service manual type mbch biased differential relay

Service Manual

Type MBCHBiased Differential Relay

HANDLING OF ELECTRONIC EQUIPMENT

A person's normal movements can easily generate electrostatic potentials of several thousand volts.Discharge of these voltages into semiconductor devices when handling electronic circuits can causeserious damage, which often may not be immediately apparent but the reliability of the circuit will havebeen reduced.

The electronic circuits of ALSTOM T&D Protection & Control Ltd products are immune to the relevant levelsof electrostatic discharge when housed in their cases. Do not expose them to the risk of damage bywithdrawing modules unnecessarily.

Each module incorporates the highest practicable protection for its semiconductor devices. However, if itbecomes necessary to withdraw a module, the following precautions should be taken to preserve the highreliability and long life for which the equipment has been designed and manufactured.

1. Before removing a module, ensure that you are at the same electrostatic potential as the equipmentby touching the case.

2. Handle the module by its front-plate, frame, or edges of the printed circuit board.Avoid touching the electronic components, printed circuit track or connectors.

3. Do not pass the module to any person without first ensuring that you are both at the sameelectrostatic potential. Shaking hands achieves equipotential.

4. Place the module on an antistatic surface, or on a conducting surface which is at the samepotential as yourself.

5. Store or transport the module in a conductive bag.

More information on safe working procedures for all electronic equipment can be found in BS5783 andIEC 60147-0F.

If you are making measurements on the internal electronic circuitry of an equipment in service, it ispreferable that you are earthed to the case with a conductive wrist strap.Wrist straps should have a resistance to ground between 500k – 10M ohms. If a wrist strap is notavailable, you should maintain regular contact with the case to prevent the build up of static.Instrumentation which may be used for making measurements should be earthed to the case wheneverpossible.

ALSTOM T&D Protection & Control Ltd strongly recommends that detailed investigations on the electroniccircuitry, or modification work, should be carried out in a Special Handling Area such as described inBS5783 or IEC 60147-0F.

Service ManualType MBCH

Biased Differential Relay

4

CONTENTS

SAFETY SECTION 7

1 DESCRIPTION 11

2 INSTALLATION 112.1 General 112.2 Unpacking 122.3 Storage 122.4 Site 12

3 COMMISSIONING 123.1 Commissioning preliminaries 123.2 Commissioning tests 13

4 APPLICATION NOTES 174.1 General 174.2 Matched line current transformers 174.3 Ratio and phase matching interposing transformers 184.4 Application of matching transformer 19

5 SETTINGS 23

DIAGRAMSFlowchart 1 24Flowchart 2 25Flowchart 3 26Flowchart 4 27Flowchart 5 28Flowchart 6 29Figure 1 Connections for checking relay settings 30Figure 2 Connections for checking relay operating time 30Figure 3 Connections for checking the bias curve 31Figure 4 MBCH 12/13/16 bias curve 32Figure 5 Connections to the relay to simulate magnetizing inrush current

waveform 33Figure 6 Mesh busbar arrangement requiring three bias inputs to the

differential relay 34Figure 7 Three winding transformer – one power source 35Figure 8 Switchgear arrangement where six bias inputs may be required 36Figure 9 Example of a 30 MVA transformer with current flow indicated 37Figure 10 Disposition of windings on matching transformer 38Figure 11 Two winding transformer with unmatched line current transformers 39

5

Figure 12 Three winding transformer showing interposing CTs 40Figure 13 Block diagram: biased differential protection relay Type MBCH12

with two biased inputs 41Figure 14 Block diagram: biased differential protection relay Type MBCH13

with three biased inputs 42Figure 15 Block diagram: biased differential protection relay Type MBCH16

with six biased inputs 43Figure 16 Connection for six change-over tripping contacts for three phase

tripping of up to six circuit breakers 44

6 COMMISSIONING TEST RECORD 45

REPAIR FORM 47

7

SAFETY SECTION

This Safety Section should be read before commencing any work onthe equipment.

Health and safety

The information in the Safety Section of the product documentation is intended toensure that products are properly installed and handled in order to maintain them ina safe condition. It is assumed that everyone who will be associated with theequipment will be familiar with the contents of the Safety Section.

Explanation of symbols and labels

The meaning of symbols and labels which may be used on the equipment or in theproduct documentation, is given below.

Caution: refer to product documentation Caution: risk of electric shock

Protective/safety *earth terminal

Functional *earth terminal.Note: this symbol may also be used for a protective/safety earth terminal if that terminal is part of aterminal block or sub-assembly eg. power supply.

*Note: The term earth used throughout the product documentation is the directequivalent of the North American term ground.

Installing, Commissioning and ServicingEquipment connections

Personnel undertaking installation, commissioning or servicing work on thisequipment should be aware of the correct working procedures to ensure safety.The product documentation should be consulted before installing, commissioning orservicing the equipment.

Terminals exposed during installation, commissioning and maintenance may presenta hazardous voltage unless the equipment is electrically isolated.

If there is unlocked access to the rear of the equipment, care should be taken by allpersonnel to avoid electric shock or energy hazards.

Voltage and current connections should be made using insulated crimp terminationsto ensure that terminal block insulation requirements are maintained for safety.To ensure that wires are correctly terminated, the correct crimp terminal and tool forthe wire size should be used.

8

Before energising the equipment it must be earthed using the protective earthterminal, or the appropriate termination of the supply plug in the case of plugconnected equipment. Omitting or disconnecting the equipment earth may cause asafety hazard.

The recommended minimum earth wire size is 2.5 mm2, unless otherwise stated inthe technical data section of the product documentation.

Before energising the equipment, the following should be checked:

Voltage rating and polarity;

CT circuit rating and integrity of connections;

Protective fuse rating;

Integrity of earth connection (where applicable)

Equipment operating conditions

The equipment should be operated within the specified electrical and environmentallimits.

Current transformer circuits

Do not open the secondary circuit of a live CT since the high voltage producedmay be lethal to personnel and could damage insulation.

External resistors

Where external resistors are fitted to relays, these may present a risk of electric shockor burns, if touched.

Battery replacement

Where internal batteries are fitted they should be replaced with the recommendedtype and be installed with the correct polarity, to avoid possible damage to theequipment.

Insulation and dielectric strength testing

Insulation testing may leave capacitors charged up to a hazardous voltage. At theend of each part of the test, the voltage should be gradually reduced to zero, todischarge capacitors, before the test leads are disconnected.

Insertion of modules and pcb cards

These must not be inserted into or withdrawn from equipment whilst it is energised,since this may result in damage.

Fibre optic communication

Where fibre optic communication devices are fitted, these should not be vieweddirectly. Optical power meters should be used to determine the operation or signallevel of the device.

9

Older ProductsElectrical adjustments

Equipments which require direct physical adjustments to their operating mechanism tochange current or voltage settings, should have the electrical power removed beforemaking the change, to avoid any risk of electric shock.

Mechanical adjustments

The electrical power to the relay contacts should be removed before checking anymechanical settings, to avoid any risk of electric shock.

Draw out case relays

Removal of the cover on equipment incorporating electromechanical operatingelements, may expose hazardous live parts such as relay contacts.

Insertion and withdrawal of extender cards

When using an extender card, this should not be inserted or withdrawn from theequipment whilst it is energised. This is to avoid possible shock or damage hazards.Hazardous live voltages may be accessible on the extender card.

Insertion and withdrawal of heavy current test plugs

When using a heavy current test plug, CT shorting links must be in place beforeinsertion or removal, to avoid potentially lethal voltages.

Decommissioning and Disposal

Decommissioning: The auxiliary supply circuit in the relay may include capacitorsacross the supply or to earth. To avoid electric shock or energyhazards, after completely isolating the supplies to the relay(both poles of any dc supply), the capacitors should be safelydischarged via the external terminals prior to decommissioning.

Disposal: It is recommended that incineration and disposal to watercourses is avoided. The product should be disposed of in a safemanner. Any products containing batteries should have themremoved before disposal, taking precautions to avoid shortcircuits. Particular regulations within the country of operation,may apply to the disposal of lithium batteries.

10

Technical SpecificationsProtective fuse rating

The recommended maximum rating of the external protective fuse for this equipmentis 16A, Red Spot type or equivalent, unless otherwise stated in the technical datasection of the product documentation.

Insulation class: IEC 61010-1: 1990/A2: 1995 This equipment requires aClass I protective (safety) earthEN 61010-1: 1993/A2: 1995 connection to ensure userClass I safety.

Installation IEC 61010-1: 1990/A2: 1995 Distribution level, fixedCategory Category III installation. Equipment in(Overvoltage): EN 61010-1: 1993/A2: 1995 this category is qualification

Category III tested at 5kV peak, 1.2/50µs,500Ω, 0.5J, between allsupply circuits and earth andalso between independentcircuits.

Environment: IEC 61010-1: 1990/A2: 1995 Compliance is demonstrated byPollution degree 2 reference to generic safetyEN 61010-1: 1993/A2: 1995 standards.Pollution degree 2

Product safety: 73/23/EEC Compliance with the EuropeanCommission Low VoltageDirective.

EN 61010-1: 1993/A2: 1995 Compliance is demonstratedEN 60950: 1992/A11:1997 by reference to generic safety

standards.

11

Section 1. DESCRIPTION

The MBCH is a range of high-speed biased differential relays suitable for protectionof two or three winding power transformers, auto-transformers or generatortransformer units.

The MBCH may also be regarded as an alternative to the high impedance relays forthe protection of reactors, motors and generators.

The relay is extremely stable during through faults and provides high speed operationon internal faults, even when energized via line current transformers of only moderateoutput. Immunity to false tripping due to large inrush currents on energization of thepower transformer, and during overfluxing conditions, is guaranteed without the useof harmonic filter circuits, therefore eliminating their associated delay.

A tapped interposing transformer for ratio matching of the line current transformers isavailable where required. The transformer taps are spaced at intervals of 4% andbetter, allowing matching to well within 2% in most cases.

The relay models available are as follows:

Type No of bias Publicationdesignation circuits Application ref no

MBCH12 2 Two winding power transformer R6070

MBCH13 3 Generally 3 winding powertransformer, where bias is required R6070for each of the 3 groups of CTs

MBCH16 6 For all applications requiring R60704, 5 or 6 bias circuits

Section 2. INSTALLATION

2.1 General

Protective relays, although generally of robust construction, require careful treatmentprior to installation and a wise selection of site. By observing a few simple rules thepossibility of premature failure is eliminated and a high degree of performance canbe expected.

The relays are either despatched individually or as part of a panel/rack mountedassembly in cartons specifically designed to protect them from damage.

Relays should be examined immediately they are received to ensure that nodamage has been sustained in transit. If damage due to rough handling is evident,a claim should be made to the transport company concerned immediately, andALSTOM T&D Protection & Control Ltd should be promptly notified.Relays which are supplied unmounted and not intended for immediate installationshould be returned to their protective polythene bags.

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2.2 Unpacking

Care must be taken when unpacking and installing the relays so that none of theparts are damaged or their settings altered, and relays must only be handled byskilled persons.

Relays should be examined for any wedges, clamps, or rubber bands necessary tosecure moving parts to prevent damage during transit and these should be removedafter installation and before commissioning.

Relays which have been removed from their cases should not be left in situationswhere they are exposed to dust or damp. This particularly applies to installationswhich are being carried out at the same time as constructional work.

2.3 Storage

If relays are not installed immediately upon receipt they should be stored in a placefree from dust and moisture in their original cartons and where de-humidifier bagshave been included in the packing they should be retained. The action of the de-humidifier crystals will be impaired if the bag has been exposed to ambientconditions and may be restored by gently heating the bag for about an hour, prior toreplacing it in the carton.

Dust which collects on a carton may, on subsequent unpacking, find its way into therelay; in damp conditions the carton and packing may become impregnated withmoisture and the de-humidifying agent will lose its efficiency.

The storage temperature range is –25°C to +70°C.

2.4 Site

The installation should be clean, dry and reasonably free from dust and excessivevibration. The site should preferably be well illuminated to facilitate inspection.

An outline diagram is normally supplied showing panel cut-outs and hole centres.For individually mounted relays these dimensions will also be found in PublicationR6017.

Publication R7012, Parts Catalogue and Assembly Instructions, will be useful whenindividual relays are to be assembled as a composite rack or panel mountedassembly.

Publication R6001 is a leaflet on the modular integrated drawout system of protectiverelay.

Publication R6014 is a list of recommended suppliers for the pre-insulatedconnectors.

Section 3. COMMISSIONING

3.1 Commissioning preliminaries

3.1.1 Electrostatic discharges

The relay uses components which could be affected by electrostatic discharges.When handling the withdrawn module, care should be taken to avoid contact withcomponents and connections. When removed for the case for storage, the moduleshould be placed in an electrically conducting anti-static bag.

13

3.1.2 Inspection

Remove the polycarbonate front cover by undoing the two knurled plastic nuts with asmall screwdriver. The module can now be withdrawn by the handles provided.

Carefully examine the module and case to see that no damage has occurred duringtransit. Check that the relay serial number on the module, case and cover areidentical and that the model number and rating information are correct.

3.1.3 Wiring

Check that the external wiring is correct to the relevant relay diagram and schemediagram. The relay diagram number appears inside the case. Note the shortingswitches shown on the relay diagram are fitted internally across the relevant caseterminals and close when the module is withdrawn. It is essential that such switchesare fitted across all CT circuits.

If a test block type MMLG is provided, the connections should be checked to thescheme diagram, particularly that the supply connections are to the ‘live’ side of thetest block (coloured orange) and with terminals allocated with odd numbers (1, 3, 5,7 etc). The auxiliary supply voltage to the scheme should be routed via test blockterminals 13 and 15.

3.1.4 Earthing

Ensure that the case earthing connection above the rear terminal block, is used toconnect the relay to a local earth bar.

3.1.5 Insulation

The relay and its associated wiring, may be insulation tested between:

– all electrically isolated circuits– all circuits and earth

An electronic or brushless insulation tester should be used, having a dc voltage notexceeding 1000V. Accessible terminals of the same circuit should first be strappedtogether. Deliberate circuit earthing links, removed for the tests, subsequently must bereplaced.

3.1.6 WARNING

DO NOT OPEN THE SECONDARY CIRCUIT OF A CURRENTTRANSFORMER SINCE THE HIGH VOLTAGE PRODUCEDMAY BE LETHAL AND COULD DAMAGE INSULATION.

When the type MMLG test block facilities are installed, it is important that the socketsin the type MMLB01 test plug, which correspond to the CT secondary windings, areLINKED BEFORE THE TEST PLUG IS INSERTED INTO THE TEST BLOCK. Similarly, aMMLB02 single finger test plug must be terminated with an ammeter BEFORE IT ISINSERTED to monitor CT secondary currents.

3.2 Commissioning tests

3.2.1 Test equipment

For relays with a rated current In = 1A, the variable auto-transformer and resistorlisted below can be used as an alternative to the overcurrent test set.Overcurrent test set (with timing facilities or separate timer).DC power supply (to suit relay auxiliary voltage Vx).

14

2 multimetersDouble pole switchSingle pole switchMMLB01 test plugMMLB02 single finger test plug8A variable auto-transformer2 Variable resistors 0 – 100 Ohms, suitably ratedDiode rated 7A for magnetising inrush test, if required.

Note: The following test instructions are based on injecting current directly into therelay terminals, however if a MMLG test block is incorporated in the scheme,then it is more convenient to inject current into the MMLG test block. Refer tothe relevant scheme diagram for connections.

3.2.2 DC auxiliary supply

Check the rated auxiliary voltage Vx on the front plate and connect a suitablesmoothed dc supply or station battery supply to relay terminals 13(+ve) and 14(–ve).

3.2.3 Relay settings

Connect the overcurrent test set to the relay as shown in Figure 1. Adjust the relayfront panel switches to give a relay setting Is = 0.1 x In (10% setting, In = relayrated current).

Slowly increase the current until the relay operates, indicated by a light emittingdiode (led) on the front plate. Note the operate (differential) current and check thatthis is within ±10% of the expected current (ie. 0.09 to 0.11A for a 1A relay, or0.45 to 0.55A for a 5A relay, with a 10% relay setting).

Check that the relay trip contacts (terminals 1,3 and 2,4 ) are closed with the currentabove the setting, and that these contacts open as the current is removed.

Check also that the relay alarm contacts (terminal 9,11) are closed with the currentabove the setting and remain closed as the current is removed.

Press the reset button on the relay front plate and check that the LED indicator resetsand that the alarm contacts open.

Repeat the test with the relay adjusted to settings of 0.2 x In, 0.3 x In, 0.4 x In and0.5 x In in turn. Check that the settings are within ±10% of the nominal value.

Notes: 1. The setting may also be checked using a variable auto-transformer,0 – 100 Ohm resistor and ammeter, as an alternative to using anovercurrent test set.

2. During commissioning do not disconnect the dc auxiliary supplywithout first removing the ac operating current, otherwise the tripcontacts on terminals 1,3 and 2,4 may remain operated.

If this does occur the contacts may be reset by removing the acoperating current, and then switching on the dc auxiliary supply at ratedvoltage.

3. It is prudent to switch off the dc supply before inserting or removingmodules.

If MMLG Test Blockis supplied

15

3.2.4 Operating time

Connect the test circuit as shown in Figure 2. Set the relay to Is = 0.2 x In (20%setting).

Inject 3.5 x In and record the relay operating time. For 50Hz, this should be withinthe range 24ms ±5ms (60Hz relays, within the range 20ms ±4ms). To checkoperation of the instantaneous circuit (high set), inject 4.5 x In and record the meanrelay operating time. For 50Hz relays, this should be less than 20ms (60Hz relays,less than 17ms).

Note: For relays with a rated current (In) of 1A the operating time may be checkedusing a variable auto-transformer and 0 – 100 Ohm (non inductive) resistor(suitably rated), as an alternative to using the overcurrent test set.

3.2.5 Bias check

3.2.5.1 Connect the test circuit as shown in Figure 3. Ensure that both variable resistors arenon-inductive.

With the relay set to Is = 0.2 x In (20% setting), adjust resistor R1 to about 40 Ohms(8 Ohms if In = 5A) and resistor R2 to about 100 Ohms (20 Ohms if In = 5A).Switch on the supply and increase the applied voltage until ammeter A1 indicates0.6 x In for MBCH 12, 13, 16. Slowly increase the differential current by decreasingresistor R2 until the relay operates as indicated by the front plate LED. Record thevalues of current A1 and A2.

Calculate the mean bias using the formula:A22

Use the bias curve Figure 4 for MBCH 12, 13, 16 to determine the theoreticaldifferential current and check that the measured current A2 is within ±20% of thistheoretical value. Note that for a 5 amp relay (In = 5A) the values of the calculatedmean bias have to be divided by 5 before applying the bias curve and thetheoretical differential current multiplied by 5 before comparing with the measuredcurrent A2.

3.2.5.2 MBCH 13 only

Repeat the above test with the third bias coil (terminal 21).

3.2.5.3 MBCH 16 only

Repeat the above test with the third to sixth bias coils (terminals 21, 19, 17 and 15respectively).

3.2.5.4 Reconnect the 2nd bias coil as shown in Figure 3 and adjust the current shown onammeter A1 to be 1.7 x In for MBCH 12, 13, 16. (Note that for a 5A relay thiscurrent may exceed the continuous rating of the variable auto transformer and shouldtherefore be switched on for short durations only).

Increase the differential current until the relay operates and check that this value iswithin ±20% of the theoretical value by calculating the mean bias as described in3.2.5.1 above.

3.2.5.5 Repeat tests 3.2.2, 3.2.3, 3.2.4, and 3.2.5 for the two relays associated with theother phases.

Mean bias = A1 + amps

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3.2.6 Bias interconnection

Check that the terminals no 12 on all three phase relays are interconnected usingscreened leads, the screen connection being made to the dc negative supply(terminal no 14).

A suitable screened lead should be provided with each relay. Only two will berequired for the interconnection.

3.2.7 Circuit breaker tripping

By interconnecting terminal no 10 of all three phase relays, up to six self-resettingchangeover contacts can be provided for the three phase tripping of up to six circuitbreakers.

If this is required, check terminals no 10 are connected together, and check that therelay trip contacts (terminals 1,3 and 2,4) on all three phase relays close as thecurrent injected into a single phase relay (as shown in Figure 1) exceeds the relaysetting.

3.2.8 On load tests

The object of the on-load tests is to check that the relay is connected correctly to thesystem.

If the relay is protecting a transformer with no tap changer then the differentialcurrent could be less than 1% of the load current. However, if the transformer has atap changer and the CTs are not matched to the transformer, then the normaldifferential current ,with the tap changer away from the nominal position, could be asmuch as 20% of the load current.

Check that the load current in each bias coil is close to the value which is expectedfor the particular application. For the MBCH 16 relay particularly, it may bepreferable to energize the transformer in different ways to ensure that all connectionsare satisfactory. Check that the differential current under any of these conditions iswithin 1–20% of the load current. The actual figure of differential current dependsupon the particular application as stated above.

Since the magnetizing current may exceed 5% of rated current for small transformers,and bearing in mind the comments of the above paragraph, it is recommended thatthe standard setting of the relay should be Is = 0.2 x In.

Check that the currents measured in the same bias or differential coils of each phaserelay are similar.

3.2.9 Magnetizing inrush test

The relay may be tested with a simulated waveform representing magnetizing inrush,by connecting a diode in series with the relay to produce a half wave rectifiedwaveform.

With reference to Figure 5, close switches S1 and S2 and set the current to 1 x In(rated current). Check that the relay operates.

Open switch S2, close switch S1 and check that the relay does not operate.

If it is preferred to test the relay with the magnetizing inrush current of thetransformer, it is suggested that the transformer is energized ten times at full ratedvoltage on no load and checked that the relay does not maloperate.

17

Section 4 APPLICATION NOTES

4.1 General

The type MBCH relay is a high speed biased differential relay suitable for theprotection of two or three winding power transformers, autotransformers, orgenerator transformer units.

Three versions of the relay are available as follows:

Designation Number of bias inputs Application

MBCH 12 2 Two winding transformers or threewinding transformers wheresignificant fault infeed can passthrough the transformer from onewinding only. See Figure 7.

MBCH 13 3 Generally three-winding transformerswhere bias is required from each ofthe three groups of CTs or;

Where a two-winding transformer hasone or other of the windingscontrolled by two circuit breakers asin mesh or one-and-a-half breakerarrangements. See Figure 6.

MBCH 16 6 For applications requiring 4, 5, or6 bias circuits. See Figure 8.

4.2 Matched line current transformers

For optimum performance, the differential scheme should be arranged so that therelay will see rated current when the full load current flows in the protected circuit.Where line current transformers are matched, but secondary current with full loadcurrent flowing is less than the relay rated current (as illustrated in Figure 9), theeffective sensitivity of the relay will be reduced.

The transformer current is 262.4A at 66kV, giving a secondary current of 4.37Afrom the 300/5A current transformer. For a 20% relay setting, the relay will operatewhen the differential exceeds 0.2 x 5 = 1A.

14.37

Thus the effective setting is 22.9% for a relay setting of 20%.

1A = x 100% = 22.9% of transformer full load current.

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4.3 Ratio and phase matching interposing transformers

Matching transformers are available for use in cases where the current transformerson one side of the protected transformer do not match, in current ratio or phaseangle, with the current transformers on the other side of the protected transformer.The following versions of matching transformer are available:

Description Reference NoSingle phase transformer 1/1A GJ0104 010Single phase transformer 5/5A GJ0104 020Single phase transformer 5/1 GJ0104 030Three phase transformer 1/1A GJ0104 050Three phase transformer 5/5A GJ0104 060Three phase transformer 5/1A GJ0104 070

4.3.1 Details of matching transformers

The winding details of the three current ratings of the matching transformers are givenin the table below and in Figure 10.

Number of turnsTransformer rating

Primarytap terminals 1/1A 5/1A 5/5A

1 – 2 5 1 12 – 3 5 1 13 – 4 5 1 14 – 5 5 1 15 – 6 125 25 25X 7 25 5 57 – 8 25 5 58 – 9 25 5 5

S1 – S2 125 125 25S3 – S4 90 90 18

Table 1.

Notes on combinations of windings.

For star-output windings:

It is permissible to use either S1-S2 or S1-S4 (with S2-S3 linked). Where S1-S2 aloneis used, the secondary winding S3-S4 is available for formation of an isolated deltaconnection to prevent zero sequence currents due to external earth faults being seenby the relay. This is for applications where phase correction is not required, butwhere a zero sequence trap is needed.

For delta output windings:

S1-S4 (with S1-S3 linked) must be used to obtain optimum protection performance.

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4.4 Application of matching transformer

Where the line current transformer ratios on the two sides of the protectedtransformer are mutually incompatible, the matching transformer may be used as inthe following examples:

4.4.1 Single phase transformer

Matching transformer ratio required = 3.9/4.875. Using secondary windings S1-S2gives 25 turns. The number of turns required on the input (primary) winding is givenby:

31 turns are available between input winding terminals 4—7 with terminals 6—Xlinked.

4.4.2 Three phase transformer with unmatched current transformers

See Figure 11.

30MVA transformer 11/66kV Delta star

11kV winding:

30 x 106

√3 x 11 x 103

Because the 11kV winding is delta connected, the associated current transformerswill be star connected and under rated load conditions will give the following currentper pilot phase:

1574.6 x 1A1600

This current is sufficiently close to the relay rated current (1A) and furthermorerequires no phase correction.

66kV winding:

30 x 106

√3 x 66 x 103

Normally the current transformers associated with the star winding of the maintransformer should be connected in delta to provide appropriate phase shiftcorrection. However, since the latter in this case are connected in star the necessaryphase correction may be carried out by means of a star delta connected matchingtransformer.

Tp = x Ts = 25 x = 31.25 = 31 turns4.875A3.9A

Normal current at 11kV = = 1574.6A

Is = = 0.984A

Normal current at 66kV = = 262.43A

200/5 A 1000/5 A195 A 780 A

4.875 A 3.9 AS1 4

S2 7

IsIp

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The output current, per phase pilot, of the 300/1A current transformers is given by:

262.43 x 1300

This should be adjusted by the interposing transformer so that 0.984A flows into therelay.

The windings S1–S2, and S3–S4 must be used in series as output windings giving(125 + 90) = 215 turns.

Primary turns (Tp) required, therefore are given by:

Is/√3Ip

0.984 x 215√3 x 0.875

say Tp = 140 turns

ie. connect each phase pilot from the 300/1A current transformers to primaryterminal nos. 2 and 6 (see Figure 11 and Table 1). Complete connections to theinterposing transformer as given below:

4.4.3 Three winding transformer

An example of the three winding transformer is shown in Figure 13. The voltage andpower rating of each winding is indicated. The current transformer ratios are chosenas a function of the winding voltage and power rating of the particular windings withwhich they are associated.

For transformer differential protection matching of current transformers is correctwhen the CT ratios are determined on a basis of associated winding voltage only.

500kV Winding:

Based on 400 MVA the rated current is given:

400 x 106

√3 x 500 x 103

Secondary current from 500/5 current transformers:

462 x 5500

The 500/5 star connected CTs are associated with the 500kV star winding, and thusthe transition to delta connected secondaries must be made by means of an

In = = 462A

Is = = 4.62A

Is = = 0.875A

∴ Primary turns (Tp) = = 139.6

Tp = x Ts

A

B

C

ToRelay

To 66kVlinecurrenttransformer

P1

P1

P1

A

B

CN

S1

S1

S1S2

S2

S2

S3

S3

S3

S4

S4

S4

P2

P2

P2

6

6

6

2

2

2

21

interposing CT. Output windings S1–S2 and S3–S4 must be connected in series togive 43 turns, thus:

Is/√3Ip

5 x 43√3 x 4.62

Table 1 indicates that primary taps nos. 3–6 will give 27 turns.

Primary turns (Tp) = = 26.86 say 27 turns.

Tp = x Ts

138kV winding:

Based on 400MVA the corresponding current would be:

400 x 106

√3 x 138 x 103

Secondary current from 138kV current transformers:

1674 x 51200

The 1200/5 star connected line CTs are associated with the 138kV star winding andthus the necessary transition to delta connection must be made by means of aninterposing CT.

The output windings S1–S2 and S3–S4 of the interposing transformer must beconnected in series to give a total of 43 turns (see Table 1).

The number of primary turns (Tp) should be

Tp = x Ts = = 17.73 say 18T

Table 1 indicates that primary tap nos. 2—9 should be used, with link 6—X removedand terminal 5 connected to terminal X.

In = = 1674A

Is = = 6.975A say 7A

Is/√3Ip

A

B

C

ToRelay


P1

P1

P1

A

B

CN

S1

S1

S1S2

S2

S2

S3

S3

S3

S4

S4

S4

P2

P2

P2

6

6

6

3

3

3

5 x 43√3 x 7

22

13.45kV winding:

Based on 400 MVA the corresponding current would be:

400 x 106

√3 x 13.45 x 103

NB In this case the transformer winding (13.45kV) is delta connected, and theassociated line current transformers are star connected. There is thus nophase angle compensation required, the associated interposing CT may bestar connected and taps selected to reduce the 17.17A output to 5A.

Using S1–S2, and S3–S4 in series as output winding, the primary tap becomes:

Primary turns (Tp) = x Ts Tp = = 12.52 say 13T

Table 1 indicates that primary taps nos. 2–8 will give 13 turns, with link X–5 insteadof X–6.

In = = 17170.2A Is = = 17.17A17170.2 x 5

5000

IsIp

S3

A

B

C


P1

P1

P1

A

B

CN

S1

S1

S1S2

S2

S2

S3

S3

S4

S4

S4

P2

P2

P2

9 5x 2

9 5x 2

9 x 25

A

B

C

ToRelay

To 13.45kVlinecurrenttransformer

P1

P1

P1

A

B

CN

S1

S1

S1S2

S2

S2

S3

S3

S3

S4

S4

S4

P2

P2

P2

N

8 5x 2

8 5x 2

8 5x 2

43 x 517.17

23

Section 5 SETTINGS

When protecting a power transformer, the differential setting should not be less than20% of the relay rated current, to give stability for moderate transient overfluxing.

The maximum spill current with through load current should generally be kept below20% of relay rated current, allowing for CT mismatch and possible tap changeroperation. This may be achieved either by appropriate choice of main line currenttransformers, or by the use of interposing transformers, as descibed in Section 4.Where higher levels of spill current exist, the relay setting may need to be increased.

24

Flowchart 1

Check that auxiliarydc supply voltage and

polarity are correct

Isolate auxiliary dc voltage.Remove module from case.Make external connectionsto module terminal block

Conclusion:Auxiliary dc circuit appears

to be working correctly.

Conclusion:Faulty pcb1

Apply correct auxiliary dc voltage.

Check internal dc rails

Conclusion:Internal wiring faulty

and/or pcb 1, 2 or 3 faulty.

Isrelay

operation onmagnetisinginrush current

incorrect.

Correct?

Check auxiliary dc current drain

Correct?

Correct?

Follow Flowchart 6

Follow Flowchart 2

Apply correctdc voltage

Suspected faulty module

NO

NO

NO

YES

NO

YES

YES

YES

YES

YES

YES

YES

YES

YES

25

Flowchart 2

Isthe relay

an MBCH 12version

?

Set Is = 0.5 Inon relay frontplate.

Monitor TP4

Inject In intoterminals 27 and

28.

Monitor tripping contacts Conclusion:faulty pcb 1, pcb 2 ortransformers T1 or T2

Conclusion:faulty pcb1

Conclusion:faulty pcb1

FollowFlowchart 4

Follow Flowchart 3

Monitor R2.Inject In into

terminals 27 and 28.

R2voltagecorrect

?

Dotrippingcontacts

close?

TP4voltagecorrect

?

YES

YES

YES

YES

YES

YES

NO

YES

YES

NO

NO

NO

26

Flowchart 3

Link terminals 26 and 27.Inject In into terminals 25

and 28. Monitor TP4.

Monitor R1.Inject In into terminals 25

and 28.

Conclusion:Faulty transformer T3.


Conclusion:Faulty pcb1, pcb2 or transformer T3.

Link terminals 24 and 27.Inject In into terminals 23

and 28.

Conclusion:relay appears to befunctioning correctly.

R1voltagecorrect

?

TP4voltagecorrect

?

TP4voltagecorrect

?

YES

YES

YES

YES

YES

YES

NO

NO

NO

27

Flowchart 4

Link terminals22 and 27.

Inject In into terminals 21 and 28

Link terminals 26 and 27.Inject In into terminals

25 and 28.Monitor TP4 (Note 3)

Monitor R1 (Note 6) Inject In into terminals

25 and 28.




Conclusion:Faulty pcb1, pcb2 or transformer T4

Conclusion:Relay appears to be functioning correctly

Conclusion:Faulty pcb1, pcb2 or

transformer T3

NO

YES

NO

NO

NO

YES

YES

YES

TP4voltagecorrect ?(note 3)


TP4voltagecorrect

?

R1voltagecorrect

?


23 and 28.


YES

R1voltagecorrect

?


21 and 28.


Conclusion:Faulty pcb1, pcb2 or

transformer T5

NO

YES

R1voltagecorrect

?

Isthe relayan MBCH

06version

?

Follow Flowchart 5

YES

NO

NO

YES

YES

YES

YES

YES

YES

28

Flowchart 5

Link terminals16 and 27.Inject In into

terminals 15 and 28


Inject In into terminals 19 and 28.

Monitor R1 Inject In into

terminals 19 and 28




Monitor R1 inject In into terminals 17

and 28


Monitor R1 inject In into terminals 1

and 28

Conclusion:Faulty pcb1, pcb2 or transformer T7

Conclusion:Relay appears to be functioning

correctly

Conclusion:Faulty pcb1,

pcb2 ortransformer T6

NO

YES

NO

NO

NO

NO

NO

YES

YES

YES

YES


YES

Conclusion:Faulty pcb1,

pcb2 or transformer T8

R1voltagecorrect ?(note 6)






YES

YES

YES

YES

YES

29

Flowchart 6

Conclusion:Faulty pcb1, pcb2, ortransformers T1 or T2

Relay trips when magnetizing inrush

current flows into the power transformer

Monitor R2 (note 4).Inject In into terminals

27 and 28

Monitor TP2 (note 7).Inject 0.5In into

terminals 27 and 28

Conclusion:Faulty pcb1 pcb2 or

transformer T1


YES

YES

YES

YES

YES

NO

NO

TP2Voltagecorrect

?

R2Voltagecorrect

?

30

MBCHRELAY

bias

differentialOvercurrenttest set

25

27

26

28

MBCHRELAY

bias

differential

25

27

26

28

Overcurrenttest set

starttimer

stoptimer

1

3

2

4

Figure 2 Connections for checking relay operating time

Figure 1 Connections for checking relay settings

31

Figure 3 Connections for checking the bias curve

A1

A2

acsupply

1st bias 2nd bias

3rd bias

4th bias

5th bias

6th bias

1516

1718

1920

2122

232425 26

27

28

VariableAuto transformer

Differentialcoil

0–100Ω

MBCH 16ONLY

MBCH 13, 16ONLY

0–100Ω

32

0.5

1.0

1.5

2.0

2.5

3.0

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.00.0

Is = 0.5 In0.4 In0.3 In0.2 In0.1 In

Mean bias current (Amps x In)

Diff

eren

tial c

urre

nt (A

mps

x I

n)

Figure 4 MBCH 12/13/16 bias curve

33

Figure 5 Connections to the relay to simulate magnetizing inrush current waveform

MBCHRELAY

bias

differential

25

27

26

28A

acsupply

variableauto transformer

0–100Ω

S2

S1

34

Figure 6 Mesh busbar arrangement requiring three bias inputs to the differential relay

87

Bias inputs

Relay TypeMBCH13

OperatingCircuit

35

Figure 7 Three winding transformer – one power source

87

Bias winding

Operating Circuit

Relay typeMBCH 12

Sole infeed

Loads

36

Figure 8 Switchgear arrangement where six bias inputs may be required

87

Bias Windings Relay TypeMBCH 16

Operatingcircuit

37

2523

2325

27

2426

28

2325

27

27

2426

28

300/

5 A

262.

4 A

66kV

/11k

V30

MVA

1574

.6 A

1800

/2.8

9 A

4.37

4 A

N.E

.R.

4.37

4 A

Rela

y Ty

peM

BCH

12

Bias

Win

ding

s

Ope

ratin

gci

rcui

t

2426

28

Figu

re 9

Exa

mpl

e of

a 3

0 M

VA tr

ansf

orm

er w

ith c

urre

nt fl

ow in

dica

ted

38

12

34

56

X7

89

S1S2

S3S4

P1P2

Out

put t

o Re

lay

Not

e:

Win

ding

Sep

arat

ion

on te

rmin

al n

os. 6

not a

vaila

ble

on e

arlie

r mod

els.

Prim

ary

win

ding

ene

rgiz

ed fr

om li

ve c

ts vi

a te

rmin

als

P1 a

nd P

2

Figu

re 1

0

Dis

posi

tion

of w

indi

ngs

on m

atch

ing

trans

form

er

39

Figu

re 1

1

Two

win

ding

tran

sfor

mer

with

unm

atch

ed li

ne c

urre

nt tr

ansf

orm

ers

15

74

.6 A

16

00

/1A

11

kV6

6kV

30

0/1

A

30

MV

A

/

0.8

75

0.8

75

A0

.98

4 A

Ratio

26

2.4

3 A

Diff

eren

tial R

elay

MBC

H1

2

0.9

84

S1S4

0.8

87

tap,

ie

. P1

P2

2 6(li

nk S

2 –

S3

)

40

21

22

23

24

25

27

28

26

21

22

23

24

25 27

2826

21

22

23

24

25 27

28

26

MBC

H13

5000

/5 A

1200

/5 A

500/

5 A

500

kV13

.45

kV13

8 kV

400

MVA

/100

MVA

/300

MVA

MBC

H13

MBC

H13

Figu

re 1

2

Thr

ee w

indi

ng tr

ansf

orm

er s

how

ing

inte

rpos

ing

CTs

41

Figu

re 1

3

Bloc

k di

agra

m: b

iase

d di

ffere

ntia

l pro

tect

ion

rela

y Ty

pe M

BCH

12 w

ith tw

o bi

ased

inpu

ts

23 24 25 26

T3

RL1 2

Out

put

circ

uits

RL2 1

1 3 5

RL1–

1

2 4 6

RL1–

2

10 13 14 12 9 11RL

2–1

12

34

56

78

910

1112

1314

1516

1718

1920

2122

2324

2526

2728

Mod

ule

term

inal

bloc

k vi

ewed

from

rear

Cas

e ea

rth

Inpu

t circ

uits

Rese

t

Bias

(see

Not

e 2)

Trip

othe

rph

ases

V xTrip

outp

ut

Ala

rm

See

follo

win

g sh

eets

2 1

2.Te

rmin

al 1

2 on

eac

h ph

ase

asse

mbl

y sh

ould

be in

terc

onne

cted

by

a sc

reen

ed le

ad G

J015

3 00

1w

ith th

e sc

reen

con

nect

ed to

term

inal

14.

Not

es:

1.(a

)C

T sh

ortin

g lin

ks m

ake

befo

re (b

) and

(c) d

isco

nnec

t.

(b)

Shor

t ter

min

als

brea

k be

fore

(c).

(c)

Long

term

inal

s.

27 28

T1T2

Inpu

t circ

uits

See

follo

win

g sh

eets

DIF

F

42

Figu

re 1

4

Bloc

k di

agra

m: b

iase

d di

ffere

ntia

l pro

tect

ion

rela

y Ty

pe M

BCH

13 w

ith th

ree

bias

ed in

puts

21 22

T5

23 24

T4

25 26

T3

RL1 2

Out

put

circ

uits

RL2 1

1 3 5

RL1–

1

2 4 6

RL1–

2

10 13 14 12 9 11RL

2–1

12

34

56

78

910

1112

1314

1516

1718

1920

2122

2324

2526

2728

Mod

ule

term

inal

bloc

k vi

ewed

from

rear

Cas

e ea

rth

Inpu

t circ

uits

Rese

t

Bias

(see

Not

e 2)

Trip

othe

rph

ases

V xTrip

outp

ut

Ala

rm

See

follo

win

g sh

eets

3 2 1

2.Te

rmin

al 1

2 on

eac

h ph

ase

asse

mbl

y sh

ould

be in

terc

onne

cted

by

a sc

reen

ed le

ad G

J015

3 00

1w

ith th

e sc

reen

con

nect

ed to

term

inal

14.

Not

es:

1.(a

)C

T sh

ortin

g lin

ks m

ake

befo

re (b

) and

(c) d

isco

nnec

t.

(b)

Shor

t ter

min

als

brea

k be

fore

(c).

(c)

Long

term

inal

s.

27 28

T1T2

Inpu

t circ

uits

See

follo

win

g sh

eets

DIF

F

43

Figu

re 1

5

Bloc

k di

agra

m: b

iase

d di

ffere

ntia

l pro

tect

ion

rela

y Ty

pe M

BCH

16 w

ith s

ix b

iase

d in

puts

15 16

T8

17 18

T7

19 20

T6

21 22

T5

23 24

T4

25 26

T3

27 28

T1T2

RL1 2

Out

put

circ

uits

RL2 1

1 3 5

RL1–

1

2 4 6

RL1–

2

10 13 14 12 9 11RL

2–1

12

34

56

78

910

1112

1314

1516

1718

1920

2122

2324

2526

2728

Mod

ule

term

inal

bloc

k vi

ewed

from

rear

Cas

e ea

rth

Inpu

t circ

uits

Inpu

t circ

uits

Rese

t

Trip

othe

rph

ases

V xTrip

outp

ut

Ala

rm

See

follo

win

g sh

eets

6 5 4 3 2 1

See

follo

win

g sh

eets

DIF

F

2.Te

rmin

al 1

2 on

eac

h ph

ase

asse

mbl

y sh

ould

be in

terc

onne

cted

by

a sc

reen

ed le

ad G

J015

3 00

1w

ith th

e sc

reen

con

nect

ed to

term

inal

14.

Not

es:

1.(a

)C

T sh

ortin

g lin

ks m

ake

befo

re (b

) and

(c) d

isco

nnec

t.

(b)

Shor

t ter

min

als

brea

k be

fore

(c).

(c)

Long

term

inal

s.

Bias

(see

Not

e 2)

44

Figure 16 Connection for six change-over tripping contacts for three phasetripping of up to six circuit breakers

Phase ‘A’

All output contacts shownare instantaneouslyinitiated for any internalfault condition whenterminals No. 10 on eachphase unit are connectedtogether as shown.

Correct phase indicationis maintained.

1

3

5

2

4

6

Phase ‘B’

1

3

5

2

4

6

Phase ‘C’

1

3

5

2

4

6

10

14

13

10

14

13

10

14

13

Vx

45

Section 6 COMMISSIONING TEST RECORD

PROTECTION RELAY TYPE MBCH Date _________________________________

Station _______________________________ Transformer ___________________________

Biased Differential Transformer Serial No. _____________________________________________

Relay Model No _______________________

Relay Serial Nos. Phase A__________________ Phase B ___________ Phase C ___________

DC Auxiliary Voltage Vx ___________________ Relay Rated Current In

3.2.2 Measure dc auxiliary voltage Vx __________V

3.2.3 Relay settings IsPhase A Phase B Phase C

0.1 x In __________ __________ __________ A

0.2 x In __________ __________ __________ A

0.3 x In __________ __________ __________ A

0.4 x In __________ __________ __________ A

0.5 x In __________ __________ __________ A

Check trip contacts operate __________ __________ __________ A

Check alarm contact operates __________ __________ __________ A

3.2.4 Operating Time

3.5 x In __________ __________ __________ ms

4.5 x In __________ __________ __________ ms

3.2.5 Bias check (setting 0.2 x In)

3.2.5.1 Current A1 0.6 x In

Measured differential current __________ __________ __________ A2

3.2.5.4 Current A1 1.7 x In

Measured differential current __________ __________ __________ A2

46

3.2.6 Check bias interconnection _____________________________________________

3.2.7 If required check 3 phase tripping_______________________________________

3.2.8 On load tests

Load conditions

Measured differential current __________ __________ __________ A

3.2.9 Magnetizing current inrush test _________________________________________

_________________________________ __________________________________Commissioning Engineer Customer Witness

_________________________________ __________________________________Date Date

47

REPAIR FORM

Please complete this form and return it to ALSTOM T&D Protection & Control Ltd with theequipment to be repaired. This form may also be used in the case of application queries.

ALSTOM T&D Protection & Control LtdSt. Leonards WorksStaffordST17 4LX,England

For: After Sales Service Department

Customer Ref: ______________________ Model No: ________________________

ALSTOM Contract Ref: ______________________ Serial No: ________________________

Date: ______________________

1. What parameters were in use at the time the fault occurred?

AC volts _____________ Main VT/Test set

DC volts _____________ Battery/Power supply

AC current _____________ Main CT/Test set

Frequency _____________

2. Which type of test was being used? ____________________________________________

3. Were all the external components fitted where required? Yes/No(Delete as appropriate.)

4. List the relay settings being used

____________________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________

5. What did you expect to happen?

____________________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________

continued overleaf

48

______________________________________ _______________________________________Signature Title

______________________________________ _______________________________________Name (in capitals) Company name

6. What did happen?

____________________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________

7. When did the fault occur?

Instant Yes/No Intermittent Yes/No

Time delayed Yes/No (Delete as appropriate).

By how long? ___________

8. What indications if any did the relay show?

____________________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________

9. Was there any visual damage?

____________________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________

10. Any other remarks which may be useful:

____________________________________________________________________________

____________________________________________________________________________

____________________________________________________________________________

A L S T O M T & D P r o t e c t i o n & C o n t r o l L t d St Leonards Works, Stafford, ST17 4LX EnglandTel: 44 (0) 1785 223251 Fax: 44 (0) 1785 212232 Email: [email protected] Internet: www.alstom.com

©1999 ALSTOM T&D Protection & Control Ltd

Our policy is one of continuous product development and the right is reserved to supply equipment which may vary from that described.

Publication R8017G Printed in England.

service manual type mbch biased differential relay

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