Generator Testing

ELECTRICAL

TESTING

OF

2

GENERATOR CROSS SECTION

THDF 115/59

GENERATOR CROSS SECTION

THRI 108/44

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.

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.

8

9

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 (I_fl) - To be calculated, using OCC ,SCC & Potier reactance

5. Excitation losses: (I_fl)2 _{x - Rotor resistance at 75}O _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)%

Un In.Xp ep Ifp Ifa Ifn

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.

PERMITTED TEMPERATURES AS PER IEC:

500 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

14

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

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

16

SENSORS FOR VIBRATION MEASUREMENT

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.

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.

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.

DETERMINATION OF X2 & R2

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.

DETERMINATION OF X0 & R0

The results obtained are extrapolated for rated current condition maintaining linear relation. X₀ and R₀ are computed with the help of following formulae;

Where:

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

I_n = Rated line current

p.u. Vn In . 3 . I V Z₀ = _{) p.u.} V I 3W (1 Z X ₂ n 2 n 2 0 0 = − p.u. ) X (Z R₀ = ₀2 − ₀2

GENERATOR TESTING

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

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.

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 500 MW R₂₀ (STATOR WDG.) 0.0014463 Ω VOLTAGE 21 kV R₂₀ (ROTOR WDG.) 0.06657Ω

CURRENT 16.166 kA POTIER REACTANCE 0.253 PU POWER FACTOR 0.85 LAG R2 0.02 PU

FREQUENCY 50 HZ X₂ (UNSAT) 0.2097 PU NO LOAD EXC. 1378 A R₀ 0.0044 PU

SC EXC.CURRENT 2655 A X₀ (UNSAT) 0.102 PU FULL LOAD EXC. 4040 A CAPACITANCE/PH 0.25 µF

FULL LOAD EXC. 340 V EXCITER VAR LOSS 46 kW SC RATIO 0.48 MIN EXC. CONST. LOSS 380 kW

MECH. LOSSES 1850 kW ROTOR CU LOSS 1367 kW IRON LOSSES 598 kW TOTAL LOSSES 6888 kW

SC+STRY LOSS 2693 kW XD (UNSAT) 2.311 PU TH BRG+ SLIP

RING LOSS 152 kW HYDROGEN PRESS. 3.5 ± 0.2 Bar EFFICIENCY(AT 100% LOAD) 98.64 %

TECHNICAL DATA OF TG FOR TESTING

(I₂)2_{*T 10}

HYDROGEN PRESSURE (g) 3.5 KG/CM2

PW FLOW: WINDING 60 M3 _/HR

BUSHING 4.5 M3 _/HR

BEARING OIL FLOW (BOTH) 57 M3 _/HR

SEAL OIL DIFF. (BOTH) 1.5 KG/CM2

PHASE SEQUENCE U-V-W

DIRECTION OF ROTATION ANTI-CLOCKWISE

(AS OBSERVED FROM TE)

TECHNICAL DATA OF TG FOR TESTING

RATING 250 MW R₂₀ (STATOR WDG.) 0.0008574 Ω VOLTAGE 16.5 kV R₂₀ (ROTOR WDG.) 0.09673 Ω

CURRENT 10.291 kA POTIER REACTANCE 0.241 PU POWER FACTOR 0.85 LAG R2 0.0284 PU

FREQUENCY 50 HZ X₂ (UNSAT) 0.196 PU NO LOAD EXC. 957 A R₀ 0.0022 PU

SC EXC.CURRENT 1511 A X₀ (UNSAT) 0.112 PU FULL LOAD EXC. A 2497 A CAPACITANCE/PH 0.35 µF

FULL LOAD EXC. V 300 V EXCITER VAR LOSS 40 kW SC RATIO 0.63 MIN EXC. CONST. LOSS 207 kW

MECH. LOSSES 400 kW ROTOR CU LOSS 734 kW IRON LOSSES 648 kW TOTAL LOSSES 2892 kW

SC+STRY LOSS 863 kW XD (UNSAT) 1.58 PU TH BRG+ SLIP

RING LOSS 152 kW HYDROGEN PRESS. 4.0 ± 0.2 Bar EFFICIENCY(AT 100% LOAD) 98.85 %

TECHNICAL DATA OF TG FOR TESTING

(I₂)2_{*T 10}

HYDROGEN PRESSURE (g) 4.0 KG/CM2

BEARING OIL FLOW (BOTH) 20.16 M3 _/HR

SEAL OIL DIFF. (BOTH) 1.5 KG/CM2

PHASE SEQUENCE U-V-W

DIRECTION OF ROTATION ANTI-CLOCKWISE (AS OBSERVED FROM TE)

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

STAGEWISE CHECKING

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