Information Notice No. NO: 85-49: Relay Calibration Problem
SSINS NO.: 6835
IN 85-49
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
July 1, 1985
Information Notice No. NO: 85-49: RELAY CALIBRATION PROBLEM
Addressees:
All nuclear power reactor facilities holding an operating license (OL) or a
construction permit (CP).
Purpose:
This information notice provides information on a potentially significant
problem pertaining to relay orientation during calibration and operation. It
is expected that recipients will review the 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.
Discussion:
South Carolina Electric and Gas Company, at the Summer nuclear power plant,
recently discovered that there was a significant error in the calibration of
several E-7000 series Agastat time-delay relays. The licensee's procedure
for replacement of Agastat timing relays did not require calibration of
these relays in the installed position. During relay replacement, these
time-delay relays were "bench" calibrated in a horizontal position, then
field mounted in a vertical orientation. Subsequent time-delay measurements
determined that the delay times of the installed devices were as much as 30%
greater than that established during "bench" calibration.
Licensee investigation of this anomaly determined that the manufacturer's
data sheet for installation and operation of these relays identifies a
potential for the observed calibration error. This data sheet states that a
dial calibration error may result if the device is mounted horizontally
without the manufacturer's supplied horizontal operation options. Because
these relays were mounted vertically at this facility, the potential for
error as a result of horizontal "bench" calibration was overlooked. Because
of this oversight, the licensee's relay replacement procedure did not
specify device orientation during calibration. Several of these relays were
functionally arrayed (sequentially or in parallel) in safety-related
applications, such as in the emergency diesel generator undervoltage start
circuitry. The above identified time-delay error went undetected for a
period of approximately 4 months for some of these relays. This occurred
because the licensee's replacement procedure specified only an operational
or functional postmaintenance test of the system containing the relays. This
method of testing did not detect the individual relay time-delay calibration
errors.
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IN 85-49
July 1, 1985
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The licensee has subsequently revised their relay calibration procedures to
calibrate or check the calibration of relays after mounting in place, where
practical. The procedures were also revised to ensure "bench" calibrations
are performed in the same orientation as mounted, where applicable.
Personnel involved in relay calibration have received training on the
revised procedures.
No specific action or written response is required by this information
notice. If you have any questions about this matter, 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: H. Bailey, IE
(301) 492-9006
Attachment: List of Recently Issued IE Information Notices
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