ML20235S951

Responds to NRC Bulletin 88-010, Test Program. Recommends That Temp Test Be Permitted as Alternate to Millivolt Drop/ Pole Resistance

ML20235S951
Person / Time
Site:	05000447
Issue date:	02/25/1989
From:	Heerlein W GENERAL ELECTRIC CO.
To:	Brach W Office of Nuclear Reactor Regulation
References
IEB-88-010, IEB-88-10, NUDOCS 8903080082
Download: ML20235S951 (2)

Text

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' GE Electrical Distribution; e-A

• and Control General Electnc Conwany .

{I;[ 41 Woodford Amnae P!amulle. CT 06062

' 203 747-7111 February 25, 1989 Mr. William Brach Chief, Vendor Inspection' Branch

- . Division of' Reactor Inspection and Safeguards U.S. Nuclear Regulatory Commission Washington, D.C. 20555

SUBJECT:

NRC BULLETIN 88-10: TEST PROGRAM

Dear Mr. Brach:

'We have carefully reviewed the Test Program included in Bulletin 88-10, comparing it with industry standards, factory and laboratory practices, and our own field. experience.

We would like to recommend modification of two portions of the program. ,

We feel that the present requirements will result'in apparent breaker failures that are actually due to limitations in test requirements, test equipment, and testing technique. They are as follows:

~

2.2 - Individual Pole Resistance or Millivolt Droo Both pole resistance.and millivolt drop are difficult to measure accurately and consistently. The purpose of the test is to determine the likelihood of overheating. A direct measurement of temperature at rated current is much preferred over either pole resistance'or millivolt drop measurements, and directly addresses the purpose of the test. Temperature measurements can be taken

-during the Rated Current Hold-In Test using a temperature probe at line and load. connection points.

Circuit breakers are typically designed for a maximum temperature rise of 50*C, but we are recommending a 55'C limit to allow for any inaccuracies in field measurements and test conditions. The 55'C rise at rated current will result in safe operating conditions and assure that thermal runaway will not occur.

We recommend that the temperature test be permitted as an alternate to Millivolt Drop / Pole Resistance.

If the Millivolt Drop Test is to be run, we recommend that use of alternating current equipment be permitted. AC equipment is needed for other portions of the test program and is much more commonly available than DC equipment. There is some concern that induced voltage will affect the millivolt readings if AC is used.

The leads from the millivolt meter to the breaker test points should be twisted together as far as possible to minimize any l.f/

possibility of induced voltage in the leads. g' i

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'l Mr. W. Brach -

2.- February 25, 1989 2.2 - Individual Pole Resistance or Millivolt Drop (Cont'd.)-

We request that the Bulletin be modified to permit AC millivolt ,

'7 drop measurements.  !

. I Finally, we suggest for both pole resistance and millivolt drop, i that a 2-to-1 variation among poles of a breaker be permitted, instead of the 50% now allowed in the bulletin. This.is

-consistent with our publication " Molded Case Circuit Breakers:

' Application and Selection," and the recommendations of other -

manufacturers. '

)

4 K 2.5.2 - Adiustable Instantaneous Settina Circuit Breakers These tests are conducted in the factory _and laboratory using l equipment with accurately adjustable pulse width and magnitude, l and with synchronous closing to eliminate offset currents.

1 Operator. experience and technique are extremely important in accurately determining the trip point. Trip points are determined in the factory and laboratory by technicians who run Instantaneous Trip. Tests daily.  !

Similar equipment sophistication and technician experience will .!

not be typically available for field testing. We, therefore, i l' recommend that the U/L trip current tolerances presently included l' in the test program be broadened. l NEMA AB-2 suggests broader limits in recognition of the importance.  !

L of equipment and test technique in accurately determining the trip point. We recommend that the trip tolerance be broadened to i25% '  ;

on the high setting and 30% on the low setting, in accordance l with NEMA AB-2.  ;

We will appreciate your consideration of our recommendations. We L. believe that these changes will serve the purpose of the test program and l will reduce misleading or erroneous results, i Sincerely, '

.. p i

W. J. Heerlein, Manager Production & Quality Eng.  ;

l clt  :

i (NRC88-10) l

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