance to remove shorting from point D Normalize the 220KV Bus-Bar diff. Protection. Normalize the tripping of 50LBB protection 15 min(35)

34. 34 The Proposed New Procedure Operation of Stator Earth Fault Relay Create single phase to earth fault with the help of Earth Rod at point B Close the Field Breaker Go on increasing excitation current till operation of master trip relay 86G1/86G2 along with FB tripping. Remove the earth rod 10 min(45)

35. 35 Close the field breaker, increase excitation gradually & record the Open circuit characteristics 15 min(60) Open circuit test The Proposed New Procedure

36. 36 NORMLIZATION Trip the TA set and bring to barring. 45 min(105) Normalize the excitation transformer HV links Normalize the modifications done for slow built up in excitation. 45 min(150)

37. 37 Hand over the machine back to operation staff Roll the TA set to 3000RPM Synchronize as per normal procedure. Total time estimated 15 min(165min) Synchronization

38. 38

39. 39 Close link X and Open link Y at TTB for Phase side diff CT

40. Achievements By Proposed Dynamic Testing Procedure Total Estimated time for completion of test is 165 minutes. Lot of time is saved. Operation of Generator and overall Differential Protection can be tested dynamically under actual fault condition Actual and accurate operating point can be located. Healthiness of Excitation system gets proved in this proposal. Safe and fine control through excitation can be achieved. By changing the 3phase shorting location from C to D we can synchronize the unit by opening the transfer bus isolator and shorting removal work can be done even after taking the unit on load. The parallel activities can be planned such as excitation normalization and excitation transformer normalization to save the time.