Generator Testing

ELECTRICAL TESTING OF TURBOGENERATORS

GENERATOR ON TEST BED

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GENERATOR CROSS SECTION THDF 115/59

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GENERATOR CROSS SECTION THRI 108/44

GENERATOR TESTING MEASUREMENT OF D.C.RESISTANCE
Resistance of Stator winding for each phase separately using Kelvin’s double bridge
Resistance of Rotor Winding by Kelvin’s double bridge I.R. MEASUREMENT OF STATOR AND ROTOR WINDINGS Stator Windings:
With 1 KV Meggar, with distillate flowing for directly cooled windings (Min 50K Ohms)
With 5 KV Meggar for indirectly cooled windings (Min 500 M Ohms) Rotor Windings: With 500 V Meggar (Min 100 M Ohms)

GENERATOR TESTING IR & CONTINUITY CHECK OF RTDs &THERMOCOUPLES (Min IR - 1 M ohms with 500 V Meggar)

MECHANICAL HEAT RUN & CALCULATION OF MECHANICAL LOSSES
Machine run at rated speed with zero excitation, under rated hydrogen pressure and all flows at rated parameters, until all temperatures get stabilised SHORT CIRCUIT HEAT RUN
Machine run at rated speed with its terminals short circuited and with an excitation value, which causes the rated stator current to flow in the winding.

GENERATOR TESTING SHORT CIRCUIT CHARACTERISTIC AND SHORT CIRCUIT LOSSES: Characteristics upto 109% / 105% of the rated stator current after achieving thermal stability in the above test. OPEN CIRCUIT HEAT RUN: All generator phase terminals shall be kept open circuited. Machine shall be run at rated speed with an excitation value that will cause the rated stator voltage across the generator terminals. OPEN CIRCUIT CHARACTERISTIC AND CALCULATION OF IRON LOSSES: OCC upto 120% / 130% rated voltage is carried out after achieving thermal stability in the above test.

GENERATOR TESTING

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GENERATOR TESTING CALCULATION OF GENERATOR EFFICIENCY 1. Mechanical losses - From mechanical heat run test 2. Short circuit losses - From the curve of stator current Vs short circuit losses corresponding to rated stator current 3. Open circuit losses - From the curve of stator voltage Vs open circuit losses corresponding to rated stator voltage 4. Full load excitation (Ifl) - To be calculated, using OCC ,SCC & Potier reactance 5. Excitation losses: (Ifl)2 x - Rotor resistance at 75O C 6. Exciter losses - As per data sheet / test results 7. Total losses - Losses at (1+2+3+5+6) above 8. Efficiency - [Output] / [Output + Losses] Tolerance permitted as per IEC is 0.1(100-η)%

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GENERATOR TESTING

ep

Ifa

In.Xp Ifp

Ifn Un

GENERATOR TESTING ESTIMATION OF FULL LOAD TEMPERATURES
Stator winding Full load temp.=Temp. during SC heat run + Temp. during OC heat run - Temp. during mechanical heat run


Rotor winding Rotor winding temperature is calculated under OC & SC heat runs. This is extrapolated for the actual field current.

11

500 MW GENERATOR TESTING PERMITTED TEMPERATURES AS PER IEC:
Stator Wdg

:120°°C
Rotor Wdg. :105°°C
Stator Core :120°°C
Bearing babbit : 90°°C

250 MW GENERATOR TESTING PERMITTED TEMPERATURES AS PER IEC:
Stator Wdg

:104°°C (for TVPI generator) (Depends upon H2 pressure and operating Voltage)
Rotor Wdg. :120°°C
Stator Core :120°°C
Bearing babbit : 90°°C

13

GENERATOR TESTING HIGH VOLTAGE TESTING OF STATOR AND ROTOR WINDINGS:
At 2U+1 for Stator winding
10 times rated voltage for Rotor winding PI MEASUREMENT OF STATOR WINDING For this test, IR measurements for one-minute and ten-minutes are to be recorded using 5 kV Motorised Meggar. Water has to be dried completely before carrying out the measurements Permitted value as per IEC is - Min. 2.0 14

GENERATOR TESTING IMPEDANCE OF ROTOR WINDING: Measured at standstill and upto 3000 rpm at intervals of 200 rpm. This is for reference of the customer VIBRATION MEASUREMENTS ON STATOR END WINDING 12 Nos. Vibration Probes mounted on stator end winding, on TE and EE. Vibrations are recorded peak to peak in 2X mode in the following regimes: a) In Mechanical regime. b) In OCC regime c) In SCC regime d) Speed variation from 47.5 Hz to 51.5 Hz at 60% voltage & 60% current after OC and SC heat run respectively

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GENERATOR TESTING

SENSORS FOR VIBRATION MEASUREMENT

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GENERATOR TESTING DISSIPATION FACTOR AND CAPACITANCE MEASUREMENT OF STATOR WINDING The dissipation factor and capacitance is measured with the help of Schering Bridge at a voltage from 0.2 Un to 1.0 Un in steps of 0.2Un.This test is performed after HV test is over. PARTIAL DISCHARGE MEASUREMENTS ON STATOR WINDING At Un and Un/√3 voltages of the machine shall be carried out on stator winding after works testing using suitable Partial Discharge Measurement equipment. The measurements shall be done on the individual phases at rated line voltage and phase voltage.

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GENERATOR TESTING VOLTAGE WAVEFORM DEVIATION FACTOR (Type test) It indicates the deviation of terminal voltage waveform with an equivalent sine wave. For this, various harmonic voltages are measured with a harmonic analyser. The amplitude ratio of each harmonic is the ratio of harmonic voltage to fundamental voltage. The waveform deviation factor is defined as the ratio of sum of amplitude ratios of all the harmonics to the fundamental voltage. Permissible value of deviation factor is < 0.1 as per IEC TELEPHONE INTERFERENCE FACTOR (T.I.F.) (Type test) TIF is considered with a view to minimize the interference between power lines and adjacent circuits. This is assessed from the line-to-line voltage, obtained with generator running at rated voltage and normal speed and on open circuit. The range of measurement shall cover all harmonics from rated frequency upto 5000 Hz. THF when measured as above, shall not exceed 0.015 p.u.

GENERATOR TESTING TEST FOR COMPUTATION OF X2 AND R2 (Type test) The negative phase sequence reactance and resistance is computed by line to line Sustained short-circuit. Two phases of stator windings are shorted keeping the third phase open. The generator is run at rated speed and excitation given to rotor winding to circulate approx. 15% of rated stator current in the shorted phases of stator winding.

GENERATOR TESTING

DETERMINATION OF X2 & R2

GENERATOR TESTING Z2 = Es.In/(Is.Vn) p.u. Cos φ = W/(Es. Is) X2 = Z2 Cos φ p.u., R2 = Z2 Sin φ p.u. where Es = Voltage between open and shorted points. Is = Short circuit current between phases W = Power loss in shorted windings. TEST FOR COMPUTATION OF X0 & R0 (Type test) The zero phase sequence reactance X0 and resistance R0 is computed by line to line and to neutral sustained short circuit test. The two phases of the generator stator winding are shorted and connected to the neutral, keeping the third phase open. The generator is run at rated speed and excitation given to rotor winding to circulate approx. 10% of rated stator current in the link between shorted phases of stator winding and the neutral.

GENERATOR TESTING

DETERMINATION OF X0 & R0

GENERATOR TESTING The results obtained are extrapolated for rated current condition maintaining linear relation. X0 and R0 are computed with the help of following formulae; V In Z0 = . 3 . p.u. I Vn 2

Where:

2

R0 = (Z0 − X0 ) p.u.

V = Measured value of the Voltage I = Measured value of the current Vn = Rated line voltage In = Rated line current

X0 = Z0

3W2 (1− 2 2 ) p.u. InVn

GENERATOR TESTING THREE PHASE SUDDEN SHORT CIRCUIT TEST: This test is carried out at 50% of the rated voltage. Generator is run at a speed slightly higher than rated (say 3020) when the drive motor is tripped. When the speed drops to 3000+3 rpm, generator stator terminals are shorted through Short Circuit Switch. Various signals are recorded for 2-3 seconds and then again after an interval of 20-25 seconds (for 2-3 seconds). Transient and sub-transient reactances are determined as per clause 40 & 41 of IEC-34-4, using the following formulae: X’d = U / i’k(0) X’’d = U / i’’k(0) Where: ‘U’ is the applied test voltage in PU ‘i’k(0)’ is transient short circuit current at limit =0 ‘i’’k(0)’ is sub-transient short circuit current at limit =0

GENERATOR TESTING

SUDDEN SHORT CIRCUIT TEST SCHEME

GENERATOR TESTING NATURAL FREQUENCY TEST FOR THE STATOR WINDING OVERHANG (Piezo – Electric Hammer Test) (Type test)
Gives an indication of natural frequency of winding bars on sample basis, although does not simulate actual vibration exciting force arising out of combined effect of core induced end winding vibration and stator current induced vibrations.
One Piezo-electric accelerometer probe is used for sensing the response on one bar at a time. Probe placed on the nose joint of the overhang bar, in both tangential and radial directions.
After the response test is finished on one bar, the whole process is repeated on the next identified bar.
Recommended frequency span for testing is 0 – 200 Hz.
Test is conducted on wound stator, before TG assembly for testing.

GENERATOR TESTING

GENERATOR TESTING OTHER SPECIAL TESTS:
HEAT RUN TEST WITH ONE COOLER OUT
HEAT RUN TEST WITH 10 % PLUGGING OF COOLER TUBES
HEAT RUN TEST AT PEAK RATING
PHASE SEQUENCE TEST
SHAFT VOLTAGE MEASUREMENT
RESIDUAL VOLTAGE TEST
MEASUREMENT OF HYDROGEN CONSUMPTION DURING WORKS TESTING
BEARING VIBRATIONS MEASUREMENT

500 MW GENERATOR TESTING TECHNICAL DATA OF TG FOR TESTING RATING VOLTAGE CURRENT

500 21

POWER FACTOR FREQUENCY

0.85

NO LOAD EXC. SC EXC.CURRENT FULL LOAD EXC. FULL LOAD EXC. SC RATIO MECH. LOSSES IRON LOSSES SC+STRY LOSS TH BRG+ SLIP RING LOSS

1378 2655 4040 340 0.48 1850 598 2693

MW kV 16.166

R20 (STATOR WDG.) 0.0014463 Ω R20 (ROTOR WDG.) 0.06657Ω kA POTIER REACTANCE

0.253

PU

LAG 50

R2 HZ

PU 0.2097

PU

A A A V MIN kW kW kW

R0 X0 (UNSAT) CAPACITANCE/PH 0.25 EXCITER VAR LOSS EXC. CONST. LOSS 380 ROTOR CU LOSS 1367 TOTAL LOSSES 6888 XD (UNSAT)

152

kW

EFFICIENCY(AT 100% LOAD) 98.64

%

0.02 X2 (UNSAT) 0.0044 0.102 µF 46 kW kW kW 2.311

HYDROGEN PRESS.

PU PU kW

PU 3.5 ± 0.2 Bar

500 MW GENERATOR TESTING TECHNICAL DATA OF TG FOR TESTING (I2)2*T

10

HYDROGEN PRESSURE (g) PW FLOW: WINDING BUSHING BEARING OIL FLOW (BOTH) SEAL OIL DIFF. (BOTH) PHASE SEQUENCE DIRECTION OF ROTATION (AS OBSERVED FROM TE)

3.5 KG/CM2 M3 /HR M3 /HR M3 /HR KG/CM2 U-V-W ANTI-CLOCKWISE

60 4.5 57 1.5

250 MW (TVPI) GENERATOR TESTING TECHNICAL DATA OF TG FOR TESTING RATING VOLTAGE CURRENT

250 16.5

POWER FACTOR FREQUENCY

0.85

NO LOAD EXC. 957 SC EXC.CURRENT 1511 FULL LOAD EXC. A 2497 FULL LOAD EXC. V300 SC RATIO 0.63 MECH. LOSSES 400 IRON LOSSES 648 SC+STRY LOSS 863 TH BRG+ SLIP RING LOSS

MW kV 10.291

R20 (STATOR WDG.) 0.0008574 Ω R20 (ROTOR WDG.) 0.09673 Ω kA POTIER REACTANCE

0.241

PU

LAG 50

R2 HZ

PU 0.196

PU

A A A V MIN kW kW kW

R0 X0 (UNSAT) CAPACITANCE/PH 0.35 EXCITER VAR LOSS EXC. CONST. LOSS 207 ROTOR CU LOSS 734 TOTAL LOSSES 2892 XD (UNSAT)

152

kW

EFFICIENCY(AT 100% LOAD) 98.85

%

0.0284 X2 (UNSAT) 0.0022 0.112 µF 40 kW kW kW 1.58

HYDROGEN PRESS.

PU PU kW

PU 4.0 ± 0.2 Bar

250 MW (TVPI) GENERATOR TESTING TECHNICAL DATA OF TG FOR TESTING (I2)2*T

10

HYDROGEN PRESSURE (g)

4.0

BEARING OIL FLOW (BOTH) SEAL OIL DIFF. (BOTH) PHASE SEQUENCE DIRECTION OF ROTATION (AS OBSERVED FROM TE)

20.16 1.5

KG/CM2

M3 /HR KG/CM2 U-V-W ANTI-CLOCKWISE

GENERATOR TESTING STAGEWISE CHECKING INCOMING MATERIALS / COMPONENTS
All incoming materials are accepted as per the supplier’s TC
Verification of dimensions
NDE Testing of weld joints
Chemical composition of materials
Ultrasonic and dye penetration tests for critical components like Retaining rings, Slot wedges etc

GENERATOR TESTING STAGE TESTING :
Hydraulic and

pneumatic testing of stator frame and end shields


Core flux test of unwound stator to detect any hot spot in the core
Checking of stator bars after laying & complete wound stator
Flow test & Helium leak test on wound stator of water cooled design
Hydraulic testing of gas coolers
Over speeding of complete rotor after dynamic balancing
Air Leak Test of assembled generator at rated pressure