GENERATOR

COMMISSIONING

Kamal Nasir

Dy. Director

NPTI (ER), Durgapur

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RUNNING THE MACHINE AT NO LOAD

DRYING THE MACHINE IN H2 MEDIUM

DRYING THE STATOR WDG BY CIRCULATING HOT AIR

DRYING OUT BY CIRCULATING HOT WATER (50 DEG C)

DRYING OF WINDING

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Run the machine at no load

Heat generated by windage losses in the machine is utilized for heating

Commission the seal oil system

Admit dry instrument air (pr = 0.2 Ksc)

Purge the moist air periodically through generator drain.

Keep gas driers in service

Regulate gas cooler outlet valve to control the stator winding temperature.

The stator winding temperature should not be greater than 75 degrees

Core temperature 95 degrees

Rotor winding 110 degrees

Measure PI/IR values every three hours

Stop heating when PI = 2

DRYING OF WINDING: RUNNING THE MACHINE AT NO LOAD

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Procedure same as that of air

Keep Hydrogen pressure at 1.15Ksc

Purge out 1 cylinder every two hours to maintain low humidity inside the Generator

DRYING OF WINDING: Using Hydrogen

DRYING OF WINDING: Circulating Hot air

ADMIT HOT AIR AT 65 Degrees

MAINTAIN AIR PRESSURE AT 2-3Ksc

ADMIT AIR BEFORE MAGNETIC FILTER

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Hot water temperature 50 degrees.

Maintain flow at 25m3 an hour

Maintain winding temperature between 65-75 degrees for 72 hours.

Drain water from winding

Blow hot air through winding

Measure IR and PI value

DRYING OF WINDING: using hot water

MEASUREMENT OF IR AND PI

WINDING SHOULD BE COMPLETELY DRY.

NEUTRAL AND PHASE POINT SHOULD BE DISCONNECTED AND EACH WINDING SHOULD BE SEPARATE

WHILE MEGGERING ONE PHASE OTHER TWO PHASE SHOULD BE GROUNDED.

ABSORPTION COEFFICIENT = R60 / R15 > 1.3

POLARISATION INDEX (PI) = R600 / R60 > 2

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IR AND PI MEASUREMENT

TAN DELTA MEASUREMENT

DC WINDING RESISTANCE

HIGH VOLTAGE TEST

ELCID TEST

GAS TIGHTNESS TEST

HYDRO TEST

TEST ON STATOR

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WINDING SHOULD BE COMPLETELY DRY.

NEUTRAL AND PHASE POINT SHOULD BE DISCONNECTED AND EACH WINDING SHOULD BE SEPARATE

WHILE MEGGERING ONE PHASE OTHER TWO PHASE SHOULD BE GROUNDED.

ABSORPTION COEFFICIENT = R60 / R15 > 1.3

POLARISATION INDEX (PI) = R600 / R60 > 2

TEST ON STATOR: IR AND PI MEASUREMENT

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Evaluation of stress grading, dielectric loss and homogenity of the winding.

The insulator cannot be made 100% pure. Also due to ageing of insulator the impurities like, dirt and moisture enter into it. These impurities provide conductive path to the current. Consequently, leakage electric current flowing from line earth through insulator has also resistive component.

In other way the healthiness of an electrical insulator can be determined by ratio of resistive component to capacitive component. For good insulator this ratio would be quite low. This ratio is commonly known as tanδ or tan delta. Sometimes it is also referred as dissipation factor.

TEST ON STATOR: TAN DELTA MEASUREMENT

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In the vector diagram above, the system voltage is drawn along x-axis. Conductive electric current i.e. resistive component of leakage current, IR will also be along x-axis.

As the capacitive component of leakage electric current IC leads system voltage by 90°, it will be drawn along y-axis.

Now, total leakage electric current IL(Ic + IR) makes an angle δ (say) with y-axis.

Now, from the diagram above, it is cleared, the ratio, IR to IC is nothing but tanδ or tan delta.

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Detects poor connection and conductor short circuit

DC resistance value is measured. After temperature correction, it is compared with factory value. Variation with in 2% is considered as normal

TEST ON STATOR: DC WINDING RESISTANCE

TEST ON STATOR: HIGH VOLTAGE TEST

At 2.5 kv, for one minute for a new rotor at site. Value may be reduced for old rotor. Generally carried out only when any repair is done on the rotor winding.

2 times the rated voltage +1 kv for first time

80% of the previous value for the second time

80% of the previous value for the subsequent times

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Electromagnetic Core Imperfection Detection Test.

Detects healthiness of stator core and lamination insulation

It is a non destructive test

TEST ON STATOR: ELCID TEST

TEST ON STATOR: GAS TIGHTNESS TEST

Keep air inside generator casing at 3.5Ksc for 24 hours.

Leakage should not be more than 1% of internal volume of stator alone and 5% in case of completely assembled generator.

Volume (H2) / Volume (air) = 3.2

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HYDRAULIC TEST FOR THE STATOR WINDING IS CONDUCTED AT

5 KG/ cm2 FOR 24 HOURS USING FILTERED DM WATER.

NO DROP IS ALLOWED.

PROBABLE LEAK POINTS ARE:

TEFLON HOSES AT THE TURBINE END

THE CONNECTING PIPES OF THE TERMINAL BUSHINGS

THE CONNECTING PIPES AT THE EXCITER END

TEST ON STATOR: HYDRO TEST OF STATOR WINDING

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GENERATOR ROTOR

BORE

SLIPRING

JOURNAL

RETAINING

RING

ROTOR

WEDGE

JOURNAL

COIL &

INSULATION

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PURGE TEST OF TG ROTOR.

GAS TIGHTNESS TEST OF ROTOR.

DYE PENETRATION TEST OF ROTOR.

D.C. WINDING RESISTANCE TEST.

IR AND PI MEASUREMENT.

TEST ON ROTOR

TEST ON ROTOR: PURGE TEST

Pressure of 3. 0 ± 0.1KG/cm2 GAUGE SHOULD BE APPLIED AT THE VENTILATING CANALS OF SLOT THROUGH THE ADOPTER.

While carrying out test on overhang, a static pressure of 50 mm of water column should be maintained under retaining ring.

The average velocity pressure in the canals of slot portion should not be less than 15 mm of water column for each zone and 21 mm of water column for each slot.

The minimum value of static pressure in individual canals of over hang portion should not be less than 15mm of water column.

Fully closed canals are not allowed in the over hang portion of rotor winding.

Ensure that all the ventilation canals/ ducts are properly sealed after the purge test.

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TEST ON ROTOR: ROTOR GAS TIGHTNESS TEST

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Dye penetration test

Ultra sonic test

These tests are carried out to check the surface of the retaining ring for any sub surface crack

TEST ON ROTOR: TEST ON ROTOR RETAINING RING

TEST ON ROTOR: AC IMPEDENCE MEASUREMENT

This is carried out at different speeds of the rotor.

To detect any displacement of winding in the slot.

To detect the presence of short circuited turns.

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Dye penetration test :

It is a non destructive testing technique to detect surface breaking defects in a non porous material.

The surface is cleaned and prepared for inspection.

Liquid penetrant is applied to the surface and is drawn into cracks and porous by capillary action

After the dwell time the liquid penetrant is wiped off and surface is dried.

A developer is sprayed on the surface n order to extract the liquid penetrant from possible defects.

After the proper time for development of indications, visual inspection is carried out in order to revel defects.

Final cleaning if the surface.

Dye Penetration Test

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The generator is rotated at the rated speed,

• all the terminals are disconnected from loads,

• the field current is set to zero first.

• Next, the field current is increased in steps and the phase voltage (whish is equal to the internal generated voltage EA since the armature current is zero) is measured.

Since the unsaturated core of the machine has a reluctance thousands times lower than the reluctance of the air-gap, the resulting flux increases linearly first. When the saturation is reached, the core reluctance greatly increases causing the flux to increase much slower with the increase of the mmf.

Open-Circuit Characteristic is the graph of generated voltage

against field current with the terminals open-circuited

and running at synchronous speed

Maintain the machine at its rated speed.

Vary the rotor current.

Measure the rotor voltage and the stator voltage.

OCC

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The generator is rotated at the rated speed, with the field current is set to zero first, and all the terminals are short-circuited through ammeters.

Next, the field current is increased in steps and the armature current IA is measured as the field current is increased.

The plot of armature current (or line current) vs. the field current is the short-circuit characteristic (SCC) of the generator.

The SCC is a straight line since, for the short-circuited terminals, the magnitude of the armature current is

SCC

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TESTING OF RELAYS

TESTING OF STATIC EXCITATION SYSTEM

CHECKING OF ANNUNCIATIONS

CHECKING OF GT COOLING SYSTEM

RUN UP OF TEST

CHECKING OF VIBRATION

SEAL OIL DRAIN TEMPERATURE AND BEARING METAL

TEMPERATURE

OPERATION OF ISOLATORS AND BREAKERS

SYNCHRONISING AND HOURLY CHECKS

STARTING OF GENERATOR

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MODE OF OPERATION – Auto & Manual

SUPPLY ARRANGEMENTS

LIMITER CARDS

BRIDGE FAILURE CONDITION

OPERATING PRINCIPLES

STATIC EXCITATION SYSTEM

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INITIAL ASSEMBLY

PREPARATION OF OIL

FILLING AND CIRCULATION OF OIL

TESTING OF OIL

TRANSFORMER TESTING

BACK CHARGING OF TRANSFORMER

CHECKING THE COOLING SYSTEM

CHECKING THE RELAYS AND ANNUNCIATIONS

GENERATOR TRANSFORMER

Thank You