ML20044C582
| ML20044C582 | |
| Person / Time | |
|---|---|
| Issue date: | 03/31/1993 |
| From: | Berlinger C Office of Nuclear Reactor Regulation |
| To: | Norberg J Office of Nuclear Reactor Regulation |
| References | |
| GL-89-10, NUDOCS 9304070099 | |
| Download: ML20044C582 (3) | |
Text
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March 31, 1993 MEMORANDUM FOR: gnetreertmeg, Chief Mec1anical Engineering Branch Division of Engineering Office of Nuclear Reactor Regulation FROM:
Carl H. Berlinger, Chief Electrical Engineering Branch Division of Engineering Office of Nuclear Reactor Regulation
SUBJECT:
EVALUATION OF DEGRADED VOLTAGE CAPABILITY OF MOTOR-0PERATED VALVES
Reference:
Memorandum from James A. Norberg, Chief Mechanical Engineering Branch to Carl H. Berlinger, Chief Electrical Engineering Branch, dated March 3,1993.
B.y the above reference, Mechanical Engineering Branch (EMEB) requested Electrical Engineering Branch's (EELB's) response to the following questions on the degraded voltage capability of motor-operated valves (M0Vs).
1.
Can the output capability of an MOV under degraded voltage and dynamic conditions be accurately estimated from motor current and torque / thrust obtained from a test of the MOV under nominal voltage and dynamic conditions using generic motor curves? If so, how would this be accomplished?
2.
In Supplement I to GL 89-10, the staff recommended that licensees use locked rotor or inrush current to determine the voltage drop from the motor control center to the motor terminals. May a licensee assume a percentage of locked rotor current (such as 60%) and obtain a sufficiently conservative prediction for voltage drop?
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3.
In February 1992, the Boiling Water Reactor Owners' Group (BWROG) distributed " Guidelines for Voltage Drop Calculations for Evaluating Degraded Voltage Conditions for Motor-0perated Valves (Generic Letter 89-10)" (Enclosure 1).
Are those guidelines acceptable? For example, is the method outlined in a Limitorque Maintenance Update (Enclosure 2) and referenced in the BWROG guidelines acceptable for astimating dc-power MOV output under degraded voltage conditions?
504-2760
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CONTACT: Amar Pal, NRR
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f v Wf March 31, 1993 James A. Norberg EELB's response to above questions is as follows:
1.
No. It is impossible to determine accurately the output capability of an MOV under degraded voltage and dynamic conditions from motor current and torque / thrust obtained from aeneric motor curves.
However, in order to determine accurately the output capability of an MOV under degraded voltage and dynamic (transient) conditions, the motor parameters ( R R,
X X2 ) during transient conditions need to be determined accu,,rateiy.3, hen, the ac motor terminal voltage at degraded 2
T voltage condition can be calculated by using voltage divider method
[ V, -
(V x Z, ) / ( Z, + Z, + Rn)].
3 The MOV motor is considered as a constant KW device during starting (locked rotor condition) and hence, has a constant impedance during locked rotor condition. The locked rotor impedance is considered constant during the entire starting transients for conservatism.
However, in the case of deep-bar or double squirrel-cage motors, the effective secondary reactance at speed is materially higher than at standstill, owing to the progressive shifting of the secondary current from the low-reactanca high resistance paths into the low-resistance high-reactance paths as the secondary, or slip,. frequency decreases.
Furthermore, if the values of torque, current etc., are desired throughout the starting transients, the value of R modified to allow for magnetic saturation and eddy. and X should be 2 currents.
Hence, in order to determine the MOV motor parameters accurately, the following tests on each motor are required:
- 1) Running-Light Test
- 2) Locked-Rotor Test
- 3) Slip Test
- 4) Stray-Load Loss Test 2.
No. The locked rotor current shall be used to calculate the motor impedance at standstill condition. The ac motor terminal voltage ( bus-voltage minus voltage drop due to cable impedance and over load heater resistance) is calculated as shown below:
V,
-V x Z, / ( Z, + Z, + Rn) 3 where, V, = Motor terminal voltage V
hs voltage Z,3 Motor impedance at standstill
- Rated voltage / V3 x locked rotor current Z, - Cable impedance Rn = Over load heater resistance i
. e March 31, 1993 b l James A. Norberg NQLE: If the calculated motor terminal voltage (Vn) by above is less than or equal to 70% of rated voltage, the torque is proportional to the square of voltage may not be applicable and hence torque at the calculated voltage shall be obtained from the manufacturer.
i 3.
Yes. However, the effect of elevated temperature on ac motor torque output has not been addressed adequately. The locked rotor torque versus the winding temperature data for each ac motor type must be' obtained from the manufacturer and the calculated torque at degra~ded
'l voltage shall be adjusted accordingly.
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The method outlined in a Limitorque Maintenance Update and j
referenced in the BWROG guidelines for estimating de-power MOV
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output under degraded voltage condition is acceptable.
j J
i Qvt f-Carl H. Berlinger, Chi Electrical Engineering Branch i
Division of Engineering
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Enclosures:
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