P14x en ap a00

Application Notes for MiCOM P14x High Impedance Protection

April 2004

P14x/EN AP/A00

HANDLING OF ELECTRONIC EQUIPMENTA persons normal movements can easily generate electrostatic potentials of several thousand volts. Discharge of these voltages into semiconductor devices when handling circuits can cause serious damage, which often may not be immediately apparent but the reliability of the circuit will have been reduced. The electronic circuits of AREVA T&D UK Ltd - Energy Automation & Information products are immune to the relevant levels of electrostatic discharge when housed in their cases. Do not expose them to the risk of damage by withdrawing modules unnecessarily. Each module incorporates the highest practicable protection for its semiconductor devices. However, if it becomes necessary to withdraw a module, the following precautions should be taken to preserve the high reliability and long life for which the equipment has been designed and manufactured. 1. 2. Before removing a module, ensure that you are a same electrostatic potential as the equipment by touching the case. Handle the module by its front-plate, frame, or edges of the printed circuit board. Avoid touching the electronic components, printed circuit track or connectors. Do not pass the module to any person without first ensuring that you are both at the same electrostatic potential. Shaking hands achieves equipotential. Place the module on an antistatic surface, or on a conducting surface which is at the same potential as yourself. Store or transport the module in a conductive bag.

3. 4. 5.

More information on safe working procedures for all electronic equipment can be found in BS5783 and IEC 60147-0F. If you are making measurements on the internal electronic circuitry of an equipment in service, it is preferable that you are earthed to the case with a conductive wrist strap. Wrist straps should have a resistance to ground between 500k 10M ohms. If a wrist strap is not available you should maintain regular contact with the case to prevent the build up of static. Instrumentation which may be used for making measurements should be earthed to the case whenever possible. AREVA T&D UK Ltd - Energy Automation & Information strongly recommends that detailed investigations on the electronic circuitry, or modification work, should be carried out in a Special Handling Area such as described in BS5783 or IEC 60147-0F.

&217(17

6$)(7< 6(&7,21+HDOWK DQG VDIHW\ ([SODQDWLRQ RI V\PEROV DQG ODEHOV

,167$//,1* &200,66,21,1* $1' 6(59,&,1* (48,30(17 23(5$7,1* &21',7,216&XUUHQW WUDQVIRUPHU FLUFXLWV ([WHUQDO UHVLVWRUV %DWWHU\ UHSODFHPHQW ,QVXODWLRQ DQG GLHOHFWULF VWUHQJWK WHVWLQJ ,QVHUWLRQ RI PRGXOHV DQG SFE FDUGV )LEUH RSWLF FRPPXQLFDWLRQ

2/'(5 352'8&76 '(&200,66,21,1* $1' ',6326$/ 7(&+1,&$/ 63(&,),&$7,216

6$)(7< 6(&7,217KLV 6DIHW\ 6HFWLRQ VKRXOG EH UHDG EHIRUH FRPPHQFLQJ DQ\ ZRUN RQ WKH HTXLSPHQW

+HDOWK DQG VDIHW\ 7KH LQIRUPDWLRQ LQ WKH 6DIHW\ 6HFWLRQ RI WKH SURGXFW GRFXPHQWDWLRQ LV LQWHQGHG WR HQVXUH WKDW SURGXFWV DUH SURSHUO\ LQVWDOOHG DQG KDQGOHG LQ RUGHU WR PDLQWDLQ WKHP LQ D VDIH FRQGLWLRQ ,W LV DVVXPHG WKDW HYHU\RQH ZKR ZLOO EH DVVRFLDWHG ZLWK WKH HTXLSPHQW ZLOO EH IDPLOLDU ZLWK WKH FRQWHQWV RI WKH 6DIHW\ 6HFWLRQ

([SODQDWLRQ RI V\PEROV DQG ODEHOV 7KH PHDQLQJ RI V\PEROV DQG ODEHOV PD\ EH XVHG RQ WKH HTXLSPHQW RU LQ WKH SURGXFW GRFXPHQWDWLRQ LV JLYHQ EHORZ

&DXWLRQ UHIHU WR SURGXFW GRFXPHQWDWLRQ

&DXWLRQ ULVN RI HOHFWULF VKRFN

3URWHFWLYHVDIHW\ HDUWK WHUPLQDO

)XQFWLRQDO HDUWK WHUPLQDO 1RWH 7KLV V\PERO PD\ DOVR EH XVHG IRU D SURWHFWLYHVDIHW\ HDUWK WHUPLQDO LI WKDW WHUPLQDO LV SDUW RI D WHUPLQDO EORFN RU VXEDVVHPEO\ HJ SRZHU VXSSO\

127( 7+( 7(50 ($57+ 86(' 7+528*+287 7+( 352'8&7 '2&80(17$7,21 ,6 7+( ',5(&7 (48,9$/(17 2) 7+( 1257+ $0(5,&$1 7(50 *5281'

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

(48,30(17 23(5$7,1* &21',7,2167KH HTXLSPHQW VKRXOG EH RSHUDWHG ZLWKLQ WKH VSHFLILHG HOHFWULFDO DQG HQYLURQPHQWDO OLPLWV

&XUUHQW WUDQVIRUPHU FLUFXLWV 'R QRW RSHQ WKH VHFRQGDU\ FLUFXLW RI D OLYH &7 VLQFH WKH KLJK OHYHO YROWDJH SURGXFHG PD\ EH OHWKDO WR SHUVRQQHO DQG FRXOG GDPDJH LQVXODWLRQ

([WHUQDO UHVLVWRUV :KHUH H[WHUQDO UHVLVWRUV DUH ILWWHG WR UHOD\V WKHVH PD\ SUHVHQW D ULVN RI HOHFWULF VKRFN RU EXUQV LI WRXFKHG

%DWWHU\ UHSODFHPHQW :KHUH LQWHUQDO EDWWHULHV DUH ILWWHG WKH\ VKRXOG EH UHSODFHG ZLWK WKH UHFRPPHQGHG W\SH DQG EH LQVWDOOHG ZLWK WKH FRUUHFW SRODULW\ WR DYRLG SRVVLEOH GDPDJH WR WKH HTXLSPHQW

,QVXODWLRQ DQG GLHOHFWULF VWUHQJWK WHVWLQJ ,QVXODWLRQ WHVWLQJ PD\ OHDYH FDSDFLWRUV FKDUJHG XS WR D KD]DUGRXV YROWDJH $W WKH HQG RI HDFK SDUW RI WKH WHVW WKH YROWDJH VKRXOG EH JUDGXDOO\ UHGXFHG WR ]HUR WR GLVFKDUJH FDSDFLWRUV EHIRUH WKH WHVW OHDGV DUH GLVFRQQHFWHG

,QVHUWLRQ RI PRGXOHV DQG SFE FDUGV 7KHVH PXVW QRW EH LQVHUWHG LQWR RU ZLWKGUDZQ IURP HTXLSPHQW ZKLVW LW LV HQHUJLVHG VLQFH WKLV PD\ UHVXOW LQ GDPDJH

)LEUH RSWLF FRPPXQLFDWLRQ :KHUH ILEUH RSWLF FRPPXQLFDWLRQ GHYLFHV DUH ILWWHG WKHVH VKRXOG QRW EH YLHZHG GLUHFWO\ 2SWLFDO SRZHU PHWHUV VKRXOG EH XVHG WR GHWHUPLQH WKH RSHUDWLRQ RU VLJQDO OHYHO RI WKH GHYLFH

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

,QVXODWLRQ &DWHJRU\ 2YHUYROWDJH

(QYLURQPHQW

,(& $ 3ROOXWLRQ GHJUHH (1 3ROOXWLRQ GHJUHH

3URGXFW 6DIHW\

((&

&RPSOLDQFH ZLWK WKH (XURSHDQ &RPPLVVLRQ /RZ 9ROWDJH 'LUHFWLYH &RPSOLDQFH LV GHPRQVWUDWHG E\ UHIHUHQFH WR JHQHULF VDIHW\ VWDQGDUGV

(1 (1

Application Notes MiCOM P141, P142, P143

P14x/EN AP A00 Page 1/20

CONTENTS1. 2. 3.3.1

INTRODUCTION USE OF METROSIL NON-LINEAR RESISTORS MiCOM P140P140 Application Considerations

3 5 77

4.4.1 4.2 4.3

APPLYING THE P140Advanced application requirements for through fault stability Transient stability limit Steady state stability limit

88 8 9

5.5.1 5.2 5.3 5.4 5.5 5.6 5.7

TYPICAL SETTING EXAMPLESRestricted earth fault protection Stability voltage Stabilising resistor Current transformer requirements Metrosil non-linear resistor requirements Advanced REF application requirements for through fault stability Transient Stability Limit

99 9 9 10 10 11 11

6.6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 6.10

BUSBAR PROTECTIONStability voltage Current setting Discriminating zone Check zone Stabilising resistor Current transformer requirements Metrosil non-linear resistor requirements Busbar supervision Advanced busbar application requirements for through fault stability Transient stability limit

1212 12 12 13 13 13 13 14 14 14



Figure 1: Principle of high impedance protection Figure 2: Double busbar generating station Figure 3: Phase and earth fault differential protection for generators, motors or reactors Figure 4: Restricted earth fault protection for 3 phase, 3 wire system-applicable to star connected generators or power transformer windings Figure 5: Balanced or restricted earth fault protection for delta winding of a power transformer with supply system earthed Figure 6: Restricted earth fault protection for 3 phase, 4 wire system-applicable to star connected generators or power transformer windings with neutral earthed at switchgear Figure 7: Restricted earth fault protection for 3 phase, 4 wire system-applicable to star connected generators or power transformer windings earthed directly at the star point Figure 8: Phase and earth fault differential protection for an auto-transformer with CTs at the neutral star point Figure 9: Busbar protection simple single zone phase and earth fault scheme Figure 10: Restricted earth fault protection on a power transformer LV winding

3 15 15 16 16 17 17 18 18 19



1.

INTRODUCTIONThe application of the P14x numerical overcurrent relay as differential protection for machines, power transformers and busbar installations is based on the high impedance differential principle, offering stability for any type of fault occurring outside the protected zone and satisfactory operation for faults within the zone. A high impedance relay is defined as a relay or relay circuit whose voltage setting is not less than the calculated maximum voltage which can appear across its terminals under the assigned maximum through fault current condition. It can be seen from Figure 1 that during an external fault the through fault current should circulate between the current transformer secondaries. The only current that can flow through the relay circuit is that due to any difference in the current transformer outputs for the same primary current. Magnetic saturation will reduce the output of a current transformer and the most extreme case for stability will be if one current transformer is completely saturated and the other unaffected.CTA CTB

Protected unit

Z MA R CTA R CTB

Z MB

RL

RL R RELAY CIRCUIT

RL

RL

Figure 1:

Principle of high impedance protection

Calculations based on the above extreme case for stability have become accepted in lieu of conjunctive scheme testing as being a satisfactory basis for application. At one end the current transformer can be considered fully saturated, with its magnetising impedance ZMB short circuited while the current transformer at the other end, being unaffected, delivers its full current output. This current will then divide between the relay and the saturated current transformer. This division will be in the inverse ratio of RRELAY CIRCUIT to (RCTB + 2RL) and, if RRELAY CIRCUIT is high compared with RCTB + 2RL, the relay will be prevented from undesirable operation, as most of the current will pass through the saturated current transformer. To achieve stability for external faults, the stability voltage for the protection (Vs) must be determined in accordance with formula 1. The setting will be dependent upon the maximum current transformer secondary current for an external fault (If) and also on the highest loop resistance value from the relaying point (RCT + 2RL). The stability of the scheme is also affected by the characteristics of the differential relay and the application (e.g. restricted earth fault, busbar etc). The value of K in the expression takes account of both of these considerations. One particular characteristic that affects the stability of the scheme is the operating time of the differential relay. The slower the relay operates the longer the spill current can exceed its setting before operation occurs and the higher the spill current that can be tolerated.



Vs > KIf (RCT + 2RL) Where: RCT = current transformer secondary winding resistance

(1)

RL = maximum lead resistance from the current transformer to the relaying point

IfK

= maximum secondary external fault current = a constant affected by the dynamic response of the relay Note: When high impedance differential protection is applied to motors or shunt reactors, there is no external fault current. Therefore, the locked rotor current or starting current of the motor, or reactor inrush current, should be used in place of the external fault current.

To obtain high speed operation for internal faults, the knee point voltage, VK, of the CTs must be significantly higher than the stability voltage, Vs. This is essential so that the operating current through the relay is a sufficient multiple of the applied current setting. Ideally a ratio of VK 4Vs would be appropriate, but where this is not possible refer to the Advanced Application Requirements for Through Fault Stability. This describes an alternative method whereby lower values of Vs may be obtained. Typical operating times for different VK/Vs ratios are shown in the following table:VK/Vs Typical operating time (ms) 2 94 4 30 8 25 16 16

These times are representative of system X/R ratios up to 120 and a fault level of 5Is or greater. Lower values of X/R and higher fault currents will tend to reduce the operating time. The kneepoint voltage of a current transformer marks the upper limit of the roughly linear portion of the secondary winding excitation characteristic. This is defined exactly in the IEC standards as that point on the excitation curve where a 10% increase in exciting voltage produces a 50% increase in exciting current. The current transformers should be of equal ratio, of similar magnetising characteristics and of low reactance construction. In cases where low reactance current transformers are not available and high reactance ones must be used, it is essential to use the reactance of the current transformer in the calculations for the voltage setting. Thus, the current transformer impedance is expressed as a complex number in the form RCT + jXCT. It is also necessary to ensure that the exciting impedance of the current transformer is large in comparison with its secondary ohmic impedance at the relay setting voltage. In the case of the high impedance relay, the operating current is adjustable in discrete steps. The primary operating current (Iop) will be a function of the current transformer ratio, the relay operating current (Ir), the number of current transformers in parallel with a relay element (n) and the magnetising current of each current transformer (Ie) at the stability voltage (Vs). This relationship can be expressed as follows:

Iop = (CT ratio) x (Ir + nIe)

(2)

In order to achieve the required primary operating current with the current transformers that are used, a current setting (Ir) must be selected for the high impedance relay, as detailed above. The setting of the stabilising resistor (RST) must be calculated in the following manner, where the setting is a function of the relay ohmic impedance at setting (Rr), the required stability voltage setting (Vs) and the relay current setting (Ir). RST = Vs - Rr Ir (3)



Note: Vs

The P140 ohmic impedance over the whole setting range is small, and so can be ignored. Therefore: (4)

RST =

Ir

2.

USE OF METROSIL NON-LINEAR RESISTORSWhen the maximum through fault current is limited by the protected circuit impedance, such as in the case of generator differential and power transformer restricted earth fault protection, it is generally found unnecessary to use non-linear voltage limiting resistors (Metrosils). However, when the maximum through fault current is high, such as in busbar protection, it is more common to use a non-linear resistor (Metrosil) across the relay circuit (relay and stabilising resistor). Metrosils are used to limit the peak voltage developed by the current transformers, under internal fault conditions, to a value below the insulation level of the current transformers, relay and interconnecting leads, which are able to withstand 3000V peak. The following formulae should be used to estimate the peak transient voltage that could be produced for an internal fault. This voltage is a function of the current transformer kneepoint voltage and the prospective voltage that would be produced for an internal fault if current transformer saturation did not occur. Note, the internal fault level, If , can be significantly higher than the external fault level, If , on generators where current can be fed from the supply system and the generator. Vp = 2 2 VK (Vf - VK) (5) (6)

Vf = If (RCT + 2RL + RST + Rr) Where: Vp VK Vf If = = = = peak voltage developed by the CT under internal fault conditions. current transformer knee-point voltage. maximum voltage that would be produced if CT saturation did not occur. maximum internal secondary fault current. current transformer secondary winding resistance. maximum lead burden from current transformer to relay. relay stabilising resistor. Relay ohmic impedance at setting.

RCT = RL =

RST = Rr =

When the value of Vp is greater than 3000V peak, non-linear resistors (Metrosils) should be applied. These Metrosils are effectively connected across the relay circuit, or phase to neutral of the ac buswires, and serve the purpose of shunting the secondary current output of the current transformer from the relay circuit in order to prevent very high secondary voltages. These Metrosils are externally mounted and take the form of annular discs, of 152mm diameter and approximately 10mm thickness. Their operating characteristics follow the expression: V = CI0.25 Where: V C = = = Instantaneous voltage applied to the non-linear resistor (Metrosil) constant of the non-linear resistor (Metrosil) instantaneous current through the non-linear resistor (Metrosil) (7)

I



With a sinusoidal voltage applied across the Metrosil, the RMS current would be approximately 0.52x the peak current. This current value can be calculated as follows: V (rms) x 2 4 I(rms) = 0.52 S C Where: Vs(rms) = rms value of the sinusoidal voltage applied across the Metrosil. This is due to the fact that the current waveform through the Metrosil is not sinusoidal but appreciably distorted. For satisfactory application of a non-linear resistor (Metrosil), its characteristic should be such that it complies with the following requirements: At the relay voltage setting, the non-linear resistor (Metrosil) current should be as low as possible, but no greater than approximately 30mA rms for 1A current transformers and approximately 100mA rms for 5A current transformers. The Metrosil units normally recommended for use with 1A CTs are as follows:Stability voltage Vs (V) rms Up to 125V Single pole 600A/S1/S256 C = 450 125-300V 600A/S1/S1088 C = 900 Recommended Metrosil type Triple pole 600A/S3/I/S802 C = 450 600A/S3/I/S1195 C = 900

(8)

The Metrosil units normally recommended for use with 5A CTs and single pole relays are as follows:Secondary internal fault Current (A) rms 50A Up to 200V 600A/S1/S1213 C = 540/640 100A 600A/S2/P/S1217 C = 470/540 150A 600A/S3/P/S1219 C = 430/500 Recommended Metrosil type Relay stability voltage, Vs (V) rms 250V 600A/S1/S1214 C = 670/800 600A/S2/P/S1215 C = 570/670 600A/S3/P/S1220 C = 520/620 275V 600A/S1/S1214 C = 670/800 600A/S2/P/S1215 C = 570/670 600A/S3/P/S1221 C = 570/670 300V 600A/S1/S1223 C = 740/870 600A/S2/P/S1196 C = 620/740 600A/S3/P/S1222 C = 620/740

The single pole Metrosil units recommended for use with 5A CTs can also be used with triple pole relays and consist of three single pole units mounted on the same central stud but electrically insulated from each other. A triple pole Metrosil type and the reference should be specified when ordering. Metrosil units for higher stability voltage settings and fault currents can be supplied if required.



3.

MiCOM P140The MiCOM P140 is a numerical 3 phase overcurrent, earth fault and sensitive earth fault relay, with 4 protection stages each. These elements can be used for 3 phase differential protection or restricted earth fault (REF) protection. It is recommended that the I>1 is used as the main protection element for 3 phase differential protection and the IREF>IS for the REF applications. The IREF>IS enabled by selecting Hi 2 REF (SEF/REF PROTN/SEF/REF options). The time delay characteristic should be selected to be definite time and with a setting of zero seconds. The output relay that is to trip the circuit breaker must be allocated for PSL for the chosen elements (i.e. I>1 or IREF>Trip). It is recommended that any output relay, allocated to the trip circuit breaker, has a 100ms dwell added to the contact conditioner. This forces the output relay to dwell in the closed state for a minimum of 100ms, even if fleeting operation of the protection should occur, ensuring positive operation of the circuit breaker, or trip relay. Separate output relays may be allocated to each phase trip if it is required to have phase segregated outputs However, the I>1 Trip A, I>1 Trip B and I>Trip C must also be assigned to Relay 3, for fault records to be generated. Phase information will be included in the fault flags. Any protection element not being used should be disabled. Setting range of I>1 and IREF>Is elements are:

I >1 IREF>Is

0.08 4In 0.05 1.0In

The ohmic impedance (Rr) of the P140 over the whole setting range is 0.04 for 1A inputs and 0.006 for 5A inputs i.e. independent of current. To comply with the definition for a high impedance relay, it is necessary, in most applications, to utilise an externally mounted stabilising resistor in series with the relay. The standard values of the stabilising resistors normally supplied with the relay, on request, are 220 and 47 for 1A and 5A relay ratings respectively. In applications such as busbar protection, where higher values of stabilising resistor are often required to obtain the desired relay voltage setting, non-standard resistor values can be supplied. The standard resistors are wire wound, continuously adjustable and have a continuous rating of 145W. 3.1 P140 Application Considerations The following data should be used as a guide in order to obtain the best performance from the relay. 3 Phase applications (e.g. Busbars, Generators, Motors etc). K-factor = 1.2 VK/VS ratio = 4

REF Applications K-factor = 1.0

VK/VS ratio = 4



4.

APPLYING THE P140The recommended relay current setting for restricted earth fault protection is usually determined by the minimum fault current available for operation of the relay and whenever possible it should not be greater than 30% of the minimum fault level. For busbar protection, it is considered good practice by some utilities to set the minimum primary operating current in excess of the rated load. Thus, if one of the current transformers becomes open circuit the high impedance relay does not maloperate. The IN>1 earth fault element in the P140 with its low current settings can be used for busbar supervision. When a CT or the buswires become open circuited the 3 phase currents will become unbalanced and residual current will flow. Hence, the IN>1 earth fault element should give an alarm for open circuit conditions but will not stop a maloperation of the differential element if the relay is set below rated load. Whenever possible the supervision primary operating current should not be more than 25 amps or 10% of the smallest circuit rating, whichever is the greater. The earth fault element (IN>1) should be connected at the star point of the stabilising resistors, as shown in Figure 9. The time delay setting for the supervision elements (IN>1 Time delay) should be at least 3 seconds to ensure that spurious operation does not occur during any through fault. This earth fault element will operate for an open circuit CT on any one phase, or two phases, but not necessarily for a fault on all three when the currents may summate to zero. The supervision may be supplemented with a spare phase protection stage (I>3) set to the same setting as the IN>1 element or its lowest setting, 0.08In, if the IN>1 supervision setting is less than 0.08In. Note that the IN current should be checked when the busbar is under load. This can be viewed in the Measurements menu in the relay. It is important that the IN>1 threshold is set above any standing IN unbalance current. The supervision element should be used to energise an auxiliary relay with hand reset contacts connected to short circuit the buswires. This renders the busbar zone protection inoperative and prevents thermal damage to the Metrosil. Contacts may also be required for busbar supervision alarm purposes. Figures 3 to 9 show how high impedance relays can be applied in a number of different situations.

4.1

Advanced application requirements for through fault stability When Vs from formula 2 becomes too restrictive for the application, the following notes should be considered. The information is based on the transient and steady state stability limits derived from conjunctive testing of the relay. Using this information will allow a lower stability voltage to be applied to the relay, but the calculations become a little more involved. There are two factors to be considered that affect the stability of the scheme. The first is saturation of the current transformers caused by the dc transient component of the fault current and the second is steady state saturation caused by the symmetrical ac component of fault current only.

4.2

Transient stability limit To ensure through fault stability with a transient offset in the fault current the required voltage setting is given by: Vs = 40 + 0.05RST + 0.04If (RCT + 2RL) (9)

If this value is lower than that given by formula 2 then it should be used instead. Vs and RST are unknowns in equation (10). However, for a relay current setting Ir, the value of RST can be calculated by substituting for Vs using equation (5), Vs = Ir RST.



RST Ir =

40 + 0.05RST + 0.04If (RCT+ 2RL)

(10)

4.3

Steady state stability limit To ensure through fault stability with non offset currents: (RCT+ 2RL) must not exceed (VK + Vs)/If. (11)

5.5.1

TYPICAL SETTING EXAMPLESRestricted earth fault protection The correct application of the P140 as a high impedance relay can best be illustrated by taking the case of the 11000/415V, 1000kVA, X = 5%, power transformer shown in Figure 10, for which restricted earth fault protection is required on the LV winding. CT ratio is 1500/5A.

5.2

Stability voltage The power transformer full load current = = 1000 x 10 3 x 415 1391A3

Maximum through fault level (ignoring source impedance) = = 100 5 x 1391 27820A

Required relay stability voltage (assuming one CT saturated) = = KIf (RCT + 2RL) 1.0 x 27820 5 x 1500 (0.3 + 0.08) 35.2V

= 5.3

Stabilising resistor Assuming that the relay effective setting for a solidly earthed power transformer is approximately 30% of full load current, we can choose a relay current setting, IN> = 20% of 5A i.e. 1A. On this basis the required value of stabilising resistor is: RST = 35.2 1 = VS

Ir

= 35.2 ohms For applications where the 5A inputs are used, such as this, a 47 resistor can be supplied on request. The resistor is continuously adjustable between 0 and 47. Thus a value of 35.2 can be set.



5.4

Current transformer requirements To ensure that internal faults are cleared in the shortest possible time the knee point voltage of the current transformers should be at least 4 times the stability voltage, Vs. VK = 4Vs = 4 x 35.2 = 141V The exciting current to be drawn by the current transformers at the relay stability voltage, Vs, will be:

I -I Ie < s n rWhere:

Is

= relay effective setting 30 5 = 100 x 1391 x 1500 = 1.4A

Ir (Io>)

= relay setting = 1A n = number of current transformers in parallel with the relay = 4

Ie @ 35.2V < 0.1A

) = 400A = 0.8In Relay primary operating current,

Iop = CT ratio x (Ir + n Ie)= 500 x (0.8 + (5 x 0.072)) = 500 x 1.16 = 580A (132% full load current)



6.4

Check zone Magnetising current taken by each CT at 99V = 0.072A Maximum number of circuits = 6 Relay current setting, Ir (I>) = 0.8A Relay primary operating current,

Iop = 500 x (0.8 + (6 x 0.072))= 500 x 1.232 = 616A (141%- full load current) Therefore, by setting Ir (I>) = 0.8A, the primary operating current of the busbar protection meets the requirements stated earlier. 6.5 Stabilising resistor The required value of the stabilising resistor is: RST = VS

Ir

99 = 0.8 = 124 Therefore the standard 220 variable resistor can be used. 6.6 Current transformer requirements To ensure that internal faults are cleared in the shortest possible time the knee point voltage of the current transformers should be at least 5 times the stability voltage, Vs. Vk/Vs Vk 6.7 =4 = 396V

Metrosil non-linear resistor requirements If the peak voltage appearing across the relay circuit under maximum internal fault conditions exceeds 3000V peak then a suitable non-linear resistor (Metrosil), externally mounted, should be connected across the relay and stabilising resistor, in order to protect the insulation of the current transformers, relay and interconnecting leads. In the present case the peak voltage can be estimated by the formula: VP = 2 2VK (Vf - VK) where VK = 396V (In practice this should be the actual current transformer kneepoint voltage, obtained from the current transformer magnetisation curve). Vr = If (RCT + 2RL + RST + Rr) 1 = 15300 x 500 x (0.7 + 2 + 124) = 30.6 x 126.7 = 3877V



Therefore substituting these values for VK and Vf into the main formula, it can be seen that the peak voltage developed by the current transformer is: Vp = 2 2VK (Vf - VK) = 2 2 x 396 x (3877 - 396)

= 3320V This value is above the maximum of 3000V peak and therefore a non-linear resistor (Metrosil) would have to be connected across the relay and the stabilising resistor. The recommended non-linear resistor type would have to be chosen in accordance with the maximum secondary internal fault current and voltage setting. 6.8 Busbar supervision Whenever possible the supervision primary operating current should not be more than 25 amps or 10% of the smallest circuit, whichever is the greater. The IN>1 earth fault element in the P140 with its low current settings can be used for busbar supervision. Assuming that 25A is greater than 10% of the smallest circuit current.

IN>1 = 25/500 = 0.05InUsing the I>3 element for 3 phase busbar supervision.

I>3 = 0.08 In (minimum setting)The time delay setting of the IN>1 and I>3 elements, used for busbar supervision, is 3s. Any elements not used should be disabled. 6.9 Advanced busbar application requirements for through fault stability The previous busbar protection example is used here to demonstrate the use of the advanced application requirements for through stability. To ensure through fault stability with a transient offset in the fault current the required voltage setting is given by: Vs = (0.005 X/R + 0.78) x If (2RL + RCT)

To be used when X/R is less or equal to 80. The standard equation should be used for X/R ratios greater than 80. If the calculated value is lower than that given by equation 1 (with K = 1.2) then it should be used instead. 6.10 Transient stability limit Vs Vs Vs 15300 = 0.005 X/R + 0.78) x 500 x (0.7 + 2) = 0.88 x 30.6 x 2.7 = 73V



The relay current setting, Ir = 0.8In RST = Vs

Ir

73 RST = 0.8 = 91 Assuming VK = 4Vs VK = 4Vs = 292V Using the advanced application method the knee point voltage requirement has been reduced to 292V compared to the conventional method where the knee point voltage was calculated to be 396V.100MVA 15kV

100MVA 132/15kV

132kV Main reserve

Figure 2:

Double busbar generating stationP1 S1 P2 S2 Protected plant P1 S1 P2 S2

A B C

A B C

21 R A Protective relays 22 v R ST

23 R B 24 v R ST

25 R C 26 v R ST

Figure 3:

Phase and earth fault differential protection for generators, motors or reactors

P14x/EN AP A00 Page 16/20P1 S1 P2 S2

Application Notes MiCOM P141, P142, P143A B C

27 P2 S2 R v P1 S1

28 R ST

Figure 4:

Restricted earth fault protection for 3 phase, 3 wire system-applicable to star connected generators or power transformer windingsP1 S1 P2 S2

A B C

27

28 R R ST

v

Figure 5:

Balanced or restricted earth fault protection for delta winding of a power transformer with supply system earthed

Application Notes MiCOM P141, P142, P143P2 S2 P1 S1

P14x/EN AP A00 Page 17/20A B C

P2 S2 27 28

P1 S1

N

R R ST v

Figure 6:

Restricted earth fault protection for 3 phase, 4 wire system-applicable to star connected generators or power transformer windings with neutral earthed at switchgearP2 S2 P1 S1

A B C

P2 S2 27 P2 S2 v 28

P1 S1 R R ST

N

P1

S1

Figure 7:

Restricted earth fault protection for 3 phase, 4 wire system-applicable to star connected generators or power transformer windings earthed directly at the star point

P14x/EN AP A00 Page 18/20A B C P1 S1 P2 S2 P2 S2 P1 S1 P2 S2


P1 S1

A B C

21 R A Protective relays 22 v R ST

23 R B 24 v R ST

25 R C 26 R ST v

Figure 8:

Phase and earth fault differential protection for an auto-transformer with CTs at the neutral star point

P1 P2 A B C P2 P1 A B C Contacts from buswire supervision auxiliary relay S2 S1

S1 S2

P2 P1

S2 S1

Protective relays 22

21 R A v R ST

23 24 27 RN 28

RB v R ST

25 R C 26 v R ST

Buswire supervision

Figure 9:

Busbar protection simple single zone phase and earth fault scheme

Application Notes MiCOM P141, P142, P14311kV 1500/5A


415V R CT

A B C RL RL

RL Data Protection: R L = 0.04 R LC = 0.3 = 5% RL R CT

Restricted earth fault protection

Transformer: X

Figure 10: Restricted earth fault protection on a power transformer LV winding



AREVA T&D UK Ltd - Automation & Information St Leonards Works, Stafford, ST17 4LX England Tel: 44 (0) 1785 223251 Fax: 44 (0) 1785 212232 Internet: www.areva-td.com2004 AREVA T&D UK Ltd - Automation & Information Our policy is one of continuous product development and the right is reserved to supply equipment which may vary slightly from that described. Publication P14x/EN AP/A00

Date post:	18-Nov-2014
Category:	Documents
Upload:	korlagon
View:	142 times
Download:	3 times

P14x en ap a00

Documents