Customer Benefits

High stability forthrough faults

Fast operation for inzone faults

Simultaneous trippingof relays at each lineend

Low current transformerrequirements

T&D

MBCI Differential Feeder and Transformer Feeder Protection

PROTECTION

Differential feeder protection requires acomparison of the currents entering andleaving the protected zone. Two MBCI relaysare therefore required, one for each end of thefeeder. A pair of pilot wires is used to transmitinformation between the two relays so thateach may be able to compare the currentflowing at its respective end with the current atthe other.

The pilot wire carries analogue circulatingcurrent - allowing correct operation even forlow specification or ageing pilots.

When applying this protection to overheadlines the limiting factor is generally the lengthof the pilot circuits: for cable feeders thelimiting factors are more likely to be the level of line charging current and the method ofsystem earthing.

MODELS AVAILABLE

> MBCI 01 - Private pilots> MBCI 02 - Telephone type

OPTIONAL EXTRAS

> MRTP supervision relay Alarm and indication of pilot failure and supervision supply failure Suitable for pilot circuits insulated for 5kV or 15kV with pilot isolation

transformers

> MVTW destabilising and Intertripping relay Destabilises the feeder protection so that tripping occurs Intertripping: injects ac voltage into pilot circuit so that tripping occurs

> MCRI instantaneous Overcurrent and start/check relay High speed operation Two phase and earth fault relay

> MCTH transformer inrush Current detector Allows MBCI to be applied to transformer feeders Blocks operation of the MBCI relay during transformer inrush conditions

A

B

C

Rs

Ts

Tt

RVD

Trip

cT1

T2

To Pilot wires

Ro

Rpp

Tr

Ro

Rpp

To

Tr

RVD

c

V

T2Trip

RsT1

ToTrTrRo

- Operating winding- Restraining winding- Tertiary winding- Linear resistor

Rppc

- Pilots padding resistor- Phase comparator

T1T2RVDTs

- Summation transformer- Auxiliary transformer- Non linear resistor- Secondary winding

V

Figure 1 Basic circuit arrangement

> Pilot supervision

Correct interchange of information over the pilot circuitis essential for the proper functioning of any differentialfeeder protection. The most common pilot failure is tothe open circuit state, caused by the accidentalexcavation of buried pilots or storm damage tooverhead pilots. With the pilots open circuited thedifferential protection will be unstable and will trip thefeeder if sufficient through current is flowing. For thisreason the circulating current system is often preferredas such schemes will fail safe and trip so that attentionis immediately drawn to the fault.

> Destabilising/intertripping

The remote unit of the differential feeder protection canbe caused to operate, provided sufficient line current isflowing, by open circuiting the pilots. If line current isnot flowing, the remote unit can be operated(intertripped) by injecting a current into the pilots.

> Overcurrent check/starting

Although the supervision scheme provides indicationof pilot failure it does not prevent the protectionoperating if primary current above setting is flowing.Where this hazard is unacceptable it is necessary toadd an overcurrent check feature to verify faultpresence.

> Emergency use for overcurrent protection

In the event of a pilot failure which cannot quickly berectified, the Translay S scheme may be adapted foruse as a definite time overcurrent relay.

2>3

RL11

PilotWires

Trip/Alarm

Outputs

MBCI

IA

IB

ICIN

RSSee

Note 5

SeeNote 2

VX

+PowerSupplyCircuits

Enable

Enable

RL12

RL22

RL31

Protected Zone

RES

OP

LevelDetector

Squarer

Squarer

KS

&

&

IA

IB

IN

MBCI

PhaseRotation

RS

Protected Zone

SeeNote 4

ABC

RO

Case EarthSee Note 3

A

BC

Moduleterminal blockviewed fromrear

(a) C.T. shorting links make before (b) & (c) disconnect.(b) Short terminals break before (c)(c) Long terminal.

RPP

Kt

3. Earthing connections are typical only.4. C.T. connections are typical only.5. For overcurrent start schemes, terminal 12 must be connected directly to D.C. +VE to provide a supply for the L.E.D. and reset circuits.

1.

2. Link terminals 11 and 13 except when used with overcurrent check replay type MCRI.

23

RL12

RL21

RL22

IC

Notes

19

18

1710

8

97

642

531

11

14

1312

282726252423

P2 P1S2 S1

2425

2627

28

P1 P2S1 S2

1 23 45 67 89 1011 1213 1415 1617 18

19 20

21 22

23 24

25 26

27 28

Case earth

RL41135

Output Contacts Change state for pilot fail

See Note 7

Module terminal blockviewed from rear

Note 1.(a) C.T. shorting links make before (b) & (c) disconnect.(b) Short terminals break before (c).(c) Long terminal.

RL42

RL42 467

RL51 9118

RL52 1012

Output Contacts Change state for supply fail

RL52

RL71

RL61

RL81

SupplyFail

PilotS/C

PilotO/C

RL22

RL32

OPReset

OPReset

OPReset

tRL31

RL21

RL11

+VE

StartRL12

RL22

RL32

RL12

A.C.Auxiliar ySupply

A.C.PowerSupply

D.C.PowerSupply

Case Earth

20

1927

28

13

14Vx

18

17

18

17

MBCI MBCIPilots

MRTP 03

S1

P1

S2

P2

P6P5P4P3P2

P1

S2

X2

X1S1

Supervisionisolation transformer

P6P5P4P3P2

P1

Pilot isolationtransformer

S1

X1

X2

S2

1 23 45 67 89 1011 1213 1415 1617 18

19 2021 2223 2425 2627 28

Case earth2

Pilot isolationtransformer

Simple differential protection - only 2pilot cores, and no MODEMS!

Figure 2 Application diagram: differential feeder protection relay type MBCI

Figure 3 Application diagram: pilot supervision relay 15kV isolation type MRTP 03

> Transformer feeders (use of transformer inrush current detector)

The inclusion of a type MCTH relay, designed toprovide a blocking signal in the presence oftransformer inrush currents, enables a pilot wiredifferential protection scheme to be applied to atransformer feeder. Where line and thereforetransformer energisation can occur at one end only ofthe transformer feeder, then a MCTH unit would berequired on that side only.

> Symbols:

15kV isolating transformer

15kV isolating transformer with injection filter

Scheme Pilot Supervision O/CInsulation Start/Check Arrangement of EquipmentLevel (kV) (Viewed from front)

A 5kV

B 15kV

C 5kV

D 15kV

E 5kV

F 15kV

G 5kV

H 15kV

Table 1. Typical scheme arragements for plain feeders. See key below.

Scheme Pilot Supervision TransformerInsulation Arrangement Arrangement of EquipmentLevel (kV) (Viewed from front)

I 5kV

J 15kV

K 5kV

L 15kV

M 5kV

N 15kV

O 5kV

P 15kV

Table 2. Typical scheme arragements for transformer feeders. See key below.

No. Type of relay

1 MBCI 01/02 Differential2 MRTP 01 Pilot supervision and injection filter3 MRTP 02 Injection filter4 MRTP 03 Pilot supervision5 MCRI 01 Overcurrent start/check6 MVTW 01 Destabilising7 MVTW 03 Destabilising and Intertripping

Schemes A to D can be fitted with relay types 6 or 7.Schemes E to H can be fitted with type 6 which will providedestabilising if the overcurrent start/check relays (MCRI 01) haveoperated. Schemes I to L must use type 7 or 8.

8 MCTH 01 Transformer inrush current detector9 MFAC 14 High impedance earth fault relay10 MMLG Test plug/block

It is advisable on all schemes to include the test unit to facilitatecommissioning and routine testing. The unit will be situated on therighthand side of the scheme.

1 1

1 1

2 1 3 1

4 1

1 5 1 5

1 5 1 5

4 1 5 1 5

1

2 1 5 3 51

1 8 9 7 1 8

1 8 9 7 1 8

1 8 2 9 7 1 8 3

1 8 4 9 7 1 8

1 8 1 8

1 8 1 8

1 8 2 1 8 3

1 8 4 1 8

Pilots

DESCRIPTION

> Differential protection

The differential feeder protection circuit is derived fromthe well known Merz-Price circulating current system.Figure 1 shows the basic circuit arrangement. Asummation current transformer T1 at each line endproduces a single phase current proportional to thesummated three phase currents in the protected line.The neutral section of the summation winding istapped to provide alternative sensitivities for earthfaults.

In order to maintain the bias characteristic at thedesigned value it is necessary to pad the pilot loopresistance to 1k. A padding resistor Rpp is providedin the relay for this purpose.

> Pilot isolation transformers

When pilot isolation transformers are used, the pilotinsulation level is raised to 15kV.

> Telephone type pilots (MBCI02)

When the pilots to be used are of the telephone type -the pilot differential voltage is limited by a metrosil(MBCI01). An alternative limiter based on a zenerdiode is available (MBCI02).

4>5

DESTABILISE AND INTERTRIPFACILITIES

> MVTW01

Operation of the destabilising relay results in thesummation current transformer in the differential relaybeing short circuited and the local relay prevented fromtripping.

The remote relay then sees a single end feed conditionand trips, provided the through current exceeds the no-load fault setting of the protection

> MVTW03

The MVTW 03 incorporates a full bridge inverter,which receives signals from an oscillator circuit at afrequency of 80Hz. This frequency was chosenbecause it lies sufficiently far from the pilot frequencyof 50 or 60Hz and cancellation of the intertrippingsignal cannot result.

To ensure intertripping occurs the output relay injects a20mA intertrip current into the pilots; the remote MBCIsees the intertrip current as a differential current whichcauses it to trip.

> Transformer inrush current detector feature

A typical scheme for a delta-star power transformer isshown in figure 4. The line current transformers areconnected in star on the delta side of the transformer.Appropriate choice of CT ratios ensures that fornormal load and through fault conditions, equalcurrents flow into the differential tripping units (MBCI)at each end. A high impedance differential relay (typeMFAC 14) is included in the neutral lead of the star-connected line transformers to provide B-N protectionon the delta side of the power transformer. The MFAC14 high impedance differential relay may be used toinitiate an intertrip unit (type MVTW 02)

Unit protection for lines and cables, including those with in-zone transformers

A

B

C

S1 S2

P2I

II

III

i

ii

iiiyn

A

B

C

P2 P1

S2 S1

N.E.R.

MCTH MCTH

MBCI MBCI

Pilots

MFAC14

RVD3

232425262728

232425262728

232425262728

232425262728

17

18

17

1819

1819

17

1

3

27

28

17

19

17

19

Note1: It is essential that the current transformer connections are earthed at one point only.

11

MVTW

03

Figure 4 Typical application diagram:overall protection of transformer feeders

TECHNICAL DATA (MBCI RELAY)

> Current rating (in)1A, 2A or 5A

> Frequency rating

50Hz or 60Hz

> Current withstand ratings

Duration (s) DifferentialContinuous 2In

3 45In2 55In1 80In0.5 100In

> Current circuit burden

Highest phase burden (with three phase rated current)

6VA N = 63.5VA N = 3

At setting current 0.5VA

> Auxiliary supply

Rated Operative Current Drain (mA)Voltage range (V) Quiescent Operated (Vx)24/27 19.2-32.4 30 17.530/34 24-37.5 15 17548/54 37.6-72 15 175110/125 87.5-150 15 90

> Contacts

Contact arrangements2 make and 2 change-over

> Contact ratings

Make and carry for 0.2s 7500VA subject tomaxima of 30A and 300V ac or dc

Carry continuously 5A ac or dc Break ac 1250VA

dc 50W resistive25W inductiveL/R = 0.045s

Subject to maxima of 5A and 300V

Pilot

Volta

ge (V

Peak)

200

160

120

80

40

0 1 0 20 30A-N fault current (x In)

MetrosilLimiter

ZenerLimiter

%In

Through Load (xIn)

100

80

60

40

20

Earth Fault SettingKs = 2.0

N = 3 N = 6

0 0.5 1.0 1.5 2.0

%In

Through Load (xIn)

50

40

30

20

10

Earth Fault SettingKs = 1.0

N = 3 N = 6

0 0.5 1.0 1.5 2.0

60

70

A-N

C-NB-N

C-NB-N

A-N

C-N

A-N

B-N

C-NB-N

A-N

240

200

160

120

80

40

01 2 3 4 5 6 10 20 30 40 50 60 80 100

Kt = 6Kt = 14Kt = 20Kt = 40

Current (multiples of setting)

Opera

tion t

ime (M

illiseco

nds)

Figure 5 Pilot voltage characteristics

Figure 6 Minimum earth fault current for operation with through load

Figure 7 Time characteristics for internal faults

6>7

PILOTS

> Pilots isolation

Pilot isolation transformers are required when anylongitudinally induced voltage in the pilot circuit is likelyto exceed 5kV: in effect this means when protectingfeeders operating at voltages in excess of 33kV, unlessthese are short in length.

> Pilot current

The pilot current is typically 30mA for normal throughload conditions and rises to a maximum of 300mAunder through fault conditions.

> Fault settings for plain feeders

The input transformer has a summation ratio of 1.25:1:Nwhere N = 3 for normal use. N = 6 is used where lowearth fault settings are needed. The minimum operatingcurrent will therefore be dependent on the phase orphases involved in the fault. The minimum earth faultcurrent (If) should be greater than twice the leastsensitive earth fault setting to ensure rapid faultclearance.

The range setting of fault settings is shown in table 3.

Table 3

Note: A stabilising resistor is required for single phase protection or when MBCI is fed from delta connected current transformers.

> Reduction of induced pilot loop voltage

Ideally the pilot cores should be wormed (twistedtogether) so that the induced loop voltage is kept to aminimum.

UNIT PROTECTION OFTRANSFORMER FEEDERS

> Fault setting

The relay internal summation is identical to that usedfor plain feeders but the turns ratio used is 2.25:6.This will result in secondary settings as given in thetable below:

Relay setting in amps = Ks x In times the Constant in the table below

A to N 0.44B to N C to N 0.17A to B 0.44B to C 0.17C to A 0.123 Phase 0.14

Table 4

Where Ks = setting multiplier which may be adjustedbetween 0.5 and 2.0

In = relay rated current

NB. The figures quoted in this table are those to beexpected under conditions of secondary injectiontesting.

Note 1: There is a restricted earth fault relay in the neutral of the star connected CTs on the delta side of the power transformer. This provides protection against earth faults on the Delta side of the power transformer when the infeed is into the delta. It will provide settings lower than any of the phase to neutral settings given above.

Note 2: The MBCI relay, when used in the transformer feed application, does not requirea stabilising resistor.

> Cases

Relay type MBCI is provided in case 6 as shown in Figure 8.

Trusted by utilities, industry and railwaysworldwide

Fault Settings(Summation ratio = 1.25/1/N) N = 3 N = 6

Ks is a setting multiplier A - N 0.19Ks.In 0.12Ks.InAnd may be varied B - N 0.25Ks.In 0.14Ks.InFrom 0.5-2.0 C - N 0.33Ks.In 0.17Ks.InIn is the rated relay current A - B 0.8Ks.In

B - C 1.0Ks.InC - A 0.44Ks.InA - B - C 0.5Ks.In

INFORMATION REQUIRED WITH ORDER

> Basic scheme reference (refer to table 1)> Types of relay

> Pilot loop resistance and intercore capacitance values. (This information is required to determine whether pilot isolating transformers are required for matching purposes.)

> Pilot insulation level (5kV or 15kV).Is pilot supervision equipment required?

> Is the overcurrent relay required?

> Is the destabilising facility or destabilising /intertrip facility required?

> Pilot voltage:Metrosil (MBCI 01) or Zener limiting (MBCI 02)

> Current rating

> Frequency rating

> Auxiliary dc supply rating

> Auxiliary ac supervision supply rating

> AC intertrip supply rating

Push buttonprojection 10 max

All dimensions in mm

Panel cut-out:Flush mounting fixing details

4 holes 4.4

Flush mounting

149

155

21232 25 min.

11

Reset

157 max.

151

159168

103.624

177

Figure 8 Case outline size 6

48 mm

48mm

2BA connectionscrews

354 mm

310 mm

342 mm

2 holes 6.5 mm

Figure 9 Stabilising resistor

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AREVA TRACK RECORD - TRANSLAY - S SCHEMES

>> MBCI is the second generation Translay - S product.>> MBCI launched in 1983, with over 13 000 in service worldwide.>> Sister product MHOR analogue differential protection, and

MiCOM P521 numerical unit protection.

Our policy is one of continuous development. Accordingly thedesign of our products may change at any time. Whilst everyeffort is made to produce up to date literature, this brochureshould only be regarded as a guide and is intended forinformation purposes only. Its contents do not constitute an offerfor sale or advise on the application of any product referred to init. We cannot be held responsible for any reliance on anydecisions taken on its contents without specific advice.