ML17157A222

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 ML18030A072
References
SEA-EE-235, SEA-EE-235-R, SEA-EE-235-R00, NUDOCS 9006290167
Download: ML17157A222 (29)

Text

OIALI TV LEVEL Ek'CTa at. 743153 SAFETY

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ENGINEERING STUDIES, ANALYSES, SEA aO.

A5NE AND EVALUATIONS COVERSHEET oci ao RTa Et aOa NIALI TT FAQE I OF 6 EVALUATION OF POTENTIAL HIGH VOLTAGE SOURCES INTO UNIT 1 AND 2 COMPUTERS 9006290i67 900619 PDR ADOCK 05000387 P PDC O gq Qo, ~ace 9 y(]x/tb REVISION NO. DATE PREPARED BY REVIEWED BY APP ROY BY

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SEA-EE-235 Page 2 of 6 EVALUATION OF POTENTIAL HIGH VOLTAGE SOURCES INTO UNIT 1 and 2 COMPUTERS 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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SEA-EE-235 Page 5 of 6 ATTACHMElIT 1 UNITS 1 5 2 TYPE COMPUTER POINT DESCRIPTION DEVICE AET 21 ESWS PP Motor A Stator Temp. RTD AET 22 ESWS PP Motor B Stator Temp. RTD AET 23 ESWS PP Motor C Stator Temp. RTD AET 24 ESWS PP Motor 0 Stator Temp. RTD GHT 11 Generator Stator Slot Temp. RTD GHT 12 Generator Stator Slot Temp. RTD GHT 13 Generator Stator Slot Temp. RTD GHT 14 Generator Stator Slot Temp. RTD GHT 15 Generator Stator Slot Temp. RTO GHT 16 Generator Stator Slot Temp. RTD GHT 17 Generator Stator Slot Temp. RTD GHT 18 Generator Stator Slot Temp. RTD GHT 19 Generator Stator Slot Temp. RTD GHT 20 Generator Stator Slot Temp. RTD GHT 21 Generator Stator Slot Temp. RTD GHT 22 Generator Stator Slot Temp. RTD GNT 04 Generator Hi-Volt Bush Temp. T/C GNT 05 Generator Hi -Volt Bush Temp. T/C GNT 06 Generator Hi-Volt Bush Temp. T/C GNT 07 Generator Hi-Volt Bush Temp. T/C GNT 08 Generator Hi-Volt Bush Temp. T/C GNT 09 Generator Hi-Volt Bush Temp. T/C GET 01 Alternator Slot Temp. RTD GET 02 Alternator Slot Temp. RTO GET 03 Alternator Slot Temp. RTD GET 04 Alternator Slot Temp. RTD GET 05 Alternator Slot Temp. RTO GET 06 Alternator Slot Temp. RTD CPT 10 CP Motor A Stator Temp. RTD CPT 20 CP Motor B Stator Temp. RTO CPT 30 CP Motor C Stator Temp. RTD CPT 40 CP Motor 0 Stator Temp. RTO WCT 10 CWP Motor A Stator Temp. RTD WCT 20 CWP Motor B Stator Temp. RTD WCT 30 CWP Motor C Stator Temp. RTO WCT 40 CWP Motor D Stator Temp. RTD NDT 01 CRD PP Motor A Stator Temp. RTD NDT 02 CRD PP Motor B Stator Temp. RTD

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SEA-EE-235 Page 6 of 6 ATTACHMENT 1 UNITS 1 5 2 TYPE COMPUTER POINT DESCRIPTION DEVICE NHT 05 RHR PP Motor A Stator Temp. RTO NHT 06 RHR PP Motor B Stator Temp. RTD NHT 07 RHR PP Motor C Stator Temp. RTD NHT 08 RHR PP Motor 0 Stator Temp. RTO NST 01 C Spray PP Motor A Stator Temp. RTD NST 02 C Spray PP Motor B Stator Temp. RTD NST 03 C Spray PP Motor C Stator Temp. RTO NST 04 C Spray PP Motor 0 Stator Temp. RTO YTT 03 SUXFRMR 10 Temp. RTD YTT 04 SUXFRMR 20 Temp. RTD YTT 06 ESSXFMR 101 Temp. RTO YTT 07 ESSXFMR 201 Temp. RTD YTT 16 111 Temp. 'SSXFMR RTD YTT 17 ESSXFMR 211 Temp. RTO YTT 01 MNXFMR 1A Temp. (2A) RTO YTT 02 MNXFMR 1B Temp. RTD YTT 05 UNIT AUX XFMR (12) RTO YTT 08 MNXFMR 2B Temp. RTD YTT 09 MNXFMR 2C Temp. RTD j pa/ms c004i (17)

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QCI<oesoi RESISTANCE THVlPKRATURE DFfECTORS DESCRIPTION perature coefficient as the other three arms. The bridge is excited by a constant d-c potential which A resistance temperature detector (RTD) is a is obtained through a constant voltage transformer resistance element, usually made of copper, and and a copper oxide reactifier. A d-c milliammeter adjusted to 10 ohms at 25 C. Operation of the RTD is connected across corners of the bridge. The is based on the principle that the electrical re- reading of this instrument depends on the current sistance of a metallic conductor varies linearly flowing through it, and this current depends only on with its temperature. 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 A~PuCAV<aN the scale of the d-c milliammeter is calibrated directly in degrees. The temperature of the RTD The RTD and its associated equipment is de- then, (which is the approximate temperature of signed for use with generators, transformers, and armature windings of a generator, for example) is other apparatus to determine winding, gas, and indicated by the d-c milliammeter.

liquid temperatures. The equipment consists of two parts: the switchboard equipment which usually In order to prevent any change in lead resistance includes a temperature meter, test resistor, (due to ambient temperature change) from affecting transfer switch, and leads; and the machine equip- the temperature meter, the RTD is connected in ment which usually includes the resistancetemper- the circuit so that there is equal lead resistance in ature detectors, leads, and terminal block with two ratio arms of the Wheatstone Bridge. Redrawing grounding connections. Fig. 1 with the lead resistance included (Fig. 2), it can be seen that the lead resistance from "A" to the A typical circuit utilizing the RTD is shown in detector element is in one arm and lead resistance Fig. 1. That part which is to the right of the dotted from "B" to the other side of the detector element line is the Temperature Meter which is outside the is in the other arm. Any change in these lead re-machine, and that part to the left is the RTD lo- sistances will appear in the two arms and the net cated inside the machine. Part of the circuit is a effect will be no change in current through the d-c Wheatstone Bridge which consists of the RTD as milliammeter. It is common practice to ground one one arm and three fixed resistors of negligible tem- lead of each RTD, because it is recognized that a TEMPKRATURC MCTCR TKRMINALS ac MILLIAMETER RTO TEMPERATURE METER I

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I20 VOLT Ac LINC CONSTANT RC5I5TOR VOLTAOK TRAN5PORMER 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 R ~ FIXEO RE5I5TOR A test 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-RTO TER MINALS ment itself is the total resistance from "A" to "B" VOLTAGE SOURCK or "A" to "C" minus the lead resistance "B" to FI ~ ER STRtlt Fig. 2. RTD and Wheatstone Bridge circuit (762A 123) 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 RESISTANCE ELEMENT safety of an operator The "B" lead is usually the one which is grounded on a generator. This makes Fig. 4. RTD construction it possible to connect all the "B" leads to a common (7624 122) grounding strip at the terminal board on the gener-ator, andruna single lead fromthisstriptothe tem- "C." The detectors are made in three princfpal perature meter. See Fig. 3. The leads from the a ~

types: the molded strip for installation in stator RTD's are brought out to the terminal board in slots next to the winding of rotating machines, the sheathed cable and conduit to protect them from sheath type for installation in air ducts, and the im-physical damage and from contact with high-voltage mersion type for use in liquids.

coils.

TEMltERATURE METER FUSES ISO V. AC A SOURCE e C

MOLDED-STRIP TYPE GRO 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.

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 TERMINAL SOARO hydrogen discharge section of the stator where they ON MACHINE will detect the highest temperatures. For reference At I to the slots in which each RTD is located, and the

.e c tC axial position in the slots, see the RTD portion 8'EAO of the connection outjine. In some cases the connec-GROUNOEO tion outline contains instructions concerning which 5 IN coil RTD's should be connected to the temperature R TO MACHINE meter. The remaining ones are reserved as spares Fig. 3. Rm connections to be used in the event that any of the other RTD's (124 C908) become inoperative.

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Resistance Temperature DeSctors GH-$ 09308 Flg. 6. Molded stnp-type RTD (5B) 353)

1. insulation thickness Fig. S. Sheath-type RTD 2. slot width (1026247)

3. cooling medium (air or hydrogen)

Coil RTD's do not detect copper temperature. 4. hydrogen pressure (slightly)

The reason is that there isatemperaturedrop from the copper to the RTD through the coil insulation. 5. armature current The RTD temperature may be 5 to 10 C lower than A further discussion of this subject can be found copper temperature in smaller machines, and may in A.I.E.E. paper No. 55-118 entitled "Turbine-be as much as 30 C lower in the larger machines. Generator Stator Winding Temperatures at Various The temperature difference is affected by the follow- Hydrogen Pressures" by J. R. M. Alger, C. E.

ing variables: Kilbourne and D. S. Snell.

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GH-80930b Reactance Temporatvre Detector SHIATH TYPE request by the customer. On smaller generators there is usually one RTD at the discharge side This detector is contained in a copper housing of each cooler. On larger machines, and whenever which provides a convenient means of attaching the requested, there are two RTD's in each cooler; unit to the stator frame. one at the inlet side of the cooler, and the other at the discharge side.

'Sheath detectors may be used in generators to Sheath-type RTD's may be used to determine detect air or hydrogen temperature. They are nor- effectiveness of the air or hydrogen coolers. They mally provided on all machines with internal water- detect the average temperature of the air or hydrogen to-gas heat exchangers and on other machines upon stream in which they are located.

GENERAL ELECTRIC

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~ P r ~t GKK 7505A TERMINAL BOARD WITH PROTECTIVE DEVICE FOR TEMPERATURE METER The terminal board, Fig. 1, consists essentially through the connection terminal (38). The "A"(red) of the insulating disk film cutouts (42), a grounding leads from the temperature detectors and the tem-strip (37), connection terminal (38) and contact clips perature meter are connected to the "A"connection (41). The contact clips connect with the leads from terminal, while the remaining leads from eachtem-the temperature detectors and temperature meter perature detector and the temperature meter are and hold the disk film cutout against the grounding connected to the "B" and "C" connection terminal.

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. OPERATION The function of the protective device is to pro- If the potential of any temperature detector should tect the temperature meter and the switchboard attain a value above the predetermined safe value, operator in the event that a dangerous potential through a failure of the armature coil insulation, should be given accidentally to any orallof the tem- the insulating film of the cutout for this detector perature detectors which are located in the genera- would break down, thus reducing the potential of the tor armature core. This is accomplished by the detector to ground potential.

breaking down of the insulating disk film cutouts, bringing the detector or detectors to ground potential.

CARE The insulating disk film cutout consists of two thin aluminum disks separated by a copper-oxide Under ordinary conditions the protective device film, the latter having such a dielectric strength that requires no attention. However, if a breakdown of its puncture voltage is well below that considered an insulating disk fQm cutout should occur, the cut-safe for indicating instrument. out must be replaced before further temperature readings can be taken. After correcting the condi-The leads from the temperature detectors are tion leading to the breakdown, replace the damaged connected with the leads from the temperature meter disk film cutout with a new one.

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~ d ~ ~ d d 43 38 NOMENCLATURE 1-.36 Typical connectors for resistance 44 Base temperature detectors- 45 Nut for stud ungrounded type 46 Support stud 37 Grounding strip 47 Washer 38 Connection terminal 48 Mounting bracket 39 Lead !erminal 49 Temperature detector located in armature ~ lot 40 Rivet semi-tubular 50 Lead support 41 Contact clip 51 Screw hole 42 Disk cutout 52 Conduit pipe 43 External tooth washer 53 Armored leads Fig. l. Terminal board for resistance temperature detectors vngrovnded type Dwg. 871 D420 GENERAL ELECTRIC 5 720M)

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oa.rw> v c TERMINAL BOARD VIITH PROTECTIVE FOR THERMOCOUPLES 'EVICE DESCRIPTION The leads from the temperature detectors are connected with the leads from the temperature The terminal board, Fig. l (see other side), con- meter through the connection terminal (1-36). See sists essentially of the insulating disk film cutouts Table I for color-coded connection instructions.

a grounding strip (3V), connection strips (1-36), '41),

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 OPERATION the grounding strip. The various parts are contained within a dust-tight metal box. Part (42) serves as If the potential of any temperature detector should a ground connection and also as a stud for attaching attain a value above the predetermined safe value, the protective device to its grounded support on through a failure of the armature coll insulation, the stator frame. the insulating film of the cutout for this detector would break down, thus reducing the potential of The function of the protective device is to pro- the detector to ground potential.

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 Under ordinary conditions the protective device cutouts, bring1ng the detector or detectors to requires no attent1on. However, if a breakdown of ground potential. an insulating disk fQm cutout should occur, thecut-out must be replaced before further temperature The 1nsulatlng disk film cutout consists of two readings can be taken. After correctingthe condi-thin aluminum disks separated by a copper-oxide tion leading to the breakdown, remove the cover of film, the latter having such a dielectric strength the protective device by removing the nuts from that its puncture voltage is well below that con- the studs (42), and replace the damaged disk film sidered safe for the indicating instrument. cutout with a new one.

h 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 49 51 Lead support 50 5I 52 Therrnocouple lead TABLE 1 Typo -"B" Terminal -"A" Tornsinal Coppi r-Constantan Blue Rod iron-Constantan White Rod Chron>ol-Constantan Pur pie Rod C hronn'I Alunlol Yo liow Rod 52 25 26 27 28 29 30 3I 32 33 34 35 36 4 45 4I 0 0 4 46 47 43 4 48 37 38 39 Fig. L Terminal board (O Ii. 871OSee)

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