4391_235_A.pdf

TP: 4391

(HM&E MANUAL)

TECHNICAL MANUAL

PROPULSION

A.C. GENERATOR

WESTINGHOUSE

400’ WAGB CLASS CUTTERS

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PUBLISHED UNDER AUTHORITY OF THE U.S. COAST GUARD

SWBS 235

SECTION A

Department of Homeland Security

UNITED STATES

COAST GUARD

Individual Manual Application Sheet

Technical Publications Number

Secton Applicability

SWBS Number 235 SWBS Element Title ELECTRIC PROPULSION

Section Identifier A

Equipment Functional Description PROPULSION A.C. GENERATOR

CI Functional Description ESWBS Code Remarks

Planset Hulls

400-WAGB 10, 11

PROPULSION A.C. GENERATOR

Diesel Engine Driven

2530 KW, 2610 KVA, 700 Volts, 1100 RPM

Westinghouse Identification

General Order ............................................... HR-32500-P Apparatus Shop Order ..................... I.................. 82PO430 Instruction Book Shop Order .................. .82PO737

Westinghouse Electric Corporation

East Pittsburgh, Pennsylvania

TABLE OF CONTENTS

Propulsion AC Generator Only

Page No.

SECTION 1 - DESCRIPTION OF GENERATOR ................................... 1-1

GENERAL INFORMATION ................................................ 1-1

Purpose .................. .................... I........................ 1-1 M achine Identification and Data ........................................ 1-1

DESCRIPTION OF APPARATUS ...................................... ...... 1-2

Illustrations ................................................... .......... 1-2 General Arrangement ........ 4 Frame, End Bells, Ventilation ............................................ 1.3 Bearing ....... ............................. 1-3...................... 1-3.Shaft Currents an Bearing Insulation Bearing Insulation ............................. d . . . . . . . . . . . . . . . . . . . . . . .1-3

Detecting Bearing Currents .......................................... 1-4.

Core . .................................. ...................... ........ 1-4 .Termina'ls ............... 1-4.................................... ......................... . 1-5Armature (Stator) W inding Shaft and Spider ... .......................... m. . ............ ...1-5 Field (Rotor) Poles ....... 1-5............................... .............ield (Rotor). W inding ............. ...... ............. !..... .... 1-5 Collector .................................................................. 1-6 Brush Rigging and Brushes ...................... ............. 1-6 M echanical Rotation ..... .......................................... 1-6 Phase Rotation ........................................................ 1-6 Space Heaters ........................ ! ................. I ............... 1-6 Ordering Renewal Parts .................................................. 1-6 Communications ................................ .............. ...... 1-6

SECTION 2 - I'NSTALLATION OF GENERATOR ................ ........... 2-1

GENERAL.INSTALLATION ........................ ..................... 2-1

Storage ........................... ................................. 2-1 Handling and Unpackin ............................................. 2-1

INSTALLATION AND ERECTION ....................... ......... ......... 2-2

General .............................................. ............ 2-2 Examination of Bearing and, journal .............. I.......... .............. 2-2 Cleaning of Collector Rings ............................................. 2-2 Alignment of Equipment ................................................ 2-2 Temperature and Ventilation ................... 2-3..........................Power Connections (Stator Leads) ................... 4........ ...... 2-3 Control W iring ........................................................ 2-3 Lubrication ..... I ...................................................... 2-4

SECTION 3 - OPERATION OF GENERATOR ................................. 3-1

PRELIM INARY STARTING .................................................. 3.1

Brush Adjustment ...................................................... 3-1 Initial Check on Insulation Resistance ...... I......... . ... .... ..... 3-1 Drying-Out W indings .. ........................... ................ 3-2 Final Check Before First Start ........................................... 3-3

Page No.

STARTING GENERATOR

Check During First Start

3-5 3-5, OPERATION OF GENERATORS

Single Generator Extended Shutdown

SECTION 4 - MAINTENANCE OF GENERATOR

GENERAL MAINTENANCE

Temperature Tossible Sources of Collector and Brush Trouble Improper Brushholder Spring Tension Brushes Requiring Replacement Unequal Current Distribution Among Brushes Dirty or Oily. Collector Rings or Brush Rigging 'Improper Brus-hes Improper Alignment of Brushholders Unbalance in the 'Rotor or Eccentricity of the

Collector Rings Rough or Marked Rings .............. I Corroded Rings ................................ (I Uneven Hardness of Ring Electrolytic Action Unusual Operating Conditions .............. I Excessive Current Densities Due to Overloads Extended Operation with a Low Value of Brush Current

3-5 .3-5 3-5

4-1 4-1 4-1 4-1 4-1 4-2 4-2 4-2 4-2 4-3

4-3 4-3 4-3 4-4 4-4 4-4 4-4 4-4

CORRECTIVE MAINTENANCE

Insulation Resistance G eneral ,,Significance of Tests Conditions for Test Method of Test Voltmeter Method ....... .. ...................... ....Preferred Method of Measuring Insulation Resistance interpretation of Results

..................Polarization Index Recommended Minimum Value of Polarization Index Alternate Methocls�of Measuring Insulation Resistance Recommended Minimum Value of Resistance ..... I Suitability for Overpotential Tests Annual Inspection Cleaning the Generator Rebabbitting Bearing Safety Precautions Preventive Maintenance Check ................. I

AIR COOLER .... ........................................G eneral Installatio n

4-4 I.

4-4 4-4 4-5 -4-5 4-6 4-6 4-7 4-7 4-7 4-8 4-8 4-10 4-10 4-10 4-11 4-12 4-12 4-14

4-16 4-16 4-16 ii

Page No.

Operation

........... .......................... ..... 4L-17 M aintenance ........... I....... ....... ............. ...... ............ 4-17 Symptoms for Failure ..................................... ........ p ...... 4-18 C leaning . .......................... :................................. 4-19 �Repair Procedures ....... ............... ...... ...... .............. 4-19

JROUBLE SHOOTING ..................................... ........... 4-20

LUBRICATION SYSTEM .......................... ..................... 4-20

Leakage ............ ........ ..... ;...... ................ I ........ 4-20 Bearing Temperature, ...................................................... 4-21 Oil F16W to Bearings .................................................... 4-22 Bearing Insulation ....................................................... 4-22 Bearing Wear .................... . . . . . . .. . . . . . . . . . . . . . 4-22

VIBRATION�AND NOISE ................ ........ .................... 4-22

COLLECTORS ....................................................... 4-23

BRUSH ES ........................................ ...................... 4-23

BRUSH HOLDERS ......................................................... 4- 4

ROTOR WINDINGS AND FAN BLADES ..................................... 4-24

BEARING AND HOUSING SEALS ........................... ................ 4-25

GENERAL MOUNTING AND ALIGNMENT ................. ............... 4-25

POLE AND FIELD WINDING REMOvAL . ...................... .............. 4-25

TROUBLE SHOOTING CHART ............................................. 4-27

SECTION 5 - RENEWAL PARTS DATA ....................................... Tab 5

SECTION 6 - SUPPLIER LEAFLETS .................... .......... ............ Tab 6

SECTION 7 - DRAWINGS .............. ..................................... . Ta 7 iii

I ILLUSTRATION INDEX

Propulsion A.C. Generator Only

The following is a list of illustrations used in the text and is not necessarily the order of their appearance.

Figure No.

I1 v

Page No.

3-3

3-4

4-6

Section 7

Section 7

Connections for Drying-Out Windings with D.C. Welder

Typical Behavior Curve of Insulation Resistance During Dry-Out Run ........ I

Diagram of Connections: for Measuring Insulation Resistance

Generator Outline

General Assembly

Polarization Index

4-8

Insulation Resistance Temperature Coefficient ..................... 4-9

2530 KW, 700 VOLT PROPULSION A.C. GENERATOR

SECTION I

DESCRIPTION OF GENERATOR

,GENERAL INFORMATION

Purpose

These instructions are intended to describe the construction and to guide in the installation operation and maintenance of the propulsion generators.

Machine Identification and Data

Rating

Thosegeneratorsarerated253OKW(2610KVA),97%powerfac'tor; 700volts 1074 amperes,6Phase,73.3Cycles,1100RPM; Excitation250volts,46.4amperesD.C., Temperature Rise per Table 1. The generators will be rated for 130% of rated current continuously at a. reduced voltage. This rating is 2630 KW (2740 KVA), 96% powerfactor 565volts,1400amperes 6Phase,73'3Cycles,1100RPM; Excitation 250 volts, 51.4 amperes D.C. At this overcurrent condition thecoolers will be supplied with 45'F cooling water and generators will receive 40'C cooling air.

Temperature rise will be 105'C rise on field windings by resistance.

TABLE 1

Temperature Rise Degrees Centigra e item Thermometer RTD Resistance

Armature Windings - - - 70 - - -

Insulated Field Windings 70

Collector Rings 75

Bea-rings 35

Cores and Mechanical Parts in Contact with Insulation 60

1-1

Namep�.ate Data

2530/2630 KW 6 Phase 700/565 Volts 73.3 Cycles 1074/1400 Amperes 1100 RPM 97/96% Power Factor 250 Exciting Volts 45.8/52.0 Exciting Amperes

Stator Serial - 1S to 6S - 82P430 Rotor Serial - 1R to 6R - 82P430 it is recommended that the nameplate readings of the new equipment be reviewed and office copies of these readings bemadeavailable.Thisinformation will be found useful in subsequent correspondence on the equipment.

Always refer to the serial number stamped on the nameplate of the machine when corresponding with the manufacturer for this is the number which identifies the machine.

Geneira�oir C�asdficaflon

a) Reference Ambient Temperature .... 500C - 400C at 130% Current

b) Table and Method of Measuring

Temperature Rise: ................ Table I

c) Class of Insulation .................. Class F

d) Degree of Enclosure ................ Totallyenclosedandwatertighttobottom of shaft

e) Method of Cooling .. ................ Totallyenclosedrecirculatingsystem withcoolerstosupply500Ccooling air to generators with seawater temperature into coolers not exceeding 850 F. At the over current condition (1 30%) the coolers will be supplied with 45'F seawater and generators will receive 40'C cooling air.

f) Manufacturer's Type ................ 8-51-22

g) Means of Excitation ................. 250 volt static regulator

h) Prime Move (Diesel Engine) ......... Others

DESCROPYRON OF APPARATUS

fflusaraflons

Reference to the Outline Drawing, Fig. 4, will be found useful in supplementing the following description.

GenetrA Anrangemena

The AC generator is coupled to the prime mover bya flexible coupling. The shaft is supported by bracket - type bearings. The stator frame of the AC generator is mounted on the prime mover sub - base.

1-2

Frame., End Bell, Mentilation (Fig. U 5)

The frame is formed of welded, hot - rolled steel members. Lifting holes are provided at the ends of the frame and heavy-, steel feet are welded to the lowertioli of the frame These fe are machi d parallel to the shaftandar drilled:por et ne tor foundation bolts and jackscrews.

The stator.- core laminations are stamped from special silicon steel. They are

�stacked on transverse bolts and are clamped by steel end rings bolted together.

Ventilating spaces are provided by finger - plate spacers permitting air to circulate.

through the core. Terminals of the armature are brought outat the top of the frame t6 a terminal box mounted on the top of the generator frame.

End bells are bolted to the frame at both of the machine 'to direct the :ventilating air and protect the armature winding.

Bearing (Fig. 4 & 5)

The shaft is supported by bracket type split sleeve bearings. Lubrication is pr.ovidedb theforced�feedsystemoithe rimemover.Afixed-drificeatthe y p bearing inlet which is fed by the, prime mover limits the oil flow through each bearingtol.5gallon.perminuteatapressureoffromeightto ten pounds gau ge.

addition to oil throwers machined on the shaft, front and rear labyrinth oil seals 'dedtopreventoilleakagefromthebearing.Thesesealspr videasealat the front and atthe rear'of the bearing.The small clearance between the shaft and the seal prevents leakage of oil along the shaft and Out of the'bearing.

Shaft Currents and Bearing Insulation

Variations in reluctance in the magnetic circuit of an alternatingcurrentmachine -may cause cyclic changes in the amount of flux which links the shaft. This change imflux may generate sufficient voltage to circulate current through the circuit consisting of shaft, bearings,- and bedplate. If this current is permitted to flow,, it soon has a destructive effect on the shaft journals and bearings.

Normally the shaft first takes on a satin finish appearanceand latersmall pits form on the surface of the shaft. The bearing babbitt in most instances will show evidence of having been eaten away by the current in small pits. Babbitt eaten away by current is characterized by deep irregular holes, which in serious cases penetrates to the bearing shell.

Bearing Insulation

As it is not practical to provide control of the generation of shaft voltages and currents it becomes necessary to insulate the front bea The bearing

Y $

ERMSUREM

1-3

O insulationinterrupts the path for circulating currents. Thisinsulation consists of a suitable thickness of synthetic resin impregnated laminate placed between the bearing and bearing bracket. The thermocouples are also insulated from the bearing.

A break in the insulation may occur during erection duetocarelesshandlingand it is well to testfor this with a bell and batteryorwithatest lamp.Tomakethistest a section in the shaft-bearing-lbedplate circuit must be free from ground, the customary procedure being to raise theshaft free from the insulated bearing.

Detecting Beadng Cuirrents

If a machine has bearing currents it is' usually possible to detect them when machine is running at rated speed and voltage by placing one end of a copper wire on the bearing bracket and touching the other end to the shaft from which sparks can be drawn.

If sparks occur when this procedure is performed at both ends of the machine, bearing currents are present, and insulation should be provided or if insulation is already provided it should be replaced with new insulation unless periodic' inspection of bearings show that insulation is unnecessary. If, however, sparking occurs at the insulated end only or at neither end, bearing currents are probably Awl& not present.

Coire

The core of the machine is built up of circular segmental laminations of silicon steel stacked on transverse studs. Ventilating spaces are formed between the frame rings and the ends of the core by finger - late spacers, and between the packages of punchings byvent- platespacersatfour positionsalongthe length of the core. This arrangement furnishes a means for dissipating heat from the core by permitting cooling air to enter the inner portion of the core. The laminations are insulated from one another --with a surface. coating of aluminum orthophosphate (alkaphoss). Finger plates at each end of the core prevent loosening of the teeth. The stator punchings have 96 slotseach havinga punched size of .651 inch Wide by 2.60 inches deep.

Teeminals

The. AC generator leads are brought out at the top of the frame. The rotor leads are cleated to the shaft and connected to the collector rings. The field leads are brought out through brushes on the collector rings into a conduit box.

1-4

Armature (Stator) Winding

Coil Grou ping.- 1 Group of 2 coils repeated 48 times 1 Group per, Pole per jphase _.�6 Groups per Pole - 96 Coils

Throw of Coi Is: Slot's 1 to 13 - 8 Poles - 6 Phase - 4 Parallels -, Star - The-six phase winding consists of two independent three phase winding star connected and each,windinghavin four parallels The two three phase windings are electrically displaced by 30 degrees.

Thestationary armature has a bore of 39 inchesand has96slotseachof which has.

iunc hed size of 0.651 inches wide by 2.60 inches deep. The armature coil is of the d amond - type and consists of 3 conductors, each of which is two strands wide by four strands deep of double glass covered copper wire. The strands are

1.072 inch th'ick and'.258 inch wide.

Glass melamine wedges are used to hold the coils in place in the slots.-The coils are roped to an insulated steel ring on each end of the winding to prevent distortion in case of short - circuit.

Shaft and Spider

TheshaftfortheACgeneratorismachinedfromasteelforgingandis rovided with a precision machined extension to accept a flexible coupling.- The spider which carries the field poles is built'up of steel laminations Hv�ted together., the assembly being pressed on and keyed to the shaft The spider.laminations a re punched with dovetail slots for mounting the field poles.

Field (Rotor) Poles

The eight poles are constructed of laminated steel punchings which are securery bound together by through rivets. Each field pole is fastened to the spider by double dovetails, which are each held in place by tv 0 tapered keys. The dovetails, are prevented from b6ckling;�by two inch welds on each side of the ends of the dovetails.

Nine 1/2 inch diameter copper damper bars are installed in each pole head. The damper bars are brazed at each end to a copper damper -segment. Damper, segments.are connected together. by a-steel ring which bolts to each segment.

Eightsheet'steelblower'sareboltedtotherotorspiderateachend.Theseblowers are suitable for either direction of rotation.

Field (Rotor) Winding

Each field.coil consists of 236turnsof.129x.229doubleglasscoveredcopperwire wound 664he pole. The w inding is insulated:from:the pole by an'insulating cell and top and bottom glass melamine washers.

1-5

The collector-assembly is shrunk on the shaft near the front journal. It consists of two bronze collector rings shrunk onto a length of steel bushing around which a sleeve of mica has been built up with the entire bushing used as a mandrel.

Insulated copper leads connect the rings to their respective field leads. The steel collector bushing is held on the shaft by a shrink fit.

Rush Rig ing and Swushes

The two brushholders are supported on an insulated steel stud mounted on the bearing bracket cap. Each brushholder contains two brushes, 3/8 inch thick by I inch wide by 1 3/8 inches long. Each generator requires four brushes. For replacement brushes, order by Westinghouse Style No. 12OA502GO2.

Mechanicag Rotation

The blowers on the generator are suitable for rotation in either direction.

Phase Roftadon

When the mechanical rotation of the generator is clockwise as viewed from the collector end, the emf's inducted in the phases will reach positive maximum values in the following order:

T1 -T2-T3-T5-T6-T7

Space Healevs

Six 500 Watt, 240 volt space heaters are located in the bottom of the machine frame. These heater's are connected two in seriesanddeltaconnected for440v,3 phase operation. Total power is 2520 watts.

Opdaing Renewag Pav2s

When ordering renewal parts, give the name of the part, the drawing and item numbers which apply, and the nameplate reading of the machine, including the serial number. The stator serial number will be found stamped on the nameplate, under the nameplate and on the machine foot. The rotor serial is stamped on the end of the shaft.

Communications

Should communication be des irable or necessary regarding the installation

1-6 covered by this instruction book, or an individual device included in the installation, replies will be greatly facilitated by citing the General Order (G.O.)

number for the complete equipment and the nameplate readings of the detail apparatus involved.

Do not fail to give the stator and/or rotor serial number and the complete nameplate reading when information is desired for a rotating machine. The stator ser .ial number is stamped on the machine name lateand in the metal under the nameplate and on the machine foot. The rotor serial number is stamped on the end of the shaft.

Should any particular information be desired, be very careful to state clearly and fully the question for consideration, and the associated conditions.

Communications should be addressed to the nearest Westinghouse ElectricCorporation Sales Office. Local sales representatives areengineering or service usually available for quick consultation.

1-7

SECTION 2

INSTALLATION OF GENERATOR

GENERAL INSTALLATION

Storage

The generator is shipped with the windings well protected from moisture. At-the destination, the rotor and stator should be placed in locations protected from the weather And from mechanical injury. Rain,� snow, water or steam from leaking pipes, or condensation from the atmosphere should be excluded. It is particularly important to keep the windings dry for moisture lowers the insulation resistance andincreasesthelikelihoodofabreakdown.Ifthemachineis roughtfromcold surroundings into a warm room, it should be kept covered until its temperature has risen to room temperature in order to prevent the condensation of moisture on the windings and other parts.

When storage over a period of time is anticipated, the machine should be completely enclosed by a tarpaulin or a covering of wood, metal or roof ing paper unless the machine is in a protected location. Also, the space heaters should be energized.

'Handling and Unpacking

It is easily possible, by rough handling orcareless useof bars or hookstodo more damage to a machine before or during erection than would be done in years of regularservice.

Care should be taken in transporting and handling the machines to see that thedings are not damaged. A blow Ipart of the i din s i likely towin upon any win injuretheinsulationandresultintheburnin outofacoil.Thegeneratorframe should be lifted by placing hooks underneath the lifting bar at top of frame.

in lifting the rotor, it is preferable to use rope slings looped around the shaft. If chains are used, the should not be, looped around the journals: unless the latter are properly protected. In no case should the ropes or chains be allowed to exert �pressure on the windings or collector rings.

2-1

ONSTALLATOON AND EREC70ON

General

The principal external dimensions of the generator set and the provisions for mounting it on the base of the prime mover are shown on the outline drawing, which appears as Fig. 4 of these instructions.

Examination of Bearing and journal

Before the machine is placed in service, the surfaces of the bearings and journals should be examined for injuries accidentally sustained during or after shipment.

Scratches on the surface of the babbitt should be smoothed out, and scratches or rust on the journal should be polished off before the machine is ass6mbled.

Cleaning of Coflectoir Rings

Remove the protective compound covering the rings. A cloth dipped in benzine or carbon tetracholoride will be useful in removing this co mpound.

Alignment of Equipment

OncetheAC generator stator has been approximatelyiocatedonthedieselsub-base with the coupling loosely fitted, the final alignment should be undertaken.

Measurements taken at the face of the couplin hub are th e guides for the alignment of the electrical equipment with the prime mover. The feet of theAC generator frame are provided with holes for jackscrews which permit either side of the frame to be raised so that sheet metal liners may be inserted between the feet and the sub - base to correct this alignment.

The position of the generator should be adjusted so thatthe following conditions are met after the frame feet bolts and coupling bolts are pulled tight:

1. The proper axial clearances exist atthe journals between thejournal oil throwers and the bearing. The clearances at the ends of the bearings should be such that they will be approximately equal after the coupling bolts are tightened.

2. The air gaps are equal around the bore within 1/64 inch. It is particularly important that the air gap between the armature core and the pole faces be uniform, for any inequality in the gap will cause unnecessary friction and heating in the bearings as well as unequal heating of the iron in the armature.

During. these adjustments, the air gap should be gaged from both ends of the machine at different points around the rotor. Gages for the purpose should extend to the center of the core.

2-2

The feeler gage should beinserted along the core between the pole face a.nd the-stator core. This procedure reduces the likelihood of reading too small a value for the air gap at a point near the end of the machine where a high punching is most likely to exist.

'If accurate readings of the air gap are requiredthe varnish should be removed from both the rotor.and stator punchings atthe air - gap surface.

3. The coupling hub outage is less than .001 inch as measured at the hub with a dial indicator. Opening between the faces of the adjacent coupling hubs to be equal all around to open .001 inch at the bottom.

4. The rotor should be axially positioned on its magnetic center. Refer to the outline drawing for the location of the magnetic center indicator.

5. The generator end play is.25 inch total. if the drive coupling is of the free float type, its end - play must be limited to .093 inch'.

Temperature and Ventilation

This is a totally enclosed generator in which the ventilating air is recirculated through an air coolerwhichwill provide5OoCairtothegenerator.Thewaterflow to the cooler is controlled by:a thermally regulated flow valve.

Power Connect ions (Stator Leads)

The main generator terminals are brought into a.terminal box located on the top of the generator frame.

Control Wiring

The rotor leads from the AC. generator field are cleated to the shaft and terminated in a conduit box.

Thespace heaterleadsarebroughtouttoaconduitboxiocatedontherighthand side (when facing the collector end) of the AC generator.

2-3

The bearing is connected to the forced - feed lubrication system of the prime mover. An orifice at the bearing inlet f 'ed by the prime mover reduces the oil pressureatthe bearingtoavaluewhich permitsan oil flowthroughthe bearingof

1.5 gallon per minute at a pressure of from 8 to 10 pounds gauge.

The lubricant recommended is turbine oil having aviscosityof 180to250seconds

Saybolt at 100'F.

2-4

SECTION 3

OPERATION OF GENERATOR

PRELIMINARY STARING

Brush Adjustment

Brushes and brushholders should be examined before the machine is started up to make sure that the brushes are in the proper position, that there is a proper fit between the collector and the brushes, and that the brushes are free in the holder. If the faces of the brushes do not conform to the curvature of the collector, it is necessary to grind them to shape. This operation is always required when: new brushes are installed.

When fitting new brushes or damaged brushes, the operator should use sandpaper, "Grade 1 - 1/2" for the roughing cut, and "Grade 0" for the final fitting. The sandpaper should be drawn in the direction of rotation under the brushes. Roundingof thobrushedgescan beavoided byreleasingpressureasthepaperisdrawnbackandbybein carefu[tokee theendsofthepaperascloseto

9 p thecollectoraspossible.Eachbrushshouldbetrleatedinturn,anditwillbefound that by this means a satisfactory contact is quickly secured.

An initial brush pressure of 1 lb. is recommended:.Oncethemachine is inservice, the pressure may be altered as necessary.

Initial Check on Insulation Resistance

The insulation resistance of an electrical machine gives an indication of whether the machine is in a suitable condition for operation. or potential tests. if the insulation resistance of awinding is below the minimum acceptable-value for new machine, the winding should be dried out.

Once the windings are in a satisfactory condition for operation, it is recommend- .ed that initial readings be taken for both the armature and field windings sdas to provide a basis for later comparison.

Further information on insulation resistance is given under the Section on "Maintenance of Generator", Section 4.

3-1

Dwying - Out Windings

If the insulation resistance indicates that the windings have absorbed moisture during shipment, the generator should be dried out before any high - potential test is made or before the generator is initially run. Oncethewindings have been dried out, the space heaters should be placed in operation whenever the machine is not running. The windings may be dried either by the use of external heat.or by the circulation of current through the windings themselves.

When external heat is to be applied, it is advisable to use resistance heaters or steam coils as sources of heat. The space heaters located inside the generatorare notofsufficientcapacityforuseindryingoutthemachine; soadditionalheaters are required. The space heaters may be used as supplementary sources of heat.

The machine should be covered, and the heaters should be placed near the bottom of the enclosure. Care should be taken to protect the machine against direct radiation from the heaters. Effectivedryingcannot beaccomplished unless means are provided to circulate the air so as to remove the moisture. The circulation of heated air can be improved by the following:

1. Forcing air into the bottom of the enclosure with small fans.

2. Having the enclosure suficiently close - fitting to cause most of the heated air to pass through the ventilating spaces in the machines.

3. Providing an opening at the top of the enclosure for the escape of moisture - laden air.

When the heating is to be accomplished by the circulation of current, a DC welding set may be used to provide the current. The current in any part of the winding should not exceed the rated value. Refer to Fig. 1.

Another method of circulating current through the stator windings of the generator without subjecting them to full voltage is to drive the machine at a convenient speed with the stator windings short - circuited and with the proper value of excitation applied to the field to give somewhat less than rated armature current.

Regardless of the method of heating used, it is essential that the heat be brought up gradually at first, the aim being to allow the water vapor to find its way out naturally through the insulation.Too rapid heating is likelytodevelopsuch steam pressure in local portions that escape passages are forced through the insulation, injuring it permanently. It is generally desirable to consume 15 to 20 hours in bringing the temperature up to the value required.

The total temperature of any part of the machine should not exceed 75'C during the early part of the drying - out period. Later, after the insulation resistance has passed its minimum value and has become nearly stablethe temperature may be raised to 125'C or slightly higher. If the windings are heated by passing current

3-2

PHASE - A

PHASE - B

D - C

WELDER

FIG.1 CONNECTIONFORDRYINGOUTWINDINGWITHD-CWELDER�

through them., temperature of the. stator coils should be determined by thermometer Is, and the temperature of the field windings may be determined by comparisonofthew:indingresistancewithitsresistanceataknowntemperature.

.Refertotheparagraphon"Temperature"Page4-iforthemethodofmeasuring temperature by change of resistance.

'Duringthedrying-outprocessmeasurerhentsofinsulationresistanceshouldbe taken at regular intervals and it is recommended that the results be plotted in the form of a curve of "Insulatio n Resistance vs. Time". A typical curve of this kind is shown as Fig. 2. The initial. drop in insulation resistance can be attributed to the effect of rising temperature, and the subsequent rise in resistance is caused bythe removal of moisture. The drying - out process should be continued until the insulation resistance becomes approximately constant at a high value.

Final Check Before First Start

Before the unit is started, the following checks should be made:

1. Be sure that all necessary work of installation and erection has been completed.

2. Carefully examine the interior of the generator.for loose objects such as bolts, nuts, and tools. Such -items should be removed from the machine, and care should betaken to preventtheir being drawn into it by magnetic attraction.

3. Check to be sure that the brushes are free in their holders and that thebrushpressureisabout2-1/2psi(roughI 11b.perbrushforthis

3-3 machine). Once the machine is in service, the pressure may be altered as necessary.

4. Check the wiring and piping to be sure that all connections have been made properly.

5. Check to see that the proper electrical clearances exist between conductors. bo not allow brush shunts to touch each other.

6. Be sure that all moving parts have sufficient clearance with respect to adjacent stationary parts.

7. Check to see that the windings are free from dirt and moisture.

8. Measure the insulation resistance of the windings, and dry,- outthe windings if the test shows this to be necessary.

9. Be sure that all coverplates have been installed over theopenings in the frame and end bells.

FIG. 2

100- TYPICAL BEHAVIOR OF INSULATION

RESISTANCE DURING DRY-OUT RUN

90-

Ul) r 80-

LW

70-

LU

U z 60 -

JUY) 50 -

z 0 40-

30-

20 -

0 10 20 30 40 50 60 70 80 90 100 110 120

DRYING TIME - HOURS

3-4

STARTING GENERATOR

Check During First Start

When the unit is first started, the following o bservations should be made:

1. Watch temperatures whenever possible to be sure that none is excessive.

2. Check the brush rigging tobesurethatthebrushesride properlyon the collector rings.

OPERATION OF GENERATORS

Single Generator when a synchronous generator operates alone and is not paralleled with other generators, the field current must be adjusted for each change in load in orderto maintain rated voltage. This adjustment can be made through manual control of the regulator, but it is preferable for this to done with the regulator set for auto--� matic operation to keep the voltage constant even though the load varies rapidly.

No change in the power factor of the generator can be affected by changing the field current of the generator, as the. power factor for a single generator is determined entirely by the characteristics of the load.

Extended Shutdown

During an extended shutdown, the following protective measures should be taken unless the generator unit can be started periodically and run for a few minutes:

1. Apply slushing compound to the shaft journals to revent rusting.

2. Remove the brushes from the rings and wipe the rings with paraff i n as the machine is coming to a stop with the rings still warm. Be sure that the generator has first been disconnected from the line and that the excitation has been removed before the brushes are raised.

3. Turn on the space heaters.

3-5

SECTION 4

MAINTENANCE OF GENERATOR

GENERAL MAINTENANCE

Temperature

The app; earance of excessive temperature in: any part of the� Machine is an ,indication of trouble. Thesituation should be investigatedimmediately and the cause of the trouble removed:. Routine checks on temperature are recommend- :�ed so that such: conditions may be discovered before serious damage is done.

The, bearing thermostat warns of excessive bearing temperature., If the alarm sounds, tfie oil supply should be checked. Shut down the unit if thetemperature cannoube reduced immediately.

�Theternperatureof the'fieldwindings ismeasured bythechangeinresistanceof the field winding itself.

When the change of resistance of a copper winding is used to measure the average tota[temperature of the winding, the following equation canbe used:

R (234.5 +.tj)2 t R, in which the resistance values (R) are both in: the same units andthe total temperatures (t) are in degrees centigrade. Subscript."i" refers to the known condition. Subscript"2"referstothecbnditionatwhichtheresistanceisknown butthelemperatureisto becalculated.Thisequation issatisfactoryfortherange of temperatures. normally obtained in electrical machines.

Possible Sources of Collector and Brush Trouble.

One of the principal indications Of im"proper brush and collector performance is arkin . The following list presents �possible causes of brush and collector trouble. USE THIS INFORMATION TO PREVENT TROUBLE As WELL AS TO

REMEDY IT.

4-1

Umproper Brushhollder Spring Tension

The spring tension should be sufficient to maintain contact between the brush and the collector ring in spite of small vibrations of the brush rigging and collector rings. However, the pressure should not be such as to cause undue mechanical wear. it has been found that a brush pressure of 2-1/2 psi of brush area gives the best brush performance. This is equivalent to approximately 1 lb.

for this machine.

Brushes Requiring Rep[lacement

Asthebrushesbecomeshorterfromw'ear,thespringsshouldbetightenedsoas to maintain the proper brush pressure. Brushes should be replaced before they reach the limit of their travel.

UnequA Current Distribution Among Brushes

Sparking may result from an unequal distribution of current among the brushes on any one ring. The spring tension should be relieved temporarily on the brush carrying the excessive current. Readjustment of the spring tension may be necessary for all the brushes on the ring to cause each brush to carry its proper share of the current.

Dirty or Oilly Collector Rings or Brush Rigging

Imperfect contact results when dirt, oil, or particles broken from the brush are present between the brush and the ring. Furthermore, dust between the brush and the holder may conduct sufficient current to fuse the. brush to the holder.

The collector rings, brushes, and brushholders should be kept clean and free from dirt, carbon dust, and oil. A piece of canvas dipped in a grease solvent is recommended for cleaning these parts.

Omproper Brushes

Brushes of the proper grade are furnished with the machine. Other types may give unsatisfactory performance. See "Brush Rigging and Brushes", Page I - 5.

Brushes of the propersizemustbe used. If thebrushesaretoo.smalltheymay be-comewedged at an angle in the holders. If they aretoo largetheywill stick inthe holders, but this can be remedied by rubbing the sides of the brush with fine sandpaper.

4-2

Improper Alignment of Brushholders

The alignment of the brushes on the ring should be checked occasionally to be sure th6t a brush does notoverhangtheedgeof the ring. If the brush isallowedto overhangthe overhanging partdevelopsathin edgewhich chipsand breaksoff.

Unbalance in the Rotor or Eccentricity of the Collector Rings

Either of theseconditionscancausethe brushesto leavethe ringsand drawan arc once every revolution. This repeated arcing at the same place on the ring in time burns the imprint of the brush on the ring-

The trueness of the rings can be checked with a dial indicator on the back of a brushwhiletheunitisrunningatiowspeed.iftherin sareeccentricontheshaft, they should be turned, or ground, and pol.ished. These operations must be done when the rotor �is turning, for if they are done at standstill or by hand the eccentricity of the rings may actually be increased.

Rough or Marked Rings

Any blackspotsthatappear on the surfaceof thecollectorshould beremovedby polishinglightlywithfinesandpaper.itisveryimportantthatthisbe,done- for while thesespots are not serious in themselves, they will lead to pitting of the rings and the necessity for regrinding. However, no harm is done to the rings if the condition is corrected at once. if the rings are very rough., they should be ground and polished with the rotor turning. This should not be done atstandstill or by hand for under these circumstances, the rings may be made eccentric and uneven.

Corroded Rings

Brush imprints may be burned on the surface of the rings as a result of causes other than unbalance and eccentricity. This burning also occurs when the rings have been left unprotected cluringan extendedshutdown.This usuallyoccurson a machine which is subjected to corrosive fumes. When the machine is shut down, the fumes act upon the surface of the rings exceptwheretheyarecovered by the brushes,. The difference in surface caused by this action produces a slight burning as the rings rotate after the machine has been returned to service. Brush,im rintsduetocorrosivefumescanappearatanypointontherin sdepending p 9 uponthepositioninwhichtherotorhappenstostop.Refertotheinstructionson "Extended Shutdown' , Page 3-5, for protective measures.

Corroded rings may require grinding and should always be polished before being returned to service.

4-3

Uneven Hardness of Ring

If a ring is not of uniform hardness around the periphery, uneven wear results, and performance becomes unsatisfactory.

Electrolytic Action

Because there is an electrolytic action at the surface of the rings, their performance is improved by reversing their polarity occasionally. In some cases, it has been found useful to do this as often as once a week.

Unusual Operating Conditions

Excessive Current Densities Due to Overloads

The mechanical contact between the brush and the ring is never absolutely perfect, and high current density at the contact surface can cause sparking with brush fits that would be sufficiently accurate for normal densities.

Extended Operation with a R ow Value of Brush Current

Brush "chatter", accompanied by sparking, has been found to result from this practice, as when machines are run without load in a stand - by capacity.

CORRECT9VE MAUNTENANCE

Onsulation Resistance

General

The insulation resistance of a winding is the resistance of the insulation to a DC voltage tending to produce leakage current through the insulation an over its creepage surfaces. Although it is not a measure of the dielectric strength of the insulation the insulation resistance indicates whether the machine is in a suitable condition for operation or for high - potential tests.

insulation resistance is affected by a number of conditionsand often an apparent inconsistency in a group of readings can be attributed to variations in one or more of the test conditions which have been incorrectly assumed as constant.

4-4

The:actual insulation resistance is lowered by the following conditions:

1. Aging of the insulation.

2. Mechanical damage to the insulation.

3. Presence of dirt in the machine.

4. Increased moisture content of the insulation.

5. Increased temperature of the insulation. (The effectof temperature of insulation resistance, is great, the resistance at 25'C, being six to fourteen times that at 75'C, depending upon the type of machine.)

Measurements of insulation resistance are lowered by the following factors:

1. Increased magnitude of the test voltage used. (Variations of test voltage as small as 2:1 or 3:1 make no appreciable difference).

2. Decreased time of application of test voltage.

Significance of Tests

Insulation resistance varies widely among machines of different sizes and voltages. Therefore, measurements of this quantity are useful chiefly for comparison with those made at other times on the same machine. MONTHLY TESTS OF INSULATION RESISTANCE ARE RECOMMENDED for detecting changes in the insulation material or creepage surfaces. In order for thesetests to be correlated properly, each test should be made under the same conditions.

A trend toward lower insulation resistance is a warning that failure of the insulation is ossible. For this reason, the readings-obtained at any particular time should be compared with the previous readings in order to be of maximum significance.

The behavior of insulation resistance while the windings of a machine are being .dried out is discussed in the section on "Drying Out Windings", Page 3-2.

Conditions for Test

In order for all the tests to be made under a proximately equal conditions of temperature and moisture, it is suggested that the insulation resistance be measured immediately after shutdown while the machine is still hot., It is preferable to use the same method and thesame circuitforalltests. In anycasel, the records of insulation resistance will be more valuable for future reference if

4-5

MOTOR FRAME

UNGROUNDED-- ---

D-C VOLTAGE +

SOURCE F1

the cond it ions oftemperature,moisture, etc., and the test circuit and voltage are noted along with the insulation resistance.

Method of Test

The insulation resistance of a winding may be measured by using either motor dr.iven megger or a DC test circuit. In either case, one connection is made to the frame (for stator windings) or to the shaft (for. rotor windings), and the other connection is made to a common terminal to which all leads of the winding in question are attached.

Voltmeter Method

Insulation resistance may be measured with the aid of a DC voltage source and a high - resistance DC voltmeter. The procedure is as follows:

1. Connect voltmeter to motor stator winding through a SPDT switch as shown in Figure 3.

MOTOR

WINDING

SPDT

SWITC

---- o

HIGH - RESISTANCE

IDC VOLTMETER

FIG. 3 CONNECTION DIAGRAM FOR MEASUREMENT OF

INSULATION RESISTANCE

2. Take voltage readingswhi le voltmeter is connected by the switch to motor winding and when connected to motor frame. These readingsarethevoltagewhenthemotorisinserieswiththewinding and the voltage of the DC source, respectively.

4-6

MOTOR -

TERMINAL

3. Calculate insulation resistance by means of the following formula:

ER-R -1

E-

E - voltage of DC source iE =volt age when motor is in series with voltmeter

R voltmeter resistance (in ohms) Ri insulation resistance (in ohms)

Preferred Method of Measuring Insulation Resistance

If facilities are available, Westinghouse recommends that any of t he instruments mentioned above be used to measure the insulation resistance over a period of ten or fifteen minutes ata potential near the operating voltage. Readings should be taken every fifteen seconds for the first two minutes, and then every minute during the remainder of the test.

Interpretation of Results

When the test voltage is applied for a period of ten minutes or Imore the plotted graph of insulation resistance values obtained represents the dielectric absorp-tion characteristic. See Fig. 7 for typical curves showing variation of insulation resistances with time. This graph may 'be interpreted as follows:

1 A steadily - rising curve is indicative of a clean dry winding.

2. A quick - flattening curve is the result of leakage current1hrough or over the surface of the winding insulation, and is generally indicative of a moist or dirty winding.

Polarization Index

The polarization index is the ratio of insulation resistance after applying a test voltage for 10 minutes to the insulation resistance after applying the same test voltage for 1 minute. The polarization index may be considered as a means of expressingthesha eofthedielectricabsorptioncharacteristiccurveintermsofa single numerical quantity. See Fig. 6. A rising curve tends to increase the polarization index While a flat curve tends to lower it. The polarization index is useful in appraising the dr ness of the insulation and suitability for over -potential tests. The polarization index is not affected by temperature when the machine temperature is constant or changing very slowly.

4-7

Soo r (i 200

U

Z

D

LU 80

70Z0 60 M= =.X j I

V��') 40 Z

DI -fy -MOIST INSULATION

ION I DE � .1)

10 P

0.1 0.2 0.3 0.4 0.5 0.7 1.0 2 3 4 5 6 7 10

TIME, MINUTES

Fig. 6 Typical Curves Showing Variation of Insulation Resistance With Time For Class B Insulated Alternating - Current Armature Windings

Recommended Minimum Value of Polarization 9ndex

The recommended minimum value of the polarization index for alternating current motors is 2.0 for all insulation systems. Thus, Minimum Polarization- Insulation Resistance after 10 min- 2 Insulation Resistance after 1 min

Alternate Methods of Measuring Insulation Resistance

If a motor driven megger or a DC test circuit are not available, a hand - driven megger may be used.

Insulation resistance measurements may be taken periodically and compared with earlier measurements. For comparable readings, a standard insulation resistance test should be used.

4-8 i0o

U 0QvI--

S4

I-- Z'

LU

U.

La.

LU

U

Uj ad D

DC

Uj 0.

IAJ

U z t;

;A � Uj De z0

D V) z

1.0

0.5

0.1 TOCONVERT OBSERVED. INSULATION RESISTANCE (R t

TO 40C MULTIPLY BY THE TEMPERATURE COEFFICIENT

K R =-R t K NOC 40C x (40C

0.05

-10 0 10 20 30 40 50 60 70 80 90 100 11

WINDING TEMPERATURE, C

Fig.,7 ApproximateinsulationResistanceTemperatureCoefficientof Rotating Machine Armature Windings

4-9

Where short - time single readings are to be made on windings, and wherethese results are to be compared with earlier and later date, test at 500 volts (DC) for a period of 60 seconds. (This test may also be used when a hand - driven megger is the only test instrument available.) Make this test when the motor is at ambient temperature, and record this temperature. Since the insulation resistance of a winding varies inversely with the winding temperature, all resistance values should be converted to the equivalent resistance at 40'C. The equivalent resistance may be calculated with the following formula:

R Kt 40C X Rt40C

R40C = unknown insulation resistance in megohms at 40'.

Rt = insulation resistance in megohms at temperature t.

Kt4OC= approximateinsulationresistancetemperaturecoefficient(Fig.

9) for temperature t.

Recommended Minimum Value of Resistance

The recommended…