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01Prot ctio R a

MiCOM P642, P643 a d P645Ad a c d Tra orm r Prot ctio a d Co tro

Transformers are high capital cost assets in electrical power systems. Elimination of all electrical and mechanical stresses,although desirable to preserve transformer life, is impractical.Adaptive techniques to measure and alarm (or trip) in suchinstances, and advise on cumulative service duty, can helpto schedule preventive maintenance before a costly failureoccurs.

Internal faults are a risk for all transformers, with short-circuitsdissipating the highest localized energy. Unless clearedquickly, the possibility to rewind windings reduces, and coredamage may become irreparable.

The MiCOM P642, P643 and P645 address all these issues- preserving service life, and offering fast protection for transformer faults. Hosted on an advanced IED platform, theP64x incorporates differential, REF, thermal, and overfluxingprotection, plus backup protection for uncleared externalfaults. Model variants cover two and three windingtransformers (including autotransformers), with up to 5 setsof three-phase CT inputs. Large CT counts are common inring bus/mesh corner applications, where the P64x summatescurrents to create each total winding current, easingapplication of backup protection. Backup overcurrent can bedirectionalized, where the user includes the optional 3-phaseVT input in their chosen model.

Key feATuRes

High-speed transformer differential protection

Simple setting wizard requires only nameplate data

Restricted earth fault (REF) boosts trip sensitivity

Voltage, frequency, thermal and over uxing elements

CT, VT, trip circuit and self-supervision:

Patented CT supervision ensures no spurious trip for CT or wiring failures

Integrated backup overcurrent per winding

Readily interfaces to multiple automation protocols, includingIEC 61850

Figure 1: Front view of P645

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02Prot ctio R a MiCOM P64x

APPlICATIOn

The MiCOM P642 is intended for two-windingtransformer applications, with one set of threephase CTs per winding. The P643 covers up to 3bias inputs (three CT sets) - either a three windingapplication, or two-winding with dual CTs on oneside. Where 4 or 5 feeding connections to theprotected transformer exist, the P645 offers vebias input sets. All models have a single-phaseVT input, mainly for over uxing application, andthe P643 and P645 allow an additional 3-phaseVT input to be connected. This allows overcurrentbackup to be directionalised, and expands themeasurement and recording analog channels

available.

As well as transformer protection, the P64x rangemay be applied to other unit applications, such asreactor and motor.

The MiCOM P64x series is supplied with a fullsuite of protection and control functions asstandard. The con guration column of the menu isused to control which functions the user requiresin the intended application, and which may bedisabled. Disabled functions are completelyremoved from the menu, to simplify setting.Differential elements have an inbuilt con gurationwizard, to avoid settings errors.

AnsI IeC61850 f at r P642 P643 P645Number of bias inputs (3-phase CT sets) 2 3 5Number of residual/star-point CTs 2 3 3Single phase VT input 1 1 1

Additional 3-phase VT ( ) ()87T LzdPDIF Transformer differential protection 64 RefPDIF Restricted earth fault protection (windings) 2 3 349 ThmPTTR Thermal overload 24 PVPH V/Hz over uxing 1 1 (2) 1 (2)LoL Loss of life Thru Through fault monitoring RTD RtfPTTR RTDs x 10 PT100 temperature probes () () ()CLIO PTUC Current loop transducer I/O (4 input / 4 output) ( ) () ()50/51 OcpPTOC Overcurrent protection per winding 50N/51N Ef_PTOC Derived or measured standby earth fault per winding 46 NgcPTOC Negative phase sequence o/c per winding

67/67N RDIR Directionalized o/c, SBEF, and NPS elements(with optional 3VT addition) () ()

50BF RBRF Breaker fail protection (number of breakers) 2 3 5

27/59/59N PTUV/PTOV Undervoltage, overvoltage and residual VN>(with optional 3VT addition) () ()

81U/81O PTUF/PTOF Under/overfrequency (with optional 3VT addition) () ()

VTS VT Supervision ( ) ()CTS Differential CTS (patented) TCS Trip circuit supervision IRIG-B IRIG-B time synchronizing input ( ) () ()

OptGGIO Optocoupled logic inputs 812 1624 1624RlyGGIO Relay output contacts 812 1624 1624FnkGGIO Function keys 10 10LedGGIO Programmable LEDs (R-red, G-green, Y-yellow) 8R 18R/G/Y 18R/G/Y

PSL Graphical programmable scheme logic Alternative setting groups 4 4 4

SOE Sequence of event records Fault waveform disturbance records

(Key: brackets ( ) denote optional features)

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funCTIOnAl OveRvIew

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Transformer DifferentialProtection P64x

1. The three-phase VT input is optional.2. The 27, 59, 59N and VTS functions require the three-phase VT input.

3. The frequency required by the 81 function is obtained from any analog signal , but the voltage signals have priority over the current signals.

Figure 2: System Overview of the P64x series example 3 winding, 4 bias application

Fast, Sensitive protection for your valuable asset

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Figure 3: Biased differential protection (87T)

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Figure 5: Restricted earth fault application

MAIn PROTeCTIOn

87T Transformer differentialThe algorithm has a triple slope percentagebias restraint, as shown in Figure 3. An internalfault will generate differential current. The biascurrent is that which merely ows through theprotected unit, as a load or through-fed externalfault. The initial characteristic is at, for easeof commissioning, rising then to bias slope(k1). K1 is a low slope for sensitivity to faultswhilst allowing for mismatch when the power transformer is at the limits of its tapchanger range,in addition to any current transformer ratio errors

At currents above rated, extra errors may begradually introduced as a result of CT saturation,hence the bias slope is increased to k2. The P64xincorporates transient bias and this combined withthe k2 bias ensures that CT knee point voltagerequirements are minimized.

The differential protection setting con gurationutility requires only known data that which

resides on the transformer rating plate, the CTrating plate, and information on any in-zoneearthing transformer.

REF: Restricted earth (Ground) fault

Restricted earth fault protection is included tocover a larger percentage of the transformer windings than might be possible with the maindifferential elements. A separate element per winding is provided (P642: HV and LV. P643/P645: HV, LV, and if required, the TV tertiary too).

Figure 5 shows a typical restricted earth fault

application. Biased REF is used, to avoid theneed for any stabilizing resistor or varistor Metrosil. REF elements operate independently of inrush detection, potentially offering faster trippingfor low or moderate fault currents, in addition toenhanced sensitivity.

Energization of a transformer causes magnetisinginrush current to ow in one winding only, andthe differential elements may need stabilizingwhilst the inrush persists. A proven secondharmonic current ratio scheme is used. Thedifferential protection may also be restrainedwhen the transformer is over uxed so that aninstantaneous trip is not issued for transientover uxing. Over uxing restraint is conditioned bythe percentage of fth harmonic current present.

A high set instantaneous differential element,not subject to harmonic restraint, is provided toensure rapid clearance of high current faults.

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Thermal overload

All models offer thermal overload protection,with the extent of protection being the choiceof the customer. The most simple applicationemploys It characteristic. Time constants areset, such that the thermal model can follow thecorrect exponential heating and cooling pro le,replicating the winding hotspot temperature.

Alarm and trip thresholds are available asoutputs.

To enhance the thermal replica, ambient and/or top-oil temperature compensation may beapplied. This is achieved by tting the RTDboard option, and positioning the PT100 probesappropriately (outdoors, or within the transformer tank). Additionally, alarm and trip setpoints can beapplied for any probe input, should an absolutemeasured temperature at the probe locationbe of interest. Ten independent probe inputsare available, making radiator pump and fancontrol an additional possibility using the relaysprogrammable scheme logic (PSL).

Thermal overload protection is a closely-relatedcompanion function to the Loss of Life monitoringfeature described later.

V/Hz Over uxing protection

The single phase voltage input may beconnected phph or ph-neutral and is providedto enable over uxing detection. Alarm andtripping characteristics, which are based on ameasurement of the voltage/frequency ratio, areprovided. The alarm is de nite time delayed whilstthe trip characteristic may be applied with upto four de nite time (DT) elements, or an IDMTcurve plus up to three DT elements. The optionaladditional 3-phase VT input available in P643 andP645 allows over uxing to be applied on both

HV and LV sides of the transformer, to ensureoptimum protection, irrespective of theload ow direction.

Both thermal overload and over uxing elementsare essentially thermal based, modelling windingand oil heating, or heating of core bolts andlaminations. Due to time constants being inminutes (rather than seconds), heating andcooling of both replicas can be relatively slow.

A pre-trip countdown is provided, displaying thetime remaining to trip if the present level of load,or ux were to be maintained.

A pre-trip alarm can be applied, notifying thedispatcher that he/she has a certain number of

minutes for remedial action, before a trip is likely. After any injection testing, all replicas can beforced to reset via a user command.

Circuit breaker failure

The breaker failure protection may be initiatedfrom internal protection within the P64x, and alsofrom external devices. In the case of Buchholz(sudden pressure) relays, the CBF elements for all breakers must be initated in parallel. Whereexternal feeder or busbar protection is appliedto trip only one (or more) breaker(s), the P64xhas the ability to initiate the CBF scheme on aper breaker basis. Retripping and backtrippingschemes are supported, all with a fastactingundercurrent check.

suPeRvIsORy funCTIOns

Voltage transformer supervision is provided todetect loss of one, two or three VT signals (P643and P645 models tted with a 3-phase VT).Current transformer supervision is provided todetect loss of phase CT input signals. Using thedifferential CTS feature (patented), the relayperforms an intelligent comparison of the negative

sequence current imbalance at all CT terminals,to determine which, if any, CTs have failed. Thiscomparison detects all CT shorts, open circuits,and wiring disconnections without an inherenttime delay. Operation of the differential protectioncan be blocked during the failure, or alternativelytemporarily desensitised to avoid an unwantedtrip. The CTS thus assures real-time stabilityof the differential elements, and any applicableREF protection.

BACK-uP PROTeCTIOn

The MiCOM P642, P643, and P645 are deliveredwith comprehensive back-up protection. Typicallythis will be used in time-delayed mode to improvefault detection dependability for system (out-of-zone) faults. System integrity can also beimproved, utilizing internal elements for load-shedding, interlocking, alarm, or other purposes.

Current-based protection

Each winding, whether the current is directlymeasured from one CT input, or is a virtualsummation from two CTs, has the followingelements available:

Phase fault overcurrent

Negative sequence overcurrent

Earth (ground) fault.Simple setting: intuitive wizardsneed only nameplate data

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Up to four stages of each element, per winding,are available with a choice of standard IEC and

ANSI / IEEE IDMT curves, instantaneous, andde nite time operation. Where a P643/P645 hasthe 3-phase VT option tted, any of the currentprotection applied on the same winding as theVT location may be directionalized. Overcurrentelements, directionalized if necessary, can beuseful to clear reverse-fed upstream faults, or for protection of adjacent busbars. At distribution andindustrial voltage levels, low-cost bus protectionschemes can be con gured using the reverseinterlocking principle. This is a logic-basedscheme, which will trip should a fault current

ow onto the busbar not be accompanied by anexternal fault start on an outgoing circuit.

The earth fault protection is con gurable tooperate either in measured, or derived mode.Measured denotes that the winding (or externalearthing transformer) has a star-point singlephase CT available in the Y-ground connection,and the user wishes this current to be used toimplement standby earth fault (SBEF). Derivedis set for delta windings, or other cases wherethe user prefers to use the calculated residualcurrent from the three phase CTs.

Voltage protection *Two stages each are available for phaseovervoltage, phase undervoltage, and residualovervoltage (neutral displacement). Suchelements are particularly useful to detect voltageregulation errors.(* Available when optional 3-phase VT input isordered in P643 or P645).

Frequency protection

Four stages of underfrequency and two stagesof overfrequency are provided, permittingload shedding and restoration schemes to beimplemented.

COnTROl

User interface

Integrated user function keys and programmableLEDs provide a cost-effective solution for fulltransformer schemes. The P643 and P645offer higher functionality, with ten function keysoperating in two modes, normal and toggled,each with an associated tricolour LED for clear indication of the logic status. Typical control,maintenance, and commissioning options areinitiated directly from simple key presses, rather than the need to navigate a menu.

Programmable scheme logic

Powerful graphical logic allows the user tocustomize the protection and control functions.The gate logic includes OR, AND and majoritygate functions, with the ability to invert the inputsand outputs, and provide feedback. The systemis optimized to ensure that the protection outputs

are not delayed by the PSL operation. Theprogrammable scheme logic is con gured usingthe graphical MiCOM S1 Studio PC software,as shown in Figure 6. The relay outputs may becon gured as latching (eg Lockout) or self-reset.Time delays and interlocking schemes arepossible within the PSL.

Figure 6: Programmable Scheme Logic editor

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Through fault monitoringThrough faults are a major cause of transformer damage and failure, stressing the insulation andmechanical integrity. An It calculation based onrecorded duration and maximum current is storedfor each phase. Calculation results are added tocumulative values, and monitored so that userscan schedule transformer maintenance or identifya need for system reinforcement. The last vetriggers are stored as special individual records.

Power system measurements (MMXU)Multiple measured analog quantities, with phaseangles, are provided. These include: Phase and neutral currents for all windings,

plus sequence components Measurements of all voltage inputs

Frequency, power factor, Watts and VArs Maximum demand and rolling values Bias currents, differential currents All thermal states, temperatures, and

loss-of-life Measurands can be assigned to CLIO

Event recordsTime-tagged event records are stored in batterybacked memory. An optional modulated or demodulated IRIG-B port is available for accuratetime synchronization.

Fault records

Indication of the faulted phase

Protection operation

Active setting group

Relay and CB operating time

Pre-fault and fault currents

Bias and differential currents

Disturbance records

High performance waveform records contain allCT and VT input channels, plus up to 32 digitalstates, extracted in COMTRADE format.

PlAnT suPeRvIsIOnTrip circuit supervision

Supervision of the trip circuit can be implementedusing optocoupled inputs and the programmablescheme logic.

Analog (Current Loop) Inputs and Outputs(CLIO)*

Four inputs are provided for transducers withranges of 0-1mA, 0-10mA, 0-20mA or 4-20mA.

Associated with each input there are two timedelayed protection stages, one for alarm andone for trip. Each stage can be set for Over or Under operation.

Four outputs are provided with ranges of 0-1mA,0-10mA, 0-20mA or 4-20mA which can alleviatethe need for separate transducers. These may beused to feed standard moving coil ammeters for analog indication of certain measured quantitiesor for input to SCADA using an existing analogRTU.(* Available when optional CLIO card is ordered).

COMMunICATIOn TO ReMOTeOPeRATORs AnD suBsTATIOnAuTOMATIOn

Two auxiliary communication ports are available;a rear port providing remote communications anda front port providing local communications. Anadditional, second rear port can be ordered as anoption. Any of the following rear port protocols canbe chosen at the time of ordering: Courier/K-Bus,MODBUS, IEC60870-5-103, DNP3.0,or IEC 61850.

Second rear Courier port

The optional second port is designed typicallyfor dialup modem access by protectionengineers / operators, when the main port isreserved for SCADA traf c.

Programmable logic andcontrol scheme exibility

MeAsuReMenTs AnD ReCORDIng

Loss of life (LoL)Frequent excesses of transformer rated current or operation at elevated temperatures will shortenthe life expectancy of the transformer. The P64xprovides a transformer loss-of-life calculation,using a thermal model that estimates the hotspot temperature.The insulation deterioration isassumed to follow an adaptation of the Arrheniustheory where insulation life and absolutetemperature are inversely proportional(as per IEEE Std. C57.91-1995).The LoL implementation includes: Daily writing into non-volatile memory Accumulated Loss of Life, Rate of Using Life,

Ageing Acceleration Factor, and Residual LifeHours stored

Alarm setpoints available on attaininginstantaneous or cumulative levels

Statistics can be reset if a device is relocatedto monitor another transformer

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D ic Track R cord -Tra orm r prot ctio

Over 15 000 MiCOM transformer differentialrelays supplied since 2001.

MiCOM P642, P643, P645 range advances on this technology.

Over 80 000 units of such relay types arein-service, worldwide.

10-2010EnergyAutomation-DS-P64x-1887c-EN

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As standards, speci cations and designs change from time to time, please ask for con rmation

of the information given in this publication.

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