ML20092F709
| ML20092F709 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 02/19/1992 |
| From: | GENERAL ELECTRIC CO. |
| To: | |
| Shared Package | |
| ML20092F288 | List:
|
| References | |
| CON-IIT05-002-005-90, CON-IIT5-2-5-90, RTR-NUREG-1410 GEK-45405B, NUDOCS 9202190474 | |
| Download: ML20092F709 (40) | |
Text
m-INSTRUCTIONS Grx-4540sa Supersedes GEK-45405 A l
DIFFERENTIAL VOLTAGE RELAYS TYPFS:
PVD21A PVD21B PYD21C PVD21D GENER AL $ ELECTRIC r
= = =..
5 PDR
GEK-45405
'1 l
CONTENTS PAGE 1
6 3
DESCRIPTION...........................................
4 APPtiCATiON...........................................
6 CONSTRUCTI0d..........................................
8 h(
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9 OPERATING PRINCIPLES..................................
VOLTAGE UNIT (87L) - PVD21A, PVD218, PVD21C, PVD210..
9 11 OVERCURRENT UNIT (87H) - PVD218, PV0210.............
12 CALCULATION OF SETTINGS...............................
12 SETTING 0F HIGH IMPEDANCE UNIT, 87L 14 SETTING OVERCURRENT UNIT, 87H.......................
14 SAMPLE CALCULATION..................................
i 16 RECEIVING, HANDLING AND STORAGE.......................
16 ACCEPTANCE TESTS......................................
17 17 h
l VISUAL INSPECTION...................................
MECHANICAL INSDECTION...............................
17 ELECTRICAL SE' TING AND INSPECTION...................
L 19 j
INSTALLATION PAOCEEDINGS..............................
19 LOCATION ANI, MOUNTING...............................
19 CONNECTIONS.........................................
20 VISUAL INSPECTION...........................-.......
20 MECHANICAL INSPECTION AND ADJUSTMENTS...............
20 TARGET AND SEAL-IN UNIT.............................
20 87H AND 87L UNITS...................................
21 PERIODIC CHECKS AND ROUTINE MAINTENANCE...............
21 CONTACT CLEANING....................................
21 PERIODIC TEST EQUIPMENT.............................
21 i
ELECTRI'AL TESTS....................................
21 h'
THYRITE8 UNIT.......................................
22 HI-SEISMIC INSTANTANE0US UNIT, 87H..................
22 HI-SEISMIC TARGET AND SEAL-IN UNIT..................
22 RENEWAL PARTS.........................................
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GEK-45405 DIFFERENTIAL VOLTAGE RELAYS TYPES:
PVD21A PVD218 PVD21C PVD21D DESCRIPTION All the the Type PVD21 relays are single phase high speed, high impedance, s
voltage operated relays that are designed to provide protection in bus differential schemes when used in conjunction with suitable current transformers. Typical operating times are shown in Figure 15.
Three PVD relays and a lockout relay are required for combined phase and ground f ault protection of a three phase bus.
Four models of the relay are available as listed in Table 1.
TABLE 1 VOLTAGE CURRENT N0.OFTHYRITh UNIT (87L)
UNIT (87H)
STACKS PVD21A Yes No
)
PVD21B Yes Yes 1
PVD21C Yes No 2
PVD210 Yes ies 2
Tg PVD21C and PVD210 models of the relay include two paralleled voltage limiting included in the PVD21A and PVD21B Thyrite stacks as opposed to the single stack models.
This feature makes the PVD21C and PVD21D models better suited to those applications where high internal f ault currents can be encountered. This 1: discussed in detail in the section on APPLICATION in this instruction book.
The PVD21A and PVD21B models of the relay include a high speed overcurrent unit (87H) in addition to the voltage operated unit (87L).
This unit may be used to supplement the high speed voltage unit, and/or when provided with a sui / 'e external timing device and auxiliaries, it may be used to implement breaker f ailure protection.
This is also disecused in detail in the APPLICATION section.
The PVD relays are mounted in a single-end M1 size drawout case, and are provided with a single seal-in and separate targets for each unit.
Outline and panel drilling dimensions for the relays are illustrated in Figure 1.
Internal connections for the various models are illustrated in Figures 2 and 3.
M Registered trademark of General Electric Co.
variations in e4WAPaent not to provide fo8 These anstructions do not purport to cowr ejJ detaals et should en cmnect ron eith instaj Jstion, operatJon or maintenance.
e ve ry pos s 4 4 J e c crit a n9e new to tre me tshould particular proalems atase wnJch are not covered sufficiently fat I
further anformataan be desired of the mettet shoujd be refetted to the Genetei Ciecttsc Cong-ant.
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GEK-45405 The external connections for the PVD21A and PVD21C relays are illustrated in h jFigure 4; those for the PVD21B and PVD210 relays are shown in Figure 5.
APPLICATION The following comments on the applications of the Types PVD21 A, PVD21B, PVD21C and PVD210 relays may be better appreciated if the detailed section on OPERATING PRINCIPLCS is reviewed before proceeding. The Type PVD21 relays can be applied for bus protection in most cases where cts having negligible leakage reactance are used.
This generally includes any kind of current transformer with a toroidal core if the windings (on the g top used) are completely distributed about the core.
The elementary diagram of the external connections for a typical application is shown in Figures 4 and 5.
A bus differential scheme utilizing Type PVD relays has certain advantages that simplify application considerations:
e Standard relaying-type bushing current transformers may be used e Performance for specific applications is subject to simple calculations e Protection is easily extended if the number of connections to the bus is increased.
The following points must be considered before a particular application is attempted:
All cts in the bus differential circuit should have the same ratia.
When adding g
to on existing bus, at least one CT in the new breaker shoul( be orde.2d with the same ratio as the bus differential cts in the existing breakers.
If the differential circuit unavoidably includes different ratio cts, the application may still be possible, but special attention must be given to protect against overvoltage conditions during internal f aults.
if one or more of the cts in Figures 4 or 5 are a dif ferent ratio than the others, it would appear that the simple solution would be to use the full winding of the lower ratio cts and a matching tap on the higher ratio cts. The high peak voltages that occur during an internal f ault will be magnified by the autotransformer action of the tapped higher ratio cts, and the peak voltages across the full winding of the higher ratio cts may exceed the capability of the insulation in that circuit.
Refer applications involving different ratio cts to the local General Electric Sales office.
l When all current transformers are of the same ratio, full windings, instead of g'
taps, should be used.
This will insure maximum sensitivity to internal faults in addition to limiting peak voltages.
In any case, CT secondary leakage reactance must j
be negligible.
It may be possible, although not desirable, to use the differential circuit cts jointly for other functions.
The performance of the system under these conditons can be calculated by including the added burden as part of the CT lead resistance.
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GEK-45405 l
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a However, consideration must be given to the hazards of f alse operation due to extra connections and errors in testing the added devices. Note that the relays may trip if a CT secondary is open circuited during normal operation of the associated bus.
Thyritehanon-linear resistance, is used in the relays to limit the voltages that can be developed across the relay during an internal f ault to safe values.
The magnitude of the voltage that can be developed will be a function of the total internal f ault current and the characteristics of the cts used in the differential circuit.
Figure 9 illustrates the safe application limits for the PVD21A and PVD218 relays as a function of the total f ault current and the knee point voltage (E ) of the poorest CT in S
)
the circuit.
If the fault current and knee point voltage are such that the intersection of these two points plots below the curve, then the application will be safe with respect to the voltage limits.
NotethattQscurveappliesforthePVD21A and PVD218 relays which have a single stack of Thyriteu.
If the application of these relays does not appear to be permissible on the basis of Figure 9, it may still be permisQble if the PVD21C or PVD21D relay is used.
These relays have two stacks of Thyrit6W connected in parallel so that significantly greater internal fault currents can be accomodated. Figure 10 may be used to determine the safe application limits for the PVD21C and PVD210 relays.
During an internal f ault, current will flow in the Thyrith stack, causing energy to be dissipated.
To protect the Thyrit6W from thermal d amage, a contact of t e lockout relay must be connected as shown in Figures 4 and 5 tgshort out the Thyr e
during an internal f ault.
The thermal limits of the Thyritew will not be exceeded provided the relay time, plus lockout relay time, is less than four cycles.
Aninstantaneousovercurrentunit,87H,isconnectedinserieswiththeThyrith in PVD218 and PVD210 models. The 87H unit, when set with the proper pickup, may be used to supplement the voltage unit, 87L, and/or implement breaker f ailure protection when a suitable timing relay and other auxiliary devices are provided by the user.
The required setting of the 87H unit is related to the actual setting of the 87L unit.
Figure 8 illustrates the setting to be made on 87H as a function of the 87L setting.
Thus, once the voltage unit setting has been calculated, the current unit setting is easily determined.
Figure 5, which applies to the PVD21B and P)@210 relays, shcws the contact of the lockout relay connected to short out the Thyrit F only.
However, the 87H unit is not shorted so that the relay can continue to operate as an overcurrent function, because it cill stay picked up until the f ault is cleared.
The 87H unit may be used to implement breaker f ailure protection.
Device 62X can be connected as shown in Figure SA to initiate operation of the breaker f ailure timer.
The curve of Figure 8, which illustrates the 87H setting as a function of the 87L setting, includes sufficient margin to insure that the overcurrent unit will not operate during an external fault. For this reason, the 87H unit will be less sensitive than the 87L unit, and it may not operate for all internal f aults.
However, it will pick up as soon as the lockout relay operates, provided the f ault current is above the pickup setting.
In those cases where the 87H unit does not pick up until the lockout relay oprates, the dropout time of 87L is sufficient to overlap the pickup time of 87H, so that a continuous input will be provided to device 62X.
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i GCK-45405
)
h and/or secondary
~i If any of the bus differential cts are protected by primary voltage limiting devices, such as vacuum gaps, which might be the case if the bus banks, additional considerations are differential zone included shunt capacitorSome means must be incorporated to prevent necessary to ensure a reliable application.
this protective equipment from shorting the operating coils of the PVD during internal Such applications may be referred to the local General Electric Sales Office.
faults.
The external connection diagrams of Figures 4 and 5 indicate that the differential points for the relays are located in the switchyard.
F or outdoor installations where there is a great distance between the breaker and the relay panel, $
junction it may be desirable to locate the differential junction in the switthyard, since the loop may otherwise be' too large (refer to the sectLn, resistance of the f ault CT CALCULATION OF SETTINGS).
Ote that the cable resistance from the junction point to it is permissible to the relay is not included as 97 cf the f ault CT loop remtance, locate junctio the desired sensitivity.
The 87L unit should be set no higher than 0.67 time-the secondary excitation voltage at ten amperes secondary excitation current (evaluated for the poorest CT in the differential circuit).
When circuit breakers are to be bypassed for maintenance purposes, or when any other means than simply opening the PVD contact other atypical setup is to be made, circuit should be used to avoid incorrect tripping.
Voltages.that exceed Me continuous rating of the PVD may be developed with the high impedance operating @,
This can be avoided by removing the g
still connected in the differential circuit.
connection plug, or if external means are required, by short circuiting studs 4 and 5 to stud 6.
The following information Sust be obtained before settings are determined for a particular application:
e Determine the seccndary winding resistance for all the cts involved e Obtain the secondary excitation curves for all the cts involved e Determine the resistance of the cable leads from the cts to the differen junction point.
CONSTRUCTION The Type PVD relays are assembled in the medium size single-end (M1) drawout caseg having studs at one end in the rear for external connections.
The electrical connections between the relay and case studs are through stationary molded inner and l
The inner block has the outer blocks, between which nests a removable connecting plug.
tenninals for the internal connections.
Every circuit in the drawout case has an auxiliary brush, as shown in Figure 13, Some to provide adequate overlap when the connecting plug is withdrawn or inserted.
circuits are equipped with shorting bars (see internal connections, Figures 2 and 3),
and it is especially important that the auxiliary brush make contact on those circuits with adequate pressure to prevent the opening of important interlocking circuits, as g.
indicated in Figure 13.
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GEK-45405 The relay mechanism is mounted in a steel f ramework called the cradle and is a
'k complete unit with all leads terminated at the inner block.
This cradle is held firmly
, j in the case with a latch at t.oth top and bottom and by a guide pin at the back of the case.
The connecting plug, besides making the electrical connections between the respective blocks of the cradle and case, also iocks the latch in place.
The cover, which is drawn to the case by thumbscrews, holds the connecting plugs in place.
The target reset mechanism is a part of the cover assembly.
The relay case is suitable for either semiflush or surf ace mounting on all panels up to two inches thick, and appropriate hardware is available; however, panel thickness must be indicated on the relay order to insure that the proper hardware will be included. Outline and panel drilling dimensions are shown in Figure 1.
~
A separate testing plug can be inserted in place of the connecting plug
']
test the relay in place on the panel, either from its own source of current and voltage, or from other sources. The relay also can be drawn out and replaced by another which has been tested in the laboratory.
The relays covered by these instructions include two hinged armature type operating units: a " low-set" voltage unit, device 87L, and a "high-set" currant unit, device 87H.
Device 87L is an instantaneous telephone-type voltage unit having its coil connected across the DC terminal of a full wave rectifier.
In turn, the rectifier is connected to a high pass filter through an attenuator network.
The 87L unit has two normally open contacts.
One set of contacts is connected between terminals 7 and 8, and the other set is connected in parallel with the r.ontacts of the seal-in unit.
Device 87H is an instantaneous *overcurrent unit, gounted in the upper right hand corner, with its coil connected in series with ThyritF resistor discs. A single set of normally open contacts is connected between terndnals 9 and 10.
Hi-Seismic Seal-in Unit A seal-in unit is mounted in the upper lef t corner of the relay (see Figure 3).
The unit has its coil in series and its contacts in parallel with a set of normally open contacts of the 87L unit. When the seal-in unit picks up, it raises a target into view.
l The target latches up and remains exposed until it is released by manual operation of the reset button, which is located at the lower left corner of the relay.
RANGES These relays are available for 60 hertz. The standard operating ranges available are given in the table below.
Factors which influence the selection of the operating range are covered in the section on CALCULATION OF SETTINGS.
7
1 GEK-45405 i
h TABLE 2 87L UNIT LINK RANGE CONTINUOUS !
i RANGE POSITION VOLTS RATING VOLTS L
75 - 200 150 75-500 H
200 - 500 150 TABLE 3 CONTINUOUS
- 0NE SECOND 87H H1-SEISMIC I"TANTANEOUS LINK
- RANGE RATING RATING
' (AMPS)
POSITION (AMPS)
(AMPS)
(AMPS) i l
L 2 - 10 3.7 139 H
10 - 50 7.5 3
-ge is approximate, which means that the 2-10, 10-50 ampere range may a, 7-50 amperes.
There will always be at least one ampere overlap Select the higher vetween the maximum L setting and the minimum H setting.
range whenever possible, since it has the higher continuous rating.
4 For other ranges, consult the local General Electric Sales Office.
87L Continuous Rating The voltage circuit included in the 87L unit has a continuous voltage rating of Refer to the ACCEPTANCE TESTS section for precautions that should be 150 volts RMS.
taken during testing.
Contacts the contacts is 30 amperes for voltages not closing rating of The current The current carrying rating is limited by the seal-in unit exceeding 150 volts.
rating.
HI-SEISMIC TARGET AND SEAL-IN UNIT The Type PVD relay is provided with a universal target and seal-in unit having 0.2 and 2.0 ampere taps as indicated in the following tabulations.
If the tripping current exceeds 30 amperes, an auxilury relay should be used. '
Its connections should be such that the tripping current does not pass through the contacts or the target and c eal-in coils of the protective relay.
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I GEK-45405 TABLE 4 RATINGS OF THE SEAL-IN UNIT COIL TAP 0.2 2.0 DC Resistance +10%
(ohms) 8.0 0.24 "i
m rating (amperes) 0.2 2.0 Carry Continuous (amperes) 0.3 3.0 Carry 30 Amperes (seconds) 0.03 4.0 Carry 10 Amperes (seconds) 0.25 30.0 60 Hertz Impedance (ohms) 52 0.53 OPERATING PRINCIPLES All of the Type PVD relays include a high impedance voltage sensing unit (87L) that operates from the voltage produced by the differentially connected cts $Aring an internal f ault. The relays are also provided with either one or two Thyrit& stacks (see Table 1) connected in parallel with the 87L unit to limit the voltage across tM relay to safe values during internal f aults.
in limiting the voltage, the ThyritW will pass significant current during internal f aults, but very little current during normal operating conditions or external f aults.
The PV021B and PV0210 relays are provideg with an instantaneous overcurrent unit (87H) connected in series with the Thyrit69.
The 87H unit is set so that i' will not operate for the maximum external fault, but will operate for heavy internal faults.
The diagrams of Figures 4 and 5 illustrate typical external connections to the relays for use in a bus differential scheme.
A conventional differential circuit is utilized, that is, the cts associated with all of the circuits nff the bus are connected in wye and paralleled on a per-phase basis.
One PVD relay per phase is required to provide complete protection for the bus.
VOLTAGE UNIT (87L) - PV021A. PVD21B, PV021C. PVD210 If a protection scheme utilizing a PVD relay is to perform satisf actorily, it must not trip for f aults external to the zone of protection, such as at ~F1 in Figure 6.
Since the PVD relay is a high impedance device, consider the effect of an external single line to ground f ault. Figure 6 illustrates this condition for the f aulted phase only. Each of the cts associated with an infeeding circuit will produce the secondary voltage necessary to drive its secondary current through its winding and leads. The CT in the f aulted circuit will produce the voltage necessary to drive the total secondary f ault current through its winding and leads. If all of the cts were to perform ideally, there would be negligible voltage developed across junction points A and D, and hence across the PVD relay. Incidentally, load flow across the bus is similar 10 effect to an external f ault, so there will also be little voltage developed across the. relay during normal operating conditions. Unfortunately, during f ault conditions cts do not always perfonn ideally, because core saturation can cause a breakdown in CT ratio.
Such core saturation is generally accentuated by DC transients in the primary current.
Any residual flux lef t in the core may also add to the tendency to saturate.
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GEK-45405
.p in the example of Figure 6,' the worst condition would-be realized -if the CT h'
associated with the faulted circuit saturated completely, thus losing its ability to i
l produce: a secondary voltage, while the other cts did-not saturate at all.
When a CT 1
(saturates completely, its' secondary impedance approaches the secondary winding resistance, provided the secondary leakage reactance is_ negligible.
This will be the case tshen cts wound on a toroidal core with completely distributed windings are used.
- The cts in the infeeding circuits would then be unassisted by the fault CT and would have to produce 'enough voltage to force their secondary currents through their own
/
. windings and leads, as well as the windings and leads of the CT associated with the faulted circuit. As a result, a voltage will be developed across the junction points, The magnitude of this voltage will simply oe
$~
' A and D, and hence across the PVD relay.
equal to the product of the total resistance in the CT loop circuit and the total f ault
- current in secondary amperes, that is, I
VR * (R$ + 2R ) - F
[y)
L where:
VR = voltage.across PVD relay RS = CT secondary winding and lead resis ~nce RL = one'way cable resistance from junction point to CT IF = RMS value of primary f ault current N = CT ratio _
Note that 'the f actor of two, appearing with the RL term, is used to account for the fact that-all of-the fault current will flow through both the outgoing cable and the return cable for single line to ground faults.
If the cts are-connected as shown in g
-Figures 4 or 5, no. current.will flow in the return lead for three phase f aults, thus the maximum voltage develope'd across the PVD relays for three phase f aults can be calculated as-follows:
VR = (R$+R)
-(2)
L
.Equotions-(1) and (2)-can be consolidated and written as follows:
VR = (Rs +-PR ) -
(3)
L
-ohere:
P = 1 for three-phase faults,..and 2 for single line to ground faults.
For the conditions-in question, this voltage, VR, is the maximum voltage that g
~
could possibly be developed across the PVD relay.
Obviously, the CT in the faulted
' circuit will not lose all of-its ability to produce an assisting voltage, and the cts in the'infeeding-circuits may tend to saturate to some degree.
In practice, the voltage deeeloped across the relay will be something less than that calculated from equation The ef fect of-CT saturation is accounted for by the CT performance f actor,
- (3).above..
K,_used in the equation for calculating the actual voltage setting, and it is discussed further in the.section CALCULATION OF SETTINGS.
L Now consider the effect of an internal fault. In this case, all_of the infeeding l
g The cts will be operating into the high impedance PVD in parallel with any idle cts.
voltage developed across the junction points A and D will now approach the open-circuit f
10
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- - - -.. ~ -. - -
3 i-GEK-45405-
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Usecondary voltage that the cts can produce.
Even for a moderate internal f ault, this poltage will-be -in excess of the value calculated for the maximum external f ault as idescrjbed above. Therefore, the high impedance voltage sensing unit, 87L, can be set cith a pickup setting high-enough so that it will not operate as the result of the maximum external f ault, but will still pick up for moderate and even slight internal
-faults. Consequently, the relay will be selective between internal f aults and external
- f aults or load flow.
The actual equation for calculating the 87L voltage unit setting, taking _ CT performance and margin into account, is as follows:
I VR = (K) (1.6) (R$ + PR )'-
F (4) t N
s chere:
K
= CT performance f actor (see Figure 7) 1.6 = margin factor i-All other terms are as described above.
i OVERCURRENT-UNIT (87H) - PVD218. - PVD210
-The PVD21B and PVD210 relays are similar to the PVD21A and PVD21C
- lays, respectively, except for the addition of the 87H unit in series with the Thyri
_The 8711 unit is set so that it will not operate on the current passed by the Thyrit during
- external f aults, but so that -it will operate on the current passed during heavy internal faults.
p i
During normal operating conditions, there will be little voltagdeveloped across the PUD relay, and hence across the series combination of the ThyritW and 87H. During 3
l external f aults, the same would be true if the cts did not saturate. Even if the CT in the f ault circuit: saturated completely, the maximum voltage that could be developed across the-relay would be limited to the drop in the CT resistance plus the associated cable resistance. Because 87L is set at some value above Me maximum expected _ drop, it is possible to determine the current through 'the Thyrit4W at the 87L setting, and so 1-
[
determine a suitable setting for 87H to insure that it does not operate for the maximum external _ f ault_.- Figure 8 illustrates the minimum safe pickup setting to be made as a-i function of the 87L setting-with suitable margin included. Thus, once the 87L setting has been-calculated, the 87H setting can be easily determined from Figure 8.
f During internal f aults, the cts will attempt to drive all of the f ault current through -the high impedance PVD relay.
As a result, the voltage will build u kquite
' rapidly. across the relay.
_ As the voltage builds up, the. nonlinear Thyritstu will L exhibit a declinin (resistance characteristic, so that significant current will flow
.through the.Thyrite and so cause 87H to operate.
Because of the margin involved in setting the 87H unit, it will not be quite as sensitive as the 87L unit and it may not operate for some low level.f aults. It is not possible to predict at exactly what f ault.
" level the 87H unit will-operate _because of the numerous f actors involved. However, 87H i
still may be'used to supplement tripping by 87L with the assurance that it will at least
!: operate for heavy internal faults. The 87H unit may also be used to implement breaker f allure protection, as described in the APPLICATION section.
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CALCULATION OF SETTINGS The formulas and procedures described in the f ollowing paragraphs for determining the relay is connected to the full windings of relay settings assume that Further, they assume that the secondary winding of each dif ferentially connected cts.
if CT has negligible leakage reactance, and that all of the cts have the same ratio, these are not the conditions that exist in your application, please contact the nearest General Electric District Sales Office.
SETTING OF THE HIGH IMPEDANCE UNIT 87L As suming that an external f ault causes complete saturation of the CT in the f aulted circuit, the current forced through this secondary by the cts in the infeeding circuits will be impeded only by the resistance of the winding and leads.
The resulting IR drop will be the maximum possible voltage which can appear across the PVD relay f or that external fault.
The setting of the high impedance 87L unit was described in OPERATING PRINCIPLES.
It is expressed as follows:
IF (5)
VR = (K) (1.6) (Rs + PR )
L N
= pickup setting of 87L unit where:
VRRS = DC resistance of f aulted CT secondary windings and leads to g
housing terminal
= single conductor DC resistance of CT cable for one way run from CT Rt housing tenninal to junction point (at highest expected operating temperature)
= 1 for three phase f aults, 2 f or single phase to ground f aults P
= external f ault current, primary RMS value IFN = CT ratio 1.6 = margin factor K = CT performance f actor f rom Figure 6.
for single The calculations only need to be made with the maximum value of IFIf the phase and three phase f aults.
perform satisf actorily for all f aults.
in OPERATING PRINCIPLES, the pessimistic value of voltage As previously noted determined by equation (5) for any of the methods outlined is never realized in g
not saturate to the point where it practice.
The CT in the f aulted circuit will Furthermore, the condition which caused the f aulted CT produces no assisting voltage.
core to saturate also tends to saturate the cores of the cts in the infeeding circuits, These effects are not resulting in a further decrease in voltage across the PVD relay.
readily calculated; however, extensive testing under simulated f ault conditions on bushing cts similar to those supplied in most circuit breakers manuf actured in the United States, has resulted in the establishment of a so-called " performance f actor,"
The perf ormance f actor, K, is not a which can be determined for each application.
constant for a given bushing CT, but varies for each installation, depending on the X is readily determined from the curve of Figure 6, which is a
l T
3 + PR ) IF/N.
i value of (R The use of this curve is explained in SAMPLE CALCULATIONS.
L based on test data.
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1 GCK-45405 The value of the 87L unit setting established by equation (5) is the minimum safe setting. Higher settings will provide more safety margin, but will result in somewhat reduced sensitivity.
The methods of utilizing equation (5) are outlined below:
Method I - Exact Method.
(1) Determine the maximum three phase and single phase to ground fault currents for f aults just beyond each of the breakers.
(2) The value RL is the one way cable DC resistance from the junction point to the f aulted CT being considered.
(3)
For each breaker in turn, calculate VR separately utilizing the associated maximum external three phase f ault current, with P = 1, and the maximum external single phase to ground f ault current, with P = 2.
(4) Use the highest of the values nf VR obtained in (3) above.
Method 11 - Simplified Conservative Method:
(1) Use the maximum interrupting rating of the circuit breaker as the maximum external single phase to ground fault current.
(2) The value RL is based on the distance from the junction point to the most distant CT.
(3) Calculate a value for VR using P = 2.
(4)
This value of VR becomes the pickup setting.
Begin with Method II. The calculated value of VR is determined as outlined in the paragraph, " Minimum Fault to Trip 87L."
If the sensitivity resulting from the value calculated is not adequate, then Method I should be used.
When the 87L pickup from Method 11 proves to yield an adequate sensitivity, a unique advantage is realized, since the 87L pickup setting will not require recalculation following changes in system configuration, which would result in higher bus f ault magnitudes.
It is desirable for the pickup voltage of the 87L unit to plot below the knee point of the excitation curve (that is, the point on the excitation curve where the slope is 45 degrees) of all the cts in use.
However, it is permissible for the 87L pickup voltage to be higher than the knee point voltage. The maximum setting f or the 87L unit is equal to the secondary excitation voltage at ten amperes secondary excitation current (evaluated for the poorest CT in the differential circuit), multiplied by 0.67.
Minimum Fault to Trip 87L Unit Af ter the pickup setting of the 87L unit;has been established for an application, a check should be made to determine the minimum internal f ault current which will just cause the unit to operate, if this value is less than the minimum internal f ault current expected, the pickup setting is suitable for the application.
The following i
a i olndicates Revision 13
f.N w
y GEK-45405 Lexpression can be used to determine the minimum internal f ault enrrent required for a $
particular 87L unit pickup setting:
(6)
'Imin "
f(I)X+IR+I.I N
x = 1-5 min = minimum internal f ault current to trip 87L where:
= number of breakers. connected to the bus, (i.e., number n
of cts per_ phase)
= secondary excitation current of individual CT at a g*
voltage equal to the pickup of 87L
= current in 87L unit atgickup voltage = VR/1700 IR
= current in_ the ThyritW unit at 87L, pickup voltage (see I]
Figure 11)
N = CT ratio I,
etc., are obtained from the secondary.exc1tation 1,
The values--of characteristics of the respective cts. The first term in equation (6) reduces to NI if ~
2 1
The relay curent,
_it is assumed that all cts have the same excitation characteristic.
. Ig, can be determined f rom the -impedance of the 87L circuit, assumed to be constant at 1700 ohms. That is:
(7)-
R
- V /1700 I
R
~ The current drawn by t.he Thyrittb unit,- 1, can be obtained ' rom that cur.ve in Figure 1) h 1
- that: applies to the relay being ased, SETTING OVERCURRENT UNIT, 87H The required setting for the overcurrent unit, 87H, is dependent on the actual Figure 8, which_ is a _ plot of. the 87H setting in RMS setting of_the voltage unit, 87L.
amper_es~ versus the 87L setting in-RMS volts, illustrates the relationship between these two; settings. _. In order to determine the required 87H-setting, it is only necessary to calculate:the 87L settin.g and then enter the curve of_ Figure 8 at that value of voltage to read the 87H setting directly.
SAMPLE CALCULATION' The various: steps for determining the settings of the PVD relay in a. typical Lapplication will-be explained with the aid of a worked example. Method II will be usede W
.with the following assumed parameters:
Number of breakers:
five L aximum breaker-interrupting rating:
40,000 amperes MCable resistance for longest'run: 0.50 ohrns at 25oC
CT ' R atio:
1200/5-The value of R5 from
' The characteristics for the 1200/5 CT are shown in Figure 12.
this figure is:
Y R _ = (0.0029) (240) 6 0.113 = 0.809 ohms 3
~
GEK-45405 The cable resistance for the longest CT run is given at 250C.
If higher operating temperatures are expected, this must be taken into account in determining the maximum Lxpected resistance. Resistance values of wire at 250C, or at any temperature, tl, may be corrected to any other temperature, t2, as follows:
1 (t2 - tl)] R Rt2 =
12 P t1 where:
Rt1 = resistance in ohms at tl, degrees Centigrade t2 = resistance in ohms at t2, degrees Centigrade R
= temperature coefficient of resistance at tl P1 For standard annealed copper, P1 = 0.00385 at t1 - 250C; therefore the value of RL at 500C is:
RL+
1 + 0.00385 (50 - 25) 0.5 = 0.548 ohms The CT performance f actor, K, must next be determined.
To do this, first calculate:
(Rs + PR ) (Ip)
L (E ) (N)
S Because Method II was selected, use P = 2.
From Figure 12, Es = 300 volts (2) (0.548)
(40.0001]
f(0.809)
+
= 1.06 (300) (240)
F rom F igure 7, K = 0.7.
Using Equation (5), the appropriate relay setting is:
(1.61 (0.7) [0.809 + (2) (0.5481] (40,000)
VR=
240 VR = 355 volts This value is just above the knee point (300 volts) of the CT characteristic, and well below 67 percent of the voltage at ten amperes excitation (0.67) (590) so the l
application is satisfactory in that respect.
l Next it is necessary to getermine whether the PV021A or PV0210, or the PV021C or l
First determine the knee point PV0210 (one versus two Thyrit6W stacks) should be used.From Figure 12, Es = 300 volts (all ct l
voltage, Es, for the poorest CT in the circuit. Assume that the maximum internal f ault current is 45, are assumed to be identical).
The curve of Figure 10, amperes primary, which is equivalent to 188 amperes secondary.
when entered at these coordinates (300 volts and 188 amperes), gows that the stacks).
If application is safe for either the PV021C or PV0210 relays (two Thyrit60 Figure 9 were entered at the same coordinates, it would show that PV021A or PV0218 would not be applicable.
The next step in the calculation is to determine the sensitivity of the relay to internal faults.
This may be done using equation (6) as follows:
GEK-45405 Frm the excitation curve of Figure 12, I at 355 volts: 0.07 amperes g
1.1 amperes (use curve for From tAe Thyrith curve of Figure 11, I at 355 volts:
two Thyriteu stacks)
From equation (7):
IR = 355/1700 = 0.209 amperes From equation (6):
h Imin =
(0.07) + 1.1 + 0.029 240 Imin = 398 amperes primary If the minimum internal primary f ault current is above 398 amperes, the pickup setting of -355 volts is adequate.
unit will be included in the relay, then the If the instantaneous overcurrent To determine the 87H setting, enter the curse of Figure 8 at the PV0210 must be used.
calculated 87L setting of 355 volts. Read the 87H setting from the scale for the PV0210 4
relay.
For the 355 volt setting of 87L, the appropriate setting for 87H is 11.8 amperes.
RECEIVING, HANDLING AND STORAGE in included as part of a control panel will be shipped These relays, when not Imediately upon receipt of a relay, cartons designed to protect them against damage.
examine it for any damage sustained in transit.
If damage resulting from rough handling is evident, file a damage claim at once with the transportation company and promptly notify the nearest General Electric Apparatus Sales Office.
Reasonable care should be exercised when unpacking the relay in order that none of If the relays are not to be the parts are damaged nor the adjustments disturbed.
installed immediately, they should be stored in their original cartons in a place that on the is free fra moisture, dust and metallic chips.
Foreign matter collected outside of the case m6y find its way inside when the cover is removed, and cause trouble in the operation of the relay.
ACCEPTANCE TESTS p,
Immediately upon receipt of the relay, an inspection and acceptance test should be in shipment and that the relay made to insure that no damage has been sustained These tests may be performed at the discretion calibrations have not been disturbed.
of the user, since most orarating companies use different procedures for acceptance and The following section includes all applicable tests that may be installation tests.
performed on these relays.
!~
4 GEK-45405 i
l VISUAL INSPECTION Check the nameplate stamping to insure that the model calibration range of the relay received agree with the requisition. number, rating and Remove the relay from its case and check that molded parts, or other signs of physical damage, and that all screws are tight.there are no broken MECHANICAL INSPECTION Cradle and Case Blocks Check that the fingers on the cradle and case agree with the internal connection diagram.
Check that the shorting bars are in the correct position, and that each finger with a shorting bar makes contact with the shorting bar.
Deflect each contact finger to insure that there is sufficient contact force available, and check that each I
auxiliary brush is bent high enough to contact the connection plug.
Contact 87L The following mechanical adjustments must be checked:
1.
The armature and contacts of the seal-in unit, as well as the armature and contacts of the instantaneous unit, should move freely when operated by hand.
There should be at least 0.015 inch wipe on the seal-in contacts.
2.
The targets in the seal-in and the instantaneous unit must come into view and latch wnen the armatures are operated by hand, and they should unlatch when the target release button is operated.
3.
The brushes and shorting bars should agree with the internal connections diagram.
4 With the telephone relays in the de-energized position, all circuit closing contacts should have a gap of 0.015 inch, and all circuit opening contacts should have a wipe of 0.005 inch.
The gap may be checked by inserting a feeler gage.
Wipe can be checked by observing the amount of deflection on the stationary contact before parting the contacts.
The armature should then be operated by hand, and the gap and wipe again checked as described above.
ELECTRICAL SETTING AND INSPECTION Hi-Seismic Instantaneous Unit, 87H Make sure the instantaneous unit link is in the correct position for the range in which it is to operate.
See internal connections diagram, Figures 3 and 4, and connect as indicated in the test circuit of Figure 14A.
Use the higher range whenever possible, since the higher range has a higher continuous rating.
kS
GEK-45405 Setting the Hi-Seismic Instantaneous 'Jnit To The instantaneous unit has an adjustable core located at the top of the unit.
set the instantaneous unit to a desired pickup, loosen the locknut and adjust the core.
Turning the core clockwise decreases the pickup; turning it counterclockwise increases It may be necessary to repeat it. Bring the current up slowly until the unit picks up.
Once the desired pickup this operation until the desired pickup value is obtained.
value is reached, tighten the locknut.
Refer to the RATINGS section for continuous and one second ratings of the Do not exceed these ratings when applying current to g
CAUTION:
instantaneous unit.
the instantaneous unit.
The range of the instantaneous unit must be obtained between one-eighth and 20 turas counterclockwise of the core from the fully clockwise position.
Hi-Seismic Tarcet and Seal-in Unit The target and seal-in unit has an operating coil tapped at 0.2 and 2.0 amperes.
The relay is shipped from the f actory with the tap screw in the lower ampere position.
To change the tap The tap screw is the screw holding the right had stationary contact.
setting, first remove one screw from the lef t-hand stationary contact and place it in Next remove the screw from the undesired tap and place it on the lef t-the desired tap.
This procedure is necessary hand stationary contact where the first screw was removed.
Screws to prevent the right-hand stationary contact from getting out of adjustment.
should never be lef t in both taps at the same time, g
TABLE 5 TAP PICKUP CURRENT OROPOUT CURRENT 0.2 0.15 - 0.195 0.05 or more 2.0 1.50 - 1.95 0.50 or more 87L Unit can be adjusted at any voltage within the range shown on its The 87L unit Four specific calibration values, for both the high and low voltage calibration plate.
range are shown on the plate, which correspond to the values stamped on the nameplate.
The 87L unit, unless otherwise specified on the requisition, will be set at the f actory g
If the unit is to be set at some other point, to operate at its minimum pickup voltage.the calibration marks should be used as a test circut of Figure 148 should then be used to make an exact setting.
l When the test plug is inserted in the relay, as depicted in Figure 146, the i
l current transformer secondaries are shorted by means of the link between the outer The adjustable test voltage is applied across terminals 5 and 6 of l
terminals 5 and 6.
Since the the relay; that is, across the voltage circuit which includes the 87L u that a hand-reset lockout relay be used in the test setup if the desired 87L setting is g
Y
)
to be above this figure.
l I
l
GEK-45405 The following procedure should be f ollowed in checking pickup of the 87L unit.
Lower Start with a test voltage considerably higher than the expected operating point.
the test voltage by successively smaller increments, closing the test switch at each point.
The lockout relay will operate each time, protecting the resonant circuit.
The Eventually, a point will be reached where the 87L unit will just f ail to operate.
preceding voltage value, therefore, is the pickup value of the 87L unit (within reasonable accuracy).
At the point where the 87L unit f ails to pick up, the test voltage must be removed at once to prevent synage to the relay.
If the 87L unit setting is to be less than the 150 volt cor.tinuous rating, it will not be necessary to use the lockout relay. The voltmeter used must have high internal impedance.
in The 87L unit operating time can be checked by using the test circuit shown Figure 148 and measuring the time elapsed between application of the input voltage and The times measured should be within plus the operation of the 87L. output contacts.
three and minus seven milliseconds of the time shown in Figure 15.
Thyritl@ Uni t Apply 120 volts cirect current to studs 3 and 6.
The current should be between 0.005 and 0.012 amperes for a single slack, and between 0.010 and 0.024 amperes for a double stack of Thyrith.
The ThyritsW is very voltage sensitive, and should be se*
in the voltmeter will be magnified four to five carefully.
Also, any meter error times, for example, a three percent meter error will have an effect on the current of from 12 to 15 percent.
INSTALLATION PROCEDURE LOCATION AND MOUNTING The relay snould be mounted on a vertical surface in a location reasonably free The_ relay case may be grounded from excessive neat, moisture, dust and vibration.
using at least *12 AWG gage copper wire. The outline and panel drilling dimensions for Type PVD relays are shown in Figure 1.
CONNECTIONS' Internal connections diagrams for the Type PV021A and PV021C, and the Type PV0218 The elementary diagram and PVD210 relays, are shown in Figures 2 and 3, respectively.
of the external connections for a typical application is shown in Figure 4.
Note in Figure 4 that when the relay is installed, a connecting jumper should be placed between terminals 4 anc 5, and that terminals 5 and 6 are then connected across differential junction points A and B of the several current transformers.
A shorting bar is provided between terminals 5 and 6 so that if the connection plug of the relay is withdrawn, the differential circuit will not be opened.
The midpoint between the Thyrith stack and unit 87H is connected to terminal 3.
l This makes it possible to test or calibrate unit 87H without the. necessity of passing
'~
i l
GEK-45405 high current through the Thyrith, and makes it possible to short out the 87H coil when its operation is not necessary.
The external connections in Figure 4 indicate that the diff erential junction, This is important in outdoor points A and B, should be located in the switchyard.
installations where the distance between the breaker and relay panel may be great, since the resistance through the f ault CT loop may otherwise be too large.
The junction points can be located at the panel, provided that the necessary relay setting gives the desired sensitivity.
There should be only one ground connection in the secondary circuit.
When the g
junction points are located in the switchyard, the ground connection should be made there rather than at the panel.
Tne voltage limiting Thyrith is short-time rated. The contacts of the auxiliary relay device 86 short circuits the differential circuit to protect it.
UNDER NO CIRCUMSTANCES SHOULD THE RELAY BE PLACE 0 IN SERVICE CAUTION:
THYRITE VOLTAGE LIMITING CIRCUIT CONNECTED; THAT IS, WITHOUT A JUMPER BETWEEN TERMINALS 4 AND 5.
OTHERWISE, THE RELAY AND SECONDARY WIRING WILL INTERNAL NOT BE PROTECTED FROM HIGH CREST VOLTAGES WHICH RESULT FROM AN FAULT.
VISUAL !NSPECTION Repeat the items described under ACCEPTANCE TESTS, VISUAL INSPECTION.
g MECHANICAL INSPECTION AND ADJUSTMENTS Repeat the items described under ACCEPTANCE TESTS, MECHANICAL INSPECTION, TARGET / SEAL-IN UNIT Set the target / seal-in unit tap screw in the desired position.
The contact adjustment will not be disturbed if a screw is fir.st transferred fran the lef t contact to the desired tap position on the right contact, and then the screw in the undesired tap is removed and transferred to the left contact.
87H AND 87L UNITS Refer to the appropriate descriptions in ACCEPTANCE TESTS for the proper method of g
setting the 87L and 87H units.
The external trip circuit wiring to the relay, as well as the relay itself, should l
the be checked by operating one of the relay units by hand and allowing it to trip Observe that the target operates upon manual operation of breaker or lockout relay.
the relay unit.
t l
t I
OO
GEK-45405 PERIODIC CHECKS AND ROUTINE MAINTENANCE In view of the vital role of protective relays in the operation of a power system, it is important that a periodic test program be f ollowed.
The interval between periodic checks will vary depending upon environment, type of relay and the user's Until the user has accumulated enough experience to experience with periodic testing.
interval best suited to his individual requirements, it is suggested select the test that the points listed under INSTALLATION PROCEDURE be checked at an interval of from one to two years.
the items described in ACCEPTANCE TESTS, both VISUAL and MECHANICAL Check Examine each component for signs of overheating, deterioration, or other INSPECTION.
damage.
Check that all connections are tight by observing that the lockwashers are fully collapsed.
CONTACT CLEANING Examine the cont' cts for pits, arc or burn marks, corrnsion and insulating films.
A flexible burnishing tool should be used for cleaning relay contacts.
This is a which in effect resembles a flexible strip of metal with an etched-roughened surf ace, licate that no scratches hre superfine file. The polishing action of this file is so de it cleans off any corrosion thorougnly and rapidly.
The lef t on the contacts, yet Relay flexibility of the tool insures the cleaning of the actual points of contact.
contacts should never te cleaned with knives, files, or abrasive paper or cloth.
PERIODIC TEST EQUIPMENT A test set is available for periodic testing of PVD relays.
It is intended to be mounted on the panel aojacent to the relays, and in addition to testing, it can also be transformers for open or short circuits, and incorrect wiring.
used to check current This test set is more fully described in instruction book GEI-50290.
ELECTRICAL TESTS Pickup of the 57L and 87H units should be measured and the results compared against the desired setting.
If a measured value is slightly different from that it is not necessarily an indication that the relay needs previously, measured The errors in all the test equipment are additive, and the total error readjustment.
of the present setup may be of opposite sign from the error present during the previous Instead of readjusting the relay, if the test results are acceptable, periodic test.
should be made.
Note the deviation on the relay test record.
After no adjustment sufficient test data has been accumulated, it will become apparent whether the measured deviations in the setting are due to random variations in the test conditions, or are due to a drift in the relay characteristics.
THYRIT[bUNIT Repeat the test described in ACCEPTANCE TESTS, ELECTRICAL INSPECTION.
I GEK-45405
(
HI-SEISMIC INSTANTANEOUS UNIT, 87H Check f or the following:
1.
Both contacts should close at the same time.
The backing should be so formed that the forked end (front) bears against the 2.
molded strip under the armature.
With the armature against the pole piece, the cross member of the "T" spring 3.
should be in a horizontal plane, and there should be at least 0.015 inch wipe g
on the contacts.
Check by inserting a 0.010 inch feeler gage between the The contacts front half of the shaded pole with the armature held closed.
should close with the feeler gage in place.
HI-SEISMIC TARGET AND SEAL-IN UNIT Check steps 1 and 2 as describea in the paragraph above for the instantaneous To check the wipe of the seal-in unit, insert a 0.010 inch feeler gage between unit.
the plastic residual bump of the armature and the pole piece with the armature held closed. The contacts should close with the feeler gage in place.
RENEWAL PARTS in stock for the prompt g
Sufficient quantities of renewal parts should be kept replacement of any that are worn, broken or camaged.
Sales Office of the General When ordering renewal parts, address the nearest Specify the name of the part watited, quantity required, and catalog Electric Company.
numbers as shown in Renewal Parts Bulletin GEF-4543.
9 4
6
GEK-45405 PANEL LOCATION (168MM)
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(FRONT VIEW) l Figure 1 (K-6209273-3) Outline and Panell Orilling Dimensions f or an M1 Case a
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GEK-45405 87L* 0tif f tlefl&L REL AY L0w $11 Unit 47 5.1.
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Type PV021A and Type PVD21C Relays
GEK-45405 87L= OlFFEREATi&L RtLAY LOW SET Unli 87M= 0lFFER DTIAL RELAY uten SET UnlT li S.I. zDIFFERDTIAL RELAY SEAL-IR H IT CW Li = REACTOR RMI: 87L CAlllRATION POT.
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