Part 21 Report - 1996-540

ACCESSION #: 9609050007 GE Nuclear Energy General Electric Company 175 Cutner Avenue, San Jose, CA 95125 August 30, 1996 96-13NRC.DOC MFN 146-96 Document Control Desk United States Nuclear Regulatory Commission Washington, DC 20555 Subject: GE Type RMS-9 Overcurrent Trip Device Programmers with Instantaneous Trip Function This letter provides the results of an evaluation by GE Nuclear Energy (GE-NE) of failures reported in the Instantaneous Trip Function of GE Type RMS-9 Overcurrent Trip Device Programmers. These devices were manufactured by GE Electrical Distribution and Control, and supplied by GE-NE as Safety Related components for balance-of-plant or unspecified applications. Since the specific applications and associated safety functions of the RMS-9 Programmers are not known to GE-NE, we transferred information to the affected licensees pursuant to 10 CFR Part 21.21(b). However, since additional licensees may have purchased these devices from other dedicating entities, we cannot assure ourselves that all end-users have been notified. We are therefore providing the results of our evaluation to the NRC for appropriate action. Evaluation A domestic BWR licensee has reported to GE Nuclear Energy (GE-NE) that a number of GE Type RMS-9 Overcurrent Trip Device Programmers were failing to operate as expected. The Instantaneous Trip Function was tripping the circuit breaker at values less than the RMS-9 Programmer switch setting would have implied. The licensee sent three (3) of these RMS-9 Programmers to GE-NE for testing, evaluation, and failure analysis. Subsequent testing confirmed that the Instantaneous Pickup Switches sometimes failed to their lowest value (1.5X). At other times, changing the switch setting had no apparent effect on the RMS-9 Programmer setting. Only the Instantaneous Pickup Switch appears to be affected. GE-NE has not identified any problem with the other switches on the RMS-9 Programmers. GE-NE has determined the cause of the problem with the Instantaneous Pickup Switch to be a polyester epoxy film on the internal switch contacts. This film acts as an insulator and consequently, when the switch position is changed, the contacts are prevented from making full contact and the RMS-9 Programmer fails to its lowest Instantaneous Pickup setting (1.5X). This film is apparently the result of insufficient curing of the conformal coating (polyester epoxy) applied to the RMS-9 Programmer during final assembly. Testing has shown that some of the conformal coating ran under the switch when it was applied and was not cured because it was shadowed by the switch during the ultraviolet curing process. Over a period of time the external contacts of the switch acted as wicks and drew some of the uncured conformal coating into the switch where it then formed the film on the internal switch contacts. Since the thickness of the film on the internal contacts varies, the effect is to cause the switch to fail to it's lowest setting. At this setting the film is thick enough to act as an open circuit and to cause the switch to operate erratically. While this same action may have occurred at other switches in the RMS-9 Programmer, the higher current through the switches allowed the film to "burn off". This is why only the Instantaneous Pickup Switch is being affected. Based on the testing performed by GE-NE the film does not appear to form between the movable contacts and the stationary contacts in the switch. This means that if the switch is operating properly and is not moved from the position verified to have proper operation, the switch will continue to operate properly. The affected RMS-9 Overcurrent Trip Device Programmers were manufactured by GE Electrical Distribution and Control, and supplied by GE-NE as Safety Related components for balance-of-plant or unspecified applications. They were variously provided as spare parts or as components of either refurbished circuit breakers or new AK7/AKR7 circuit breakers. An RMS-9 Programmer with the Instantaneous Pickup Function failed to it's lowest value or at some value lower than anticipated could result in the inability to start a motor due to the starting current of the motor being above the Instantaneous Pickup setpoint of the RMS-9 Programmer. Likewise, if the Instantaneous Pickup setpoint is at some value higher than expected, it is possible that a circuit fault could result in the circuit breaker not tripping in accordance with the selective tripping scheme of the power system. This could result in losing significant portions of the power system due to the circuit breaker failing to trip when expected and thus forcing upstream circuit breakers to isolate a fault. GE-NE recommends that as the final step in any procedure requiring the repositioning of the Instantaneous Pickup Switch, the proper operation of the Instantaneous Trip Function be verified by testing. This testing may be performed by Primary Current Injection or by using the GE TVRMS Test Set to verify the "electronic" position of the Instantaneous Pickup Switch. This recommendation is based on the evidence that a properly operating switch will continue to operate properly unless and until the switch position is changed such that the film (if present) comes into play. 2 If you have any questions, please call me at (408) 925-1019. Sincerely, Michael A. Smith, Manager Safety Evaluations Project cc: G. C. Cwalina (NRC-NRR/DOTS/TSIB) J. M. Austin (GE-NE) C. R. Flanigan (GE-NE) D. Fletcher (GE ED&C/Plainville) H. J. Neems (GE-NE) N. C. Shirley (GE-NE) PRC File 3 *** END OF DOCUMENT ***

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