Generator Stator Rewind - A Case Study

Generator Stator Rewind A Case Study W. Howard Moudy Director of Service Management National Electric Coil hmoudy@national‐electric‐coil.com 724‐787‐4967 www.National‐Electric‐Coil.com

ARIPPA Technical Symposium Hershey, PA 8/20/2014

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Unit Information • General Electric • Rating 204,000 KVA; 18,000 volts 3600 RPM; 3 Ph; 60 Cy • Stator Amperage 6543 • Power Factor 0.85 • Hydrogen Pressure 30 psig • Number of Slots 60 straight slots • Commissioned 2005 2

Background Information • Inspected in April, 2007 – stator coils unsuitable for extended service. – extensive looseness and deterioration of the stator coil insulation. – End Windings, Phase Rings, & Phase Leads exhibited severe Dusting and other indications of looseness / movement 3

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Generator Stator Rewind - A Case Study

As Found Dusting

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Original Design

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Rewind Considerations Newer vs. Older Newer Vintage • Rewind Cause – normally one or a combination of: – Design concern – Material concern – Operational concern

• What is the root cause? – Specific – not a symptom – How can it best be corrected

• How can long-term reliable life best be achieved?

Older Vintage • Rewind Cause – normally age deterioration of components. Possibly machine characteristic change to support system needs. • Were there any major technical deficiencies in the machine? • Is an Up-Rate desirable? • Incorporation of new materials and technologies 6

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Generator Stator Rewind - A Case Study

Redesign

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Redesign End Winding Modifications • Added end winding support brackets to CE – increased from 12 to 15 • Added 15 end winding support brackets to TE • Radial tightening studs clamping bus ring to braces • Solid phase leads replaced with stranded • Tapered series blocking • Nose ring 8

Rewind Pictorial

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Generator Stator Rewind - A Case Study

Rotor Removed ElCid Testing Being Performed

4-11-2012 10

Preparation For Top Bar Removal

4-12-2012

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Removal of Top Bars

4-13-2012

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Generator Stator Rewind - A Case Study

Coils Removed

CE

TE

4-15-2012

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Buss Ring Removal & Shipping

4-15-2012

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Coil Staging For Rewind

4-18-2012

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Generator Stator Rewind - A Case Study

Installing Coils For Series Connection Lineup

4-18-2012

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Drilling, Tapping & Installing New TE Coil Support Brackets

4-19-2012 17

Installing Coils, Blocking, & Intermediate Rings

5-3-2012 18

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Generator Stator Rewind - A Case Study

Temporary Alignment Clip & Side Packing 5-3-2012

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Improved OCP & Side Ripple

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Krempel semi-conductive side ripple springs – – –

Proven track record Resistance to steady state pounding forces Maintains sideways load on coil and continuous contact with core iron

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Hi-Pot Testing 69 KVDC

5-4-2012 21

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Generator Stator Rewind - A Case Study

Series Connection Brazing 5-4-2012

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Series Connection Brazing 5-5-2012

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Installing Slot Wedges 5/ 5-7/2012

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Generator Stator Rewind - A Case Study

RTD Cabling Permanently Installed

5-6-2012 25

Windings Under Wedge DC Hi-Pot Test

5-7-2012 26

TE Brazing Complete Ready for Nose Ring and Caps (Note New Coil Support Brackets)

5-7-2012 27

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Generator Stator Rewind - A Case Study

CE Brazing Complete Nose Ring Being Installed

5-7-2012 28

Installing Buss Rings 5-8-2012

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Flux Probe Installed On CE

5-8-2012 30

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Generator Stator Rewind - A Case Study

Series Connection Cap Installation 5-8-2012

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Buss Rings Blocked & Tied

5-9-2012 32

TE Series Caps, Nose Ring, & Blocking Complete

5-9-2012 33

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Generator Stator Rewind - A Case Study

Phase Lead Connections 5/10-11/2012

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Original

Insulating Phase Connections 5-11-2012

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Bushings After Insulating

5-11-2012 36

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Generator Stator Rewind - A Case Study

Phase Ring Clamping Assembly Glass Stud Locked with Tie Cord after Torqued to 50 ft-lbs

5-11-2012 37

Heating and Curing Complete

TE 5-12-2012 38

Connecting RTD’s To Terminal Board

5-12-2012 39

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Generator Stator Rewind - A Case Study

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Vibration sensors at 10:00 position

5-13-2012

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CE after curing and painting bore

5-14-2012

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Set Up For Final Hi-Pot Test AC Hi-Pot test at 2E+1KV times the line voltage, 37,000 Volts AC, 60 Hz. per IEEE 43 or D.C. equivalent

5-15-2012 41

Frequency Response Test – Bump Test Insure installed components are not subject to resonant vibration • Bump test on the stator end winding support system • Bump test on the parallel ring support assembly

5-15-2012

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Generator Stator Rewind - A Case Study

Paint Dry - Ready To Assemble Final Visual Examination (crawl through) Complete

5-16-2012

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Conclusions • All generator rewinds are challenging. • Advanced planning starting with insight from an effective maintenance program is one important element for success. • Understanding and designing around the root cause for the rewind, is critical to insure long term reliable operation.

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Questions ?

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