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Information Notice No. 84-84: Deficiencies in Ferro-Resonant Transformers
SSINS No.: 6835 IN 84-84 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555 November 27, 1984 Information Notice No. 84-84: DEFICIENCIES IN FERRO-RESONANT TRANSFORMERS Addressees: All nuclear power reactor facilities holding an operating license (OL) or a construction permit (CP). Purpose: This information notice is provided as a notification of two potentially significant deficiencies pertaining to ferro-resonant transformers manufactured by General Electric Company (GE). Such transformers have been used by Westinghouse Electric Corporation (Westinghouse) as integral components of vital 7.5 kVA inverters. In addition, similar deficiencies may exist on 30 and 45 kVA inverters utilizing similar but larger ferro-resonant transformers. Westinghouse has provided such inverters to several utilities for non-safety related applications such as supplying power to computers. It is expected that recipients will review the information for applicability to their facilities and consider actions, if appropriate, to preclude similar problems 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: The subject ferro-resonant transformers produce a simulated ac signal from either an ac or dc source; the inverters provide instrumentation power to both protection and control systems of nuclear power facilities. Westinghouse recently informed the Nuclear Regulatory Commission (NRC) of two deficiencies involving the subject ferro-resonant transformers. In addition, Westinghouse identified its utility customers known to have received inverters with suspect transformers and stated that these customers had been informed of the issue. Westinghouse also stated that it was possible that other utilities could be affected by these issues; therefore, this notice is being issued to ensure that all affected utilities are aware of the potential deficiencies. First Deficiency: By letter dated September 14, 1984, Westinghouse informed the NRC of the first of two deficiencies involving the subject ferro-resonant transformers. This deficiency was discovered by Westinghouse during its long-term aging program, and reportedly occurred at the manufacturer's plant in 1977, at which time . IN 84-84 November 27, 1984 Page 2 of 3 the capacitor terminals had been changed from "ring-tongue" to "fast-on" terminal connections. It is our understanding that GE made these changes concurrent with changing the capacitors from a polychlorinated biphenyl (PCB) design to a non-PCB design. Since all capacitors may not have been changed to a non-PCB design, this notice also informs the addressees that their facilities may be using ferro-resonant transformers with capacitors containing PCB. Westinghouse described its concern with the capacitor fast-on terminations in its September 14, 1984, letter as follows: Each capacitor terminal has three connection points--two fast-on lugs and one solder lug. The capacitor wire terminations are fast-on style as well. For the two transformers in the Westinghouse test program, some wire terminations had incorrectly been forced on the solder lugs. Were this connection to fall off due to a seismic event, the most severe consequence would be a detuning of the transformer, increased harmonic distortion and reduced output (from 118 volts to as low as 60 volts). This decreased voltage could both increase the error of instrumentation powered by this inverter and could potentially cause an indeterminant number of relays in both the protection and control systems to drop out due to the reduced voltage. Westinghouse issued a technical bulletin (Attachment 1) to facilities potentially having capacitors with incorrect terminations. This attachment describes the potential problem and provides instructions for proper connection of the capacitors. However, because facilities other than those listed may be using inverters with suspect ferro-resonant transformers, a copy of the Westinghouse technical bulletin is attached, thereby assuring that affected plants are aware of the deficiency and Westinghouse's recommendations. Second Deficiency: By letter dated September 26, 1984, Westinghouse informed the NRC of the second deficiency involving the subject ferro-resonant transformers. Westinghouse was informed of this deficiency by Comanche Peak where three separate transformers failed shortly after they were initially electrically loaded. The failed units were returned to the manufacturer, GE, for evaluation. The determination made by GE was that the affected transformer reactors were inadequately secured, thereby allowing the center leg to shift and vibrate while energized. The vibration, in turn, caused an insulation breakdown. The Westinghouse letter of September 26 indicates that if a transformer were to short to ground, the inverter would continue to try to supply the load resulting in a collapsing output voltage (e.g., 60-65 volts was noted at Comanche Peak). GE has determined that if the transformer has been under load for six months, the magnetic forces applied would have caused a failure if the manufacturing defect were initially present. . IN 84-84 November 27, 1984 Page 3 of 3 Westinghouse has issued a technical bulletin (Attachment 2) to facilities potentially having transformers with loose reactor legs. This attachment describes the potential problem and provides recommended corrective actions for the suspected defect. However, because facilities other than those listed in Attachment 2 may be using inverters with the above described defects, a copy of the Westinghouse technical bulletin is attached, thereby ensuring that affected plants are aware of the deficiency and Westinghouse's recommendations. No specific action or written response is required by this information notice; however, if you have any question regarding this notice, please contact the Regional Administrator of the appropriate NRC Regional Office or the technical contact listed below. Edward L. Jordan, Director Division of Emergency Preparedness and Engineering Response Office of Inspection and Enforcement Technical Contact: I. Villalva, IE (301) 492-9006 Attachments: 1. Westinghouse Technical Bulletin No. NSD-TB-84-08 2. Westinghouse Technical Bulletin No. NSID-TB-84-11 3. List of Recently Issued IE Information Notices
Page Last Reviewed/Updated Friday, May 22, 2015
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