CBIP Recommondations

BASIC CONCEPTS OF PROTECTION OF

IN A 400KV SUBSTATION ( as Per CBIP Recommendations) P. GOPALA KRISHNA ADE/400KV/APTRANSCO

CBIP Guidelines on Protection

NORMS OF PROTECTION FOLLOWED IN UTILITIES Sr.No 1. 2. 3. 4. 5. 6. 7.

VOLTAGE 11 KV LINES 33 KV LINES 66 KV LINES 132 KV LINES

MAIN- 1 PROTECTION

MAIN-2 PROTECTION/ BACKUP PROTECTION

2 O/L + E/F ( 51 + 51N )

-

3 O/L + E/F ( 51 + 51N )

-

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

DIRECTIONAL O/L & E/F RELAYS WITH HIGH SET ( 67 + 67N )

NON SWITCHED DISTANCE SCHEME OR SWITCHED DISTANCE SCHEME OR 220 KV LINES NUMERICAL DISTANCE SCHEME (21P + 21N) NUMERICAL DISTANCE SCHEME (21P+ 21N) DISTANCE SCHEME (21P + 21N) NUMERICAL DISTANCE SCHEME (21) OR LINE 400 KV LINES NUMERICAL + in BUILT DEF RELAY(67N) DIFFERENTIAL SCHEME (87L) WITH 67N DISTANCE SCHEME (21P + 21N) NUMERICAL DISTANCE SCHEME (21) OR LINE 765 KV LINES NUMERICAL + in BUILT DEF RELAY(67N) DIFFERENTIAL SCHEME (87L) WITH 67N

The DEF 67N is in built to detect high resistance fault which distance relay cannot. REACH SETTINGS ZONE-1: 80-85% OF PROTECTED LINE ZONE-2: 120% = 100% OF MAIN LINE + 50% OF SHORTEST LINE AT OTHER END / 6O% OF T/F ZONE-3: 200% = 100% OF MAIN LINE + 100% OF LONGEST LINE AT OTHER END / 100% OF T/F ZONE-4: 100% OF MAIN LINE + (100% OF SHORTEST LINE + 100% OF LONGEST LINE) AT OTHER END. R-REACH: UP TO LOAD POINT ENCROACHMENT TIME SETTINGS ZONE-1: INSTANTENEOUS ZONE-2: 0.3 SEC FOR SHORT LINES & 0.5 SEC FOR LONG LINES for Discrimination ZONE-3: 0.6 SEC ZONE-4: 0.9 SEC

CBIP Guidelines on Protection 400 kV Lines ¾

NEED OF LINE PROTECTION The 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

CBIP Guidelines on Protection 400kV Lines ¾ 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 nonswitched Three/ Four zone distance protection. ¾ 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. ¾ 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. ¾ Both should be suitable for single and three phase tripping.

CBIP Guidelines on Protection ¾ 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

CBIP Guidelines on Protection 220 kV Lines ¾ There should be at least one carrier aided nonswitched three zone Distance protection scheme. ¾ In addition to this another non-switched / switched distance scheme or directional over current and earth fault relays should be provided as back up. ¾ Main protection should be suitable for single and three phase tripping. ¾ Auto-reclose relay suitable for 1 ph / 3 ph reclosure shall be provided. ¾ In case of both line protections being Distance Protections, IDMT type E / F relay shall also be provided additionally.

CBIP Guidelines on Protection SPECIAL COMMENTS (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 the distance 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.

CBIP Guidelines on Protection SETTING CRITERIA

Reach settings of distance protection

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.

CBIP Guidelines on 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.

CBIP Guidelines on Protection Time setting of distance protection ¾ 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. ¾ 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.

CBIP Guidelines on Protection O / V Protection ¾ Low set voltage may be set at 110% with a typical time delay of 5 seconds. ¾ A time grading of 1 second may be provided between relays of different lines at a station. ¾ 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. ¾High set stage may be set at 150% with a time delay of 100 m second. 3.4 PSB Function Associated with Distance Relays ¾ Decisions pertaining to allowing which Zone to trip and which to block should be taken based on system studies on case to case basis.

CBIP Guidelines on Protection DISTANCE PROTECTION REQUIREMENTS 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 wherever applicable. 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 compensation ix) 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 shaped characteristics 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 Protection PHASE COMPARISION 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 Protection PHASE SEGREGATED LINE DIFFERENTIAL PROTECTION 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 ITUT(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.

CBIP Guidelines on Protection OVER VOLTAGE PROTECTION REQUIREMENTS

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.


CBIP Guidelines on Protection GENERAL ¾ The auto-reclosing of power lines has become a generally accepted practice. ¾ 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. ¾ Auto reclosing advantages.

therefore

provides

significant

¾ Outage times will be short compared to where station personnel have to re-energize the lines after a fault. ¾ In interconnected networks auto-reclosing helps in maintaining system stability

CBIP Guidelines on Protection Recommendations for provisions of auto-reclosing ¾ 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. ¾ 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.

CBIP Guidelines on Protection FAULTS ARE THREE TYPES 1. 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. ¾ 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. ¾ ADVANTAGES: A. Decreasing outage time. B. Improving Reliability. C. Improving system stability. D. Reduce fault damage and Maintenance Time.

¾

CBIP Guidelines on Protection TYPES OF AUTO-RECLOSING 1. BASED ON PHASE A. THREE PHASE AUTO-RECLOSING. B. SINGLE PHASE AUTO-RECLOSING. 2. BASED ON ATTEMPTS OF RECLOSURE A. 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.

CBIP Guidelines on Protection SETTING CRITERIA Dead Time ¾ DEAD TIME: The time between the Auto-reclosing Scheme being energized and the operation of the contacts which energize the Circuit Breaker closing circuit. ¾Auto- reclosing requires a dead time which exceeds the de-ionising time ¾ 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. ¾ Single phase dead time of 1.0 sec is recommended for both 400kV and 220kV system.

CBIP Guidelines on Protection Reclaim Time ¾ 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. ¾The time during which a new start of the auto-reclosing equipment is blocked. ¾ 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. ¾ After the reclaim time has elapsed, the auto-reclosing equipment returns to the starting position and a new reclosing sequence can occur. ¾ 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. ¾If the breaker is closed manually, the auto reclosing equipment is blocked and cannot start again until the reclaim time has elapsed. ¾ 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.

CBIP Guidelines on Protection 2.3 Circuit Breaker Requirement

¾ 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 ¾ The recommended operating cycle at 400kV and 220kV is as per the IEC standard. ¾ Reclaim time of 25 sec is recommended.

CBIP Guidelines on Protection AUTO-RECLOSING RELAY REQUIREMENTS 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.

CBIP Guidelines on Protection 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 Protection GENERAL & NEED OF PROTECTION FOR TRANSFORMER

¾ A Power Transformer is a very valuable and vital link in a Power Transmission system ¾ 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. ¾ Faults in a Transformer occur due to insulation breakdown, ageing of insulation, overheating due to overexcitation, oil contamination and leakage or reduced cooling.

¾ 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.

CBIP Guidelines on Protection 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. ¾ PROTECTION DEVICES INBUILT OR MOUNTED ON POWER T/F A. 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 Protection TRANSFORMER 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 galvanically interconnected 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 Protection RESTRICTED 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 Protection BACK 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).

NORMALLY ADOPTED POWER TRANSFORMERS CAPACITIES BY UTILITIES IN 400KV / 220KV SYSTEM CAPACITY OF TRANSFORMER

315 MVA 500 MVA 630 MVA

HV VOLTAGE HV CURRENT

400 KV 400 KV 400 KV

454.68 A 721.71 A 909.35 A

IV VOLTAGE

IV CURRENT

220 KV 220 KV 220 KV

0826.68 A 1312.20 A 1653.37 A

IN 765KV / 400KV SYSTEM CAPACITY OF TRANSFORMER

630 MVA 750 MVA 1000 MVA 1500 MVA

HV VOLTAGE HV CURRENT

765 KV 765 KV 765 KV 765 KV

0475.48 A 0566.05 A 0754.73 A 1132.10 A

IV VOLTAGE

IV CURRENT

400 KV 400 KV 400 KV 400 KV

0909.35 A 1082.56 A 1443.42 A 2165.14 A

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

220 / 33

6

220 / 66

7

31.5, 50 & 100 100, 200 & 250

400 / 132

8

100 & 160

220 / 132

9

315, 500 & 630

400 / 220

10

630, 750,

765 / 400

1000 & 1500

HV & LV REF 64

LV

3 OL + 1 EL (51)

3 DIR OL (HIGHSET) + 1 DIR EL (HIGHSET)

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

ADDITIONAL SPECIAL PROTECTION PROTECTION BUCHHOLZ, OLTC OSR OIL TEMP WDNG TEMP

BUCHHOLZ OVER FLUX OLTC OSR PRV/PRD OIL TEMP WDNG TEMP

64REF IS 1-PH HIGH IMPEDANCE DIFFERENTIAL RELAY 87TH IS 3-PH HIGH IMPEDANCE DIFFERENTIAL RELAY (PRINCPLE : CIRCULATING CURRENT)

31.5, 50

HV

3 OVER LOAD + 1 EARTH FAULT RELAY ( 51 )

5

BACK UP PROTECTION

3 OVER LOAD + 1 DIRECTIONAL EARTH FAULT RELAY ( 51P + 67N)

132 / 33

87 TH / 64 REF

16 , 31.5 50 & 80

132 / 11

PROTECTION

HV REF (64)

4

2

MAIN-2

NIL

66 / 33

1

MAIN-1

87 TL DIFFERENTIAL RELAY

66 / 11

3

7.5 & 16 7.5 , 16 & 25 7.5 , 16 , 25 & 31.5

S.N o

T Y P E

( LOW IMPEDANCE PERCENTAGE BIASED PHASE SEGREGATED DIFFERENTIAL RELAY PRINCIPLE: MERZ PRICE)

VOLTAGE RATIO IN KV

2 WINDING TRANSFORMER (STAR/STAR) ICT / AUTO TFR

CAPACITY IN MVA

OVER LOAD ALARM RELAY + NEUTRAL CURRENT E/F RELAY

CBIP Guidelines on Protection DIFFERENTIAL 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 setting iv) 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 Protection REF 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 Protection BACKUP 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 Protection OVER LOAD ALARM RELAY REQUIREMENTS

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. OVER FLUX PROTECTION RELAY REQUIREMENTS (HV&LV)

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 Protection SPECIAL 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 Protection TYPES OF REACTORS

¾ A. BASED ON REACTOR CONNECTION i) SHUNT REACTOR. ii) SERIES REACTOR. ¾ B. BASED ON REACTOR LOCATION i) BUS REACTOR ii) LINE REACTOR iii)THROUGH CB TO THE TERITIARY WNDG OF ICT ¾ C. BASED ON CONTROL i) 3-PH OIL IMMERSED REACTOR WITH GAPPED IRON CORE. ii) THYRISTOR CONTROLLED REACTOR (STATIC VAR COMPENSATOR)

CBIP Guidelines on Protection NEED OF SHUNT REACTOR

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

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.

CBIP Guidelines on Protection PROTECTION 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 Protection RECOMMENDED 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 Protection DIFFERENTIAL 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 msec at 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 Protection REF 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.

CBIP Guidelines on Protection BACKUP PROTECTION REQUIREMENTS

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. OR i) 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.


¾ Connection of restricted earth fault protection on the neutral side shall be from residually connected Bushing CTs or from the ground side CT. ¾ 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. SETTING CRITERIA

¾ The magnitude and nature of the switching-in currents should be considered when determining settings of reactor protections ¾ Typical settings of o/c relays are: Current Setting- 1.3 x Rated current , Time setting - 1 sec ¾ Typical settings of impedance relays are: Reach - 60% of Reactor Impedance, Time setting - 1 sec


CBIP Guidelines on Protection LBB/ BFR PROTECTION COMMENTS GENERAL

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.

CBIP Guidelines on Protection RECOMMENDATIONS 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 Protection LBB/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

¾ Operating Time ¾ Breaking Capacity ¾ Stuck Breaker Probability ¾ Operating Sequence / Duty cycle

CBIP Guidelines on Protection LBB/BFR OPERATION

¾ The Breaker Failure Protection operate single-stage/two-stage.

(LBB/BFR)

can

¾ When used as single-stage protection, the Bus trip command is given to the adjacent Circuit Breakers if the protected feeder Breaker fails. ¾ 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 Protection LBB/BFR FLOW CHART

MAIN PROTECTION OPERATED

YES

TRIP MAIN BREAKER

FAULT CLEARED

YES

RESET BREAKER FAILURE SCHEME

NO RETRIP

YES

INITIATE BFR

WAIT FOR FAULT CLEARENCE

AND

TRIP BACK-UP/ Adjacent BREAKERS

CBIP Guidelines on Protection LBB/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 Protection LBB/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.


CBIP Guidelines on Protection GENERAL

¾ Bus bar protection is provided for high speed sensitive clearance of bus bar faults by tripping all the circuit breakers connected to faulty bus. ¾ Recommendations for providing Bus bar protection at different voltage 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 Protection TYPES OF BUSBAR PROTECTION SCHEMES ¾

¾

¾ A.

B.

¾ A. B.

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. 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. 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. CENTRALISED ARCHITECTURE. 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 Protection REQUIREMENTS 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..

CBIP Guidelines on Protection SETTING CRITERIA ¾

¾

¾

¾

¾

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.

CBIP Guidelines on Protection DUPLICATION OF BUSBAR PROTECTION

¾ It is possible to provide Back-up protection of Bus Bars by duplicating the dedicated protection. ¾ For Substations of High strategic importance i.e. 1200KV or 765KV or 400KV Systems, the complete Bus bar protection can be fully duplicated. ¾ 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. ¾ 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.


CBIP Guidelines on Protection Disturbance Recorder ¾ Provides better understanding of the behavior of Power network after a disturbance. ¾ Gives useful information to improve existing Equipment and in planning or designing new installations. ¾ 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. ¾ Disturbance recorders are recommended for all the 400kV lines. ¾ At 220kV level also they are recommended for all interconnecting lines. ¾ It is also recommended that all the disturbance recorders in the station are synchronized with GPS.

CBIP Guidelines on Protection Fault Locator ¾ Distance to fault locator is recommended to be provided as a standard for all 400kV and 220kV lines on both ends. ¾ 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 ¾ The Event Logger is used to record the state of switchyard equipment and relays and occurrences of alarms. ¾ 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.

CBIP Guidelines on Protection SPECIAL COMMENTS ¾ 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. ¾ 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. ¾ In case of DR being part of main protection, it should be possible to connect external binary inputs. ¾ Stand alone DR which can cater to more than one bay / circuit can also be used.

400KV SUBSTATION: MAMIDIPALLY 19 MAR 2004 13:00:00 A 13:09:37.090 # 195 A 13:09:37.096 # 188 A 13:09:37.097 # 187 A 13:09:37.100 # 181 A 13:09:37.104 # 162 A 13:09:37.110 # 196 A 13:09:37.110 # 170 A 13:09:37.111 # 161 A 13:09:37.111 # 163 A 13:09:37.111 # 169 A 13:09:37.112 # 168 A 13:09:37.113 # 182 A 13:09:37.126 # 199 A 13:09:37.140 # 185 N 13:09:37.147 # 195 N 13:09:37.148 # 196 N 13:09:37.175 # 187 N 13:09:37.176 # 181 N 13:09:37.176 # 188 N 13:09:37.185 # 182 N 13:09:37.257 # 199 N 13:09:37.279 # 185 19 MAR 2004 14:00:00 N 14:09:48.702 # 163 N 14:09:48.704 # 161 N 14:09:48.720 # 162 N 14:10:00.903 # 169 N 14:10:00.907 # 168 N 14:10:00.907 # 170 19 MAR 2004 15:00:00

EVENT LOGGER EVENTS INFORMATION

400KV SRISAILAM-2 MAIN-2 RAZFE PROT TRIP 400KV SRISAILAM-2 MAIN-1 REL100 PROT START’Y’ 400KV SRISAILAM-2 MAIN-1 REL100 PROT START’R’ 400KV SRISAILAM-2 MAIN-1 REL100 PROT TRIP 400KV SRISAILAM-2 MAIN CB 752 Y-PH OPEN 400KV SRISAILAM-2 MAIN-2 RAZFE CARRIER SEND 400KV SRISAILAM-2 AT/F-2 TIE CB 852 B-PH OPEN 400KV SRISAILAM-2 MAIN CB 752 R-PH OPEN 400KV SRISAILAM-2 MAIN CB 752 B-PH OPEN 400KV SRISAILAM-2 AT/F-2 TIE CB 852 Y-PH OPEN 400KV SRISAILAM-2 AT/F-2 TIE CB 852 R-PH OPEN 400KV SRISAILAM-2 MAIN-1 REL100 CARRIER SEND 400KV SRISAILAM-2 CARRIER PROT CH-2 RECEIVED 400KV SRISAILAM-2 CARRIER PROT CH-1 RECEIVED 400KV SRISAILAM-2 MAIN-2 RAZFE PROT TRIP RESET 400KV SRISAILAM-2 MAIN-2 RAZFE CARRIER SEND RESET 400KV SRISAILAM-2 MAIN-1 REL100 START ‘R’ RESET 400KV SRISAILAM-2 MAIN-1 REL100 PROT TRIP RESET 400KV SRISAILAM-2 MAIN-1 REL100 START ‘Y’ RESET 400KV SRISAILAM-2 MAIN-1 REL100 CARRIER SEND RESET 400KV SRISAILAM-2 CARRIER PROT CH-2 RECEIVED RESET 400KV SRISAILAM-2 CARRIER PROT CH-1 RECEIVED RESET 400KV 400KV 400KV 400KV 400KV 400KV

SRISAILAM-2 SRISAILAM-2 SRISAILAM-2 SRISAILAM-2 SRISAILAM-2 SRISAILAM-2

MAIN CB 752 B-PH CLOSE MAIN CB 752 R-PH CLOSE MAIN CB 752 Y-PH CLOSE AT/F-2 TIE CB 852 Y-PH CLOSE AT/F-2 TIE CB 852 R-PH CLOSE AT/F-2 TIE CB 852 B-PH CLOSE

DISTURBANCE RECORDER

R PH VOLTAGE Y PH VOLTAGE B PH VOLTAGE OPEN DELTA VOLTAGE R PH CURRENT Y PH CURRENT B PH CURRENT STAR/NEUTRAL CURRENT MAIN CB R PH OPEN MAIN CB Y PH OPEN MAIN CB B PH OPEN TIE CB R PH OPEN TIE CB Y PH OPEN TIE CB B PH OPEN MAIN/TIE CB LBB OPTD DIRECT TRIP CH-1/2 OPTD BUSBAR PROT OPTD MAIN-1 PROT OPTD MAIN-2 PROT OPTD OVER VOLTAGE STAGE-1/2 OPTD STUB PROT-1/2 OPTD MAIN-1 PROT CARRIER RECEIVE MAIN-2 PROT CARRIER RECEIVE DF/DT OPTD EVENT NO NAME OF FEEDER DATE & TIME

PREFERRED DISTURBANCE RECORDER 400 KV LINES

400 KV TRANSFORMER

ANALOG CHANNELS

ANALOG CHANNELS

DIGITAL CHANNELS

1. 2. 3. 4. 5. 6. 7. 8.

1. HV 2. HV 3. HV 4. HV 5. LV 6. LV 7. LV 8. LV 9. HV 10. HV 11. HV 12. HV 13. LV 14. LV 15. LV 16. LV

1. HV MAIN CB R-PH OPEN 2. HV MAIN CB Y-PH OPEN 3. HV MAIN CB B-PH OPEN 4. HV TIE CB R-PH OPEN 5. HV TIE CB Y-PH OPEN 6. HV TIE CB B-PH OPEN 7. LV 220 CB R-PH OPEN 8. LV 220 CB Y-PH OPEN 9. LV 220 CB B-PH OPEN 10 87 LZ DIFF RLY OPERATED 11. HV 67 ABCN OPERATED 12. LV 67 ABCN OPERATED 13. 51 O/L RLY OPERATED 14. 64 REF / 87 HZ RLY OPERATED 15. NDR RLY OPERATED 16. HV 99T OVER FLUX OPTD 17. LV 99T OVER FLUX OPTD 18. HV 400 BUSBAR OPERATED 19. LV 220 BUSBAR OPERATED 20. HV MAIN CB LBB OPERATED 21. HV TIE CB LBB OPERATED 22. LV 220 CB LBB OPERATED 23. HV 86 GR-A/B RELAY OPTD 24. LV 86 GR-A/B RELAY OPTD 25. AT/F 21T UZ RELAY OPERATED 26. OIL TEMP HIGH TRIP 27. WNDG TEMP HV/IV/LV TRIP 28. BUCHHOLZ MAIN/OLTC TRIP 29. PRD 1/ 2 TRIP 30. AT/F NEUTRAL CURRENT TRIP

R-PH VOLTAGE Y-PH VOLTAGE B-PH VOLTAGE OPEN DELTA VOLTAGE R-PH CURRENT Y-PH CURRENT B-PH CURRENT NEUTRAL/STAR CURRENT

DIGITAL CHANNELS 1. HV MAIN CB R-PH OPEN 2. HV MAIN CB Y-PH OPEN 3. HV MAIN CB B-PH OPEN 4. HV TIE CB R-PH OPEN 5. HV TIE CB Y-PH OPEN 6. HV TIE CB B-PH OPEN 7. 21 MAIN1 REL 521 OPERATED 8. 21 MAIN2 REL 316 OPERATED 9. 87 BUSBAR RELAY OPERATED 10. MAIN CB A/R OPERATED 11. TIE CB A/R OPERATED 12. PSB OPERATED 13. SOTF OPERATED 14. 27 O/V STG-1/2 OPERATED 15. 51 STUB-1/2 OPERATED 16. 87HZ / LZ TEED-1/2 OPERATED 17. MAIN CB LBB OPERATED 18. TIE CB LBB OPERATED 19. DIRECT TRIP CH-1/2 RECEIVED 20. 21M1 / 21M2 CARRIER RECEIVE 21. 86 GR-A/B RELAY OPERATED 22. 67N DEF/TEF RLY OPERATED 23. DF/DT RELAY OPERATED

R-PH VOLTAGE Y-PH VOLTAGE B-PH VOLTAGE OPEN DELTA VOLTAGE R-PH VOLTAGE Y-PH VOLTAGE B-PH VOLTAGE OPEN DELTA VOLTAGE R-PH CURRENT Y-PH CURRENT B-PH CURRENT NEUTRAL/STAR CURRENT R-PH CURRENT Y-PH CURRENT B-PH CURRENT NEUTRAL/STAR CURRENT



¾ 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. ¾ Wherever two sets of DC sources are available, to obtain redundancy and to be able to take protection out for maintenance, while equipment. ¾ in service, the relays are electrically and physically segregated into two groups. ¾ Interconnection between these two groups shall not generally be attempted. ¾ Segregation of protections and trip circuits in two groups may be considered by giving DC supplies through separate fuses.

CBIP Guidelines on Protection GR-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 following 1. Protection 2. CB control 3. Isolator / earth switch control 4. 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 Functions Trip coil 1 & 2 shall be fed from separate sources. Closing coil can be from either of these two sources. c) Isolator / Earth switch These 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 & Indication For 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 Functions These 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 Protection Cabling 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 TRIPPINGS LINE PROTECTION

GROUP-A MAIN-1 PROTECTION M1 BUILT IN FUNCTIONS TEED-1 PROTECTION OVER VOLTAGE STAGE-1 PROT DIRECT TRIP CHANNEL-1 RECEIVED

GROUP-B MAIN-2 PROTCTION M2 BUILT IN FUNCTIONS TEED-2 PROTECTION OVER VOLTAGE STAGE-2 PROT LBB/BFR RELAY DIRECT TRIP CHANNEL-2 RECEIVED

TRANSFORMER PROTECTION

GROUP-A T/F DIFFERENTIAL RELAY T/F IMP / 21T RELAY T/F HV BACKUP RELAY T/F HV OVERFLUX RELAY OIL TEMP HIGH TRIP PRESURE RELIEF TRIP TERITIARY DELTA WNDG NDR PROT GROUP-B T/F REF / HIGH Z DIFF RELAY T/F NEUTRAL CURRENT / 51 O/C RLY T/F LV BACKUP RELAY OVER LOAD PROT (ALARM ONLY) T/F LV OVERFLUX RELAY BUCHHOLZ TRIP OLTC BUCHHOLZ TRIP WINDING TEMP HIGH TRIP LOW/ HIGH OIL LEVEL TRIP

REACTOR PROTECTION

GROUP-A REACTOR DIFFERENTIAL RELAY REACTOR BACKUP / 21R RELAY OIL TEMP HIGH TRIP PRESURE RELIEF TRIP

GROUP-B REACTOR REF RELAY BUCHHOLZ TRIP WINDING TEMP HIGH TRIP LOW/ HIGH OIL LEVEL TRIP FIRE PROTECTION TRIP



¾ 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. ¾ 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. ¾ Given below are some examples of different bus configurations showing suitable location of CTs & VTs.

CBIP Guidelines on Protection CURRENT TRANSFORMER

CT Polarity ¾ As a practice the P1 terminal of the CT shall be towards the bus and P2 away from the bus. Double Bus Arrangement ¾ The CTs shall be placed near the circuit breakers (CBs) and on the Line side. ¾ 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. ¾ In the improbable case of a fault between the CT and CB the Bus Bar protection will detect and clear the fault.

CBIP Guidelines on Protection Double Main and Transfer Bus Arrangement ¾It 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. ¾A 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 ¾A set of CT is necessary to enable different bus bar protection zones to be formed. ¾The protection can be arranged to give complete fault clearing with a short time-delay (LBB time) for faults between CB and CT. ¾Only one set of CTs is recommended.

CBIP Guidelines on Protection Double Main and Bypass CB Arrangement ¾

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 ¾ A set of CT is necessary to enable different Bus bar protection zones to be formed. ¾ The protection can be arranged to give complete fault clearing with a short time-delay (LBB time) for faults between CB and CT. ¾ Only one set of CTs is recommended.

CBIP Guidelines on Protection One and Half Breaker System ¾ The CTs are located close to the CBs. ¾ At the central CB ( Tie CB) two CT sets are used. ¾ 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. ¾ Alternative way of locating the CTs requires 5 CTs. The advantages with this arrangement are: ¾ Paralleling of two CTs to the main line protection is not required. This gives better transient response. ¾ Separate stub protection can be connected. (TEED). ¾ It is recommended that continued to be adopted.

4

CT

arrangement

is

CBIP Guidelines on Protection Double Bus Double Breaker System ¾ It is usual to locate the CTs on the line side after the CBs. ¾ The two CTs shall be identical. ¾ To get the line current the secondary current of the two CTs are summated.

CBIP Guidelines on Protection Voltage Transformers Line CVTs ¾ CVTs are used synchronization.

for

metering,

protection

and

¾ Located at the line entry they also enable indication of voltage on a line energized from the opposite end. ¾ CVTs can also be used as coupling capacitors for power line carrier (PLCC) Communication. ¾ They are then to be located at the line side of the line traps and Line Earthing switches. ¾ For 400kV level it is recommended that each Line Bay is provided with CVTs all the three phases. ¾ 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 Protection Bus CVTs ¾ Three phase VTs / CVTs on the busbars provide input for directional relays and reference voltage for synchronization. ¾ These VTs will have to be selected by using voltage selection scheme. CT / VT Earthing ¾ CT / VT secondary neutrals should be earthed at one point only. ¾ VT secondary neutral earthing is done at equipment itself. ¾ It is preferable to earth the CT secondary neutral in the control / protection cubicle in order to provide maximum security to the operating personnel.

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