Text

Rev 0 to SEA-EE-235, Evaluation of Potential High Voltage Sources Into Unit 1 & 2 Computers
	ML17157A222
Person / Time
Site:	Susquehanna
Issue date:	04/17/1990
From:	Arus J; PENNSYLVANIA POWER & LIGHT CO.
To:	;
Shared Package
ML17157A218	List: ML17157A217; ML17157A219; ML17157A220; ML17157A221; ML17157A222; PLA-3396, Forwards Rev 1 to SEA-EE-183, Evaluation of Unit 1 Computer Class 1E - Non-Class 1E Interfaces & Rev 1 to SEA-EE-184, Evaluation of Unit 1 Annunciator Class 1E - Non-Class 1E Interfaces;
References
	SEA-EE-235, SEA-EE-235-R, SEA-EE-235-R00, NUDOCS 9006290167
	Download: ML17157A222 (29)
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ENGINEERING STUDIES,

ANALYSES, AND EVALUATIONS COVERSHEET OIALITV LEVEL SAFETY A5NE RTa Et aOa NIALITT Ek'CTa at. 743153 SEA aO.

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EVALUATION OF POTENTIAL HIGH VOLTAGE SOURCES INTO UNIT 1

AND 2 COMPUTERS 9006290i67 900619 PDR ADOCK 05000387 P

PDC O

gq Qo, ~ace 9 REVISION NO.

DATE PREPARED BY y(]x/tb REVIEWED BY APP ROY BY

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EVALUATION OF POTENTIAL HIGH VOLTAGE SOURCES INTO UNIT 1 and 2 COMPUTERS SEA-EE-235 Page 2 of 6 1.0 SCOPE The purpose of this SEA is to identify and evaluate potential high voltage sources which could migrate through the plant computers to safety-related systems and prevent these safety systems from meeting their minimum performance requirements.

SEA-EE-181 and SEA-EE-182 evaluated the affects of potential high voltages developed from current transformers and potential transformers respectively.

SEA-EE-180, SEA-EE-183, SEA-EE-184 and SEA-EE-221 evaluated the affects of impressed 120 VAC and 250 VDC voltages on safety-related systems connected to the computers.

SEA-EE-204 evaluated the affects of potential high voltages developed from generator DC field circuits.

The above potential voltage sources are not included in this SEA.

2.0 CONCLUSION

S AND RECOMMENDATIONS

2. 1 CONCLUS IONS The analysis in Section 5 of this SEA shows that there are no potential high voltage sources, which have not been previously evaluated, that could migrate through the plant computers to safety systems and prevent these safety systems from their minimum performance requirements.

High voltage cables (480 VAC and higher) are not potential sources since these cables do not come in contact with the computer input cables.

Rotating machine and distribution transformer temperature sensors are not high voltage sources into the computer since one lead of these devices is connected to ground or through insulating film disc devices preventing high voltages from developing at the sensor outpats.

2. 2 RECOMMENDATIONS The present practice of connecting one lead of rotating machine and transformer temperature sensors directly to ground or through insulating film disc devices to ground should be continued.

This assures that high voltages are not developed at the sensors output in the event the sensor insulation breaks down.

3.0 INPUTS AND ASSUMPTIONS 3.1 INPUTS Current transformers, potential transformers and control raceway impressed voltage faults have been previously evaluated and are not included in this SEA.

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SEA-EE-235 Page 3 of 6 Only in-plant electrical AC and DC systems are considered as potential high voltage sources to the computers.

No OFF-SITE transients are considered in this SEA.

All Class lE and non-Class 1E potential high voltage sources are to be evaluated.

This study covers inputs to the Units 1 and 2 computers.

3.2 ASSUMPTIONS This study is based on as-built drawings and documents'ssued as of the date of task initiation.

4.0 METHOD The AC and DC systems were reviewed to determine potential high voltage sources into the computer.

The results'of this review were examined to determine which sources were previously evaluated.

The Susquehanna SES Units 1 and 2 Computer I/O Specification Listing dated November 8, 1989 was reviewed to identify computer points which could be high voltage sources.

The identified computer point input circuits were evaluated to determine if these devices are potential high voltage sources into the computer and their impact on Class 1E circuits connected to the computer.

5.0 RESULTS The results of the review of in-plant AC and DC systems showed that the only potential high voltages into the computer which have not been previously evaluated are:

o High voltage cable faults (i.e.

480 VAC and higher).

o Temperature sensing devices from rotating machines and distribution transformer windings (i.e.

RTD's and thermocouples).

The high voltage cables are not potential voltage sources into'he plant computer since these cables run in different and separate raceway systems than the computer input cables and do not come in contact with the computer cables.

The 480 VAC cables and computer input cables could be in close proximity in motor-control centers, motor-operated valves and terminal boxes.

In the event 480 VAC cables bridge to computer cables, the resulting impressed voltages could be 277 VAC.

This is the expected voltage since the computer cable shields are grounded, thus an impressed voltage fault is phase to ground (277VAC).

The affects of this magnitude fault are the

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SEA-EE-235 Page 4 of 6 same as analyzed in SEA-EE-180, SEA-EE-183, SEA-EE-184 and SEA-EE-221.

Therefore, further consideration for these faults is not required.

The computer points derived from rotating machine and distribution transformers RTO's and thermocouples are listed in Attachment 1.

All of these temperature sensors have one lead connected directly to ground or connected to ground through insulating film disc devices.

The direct connections hold the sensors at ground potential at all times assuring that high voltages are not developed at their outputs.

(See attached GEI-509308, Pgs.

1 and 2).

The insulating film disc devices are designed to function by electrically breaking down the disc dielectric reducing the sensor to ground potential if the potential at the sensor attains a valve above a predetermined safe value.

(See attached GEK 7605A and GEI 74417C).

This value is well below that considered safe for instruments.

Thus, the physical connections of the RTO's and thermocouples prevent high voltages from developing on their 'outputs.

Therefore, these devices are not high voltage sources to the computer and evaluation of the Class 1E circuits connected to the computer does not require further consideration.

6.0 REFERENCES

6.1 SEA-EE-180, Rev.

0.

6.2 SEA-EE-181, Rev.

1.

6.3 SEA-EE-182, Rev.

0.

6.4 SEA-EE-183, Rev. 0.

6.5 SEA-EE-184, Rev.

0.

6.6 SEA-EE-221, Rev. 0.

6.7 Susquehanna SES Units 1 and 2 I/O Specification Listing, dated November 8, 1989.

6.8 IOM 78 RHR Motors.

6.9 IOM 527 Core Spray Motors.

6. 10 IOM 119 Turbine Generator.

6.11 SEA-EE-204, Rev.

1.

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UNITS 1 5 2 COMPUTER POINT AET 21 AET 22 AET 23 AET 24 GHT 11 GHT 12 GHT 13 GHT 14 GHT 15 GHT 16 GHT 17 GHT 18 GHT 19 GHT 20 GHT 21 GHT 22 GNT 04 GNT 05 GNT 06 GNT 07 GNT 08 GNT 09 GET 01 GET 02 GET 03 GET 04 GET 05 GET 06 CPT 10 CPT 20 CPT 30 CPT 40 WCT 10 WCT 20 WCT 30 WCT 40 NDT 01 NDT 02 ATTACHMElIT 1 DESCRIPTION ESWS PP Motor A Stator Temp.

ESWS PP Motor B Stator Temp.

ESWS PP Motor C Stator Temp.

ESWS PP Motor 0 Stator Temp.

Generator Stator Slot Temp.

Generator Hi-Volt Bush Temp.

Alternator Slot Temp.

CP Motor A Stator Temp.

CP Motor B Stator Temp.

CP Motor C Stator Temp.

CP Motor 0 Stator Temp.

CWP Motor A Stator Temp.

CWP Motor B Stator Temp.

CWP Motor C Stator Temp.

CWP Motor D Stator Temp.

CRD PP Motor A Stator Temp.

CRD PP Motor B Stator Temp.

SEA-EE-235 Page 5 of 6 TYPE DEVICE RTD RTD RTD RTD RTD RTD RTD RTD RTO RTD RTD RTD RTD RTD RTD RTD T/C T/C T/C T/C T/C T/C RTD RTO RTD RTD RTO RTD RTD RTO RTD RTO RTD RTD RTO RTD RTD RTD

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UNITS 1 5 2 COMPUTER POINT NHT 05 NHT 06 NHT 07 NHT 08 ATTACHMENT 1 DESCRIPTION RHR PP Motor A Stator Temp.

RHR PP Motor B Stator Temp.

RHR PP Motor C Stator Temp.

RHR PP Motor 0 Stator Temp.

SEA-EE-235 Page 6 of 6 TYPE DEVICE RTO RTD RTD RTO NST 01 NST 02 NST 03 NST 04 YTT 03 YTT 04 YTT 06 YTT 07 YTT 16 YTT 17 YTT 01 YTT 02 YTT 05 YTT 08 YTT 09 C Spray PP Motor A Stator C Spray PP Motor B Stator C Spray PP Motor C Stator C Spray PP Motor 0 Stator SUXFRMR 10 Temp.

SUXFRMR 20 Temp.

ESSXFMR 101 Temp.

ESSXFMR 201 Temp.

'SSXFMR 111 Temp.

ESSXFMR 211 Temp.

MNXFMR 1A Temp.

(2A)

MNXFMR 1B Temp.

UNIT AUX XFMR (12)

MNXFMR 2B Temp.

MNXFMR 2C Temp.

Temp.

RTD RTD RTO RTO RTD RTD RTO RTD RTD RTO RTO RTD RTO RTD RTD jpa/ms c004i (17)

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QCI<oesoi RESISTANCE THVlPKRATURE DFfECTORS DESCRIPTION A resistance temperature detector (RTD) is a resistance

element, usually made of copper, and adjusted to 10 ohms at 25 C. Operation of the RTD is based on the principle that the electrical re-sistance of a metallic conductor varies linearly with its temperature.

A~PuCAV<aN The RTD and its associated equipment is de-signed for use with generators, transformers, and other apparatus to determine

winding, gas, and liquid temperatures.

The equipment consists of two parts:

the switchboard equipment which usually includes a

temperature

meter, test

resistor, transfer switch, and leads; and the machine equip-ment which usually includes the resistancetemper-ature detectors,

leads, and terminal block with grounding connections.

A typical circuit utilizing the RTD is shown in Fig. 1. That part which is to the right of the dotted line is the Temperature Meter which is outside the

machine, and that part to the left is the RTD lo-cated inside the machine.

Part of the circuit is a Wheatstone Bridge which consists of the RTD as one arm and three fixed resistors of negligible tem-perature coefficient as the other three arms. The bridge is excited by a constant d-c potential which is obtained through a constant voltage transformer and a copper oxide reactifier. A d-c milliammeter is connected across corners of the bridge. The reading of this instrument depends on the current flowing through it, and this current depends only on the resistance of the RTD (since the other re-sistances of the bridge are fixed.) The resistance of the RTD depends upon its temperature and thus the scale of the d-c milliammeter is calibrated directly in degrees.

The temperature of the RTD

then, (which is the approximate temperature of armature windings of a generator, for example) is indicated by the d-c milliammeter.

In order to prevent any change in lead resistance (due to ambient temperature change) from affecting the temperature meter, the RTD is connected in the circuit so that there is equal lead resistance in two ratio arms of the Wheatstone Bridge. Redrawing Fig.

1 with the lead resistance included (Fig. 2), it can be seen that the lead resistance from"A"to the detector element is in one arm and lead resistance from "B" to the other side of the detector element is in the other arm. Any change in these lead re-sistances will appear in the two arms and the net effect will be no change in current through the d-c milliammeter. It is common practice to ground one lead of each RTD, because it is recognized that a TEMPKRATURC MCTCR TKRMINALS RTO I

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ac MILLIAMETER RECTIPICR RE5ISTORS TEMPERATURE METER TER MINAL5 I20 VOLT Ac LINC CONSTANT VOLTAOK TRAN5PORMER RC5I5TOR R a SRIOOKARM fIXCO RK5ISTOR Fig. I.

RTO and temperature meter circuit (124 C909)

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F OH-S0930b Reastance Temperature Detectan RTU TERlllHAL RTO TER MINALS R ~ FIXEO RE5I5TOR VOLTAGE SOURCK Atest resistor is usually provided for periodically checking jhe calibration of the temperature meter.

This resistor has a value of resistance of 11.73 ohms, which corresponds to the resistance of a de-tector at a temperature of 70 C.

A transfer switch is used toconnect the temperature meter to any one of several detectors in the machine.

The design is such that the c ontacts are opened and closed in proper sequence when transferring from one detector to another.

Another positionconnects to the calibrated test resistor to check the temperature meter at the 70-degreepoint. Theconstructionof RTD'sis shown in Fig. 4. Each detector has three leads designated as "A,""B," and "C." The resistance of the ele-ment itself is the total resistance from "A"to "B" or "A"to "C" minus the lead resistance "B"to Fig. 2.

RTD and Wheatstone Bridge circuit (762A 123)

FI ~ ER STRtlt IREOI lett ITS WtttTEI breakdown in stator coil insulation to an RTD ele>>

ment in a machine is possible.

The RTD's are thus held at ground potential at all times assuring the safety of an operator The "B" lead is usually the one which is grounded on a generator.

This makes itpossible to connect all the "B" leads to a common grounding strip at the terminal board on the gener-a

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ator, andruna single lead fromthisstriptothe tem-perature meter.

See Fig. 3.

The leads from the RTD's are brought out to the terminal board in sheathed cable and conduit to protect them from physical damage and from contact with high-voltage coils.

TEMltERATURE METER FUSES RESISTANCE ELEMENT Fig. 4.

RTD construction (7624 122)

"C." The detectors are made in three princfpal types:

the molded strip for installation in stator slots next to the winding of rotating machines, the sheath type for installation in air ducts, and the im-mersion type for use in liquids.

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GRO MOLDED-STRIP TYPE TEST RESISTOR TRAN5FER SWITCH The resistance vrfre of these detectors is molded into a fiberglass strip which is approximately 1/16-fn. thick and trimmed to slot width. Allmolded-strip detectors are noninductively wound to cancel the extraneous voltage induced in them.

TERMINAL SOARO ON MACHINE At I

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tC 8'EAO GROUNOEO R TO 5 IN MACHINE Fig. 3.

Rm connections (124 C908)

Molded-strip detectors are used in generators to detect the approximate temperature of armatur'e coils and are known as "coil RTD's." They are lo-cated between coil sides in the slotandin the air or hydrogen discharge section of the stator where they willdetect the highest temperatures.

For reference to the slots in which each RTD is located, and the axial position in the slots, see the RTD portion of the connection outjine. In some cases the connec-tion outline contains instructions concerning which coil RTD's should be connected to the temperature meter. The remaining ones are reserved as spares to be used in the event that any of the other RTD's become inoperative.

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Molded stnp-type RTD (5B)353)

Fig. S.

Sheath-type RTD (1026247)

Coil RTD's do not detect copper temperature.

The reason is that there isatemperaturedrop from the copper to the RTD through the coil insulation.

The RTD temperature may be 5 to 10 C lower than copper temperature in smaller machines, and may be as much as 30 C lower in the larger machines.

The temperature difference is affected by the follow-ing variables:

1. insulation thickness

2. slot width

3. cooling medium (air or hydrogen)

4. hydrogen pressure (slightly)

5. armature current A further discussion of this subject can be found in A.I.E.E. paper No. 55-118 entitled "Turbine-Generator Stator Winding Temperatures at Various Hydrogen Pressures" by J.

R. M. Alger, C.

E.

Kilbourne and D. S. Snell.

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SO 40 SO SO IOO TCliPCRATURC IN OCORCCS CCNTICRSOC Fig. 7.

Resistance telnperatvre cvrve of copper RTO (10 ohms at 25 C)

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GH-80930b Reactance Temporatvre Detector SHIATH TYPE This detector is contained in a copper housing which provides a convenient means of attaching the unit to the stator frame.

'Sheath detectors may be used in generators to detect air or hydrogen temperature.

They are nor-mally provided on all machines withinternal water-to-gas heat exchangers and on other machines upon request by the customer.

On smaller generators there is usually one RTD at the discharge side of each cooler.

On larger machines, and whenever requested, there are two RTD's in each cooler; one at the inlet side of the cooler, and the other at the discharge side.

Sheath-type RTD's may be used to determine effectiveness of the air or hydrogen coolers. They detect the average temperature of the air or hydrogen stream in which they are located.

GENERAL

ELECTRIC

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~t GKK 7505A TERMINAL BOARD WITH PROTECTIVE DEVICE FOR TEMPERATURE METER The terminal board, Fig. 1, consists essentially of the insulating disk film cutouts (42), a grounding strip (37), connection terminal (38) and contact clips (41). The contact clips connect with the leads from the temperature detectors and temperature meter and hold the disk film cutout against the grounding strip.

Part (46) serves as a ground connection,and also as a stud for attaching the protective device to its grounded support on the stator frame.

The function of the protective device is to pro-tect the temperature meter and the switchboard operator in the event that a dangerous potential should be given accidentally to any orallof the tem-perature detectors which are located in the genera-tor armature core. This is accomplished by the breaking down of the insulating disk film cutouts, bringing the detector or detectors to ground potential.

The insulating disk film cutout consists of two thin aluminum disks separated by a copper-oxide film, the latter having such a dielectric strength that its puncture voltage is well below that considered safe for indicating instrument.

The leads from the temperature detectors are connected with the leads from the temperature meter through the connection terminal (38). The "A"(red) leads from the temperature detectors and the tem-perature meter are connected to the "A"connection terminal, while the remaining leads from eachtem-perature detector and the temperature meter are connected to the "B" and "C" connection terminal.

OPERATION If the potential of any temperature detector should attain a value above the predetermined safe value, through a failure of the armature coil insulation, the insulating film of the cutout for this detector would break down, thus reducing the potential ofthe detector to ground potential.

CARE Under ordinary conditions the protective device requires no attention. However, if a breakdown of an insulating disk fQm cutout should occur, the cut-out must be replaced before further temperature readings can be taken. After correcting the condi-tion leading to the breakdown, replace the damaged disk film cutout with a new one.

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43 47 48 38 1-.36 37 38 39 40 41 42 43 Typical connectors for resistance temperature detectors-ungrounded type Grounding strip Connection terminal Lead !erminal Rivet semi-tubular Contact clip Disk cutout External tooth washer NOMENCLATURE 44 Base 45 Nut for stud 46 Support stud 47 Washer 48 Mounting bracket 49 Temperature detector located in armature

~ lot 50 Lead support 51 Screw hole 52 Conduit pipe 53 Armored leads Fig. l.

Terminal board for resistance temperature detectors vngrovnded type Dwg. 871 D420 GENERAL

ELECTRIC 5 720M)

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'EVICE FOR THERMOCOUPLES DESCRIPTION The terminal board, Fig. l (see other side), con-sists essentially of the insulating disk film cutouts

'41),

a grounding strip (3V), connection strips (1-36),

and contact clips (40). The latter connect with the leads from the temperature detectors and temper-ature meter and hold the disk film cutout against the grounding strip. The various parts are contained within a dust-tight metal box. Part (42) serves as a ground connection and also as a stud for attaching the protective device to its grounded support on the stator frame.

The function of the protective device is to pro-tect the temperature meter and the switchboard operator in the event that a dangerous potential should be given accidentally to any or all of the temperature detectors which are located 1n the generator armature core.

This is accomplished by the breaking down of the insulating disk film

cutouts, bring1ng the detector or detectors to ground potential.

The 1nsulatlng disk film cutout consists of two thin aluminum disks separated by a copper-oxide film, the latter having such a dielectric strength that its puncture voltage is well below that con-sidered safe for the indicating instrument.

The leads from the temperature detectors are connected with the leads from the temperature meter through the connection terminal (1-36).

See Table I for color-coded connection instructions.

OPERATION If the potential of any temperature detector should attain a value above the predetermined safe value, through a failure of the armature coll insulation, the insulating film of the cutout for this detector would break down, thus reducing the potential of the detector to ground potential.

Under ordinary conditions the protective device requires no attent1on.

However, if a breakdown of an insulating disk fQm cutout should occur, thecut-out must be replaced before further temperature readings can be taken. After correctingthe condi-tion leading to the breakdown, remove the cover of the protective device by removing the nuts from the studs (42), and replace the damaged disk film cutout with a new one.

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NOMENCLATURE 1-36 Typical connectors for thermocouples 37 Grounding strip 38 Connection terminal 39 Lead terminal 40 Contact clip 41 Disk cutout 42 Stud 43 Rivet 44 External tooth washer 45 Washer 46 Nut 47 Mounting support 48 Terminal board 49 Thermocouple located on flange shield 50 Screw 51 Lead support 52 Therrnocouple lead TABLE 1 49 50 5I Typo

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45 46 47 48 37 38 39 Fig. L Terminal board (O Ii. 871OSee)

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NRCAN END BATCH MAN't0004235X BOX LABEL: LM-14-OJ-27855 Segment Inventory: Christine. williams on US06WHC102 at 2016-10-27 14:28 a c onro ee

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ML17157A222

Text

2.0 CONCLUSION

6.0 REFERENCES

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