NL-92-170, Rev 0 to Engineering Analysis EA-A-NL-92-170-01, Performance Testing of Kohm Resistors Used as Isolators
| ML20126J141 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 12/29/1992 |
| From: | CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | |
| Shared Package | |
| ML18058B311 | List: |
| References | |
| EA-A-NL-92-170, ES-A-NL-92-170-01-R0, ES-A-NL-92-170-1-R, NUDOCS 9301060049 | |
| Download: ML20126J141 (21) | |
Text
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I ATTACHMENT 1 Consumers Power Company Palisades Plant Docket 50-255-'
TESTING OF 100 K0HM RESISTORS USED AS-ISOLATORS
. December-29,--1992 r-
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ENGINEERING ANALYSIS WORK SHEET Total Nuntw of Sheeti 1_
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- Title AtiQInanctleillDg of 100 KOhm Resis10LLuled as isolators
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INITIATION AND REVIEW i
Calculation Status Preliminary Pending Final Superseded O
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O Revew Method Techncally Reviewed Revr initeted ind Rev Desenption Appd Art Det Qual Appd CPCo s
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Reference / Comment 1.0 OBJECTIVE The Obiective of this Engineering Analysis is to document qualification testing performed to confirm the adequacy of 100 KOhm resistors used as devices to isolate ungrounded Class 1E current instrument loops from Non-Class 1 E circuits as described in IEEE 384 1977.
2.0 REFERENCES
" instrumentation for Light Water-Revision 3
' Cooled Nuclear Power Plants to May 1983 Ass /M 'lant and Environs Conditions Dur la. id Following an Accident"
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- PAllSADES NUCLEAR PLANT EA, A NL 9217001 ANALYSIS CONTINUATION SHEET sneet 2
p,y, A 3ricumANEN88EIs Peter newcomment 2.2 Letter to the NRC Dated April 30,1992
" Regulatory Guide 1.97 Outstanding items
- 2.3 IEEE 384 1977
'IEEE Standard Criteria for Independence of Class 1 E Equipment and Circuits' 2.4 A - NL 92 170
" Regulatory Guide 1.97 Outstanding items
- 3.0 ATTACHMENTS 1.
Test Equipment 2.
Test Configuration 3.
Graphical Test Results 4.0 ANALYSIS INPUT All References and Attachments provided analysis input into this Engineering Analysis.
5.0 ASSUMPTIONS Major:
The isolation resistors are installed in the plantin a manner similar to that shown in Figure 2: 7est Configuration" and are in close proximity to the Class 1E current instrumentation loop.
There are no minor assumptions in this Engineering Analysis.
L PAltSADES NUCLEAR Pt. ANT EA, A NL-92170 01 3ncinacOE8$hlSs ANALYSIS CONTINUATION SHEET sheet 3
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Reference / comment 6.0 ANALYSIS Backaround Regulatory Guide 1.97 requires category 1 instrumentation installed to meet the requirements of this guide be electrically independent and physically separated from each other in accordance with Regulatory Guide 1.75 up to and including any isolation device. Regulatory Guide 1.75 endorses IEEE 384 1977 which requires Class 1E instrument loops be isolated from Non Class 1 E circuits such that the maximum credible voltage or current transient applied to the Non Class 1E side of the isolation device will not degrade the operation of the Class 1E circuit connected to the device below an acceptable level.
At Palisades, certain Non Class 1E computers and recorders are used to provide Operators information from Class 1E systems. Various methods are used to achieve the isolation required by IEEE 384 1977. One isolation method utilized for ungrounded current loops is 100 KOhm resistors. When used in close proximity to the Class 1 E instrumentation loop dropping resistors, the 100 KOhm isolation resistors prevent voltage or current transients on the Non Class 1E side of the resistors from having a significant effect on the Class 1E side.
During the week of January 13 17,1992, NRC Region lit personnel performed an inspection of Palisades compliance with the requirements of Regulatory Guide 1.97. During the course of the review, the inspector indicated that the NRC did not consider that use of resistors as isolation devices met the intent of Regulatory Guide 1.75. In response to this item, Palisades committed to perform testing of the 100 KOhm resistor isolation configuration utilized at Palisades to confirm the adequacy of tnis isolation method. This EA documents the result of that testing.
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1 Reference / Comment -
Maximum Credible Fault The maximum credible voltage fault which can be applied to the Non-Class 1 E side of the 100 KOhm isolators was determined to be 120 VAC or.
125 VDC. Selection of these voltage levets is based on the following:
1.
Routing of the cables from the isolators to their Non-Class 1 E destination is made via instrumentation cable trays or conduit. These raceways do not contain any circuits rated above 120 VAC or 125 VDC.
2.
The ends of the cables terminate in various control cabinets throughout the plant. The maximum voltages in these control cabinets do not exceed 120 VAC or 125-D a.
Testing of the isolators was actually performed at voltage levels of 135 VAC and 150 VDC. The higher AC voltage accounts for a +10%
margin in the nominal 120 VAC system while the higher DC voltage accounts for +10% margin over the 138 VDC available during battery charging operations.
Fuse sizing of the fault source was not considered to be a design criteria
- as the 100 KOhm isolation resistors limit fault currents to very low
- levels for any postulated voltage fault.-
H Examnia Fault Calculation -
L
- r To demonstrate the very low fault currents resulting from the maximum credible fault voltage, an example calculation is shown below. This -
circuit is a representative' ungrounded 4 20 mA current loop with'an
' applied fault voltage of 150 VOC on the isolation r'esistors.
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ANALYSIS CONTINUATION SHEET sheet 5-
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Transmitter Isolation Fault I
Point
+ R(T).
Resistors 100 KOhm l
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Example Faulted Current Loop Assuming an initial condition of 12 mA, R(T) = 1833 Ohm Loop analysis yields:
Loop 1:
28 = l(1)[1833 + 250 + 250] 1(2)[250] -
Loop 2:
150 = 1(1)[250] e f(2)[100.000 (250 + 100,000]
The resulting currents would be:
1(1) - 11.92 mA l(2) - 0.73 mA Thus, application of the 150_VDC fault changes the Class 1E-instrumentation loop curre_ t from 12.0 mA to 11.92 mA, a difference n
of only 0,66%. The other combinations of applied fault voltages yield -
1 similar results. This calculation has shown that there should be negligible affect on the Class 1E instrumentation loop for the maximum credible faults on the Non Class 1E side of the isolators.
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6-seve: 0 Reference / Comment Test Summarv To further demonstrate that the 100 KOhm resistors are adequate :
isolation devices, testing was performed in the plant l&C lab on.
August 28,1992. This testing consisted of applying fault voltages, short 1
circuits and ground faults to the downseam side of the isolation resistors and observing the affects produced in a typical 4 20 mA current loop.
Figure 2 Test Configuration" shows the configuration of the test instrumentation loop. The individual equipment is identified in
- Attachment 1. The test configuration includes an ungrounded current instrument loop (representing the Class 1 E loop) with a power supply and a transmitter simulator. The current and voltage in the -
loop are monitored with indicators._ A computer input is simulated -
with a dropping resistor and two 100 KOhm resistors acting as the isolators (representing the Non Class 1E loop). The voltage is applied as if a failure has occurred in the Non Class 1E circuit.- A recorder is used to monitor the loop characteristics at the three points identified on Figure 2 as the test is run.
. Test Results Eight separate tests were completed on the ungrounded instrumentation loop.1 The tests hypothesized the failure on the Non-Class 1E side of the
isolator resulting in application of 135 VAC or.150 VDC to the 100 KOhm isolation resistors. This was recorded on channel 1 of the recorder. The resulting voltage introduced into the Class 1 E loop was :
- then recorded on channels 2 and 3 of the recorder, Also a visual inspection of the indicators was performed to verify no disturbance had resulted in the loop. Table 1 " Test Results" shows the results of each of -
the eight tests. Attachment 3 shows a graphical measure of the voltage at the three points described above and noted on Figure _2.,
L As is notwt in Table 1, there was no measurable disturbance in the ungrounded Class 1E instrumentation loop from the failure of the Non-
~
Class 1 E instrumentation loop. This was due to the current limiting effects of the 100 KOhm resistors. Therefore as required by IEEE 384 -
1977, the ' Isolation Device" has prevented the maximum credible -
voltage applied to the.Non-Class 1E side from degrading the operations of
~
the Class 1E current loop.
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Reference / Comment Floure 2: Test ConflaWIR119D (See Attachment 1 for equipment list) h Power Supply O
O h
Transmitter Simulator s
Sigma 4 20 mA h
Channel #2 L4 ass 1E Current Instrumentation Non Class isolation loop Simulation 1E Cirmitry Resiste:s h100 KOhm Simulation h
- 1 h
Dropping
\\ Resistor 250 0hms
- 2 100 KOhm Channel #3 O-Channel #1
- Versatile 1 5 VDC O
- Channel #1 uses X10 probe
PALISADES NUCLEAR PLANT EA. A NL 9217001 E
s ANALYSIS CONTINUATION SHEET Sheet 8
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uscitiGANf O Reference / Comment Table 1: Test Results Test Loop Fault Meter Variation Number Current 4 20 mA 15V 1
12 mA DC 150 V DC None None 150 V DC None None 2
12 mA DC Reverse Polarity 150 V DC to #1 None N'ne 3
12 mA DC and to ground 150 V DC to #2 None None 4
12 rr.A DC and to ground 5
12 mA DC 135 V AC Norie None 6
- ntg nd 135 V AC to #1 7
- and to ground Terminals 1 8
12 mA DC None None and 2 shorted
' Graphkal results showed a low magnitude (< 0.1 V) ripple, howevec this was not detectable on the indicators.
7.0 CONCLUSION
i The test performed on August 28,1992 verified the acceptability of 100 KOhm resistors as isolation devices for ungrounded currentloops in applications at the Palisades Plant where the maximum credible fault voltage is nomina:ly 120 VAC or 125 VDC. These devices have been analyzed and tested to adequately perform the IEEE 384 - 1977 required I
isolation function and therefore are acceptable for use in configurations installed similarily to Figure 2 and as described in section 5.0 Assumptions.
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EA-A hb92 170 Revision 0 Page1of1 Test Equipment 6106A DC Power Supply Hewlett Packard Hewlett Packard 0 2A 6218A Power Supp1y
- 1. CPCo #842810102 CPCo # 8428 - 10090 I&C # N1 (#3)
I&C # N1 (N3)
Type W5MT3A Power Supply 88 500 0200 Metered Variac General Radio Storage Unit - 88 500 2100 Company Control Unit - 88 500 0100 SE561 Line 120V 50 - 60 Cycles Chart Recorder-88 500 4100 Load 0 140 5 Amps CPCo Cal # 8428 - 012444 CPCo #842810103 Calibration Date: October 4,1991 I&C # N1 345 (N3)
Calibration Duc Date: October 4,1992 h
Versatile - Voltage Indicator h
Dropping Resistor: Genres Model 9283 D - VB - 13M 8E16B Serial No.19033 H8125 (250 Ohm)+/ 0.25%
1-5VDC h
100 KOhm Precision Resistor h
Sigma - International Instruments 0.5 Watt Current Indicator (same type as used in the Model 9223 - E30 plant)
Serial No. U133 4 20 mA h
Ronan Calibrator / Transmitter Simulator Medel X86 Serial No. I1202 L
CPCo Cal # 8428 - 010169 Calibration Date: June 3.1992 Calibmdon Due Date: January 3,1992
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