Sunday, June 21, 2009

POWER GENERATION SERVICES CAPABILITIES

PLEASE VISIT THE OTHER PAGES BLOG:
HIGH REVERSE POWER FROM GSU POWER TRANSFORER 150 KV / 11.5 KV
ON GE GENERATOR 125 MW, 11.5KV, 3000 RPM



Power Generation Maintenance Project Experiences and Workshop Capabilities

It is our great pleasure to introduce you our Power Generation Services Team with supporting with modern instruments and equipments also supporting by International World Wide Independent Company, we offer solution to maintenance, Assessment and Analysis and repair of Generators (Turbo / Hydro), Power Transformer, Furnace Transformer, HV / LV Electric Motors, DC / Traction Motors.

Following are our capabilities and facilities to perform Maintenance and Repair of Power Generation :
1. Insulation monitoring conditions assessment to extend of machine life time
2. Testing and analysis of insulation
3. Failure investigation and analysis
4. Stator winding refurbishment and rewinding
5. Rotor winding refurbishment and rewinding
6. Replacement, material improvement, modification stator wedges
7. Stator core analysis by Digital EL CID (Electromagnetic Core Imperfection Detection)technology
8. Wedge tightening analysis by WTD technology
9. Natural frequency test to analysis of vibration effect on the end winding, and overhang
10. Contact coefficient test to analysis loss contact of semiconductor as a corona protection on the stator winding to ground
11. Off Line Partial Discharge analysis with Bar to bar scanning to evaluate partial dischargeeffect on the each coil stator
12. On line Partial Discharge Monitoring and analysis
13. Insulation Dissipation Power Factor test and analysis
14. Endoscopic inspection on the stator winding and rotor winding under retaining rings
15. Semiconductive corona protection refurbishment on the stator winding
16. NDT inspection on the retaining rings, centering rings, journal shaft, bearings, etc
17. Insitu balancing and vibration analyzer
18. Major Outage
19. Spare parts supplies with OEM specification
20. High Voltage Coil Manufacture for Generators / Motors
21. Furaldehyde oil in Power Transformer
22. Degree of Polymerization (DP) analysis on solid insulation transformer
24. DGA (Dissolve Gas Analysis) on Oil Transformer

Hoping our facilities and capabilities can offer best solution and will meet to your maintenance programs requirements and looking forward to hear you soon.

Thank you
Your sincerely
Siswanto

Email:

Mobile phone:
++6281311422270,

Please check also the following link:

• Forum Thread: Motor externally by spraying water?
http://cr4.globalspec.com/thread/30973

• Forum Thread: motor winding status
http://cr4.globalspec.com/thread/30820

• Forum Thread: Transformer Turn Ratio (TTR) Testing
http://cr4.globalspec.com/thread/49397

• Forum Thread: 11 kw Ingersoll Rand Motor
http://cr4.globalspec.com/thread/49317

• Forum Thread: Calculating Busbar Size for Temperature Rise in 440V LV Panels
http://cr4.globalspec.com/thread/48036

• Forum Thread: Standards Limits for Power Transformer
http://cr4.globalspec.com/thread/48118

• Forum Thread: Degaussing
http://cr4.globalspec.com/thread/48139

• Forum Thread: High Voltage Motor Test.
http://cr4.globalspec.com/thread/47864

• Forum Thread: High PD value on 13.8KV, 12,5 MW steam turbine generator
http://cr4.globalspec.com/thread/33406

• Forum Thread: Power Transformer testing - tan delta test
http://cr4.globalspec.com/thread/32684

• Forum Thread: How to Repair a Partial Core Stator Generator
http://cr4.globalspec.com/thread/32530

• Forum Thread: Transformer insulation resistance
http://cr4.globalspec.com/thread/31112








I. INTRODUCTION
Wound stator / rotor windings operating in utility and industrial plants have failed when exposed to the fast rise-time voltage surges coming from unbalance load, drives, breaker, lightning impulse, etc.

Machine failure is due to a combination of bad luck in winding insulation process and material quality show that these surges create partial discharges (also called corona) and these discharges may eventually destroy the turn-to-turn and/or phase-to-phase insulation, resulting in premature machine failure.
The fast rise-time voltage surges can lead to an electrical breakdown of the turn insulation in motors / generators stator / transformer windings . If the turn insulation is of an insufficient thickness, or has aged in service, the insulation will puncture when a short rise-time voltage surge occurs. Punctured turn insulation allows for a very high circulating current to flow into the affected copper turn, rapidly melting the copper conductors, which, in turn, results in a consequent burning/melting of the slot liner insulation, thus leading to a stator winding ground fault .
Our expert staff and specialized facilities offer the know-how and in depth experiences to deliver reliable engineering services and testing capabilities that can help prevent machine failures, reduce maintenance and improve day to day operations from failures incidents




II. POWER GENERATION PROJECT EXPERIENCES

Some of these project experiences as listed below was supported by our worldwide companies partner ship:

Stator wedge replacement for 250 MVA Toshiba and Alstom 87 MVA, was supplied by
Digital ELCID and PD off line by probe scanning test : was supported by Powertech Lab Inc Canada

Complete Rewind Rotor GE 237 MVA,: was supported by Rotor Pro South Africa, and the following companies also involving under coordination by Rotor Pro:

a. Vibra Mac performing vibration analyzer and site balancing
b. TUV Rhineland Inspection Services (Pty) Ltd, performing NDT test
c. Westward Monitoring Systems (Pty) Ltd, performing Degaussing
d. Powertech Calidus, supply of Generator Rotor Insulation.
Volt Industries Inc. Canada




PROJECT EXPERIENCE LIST

1 Rewinding Stator IDEAL Generator, 21 MVA, 13 KV
Pertamina Dumai. Indoensia. May 2004

2 Major Outage Gas Turbine GE generator,44 930 KVA, 11.5 KV, 3000 RPM
PT. Petrokimia, Gresik, East Java, Indonesia
August 2005

3. Rewinding Rotor Shandong Generator 8823 KVA, 10.5 KV, 3000 RPM
PT. Pura Barutama Power Plant. Kudus, Central Java, Indonesia
November 2005

4. Replacement and improvement of Stator Wedges class B material to NEMA G 11 with radial springs and Outage Stator TOSHIBA Generator 250 MVA, 15 KV, 3000 RPM
PT. PLN Pembangkitan Jawa Bali,. Gresik. East Java. Indonesia
December 2005

5. Rewinding (Re insulate 18 Coils) Stator Alstom Generator 87,5 MVA / 11000 V / 3000 RPM
PT. DSS / APP , Serang, West Java. Indonesia
November – Dec 2006

6. Rewinding Rotor Generator Xandong 7.5 MVA / 6.6 KV / 3000 RPM
PT. Pabrik Gula Permata Dua Sukses Makur. Cilegon. West Java. Indonesia
June 2007

7. Repair Endwinding and Replacement Blocking Coil Rotor Generator GE 28.5 MVA ,
with retaining rings removal, PT. PLN PJB Unit Gili Timur. Madura. Indonesia
April 2007.


8. Tangent Delta Test on 7 unit Electric motors from 2 MW 10 kV up to 10 MW, 10 kV
PT. Tanjung Jati Power Services. Jepara. Central Java. Indonesia
July 2007


9. Off line Partial Discharge Test by Probe Scanning. Mitsubishi 125 MVA , 15 KV

PT PLN Pembangkitan Jawa Bali. Unit Muarakarang. Jakarta. Indonesia
Sept 2007


10. Major Overhaul on Alstom 30 MW, 11 kV, 3000 RPM

PT KDM . Bontang East Kalimantan. Indonesia
26 October – 9 November 2007


11. Rewinding Stator GE Generator 30 MW / 3000 RPM / 11 500 Volts

PT PLN PJB / PJBS Medan. Sumatera. Indonesia
Dec 07 – Feb 08


12. Rewinding ELIN Hydro Generator 50 MW

PLTA Singkarak. Sumatera, Indonesia, 2008

13. Replacement and modified Stator Wedge ELIN Hydro Generator 60 MVA

PT INCO, Sulawesi. Indonesia
March 2009

14. Total reinsulated Stator winding ELIN Hydro Generator 34 MVA

PLTA Jatiluhur. West Java, Indonesia
Nov 2008 – Feb 2009

15. Total Rewinding Rotor GE Generator 237.5 MVA / 3000 RPM,

Scope include:
- Total rewind rotor
- Demagnetizing HP/LP/ Bearings, Casing, Turbine
- Demagnetizing Rotor generator
- NDT inspection
- Low speed Balancing by IRD machine
- Site balancing by Bently Nevada instruments
- Test and commissioning
PT PLN PJB Unit Muarakarang. Indonesia
June – August 2008


16. Repair Exciter Rotor Alstom Generator 2 x 30 MW

Ranhill – Powertron. Kinabalu. Malaysia
Feb / April, 2009

17. Rewinding 2 Unit Furnace Transformer, 40 KA and 63 kA, Voltage 20 kV / 220 Volts

PT. Master Steel , Jakarta, Indonesia
April 2007


18. Rewinding Power Trasnformer 40 MVA, 150 kV

PT PLN Unit Tg Priok. Jakarta. Indonesia, 2006

19. Rewinding Power Transformer 4x 60 MVA. 20 kV / 150 KV
PT PLN Unit Waru.. Surabaya East Java. Indonesia, 2009

20. Repair “MR” OLTC V / III / 200 Y, and V / I / 200 Y
Sumatera, 2007

21.Inspections 125 MW GE Generator,
PT Tugu Kresna Pratama General Insurance / PT.PLN PJB Unit Muara Karang, Jakarta. Inspections including:
- Preliminary Inspection
- Digital EL CID
- Frame Inspection
- NDT Inspections Rotor Shaft, RR’s
- Electric Round-out Rotor Shaft
- Recommendations


 
22. Inspection and Recommendation for Mitsubishi Power Transformer 155 MVA,
150 kV / 11.5 kV. PT. Satria Dharma Pusaka Crawford THG / PT. PLN PJB Muara Karang. Jakarta

23.Inspection, and Recommendation for Hyundai Power Transformer 80 MVA,
150 kV / 22 kV. PT. Satria Dharma Pusaka Crawford THG / PT. Tokio Marine General Insurance / PT. Asahimas Chemical. Cilegon



COURSE PROGRAM EXPERIENCES

Course experiences for Rotating Electric Machinery’s Maintenance (QC Improvement) Management for Power Generation, Electric Motors and Power Transformer Diagnostics as Instructor

 
No
Company
Venue
Course
1


PT. Batu Bara Bukit Asam
Tanjung Enim 
Tg. Enim. Sumatera

Salient Pole Generator
and Electric Motor
inspection, testing,
analysis and improvement
2

PT. PLN Pembangkitan
Jawa Bali
Tretes. East Java
High Voltage Generator
and Electric Motor
inspection, testing,
analysis and improvement
3

PT. Kaltim
Parna Industri

Sofyan Hotel

High Voltage Generator
and Electric Motor
inspection, testing,
analysis and improvement
4

PT. Semen Padang
Treva Hotel.Jakarta

High Voltage Generator
and Electric Motor
inspection, testing,
analysis and improvement
5

PT. Petrokima Gresik 

Sofyan Hotel. Jakarta

High Voltage Generator
and Electric Motor
inspection, testing,
analysis and improvement
6


PT. Krakatau Steel .Cilegon 

Sofyan Hotel. Jakarta
Electric Motor
inspection, testing,
analysis and improvement
7

PT. Pertamina Persero
DOH JBB
IBIS Hotel.
Jakarta

Electric Motor
 inspection, testing,
analysis and improvement
8

PT. Power Gen. Paiton 
Treva Hotel.Jakarta
Electric Motor
inspection, testing,
analysis and improvement
9

PT. ISM Bogasari Flour Mills

Treva Hotel.Jakarta

Electric Motor
inspection,
testing, analysis
and improvemet
10

PT. PLN Pembangkitan
Jawa Bal.
Gresik
Treva Hotel.Jakarta

High Voltage
Turbo Generator
inspection,
testing, analysis,
improvement
11

PT. Astra
Honda Motor
Treva Hotel.Jakarta
Electric Motor
inspection, testing,
analysis and improvement
12

PT. Showa Esterindo Indonesia, Cilegon 
Treva Hotel.Jakarta

Electric Motor
inspection, testing,
analysis and improvement
13

PT. MC Pet Film Indonesia, Cilegon
Treva Hotel.Jakarta

Electric Motor
inspection, testing,
analysis and improvement
14

PUSDIKLAT ISBI (Institut Semen Beton Indonesia),
Cileungsi ISBI Building

Low Voltage Salient Pole
Generator,
Inspection, Testing, Analysis ,
Improvement and Repair
Electric Motor
 inspection, testing,
analysis and repair
15

PUSDIKLAT ISBI (Institut Semen Beton Indonesia),
Cileungsi ISBI Building

Low Voltage Salient Pole
Generator,
Inspection, Testing, Analysis ,
Improvement and Repair
Electric Motor
 inspection, testing,
analysis and repair
16

PT. PINDAD, Bandung 
PINDAD

Electric Motors,
 Repair,
Testing, Analysis
17

BKPM. Jakarta 
BKPM Bldg
Electrical Machine
for Non Electrician
18
PT PLN PJB
Inna Garuda, Yogya
High Voltage
Turbo Generator
inspection, testing, analysis,
improvement
19

PT. PLN Indonesia Power 
PLN Build.
Jakarta
High Voltage
Turbo Generator
inspection, testing, analysis,
20

CEVRON Indonesia
Papandayan Hotel. Bnadung
Electric Motors,
Repair,
Testing, Analysis
21

PT.AQUA DANONE
Aqua Factory. Sukabumi
Power Transformer
Inspection,
Testing and Fault Analysis
22

PT PLN PJB 

Salak Hotel,
Bogor

High Voltage Turbo Generator,
Inspection, Testing, Analysis ,
Improvement and Repair
Electric Motor inspection,
testing, analysis and repair
23
PT Polysindo
Polysindo Factory, Krawang Timur
Power Transformer
Inspection, Testing
and Fault Analysis
24

PT. Indocement Tunggal Prakarsa
Indocement Factory, Citereup
Power Transformer
Diagnostic and analysis,
25





PT. Petro Kimia Gresik




Petro Kimia Factory




- High Voltage Turbo Generator,
Inspection, Testing, Analysis ,
 Improvement and Repair
- Power Transformer Diagnostic
and analysis.
- Electric Motor inspection, testing,
analysis and repair
26





PT PLN PJB





Unit Muara
Karang




Moisture Analysis
on Power Transformer
using PDC and FDS
Site measurement
using DIRANA for
HV Motor 6kV,
145 MW ABB Generator,
500MVA, 500kV Power
Transformer
27
PT PLN PJB
Salak Hotel
Bogor
Power Transformer
Diagnostic and analysis
28
PT. Petro Kimia Gresik
Petro Kimia Factory
High Voltage Turbo Generator,
Inspection, Testing, Analysis ,
Improvement and Repair
Electric Motor
inspection,
testing, analysis and repair
29
PT .PJB UPHT
Agro Wisata
Hotel, Batu
Malang
High Voltage Turbo Generator,
Inspection, Testing, Analysis ,
Improvement and Repair
Power Transformer Diagnostic
and analysis.
SCOPE OF SUPPLY PROVIDED FOR POWER GENERATION
TURBO AND HYDRO GENERATOR, TRANSFORMER,
HV/LV ELECTRIC MOTORS, DC/TRACTION MOTORS


1. Complete or partial rewinding with new coil
2. Complete or partial re insulate
3. Repair of Semiconductive protection by injection Stator wedges quick repair by epoxy resin / RTV
4. Partial or complete replacement of stator wedges with NEMA Li G11 material
5. Modified or replacement of stator wedges radial spring Class F material
6. Repair stress grading coating at end winding

Inspection and Testing for Stator
1. Visual Inspection
2. Stator bar Partial Discharge inspection phenomenon by borescopic inspection
3. Stator wedges mapping by manual tapping
4. Stator wedges mapping by WTD method
5. Insulation Resistance and Polarization Index
6. Copper winding DC resistance Insulation
7. Power Factor Tangent Delta
8. Off line Partial Discharge Inspection by Scanning Probe
9. Off Line Partial Discharge Inspection by “C” Coupler Sensors
10. On Line Partial Discharge inspection by “C” Coupler Sensors
11. Stator Bars Contact Coefficient
12. End winding frequency mapping
13. Surge comparison
14. Digital ELCID
15. Hi Pot


A.2. ROTOR AND SHAFT + CRR’s

Improvements
1. Partial or complete rewinding for salient pole generators
2. Partial or complete rewinding for turbo generators with new copper bar or re used
3. Steel wedge manufacture
4. Repair end winding for turbo generator
5. Replacement of CRR’s insulation with PTFE Glass G11 materials

Inspection and Testing
1. Visual inspection Insulation
2. Resistance and Polarization Index
3. Copper winding DC resistance
4. AC Impedance Test
5. Voltage Drop Test Recurrent
6. Surge comparison test
7. Surge Oscillation (RSO)
8. NDT inspection ( Penetrant, UT, MPI)
9. Demagnetizing on the Journal, bearings, coupling


A.3 EXCITER ROTOR / STATOR, ROTATING DIODES, FUSES, BRUSH RIGGING, CARBON BRUSHES, RTD’s

1. Visual inspection Insulation
2. Resistance Polarization Index
3. Copper winding DC resistance
4. Resurfacing and run-out of collector rings
5. Brushes supply

A.4. COMPLETE UNIT
1. Cleaning
2. Insulation coating
3. Curing with High current DC MG Set supply
4. Low speed balancing
5. Pull-In / Pull-Out Rotor
6. Unit alignment by Laser Alignment equipments
7. Vibration Record and analyzer by Pruftechnick
8. ibration analyzer and site balancing by Bently Nevada
9. Commissioning and comprehensive technical report incl recommendations


B. POWER TRANSFORMER , DISTRIBUTION TRANSFORMER, FURNACE TRANSFORMER AND OLTC’s

IMPROVEMENT
1. Complete or partial phase rewinding for LV / HV side
2. Oil replacement and reclamation
3. Repair and replacement of OLTC’s
4. Replacement / modification FOT monitoring
5. Overhaul

INSPECTION
1. Visual inspection
2. IR / PI
3. Copper dc resistance
4. Surge comparison
5. TTR
6. Kick polarity
7. Voltage impedance
8. Open / short circuit test
9. Induced test
10. Oil breakdown voltage test
11. SFRA test
12. Insulation Tan Delta DGA test
13. Furan test Visual inspection of OLTC’s
14. Inspection/ Overhaul / Repair / replacement of OLTC’s contacts and insert

C. ELECTRIC MOTOR ( AC / DC / TRACTION

C.1. STATOR

IMPROVEMENT
1. Rewinding class F, H
2. Overhaul (cleaning, dry out, re insulation coating)
3. Partial rewinding pole per pole for DC motors / Traction Motors
4. Partial / total re stacking


TESTING
1. IR / PI
2. Copper dc resistance
3. Surge comparison
4. Pole drop


C.2. ROTOR
IMPROVEMENT
1. Partial rewinding for dc motors
2. Total rewinding slipring and dc motors
3. Reinsulate
4. Rotor bars replacement for broken bars for SQ motors
5. Shaft repair / replacement
6. Commutator repair and replacement
7. Slipring repair and replacement
8. Resurfacing for commutator / slipring for site works and shop
9. Brush rigging repair / replacement
10. Carbon Brush replacement based on the original specification

TESTING
1. IR / PI
2. Copper dc resistance
3. Surge comparison Voltage drop
4. Grawler
5. Brush alignment
6. Zero adjustment

D. OTHERS
1. Bearing replacement
2. Replacement of Bearing insulation
3. Site installation / re alignment
4. Parts supply as per OEM standard specification
5. Maintenance course
6. Supervising and consulting



II. DETAIL SCOPE OF SUPPLY

A. ROTOR PULL IN / PULL OUT FOR TURBO / SALIENT POLES GENERATOR

Many method to perform this activities, run way method using with special tools or jacking systems combined with heavy crane is our standard procedure. Normally special tools is provided by machine manufacturer, if its not available at site special tools fabrication is require. Following activities should be perform during machine dismantling.
A. TURBO / HYDRO GENERATORS, LARGE HV MOTORS

A.1. STATOR
Improvement

Dismantling. Frame Assembly
Rotor Pull Out preparation
Rotor Pull Out


video
Pull-Out rotor Video

Re Assembly


B. RECORD THE VIBRATION AND GENERATOR ALIGNMENT , BEFORE AND AFTER GENERATOR DISASSEMBLED

This activities should be recorded before machine shutdown, alignment in cold condition after machine shutdown, Optic alignment is our standard procedure to this activities, our “PRUFTECKNIK” expert will be performed this task.



 

C. INSPECTION


















GE Generator 237 MVA / 15.5 kV


C.1. STATOR INSPECTION

Stator bore cleanliness
Important information on the general condition of the machine may be obtained from a general view of the bore area and frame.













HV Bushing and Flexible Bus Connection







HV termination for H2 cooled generator

HV Bushing sometimes have passages built inside them to allow the flow of air or hydrogen for cooling purpose. It is important that the vent are inspected to see if they are uncloged, cracking, dust deposit loose part, its could be arise from any sudden load change, vibration over long time period, overheating of the lead,


End Winding ,Connection Rings and support




Blocking condition, Ties between coils tight



The blocking consist of the material used to separate the side of the coils at the end-winding and between end-winding connection.
Blocking coils are used to determine the clearance between the coil side at the end region, to eliminate mechanical stresses arising coil movement, that will be resulting coil touching each other at the end-winding. sudden change of load (or external short-circuit) will be create large movement of the coils end, and combined with different temperature relate expansion of coils are strongly reduced coil insulation properties.


Surge ring insulation condition, Ties to surge rings tight ?,
The end-winding of electric machine are subject to substantial movement during sudden change load, vibration on normal operation. To minimize of end-winding movement the side coils are tied to a circular rings are commonly called : “surge-rings or support rings “.
In large machine surge-rings are normally made of steel, and the steel are covered with several layer o insulation. Te purpose of insulation on surge-rings is to minimize of a ground fault to the rings. The surge rings insulation can deteriorate due to electrostatic discharge from the coil, is appear as electrical tracking and/or burnlike marks on the insulation.





Surge ring support assembly



Sludge and white powder on the support and ties are indicate high vibration


Out going cable support

Cable support is designed to out going lead cable from generator stator winding to termination, loose on the clamps support can occur due to vibration during machine in operation, loose support can caused crack on the termination and lead cable insulation.

White powder is indicate excessive vibration .

Insulation Condition
Thermoplastic, resin / epoxy polyester binder, insulation system when exposed temperature will become dry and brittle, the exposed temperature may arise from overload condition, poor cooling, damage core section, negative sequence current due to unbalance, etc.




A problem common to machines with thermoplastic insulation is that the normal thermal cycling is causes coil movement in the slot, tend to generate crack within the ground wall insulation.
A tape separation is a separation of tape covering the wall insulation of the coil due to axial expansion and contraction of the conductors and the opposing forces of the slot applied to the wall insulation.


In some cases only the armor tape is separated, in other cases the mica-tape comprising the ground-wall insulation is also affected , when this occur a few layer may be affected and the whole tape will move creating “ a neck” in the coil.




Insulation Galling/necking beyond slot

Necking is a lack of insulation which has been cracked and separated causes by thermo cycling in thermoplastic insulation.
Necking is always a sign of a weak point in the groundwall insulation. Some of the coils are made in the slot portion with a slot wrapper, while at the end-winding region a tape is used.
The interface between the two region close to the end of core is called a “ scarf joint. “.


Scarf joint represent a weak mechanical point in the structure of the coil, tending to separate under thermal stresses .














Insulation bulging into Air Duct

Bulging of the insulation right outside the slot and in the cooling vents is an indication of a soft spot , tape separation, girth cracks or insulation migration.



Endwinding blocking coil and ties
The blocking consist of the material used to separate the side of the coils at the end-winding and between end-winding connection. Blocking coils are used to determine the clearance between the coil side at the end region, to eliminate mechanical stresses arising coil movement, that will be resulting coil touching each other at the end-winding. Blocking coils are almost made from solid insulation materials (such as textolite, felt, etc) which is soaked in resin.
Blocking coil is always held in place with ties. Often solid separator tend to loose after long period of operation, in severe cases it will fall from the winding.

 

Corona activity
Corona is define as the ionization of gas when exposed to an intense electric field , the discharge have a wide range of frequencies [ 40 kHz to 100 MHz ].

Corona activity in the rotating machine :- Corona at end winding ( End-winding Discharge )
- Corona at inside of the insulation ( Internal Discharge )
- Corona at ground-wall insulation ( Slot Discharge )
- Corona at overhang of winding ( Surface Discharge ) ==>  see PD Testing

Endoscopic Inspection
Corona activities at endwinding can inpected with naked eyes, but corona at wall insulation caused by slot discharge only can inspected by measurement and indoscopic method.




video
Video: ALSTOM 87 MVA / 11 KV, 18 top Stator Bars burnt due to PD activities

RTD and TC
Resistance Temperature Detector ( RTD ) and or Thermocouple ( TC ) are mainly found in the winding, cooling gas flow path, cooling water paths and bearings.
Winding temperature detector normally of RTD type are located between the coils in inaccessible area. However wiring to and from these devices is partially accessible for visual inspection, its should be tight and secured along its path to the coils, frame and termination casing. If winding temperature detector are faulty, they can be replaced during a major inspection. the damage of RTD are left in place with their wires are disconnected or removed and the new RTD are taped and glued to the coils as close to the damaged of RTD as possible, in generally they will be located in the end-winding.


Bar Bottomed in Slot

Is bar seated tightly on the bottom of the slots. Coils not bottomed in slots indicate a loose-coil condition with all the problems and consequences coils movement within the slot, thus the semi conductive and wall insulation will be damaged.
A mirror or AV camera permits inspection around the end-winding and observation of the end core area and the bottom of coils.







Core inspection

Core condition
All parts in generator are exposed to continual vibration, temperature change and other mechanical stresses. They may become loose, fractured or broken. Its important to search for these abnormalities during the inspection before they develop into major troubles. In particularly all components of the core assembly are subjected to mechanical stresses due to sudden load change, such as during loss load, short-circuit, closing out of synchronism. In general condition core can be inspected with visual, beside inspection with a measurement ( EL CID, Loop)
.

 Lamination Bent or Broken in the Bore ?

Core lamination are often damaged during removal rotor, when this occurs its become partially short-circuit, if left on this condition they may become reach excessive temperature during operation, and will resulting damage to the insulation between of lamination’
If found short-circuit in the lamination or group of lamination, the top lamination should be separated and impregnated with resin or epoxy.
Its most important to identify lamination that are broken or in the bent, any broken of pieces lamination will got loose and most probably will damage the insulation of coil










Slot and Wedges

Wedge Function and Tightening Test by manual tapping

The wedge is one of the main elements controlling the tightness of the coils in the slots, maintain the positive pressure on the coils reduces their movement within the slots to minimizing loss of semiconducting coating and wall insulation. Slot electromagnetic forces are high and deterioration is common and can be severe. The slot portion of the stator winding is probably the most critical and difficult area of a generator to properly inspect. Most of the important areas of interest are enclosed behind the wedges and the core iron.

The common way to inspect wedge condition is to tape on one side of the wedge with a small hammer and sense the amount of movement with the other hand touching the other side of the wedge. Given the response the wedge condition can be classified either as tight, loose or hollow

.







Stator wedge
 







Radial Spring Class F

Following are threshold criteria of unsatisfactory wedge standard reference, Some literature and manufacturer have a different criteria for unsatisfactory threshold of wedge to decision re-wedge , repair or continues to operation.

This information taken from TOSHIBAToshiba Corporation TIL ECS – 990506P for Preventive Maintenance of 125 and 250 MVA Turbine Generator, recommend a threshold criteria as follow:

If there are 2 (two) consecutive looseness wedge in the same slot or if the percentage of nonconsecutive looseness wedge is less than 30% from total number of wedges in a same slot, the looseness wedges are applied the epoxy resin by brush between stator core and stator bar wedge
If there are 3 (three) or more consecutive looseness wedges in a same slot, or if the percentage of nonconsecutive looseness wedges reached 30% or more of total number of wedges in a same slot, the all wedges in the slot shall be disassembled and replaced with new ones.
Note: Application of epoxy resin is only temporary countermeasure for the looseness. Some literatures explain : more than 25%, of total wedge were loose, must be replace, less than 25% should be repair.



Filler Slipping Out at End








Filler slip out on Gen GE 25 MVA and Side filler slip-out on Mitsubishi Generator 125 MVA
Another indication of loose coils at least radial direction is movement out of the bottom and or top slot filler . Normally the filler are driven back (if possible) 0r broken at the end of core. In both cases they are secured with resin-epoxy or RTV .As with the movement of end wedge large number of fillers slipping out of core by several inches may indicate a loose winding condition. However filler movement can also be result of elongation and contraction of the coils due to thermal cycles, even in tight coils.



C.2 ROTOR INSPECTION

C.2.1. Cylindrical rotor
















Rotor Cleanliness

Inspection on endwinding to verify copper powder deposit

A rotor exhibiting numerous deposits of copper powder indicate excessive movement of the DC field coils, the excessive copper dust should alert the inspector to possibility of the existence or the development of shorted turn and / or ground fault.
Copper dust, iron dust, or any other telltale material my concealed in a mixture of oil and dirt, can mask cracks on the surface of critical components such as wedges, fan hub and blades, retaining rings, bar connection, etc. Heavy dust deposit affect to the flow of the cooling gas or air, in affect de-rating the machine


.


Rotor Wedge Inspection

During unbalanced load or supply condition, motoring serve or generation with the field off (induction mode operation), inspection of the rotor should always include inspection of the wedge-ring contact area, as well as between the wedges themselves and between wedge to the rotor body, its important to note that any sign of burning should be carefully investigation.
During systems oscillation or other type of abnormal operation, alternating current are established in the body of the rotor.


When bridging high resistance contact area, these current may give rise to very localized pitting of the metal. These high-resistance area mainly found in the contact surface between the wedge and the slot, between different wedge, and between wedge and retaining ring.




Pitting sign found on the rotor wedge due to alternating current are established in the body rotor

video


Video: INSPECTION ROTOR ALSTOM 87MVA

Retaining Rings Visual Appearance
The retaining ring are the most critical component in the rotor and normally the most highly stressed rotor component. These rings are critical in the sense that their mechanical failure causes by SCC (stresses corrosion crack), mostly 18-5 type of ring (18% manganese-5% chromium alloy)



Endwinding blocking inspection
 








End winding blocking arrangement

The endwinding blocking must support the winding to prevent permanent distortion, yet also allow for thermal expansion. (See Figure.) The blocking materials that are currently utilized are epoxy glass laminates. It is important to employ a service-proven blocking pattern that is compatible with the specific endwinding geometry being used, since it is the blocking pattern which allows for thermal expansion movement and ventilation. Also, special consideration must be given to the blocking and support of pole-to-pole, coil-to-coil and terminal connectors. It should be noted that asbestos was used extensively in older generation distance blocks and rotor insulation; maintenance/ repair processes must take this into account. Some design features are added when high cyclic duty is anticipated. These include reliefs in either the copper or body at the end of the coil slots to prevent armor damage, reliefs between the slot armor ends, and the blocks just outside the body when rigid armors are utilized.

Loose blockingSome times centering is constructed with narrow space , hand touching and conventional camera is inaccessible to inspect the endwinding blocking and other parts under retaining ring area. borescope camera is require to inspection.



Loose blocking on GE Rotor 49 MVA

video


 
Video: Rotor Inspection on GE 49 MVA

When the rotor winding or other parts under retaining rings failure, detail inspection should be carried out with retaining rings removal. to remove retaining rings should be done by an expert or supervising with the appropriate equipment , Many people have attempted to do this kind of work with disastrous results and I really mean disastrous

Retaining rings removal inspection.
Borescope inspection under retaining rings




Rotor winding inspection by using indoscopic camera when retaining ring in place



ROTOR AREA INSPECTION



PT : Dye Penetrant Test, MT : Magnetic Particle Test, UT : Ultrasonic Test, VT : Visual Test ( damage, rust, discoloration), when retaining l in place or removal / complete rewinding. NDT Inspection on the rotor, is designed to verify any anomalies on the retaining rings, centering rings, rotor fans , journal shaft and bearings







Demagnetizing
Magnetism in Machinery, account for many machinery failures, in particular the deterioration of bearings, seals, geras, couplings and journal has been attributed to electrical currents in machinery. Often on machinery groupings contain no components with electrical windings or intended magnetism, ie. No motors, generators. Manufacturers of electrical equipment have recognized and protected against the effects of electrical shaft currents, bearing insulation has been utilized for such purposes.

There are number of ways in which steel machinery parts can become magnetized. Placing a part in a strong magnetic field can leave substantial residual magnetism. Mechanical shock and high stressing of some materials can also initiate a residual field.
Another that can creating residual magnetism is the passing of electrical current through the parts, electrical system faults nearby heavy electrical currents such as rectified supplies and lightning, electrostatic discharges, which are credited with causing bearing and seal pitting, the use of electrical welding and heaters on pipes and other parts is common and if not used properly can induce residual magnetism.

 


C.2.2 Salient Poles Rotor
Hydrogenerators and four or more pole generator have salient pole rotor windings. Each field pole is constructed separately and the rotor winding made by mounting the completed poles on the rotor rim or directly to an integral solid steel body

The magnet wire usually has a rectangular cross section, and many hundreds of turns are wound on the pole, several magnet wire layers deep. The turn insulation is the magnet wire insulation. Looking from the axial direction, the laminations are shaped to have a pole tip (which is the part of the rotor pole closest to the stator) to support the winding against the centrifugal force. Insulating washers and strips are placed between the magnet wire and the laminations to act as the ground insulation

.
Multi turn wire-wound type and strip on edge type winding




V Block – Starting bars (damper winding) Rotor Inspection


The main problems associated with salient pole winding are due to the large centrifugal forces acting upon the winding. These forces tend to distort the conductors. In addition the continuous vibration and movement of the poles as centrifugal force, tend to result in abrasion of wire and or turn insulation. V-block wedging two adjacent poles are using to keep adjacent poles distance.

Visual inspection should search for coil deformation for insulation dust indicating excessive movement between layers (not enough pressure), for broken or cracked collars (washer).
Salient pole machine are frequently fitted with a starting winding. This can take the form of squirrel cage winding occupying the entire circumference of the rotor or, as with most large machines, the starting winding is restricted to the pole regions. At the poles the cage bars are embedded in the face of the pole . these bars which are short-circuited at the ends, function like as induction machines squirrel cage during start up operation, allowing machine to start from zero speed and go up nearly to full speed, without the need variable frequency drives. In addition the bars provide electrical damping to oscillation during the synchronous operation of the machine.

Starting (amortissuer) winding is designed in accordance with the chosen mode of starting. For example: some machine are designed to start at reduced voltage, while order the start at full voltage, operator error such as higher then designed voltage starting , starting too often, prolonged asynchronous operation and other abnormal conditions, can result in overstressing of the starting winding.
The shortcircuiting ring on one side of the cage broke loose from the bars, completely destroying the entire end winding on that side of the stator winding.
Visual inspection is very effective in this case to assess the conditions of the damper bars. Discoloration and / or deformation at test to abnormal operation. The bars should be checked for the crack or breaks. In some cases removal of the paint in the region of the junction between the short bars and the short rings allow for more effective visual inspection. If hairline cracks are suspected, non destructive (NDT) with penetrating dye ink should be performed.


Insulation between turn 
The salient pole DC field winding come in essentially two distinctive designs, the strip on edge type and the wire wound type.
The strip on edge type , encounter mainly in large hydro generator and relatively high peripheral speed machine, is made out of layers of copper strip joined at the corner or bent to form a multilayer coil around the pole.
The ground insulation is located between the coil and the side, top and bottom of the pole. In older machine the insulation is made of mica , asbestos and fish paper bonded with shellac or order organic materials, inrecently manufactured machine asbestos insulation has been eliminated from the list of allowed insulation materials. The coils is insulated from the top and bottom of the pole with insulation materials having high mechanical compression qualities, at the past is mainly asbestos board, nowdays they are made of materials other than asbestos with similar electrical and mechanical qualities.




Bull-Ring Segment and Bracing to Starting Bars

Bull ring segments or short circuiting rings, are the electrically active elements to which the starting bars are forced at both ends of the machine.
As explained previously for the bars, the short circuiting segment s should be inspected for crack and overheating, in particularly the junction of the rings and the bars should be closely inspected , this region most prone to failure in the starting winding.










D. TESTING

D.1 STATOR

1. Insulation Resistance and Polarization Index

The Insulation Resistance test is purpose for this test is the measurement of the ohmic value between the conductors and the iron core [normally grounded]. The measurement in the Mega Ohm region after the winding is subjected to a DC voltage for 60 second. The insulation resistance test is refer to IEEE transaction No. 43 – 2000 standard.

Voltage test applied:
DC test voltage applied for Stator winding is 1000 - 5000 volt dc depend on the winding voltage
DC test voltage applied for Rotor winding is 500 volt dc

Polarization Index [PI ] test is purpose, to evaluate how clean and dry a winding is. The Polarization Index [PI] is the ratio between the resistance reading at 10 minutes and the reading 1 minute. Winding with the low PI are usually relate to moisture and / or dirt contamination. The recommended minimum PI values with refer to EPRI EL – 5036, or IEEE 43 -2000 are:
- Class A insulation : 1.5
- Class B insulation : 2,0
- Class F insulation : 2,0
* EPRI : Electric Power Research Institute

2. Winding Resistance

During this test, the measurement of the ohmic value between terminals winding is carried out. Given the relatively low series dc resistance of winding.
The purpose of this test is to detect shorted turns, bad connections, wrong connection and open circuit. Acceptable test result consist of three resistance value each phase to be balanced in
The resistance should be corrected to temperature:




When the resistance, Rt2 : of a winding has been determined by test at winding temperature,
t1 : the resistance may be corrected to a specified temperature,
t2 : the temperature test of winding
k : is 234.5 for 100% IACS conductivity copper, or 225 for aluminum, based on a volume conductivity of 62% 
3. Hi Pot (its destructive test, NOT RECOMMENDED FOR MAINTENANCE TEST)

High Potential Testing
A high potential test is a pass/fail dielectric examination of the winding insulation system. A high potential test can be performed utilizing either AC or DC test equipment. Both types of tests have their very own specific characteristics, benefits (both positive and negative), and results

4. EL CID ( Electromagnetic Core Imperfection Detection)
Electromagnetic Core Imperfection Detection (EL CID) is used to check the integrity of inter-lamination insulation for stator cores of generators and motors. A fault current occurring within the laminated stator core results in a hot spot and can cause a catastrophic failure of a generator and motor in service. An EL CID test can :

• detect faults and defects in the stator core;
• check effectiveness of core repairs;
• test the stator core before and after a stator rewind to check any damages caused by rewind;
• check the quality of a new stator core;
• trend the stator core condition.

In comparison with a traditional loop (ring flux) test, an EL CID test offers the following
benefits:

• Uses a portable excitation transformer instead of a large excitation transformer in a loop test to considerably reduce test cost;
• Saves 30% of test time and labor cost of a loop test.
• Conducts low power testing (EL CID uses only 4% of the rated magnetic flux) to avoid further damage to fault areas;
• Does not have safety concerns to test personnel;
• Records test data by a computer for trending of test results.
• Provides an easy and in-expensive test method to check the quality of a core repair or a re-wedging operation.




video


Video: ELCID Test on GE 49 MVA


5. Insulation Dissipation Power Factor and Tip Up

Theory


Power factor testing of rotating machinery is a non-destructive AC test performed off-line at apparatus frequency. When a 50 Hz voltage is impressed across generator stator insulation, the total current that flows is similar to that of any capacitor. The total current has two components: a relatively large capacitive current (ic) which leads the voltage by 90°; and a smaller resistive current (ir) which is in-phase with the voltage. The dielectric of this simulated capacitor is the insulation system which is embedded between two electrodes, the high voltage copper conductors and the stator iron core.

Definition of dielectric variable
Total charging current tan ∂ = ir / ic
The power factor is the Cos Ø = ir / it





The leakage current IL through the insulation stator winding consist of capacitance current a loss current as describe on figure.

On the other hand capacitance “C” is filled up the gas to make energy loss in capacitive is negligible.

Power factor Tip-up is defined as the power factor measured at the line-ground voltage minus the low voltage power factor (typically performed at 100% and 20% of the line-ground voltage). Since all dry type insulation systems contain voids, the power factor will increase with an increase in test voltage

Power factor is a dimensionless quantity and thus can be compared amongst different volumes of insulation systems. It is a measure of the dielectric losses of the insulation and provides valuable information about the insulation quality. Power factor is performed per phase at incremental voltages starting at a voltage below corona inception and continuing up to the line-ground voltage rating of the machine and possibly 20% over.

Tan Delta Test Circuit



 
 
The increases in power-factor as a function of voltage are due to the ionization of the gas in the voids of the insulation system. An insulation system with excessive voids will have a higher power factor tip-up.

Excessive voids may be due to the aging of the paper tape or of the bonding material in the insulation system. Aging of these materials leads to a reduction of physical strength, and thus the production of voids. Once excessive voids are present, partial discharge will occur which also damages the bonding materials. The degradation of the insulation system may occur internally or on the surface of the coil/bar, due to loose coils within the slot, deterioration of the semicond grading paint and/or inadequate coil spacing .











video

Video: Tangent Delta Test on 10MW / 10KV Toshiba Motor


6. Partial Discharge

A problem common to machines with thermoplastic insulation is that the normal thermal cycling is causes coil movement in the slot, tend to generate crack within the ground wall insulation.
A tape separation is a separation of tape covering the wall insulation of the coil due to axial expansion and contraction of the conductors and the opposing forces of the slot applied to the wall insulation.

In some cases only the armor tape is separated, in other cases the mica-tape comprising the ground-wall insulation is also affected , when this occur a few layer may be affected and the whole tape will move creating “ a neck” in the coil.

Corona activity
Corona is define as the ionization of gas when exposed to an intense electric field , the discharge have a wide range of frequencies [ 40 kHz to 100 MHz ].
Partial Discharge (PD) in the large generator application, is usually associated with the high voltage stator conductor bars.
Off Line Partial Discharge
Partial discharges are a symptom and sometimes a cause of many types of stator winding insulation system deterioration mechanisms. off line / on line PD measurement has been able to determine if the electrical insulation is deteriorating due to loose coils in the slots resulting in insulation abrasion; thermal deterioration or load cycling leading to insulation delamination; and electrical tracking caused by partly conductive contamination of the endwindings .

Corona probe measurements
Corona probe testing can pinpoint partial discharge location in each slot. It supplements on-line/off-line partial discharge tests by precisely locating partial discharge to a particular coil or a spot. The corona probe can also be used as a testing tool to measure levels of PD activity. Corona probe testing can be performed either with the rotor in or out of the machine.

Test method




PD probe tests performed on the generator to identify the bad bars. The probe scanned each slot to pinpoint partial discharge locations in each slot. An HV transformer used to apply Un/√3 kV to each phase of the generator. While one phase was energized with the other two phases grounded, the probe scanned only these slots in the energized phase.

The PD levels in mA is the representative of corona activities in the winding normally there is a concern over 20 mA, slot discharge can also develop surface discharge if the air gap of coil to slot is big enough. Surface discharge can produce excessive heat to cause further thermal damages to the semi-conductive coating and the fillers.
Loose wedge also caused movement of the bars in the slots and abraded away the semi-conductive coating, therefore resulting in slot discharges and surface discharges which can lean to insulation failures.

video

Video : Off line PD test ALSTOM 87 MVA / 11 kV

Corona activity in the rotating machine

- Surface discharge due to Corona at end winding ( End-winding Discharge )
- Internal discharge due to Corona at inside of the insulation ( voids or delamination)
- Slot discharge Corona at ground-wall insulation resulting from loss contact between bar and core. (damaged on the semiconductive coating on the stator bar)
- Surface discharge due to Corona at overhang of winding resulting from bar vibration



Partial Discharge (PD) that produced on the stator winding due to coil vibration and semiconductive failure can be repaired with repairing semiconductive coating on the stator bar and re coating also re bending at end winding portion.
Repair semiconductive coating on the stator bar can performed by injection systems with stator wedge removal.
Following are illustration of winding structure and semiconductive injection on the stator bar.







7. Frequency Mapping

Premature winding failure may occur due to excessive end winding vibration. Large turbine generators and hydro generators are most susceptible. Routine measurement of vibration amplitude and frequency is important in detecting looseness, which can lead to fatigue and failure of copper conductors and insulation systems.











8. Contact coefficient

Loose contact between semiconductive to core normally ground can produced high resistivity in the corona protection winding. Contact restivity of corona suppression can be measured through end winding beyond the stator core and vent holes of stator core or direct contact winding to core. with 0r without stator wedge removal




D.2 ROTOR AND EXCITER

1. Insulation Resistance and Polarization Index
See explanation D1.1 as mentioned above

2. Winding Resistance
See explanation D.1.2 as mentioned above

3. Turn to turn short Test

Theory:
Shorted turn in the rotor winding are associated with turn shorts on the copper winding as opposed to turn to ground faults. Rotor winding shorted turns or inter turn –turn shorts can occur from an electrical break down of the inter turn insulation , mechanical damaged to the inter turn insulation allowing adjacent turn to turn contact or contamination in the slot which allows leakage current between turn.
When the shorted turn occur, the total ampere-turns produced by the rotor are reduced, since the effective number of turns are reduced by the number of turn shorted. The result is an increase in the required field current in the rotor to maintain the same load point and an increase in rotor winding temperature.
At the location of the short, there is also a high probability of localized heating of the copper winding and arcing damage to the insulation between the turns. This type of damage can propagate and worsen the fault such that more turns are affected or the ground-wall insulation becomes damaged and a rotor winding ground occurs.
Although shorted turn maybe exist in a rotor, in many cases the rotor will still run with out significant effect on the operation of the generator. In addition short can occur anywhere in the rotor winding, but they often found In the end winding under the retaining rings


Test Type:

1.AC Impedance,

This test is designed to determined the existences of shorted turn in the DC excitation field winding. In round rotor, the individual windings are for all practical purpose inaccessible, unless the retaining rings are removed,
The Generator Field AC Impedance Test is performed on Field to determine the winding impedance at various voltage. Under some circumstances it is possible to detect the presence of shorted turn or changes in the number of shorted turn in the winding by changes in impedance at various test voltage when compared to data taken previously if available.
Gradual change of impedance by change of voltage should be not more then 10 % ,

2. RSO: (Recurrent Surge Oscillation) Test






RSO Inspection during rotor spin  without excitation at 1500 to 3000 RPM



Test function
When rotor stand still all rotor winding is mechanical force free, but during rotor spinning all of rotor winding parts was forced out by centrifugal force. Minor insulation fail ( inter turn or turn to ground short) may not identified when rotor standstill due to rotor winding insulation is free from mechanical force, this test is very sensitive to mechanical force change.
RSO is useful to identified short inter turn on the rotor winding when rotor standstill or rotor running without excitation



3. Voltage drop

Pole / Coil Drop Testing
performed off-line, preferably with retaining rings removal DC voltage is applied across the winding and voltage is read on each accessible coil and pole connection Reading are compared between coils of same location and with as new condition. Voltage can also be applied using an excitation coil coupled magnetically to the field winding coil.

Turn Drop Test

Similar to the Pole/Coil Drop test. Generally the retaining rings must be removed, However, on some direct cooled field designs, there may be sufficient access through the wedge ventilation holes to permit fully assembled testing. Data are examined for turns which show no voltage drop (change).


A. REPAIR AND IMPROVEMENTE.

1 STATOR 
1. Endwinding , support reinforcement
Coils will rub each other at 2 x f during machine in the operation, and during starting, sudden change of load (or external short-circuit) will be create large movement of the coils end, and combined with different temperature relate expansion of coils are strongly reduced coil insulation properties. The end-winding of electric machine are subject to substantial movement during sudden change load, vibration on normal operation. To minimize of end-winding movement the side coils are tied to a circular rings are commonly called : “surge-rings or support rings “..
In large machine surge-rings are normally made of steel, and the steel are covered with several layer o insulation. Te purpose of insulation on surge-rings is to minimize of a ground fault to the rings. The surge rings insulation can deteriorate due to electrostatic discharge from the coil, is appear as electrical tracking and/or burnlike marks on the insulation. See part C.1 Inspection on the stator winding explanation on previous pages.
Inspection and re enforcement on these parts is our standard procedure during major outage when rotor is removal


.


2. Stator wedge replacement and upgrade
Loose wedge can lead insulation failure on the stator winding. Each inspector have a different criteria standard requirement to rewedging, we have extensive experiences to replace or modified stator wedge from conventional method to radial springs, high pressure laminate with high flexure strength and low dissipation material NEMA G11certified is our standard product grade to upgrade the existing wedge.



Replace and upgrade material for stator wedges Toshiba Generator 250 MVA
 


Rewdeges (material improvement and design modification) for ELIN 50 MW Hydro Generator
 
3. Repair Anti corona protection on the stator winding

Semiconductivel loose contact will produced high PD activities on the slot its can lead winding insulation failure due to PD reaction. We have good knowledge and experiences to refurbish semi conductive protection on the stator winding when the winding is in place, injection semi conductive on the stator wall insulation winding is conducted during in major outage with stator wedge removal.

 
 
Semiconductive refurbishment by injection method on the stator winding ELIN Hydro Generator 50 MW / 11 kV.. The effectiveness of semiconductive can evaluate by PD probe test with winding energized.

4. Rewinding
We have extensive experiences to rewound of HV machine winding ( generators and motors), our workshop has been provided facilities and instruments as well expert engineers. The class F materials is our basically standard quality to rewound of generator winding.


18 Stator coil Alstom Generator 87.5 MVA / 11kV, being remove to rewound at workshop


High voltage test on each coil at (2xUn + 1000) x 1.4, Vac is higher than standard requirement

Partial rewind and core repair for ELIN 30 MW Hydro Generator



Total rewinding on ALSTOM Generator 30 MVA / 13000 V / 3000 RPM


 
 

E.2. ROTOR

1. Repair Endwinding
Rotor end winding is subject to mechanical forced, insulation deterioration (crack, delamination) can occur due to mechanical and thermal stress during machine in operation. repair of endwinding and blocking is possible to perform when the retaining rings are removal.

Repair endwinding and replacement of end blocking coil on Rotor GE Generator 28 MVA


 





video

Video : Rewinding Rotor GE Generator 237 MVA Part#1
 
Complete Rewinding Rotor GE 180 MW with re used copper bars

video

video: Rewinding Rotor GE Generator 237 MVA, Part#2


video

Video: Rewinding Rotor GE Generator 237 MVA, Part#3


video

Video: Rewinding GE Rotor 237 MVA -Part 4


SALIENT POLE ROTOR GENERATORS
Rewinding Rotor Slaient Poles



Repair Exciter Alstom Generator 2x30 MW, Location Malaysia













3. Balancing

Site balancing
Balancing is required to be performed since there was found changed of weight in the rotating parts, due to rotor end winding and its blocking are repaired and replaced rotor vibration can occur during machine in operation , based on those reasons re balancing should be provided.
To avoid mechanical damage during in transportation for balancing purpose, site balancing at full speed with driven by the turbine


 

Ste balancing on the Alstom 46.25 MVA / 3000 RPM
 



4. Cleaning and re varnishes
Wipe all accessible surface areas with a clean cloth, the remaining dust accumulation on the inaccessible area to be blown out by low pressure dry air or pure nitrogen gas, and the remaining dust to be removed by a clean cloth with dampened by fluid cleaner. Heavy contaminant (dust mixed oil) can be remove by using very soft plastic brush wiping carefully to the winding and vents


.


ELECTRIC MOTORS

TOTAL RESTACKING AND REWINDING VERTICAL MOTOR
2700 KW / 6000 VOLTS / 1475 RPM


Rewinding Rotor DC Motor 3200 HP and 1900 KW




Rewinding Furnace Transformer 63 KA - 20KV/220 V
Rewinding Power Transformer 60 MVA, 150 kV / 70 kV



Repair "MR" OLTC V / III / 200 / Y

video

Video : Repair "MR" OLTC V / III / 200 / Y


Repair "MR" OLTC V / I / 250

video

Video: Repair MR OLTC V / I / 700



Following is normal regular preventive maintenance on the Generator, each manufacture may have different criteria and regular time to inspection,

INSPECTION INTERVAL
V. REGULAR MAINTENANCE FOR POWER GENERATION



















1. FULL INSPECTION
Covers overhaul of generator rotor

2. MEDIUM INSPECTION
Cover inspection of internal parts with the upper half of each outer end shield dismantled

3. SMALL INSPECTION
Cover overhaul inspection of the bearing metal

Recommendation : Full inspection perform every 4 years

GENERATOR INSPECTION PARTS

1. STATOR
· STATOR WINDING
· STATOR COIL WEDGE
· STATOR CORE
· HIGH VOLTAGE BUSHING
· GLAND PACKING
· SUPPORT STRUCTURE

2. ROTOR
· ROTOR WINDING
· ROTOR COIL MAIN LEAD
· ROTOR COIL POLE TO POLE CONNECTOR
· RETAINING RINGS
· ROTOR SHAFT, WEDGE AND FAN BLADE
· COLLECTOR RING AND BRUSH HOLDER / EXCITATION

3. AUXILIARIES
· BEARING METAL AND SEAL RING
· COOLER ( HYDROGEN IF PROVIDED)
· SEAL OIL UNIT
· STATOR COOLING WATER UNIT

REGULAR PREVENTIVE MAINTENANCE ITEMS (STATOR)
REGULAR PREVENTIVE MAINTENANCE ITEMS (AUXILIARIES)




TABLE : STANDARD OVERHAUL INTERVAL OF HYDROGEN COOLED TURBINE GENERATOR


 

REGULAR PREVENTIVE MAINTENANCE ITEMS (ROTOR)



PLEASE ALSO VISIT THE OTHER PAGES BLOG:
HIGH REVERSE POWER FROM GSU POWER TRANSFORER 150 KV / 11.5 KV ON GE GENERATOR 125 MW, 11.5KV, 3000 RPM

Thank you for your visit this Power Generation Services Blog.

Siswanto
Specialist Engineer
Power Generation Services

Email :
sis_cahya@yahoo.com
siscahyabhuwana@gmail.com

Mobile phones:

+62 81 311422270