Service Manual Type MBCH Biased Differential Relay
Transcript of 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
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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
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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
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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.
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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.
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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.
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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.
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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.
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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).
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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
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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.
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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
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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
To 500kVlinecurrenttransformer
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
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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
To 138kVlinecurrenttransformer
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
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.
Link terminals24 and 27.
Inject In into terminals 23 and 28
Conclusion:Faulty pcb1
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 ?(note 3)
TP4voltagecorrect
?
R1voltagecorrect
?
Monitor R1 (Note 6) Inject In into terminals
23 and 28.
Conclusion:Faulty pcb1
YES
R1voltagecorrect
?
Monitor R1 (Note 6) Inject In into terminals
21 and 28.
Conclusion:Faulty pcb1
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
Link terminals2 and 27.
Inject In into terminals 19 and 28.
Monitor R1 Inject In into
terminals 19 and 28
Link terminals18 and 27.
Inject In into terminals 17 and 28
Conclusion:Faulty pcb1
Monitor R1 inject In into terminals 17
and 28
Conclusion:Faulty pcb1
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
Conclusion:Faulty pcb1
YES
Conclusion:Faulty pcb1,
pcb2 or transformer T8
R1voltagecorrect ?(note 6)
TP4voltagecorrect ?(note 3)
R1voltagecorrect ?(note 6)
TP4voltagecorrect ?(note 3)
TP4voltagecorrect ?(note 3)
R1voltagecorrect ?(note 3)
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
Conclusion:Faulty pcb1
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:
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
49
50
51
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.