Information Notice 1995-05, Undervoltage Protection Relay Settings Out of Tolerance Due to Test Equipment Harmonics

Undervoltage Protection Relay Settings Out of Tolerance Due to Test Equipment Harmonics

ML031060397
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant, Crane
Issue date:	01/20/1985
From:	Grimes B Office of Nuclear Reactor Regulation
To:
References
IN-95-005, NUDOCS 9501120037
Download: ML031060397 (8)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C.

20555

January 20, 1995

NRC INFORMATION NOTICE 95-05: UNDERVOLTAGE PROTECTION RELAY SETTINGS OUT OF

Addressees

All holders of operating licenses or construction permits for nuclear power

reactors.

PurDose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information

notice to alert addressees that undervoltage relay settings could be out of

tolerance because of test equipment harmonics. It is expected that recipients

will review the information for applicability to their facilities and consider

actions, as appropriate, to avoid similar problems. However, suggestions

contained in this information notice are not NRC requirements; therefore, no

specific action or written response is required.

Description of Circumstances

The following occurrences indicate that test equipment harmonics could result

in undervoltage relay actuation settings that are out of tolerance.

Dresden Nuclear Power Station

On April 11,

1994, during routine calibration of the Dresden Unit 3 Asea Brown

Boveri (ABB) Model ITE 27N undervoltage relays, both relays were found to be

out of tolerance. Additional testing of the 27N relay showed that the relay

operating point was influenced by the polarity of the lead wires from the

voltage test source (power supply) producing the sinusoidal voltage signal.

The test source was diagnosed and verified, using an oscilloscope, as having a

distortion on the positive side of the single-phase 120-Vac sine wave.

In

addition, further evaluation showed that the Unit 2 degraded voltage relays

had also been calibrated using the same power supply in October 1992 and

April 1993.

The Dresden 27N relays were originally equipped with a harmonic filter and

time delay circuit. However, in 1992, ABB notified the NRC, pursuant to

Part 21 of Title 10 of the Code of Federal Regulations, that the relay time

delay circuit could fail to initiate the appropriate time delay when exposed

to radiation levels between 22.5 and 45 Gray (Gy) (2.25E03 and 4.5E03 rad). In

addition, ABB indicated that the harmonic filter option could cause the

pickup/dropout operating points to shift high at radiation levels above those

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9501120037 I (f

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IN 95-05 January 20, 1995 affecting the time delay, but below 630 Gy (6.3E04 rad). In response to the

notification, the licensee modified the 27N relays in accordance with the

instructions of the manufacturer to remove the harmonic filter and time delay

components. The licensee is now replacing the 27N relays with 27N-R relays

for second-level undervoltage protection. The 27N-R relay is equipped with

radiation-resistant harmonic filter and time delay circuitry.

Before this event, the voltage test source was classified as a 'general usage"

piece of test equipment; its electrical output characteristics, therefore, were not periodically verified. After this event, as a corrective action, the

licensee added the ac voltage test source to a general surveillance program.

The test source output characteristics are now verified annually to meet

manufacturer specifications. In addition the licensee is performing a review

of electrical and electronic measuring and testing equipment for both

certified and general usage to determine if other vulnerabilities exist.

Comanche Peak Steam Electric Station

On May 23, 1994, Comanche Peak Unit 2, was in Mode 5 during its mid-cycle

outage. During the performance of the Train A undervoltage relay calibration

and response time surveillance testing, 14 of 16 relays were found to be

outside their respective allowable technical specification values. The relay

dropouts were found to be 1 to 3 V outside the expected values. These relays

were adjusted to correct setting values.

Following this discovery and

corrective action, the licensee performed a comprehensive root cause

evaluation. This evaluation showed that the testing device used to calibrate

the undervoltage relays did not provide accurate as-found data, because of

harmonic distortion that affected peak values of the ac testing voltage

waveform. From May 26 to May 28, 1994, the licensee reverified both Train A

and Train B relay actuation settings using a clean (low harmonic distortion)

ac power supply. On May 28, 1994, during the reverification process, it

appeared that five of the Train A relays, Types ITE-27N and ITE-27H, were

outside the technical specification values using the most conservative data.

To preclude recurrence, the corrective action taken by the licensee was to

implement a procedural change to require the use of a power source with low

harmonic distortion for testing these types of relays.

Point Beach Nuclear Plant

In February 1994, the Point Beach licensee replaced the installed Type 27D

degraded voltage relays with Type 27N. The 27N relays were more accurate and

had an adjustable reset. These relays were recently recalibrated, and all 12 were found to have "drifted' approximately 0.5 V high (120-V base). Although

the drift did not exceed calibration tolerances, the licensee had not

previously experienced similar calibration shifts for the 27D relays. A

further investigation by the licensee showed that the calibration shift was

attributed to harmonics present in the ac test voltage power source. The

licensee noted that the relays were not sensitive to harmonic frequencies,

IN 95-05 January 20, 1995 but were sensitive to harmonic amplitudes. The licensee measured the harmonic

distortion attendant to the ac voltage test source and the safeguards buses, and concluded that the relay operating point was affected by the harmonic

distortion of both the ac voltage test source and the safeguards buses when

supplied by the offsite power system. Because the system harmonics may vary, the licensee is installing the harmonic filters in all of the 27N degraded

voltage relays. The harmonic filters will attenuate harmonics attendant to

the ac voltage test source and the offsite power system.

Discussion

All three occurrences were attributed to test equipment harmonics. When the

harmonic filters were removed from the 27N relays at Dresden, harmonic

distortion in an ac voltage source waveform had a noticeable effect on relay

operating point. The 27N relay uses a peak detector circuit. This peak

detector circuit samples half of the voltage source waveform and measures its

peak value. Although the peak detector circuit is very accurate, it is

sensitive to harmonic distortion. The relay manufacturer (ABB) recommends an

ac voltage test source with less than 0.3 percent harmonic distortion. As

indicated above, the licensees used ac voltage test sources which were

subsequently found to have high harmonic distortion.

During relay

calibration, a calibrated digital voltmeter (DVM) was used to measure the

relay input voltage to determine its trip setpoint. The DVM measures the root

mean square (RMS) value of the ac voltage test source sinusoidal waveform.

A change in the peak voltage of the ac voltage test source sinusoidal waveform

caused by harmonic distortion does not result in an equivalent change in the

RMS voltage as indicated by the DVM.

The relay operating point is

significantly influenced by its peak voltage detection circuitry. Therefore, if the voltage test source power supply is not included in a calibration

program, the DVM may not accurately reflect the setpoint of the solid-state

relay.

Using harmonic filters in the 27N relays will attenuate both ac voltage test

source harmonics and system harmonics.

However, ABB pointed out that the

harmonic filter option could cause the pickup/dropout operating points to

shift high at radiation levels below the testing end point of 630 Gy

(6.3E04 rad).

In addition, ABB documentation indicates that using the

harmonic distortion filter option increases the repeatability tolerance of the

relays as a function of temperature variations. As documented in ABB

Instructions IB 7.4.1.7-7 Issue D for Type 27N relays, temperature variations, such as -20 to +700C (-4 to 158'F), increase the relay repeatability tolerance

from +/-0.7 to +/-1.5 percent of relay pickup and dropout settings. Therefore, adding the harmonic filter option may necessitate revising the undervoltage

relay setpoint calculations. If harmonic filters are not used, system

harmonics can be determined and the test source harmonic distortion matched to

the system harmonic distortion within the tolerance band to ensure that relays

pick up and drop out at required system setpoints.

IN 95-05 January 20, 1995 This information notice requires no specific action or written response. If

you have any questions about the information in this notice, please contact

one of the technical contacts listed below or the appropriate Office of

Nuclear Reactor Regulation (NRR) project manager.

Brian K. Grimes, Director

Division of Project Support

Office of Nuclear Reactor Regulation

Technical contacts:

D. Nguyen, NRR

(301) 504-3202

D. Butler, RIII

(708) 829-9720

F. Ashe, NRR

(301) 504-2785

D. Skeen, NRR

(301) 504-1174 Attachment:

List of Recently Issued

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Information Notices

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IN 95-05 January 20, 1995 This information notice requires no specific action or written response.

If

you have any questions about the information in this notice, please contact

one of the technical contacts listed below or the appropriate Office of

Nuclear Reactor Regulation (NRR) project manager.

Original signed by Brian K. GVimes

Brian K. Grimes, Director

Division of Project Support

Office of Nuclear Reactor Regulation

Technical contacts:

D. Nguyen, NRR

(301) 504-3202

D. Butler, RIII

(708) 829-9720

F. Ashe, NRR

(301) 504-2785

D. Skeen, NRR

(301) 504-1174 Attachment:

List of Recently Issued Information Notices

DOCUMENT NAME:

95-05.IN

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IN 94-XX

December XX, 1994

This information notice requires no specific action or written response. If

you have any questions about the information in this notice, please contact

one of the technical contacts listed below or the appropriate Office of

Nuclear Reactor Regulation (NRR) project manager.

Brian K. Grimes, Director

Division of Project Support

Office of Nuclear Reactor Regulation

Technical contacts:

D. Nguyen, NRR

(301) 504-3202

D. Butler, RIII

(708) 829-9720

F. Ashe, NRR

(301) 504-2785

D. Skeen, NRR

(301) 504-1174 Attachment: List of Recently Issued Information Notices

DOCUMENT NAME:

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IN 94-XX

Month XX, 1994 This information notice requires no specific action or written response. If

you have any questions about the information in this notice, please contact

one of the technical contacts listed below or the appropriate Office of

Nuclear Reactor Regulation (NRR) project manager.

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contacts:

D. Nguyen, NRR

(301) 504-3202

F. Ashe, NRR

(301) 504-2785

D. Butler, RIII

(708) 829-9720

D. Skeen, NRR

(301) 504-1174 Attachment:

List of Recently Issued NRC Information Notices

• PREVIOUS CONCURRENCE

OFC

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Attachment

IN 95-05

January 20, 1995 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information

Date of

Notice No.

Subject

Issuance

Issued to

95-04

95-03

95-02

95-01

94-90

94-89

94-88

Excessive Cooldown and

Depressurization of the

Reactor Coolant System

Following a Loss of

Offsite Power

Loss of Reactor Coolant

Inventory and Potential

Loss of Emergency Mitiga- tion Functions While in

a Shutdown Condition

Problems with General

Electric CR2940 Contact

Blocks in Medium-Voltage

Circuit Breakers

DOT Safety Advisory:

High Pressure Aluminum

Seamless and Aluminum

Composite Hoop-Wrapped

Cylinders

Transient Resulting in a

Reactor Trip and Multiple

Safety Injection System

Actuations at Salem

Equipment Failures at

Irradiator Facilities

Inservice Inspection

Deficiencies Result in

Severely Degraded Steam

Generator Tubes

01/19/95

01/18/95

01/17/95

01/04/95

12/30/94

12/28/94

12/23/94

All holders of OLs or CPs

for nuclear power reactors.

All holders of Ols or CPs

for nuclear power reactors.

All holders of OLs or CPs

for nuclear power reactors.

All U.S. Nuclear Regulatory

Commission licensees.

All holders of OLs or CPs

for nuclear power reactors.

All U.S. Nuclear Regulatory

Commission irradiator

licensees.

All holders of OLs or CPs

for pressurized water

reactors.

OL - Operating License

CP -

Construction Permit