Information Notice 1989-11, Failure of DC Motor-Operated Valves to Develop Rated Torque Because of Improper Cable Sizing

Failure of DC Motor-Operated Valves to Develop Rated Torque Because of Improper Cable Sizing
	ML031180511
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, Three Mile Island, 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, 05000000, Zimmer, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	02/02/1989
From:	Rossi C; Office of Nuclear Reactor Regulation
To:	;
References
	IN-89-011, NUDOCS 8901270329
	Download: ML031180511 (9)
	v • d • e

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 February 2, 1989 NRC INFORMATION NOTICE NO. 89-11: FAILURE OF DC MOTOR-OPERATED VALVES TO

DEVELOP RATED TORQUE BECAUSE OF IMPROPER

CABLE SIZING

Addressees

All holders of operating licenses or construction permits for nuclear power

reactors.

Purpose

This information notice is being provided to alert addressees to potential

,z`problems resulting from motor-operated valves (MOYs) not developing rated

torque because of the failure of the original cable sizing calculations to

include the proper current values and cable resistances. It is expected

that recipients will review the information for applicability to their faci- lities and consider actions, as appropriate, to avoid similar problems. How- ever, suggestions contained in this information notice do not constitute NRC

requirements; therefore, no specific action or written response is required.

Description of Circumstances

As a part of the Equipment Qualification and Nuclear Plant Aging Studies, the

NRC obtained a motor-operated wedge-gate valve from the Shippingport Atomic

Power Station following its decommissioning. The valve had been installed

in a secondary system for the 25-year life of the plant. A review of the

maintenance records for the valve and the operator indicated that there were

no reportable incidents associated with either the valve or the operator.

Following removal, the valve and the operator were refurbished by an NRC

contractor and tested to demonstrate the valve's ability to operate at the

conditions expected during the forthcoming testing. The valve, the operator, and the controller were then transported to Germany where they were installed

in the Heissdampfreactor (HOR) decommissioned reactor test facility as part of

a jointly sponsored seismic test research program. With the exception of the

use of equivalent metric-sized cable, the electrical installation of the

operator was identical to that at Shippingport.

Each test of the valve consisted of a closure cycle, an opening cycle, and

a final closure cycle. When the data from these tests was analyzed, it was

determined that the valve had routinely failed to fully seat during the second

closing cycle of each test which had subjected the valve to system pressure and

flow and ambient temperature conditions. In addition, the valve had routinely

8901270329 Z.k ) 75e/C

IN 89-11 February 2, 1989 failed to fully seat during both closing cycles of each test which had sub- jected the valve to system pressure, flow, and elevated temperature conditions.

Further evaluation of the data indicated that (1) although the motor had

stalled, the output torque had not been sufficient to open the torque switch;

(2) the maximum recorded current appeared to be significantly less than that

expected for a stalled motor; and (3) the motor voltage at stall was only

slightly less than the running voltage. In response to a request from NRC, the

contractor conducted a second series of tests at HDR. Because of the concern

that degraded voltage might have been a contributor to the failures, the elec- trical instrumentation inputs were moved from the motor control center to the

junction strip in the switch compartment of the motor operator.

The second test series produced the same valve failure pattern that had been

obtained in the initial test series. As the second test series was thought

to have eliminated degraded voltage as a cause, it appeared that the problem

might be improper motor operator sizing. The NRC requested the contractor to

conduct additional testing to determine whether the motor and the operator had

been properly sized initially or whether they had degraded during their service

at Shippingport. To accomplish this testing, the motor operator and the control- ler were removed from the HDR decommissioned reactor test facility and shipped

to the Limitorque manufacturing facilities for dynamometer testing.

The dynamometer testing of the motor operator by Limitorque demonstrated that

the performance of the motor operator was better than that at HDR, but that the

motor performance was less than that originally specified. It was therefore

decided to perform motor dynamometer testing at the motor manufacturer's

facilities. To accomplish this testing, the motor was removed from the motor

operator and shipped to the motor manufacturer. The motor dynamometer testing

by the motor manufacturer demonstrated that the motor's performance did not

differ appreciably from that of a new motor.

However, before any additional evaluations could be performed, the NRC contrac- tor became aware of the recent MOY failures at Brunswick Steam Electric Plant, Unit 1, which had been described in NRC Information Notice 88-72, "Inadequacies

in the Design of DC Motor-Operated Valves." Because of the similarity of

conditions noted in the HDR and Brunswick failures, the NRC contractor, working

with Limitorque, focused on the analysis of the cable sizing for the MOY. This

analysis pointed out the following two factors:

(1) The first factor concerned the current values that should be used to

establish the cable size. As a motor operator is not a continuous-duty

device, the normal operating voltage and current data contained on the

nameplate are of only limited applicability to cable sizing. Rather, it

is the voltage and current required to develop the rated output torque of

the motor operator that is important. As the current required for~this

rated torque must be developed during locked rotor conditions, the cable

should be sized on the locked rotor current instead of on the full load

current. The ratio of these currents is quite large as the locked rotor

current is typically in excess of five times the full load current stated

on the nameplate.

IN 89-11 February 2, 1989 (2) The second factor concerned the cable resistance that should be considered

in the analysis. The wiring diagram for a typical motor operator is shown

in Attachment 1. Significant cable resistances and the location of the

voltage measurement during the second HDR tests are also shown. Attach- ment 2 presents a simplified schematic of the same circuit. As can be

seen, any attempt to measure the voltage drop at the power supply bus

(i.e., the sum of the voltage drops across the armature and the series

field) includes the resistance contribution from four cables. Even taking

the voltage measurement at the motor (as was done during the second HDR

tests) will result in including the voltage drop across three cables.

From the above information, it can be seen that the required current for the

MOY to develop the design torque should be based on the motor resistance and

the cable resistance (i.e., four times that of a single cable) under a minimum

postulated bus voltage.

As indicated in their August 17, 1988, maintenance update, Limitorque recom- mends that the cable be sized to allow for five times full load current flow at

the minimum voltage condition. This maintenance update also contained a method

for calculating the maximum current draw at locked rotor conditions.

No specific action or written response is required by this information notice.

If you have any questions about this matter, please contact one of the techni- cal contacts listed below or the Regional Administrator of the appropriate

regional office.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: Yun-Seng Huang, NRR

(301) 492-0921 Peter J. Kang, NRR

(301) 492-0812 Richard J. Kiessel, NRR

(301) 492-1154 Attachments:

1. Cable Resistances and Voltage Measurements Identified

2. Motor Functional Schematic

3. List of Recently Issued NRC Information Notices

Cable Resistances and Voltage Measurements Identif ied

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Motor Functional Schematic

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Attachment 3 IN 89-11 February 2, 1989 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

89-10 Undetected Installation 1/27/89 All holders of OLs

Errors In Main Steam Line or CPs for BWRs.

Pipe Tunnel Differential

Temperature-Sensing Elements

at Boiling Water Reactors.

89-09 Credit for Control Rods 1/26/89 All holders of OLs

Without Scram Capability or CPs for test and

in the Calculation of the research reactors.

Shutdown Margin

89-08 Pump Damage Caused by 1/26/89 All holders of OLs

Low-Flow Operation or CPs for nuclear

power reactors.

89-07 Failures of Small-Diameter 1/25/89 All holders of OLs

Tubing in Control Air, Fuel or CPs for nuclear

Oil, and Lube Oil Systems power reactors.

Which Render Emergency Diesel

Generators Inoperable

89-06 Bent Anchor Bolts in 1/24/89 All holders of OLs

Boiling Water Reactor or CPs for BWRs with

Torus Supports Mark I steel torus

shells.

89-05 Use of Deadly Force by 1/19/89 All holders of OLs

Guards Protecting Nuclear for nuclear power

Power Reactors Against reactors.

Radiological Sabotage

89-04 Potential Problems from 1/17/89 All holders of OLs

the Use of Space Heaters or CPs for nuclear

power reactors and

test and research

reactors.

89-03 Potential Electrical 1/11/89 All fuel cycle and

Equipment Problems major nuclear materials

licensees.

OL = Operating License

CP = Construction Permit