CBIP-Recommondations for 400kv Protection

BASIC CONCEPTSOF PROTECTION OF

IN A 400KV SUBSTATION( as Per CBIP Recommendations)

P. GOPALA KRISHNAADE/400KV/APTRANSCO

CBIP Guidelines on Protection

NORMS OF PROTECTION FOLLOWED IN UTILITIES Sr.No VOLTAGE MAIN- 1 PROTECTION MAIN-2 PROTECTION/ BACKUP PROTECTION

1. 11 KV LINES 2 O/L + E/F ( 51 + 51N ) -2. 33 KV LINES 3 O/L + E/F ( 51 + 51N ) -3. 66 KV LINES SWITCHED DISTANCE SCHEME OR

NUMERICAL DISTANCE SCHEME (21P+ 21N)DIRECTIONAL O/L & E/F RELAYS WITH HIGH

SET ( 67 + 67N )4. 132 KV LINES5. 220 KV LINES NON SWITCHED DISTANCE SCHEME OR

NUMERICAL DISTANCE SCHEME (21P + 21N)SWITCHED DISTANCE SCHEME OR

NUMERICAL DISTANCE SCHEME (21P+ 21N)

6. 400 KV LINES NUMERICAL DISTANCE SCHEME (21P + 21N) + in BUILT DEF RELAY(67N)

NUMERICAL DISTANCE SCHEME (21) OR LINE DIFFERENTIAL SCHEME (87L) WITH 67N

7. 765 KV LINES NUMERICAL DISTANCE SCHEME (21P + 21N) + in BUILT DEF RELAY(67N)

NUMERICAL DISTANCE SCHEME (21) OR LINE DIFFERENTIAL SCHEME (87L) WITH 67N

The DEF 67N is in built to detect high resistance fault which distance relay cannot.REACH SETTINGSZONE-1: 80-85% OF PROTECTED LINEZONE-2: 120% = 100% OF MAIN LINE + 50% OF SHORTEST LINE AT OTHER END / 6O% OF T/FZONE-3: 200% = 100% OF MAIN LINE + 100% OF LONGEST LINE AT OTHER END / 100% OF T/FZONE-4: 100% OF MAIN LINE + (100% OF SHORTEST LINE + 100% OF LONGEST LINE) AT OTHER END.

R-REACH: UP TO LOAD POINT ENCROACHMENTTIME SETTINGSZONE-1: INSTANTENEOUSZONE-2: 0.3 SEC FOR SHORT LINES & 0.5 SEC FOR LONG LINES for DiscriminationZONE-3: 0.6 SECZONE-4: 0.9 SEC

CBIP Guidelines on Protection400 kV Lines

NEED OF LINE PROTECTIONThe line protection relays are required to protect

the line and clear all types of faults on it within the shortest possible time with reliability, selectivity and sensitivity.

The line protection relays shall be suitable for use with capacitive voltage transformers having passive damping and transient response as per IEC 186


There should be two independent High Speed Main protection schemes called Main-I and Main-II with at least one of them being carrier aided non-switched Three/ Four zone distance protection.

The other protection may be a phase segregated current differential (this may require digital communication), phase comparison, directional comparison type or a carrier aided non-switched Distance protection.

If Main-I and Main-II are both distance protection schemes, then they should be preferably of different types. They need not necessarily of different make.

Both should be suitable for single and three phase tripping.

400kV Lines

ADDITIONAL PROTECTION

ii) Two stage Over Voltage Protection.

iii) Auto-reclose relay suitable for 1-ph / 3-ph (with dead line charging and synchro-check facility).

iv) Sensitive IDMT Directional E/F Relay(67N).

According BUSBAR Arrangements (One & Half Circuit Breaker System)

v) STUB Protection

vi) TEED Protection



There should be at least one carrier aided non-switched three zone Distance protection scheme.

In addition to this another non-switched / switched distance scheme or directional over current and earth fault relays should be provided as back up.

Main protection should be suitable for single and three phase tripping.

Auto-reclose relay suitable for 1 ph / 3 ph reclosure shall be provided.

In case of both line protections being Distance Protections, IDMT type E / F relay shall also be provided additionally.

220 kV Lines


(i) If found necessary, at certain locations, out of step tripping relays shall be provided for islanding the system during disturbances.

(ii) For short line application distance relays should have shaped characteristics for ground faults and be used in permissive over reach mode with weak end infeed logic. Further, if it is a double circuit line, current reversal should also be available.

(iii)O/V relay for 400 kV lines shall be connected to trip concerned line breaker, start LBB, block auto reclosure and send direct trip command.

(iv)The directional earth fault relay recommended along with thedistance relay should be seen as a supplement to it and not as a back up. It helps to detect very high resistance fault which distance relay cannot.

(v)HVDC Systems connected to AC networks with low short circuit levels can influence AC line protections in its vicinity. This aspect needs to be looked into on case to case basis.

SPECIAL COMMENTS


I. Zone-I: to be set to cover 80-85% of protected Line length.

II.Zone II: to be set to cover minimum 120% of length of principle line section. However, in case of D/C lines 150% coverage must be provided to take care of, under reaching due to mutual coupling effect but, care is to be taken that it does not reach into next lower voltage level.

SETTING CRITERIA

Reach settings of distance protection


(iii) Zone-III:For 400kV lines Zone-III to be set to cover120% of

principle section plus adjacent longest section subject to a reach restriction so that it does not reach into next lower voltage level.

For 220 kV lines, Zone-III reach may be provided to cover adjacent longest section if there is no provision of LBB or all protection are connected to single DC source at remote end substation.

(iv) Resistive reach should be set to give maximum coverage subject to check of possibility against load point encroachment considering minimum expected voltage and maximum load. Attention has to be given to any limitations indicated by manufacturer in respect of resistive setting vis-a-vis reactance setting.


A Zone-II timing of 0.3 second is recommended. If a long line is followed by a short line, then a higher setting may be adopted on long line to avoid indiscriminate tripping through Zone-II operation on both lines.

Zone-III timer should be set so as to provide discrimination with the operating time of relays provided in subsequent sections with which Zone- III reach of relay being set overlaps.

Time setting of distance protection


Low set voltage may be set at 110% with a typical time delay of 5 seconds.

A time grading of 1 second may be provided between relays of different lines at a station.

Longest time delay should be checked with expected operating time of over fluxing relay of the transformer to ensure disconnection of line before tripping of transformer.

High set stage may be set at 150% with a time delay of 100 m second.

O / V Protection

Decisions pertaining to allowing which Zone to trip and which to block should be taken based on system studies on case to case basis.

3.4 PSB Function Associated with Distance Relays

i) Four Independent Zones (at least 3).ii)Seperate Measurement for Ph-Ph & Ph-E faults (Non Switched scheme).iii) Capable of 1-Ph & 3-Ph tripping iv) Directional Characteristics (Mho or quad or any other suitably shaped) for all zones.v) Capable of Operation for close-up 3-ph faults & SOTF.vi) Adjustable characteristic angle to match line angle whereverapplicable. vii) Accuracy ≤ 5% for Z1 & ≤ 10% for Z2, Z3, Z4 for Set Value of Reach Measurement.vii) Accuracy ≤ 5% for Z2, Z3, Z4 for Set Value of Time Measurement.viii) Variable residual compensationix) Power swing blocking feature shall include.x) Fuse Failure Protection & Monitor feature shall include.xi) Week End Infeed Logic(27 WI) feature shall include.xii) Distance To Fault Locator(21 FL).( % or Km or Miles or R+jx ).xiii) for Short Line applications it should have suitably shapedcharacteristics for ground faults and be used in POTT mode with WI Logic. Further, if it is a DC Line, current reversal logic should also be available. xiii) any other features required by customer

CBIP Guidelines on ProtectionDISTANCE PROTECTION REQUIREMENTS

i) shall be a unit system of protection ii) Shall be Phase Comparison type.iii) Shall be suitable for operation with one signally channel.iv) Shall be high sensitivity for all types of faults. v) Shall be capable of 1-Ph & 3-Ph tripping .vi) Shall have facility for Blocking/Permissive trip modes. vi) Shall have a facility for Direct Transfer Tripping.vii) Shall have comprehensive alarm and test facilities.vii) shall not affected by Heavy Load Transfer, Power Swings, CT saturation, CT Phase errors, Propagation delays, Capacitance current etc., as is typical of unit protection.viii) any other features required by customer.

CBIP Guidelines on ProtectionPHASE COMPARISION PROTECTION REQUIREMENTS

i)shall be a unit system of protection ii)shall be all Digital Multi Microprocessor based, designated for use with Modern Digital Telecommunication system multiplexer confirming to ITU-T(CCITT) Specifications and Fibre Optic Medium .iii) Each Phase Current shall be separately evaluated at both ends for both Amplitude and Phase.iv) Shall be suitable of 1-Ph & 3-Ph tripping and Auto-reclosing.v) The message Transmitted by the relay to other end shall include information on current, supervision information, CT Saturation detection, Synchronization of terminals etc. vi) The Measurement shall be stabilized Phase by Phase for CT Saturation. vii) The Communication delay shall be continuously measured and automatically compensated for in the differential Measurement.viii) Communication telegram shall have error detection and correction feature.ix) Suitable Programmable evaluation algorithm will be provided to ensure proper security and dependability of the message.x) The Relay shall have Communication port for Remote Monitoring, Programming and Control.xi) The Direct inter trip signal shall be transmitted as part of telegram. xii) any other features required by customer.

PHASE SEGREGATED LINE DIFFERENTIAL PROTECTIONCBIP Guidelines on Protection

The Relay shall have following features.

i) Have a High drop off to Pick ratio.

ii) Have adjustable setting range for voltage & time.

iii) Have Two stages.

iv) Low set stage shall monitor any one Phase to Phase Voltage and shall be associated timer.

v) High set stage shall monitor all three Phase to Phase Voltage and shall be associated timer.

vi) Over Voltage relay for 400KV Lines shall be connected to trip concerned Line Breaker(s), Start LBB, Block A/R and send Direct Trip command.

OVER VOLTAGE PROTECTION REQUIREMENTSCBIP Guidelines on Protection


CBIP Guidelines on ProtectionGENERAL

The auto-reclosing of power lines has become a generally accepted practice.

Reports from different parts of the world show that in certain networks in region subject to a high lightening intensity only about 5% of the faults are permanent.

Auto reclosing therefore provides significant advantages.

Outage times will be short compared to where station personnel have to re-energize the lines after a fault.

In interconnected networks auto-reclosing helps in maintaining system stability

CBIP Guidelines on ProtectionRecommendations for provisions of auto-reclosing

Presently 1 phase high speed auto-reclosure (HSAR) at 400kV and 220kV level is widely practised including on lines emanating from Generating Stations and the same is recommended for adoption.

If 3-phase auto-reclosure is adopted in future the application of the same on lines emanating from generating stations should be studied and decision taken on case to case basis.

FAULTS ARE THREE TYPES1. TRANSIENT FAULT: These are cleared by the

immediate tripping of Circuit Breakers and do not reoccur when the line is re-energized.

2. SEMI-PERMANENT FAULTS: These require a time interval to disappear before a line is charged again.

3. PERMANENT FAULTS: These are to be located and repaired before the line is re-energized.

About 80-90% of the faults occurring are transient in nature. Hence the Automatic Reclosure of breaker (after tripping on Fault) will result in the line being successfully re-energized.

ADVANTAGES:A. Decreasing outage time.B. Improving Reliability.C. Improving system stability.D. Reduce fault damage and Maintenance Time.



1. BASED ON PHASEA. THREE PHASE AUTO-RECLOSING.B. SINGLE PHASE AUTO-RECLOSING.

2. BASED ON ATTEMPTS OF RECLOSUREA. SINGLE SHOT AUTO-RECLOSING.B. MULTI-SHOT AUTO-RECLOSING.

3. DEPENDING ON SPEED:A. HIGH-SPEED AUTO-RECLOSING. B. LOW SPEED OR DELAYED AUTO RECLOSING.

4. CHOICES OF EHV SYSTEM:A. CHOICE OF ZONE:This should normally kept in Zone-1. It is a Zone-1 fault and SLG fault only auto-reclosure is comes in to picture. In other zones the auto reclosure is blocked.

TYPES OF AUTO-RECLOSING

CBIP Guidelines on ProtectionSETTING CRITERIA

Dead Time

DEAD TIME: The time between the Auto-reclosingScheme being energized and the operation of the contacts which energize the Circuit Breaker closing circuit.

Auto- reclosing requires a dead time which exceeds the de-ionising time

Time required for the de-ionising of the fault path depends on:- arcing time, fault duration, wind conditions, circuit voltage, capacitive coupling to adjacent conductors, etc.

Single phase dead time of 1.0 sec is recommended for both 400kV and 220kV system.

CBIP Guidelines on ProtectionReclaim Time

RECLAIM TIME: The Time Following a successful closing operation measured from the instant the Auto-Reclosing relay closing contacts make which must elapse before the Auto-Reclosing relay initiates another reclosing attempt. In other words, it may be said to be the time between 1st and 2nd Auto-Reclosure.

The time during which a new start of the auto-reclosing equipment is blocked.If reclosing shot has been carried out and the line is energized and a new fault

occurs before the reclaim time has elapsed, the auto-reclosing equipment is blocked and a signal for definite tripping of the breaker is obtained.

After the reclaim time has elapsed, the auto-reclosing equipment returns to the starting position and a new reclosing sequence can occur.

The reclaim time must not be set to such a low value that the intended operating cycle of the breaker is exceeded, when two faults incidents occur close together.

If the breaker is closed manually, the auto reclosing equipment is blocked and cannot start again until the reclaim time has elapsed.

For the breaker to be used for auto-reclosing, it is essential that it has the operating mechanism and breaking capacity necessary for it to be able to perform the auto-reclosing sequences required.

2.3 Circuit Breaker Requirement

According to IEC Publication 56.2, a breaker must be capable of withstanding the following operating cycle with full rated breaking current:

O + 0.3 s + CO + 3 min + CO

The recommended operating cycle at 400kV and 220kV is as per the IEC standard.

Reclaim time of 25 sec is recommended.



i) Having 1-Ph and/or 3-ph reclosing facilities.ii) Have a continuously Variable Single Phase Dead

Time.iii) Have a continuously Variable Three Phase Dead

Time.iv) Have a continuously Variable Reclaim Time.v) Incorporate a facility of selecting 1-Ph / 3-Ph / 1-Ph

& 3-Ph Auto-reclose and Non-auto reclosure modes. vi) Having a facilities for selecting check synchronising

(SC) or dead Line charging (DLC) features.vii) Be of high speed single shot type.viii) Suitable relays for SC and DLC should be included

in the overall auto-reclose scheme.viii) Should allow sequential reclosing of Breakers in

One and Half Breaker or Double Breaker Arrangement.

AUTO-RECLOSING RELAY REQUIREMENTS


PROTECTIONS which BLOCK A/R RELAY are

i) Zone 2/3/4 of Distance Protection.

ii) Carrier fail Conditions.

iii) Circuit Breaker problems.

iv) Direct Transfer Trip signal Received.

v) LBB/BFR relay operates.

vi) Line Reactor Protections.

vii) Over Voltage Protection.

viii) Busbar Protection Operated


CBIP Guidelines on ProtectionGENERAL & NEED OF PROTECTION FOR TRANSFORMER

A Power Transformer is a very valuable and vital link in a Power Transmission system

Fast protection system for transformer is essential to minimize the damage in case of an internal fault with suitable back-up protection scheme to take care of uncleared system faults.

Faults in a Transformer occur due to insulation break-down, ageing of insulation, overheating due to over-excitation, oil contamination and leakage or reduced cooling.

To give an early warning and to minimise the damage in case of fault it is necessary to equip it with monitors and protective relays.

Power T/F Protection is usually installed :A. Internal SCs and E/Fs in the T/F and its connected circuits.B. External faults on other circuits. (Back-up protection)C. Abnormal service conditions such as overload & over voltage.

PROTECTION DEVICES INBUILT OR MOUNTED ON POWER T/FA. Oil immersed power T/F usually have a gas detector and oil surge Detector (buchholz alarm & trip devices), which are excellent for detecting internal faults.B. Load tap-changer compartments may have a similar over pressure device. C. Temperature monitors for oil & winding provide good O/L Protection.D. PRD is provided to safe guard the T/F from High Pressures.


CBIP Guidelines on ProtectionTRANSFORMER DIFFERENTIAL PROTECTION

It is widely used as instantaneous protection for short circuit faults with in the differential zone. This is treated as Main-1 Protection for T/F. The most common type of protection is the current restraint type. Some type of DIFFERENTIAL RELAYS require interposing CTs for CT ratio matching and/or phase shift. High impedance differential protection can be used on auto T/F or ICT & Reactors. It covers one galvanicallyinterconnected winding (Winding Differential). But not a separate tertiary winding. It requires a three phase set of CTs at the neutral side of winding.

In case of Auto Transformer, 3-ph High Impedance Differential relay is used as Main-2 Protection in addition to Percentage Biased Differential Protection is used as Main-1.

CBIP Guidelines on ProtectionRESTRICTED EARTH FAULT PROTECTION

An Alternative to Differential Protection that can be applied to AT/Fs. A Circulating Current System is arranged between Equal Ratio CTs in the two Groups of Line Connections and the Neutral End Connections. The Line CTs can be connected in Parallel to A Single Element Relay, Thus providing a Scheme Responsive to E/F Only. If CTs are fitted in Each Phase at the Neutral End of the Windings and a Three-Element Relay is used, A Differential System can be provided, giving Full Protection against Phase and Earth Faults. This Provides High-speed Sensitive Protection. It is Unaffected by Ratio Changes on the T/F due to Tap-changing and is immune to the Effects of Magnetizing In Rush Current. It does not respond to Inter-turn Faults. In Addition, This Scheme does not respond to any Fault in a Tertiary Winding. Unloaded Delta- connected Tertiary Windings are often not Protected.

CBIP Guidelines on ProtectionBACK UP PROTECTION

A. OVER CURRENT & EARTH FAULT PROTECTION. (67P&N, HV & LV)

B. UNDER IMPEDENCE / DISTANCE ( Z<)(21T).C. NEUTRAL DISPLACEMENT PROTECTION (Un>).

OTHER TYPES OF RELAYS

A. OVER VOLTAGE RELAY (U >).B. OVER FLUX/ EXCITATION (V/F >)( INVERSE TIME & DIFENITE TIME). FOR 400KV/220KV & 765/400KV TRANSFORMERS BOTH SIDES( i.e HV & LV) OVER FLUX RELAYS ARE PROVIDED BECAUSE BOTH SIDES HAVING GRID.C. AT/F NEUTRAL CURRENT RELAY (51N).D. OVER LOAD RELAY FOR ALARM (51).

CAPACITY OF TRANSFORMER HV VOLTAGE HV CURRENT IV VOLTAGE IV CURRENT

315 MVA 400 KV 454.68 A 220 KV 0826.68 A500 MVA 400 KV 721.71 A 220 KV 1312.20 A630 MVA 400 KV 909.35 A 220 KV 1653.37 A

NORMALLY ADOPTED POWER TRANSFORMERS CAPACITIES

BY UTILITIES IN 400KV / 220KV SYSTEM

CAPACITY OF TRANSFORMER HV VOLTAGE HV CURRENT IV VOLTAGE IV CURRENT

630 MVA 765 KV 0475.48 A 400 KV 0909.35 A750 MVA 765 KV 0566.05 A 400 KV 1082.56 A

1000 MVA 765 KV 0754.73 A 400 KV 1443.42 A1500 MVA 765 KV 1132.10 A 400 KV 2165.14 A

IN 765KV / 400KV SYSTEM

NORMS OF PROTECTION FOLLOWED BY UTILITIES FOR POWER TRANSFORMERS & AUTO TRANSFORMERS

3 OL + 1 DIR EL (51P + 67N)

400 / 132100, 200 & 2507

HV & LV REF 64

220 / 6631.5, 50 & 1006

66 / 337.5 , 16 & 252

BUCHHOLZOVER FLUX OLTC OSRPRV/PRDOIL TEMP

WDNG TEMP

132 / 33 16 , 31.5 50 & 804

765 / 400630, 750, 1000 & 1500

10

3 DIR OL (HIGHSET)

+ 1 DIR EL

(HIGHSET)

3 DIR OL (HIGHSET)

+ 1 DIR EL

(HIGHSET)

400 / 220315, 500 & 630

9

OVER LOAD ALARM

RELAY + NEUTRAL

CURRENT E/F RELAY

87 TH / 64 REF

ICT / AUTO TFR

220 / 132100 & 1608

2 WINDING TRANSFORMER (STAR/STAR)

TYPE

220 / 3331.5, 5053 OVER LOAD + 1 DIRECTIONAL

EARTH FAULT RELAY ( 51P + 67N)

HV REF (64)

132 / 117.5 , 16 ,25 & 31.53

64REF IS 1-PH

HIG

H IM

PEDA

NC

E D

IFFEREN

TIAL R

ELAY

87TH IS 3-PH

HIG

H IM

PEDA

NC

E D

IFFEREN

TIAL R

ELAY

(PRIN

CPLE : C

IRC

ULA

TING

CU

RR

ENT)

BUCHHOLZ, OLTC OSROIL TEMP

WDNG TEMP3 OVER LOAD + 1 EARTH FAULT

RELAY ( 51 )

3 OL +1 EL (51)

NIL

87 TL DIFFER

ENTIA

L RELA

Y ( LO

W IM

PEDA

NC

E PERC

ENTA

GE B

IASED

PHA

SE SEGR

EGA

TED

DIFFER

ENTIA

L RELA

Y PRIN

CIPLE: M

ERZ PR

ICE)

66 / 117.5 & 161

LVHVPROTECTIONSPECIAL

PROTECTIONADDITIONAL PROTECTION

BACK UPPROTECTIONMAIN-2MAIN-1VOLTAGE

RATIO IN KV

CAPACITYIN

MVAS.No

CBIP Guidelines on ProtectionDIFFERENTIAL PROTECTION REQUIREMENTS

i) Triple Pole with Individual Indication.ii) Have Unrestrained instantaneous high-set which

should not operate during in rush.iii) Have an adjustable or Multi Bias settingiv) Have second Harmonic or other inrush proof

features and should be stable under normal Over Fluxing conditions, Magnetizing inrush proof feature shall not be achieved through any intentional time delay e.g. use of timers to block relay operation or using disc operated relays.

v) Have one Bias Winding Per Phase for CT input.vi) Have an adjustable operating Current.vii) Have an operating time not grater than 30 msec at

5 times of setting. viii) The scheme shall have facility for ration and

phase angle correction either through auxiliary transformer or through in-built Provisions.

CBIP Guidelines on ProtectionREF PROTECTION REQUIREMENTS

i) shall be single Pole.ii) Have an operating current sensitivity at least 10%

of nominal current.iii) be tuned with system frequency.iv) Have a suitable non-linear resistor to limit the peak

voltage during in-zone faults in case of high impedance type.

v) Shall be high or low impedance Principle type.vi) Whenever separate Ph-wise CTs are available on

neutral side of T/F, a 3-pole High Impedance Relay may be provided instead of 1-ph REF.

CBIP Guidelines on ProtectionBACKUP O/C PROTECTION RELAY REQUIREMENTS (HV&LV)

i) Shall be 3-pole type.ii) Have IDMT characteristic (direction on T/F)iii) Have a Variable setting range of 50-200% of rated current.iv) Have a Characteristic angle, 30/45 deg Lead. v) Shall include high unit having low transient over-reach and

variable setting range of typically 500-2000% of rated current. vi) include hand reset indicators per phase.BACKUP E/F PROTECTION RELAY REQUIREMENTS (HV&LV)

i) Shall be 1-pole type.ii) Have IDMT characteristic (direction on T/F)iii) Have a Variable setting range of 20-80% of rated current.iv) Have a Characteristic angle, 45/60 deg Lag. v) Shall include high unit having low transient over-reach and

variable setting range of typically 200-800% of rated current. vi) include hand reset indicators.

CBIP Guidelines on ProtectionOVER LOAD ALARM RELAY REQUIREMENTS

OVER FLUX PROTECTION RELAY REQUIREMENTS (HV&LV)

i) Shall be 1-pole type.ii) Shall be of definite time over current type.iii) Shall have a continuously variable current range of 50-200%

of rated current and continuously variable timer setting range of 1-10 sec.

iv) Shall have a drop off to pickup ratio of 95% better.

i) Shall be Phase to Phase connected.ii) Operate on the Principle of Measurement of Voltage to Frequency

ratio. iii) Have inverse time characteristics compatible with transformer over

fluxing.iv) Provide on independent alarm with a definite time delay at value of

V/F between 100% to 130% of rated value. v) Have high resetting ratio of 98% or better.vi) The T/F, V/F relay has been recommended on both sides of ICTs.

CBIP Guidelines on ProtectionSPECIAL COMMENTS

i) In case of Breaker and Half schemes, the differential Protection CTs associated with Main and Tie Breakers should be connected to separate bias windings and these should not be paralleled in order to avoid false operation due to dissimilar CT transient response.

ii) The current setting of the Backup O/C relay shall be set above the expected maximum load current so as to allow possible overload an account of loss of one of the parallel T/Fs.

iii) Over Load relay shall be set at 110% of rated current with delay of 5 sec. This shall be connected to give only alarm and not for tripping.

iv) Whenever separate Ph-wise Bushing CTs are available on neutral side of T/F, a 3-pole High Impedance Relay may be provided instead of 1-ph REF.

v) Over-fluxing relay shall be provided on the untapped winding of the Transformer


CBIP Guidelines on ProtectionTYPES OF REACTORS

A. BASED ON REACTOR CONNECTIONi) SHUNT REACTOR. ii) SERIES REACTOR.

B. BASED ON REACTOR LOCATIONi) BUS REACTOR ii) LINE REACTORiii)THROUGH CB TO THE TERITIARY WNDG OF ICT

C. BASED ON CONTROLi) 3-PH OIL IMMERSED REACTOR WITH GAPPED IRON

CORE. ii) THYRISTOR CONTROLLED REACTOR (STATIC VAR

COMPENSATOR)

CBIP Guidelines on ProtectionNEED OF SHUNT REACTOR

The purpose of the Protection Relaying is to disconnect the Reactor and limit damage in case of internal short circuits, Earth faults, inter-turn faults and over voltage or over load. The reactor forms certain impedance for rated frequency, and as it is shunt connected, as over load may be caused by over voltage or harmonics in voltage and current.

Shunt Reactors are used in EHV systems to limit the over voltages due to capacitive VAR Generation (Ferranti effect) in Long transmission Lines.

PURPOSE OF SHUNT REACTOR

CBIP Guidelines on ProtectionPROTECTION DEVICES MOUNTED ON REACTOR

A) Oil immersed Reactor usually have a Gas detector and Oil surge. Detector (Buchholz Alarm & Trip devices), which are excellent for detecting internal faults.

B) Temperature Monitors for Oil & Winding provide good Over Load Protection.

C)Pressure Relief Device is provided to safe guard the Reactor from High Pressures.

CBIP Guidelines on ProtectionRECOMMENDED PROTECTIONS FOR REACTOR

1) Reactor Differential Function.

2) Reactor REF Protection.

3) Reactor Backup Protection ( Impedance type or Def Time O/L&E/F).

4) Protections and Monitors built in to Reactor.

CBIP Guidelines on ProtectionDIFFERENTIAL PROTECTION REQUIREMENTS

i) Shall be Triple Pole Type.

ii) Have an operating current sensitivity at least 10% of nominal current.

iii) be tuned with system frequency.

iv) Have an operating time not grater than 30 msecat 5 times of setting.

v) Have a suitable non-linear resistor to limit the peak voltage during in-zone faults in case of high impedance type.

vi) Shall be high or low impedance Principle type.

CBIP Guidelines on ProtectionREF PROTECTION REQUIREMENTS

i) shall be single Pole.

ii) Have an operating current sensitivity at least 10% of nominal current.

iii) be tuned with system frequency.

iv) Have a suitable non-linear resistor to limit the peak voltage during in-zone faults in case of high impedance type.

v) Shall be high or low impedance Principle type.


i) Shall be Triple pole type.ii) Shall be single step Polarized ‘MHO’ or Impedance Distance relay suitable for Measuring Phase to Ground and Phase to Phase to faults.iii)Shall grounds a Characteristic angle between 60-80 deg. iv)Shall have adjustable definite time delay with setting range of 0.2 to 2.0 sec.v) Shall have a suitable range for covering 60% of Reactor impedance.

ORi) Shall be single stage Definite Time 3 Pole, Over Current relay with adjustable current and Time.ii) Shall be connected for 2 O/C and 1 E/F connection and shall be non-directional with reset ratio and low Transient Overreach.

BACKUP PROTECTION REQUIREMENTS


Connection of restricted earth fault protection on the neutral side shall be from residually connected Bushing CTs or from the ground side CT.

The impedance or over current backup protection may not be able to detect inter-turn fault in the reactor, for which buchholz may be the only answer, unless the number of turns involved is very high.

The magnitude and nature of the switching-in currents should be considered when determining settings of reactor protectionsTypical settings of o/c relays are:Current Setting- 1.3 x Rated current , Time setting - 1 secTypical settings of impedance relays are:Reach - 60% of Reactor Impedance, Time setting - 1 sec

SETTING CRITERIA


CBIP Guidelines on ProtectionLBB/ BFR PROTECTION COMMENTS

In the event of any CB fails to trip on receipt of command from Protection relays, all CBs connected to the Bus section to which the faulty circuit Breaker is connected are required to be tripped with minimum possibly delay through LBB Protection.

This Protection also Provides coverage for faults between CB and CT which are not cleared by other protections.

GENERAL

CBIP Guidelines on ProtectionRECOMMENDATIONS FOR LBB/BFR PROTECTION

i) In all new 400KV and 220KV Substations as well as Generating Stations Switch Yard, it must be provided for each Circuit Breaker.

ii) For existing Switch Yards, it is considered a must at 400KV level and also 220KV Switch Yards having multiple feed.

iii)In case of radially fed 220KV Substations, Provision of LBB Protection is desirable but not essential.

CBIP Guidelines on ProtectionLBB/BFR REQUIREMENTS

i) Have Short Operation and Drop off times.

ii) Have 3 Phase Current elements with facility for Phase wise initiation.

iii)Have current setting range such that these can be set minimum 200mA for Line and 50mA for generators (for 1A CT for secondary).

iv) Have one common associated timer with adjustable setting.

REQUIREMENTS OF CIRCUIT BREAKERS

Operating Time

Breaking Capacity

Stuck Breaker Probability

Operating Sequence / Duty cycle

CBIP Guidelines on ProtectionLBB/BFR OPERATION

The Breaker Failure Protection (LBB/BFR) can operate single-stage/two-stage.

When used as single-stage protection, the Bus trip command is given to the adjacent Circuit Breakers if the protected feeder Breaker fails.

When used as two-stage protection, the first stage can be used to repeat the trip command to the relevant feeder Breaker, normally on a different trip coil, if the initial trip command from the feeder protection is not successful. The second stage will result in a Bus trip to the adjacent Breakers, if the command of the first stage is not successful. (This is More recommended)

CBIP Guidelines on ProtectionLBB/BFR FLOW CHART

MAIN PROTECTIONOPERATED

YES

YES

TRIP MAIN

BREAKER

INITIATEBFR

WAIT FOR FAULT

CLEARENCEAND

FAULT CLEARED

YES

NO

RESETBREAKER FAILURE SCHEME

TRIPBACK-UP/Adjacent

BREAKERS

RETRIP

CBIP Guidelines on ProtectionLBB/BFR SPECIAL COMMENTS

(i) The relay is separate for each breaker and is to be connected in the secondary circuit of the CTs associated with that particular breaker.

(ii) For line breakers, direct tripping of remote end breaker(s) should be arranged on operation of LBB protection.

For transformer breakers, direct tripping of breaker(s) on the other side of the transformer should be arranged on operation of LBB protection

(iii) For lines employing single phase auto reclosing, the LBB relays should be started on a single phase basis from the trip relays.


(iv) The CT sec core may be separate core, if available. Other wise it shall be Clubbed (in series) with Main-1 or Main-2 protection.

(v)It is considered a good practice to have DC circuits of Gr.A and Gr. B protections and relay independent.

(vi) LBB cannot operate without proper initiation. It is good practice to provide redundant trip output and breaker fail input where other forms of redundancy does not exist.

(vii) Separation should be maintained between protective relay and CB trip coil DC circuit so that short circuit or blown fuse in the CB circuit will not prevent the protective relay from energizing the LBB scheme.


(viii) In addition to other fault sensing relays the LBB relay should be initiated by Bus bar protection, since failure of CB to clear a bus fault would result in the loss of entire station if BFP relay is not initiated

(ix) Tripping logic of the bus bar protection scheme shall be used for LBB protection also.

(x) For breaker-fail relaying for low energy faults like buchholz operation, special considerations may have to be given to ensure proper scheme operation by using C.B. contact logic in addition to current detectors.

CBIP Guidelines on ProtectionLBB/BFR SETTING CRITERIA

(i) Current level detectors should be set as sensitive as the main protections

A general setting of 0.2 A is commonly practiced for Lines and Transformers

(ii)Timer setting should be set considering breaker interrupting time, current detector reset time and a margin. Generally a timer setting of 200 ms has been found to be adequate.



Bus bar protection is provided for high speed sensitive clearance of bus bar faults by tripping all the circuit breakers connected to faulty bus.

Recommendations for providing Bus bar protection at differentvoltage levels are as follows:

(i) Bus bar protection must be provided in all new 400kV and 220kV substations as well as generating station switchyards.

(ii) For existing substations, provision of Bus bar protection is considered must at 400kV level and at 220kV level.

In case of radially fed 220kV substations, having more than one bus it is desirable to have bus bar protection but is not a must.

CBIP Guidelines on ProtectionTYPES OF BUSBAR PROTECTION SCHEMES

HIGH IMPEDENCE BUSBAR PROTECTION: The Measuring Circuit comprises a High impedance stabilising Resistor (Metrosil) connected across the circulating current arrangement of all the CT’s in parallel. The Value of Stabilising Resistor chosen such that the voltage drop across the relay circuit is insufficient to operate the relay for faults outside the protection zone.MODERATE/ MEDIUM IMPEDENCE BUSBAR PROTECTION: which is combination of the

normal High-Impedance and Stabilised differential scheme. medium impedance type of Bus bar protection relays, during internal faults, but low impedance protection during load and external faults.LOW IMPEDENCE BUSBAR PROTECTION: A no of Different Measurement principles are employed in Low Impedance Schemes.

A. CURRENT DIFFERENTIAL PROTECTION: Which is current comparison with current restraint, biased or percentage differential relaying. The operating current is the Phasor sum of all feeder currents and the restraint current is the arithmetic sum. A trip command is given when operating current is greater than its pickup level and the stabilising factor the ratio of operating current to restraint current.

B. PHASE COMPARISION PROTECTION: The Measuring principle for Phase comparison protection is based on the assumption that the feeder currents are phase coincident during bus bar fault. The duration of phase coincidence of all feeder currents is checked for positive and negative half-cycles. The pickup level is set above the load current. NUMERICAL BUSBAR PROTECTION: in this two types are available.

A. CENTRALISED ARCHITECTURE.B. DECENTRLAISED ARCHITECTURE.


i) DC Supply for Bus bar protection shall be independent from feeder.

ii) Faults between CB & CT shall be cleared from one side by opening of CB on Bus bar Protection Operation.

iii)However clearing of Fault from other side shall be through breaker failure protection.

iv)3–ph trip relays shall be provided for each CB which shall also initiate LBB/BFR Protection.

v) in case of existing SS where CTs are different ratios, biased type differential protection/ Numerical Bus bar protection is recommended.

vi)Length of secondary leads should be kept as minimum as possible.

vii)Where lead runs are excessive, an increase in wire size or use of parallel conductors are meant to reduce lead resistance.

CBIP Guidelines on ProtectionREQUIREMENTS

i) it shall be 3-ph type and operate selectively for each bus bar section.ii) it shall operate on differential principle and provide independent zones of protection for each bus.iii) it shall provide zone indication.iv) it shall be stable for through fault conditions up to maximum 40KA fault level.v) For applications where bus differential protection sensitivity has to be set below load current, as may be a case with use of concrete structures, it is recommended that a separate check zone is provided, other wise separate check zone is not essential. Check zone, if provided, shall be of High Impedance type.vi) it shall incorporate continuous supervision for CT secondary against any possible open circuits. In case of detection of open circuiting of CT secondary, after a time delay, the effected zone of protection shall be rendered inoperative and alarm initiated. vii) it shall be include DC supply supervision.viii) include adequate number of high speed tripping relays.ix) whenever CT switching is involved the scheme shall include necessary CT switching relays and have provision for CT switching incomplete alarm.x) it shall be include IN/OUT switching facility for each zone..


C.T wire supervision relays should be set with a sensitivity such that they can detect C.T secondary open circuit even in case of least loaded feeder.Bus bar differential protection should have overall sensitivity above heaviest loaded feeder current unless a separate check zone has been provided.In case where faults currents are expected to be low, the protection should be sensitive enough to take care of such expected low fault current.In case of voltage operated high impedance type protection, the voltage setting should be above expected voltage developed across the relay during maximum through fault current condition.In case of current operated relays for stability under through fault condition, external resistance is to be set such that voltage developed across relay and resistance combination is below the voltage required for forcing required relay operating current.

SETTING CRITERIA


It is possible to provide Back-up protection of Bus Bars by duplicating the dedicated protection.For Substations of High strategic importance i.e. 1200KV or 765KV or 400KV Systems, the complete Bus bar protection can be fully duplicated.Dedicated Protections invariably employ separate DC circuits and CT cores. They send trip impulses to separate trip coils and use separate isolator position auxiliary contacts. Cross tripping of both trip coils is also done.For substations of 1200KV or 765KV, instead of Providing Duplicate Bus bar Protection, Providing of Two Different Manufacturers Numerical Centralised or Distributed Architecture Bus bar Protection.

DUPLICATION OF BUSBAR PROTECTION



Provides better understanding of the behavior of Power network after a disturbance.Gives useful information to improve existing Equipment and in planning or designing new installations.Disturbance recorder shall be microprocessor based and shall be used to record the graphic form of instantaneous of values voltage and current in all three phases, open delta voltage and neutral current, open or closed positions of relay contacts and breaker during the system disturbances.Disturbance recorders are recommended for all the 400kV lines.At 220kV level also they are recommended for all interconnecting lines.It is also recommended that all the disturbance recorders in the station are synchronized with GPS.

Disturbance Recorder

CBIP Guidelines on ProtectionFault Locator

Distance to fault locator is recommended to be provided as a standard for all 400kV and 220kV lines on both ends.However for short lines of length up to 20kms, fault locator can be provided at one end only. Normally in case of Numerical Relay having inbuilt feature.

Event Logger

The Event Logger is used to record the state of switchyard equipment and relays and occurrences of alarms.The equipment also records events recorded by disturbance recorder, as also changes in digital inputs, i.e operation and resetting of relay contact and switching of primary plant within the substation.


Start function to disturbance recorder is to be provided by change in state of one or more of the events connected and / or by any external triggering so that recording of events during a fault or system disturbance can be obtained.

If disturbance recorder function or fault locator functions are available as integral part of any of main protection, then separate stand alone units for this function are not required.

In case of DR being part of main protection, it should be possible to connect external binary inputs.

Stand alone DR which can cater to more than one bay / circuit can also be used.

400KV SUBSTATION: MAMIDIPALLY EVENT LOGGER EVENTS INFORMATION19 MAR 2004 13:00:00A 13:09:37.090 # 195 400KV SRISAILAM-2 MAIN-2 RAZFE PROT TRIP A 13:09:37.096 # 188 400KV SRISAILAM-2 MAIN-1 REL100 PROT START’Y’A 13:09:37.097 # 187 400KV SRISAILAM-2 MAIN-1 REL100 PROT START’R’A 13:09:37.100 # 181 400KV SRISAILAM-2 MAIN-1 REL100 PROT TRIPA 13:09:37.104 # 162 400KV SRISAILAM-2 MAIN CB 752 Y-PH OPENA 13:09:37.110 # 196 400KV SRISAILAM-2 MAIN-2 RAZFE CARRIER SENDA 13:09:37.110 # 170 400KV SRISAILAM-2 AT/F-2 TIE CB 852 B-PH OPENA 13:09:37.111 # 161 400KV SRISAILAM-2 MAIN CB 752 R-PH OPENA 13:09:37.111 # 163 400KV SRISAILAM-2 MAIN CB 752 B-PH OPENA 13:09:37.111 # 169 400KV SRISAILAM-2 AT/F-2 TIE CB 852 Y-PH OPENA 13:09:37.112 # 168 400KV SRISAILAM-2 AT/F-2 TIE CB 852 R-PH OPENA 13:09:37.113 # 182 400KV SRISAILAM-2 MAIN-1 REL100 CARRIER SENDA 13:09:37.126 # 199 400KV SRISAILAM-2 CARRIER PROT CH-2 RECEIVEDA 13:09:37.140 # 185 400KV SRISAILAM-2 CARRIER PROT CH-1 RECEIVEDN 13:09:37.147 # 195 400KV SRISAILAM-2 MAIN-2 RAZFE PROT TRIP RESETN 13:09:37.148 # 196 400KV SRISAILAM-2 MAIN-2 RAZFE CARRIER SEND RESETN 13:09:37.175 # 187 400KV SRISAILAM-2 MAIN-1 REL100 START ‘R’ RESETN 13:09:37.176 # 181 400KV SRISAILAM-2 MAIN-1 REL100 PROT TRIP RESETN 13:09:37.176 # 188 400KV SRISAILAM-2 MAIN-1 REL100 START ‘Y’ RESETN 13:09:37.185 # 182 400KV SRISAILAM-2 MAIN-1 REL100 CARRIER SEND RESETN 13:09:37.257 # 199 400KV SRISAILAM-2 CARRIER PROT CH-2 RECEIVED RESETN 13:09:37.279 # 185 400KV SRISAILAM-2 CARRIER PROT CH-1 RECEIVED RESET19 MAR 2004 14:00:00N 14:09:48.702 # 163 400KV SRISAILAM-2 MAIN CB 752 B-PH CLOSEN 14:09:48.704 # 161 400KV SRISAILAM-2 MAIN CB 752 R-PH CLOSEN 14:09:48.720 # 162 400KV SRISAILAM-2 MAIN CB 752 Y-PH CLOSEN 14:10:00.903 # 169 400KV SRISAILAM-2 AT/F-2 TIE CB 852 Y-PH CLOSEN 14:10:00.907 # 168 400KV SRISAILAM-2 AT/F-2 TIE CB 852 R-PH CLOSEN 14:10:00.907 # 170 400KV SRISAILAM-2 AT/F-2 TIE CB 852 B-PH CLOSE19 MAR 2004 15:00:00

R PH VOLTAGE

Y PH VOLTAGE

B PH VOLTAGE

OPEN DELTA VOLTAGE

R PH CURRENT

Y PH CURRENT

B PH CURRENT

STAR/NEUTRAL CURRENTMAIN CB R PH OPENMAIN CB Y PH OPENMAIN CB B PH OPEN

TIE CB R PH OPENTIE CB Y PH OPENTIE CB B PH OPEN

MAIN/TIE CB LBB OPTDDIRECT TRIP CH-1/2 OPTD

BUSBAR PROT OPTDMAIN-1 PROT OPTDMAIN-2 PROT OPTD

OVER VOLTAGE STAGE-1/2 OPTDSTUB PROT-1/2 OPTD

MAIN-1 PROT CARRIER RECEIVEMAIN-2 PROT CARRIER RECEIVE

DF/DT OPTD

EVENT NONAME OF FEEDERDATE & TIMED

ISTU

RB

AN

CE

RE

CO

RD

ER

PREFERRED DISTURBANCE RECORDER 400 KV LINES 400 KV TRANSFORMER

ANALOG CHANNELS1. R-PH VOLTAGE2. Y-PH VOLTAGE3. B-PH VOLTAGE4. OPEN DELTA VOLTAGE5. R-PH CURRENT6. Y-PH CURRENT7. B-PH CURRENT8. NEUTRAL/STAR CURRENTDIGITAL CHANNELS1. HV MAIN CB R-PH OPEN2. HV MAIN CB Y-PH OPEN3. HV MAIN CB B-PH OPEN4. HV TIE CB R-PH OPEN5. HV TIE CB Y-PH OPEN6. HV TIE CB B-PH OPEN7. 21 MAIN1 REL 521 OPERATED8. 21 MAIN2 REL 316 OPERATED9. 87 BUSBAR RELAY OPERATED10. MAIN CB A/R OPERATED11. TIE CB A/R OPERATED12. PSB OPERATED13. SOTF OPERATED14. 27 O/V STG-1/2 OPERATED15. 51 STUB-1/2 OPERATED16. 87HZ / LZ TEED-1/2 OPERATED17. MAIN CB LBB OPERATED18. TIE CB LBB OPERATED 19. DIRECT TRIP CH-1/2 RECEIVED20. 21M1 / 21M2 CARRIER RECEIVE21. 86 GR-A/B RELAY OPERATED22. 67N DEF/TEF RLY OPERATED23. DF/DT RELAY OPERATED

ANALOG CHANNELS1. HV R-PH VOLTAGE2. HV Y-PH VOLTAGE3. HV B-PH VOLTAGE4. HV OPEN DELTA VOLTAGE5. LV R-PH VOLTAGE6. LV Y-PH VOLTAGE7. LV B-PH VOLTAGE8. LV OPEN DELTA VOLTAGE9. HV R-PH CURRENT10. HV Y-PH CURRENT11. HV B-PH CURRENT12. HV NEUTRAL/STAR CURRENT13. LV R-PH CURRENT14. LV Y-PH CURRENT15. LV B-PH CURRENT16. LV NEUTRAL/STAR CURRENT

DIGITAL CHANNELS1. HV MAIN CB R-PH OPEN2. HV MAIN CB Y-PH OPEN3. HV MAIN CB B-PH OPEN4. HV TIE CB R-PH OPEN5. HV TIE CB Y-PH OPEN6. HV TIE CB B-PH OPEN7. LV 220 CB R-PH OPEN8. LV 220 CB Y-PH OPEN9. LV 220 CB B-PH OPEN10 87 LZ DIFF RLY OPERATED11. HV 67 ABCN OPERATED12. LV 67 ABCN OPERATED13. 51 O/L RLY OPERATED14. 64 REF / 87 HZ RLY OPERATED15. NDR RLY OPERATED 16. HV 99T OVER FLUX OPTD17. LV 99T OVER FLUX OPTD18. HV 400 BUSBAR OPERATED19. LV 220 BUSBAR OPERATED20. HV MAIN CB LBB OPERATED21. HV TIE CB LBB OPERATED 22. LV 220 CB LBB OPERATED23. HV 86 GR-A/B RELAY OPTD24. LV 86 GR-A/B RELAY OPTD25. AT/F 21T UZ RELAY OPERATED26. OIL TEMP HIGH TRIP27. WNDG TEMP HV/IV/LV TRIP28. BUCHHOLZ MAIN/OLTC TRIP29. PRD 1/ 2 TRIP 30. AT/F NEUTRAL CURRENT TRIP



Some broad guidelines for Engineering of Protection System are given below and could be refined if felt necessary by the Utility according to its specific needs and practices.

Wherever two sets of DC sources are available, to obtain redundancy and to be able to take protection out for maintenance, while equipment.

in service, the relays are electrically and physically segregated into two groups.

Interconnection between these two groups shall not generally be attempted.

Segregation of protections and trip circuits in two groups may be considered by giving DC supplies through separate fuses.

CBIP Guidelines on ProtectionGR-A & GR-B TRIPPINGS

For 400kV stations there shall be two separate Battery Systems available for Protection, Control & Tripping/ Closing operations. To obtain Redundancy and to be able to take Protection out for Maintenance, while equipment is in service, the Relays are Electrically and Physically segregated in to Two groups. Grouping is done to the extent possible in such a way that each group can independently carryout Protective functions with near equal redundancy. Inter connection of these two groups shall not be generally be attempted.Distribution of DC supply shall be done bay wise to feed the following1. Protection2. CB control3. Isolator / earth switch control4. Annunciation / indication


a) Protection Function:For each group of protection, separate DC sources are recommended.Example: Group-1: 21L1, 87T1, 67HV, 87R, 87BB1

Group-2: 21L2, 87T2, 67LV, 21R, 87BB2

b) CB FunctionsTrip coil 1 & 2 shall be fed from separate sources. Closing coil can be from either of these two sources.

c) Isolator / Earth switchThese associated with any one circuit shall be fed from one of the two DC sources.

In the case of One and half (1 & ½) CB arrangement, the Isolator / Earth switch associated with the tie CB can be fed from either source 1 or 2.


d) Annunciation & IndicationFor each bay, these functions can be fed from either one of the two sources. Each function shall be fed however through separate feeds.

e) Monitoring FunctionsThese shall be grouped in 3 groups

(i) Disturbance Recorders

(ii) Fault Locators

(iii) Event Loggers

All the three groups shall be fed through separate feeds from either of the two sources.Now days Numerical IEDs / Protective Relays are Having above functions are offered as inbuilt. Most of the Utilities are accepting this.

CBIP Guidelines on ProtectionCabling

It is recommended that:

(i) Separate cables are used for AC & DC circuit.

(ii) Separate cables are used for DC 1 & DC 2 circuits.

(iii) For different cores of CT & CVT separate cables shall be used.

GROUP-A & GROUP-B TRIPPINGSLINE PROTECTION TRANSFORMER

PROTECTIONREACTOR PROTECTION

GROUP-AMAIN-1 PROTECTION M1 BUILT IN FUNCTIONSTEED-1 PROTECTIONOVER VOLTAGE STAGE-1 PROTDIRECT TRIP CHANNEL-1 RECEIVED

GROUP-BMAIN-2 PROTCTIONM2 BUILT IN FUNCTIONSTEED-2 PROTECTIONOVER VOLTAGE STAGE-2 PROTLBB/BFR RELAYDIRECT TRIP CHANNEL-2 RECEIVED

GROUP-AT/F DIFFERENTIAL RELAYT/F IMP / 21T RELAYT/F HV BACKUP RELAYT/F HV OVERFLUX RELAYOIL TEMP HIGH TRIPPRESURE RELIEF TRIPTERITIARY DELTA WNDG NDR PROT GROUP-BT/F REF / HIGH Z DIFF RELAYT/F NEUTRAL CURRENT / 51 O/C RLYT/F LV BACKUP RELAYOVER LOAD PROT (ALARM ONLY)T/F LV OVERFLUX RELAYBUCHHOLZ TRIPOLTC BUCHHOLZ TRIPWINDING TEMP HIGH TRIPLOW/ HIGH OIL LEVEL TRIP

GROUP-AREACTOR DIFFERENTIAL RELAYREACTOR BACKUP / 21R RELAYOIL TEMP HIGH TRIPPRESURE RELIEF TRIP

GROUP-BREACTOR REF RELAYBUCHHOLZ TRIPWINDING TEMP HIGH TRIPLOW/ HIGH OIL LEVEL TRIPFIRE PROTECTION TRIP



Instrument transformers (CTs and VTs) are used to obtain measured quantities of current and voltage in appropriate form for use in Control, Protection and Measuring equipment such as Energy meters, indicating instruments, Protective relays, fault locators, fault recorders, synchronizers.

These are installed in different bays such as Line, Transformer, Reactor, Bus Coupler, Transfer Bus Coupler, Bus Sectionalizer Bays and also at the Bus Bar.

Given below are some examples of different bus configurations showing suitable location of CTs & VTs.


The CTs shall be placed near the circuit breakers (CBs) and on the Line side.The detection zones of Line Relays and Bus Bar relays start at the CTs. It is advantageous if these two points are close to each other.In the improbable case of a fault between the CT and CB the Bus Bar protection will detect and clear the fault.

Double Bus Arrangement

CURRENT TRANSFORMER

CT Polarity

As a practice the P1 terminal of the CT shall be towards the bus and P2 away from the bus.

CBIP Guidelines on ProtectionDouble Main and Transfer Bus Arrangement

It is advantageous to locate the CTs on the line side of the disconnectors for Line and Transformer bays. In this way the Protective Relay connected to the CT will remain connected to the line or Transformer when it is switched over to the Transfer / Auxiliary Bus.A separate CT is required to be provided in the Transfer bus coupler bay to obtain selective bus tripping for faults on Transfer bus.

Bus Coupler and Bus Sectionalizer Bays

A set of CT is necessary to enable different bus bar protection zones to be formed.The protection can be arranged to give complete fault clearing with a short time-delay (LBB time) for faults between CB and CT.Only one set of CTs is recommended.

CBIP Guidelines on ProtectionDouble Main and Bypass CB Arrangement

It is advantageous to locate the CTs on the Line side of the disconnectors for Line and Transformer bays. In this way the Protective Relay connected to the CT will remain connected to the line or Transformer when the CB is Bi-passed and protection Transferred to Bus Coupler.

Bus Coupler and Bus Sectionalizer Bays

A set of CT is necessary to enable different Bus bar protection zones to be formed.The protection can be arranged to give complete fault clearing with a short time-delay (LBB time) for faults between CB and CT.Only one set of CTs is recommended.

CBIP Guidelines on ProtectionOne and Half Breaker System

The CTs are located close to the CBs.

At the central CB ( Tie CB) two CT sets are used.

This arrangement utilizes 4 CTs. However it is also possible to use a single of CT with the tie CB thus reducing number of CTs to 3 per diameter.

Alternative way of locating the CTs requires 5 CTs. The advantages with this arrangement are:

Paralleling of two CTs to the main line protection is not required. This gives better transient response.

Separate stub protection can be connected. (TEED).

It is recommended that 4 CT arrangement is continued to be adopted.

CBIP Guidelines on ProtectionDouble Bus Double Breaker System

It is usual to locate the CTs on the line side after the CBs.

The two CTs shall be identical.

To get the line current the secondary current of the two CTs are summated.

CBIP Guidelines on ProtectionVoltage Transformers

Line CVTs

CVTs are used for metering, protection and synchronization.

Located at the line entry they also enable indication of voltage on a line energized from the opposite end.

CVTs can also be used as coupling capacitors for power line carrier (PLCC) Communication.

They are then to be located at the line side of the line traps and Line Earthing switches.

For 400kV level it is recommended that each Line Bay is provided with CVTs all the three phases.

However, depending on utility practice CVTs in one phase may also be provided in which case protections will have to be connected to bus VTs.

CBIP Guidelines on ProtectionBus CVTs

Three phase VTs / CVTs on the busbars provide input for directional relays and reference voltage for synchronization.

These VTs will have to be selected by using voltage selection scheme.

CT / VT Earthing

CT / VT secondary neutrals should be earthed at one point only.

VT secondary neutral earthing is done at equipment itself.

It is preferable to earth the CT secondary neutral in the control / protection cubicle in order to provide maximum security to the operating personnel.

Documents

CBIP-Recommondations for 400kv Protection