Information Notice No. 86-26: Potential Problems in Generators Manufactured by Electrical Products Incorporated
SSINS No: 6835
IN 86-26
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, DC 20555
April 17, 1986
INFORMATION NOTICE NO 86-26: POTENTIAL PROBLEMS IN GENERATORS
MANUFACTURED BY ELECTRICAL PRODUCTS
INCORPORATED
Addressees:
All nuclear power reactor facilities holding an operating license (OL) or a
construction permit (CP)
Purpose:
This notice is to alert recipients to a potentially significant problem
involving the failure of Electrical Products Incorporated (EPI) diesel
generators without prior warning during an emergency demand Actions taken
by licensees to prevent recurrence also are discussed It is expected that
recipients will review this information for applicability to their
facilities and consider actions, if appropriate, to preclude a similar
problem occurring at their facilities However, suggestions contained in
this information notice do not constitute NRC requirements; therefore, no
specific action or written response is required
Description of Circumstances:
Washington Public Power Supply System (WPPSS) Unit 2
On July 21, 1983, emergency diesel generator (DG) 1A had high vibration
level readings accompanied by sparks from the rotor shaft bearing area Upon
disassembly it was determined that a shim, required to maintain clearance at
the thrust bearing, was missing Inspection of DG 1B showed that the same
shim was missing The two generators were returned to EPI (Cleveland, Ohio)
where the missing shim was installed and the damaged areas refurbished The
original design, which placed electrical insulation between the rotor shaft
and the slip-ring end bearing inner race, was maintained
On July 9, 1984, during monthly surveillance testing, a high vibration alarm
was observed on emergency DG 1B Investigation after completion of the
4-hour test revealed that the slip-ring end bearing had turned on the shaft
insulation destroying the insulation The reduction in insulation cross
sectional thickness allowed the rotor shaft to drop slightly and rub on the
bearing housing The corrective action employed after this failure was a
design modification The insulation between the bearing and the shaft was
removed and the bearing was mounted directly on the shaft The bearing
housing was insulated to provide the required electrical insulation No
failure has been reported since the reported test failure in July 1984
8604150542
IN 86-26
April 17, 1986
Page 2 of 3
Grand Gulf Unit 1
At Grand Gulf Unit 1, the high pressure core spray pump is powered by a
dedicated DG On July 13, 1985, during surveillance testing, the generator
failed and was observed to be emitting sparks Power Systems Division (PSD)
of Morrison Knudsen, the supplier of the DG unit, determined that the
electrical insulation between the inner race of the cylindrical roller
bearing at the slip-ring end and the rotor shaft had degraded The
degradation allowed the shaft to drop down and rub the inner and outer oil
seals causing the sparks EPI and PSD have developed a procedure to
implement the same design modification at Grand Gulf as used previously at
WPPSS
Watts Bar Unit 2
On June 10, 1983, during the performance of a test, the generator shaft was
observed to be rubbing against the inner and outer oil seals at the
slip-ring end Examination after disassembly revealed that the thickness of
the oil thrower was less than specified, causing a mismatch between the
inner and outer races of the slip-ring end bearing that resulted in the
inner race breaking loose and turning on the underlying electrical
insulation
The repairs at a Tennessee Valley Authority (TVA) workshop consisted of
rebuilding oil seals, polishing the shaft under the oil seals, replacing the
insulation material under the bearing, machining the bearing housing cap to
correct the alignment, adding a shim to restrain the outer race, and
installing new bearings TVA inspected four other generators and made
similar modifications
Background:
The failures occurred in electrical generators manufactured at EPI located
in Cleveland, Ohio EPI was a division of Portec from 1969-1979 In 1979,
Portec sold EPI to Northern Electrical Industries-Parsons Peebles
(NEI-Peebles) of Great Britain The manufacturing operations at Cleveland
ceased in the Fall of 1984 Currently, EPI furnishes spare parts and
modifications to existing units
Discussion:
The failures described above have all occurred at the slip-ring end of the
tandem diesel engine configurations Installation of the insulation between
the rotor shaft and the bearing also is used for single engine applications
and in some cases it is installed under the shaft bearing at the other end
of the generator as well The purpose of the insulation (3M Scotchply brand,
type 1009, glass/epoxy composite tape) is to prevent circulating currents
through the generator shaft This insulation method was limited by EPI to
8-pole 900-rpm machines The initiating failure mechanism of the insulation
has been attributed by various sources to insulation creep fatigue,
misalignment of the engines, poor insulation workmanship, or inadequate
original design The first WPPSS and the Watts Bar failures appear to be
isolated cases of improperly machined pieces; however, the failures manifest
themselves in a similar manner and may be discovered during the checks for
insulation damage
IN 86-26
April 17, 1986
Page 3 of 3
PSD has stated that a procedure to monitor shaft movement will have to be
specific for each plant because of design differences that impact the
allowable movement and the jacking force Jacking the shaft up and down and
recording the movement will determine the vertical play between the shaft
and bearing housing, but care should be taken to use a load cell or circle
force gauge between the jack and the generator shaft to prevent damage
Other suppliers that have used EPI generators include Stewart & Stevenson,
Alco and Bruce GM (EMD) See Attachment 1 for a list of facilities
identified by EPI and PSD as recipients of the subject generators Some of
the generators have been resold from the original customer or user and some
have been cancelled; therefore specific plant applications may be different
than originally supplied
No specific action or written response is required by this notice If you
have any questions regarding this notice, please contact the Regional
Administrator of the appropriate NRC regional office or this office
Edward L Jordan Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact: James C Stewart, IE
(301) 492-9061
K R Naidu, IE
(301) 492-4179
Attachments:
1 List of EPI 900 RPM Generators
2 List of Recently Issued IE Information Notices
Attachment 1
IN 86-26
April 17, 1986
Page 1 of 1
Domestic EPI 900 RPM Generators
Customer/Site No Units D/G Supplier
Arkansas P&L/Nuclear 1 2 Stewart & Stevenson
Boston Edison/Pilgrim 1 2 ALCO
Duke Power/Oconee 1 PSD
Florida P&L/St Lucie 2 PSD
Houston L&P/Allens Creek 1 (See Note 1) PSD
Jersey Central P&L/Oyster Creek 2 (See Note 1) PSD
Mississippi P&L/Grand Gulf 2 PSD
Mississippi P&L/Grand Gulf 2 Bruce GM (EMD)
New York State Power 4 Bruce GM (EMD)
Authority/FitzPatrick
Pacific G&E/Diablo Canyon 5 ALCO
Portland G&E/Trojan 2 PSD
Public Service of Oklahoma/Black Fox 2 (See Note 3) PSD
Puget Sound/Skaggit 1 PSD
SMUD/Rancho Seco 2 Bruce GM (EMD)
TVA/Hartsville, Phipps Bend 6 (See Note 4) PSD
TVA/Sequayah 4 Bruce GM (EMD)
TVA/Sequayah 1 PSD
TVA/Watts Bar 6 PSD
Vepco/North Anna 4 Stewart & Stevenson
WPPSS/Hanford 2 Stewart & Stevenson
Notes: 1 Generator returned to PSD
2 Obtained from TVA
3 One unit sent to foreign plant, one unit spare
4 Two units to Oyster Creek, three units sent to foreign
plants, one unit sent to NASA
Page Last Reviewed/Updated Friday, May 22, 2015