ML18026A379

Forwards Util Position & Justification on Dc Sys Indication for SER

ML18026A379
Person / Time
Site:	Susquehanna
Issue date:	11/06/1981
From:	Curtis N PENNSYLVANIA POWER & LIGHT CO.
To:	Schwencer A Office of Nuclear Reactor Regulation
References
PLA-959, NUDOCS 8111130570
Download: ML18026A379 (9)

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<OVL2 1981~-

Mes <eave tucu~gg'" i If NaMhgSsgW Norman W. Curtis Vice President-Engineering

& Construction-Nuclear 21 5 I 770-5381 November 6,

1981 Pennsylvania Power 8 Light Company Two North Ninth Street

~ Allentown, PA 18101, 705151

"'.r Mr. A. Schwencer, Chief Licensing Branch No.

2 U.S. Nuclear Regulatory Commission Washington, D.C.

20555 Docket Nos.

50-387 50-388 SUSQUEHANNA STEAM ELECTRIC STATION DC SYSTEM INDICATION ER 100450 FILE 841-2 PLA-959

Dear Mr. Schwencer:

As requested by the Power Systems

Branch, the attached is Pennsylvania Power and Light Company's position and justification on the DC system indication.

If you have any questions, please contact us.

Very truly yours, N.

W. Curtis Vice President-Engineering and Construction-Nuclear CTC/mks Attachment cc:

R. Perch NRC 8ii1130570 8iii06 PDR ADOCK 05000387 E

PDR eeL

SUSQUEHANNA STEAM ELECTRIC STATION (SSES)

SER Open Item:

Control Room Monitoring of Class 1E DC Power Systems

RESPONSE

The following indications and alarms for the Class 1E DC'power systems are provided as follows:

ALARM or INDICATION LOCATION LOCAL CONTROL RN.

NOTES Bus Undervoltage Alarm Bus Ground Alarm Battery Monitor Alarm

'attezy Charger Trouble Alarm Battery Charger Overvoltage Alarm Bus Ammeter Bus Vol tmeter Battery Charger Ammeter Battery Charger Voltmeter DC System Trouble Alarm X

X X

X X

X X

X X

1,2 1,2 1,2,4 3

3 3

3 7

NOTES:

1) 2)

See Table 1, Figure 2 for specific local annunciation.

These are locally indicat'ed and actuate DC system Trouble Alarm, see Table 1 and Figure l.

3)

Meters provided locally, see Figure 3.

4)

Battery monitor compares the voltage between battery halves and alarms when either the voltages aren't equal. (degraded cell or discharged state) or an open circuit (such as an open fuse) exists in the battery circuit.

5)

Battery Charger Trouble indicates AC power failure, DC output breaker open, or charger current less than or equal to zero.

6)

This monitor/alarm will be added by initial start'or Unit 2, and prior to restart after first refueling outage for Unit l.

7)

One window for each channel/division Class 1E DC system.

The monitoring scheme provided for the DC power systems is based on the degree of control provided to the Control Room Operator.

Instrumentation is provided locally in full compliance with the requirements of IEEE 308, 1974 and Regulatory Guide 1.47.

A single system level. DC trouble annunciator window for each channel/division is provided in the control room, consistent with the system level alarm criteria set fozth in Section B of R.G. 1.47.

The following indications and alarms listed in the SER have not been specifically provided in the control room for the following reasons:

(1)

Battery Current (ammeter - charge/discharge)

Under normal conditions, the floating charge current for the battery is very small,. requiring a very sensitive ammeter.

Shunt bypasses are employed to protect the meter movement'rom the much larger battery discharge currents (on the order of 2000 AMPS) possible in, this circuit.

These shunts must be manually removed when reading

the normal small current.

Thus, this reading cannot be continuous and no automatic indications or alarms can be given.

Since the intent of indicating "Battery Current" is to determine the battery condition, the method used to accomplish this purpose should not be important.

For the Class 1E batteries SSES employs a battery monitoring device which operates like an 'extremely sensitive undexvoltage relay.

This device compares the voltage.of half of the battery's cells to the other half to determine if a voltage imbalance greater than + 2% exists.

Under these conditions (indicating a degraded cell or a discharged state) the general DC System Trouble alarm annunciates in the control room, and an operator is dispatched to locally assess the cause of the condition and initiate corrective action.

Specific indication is provided on the local reflasher panels.

This response is exactly what would be achieved if an improper state of battery current (which would cause the voltage imbalance) were indicated on an ammeter in the contxol room.

The SSES method is faster and more reliable si'nce the condition is automatically alarmed.

Furthermore, this approach is consistent with the human factors engineering goal to not overburden the operator with unnecessary information.

Since the DC power system equipment cannot be remotely controlled, it serves no useful purpose for the control room operator to determine the exact cause of the problem.

Rather, the analysis of the problem in the control xoom might distract the operator from more vital duties.

The SSES design accomplishes the purpose of a battery current monitor in a manner better suited to the operation of the plant.

(2)

Battery Charger Output Current (ammeter)

This ammeter is located on the front of the charger panel where it provides useful information to maintenance and service personnel.

This information is not required in the main control room since any significant current deviations result in a DC system level trouble alarm in the control room due to actuation of the local charger trouble or overvoltage alarms.

This alarm philosophy is consistent with general principle of giving the operator only necessary information so as not to overwhelm him with unnecessary inputs.

(3)

DC Bus Uoltage (voltmeter)

The purpose of a bus voltmeter would be to enable the operator to dispatch someone to take corrective action locally to correct abnormal bus voltage conditions.

On SSES, bus undervoltage is monitored directly, overvoltage conditions are monitored at the charger output as"detailed in discussions (4) and (6) below, and both are alarmed in the control room via the general system level trouble alarms, This design automatically. alerts the operator to unusual voltage conditions without unnecessarily requiring his periodic attention and analysis.

As a result, this voltmeter has been excluded from the Control Room and has been provided on the front of the load center where it provides useful information during surveillance and maintenance activities.

"(4)

Battery Charger Output Voltage (voltmeter)

This voltmeter is located on the front of the charger panel as an aid to maintenance and service personnel.

With the charger output breaker closed

('an open breaker trill activate the system trouble alarm) the charger output and bus voltages axe the same due to the close proximity of the charger to the load centex.

Thus, all abnormal voltage conditions are already monitored (see discussion (3) and ('6)) and this voltmeter would not provide any. additional necessary information.

(5)

Battery High Discharge Rate Alarm This condition can only occur if there is an undervoltage on the DC bus or a ground between the bus and the battery.

Since the system trouble alarm will sound on either of these conditions, the addition of this alarm in the Control Room would not add to the operator's information on the situation and could be distracting.

As such, this alarm would be inconsistent with the SSES alarm design philosophy and has been excluded.

{6)

Direct Current Bus Overvoltage Alarm We have reviewed the requirement for this additional alarm and alternatively decided to provide a local indication for battery charger overvoltage tied into the Control Room system level alarm.

Per the previous discussion

{4), bus and charger output voltage are the same except when:the charger output breaker is open, and that condition is alarmed.

Since overvoltage on the bus could occur only when the charger is connected to the bus, charger overvoltage monitoring provides sufficient information to meet the intended purpose of the proposed alarm.

This condition is specifically indicated locally and alarmed on a system level in the Control Room, consistent with SSES design philosophy.

(7)

Battery Tuse Open Alarm This condition is detected via the battery monitor previously discussed (1).

The battery monitor indicator will light on the local reflasher panel, and the DC system trouble alarm will sound in the Control Room.

Since annunciatiwg this specific condition wou3d not provide any enIiancement of the Control Room operator's ability to deal with the situation, it is inconsistent with the alarm design philosophy, and has been excluded on that basis.

The SSES design conveys sufficient DC system information to the operator without giving him more than he requires..

The design is based on the general criteria that, if the operator can perform some correctiee action in the Control Room in response to a specific input, that information has been spec9.'focally provided.

However, if the only response required is to dispatch an operator to an area removed from the Control Room, then the only information required in the Control Room is general information with only the level of specificity required to diect that operator to.the proper location.

The DC system general trouble alarms and specific local indicators in conjunction with the 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> routine surveillance provide positive assurance that the Class 1E DC Power Systems willbe maintained in a steady state ready to perform their intended function.

250V DC S stem Reflash Panel Indicators (1L650) 1.

250V DC System Low Voltage 2.

250V DC System Ground 3.

Battery Monitor (indicates batt ry degradation or open battery fuses) 4.

Battery Charger Trouble (indicates (1)

AC power failure, (2)

DC output breaker open, or (3) charger current < 0) 5.

Load Center Incoming Breakers Trip 72-65212/22 (battery charger supplies) 6.

RCIC & Isolation Valves Control Center 1D254 Trouble (load center breaker tripped) 7.

Turbine Building Control Center 1D155 Trouble (load center breaker tripped) 8.

Computer UPS Supply Breaker Trip 9.

Battery Charger Output Overvoltage 10.

Reflash Panel Loss of Power 125V DC S stem Reflash Panel Indicators (1L610) l.

125V DC System Low Voltage 2.

125V DC System Ground 3.

Battery Monitor (indicates battery degradation or open battery fuses) 4.

Battery Charger Trouble (indicates (1)

AC power failure, (2)

DC output breaker open, or (3) charger current < 0) 5.

125V DC Distribution Panel 1D614 Low Voltage 6.

125V DC Distribution Panel 1D615 Low Voltage 7.

Battery Charger Output Overvoltage 8.

Reflash Panel Loss of Power

DIVISION 1 250V DC LOCAL REFLASH PANEL WITH INDICATION 1L650 MULTIPLE ALARM INPUTS FROM 250V DC DIVISION 3.

POWER SYSTEM PER TABLE 1 CHANNEL A 125V DC LOCAL REFLASH PANEL WITH INDICATION 1L610 MULTIPLE ALARM INPUTS FROM 125V DC GiANNEL A POWER SYSTEM PER TABLE 1 CONTROL ROOM PANEL 1C651 ANNUNCIATOR DC SYSTEM ALARM INPUTS FROM OTHER REFLASH "PANELS (similar to above)

~"125V DC SYSTEM TROUBLE 1D610"

~"250V DC SYSTEM TROUBLE 1D650"

~ IIETC ll REF.

DWGS.:

E-323 E-328 FIGURE 1

0 Indicator Light.

Reflash Panel Loss of Power Nameplate 250V DC System Low Voltage 250V DC System Ground Battery Monitor Battery Charger Load Center Incoming Breakers Trip 72-65212/22 RCIC

& ISO Valves Control Center 1D254 Trouble Turbine Building Control Center lD155 Trouble Computer UPS Supply Breaker Trip BATTERY CHARGER OUTPUT OVERVOLTAGE Front View Local Annunciator Ref lasher Panel (Typical)

The reflasher panel (one panel per battery system) is located in the battery area.

When an alarm input is

received, the reflasher panel simultaneously lights the respective indicator on the face of the reflasher.

and actuates the remote Main Control Room "DC System Trouble" alarm.

Figure 2

Battery Charger QA Ammeter Voltmeter Battery Bank Fuse Battery Monitor A

Ammeter' Voltmeter System Ground Indicators DC LOAD CENTER Loads Loads See Table l for Alarms DC S stem Indication (T

ical)

Figure 3