POWER

POWER PRODUCTION POWER CONSUMER

TURBINE GENERATOR COMPRESSORS

THERMAL GAS STATOR ROTAR EXICITER PIPE CONDENSORS COMPRESSORS

POWER GENERATION.

POWER TRANSMISION STEPUP

POWER DISTRIBUTION STEP DOWN

COUSTOMERS USE

BULB FAN COOLERS IRONBOX TAPES FACTORIES etc

GENERATOR

STATOR ROTOR EXCITER

CORE RTD WINDING FORGING WINDING YOKE ARMATURE

TESTING PROCESS

MANUFACTURE ASSEMBLING PERFORMANCE

GENERATOR READY FOR PRODUCTION

. .

INTRODUCTION

It is a well-known fact that all power plants are located in such a place where

there are lots of resources. For example THERMAL POWER PLANTS near coal

resources, HYDRALPOWER PLANT where there is lot of water is present.

As we all know that in KOTHAGUDAM we have we have one THERMAL power

plant. There we have TURBINES, BIOLERS, COMPRESSORS, CONDENSERS

and GENERATORS. We need all these Machines to produce POWER.

We need coal to produce steam, Steam helps to rotate the turbine, turbine will

be rotating the shaft of the rotator and in turn exciter is also been rotated to

produce power. Boiler is used to produce steam for rotating turbine

GENERATOR

TURBO GENERATOR

The Genera to r cons is ts o f the fo l low ing components :

STATORStator Frame,Stator Core,Stator Winding,Generator Coolers,Stator End Covers.

ROTORRotor shaft,Rotor winding,Rotor Retaining Ring,Field Connections.

EXCITERDesign features,Rectifier wheels,Field Connections.

BEARINGS

SKID

TESTING PROCESS

Dur ing manufac tu r ing p rocess ,Dur ing Assembl ing ,Per fo rmance tes t .

BREAKERS

NOTES ON GENERATOR

INTRODUCTION

Types of Generators

GENERATOR BEARINGS

The generator rotor is supported at two journal bearings. The bearings

consist of a bearing pedestal and bearing shell is split into two halves to facilitate

assembly. The bearing pedestals are iron castings and the bearing shells are

steel castings. The bearing pedestal is provided with a spherical seating surface

and the bearing shell rests in it with its outer spherical surface. The inner surface

of bearing shell is provided with spiral grooves and cast with Babbitt metal.

Bearing Oil Supply:

The o i l requ i red fo r bear ing lub r i ca t ion and coo l ing i s

ob ta ined f rom the tu rb ine o i l supp ly sys tem and supp l ied to the

lub r i ca t ing g roove in the bo t tom-bear ing s leeve . The upper

bear ing s leeve cons is ts o f a w ide over f l ow g roove th rough

wh ich o i l i s d is t r ibu ted over the sha f t j ou rna l and fed to the

lub r i ca t ing gap .

Bearing Temperatures:

The temperature of each bearing is monitored by one double-element

RTD. The RTD is screwed in position on side of the lower bearing sleeve from

outside with the detector extending to the Babbitt liner.

STATOR

INTRODUCTION: Stator frame is of welded construction, supports the core and the windings. It

consists of air duct pipes and radial ribs, which provide rigidity to the frame.

Foo t ings a re p rov ided to suppor t the s ta to r on the sk id . The

s ta to r f rame shou ld be r ig id due to the var ious fo rces and

to rques dur ing opera t ion . The we lded s ta to r f rame cons is ts o f

two end p la tes , ax ia l and rad ia l r ibs . The a r rangement and

d imens ion ing o f the r ibs a re de te rmined by the coo l ing a i r

passages , the requ i red mechan ica l s t reng th and s t i f fness . The

end covers a re a lumin ium a l loy cas t ings . The s ta to r f rame is

f i xed to the sk id w i th the he lp o f hexagona l bo l t s . The sk id i s

in te r im f i xed to the concre te founda t ion th rough founda t ion

bo l t s .

Stator core:

The core packed into the stacking frame is pressed firmly together

between the end plates of the machine frame and fixed in this position by welding

the axial ribs of the core and the end plates of the frame. End fingers on the

inside diameter of the end plates transmit the pressure to the teeth of the core.

The compressive force produced prevents the laminations and teeth from

vibrating. An eye is welded to each end plate for attaching suitable lifting gear

with adequate lifting capacity for transporting the complete machine. All the

forces that occur during normal operation or on short circuits are transmitted from

the stator yoke to the base frame via the seating plates and into the foundation.

Location of Bars:

A semi -conduc t ing wrapper o f g raph i te paper in the s lo t

p ro tec ts the bar . The s ta to r w ind ing i s p ro tec ted aga ins t the

e f fec ts o f cu r ren t fo rces in the s lo t sec t ion . To ensure t igh t

sea t ing o f the bar a t the s lo t bo t tom, a s lo t bo t tom-equa l i z ing

s t r ip o f p ress pa th i s inser ted . A top r ipp le spr ing i s a r ranged

be tween two compress ion s t r ips to exer t a con t inuous p ressure

on the bars . The bars a re shaped so tha t , cone shaped end

w ind ings a re ob ta ined . In o rder to reduce the s t ray losses a

sma l l cone taper o f (13-20 ) i s used . On the w ide s ides o f the

bars spacers o f insu la t ing mate r ia l a re inser ted a t regu la r

in te rva ls .

Bearings :

The rotor runs in two floating type guide bearings, designed as pedestal

bearings, with forced oil or oil-ring lubrication. The driven end bearing is secured

to the base frame and insulated from the latter. As the connections are designed

to prevent short-circuiting of the insulation.

Enclosure :

The enclosure consists of the inner and outer components. The inner

components comprises of the winding covers, which form an angular enclosure

of the overhang of the stator winding and are also used as air ventilator rings.

The outer enclosure consists of top and bottom parts and is designed as required

for the particular degree of protection, as indicated in the dimension drawing or in

“Technical data”. The ventilating circuit is of the double - ended symmetrical

arrangement.

STATOR CORE:

Stator core is stacked from insulated electrical sheet laminations and suspended

in the stator frame from insulated dovetailed guide bars. Axial compression is

obtained from clamping fingers, clamping plates and non-magnetic clamping

bolts which are insulated from the core. In order to minimize the hysterics and

eddy current losses of the rotating magnetic flux which interacts with the core.

The entire core is built up of laminations, each layer of which is made from a

number of individual segments. The segments are punched from silicon steel. In

the outer circumference the segments are stacked in insulated trapezoidal guide

bars, which hold them in position. The guide bar is not insulated to provide for

grounding the core. The laminations are hydraulically compressed and heated

during the stacking procedure. The complete stack is kept under pressure and

fixed in the frame by means of cell

STATOR

Stator frame is of welded construction, supports the core and the windings. It

consists of air duct pipes and radial ribs, which provide rigidity to the frame.

STATOR

Stator frame is of welded construction, supports the core and the windings .It

consists of air duct pipes and radial ribs, which provide rigidity to the frame.

Footings are provided to support the stator on the skid. The stator frame should

be rigid due to the various forces and torque’s during operation. The welded

stator frame consists of two end plates, axial and radial ribs. The arrangement

and dimensioning of the ribs are determined by the cooling air passages, the

required mechanical strength and stiffness. The end covers are aluminium alloy

castings. The stator frame is fixed to the skid with the help of hexagonal bolts.

The skid is interim fixed to the concrete foundation through foundation bolts.

Electrical Connection of Bars and Phase Connections:

Brazing makes Electrical Connection of Bars: Electrical connection

between the top and bottom bars, one top bar being brazed to associated bottom

bar. The coil connections are wrapped with tapes. The thickness of the wrapper

depends on the machine voltage. After taping, an insulating varnish is applied.

Phase Connectors: The phase connectors consist of flat copper sections, the

cross-section of which results in a low specific current loading. The connections

to the stator winding are of riveted and soldered type. The phase connectors are

wrapped with resin-rich mica tape, which contain synthetic resin having very

good penetration properties. The phase connections are then cured at a certain

temperature, with the shrinking tapes contracting so that a void free insulation is

obtained.

Output Leads:

The beginning and ends of the three phase windings are solidly bolted to

the output leads with flexible. The output leads consist of flat copper sections

with mica insulation. To prevent eddy-current losses and inadmissible

temperature rises; the output leads are brought out through insulating plates.

ROTOR

Introduction:

ROTOR WINDING

Construction:

The field winding consists of several series connected coils inserted into

the longitudinal slots of the rotor body. The coils are wound so those two poles

are obtained. The solid conductors have a rectangular cross-section and are

provided with axial slots for radial discharge of the cooling gas. The individual

conductors are bent to obtain half turns. After insertion into the rotor slots, these

turns are combined to form full turns of series connected turns of one slot

constituting one coil. The individual coils of the rotor winding are electrically

series connected so that one north and one south magnetic pole are obtained.

Insulation:

The insulation between the individual turns is made of layers of glass fiber

laminate. The coils are insulated from the rotor body with L shaped strips of glass

fiber laminate with Nomex interlinear. The strips are provided with axial slot of the

same cross- section and spacing as used on the rotor windings.

Rotor Slot Wedges:

To protect the winding against the effects of the centrifugal force, the

winding is secured in the slots with wedges. The slot wedges are made from an

alloy of high strength and good electrical conductivity, and are also used as

damper wedged bars. The retaining rings act as short circuit rings to induced

currents in the damper windings.

ROTOR SHAFT:

The rotor shaft is forged from a vacuum cast steel ingot. The high

mechanical stresses resulting from the centrifugal forces and short circuit

torque’s call for high quality heat-treated steel. The rotor consists of an

electrically active portion and two shaft ends. Approximately 60% of the rotor

body circumference has longitudinal slots, which hold the field winding. Slot pitch

is selected so that 180 displace the two solid poles. The rotor wedges act as

damper winding within the range of the winding slots. The rotor teeth at the ends

are provided with axial and radial holes, enabling the cooling gas to be

discharged into the air gap after, intensive cooling of the end windings.

COOLING OF ROTOR WINDINGS:

Each tu rn i s subd iv ided in to four para l le l coo l ing zones .

One coo l ing zone inc ludes the s lo t f rom the cen te r to the end o f

the ro to r body , wh i le ano ther covers ha l f the end w ind ing to the

cen te r o f the ro to r body . The coo l ing A i r fo r the s lo t por t ion i s a

l im i ted in to the s lo t bo t tom duc ts be low the ro to r w ind ing . The

ho t gas a t the end o f the ro to r body i s then d ischarged in to the

a i r gap be tween the ro to r body and s ta to r co re though rad ia l

open ings in the conduc to rs and in the ro to r s lo t wages . The

coo l ing a i r fo r the end w ind ing i s d rawn f rom be low the ro to r -

re ta in ing r ing . I t r i ses rad ica l l y a long the ind iv idua l co i l s and i s

then d ischarged in to the a i r gap v ia ax ia l and rad ia l s lo ts in the

end por t ions o f the ro to r tee th .

Direct Cooling: Usually use in the rotor to eliminate hotspots and differential

temperatures between adjacent components, which would result in mechanical

stress particularly in the copper conductors.

Indirect Cooling: Used for stator windings.

AIR COOLING CIRCUIT:

Air is circulated using two axial flow fans arranged in the rotor shaft. The fans

draw cold air from the cooler unit, which is divided, into 3 flow paths.

1. It is directed into rotor end winding space. Part of it also flows over the

individual coils for cooling in the rotor end winding and then leaves the end

windings via the bores in the rotor teeth. Other part flows from the rotor

end winding space into slot bottom ducts. From this it will discharge into

the air gap via radial ventilating ducts.

2. Air is directed over stator end windings to the air ducts into the space

between the generator housing and the stator core. Then air flows into the

ventilating slot of the stator core, where it absorbs heat from the stator

core and stator windings.

3. It is circulated into the air gap via the rotor-retaining ring. The air then

mixes with the hot air flowing via ventilating ducts in the stator core into

the outer hot air compartment in the stator frame for being returned to the

cooler.

The three flow paths in the air gap and hot air is returned to the cooler

via hot air ducts for re-cooling and drawn again by the fans.

ROTOR WINDING

Construction:

The field winding consists of several series connected coils inserted into

the longitudinal slots of the rotor body. The coils are wound so those two poles

are obtained. The solid conductors have a rectangular cross-section and are

provided with axial slots for radial discharge of the cooling gas. The individual

conductors are bent to obtain half turns. After insertion into the rotor slots, these

turns are combined to form full turns of series connected turns of one slot

constituting one coil. The individual coils of the rotor winding are electrically

series connected so that one north and one south magnetic pole are obtained.

Insulation:

The insulation between the individual turns is made of layers of glass fiber

laminate. The coils are insulated from the rotor body with L shaped strips of glass

fiber laminate with Nomex interlinear. The strips are provided with axial slot of the

same cross- section and spacing as used on the rotor windings.

Rotor Slot Wedges:

To protect the winding against the effects of the centrifugal force, the

winding is secured in the slots with wedges. The slot wedges are made from an

alloy of high strength and good electrical conductivity, and are also used as

damper wedged bars. The retaining rings act as short circuit rings to induced

currents in the damper windings.

ROTOR RETAINING RING:

The ro to r re ta in ing r ings w i th s tand the cen t r i fuga l fo rces

due to the end w ind ings one end o f each r ing i s sh runk on the

ro to r body , wh i le the o ther end o f the r ing overhangs the end

w ind ings w i thou t con tac t on the sha f t . The shrunk on hub a t the

f ree end o f the re ta in ing r ing serves to re in fo rce the re ta in ing

r ing and secures the end w ind ing in the ax ia l d i rec to r a t the

same t ime. The shr ink sea t o f the re ta in ing r ing i s s i l ve red

p la ted , ensur ing a low con tac t res is tance fo r induced cur ren t .

To reduce the s t ray losses and have h igh s t reng th , the r ings

a re made o f non-magnet i c , co ld worked mater ia ls .

FIELD CONNECTIONS:

The field connections provide the electrical connection between the rotor

winding and the exciter.

Terminal Lug:

Consists of a copper conductor of rectangular cross-section. One end of

the terminal lug is brazed to the rotor winding, while the other end is screwed to

the radial bolt.

Radial Bolt:

The field current lead located in the shaft bore is connected to the terminal

lug through a radial bolt. The radial bolt is made from steel and screwed into the

field current lead in the shaft bore.

ROTOR FAN:

The generator cooling air circulated by two axial flow fans located on the rotor

shaft one at either end. To augment the cooling of the rotor winding the pressure

established by the fan works in conjunction with the air expelled from the discharge ports

along the rotor. The blades of the fan have threaded roots for being screwed into the rotor

shaft. The blades are forged from an aluminum alloy. Threaded root fastening permits the

blade angle to be changed. TEST PROCEDURES

Mechanical run and measurement of vibrations at rated speed: This test is run

after assembly of machine on test bed.

Equipment for running test:

D.C motor drives system.

Bearing lubricating system

Cooling water system.

Current transformers - 2 nos.

Potential transformers - 2nos.

D.C current shunts - 2 nos.

A.C volt meters - 3nos.

DC millivolt meters - 2 nos.

Phase sequence indicator.

Multi meter for continuity checks.

Vibration monitor.

RTDs temperature monitor.

50 Hz A.C High voltage test equipment.

Meggers

Micro ohm meter.

Connecting leads and earthing cables.

The turbo-generator under test is assembled separately with out coolers and

enclosures (if any), on a test foundation frame using it's own bearings and

coupled to a calibrated D.C. drive motor with gearbox of suitable capacity (1900

kw /1300/290 kw). The generators, which have brush less excitation system, are

tested with additional test pit slip rind shaft. The power to the drive motor and the

field of the generator are drawn independently from the Thyristor connectors /

Ward - Leonard sets situated in electrical machine rooms and controlled from test

gallery.

The machine is rolled and run at rated speed after ensuring the bearing oil, and

kept at rated speed for stabilization of bearing temperatures. The vibrations are

measured at rated speed on both the bearings housings (pedestals) in

Horizontal, vertical and Axial directions with the help of vibrating meters which is

internally connected to the monitor and the vibrations are noted in the form of

graphs. The temperature of stator is monitored by RTDs / Thermocouples

embedded in winding, core and tooth.

Measurement of mechanical losses, short circuit characteristic and losses:

The machine is prepared for short circuit characteristics using current

transformers and shorting links. The machine is run at rated speed and drive

motor input voltage and current are noted and m/c is excited gradually in steps,

at 20%, 30%, 40%, 50%. At each step the following parameters are noted.

Stator current (Ia and Ib)

Rotor current corresponding to stator current (If).

Drive motor voltage and current corresponding to stator current (Vd & Id)

Bearing vibrations at rated stator current.

RTD readings at rated stator current.

The excitation is reduced and cut off. The speed is reduced and the machine is

cooled at lower speed. The temperatures are checked from RTDs. The machine

is stopped when it is sufficiently cooled down.

From above data, the characteristic curves are plotted as follows -

% In v/s If.

% In v/s m/c losses in kw. (Fig 6 sample of m/c losses curves) xerox 11

output% Efficiency of TG = . 100

output +total losses

Field current at 100% En from OCCS.C.R =

Field current at 100% In from SCC

Measurement of mechanical losses, open circuit characteristic and losses.

The machine is prepared for open circuit characteristic.

The machine is run at rated speed and drive motor in put voltage and

current are noted and m/c is excited gradually in steps, at

20%,30%,40%,50%,60%,80%,95%,100%,105%,110%,115%,120%,125%130

%

At each step the following parameters are noted.

1. Stator voltages (Vab,Vbc, & Vca)

2. Rotor current corresponding to stator voltage (If)

3. Drive motor voltage and current corresponding to stator voltage. (Vc & Id)

At 95% En following parameters are noted.

4. Shaft voltage.

5. Checking of phase sequence.

6. Bearing vibrations at rated stator voltage.

7. RTD readings at rated stator voltage.

The excitation is reduced and cut off. The speed is reduced and the machine is

cooled at lower speed. The temperatures are checked from m/c RTDs. The m/c

is stopped when it is sufficiently cooled down.

From the above data, characteristic curves are plotted as follows -

% En v/s If.

% En v/s m/c losses in kw.

Measurement of Shaft voltage:

Shaft voltage of generator is measured using multimeter or a high input

impedance a.c voltmeter across the two ends of the rotor when machine is in

O.C. condition at 100%

Checking of Phase sequence:

Phase sequence of generator is checked using a phase sequence indicator

across PT output terminals when m/c is in OC. Condition at 100%.

Measurement of rotor impedance.

Equipment

50 Hz (Power frequency) A.C source.

A.C.Voltmeter.

A.C.Ammeter

Multimeter for continuity checks.

Current trasformer (50 / 5A OR 100 / 5A)

Connecting leads.

Rotor impedance is measured at standstill and at rated speed of the machine.

Evaluation of Impedance:

VZ =

IWhere Z : Impedance in ohm

V : Voltage in Volts.

I : Current in Amps.

Measurement of insulation resistances of rotor windings before and after high

voltage test.

Equipment:

Motorized Megger (1000 V/ 2500 V)

Earthing Rod & earthing cable.

Insulation resistance of the rotor windings are measured before and after high

voltage test using Megger of 1000 V for rotor windings. The values are taken at

15 sec. And at 60 sec. A absorption coefficient of insulation is found out as ,

IR at 60 "Absorption coefficient =

IR at 15 "

This value for H.V. test should be 1.5

The winding is discharged to earth after each measurement.

High voltage test on rotor windings

50 Hz A.C High Voltage transformer and its Induction Regulator / Input

autotransformer.

Potential transformer

Volt meter

Binding wire.

Earthing rod & earthing cable.

The m/c is prepared for High voltage test. When high voltage test is done on one

phase, all other phases and rotor winding, instrumentation cables are earthed.

The high voltage is applied to winding by increasing gradually to required value

and maintained for one minute and reduced gradually to minimum. The

transformer is switched off and winding is discharged to earth. The test is

conducted on all the phases and rotor winding separately.

High voltage levels:

Rotor winding: (10.up) volts.

With minimum of 1500v and maximum of 3500v.

Where, Up = Excitation voltage.

Measurement of DC resistance of rotor windings in cold condition:

Equipment's:

Digital micro ohmmeter and it's measuring leads.

Thermometer.

DC resistances of rotor windings are measured separately using micro

ohmmeter.

Evaluation of resistances at 200 C is done by using formula:

Rt . (235+20)R20 = m

(235+T)

where,

R20 = Resistance at 200 C in m

T = average temperature of the rotor winding in 0 C

Rt = measured resistance of winding in m

Measurement of D.C. resistances and insulation resistance of RTDs and /or

thermocouples:

The D.C. resistances and insulation resistances of RTDs / thermocouples are

measured using multimeter and megger respectively and noted.

EXCITER

Design Features :

The exciter consists of

Rectifier wheels

Three-phase main exciter

Three-phase pilot exciter

The three-phase pilot exciter has a revolving field with permanent-magnet

poles. The three-phase ac is fed to the field of the revolving-armature main

exciter via a stationary regulator and rectifier unit. The three phase ac induced in

the rotor of the main exciter is rectified by the rotating rectifier bridge and fed to

the field winding of the generator rotor through the dc lead in the rotor shaft.

A common shaft carries the rectifier wheels, the rotor of the main exciter

and the permanent-magnet rotor of the pilot exciter. The generator and exciter

rotors are thus supported on a total of three bearings. Mechanical coupling of the

two shaft assemblies’ results in coupling of the dc leads in the central shaft bore

through the Multi contact electrical contact system.

Rectifier Wheels:

The main components of the rectifier wheels are the silicon diodes, which

are arranged in the rectifier wheels in a three-phase bridge circuit. A plate spring

assembly produces the contact pressure for the silicon wafer of the diodes. One

diode each is mounted in each light metal heat sink and then connected in

parallel. Associated with each diode is a fuse, which serves to switch off the

diode from the circuit if it fails. Each arm of the diode bridge is provided with one

R.C.block. The three-phase connection between armature and diodes is obtained

via copper conductors arranged on the shaft circumference between the rectifier

wheels and the main exciter. One conductor is provided for each arm of Diode

Bridge. The conductors originate at a bus ring system of the main exciter.

Three-phase Pilot Exciter:

The three-phase pilot exciter has a frame, which accommodates the

laminated core with the three-phase winding. The rotor consists of a hub with

mounted poles. Each pole consists of separate permanent magnets, which are

housed, in a non-magnetic metallic enclosure.

Three-phase Main Exciter:

The three-phase main exciter is a six revolving armature unit, the frame

poles with the field and damper winding. The field winding is arranged on the

laminated magnetic poles. The rotor consists of stacked laminations, which are

compressed by through bolts over compression rings. The three-phase winding

is inserted in the slots of the laminated rotor. The winding conductors are

transposed within the core length and the end turns of the winding are secured

with steel bands. The winding ends are run to a bus ring system to which the

three-phase leads leading to the rectifier wheels are also connected. After full

impregnation with epoxy resin and curing, the complete rotor is shrunk onto the

shaft.

* Using a DC generator we have a problem of connections at high speeds

like 3000 rpm, which is usually reduced to 1000 rpm with the help of gearbox. It

is difficult to obtain commutation at this speed without sparks. In order to avoid

this various brush less exciter is used whose circuit diagram is as follows:

The generator rotor is supported at two journal bearings. The bearings

consist of a bearing pedestal and bearing shell is split into two halves to facilitate

assembly. The bearing pedestals are iron castings and the bearing shells are

steel castings. The bearing pedestal is provided with a spherical seating surface

and the bearing shell rests in it with its outer spherical surface. The inner surface

of bearing shell is provided with spiral grooves and cast with Babbitt metal.

Bearing Oil Supply:

The o i l requ i red fo r bear ing lub r i ca t ion and coo l ing i s

ob ta ined f rom the tu rb ine o i l supp ly sys tem and supp l ied to the

lub r i ca t ing g roove in the bo t tom-bear ing s leeve . The upper

bear ing s leeve cons is ts o f a w ide over f l ow g roove th rough

wh ich o i l i s d is t r ibu ted over the sha f t j ou rna l and fed to the

lub r i ca t ing gap .

Bearing Temperatures:

The temperatures of each bearing are monitored by one double-element

RTD. The RTD is screwed in position on side of the lower bearing sleeve from

outside with the detector extending to the Babbitt liner.

Exciters

Test conducted in exciters

Mechanical run and measurement of vibrations at rated speed.

The machine is run to rated rpm after ensuring the bearing oil and kept at rated

speed for stabilisation of bearing temperatures. The vibrations are measured on

both the bearing housing (pedestals) using vibration probes and vibration

monitors in horizontal, vertical and axial directions. Drive motor input voltage and

current are measured to evaluate losses.

Open circuit characteristic:

The machine is prepared for open circuit characteristic and a 500 resistance

is connected across the slip rings. This is to allow a minimum current to pass

through the diodes for voltage measurement. The machine is run at rated speed

and field is excited gradually in suitable steps upto rated output voltage.

At each step following parameters are noted:

Va : out put voltage of exciter.

If : field current of the exciter.

Vq1,Vq2 : quadrature axis coil voltages, and

Vd : Drive motor voltage.

Id : drive motor current. and bearing vibrations.

Load magnetization characteristics and calibration of quadratic axis coils:

The machine is prepared for load magnetization characteristics. A variable water

load resistance is connected across the slip rings.

The machine is run at rated speed, load breaker is closed and m/c is excited

gradually. The following parameters are noted down in steps up to the rated

current by adjusting load resistance to R40. The load resistance is maintained at

R40 at all the steps by the adjusting the water load resistance.

Measurement of DC Resistances of armature windings, main pole winding

and quadrature axis coils:

After dynamic tests the machine is allowed for cooling and when it is sufficiently

cooled, the DC resistances of all the three armature windings, main pole winding

and quadrature axis coil are measured separately by micro ohm meter. The

ambient temperature is also recorded and evaluation of resistances at 200 C is

done by using the formula:

Rt . (235 +20)

R20 = ------------------

( 235+t)

R20 = D.C. resistance at 200 C

T = temperature of the winding in 0 C

Rt = DC resistance of the winding at 0 C

Measurement of IR value and high voltage tests:

Before performing these tests, all the diodes are shorted by the copper wire. This

is to protect the diodes during meggering and HV tests on armature winding.

Rotor and stator bodies are properly earthed. IR values of the windings are

measured with 500 or 1000 volts megger and values at 15" and 69" are noted

before and after High voltage tests.

HV test is done on individual windings using high voltage test kit by regulating

primary voltage to transformer. Slowly HV is reached and maintained for one

minute and reduced to zero. The object is then discharged by earth rod and IR

values are taken. When test is done on one winding, the other windings are

earthed.

Testing of permanent magnet generator

The PMG is assembled along with Brush less Exciter on the test foundation

frame. The output is connected to a three-phase resistance load (variable in

steps). As PMG has got permanently magnetised field poles, it starts generating

voltage right from start of mechanical run.

TESTING OF TURBO GENERATORS

The various tests conducted on Turbo Generators are as follows:

1. Air leak test & determination of leakage per day.

2. Mechanical run test in air medium.

3. Bearing vibration measurements.

4. Over hang winding and core vibration measurement at 2850, 3000 & 3150

rpm.

5. Mechanical heat run test at rated speed (i.e. 3000 rpm) to determine the

heat up as a result of Mechanical losses in Hydrogen medium.

6. Noise level measurement with meter dB(A) at 3000 rpm.

7. Three phase short circuit characteristic and losses measurement up to

110% In i.e. 11679.8A in steps at 20%, 40%, 60%, 80%, 100% and 110%

In.

8. IR value measurement of stator windings after S C C heat run test.

9. Open circuit characteristic and losses measurement up to 120% En i.e.

12.6 KV in steps at 20%, 40%, 60%, 80%, 90%, 95%, 100%, 105%, 110%

& 120% En.

10. Shaft voltage measurement at 100% En.

11. Phase sequence and voltage balance checks.

12. Impedance measurement of rotor with 50Hz supply.

13 . IR va lue measurement o f the s ta to r and ro to r w ind ings

a f te r hydrogen purg ing ou t .

14. Impedance measurement of Rotor at stand still, 1000, 2000 & 3000 rpm

by 50 Hz ac supply at 5A, 10A (Voltage limited to generator terminals

open circuited in air medium).

15. Impedance measurement of Rotor at stand still, 1000, 2000 & 3000 rpm

by 50 Hz ac supply at 5A, 10A (Voltage limited to 250v) generator

terminals short-circuited in air medium.

16 . IR va lue measurement and h igh vo l tage ( leve l : 1000 v ) on

Roto r w ind ing a t 3000 rpm.

Testing of Turbo Generators

The a re d i f fe ren t t ypes o f TESTS are :

1. EXAMINATION OF THE ROTOR FORGINGS.

2. ROTOR COIL BINDING RING TEST.

3. HYDRAULIC TEST ON THE STATOR CASING.

4. CORE FLUX TEST.

5. ROTOR WINDING AND CELL INSULATION TESTS.

6. TESTS ON THE STATOR COIL.

7. BALANCING AND OVER SPEEDING OF THE ROTORS.

LET US DISCUSS BRIEFLY ABOUT ALL THESE TESTS,

1. EXAMINATION OF THE ROTOR FORGINGS

THE ROTOR, BEING THE MOST HIGHLY STRESTED

PART OF THE TURBO GENERATOR, MUST BE PROVED

THROUGHLY SOUND BEFORE IT IS PASSED INTO SERVICE.

IT IS SUBJECTED TO A LARGE NUMBER OF RIGOROUS

DYNAMIC PHYSICAL, OPTICAL AND ELETRICAL INSPECTION

TESTS. THESE TESTS ARE DESIGNED TO DETECT L IKELY

FLAWS IN THE NMATERIAL, AS EARLY AS POSSIBLE. INTIAL

tes ts a re done a t fo rg ing manufac tu res works .

SPECIMEN PIECES ARE OUT FROM THE SHAFT AND ROTOR BODY

AND SUBJECTED TO (A) TENSILE (B) BENDING (C) PREMEABILITY

TESTS TO CHECK ITS CONFORMITY WITH THE SPECIFICATION.

SULPHUR PRINTS ARE TAKEN AT SHAFT END AND ON ROTOR

BODY FOR MICROSCOPIC EXAMINATION TO STUDY THE PRESENCE OF

SULPHIDE.

A SURFACE INSPECTION IS MADE AAFTER ROUGH MACHINING AT

STEEL MAKERS WORKS.

MAGNETIC TESTS ARE CONDUCTED TO DISCLOSE

ANY HAIR CRACKS NOT VISUALLY DETECTABLE. THE

PROCESS cons is ts o f magnet i z ing the fo rg ing and expos ing the

sur face under examina t ion to a s t ream o f para f f in ca r ry ing

magnet i ca l l y p repared f ine ly d iv ided i ron powder . F ine c racks

a re d isc losed by a concen t ra t ion o f i ron par t i c les b r idg ing the

c racks under the in f luence o f the magnet i c f i e ld .

The ro to r fo rg ing i s bored a long i t s ax is and magnet i c

c rack de tec t ion tes t ca r r ied ou t . the core o f a ro to r fo rg ing i s

t repanned and rough mach ined s tage these tes ts de tec t sub

sur face unsoundness , c racks o r non meta l l i c inc lus ions .

The serv ices o f spec ia l i s t s ta f f i n meta ls sec t ion o f Research

and deve lopment d iv i s ion o f H .E .a re u t i l i zed fo r a l l t he above-

ment ioned tes ts .

ROTOR COIL B INDING RING TESTS :

These a re the mos t h igh ly s t ressed par ts o f the ro to r , made

o f non magnet i c aus ten i t i c s tee l fo rg ing and warm worked by a

spec ia l p rocess ca l led “mandre l Expand ing” . To avo id loca l

concen t ra t ion o f h igh s t resses , ven t i l a t ing o r loca t ing purposes .

Spec imen taken f rom ends o f fo rg ing a re sub jec ted to

tens i le and bend ing tes ts .

Crack de tec t ion : Magnet i c c rack de tec t ion techn ique i s no t

e f fec t i ve because o f the non-magnet i c mate r ia ls o f r ings . the

method adop ted i s dye-pene t ra t ing tes ts . The sur faces to be

examined a re mach ined to a smooth f in i sh and a re sprayed w i th

a f ine wh i te powder , such as F rench cha lk . The dye w i l l appear

on the cha lk as c lear l y v i s ib le red l i nes aga ins t the wh i te

background i f c racks a re p resen t .

HYDRAULIC TESTS : R ings a re sub jec ted to hydrau l i c tes ts w i th

o i l under p ressure , wh ich induces s t resses up to 65% o f the

y ie ld po in t .

Hydrau l i c tes t on s ta to r cas ing : the purpose o f th i s tes ts i s to

ensure tha t the f rame is sound top the ex ten t o f w i ths tand ing

the p ressure assoc ia ted w i th exp los ion o f a m ix tu re o f a i r i n

hydrogenated a lso to check tha t a l l t he we lds a re sound and

f ree f rom leakage c racks . the tes t p ressure o f wa te r fo r a l l

hydrogen coo led s ta to rs i s 70 l bs / inch2 i r respec t i ve o f cas ing

hydrogen des ign p ressure . Every hour , fo r s i x hours , the

p ressure i s f i r s t i nc reased to max imum va lue and then reduced

to zero sudden ly , the reby g iv ing p ressure impac ts .

Stator core Flux Test : Immed ia te ly a f te r t he core i s bu i l t

up and be fo re i t i s wound, a tes t i s made to de tec t the

p resence o f loca l “ho t spo t ” . Whenever there a re shor ts

be tween ad jacen t co re lamina t ion s , due to b reak o f in te r

laminar insu la t ion o r bur rs on the edges , h igh eddy cur ren ts

f low g iv ing r i se to tempera tu re r i se in tha t zone . Severa l tu rns

o f cab le a re wound th rough the mach ine bore and ou t s ide

f rame. The w ind ing i s fed f rom a s ing le -phase var iab le vo l tage

50 cyc les supp ly . The ob jec t i s to se t up in the core , the fu l l

work ing f lux cor respond ing to ra ted vo l tage o f the mach ine .

Bad loca l hea t ing i s caused by shor ted and bur red core

lamina t ions and may be de tec ted a f te r a shor t t ime by runn ing

the hand over the sur face o f the core . A se t o f read ing on

core thermocoup les i s a lso taken as we l l as ex te rna l con tac t

the rmometers a re used to take tempera tu re a t o ther po in ts o f

yoke and core . The remedy fo r such de fec ts i s to in t roduce

fu r ther insu la t ion be tween lamina t ions and in a l l , bu t the wors t

cases ; th i s may be done w i th ou t d ismant l ing the core .

Wat tmete r connec ted to the inpu t ind ica tes the i ron loss and

by keep ing comprehens ive records fo r every s ize and type o f

mach ine , the read ings ob ta ined may be used to es t imate the

s ta to r co re loss in se rv ice . By in te l l i gen t ana lys is o f the

resu l t s a bad core w i th perhaps an excess ive i ron loss may be

de tec ted and remed ied be fo re i t i s wound.

ROTOR WINDING AND CELL TESTS BEFORE ASSEMBLY :

The ro to r co i l s and the i r i nsu la t ion a re sub jec ted to h igh

s t ress when in norma l opera t ion . Thus a th rough inspec t ion o f

these i s necessary be fo re pu t t ing them in the ro to r s lo ts as

o therw ise any rep lacement o f the fau l t y insu la t ion o r ce l l wou ld

necess i ta te remov ing the co i l b ind ing r ings and wedges , wh ich

i s cumbersome job . The ro to r w ind ing i s sub jec ted to a f ina l

sh ipp ing p ressure tes t o f 3 .5 kV fo r one minu te in case o f 30

Mv and 120MW.

TESTS ON ROTOR SLOT CELLS : The epoxy impregna ted g lass

ce l l fo rms g round insu la t ion and fo r H .E . ro to rs , a vo l tage tes t

o f 10 KV fo r one minu te i s app l ied in the in i t i a l s tage .

Subsequent to the tes t ing o f the ce l l du r ing var ious s tages o f

assemble a t reduced , the en t i re w ind ing i s f i na l l y sub jec ted to

a sh ipp ing tes t vo l tage o f 3500 vo l t s .

TESTS ON ROTOR COILS:

TESTS ON ROTOR COILS :

Tes t Be tween tu rns : The ro to r co i l sec t ions a re made up

o f a number o f tu rns wh ich a re fo rmed in ha lves and then

assembled w i th the i r i n te r tu rn insu la t ion and bonded w i th

an adhes ive in the s team hea ted p ress . A l though norma l

work ing vo l tage per tu rn may be very sma l l , a tu rn - to - tu rn

tes t o f 240vo l t s i s done to exerc ise qua l i t y con t ro l .

TOP TURN TROUGH: The insu la t ion a t top and bo t tom o f

the ro to r s lo t p rov ides adequate and sa fe c reep age

d is tance be tween copper and ro to r s tee l , i n case o f

s lo t ted copper 500 vo l t s fo r one minu te i s app l ied fo r one

minu te to tes t the top th rough .

Tes t On Comple te Roto r Wind ing : A f te r p lac ing the co i l i n

the s lo ts , be fo re jo in ing a f te r jo in t ing , f i t t i ng dampers and

wedges and f i t t i ng co i l b ind ing r ings connec ted to the

co l lec to r r ings up to run a t speed , the g raded h igh vo l tage

tes ts a re car r ied ou t a t each s tage , s ta r t ing w i th down to

sh ipp ing p ressure tes t a f te r over speed run . Sh ipp ing tes t

on ro to r i s bo th in s tands t i l l and runn ing cond i t ion .

COLLECTOR LEADS : A h igh vo l tage equ iva len t to the

sh ipp ing tes t p lus 1500 vo l t s i s app l ied to co l lec to r leads

when f i t ted in bore w i th s tuds o f sea ls f i t t ed bu t be fo re

connec t ing to w ind ings .

TESTS ON STATOR COILS : As per the s tandards , the

s ta to r w ind ing has to be sub jec ted to sh ipp ing p ressure

tes t o f (2 l i ne vo l t s +1KV) . Incase o f 30Mw and 120MW

genera to r . In o rder tha t mach ine when wound w i ths tands

th is f i na l vo l tage tes t , and any fau l t y co i l i s e l im ina ted

dur ing the var ious s tages o f co i l manufac tu re and w ind ing .

Because the con t inued app l i ca t ion o f h igh vo l tage tes ts

may over s t ress the w ind ing insu la t ion , the vo l tage i s

reduced a t va r ious s tages .

Test between paral lel straps : Th is i s a tes t o f

s t rap insu la t ion p rov ided fo r eddy E . M. F . , a low vo l tage

o f the o rder o f 350 vo l t s fo r 3seconds i s app l ied .

COILS IN MANUFACTURE AND WINDING SECTIONS :

When the co i l s a re f i r s t tes ted , a vo l tage o f 8 K V in

excess o f sh ipp ing p ressure tes t i s app l ied and th is

vo l tage tes ts a re repea ted .

TESTS ON THERMOCOUPLES : 1000 Vo l t s megger tes t i s

app l ied to the thermocoup les .

BALANCING AND OVERSPEEDING OF ROTORS:

BALANCING: one o f the mos t impor tan t p re l im inar ies to

tes t ing i s tha t o f ba lanc ing the ro to rs . Be fo re over

speed ing , the ro to r i s dynamica l l y ba lanced , in co ld as

we l l as ho t cond i t ions . A se t o f run up and run down

curves i s taken sure those c r i t i ca l speeds o f v ib ra t ion

amp l i tudes . The des ign makes sure tha t the c r i t i ca l speed

i s we l l away f rom the runn ing speed .

OVERSPEEDING: In o rder to check the soundness o f a l l

pa r ts and f i t t i ng on ro to r assembly , the ro to r i s run a t an

over speed ing tes t house a t Bhopa l i s one o f the mos t

modern in the wor ld .

Performance Tests

WORKS TESTS ON COMPLETED MECHINE:

There a re two types o f tes ts they a re :

Rou t ine tes ts

Type test.

ROUTINE TESTS ON TURBOGENERATOR

1.0.0 Scope: This test procedure covers procedures for Routine Tests on

Turbo generators.

2.0.0 Tests conducted:

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

Mechanical run and measurement of vibrations at rated speed.

Measurement of mechanical losses, short circuit characteristic and

losses.

Measurement of mechanical losses, open circuit characteristic and

losses.

Measurement of shaft voltage.

Checking of phase sequence.

Measurement of Rotor Impedance (rotor inside stator).

Measurement of insulation resistance of stator & rotor windings before

and after high voltage test (m/c at rest).

High Voltage test on stator and rotor windings (m/c at rest).

Measurement of Polarization Index of stator winding.

Measurement of d.c. Resistance of stator & rotor windings in cold

condition.

Measurement of d.c. Resistance and insulation resistance of RTDs.

TYPE TESTS ON TURBOGENERATORS1.0.0 Scope: This test procedure covers procedures for Type Tests on

Turbo generators.

2.0.0 Tests conducted1. Measurement of Capacitance of stator winding. 2. Measurement of Tan of sample coils of stator winding

impregnated along with stator. 3. Heat run tests:

a) Mechanical heat run test.b) Short circuit heat run test.c) Open circuit heat run test.

4. Voltage waveform analysis and determination of Telephone harmonic factor (THF).

5. Measurement of residual voltage of stator windings at rated speed.

6. Line to Line sustained short circuit test and determination of Negative sequence reactance (X2).

7. Line to Line and to Neutral sustained short circuit test and determination of Zero sequence reactance (Xo).

8. Retardation test for determination of GD2. 9. Three phase sudden short circuit test at 30%En and

determination of reactance’s and time constants.

1 . C i rcu i t Dry ou t Insu la t ion res is tance o f ro to r and s ta to r

2 . Res is tance o f mach ine w ind ing .

3 . Phase sequence tes t .

4 . Hydrogen Leakage tes ts .

5 . Zero Exc i ta t ion ra ted speed run

6 . Open charac te r i s t i c cu rve and losses .

7 . Shor t -c i rcu i t charac te r i s t i c cu rve and losses .

8 . Zero power fac to r cu rve po in t and wat t les tempera tu re tes t .

9 . Wavefo rm and harmon ic ana lys is o f vo l tage wave fo rm.

10 . Negat i ve sequence and zero sequence reac tance .

11 . Sudden shor t c i r cu i t and osc i l l og rams.

12 . Sh ipp ing p ressure tes t .

WORK TEST ON COMPLETED MACHINE PERFORMANCE TESTS: The mach ine i s assembled and e rec ted a t the heavy ro ta t ing p lan t tes t bay fo r tes t .

DRY OUT – INSULATION RESISTED OF ROTOR AND STATOR WINDINGS:Befo re s ta r t ing w i th runn ing tes ts , the s ta to r w ind ings a re d r ied

ou t by c i rcu la t ing cur ren t in the w ind ings f rom an ex te rna l dc

source . Inpu t o f power i s so con t ro l led as to l im i t the

tempera tu re o f the end w ind ings to a max imum o f 80cby

thermometer .

Progress o f d ry ou t i s observed by one minu te insu la t ion

res is tance read ing w i th 1000 vo l t s Mugger . Wi th the app l i ca t ion

o f hea t , the insu la t ion res is tance w i l l i n i t i a l l y d rop and then w i l l

r i se aga in over a per iod o f t ime and f ina l l y becomes

approx imate ly cons tan t a t cons tan t tempera tu re . Ra t io o f ten

minu te read ing i .e . po la r i za t ion index , when more than 2 g ives

an ind ica t ion o f good d ry ou t . Insu la t ion res is tance read ing o f

each phase , w i th o thers g rounded i s recorded . S im i la r l y

insu la t ion res is tance read ings o f ro to r w ind ing to g round a re

taken .

RESISTANCE OF MACHINE WINDINGS:

Measurement o f co ld w ind ing res is tance 's , bo th fo r s ta to r and

ro to r mus t be very accura te s ince i t fo rms the bas is o f (a )

ca lcu la t ing copper under co ld and ho t cond i t ions , and (b ) fo r

de te rmin ing the r i se in tempera tu re o f ro to r w ind ing by

res is tance method a t the end o f the tempera tu re tes t . A l l

p recau t ions a re taken to as cer ta in co r rec t tempera tu re o f the

w ind ing wh i le measur ing co ld res is tance . S ince the w ind ing

res is tance o f tu rbo genera to r i s qu i te low; a mod i f ied fo rm o f

whe ts tone b r idge i .e . Ke lv in ’s doub le b r idge i s emp loyed fo r

measurement . the doub le b r idge i s emp loyed fo r measurement .

The b r idge does away w i th the necess i t y o f accoun t ing fo r the

res is tance o f loads . Res is tance be tween phases fo r s ta to r and

be tween s l ip r ings fo r i s recorded a long w i th the co ld w ind ing

tempera tu re a t the t ime o f measurement .

For ca lcu la t ing res is tance a t any o ther tempera tu re t2 the

fo l low ing fo rmu la i s used :

FORMULA WRITE

K= cons tan t fo r copper=234.5

PHASE SEQUENCE TEST : The phase sequence tes t i s to check

the agreement o f the te rmina l mark ings tha t have been

spec i f ied . Phase sequence ind ica to r .

HYDROGEN LEAKAGE TEST : Be fo re admi t t ing hydrogen in to

the cas ing , i t mus t be made sure tha t mach ine i s gas t igh t and

exp los ion p roo f . I t s sub jec ted to a pneumat ic tes t o r 3 .16

kg /cm2. la rger leaks a re de tec ted by us ing soap wate r so lu t ion

and soon as these a re remed ied , a i r supp ly i s cu t o f f to o ld the

p ressure in the cas ing over 24 hours . F rom in i t i a l and f ina l

p ressure as we l l as tempera tu re read ing , the amount o f leakage

can be ca lcu la ted .

ZERO EXITATION RATED SPEED RUN : A t r ia l run i s made on

the tu rbo genera to r to check s ta te o f ba lance and to ensure

tha t the bear ings a re run in and tha t bear ing o i l tempera tu re i s

reaso f romthe nab ly cons tan t . A synchronous d r i v ing moto r

th rough speed inc reas ing gears d r i ves the mach ine . The

ca l ib ra t ion curve o f d r i v ing moto r w i th gear i s es tab l i shed p r io r

to s ta to r o f tes ts . The mach ine i s b rough t to ra ted speed o f

3000rpm w i th no exc i ta t ion and inpu t read ings on the d r i v ing

moto r recorded by wat tmete r method when cond i t ion s s teady .

F rom the resu l t o f above tes t a f te r deduc t ing der i ved motor and

gear losses , f r i c t ion and w indage losses o f the mach ine under

tes t a re computed . These losses a re fo r ra ted speed . Bear ing

o i l quan t i t i es w i th in le t tempera tu res o f o i l can y ie ld

ca lcu la t ions fo r bear ing loss . F rom a p rev ious da ta on sea l face

losses de te rmined f rom a p ro to type tes t , the to ta l f r i c t ion loss

in bear ing and sea ls can be es tab l i shed . The w indage loss i s

computed fo r des ign o f f i ce use by the d i f fe rence . S ince bear ing

loss goes to o i l , any hea t ca r r ied ou t on the unexc i ted mach ine

w i l l g i ve tempera tu re r i se due to w indage.

LET US DISCUS BRIEFLY ABOUT ALL THESE TESTS,

1.: EXAMINATION OF THE ROTOR FORGINGS

The ro tor , be ing the most h igh ly s t ressed par t o f the

tu rbo genera tor , must be proved thorough ly sound before i t i s

passed in to serv ice . I t i s sub jec ted to a la rge number o f

r igorous dynamic phys ica l , op t ica l and e lec t r i ca l inspec t ion

tes ts . These tes ts a re des igned to de tec t l i ke ly f l aws in the

mater ia l , as ear ly as poss ib le . In i t ia l tes ts a re done a t

fo rg ing manufac tures works .

Specimen pieces are out from the shaft and rotor body and subjected

to (a) tensile (b) bending (c) permeability tests to check its conformity with

the specification.

Sculpture prints are taken at shaft end and on rotor body for

microscopic examination to study the presence of supplied.

A surface inspection is made after rough machining at steel makers

works.

Magnet ic tes ts a re conducted to d isc lose any ha i r

c racks no t v isua l ly de tec tab le .The process cons is ts o f

magnet iz ing the fo rg ing and expos ing the sur face under

examinat ion to a s t ream o f para f f in car ry ing magnet ica l l y

p repared f ine ly d iv ided i ron powder . F ine c racks are

d isc losed by a concent ra t ion o f i ron par t i c les br idg ing the

c racks under the in f luence o f the magnet ic f ie ld .

The ro tor fo rg ing is bored a long i t s ex i ts and magnet ic

c rack de tec t ion tes t car r ied ou t . the core o f a ro to r fo rg ing is

t repanned and rough mach ined s tage these tes ts de tec t sub

sur face unsoundness , c racks or non meta l l i c inc lus ions .

The serv ices o f spec ia l i s t s ta f f in meta ls sec t ion o f Research

and deve lopment d iv is ion o f H.E .a re u t i l i zed fo r a l l the

above-ment ioned tes ts .

ROTOR COIL BINDING RING TESTS :

These are the most h igh ly s t ressed par ts o f the ro tor ,

made o f non magnet ic aus ten i t i c s tee l fo rg ing and warm

worked by a spec ia l p rocess ca l led “mandre l Expand ing” . To

avo id loca l concent ra t ion o f h igh s t resses , vent i la t ing or

loca t ing purposes.

Spec imen taken f rom ends o f fo rg ing are sub jec ted to

tens i le and bend ing tes ts .

Crack de tec t ion : Magnet ic c rack de tec t ion techn ique is no t

e f fec t ive because o f the non-magnet ic mater ia ls o f r ings . the

method adopted is dye-penet ra t ing tes ts . The sur faces to be

examined are mach ined to a smooth f in ish and are sprayed

w i th a f ine wh i te powder , such as French cha lk . The dye w i l l

appear on the cha lk as c lear ly v is ib le red l ines aga ins t the

wh i te background i f c racks are present .

HYDRAULIC TESTS: R ings are sub jec ted to hydrau l ic tes ts

w i th o i l under p ressure , wh ich induces s t resses up to 65% of

the y ie ld po in t .

Hydrau l ic tes t on s ta tor cas ing : the purpose o f th is tes ts i s

to ensure tha t the f rame is sound top the ex ten t o f

w i ths tand ing the pressure assoc ia ted w i th exp los ion o f a

mix ture o f a i r in hydrogenated a lso to check tha t a l l the we lds

are sound and f ree f rom leakage c racks . the tes t p ressure o f

water fo r a l l hydrogen coo led s ta tors i s 70 l bs / inch2

i r respect ive o f cas ing hydrogen des ign pressure . Every hour ,

fo r s ix hours , the pressure is f i rs t inc reased to max imum

va lue and then reduced to zero sudden ly , thereby g iv ing

pressure impacts .

Stator core Flux Test: Immediately a f te r the core

is bu i l t up and before i t i s wound, a tes t i s made to de tec t

the presence o f loca l “ho t spot ” . Whenever there are shor ts

be tween ad jacent core laminat ion s , due to b reak o f in te r

l aminar insu la t ion or bur rs on the edges, h igh eddy cur ren ts

f low g iv ing r i se to tempera ture r i se in tha t zone. Severa l

tu rns o f cab le are wound th rough the mach ine bore and out

s ide f rame. The w ind ing is fed f rom a s ing le -phase var iab le

vo l tage 50 cyc les supp ly . The ob jec t i s to se t up in the core ,

the fu l l work ing f lux cor respond ing to ra ted vo l tage o f the

mach ine . Bad loca l heat ing is caused by shor ted and bur red

core laminat ions and may be detec ted a f te r a shor t t ime by

runn ing the hand over the sur face o f the core . A se t o f

read ing on core thermocoup les is a lso taken as we l l as

ex terna l contac t thermometers are used to take tempera ture

a t o ther po in ts o f yoke and core . The remedy fo r such

defec ts a re to in t roduce fu r ther insu la t ion be tween

laminat ions and in a l l , bu t the wors t cases ; th is may be done

w i th ou t d ismant l ing the core . Wat tmeter connected to the

input ind ica tes the i ron loss and by keep ing comprehens ive

records fo r every s ize and type o f mach ine , the read ings

ob ta ined may be used to es t imate the s ta tor core loss in

serv ice . By in te l l igent ana lys is o f the resu l ts a bad core w i th

perhaps an excess ive i ron loss may be detec ted and

remedied be fore i t i s wound.

ROTOR WINDING AND CELL TESTS BEFORE ASSEMBLY :

The ro tor co i l s and the i r insu la t ion are sub jec ted to h igh

s t ress when in normal opera t ion . Thus a th rough inspect ion

o f these is necessary be fore pu t t ing them in the ro tor s lo ts

as o therwise any rep lacement o f the fau l ty insu la t ion or ce l l

wou ld necess i ta te remov ing the co i l b ind ing r ings and

wedges, wh ich is cumbersome job . The ro tor w ind ing is

sub jec ted to a f ina l sh ipp ing pressure tes t o f 3 .5 kV fo r one

minute in case o f 30 MW and 120MW.

TESTS ON ROTOR SLOT CELLS : The epoxy impregnated

g lass ce l l fo rms ground insu la t ion and fo r H.E. ro tors , a

vo l tage tes t o f 10 KV fo r one minute is app l ied in the in i t ia l

s tage. Subsequent to the tes t ing o f the ce l l dur ing var ious

s tages o f assemble a t reduced, the en t i re w ind ing is f ina l l y

sub jec ted to a sh ipp ing tes t vo l tage o f 3500 vo l ts .

TESTS ON ROTOR COILS:

TESTS ON ROTOR COILS :

Tes t Between tu rns : The ro tor co i l sec t ions are made up o f a

number o f tu rns wh ich are fo rmed in ha lves and then

assembled w i th the i r in te r tu rn insu la t ion and bonded w i th an

adhes ive in the s team heated press . A l though normal work ing

vo l tage per tu rn may be very smal l , a tu rn- to - tu rn tes t o f

240vo l ts i s done to exerc ise qua l i t y cont ro l .

TOP TURN TROUGH : The insu la t ion a t top and bo t tom o f the

ro to r s lo t p rov ides adequate and sa fe c reep age d is tance

be tween copper and ro to r s tee l , i n case o f s lo t ted copper 500

vo l t s fo r one minu te i s app l ied fo r one minu te to tes t the top

th rough .

Tes t On Comple te Roto r Wind ing : A f te r p lac ing the co i l i n the

s lo ts , be fo re jo in ing a f te r jo in t ing , f i t t i ng dampers and wedges

and f i t t i ng co i l b ind ing r ings connec ted to the co l lec to r r ings up

to run a t speed , the g raded h igh vo l tage tes ts a re car r ied ou t a t

each s tage , s ta r t ing w i th down to sh ipp ing p ressure tes t a f te r

over speed run . Sh ipp ing tes t on ro to r i s bo th in s tands t i l l and

runn ing cond i t ion .

COLLECTOR LEADS: A h igh vo l tage equ iva len t to the

sh ipp ing tes t p lus 1500 vo l ts i s app l ied to co l lec tor leads

when f i t ted in bore w i th s tuds o f sea ls f i t ted bu t be fore

connect ing to w ind ings .

TESTS ON STATOR COILS : As per the s tandards , the s ta tor

w ind ing has to be sub jec ted to sh ipp ing pressure tes t o f (2

l ine vo l ts +1KV) . In case o f 30Mwand 120MW genera tor . In

o rder tha t mach ine when wound w i ths tands th is f ina l vo l tage

tes t , and any fau l ty co i l i s e l im ina ted dur ing the var ious

s tages o f co i l manufac ture and w ind ing . Because the

cont inued app l ica t ion o f h igh vo l tage tes ts may over s t ress

the w ind ing insu la t ion , the vo l tage is reduced a t var ious

s tages .

Test between paral le l s t raps : Th is i s a tes t o f s t rap

insu la t ion prov ided fo r eddy E. M. F . , a low vo l tage o f the

order o f 350 vo l ts fo r 3seconds is app l ied .

COILS IN MANUFACTURE AND WINDING SECTIONS : When

the co i l s a re f i rs t tes ted , a vo l tage o f 8 K V in excess o f

sh ipp ing pressure tes t i s app l ied and th is vo l tage tes ts a re

repeated.

TESTS ON THERMOCOUPLES : 1000 Vo l ts megger tes t i s

app l ied to the thermocoup les .

BALANCING AND OVERSPEEDING OF ROTORS:

BALANCING: one o f the most impor tan t p re l im inar ies to

tes t ing is tha t o f ba lanc ing the ro tors . Before over speed ing ,

the ro tor i s dynamica l ly ba lanced, in co ld as we l l as ho t

cond i t ions . A se t o f run up and run down curves is taken sure

those c r i t i ca l speeds o f v ib ra t ion ampl i tudes . The des ign

makes sure tha t the c r i t i ca l speed is we l l away f rom the

runn ing speed.

OVERSPEEDING: In o rder to check the soundness o f a l l

par ts and f i t t ing on ro tor assembly , the ro tor i s run a t an over

speed ing tes t house a t Bhopa l i s one o f the most modern in

the wor ld .

I. OCC:

% En 80 100 110 120Calculated If(A)Evaluated If(A)

If(A) at 100% In on 3 S.C test =

Full load If(A) at rated p.f. =

S.C ratio =

Resistance at 20C (ohm)=

Stator Winding Rotor WindingCalculatedEvaluatedLosses in KW

SC St. CuLosses

RotorCu.Losses

IronLosses

Mech.Losses

CalculatedEvaluated

2. Determination of SCR %Xd and No load Vn = Ifo = Ife =S C R =

Rated output excitation at 0.8 pf Ifn =Xd = Xd =

3. Heat run test

Mech heat run

O.C Heat run at 110% En

S.C Heat run

Stator voltageStator current Rotor field voltsRt field current

4. Cooling medium : stator pressurised at 3bar HydrogenTotal windage and frictional losses

Mechanical heat run

O.C heat run at 110% En

S.C heat run

SC lossesIron losses at 110% En

Iron losses at 110% In

Rotor losses

5. Measurement of leakage reactance’s

Zn =Vn / (1.732 X In )

Z =V /(1.732 X I)

R =P/(3 X I2 )

Xa =(Z2 X R2 )(1/2)

%Xa =(Xa /Zn )X100

%Xp =0.63(%Xa)

6. Capacitance & tan measurement on stator winding

Arrangement Volt. appld

R4 N R3 S C4 Cx % tan

U

V

W

7. Capacitance & tan measurement :

Cx = C4 X R4 (R3+100) N X (R3 + S)

% tan = ( x R4x C4 x 10-4) x 100

8. Measurement of D.C.resistance of Stator & Rotor Windings :

Winding Phase Resistance (mohm) R at

20 CStator A - A0

B - B0

C - C0

9. Insulation resistance measurement & high voltage test :Phase Phase

EarthedBefore

High Volt.After

High Volt.15” 60”

Here we use a megger which produce 5000 V

10. Measurement of Ohmic resistance and I.R. values of RTD’s.RTD No. Ohmic resistance Insulation

Resistance (Mohm)

11. High Voltage test on Rotor Winding :Here we use 1000 V Megger.

Rotor Winding

Shaft Before High Volt.

AfterHigh Volt.

15” 60”

12. Impedance of Rotor Winding at Stand still and at different speeds.Speed (rpm) V I Z

300020001000

Stand stillSimilarly we perform for different frequencies of ac voltage (50-500)Hz.

13. Short circuit heat run test at 100% In :Time Rotor Volt. Rotor Curr. Rotor R

14. Open Circuit characteristic & measurement of losses:

Vuv Vvw Vwu %Vn Iv Vd Id Losses

The same experiment is carried out both in Air and Hydrogen medium.

15. Three phase short circuit characteristic and measurement of losses.

Ia Ib %In Ir Vd Id Losses

PREPARATION FOR STARTING:It is prerequisite for start up of the turbo generator that continuous

contacts be maintained between all plant sections directly or indirectly involved in the starting procedure.

Checking the Transmitters:Prior to startup, all connections should be rechecked. This applies to

piping as well as to cabling. When checking the cabling, special attention should be paid to testing the metering and signal cables. All alarm systems should be checked by changing the setting of the contacts. All temperature measuring points should also be checked. Unless temperature rises were brought about by other preparatory work at the measuring points. When doubt exists regarding the electrical temperature measurements, calibration and line compensation should be repeated.

Cooling Water Supply:

The coolers should be filled with water on their cooling watersides. To do this, the cooler vents should be opened.

RUN UP OF GENERATOR:

Start up of generator:Prior to running the generator oil system should be placed into operation.

The oil flow to the bearings should be checked to ensure an adequate flow. In addition, drains should be inspected for proper operation.

Run up:

During run up to rated speed, the bearing oil inlet temperature should be

in accordance with the turbine manual. During run up the critical speed ranges

should be passed through quickly and at a uniform rate. Smooth running

depends on several factors. Even minor temperature difference of 1 to 2 dig C

between opposite sides of the rotor may result in rotor distortion, which could

lead to inadmissible vibrations due to unbalance.

Varsity:

To protect the rectifier bridge against over voltages occurring during starting or

during fault conditions, a non-linear resistor is provided. This protective resistor

consists of 6 varistor discs parallel connected between the positive and negative

bus rings.

The varistor discs are clamped between the bush rings by means of insulated

screws. Electrical contact between the varistor discs and the bus rings is ensured

by discs of annealed copper inserted between them.

End shields:

The end of the brushless exciter are closed by endshields. Depending on the

degree of protection of the machine, these endshields have either ventilating

slots or welded-on connection pieces for ventilating ducts.

The endshields on one end is of split construction and has a split sealing ring

screwed to its inner diameter and embracing the sleeve of the rotor hub with little

clearance. The end shield on the other end of the exciter is unplugging.

Ventilation:

The b rush less exc i te r used c losed c i rcu i t coo l ing , the a i r i n le t

be ing on one end and the ou t le t on o ther end . The ro to r sp ider

i s p rov ided w i th open ings , permi t t i ng the passage o f coo l ing a i r

pas t the rec t i f i e r hea t s inks and a lso over the bus r ings

toge ther w i th the var i s to rs and the car r ie r s to rage-e f fec t c i r cu i t .

Maintenance:

The brushless exciter requires only a minimum of maintenance. The machine is

inspected for dust deposits at suitable intervals and are removed when

necessary, usually it is found in the region of heat sinks. A suitable method of

blowing with compressed air is used for this purpose.

MEASURING DEVICES AND SUPERVISORY EQUIPMENT

INTRODUCTION:

The supervisory equipment, consisting of alarm and measuring devices

gives a visual indication of the system parameters. The supervisory equipments

are regulating systems, automatic control and protective devices, which provides

for a reduction of the manual supervisory work.

TEMPERATURE DETECTORS

Resistance Temperature Detectors (RTDs):

Temperature measurements on the generator are made with RTDs. When

making measurements with RTDs the resistance element is exposed to the

temperature to be measured. The RTD works on principle of the change in

electrical resistance of a conductor due to temperature.

R = Ro(1 + a.T)

Ro= reference resistance at 0C

a = temperature coefficient

T = temperature in C

The temperature coefficient (a) is 3850/deg C, this being the mean value

for the range 0 - 100C.

Rod Type Thermostats :

Rod- type thermos ta ts a re used fo r de tec t ing tempera tu re

l im i t s . These ins t ruments u t i l i ze the d i f fe ren t coe f f i c ien ts o f

the rma l expans ion o f two d iss im i la r meta ls . When exposed to a

tempera tu re r i se a rod a r ranged ins ide a tube and f i t ted to one

end o f i t f ea tu res a l i near expans ion d i f fe ren t f rom tha t o f the

sur round ing tube . As a resu l t o f th i s a movement i s in i t i a ted in

a sw i tch ing head a t the o ther end o f the de tec to r tube , wh ich in

tu rn ac tua tes a change over con tac t . Th is changeover con tac t

opera tes on r i s ing and fa l l i ng tempera tu re when the se t va lue i s

reached . The con tac ts a re connec ted to the de tec to r tube . The

rod type thermos ta ts a re emp loyed fo r tempera tu re de tec t ion in

p ressur i zed sur round ings .

VIBRATION PICKUP

Bearing Housing Vibration Measurement:

The vibration pickup for measurement of the absolute bearing vibration

converts mechanical vibrations into an electrical signal in a seismic type

transducer operating on the permanent magnet plunger coil principle. The

permanent magnet and magnetic flux return path elements are solidly connected

to the sensor casing. The plunger coil is suspended in the sensor casing by

means of a spring.

The maximum velocity of the absolute vibration is measured by means of

the transducer, which is attached to the bearing housing. Vibration in the bearing

housing produce a relative movement between the permanent magnet and the

plunger coil, which induces a voltage in the coil portion to the vibration velocity.

The output signal of the transducers is integrated amplified and then

displayed and recorded as peak-to-peak maximum velocity vibration values.