BE1-87T Transformer Differential Relay

1 BE1-87 TUHA-74-10BE1-87 TTRANSFORMERDIFFERENTIAL Relay FUNCTIONALDESCRIPTIONP ages 2-5 SPECIFICATIONSP ages 6-7 EXTERNALCONNECTIONSP ages 8-9 ORDERINGP ages 10-11 The BE1-87T Transformer Differential Relay is designed as primary protection forpower transformers against internal faults. Available in either single- or three-phaseconfigurations, this solid-state Relay compares the currents entering and leaving theprotected Transformer . If any imbalance is detected that is not attributable to other(tested) factors, the Relay provides a contact closure to isolate the power trans-former to limit Single- and three-phase configurations.

2 Input isolation. Three-phase configuration includes internal phase shift compensationwith zero-sequence current blocking. 2nd- and 5th-harmonic restraint. Adjustable through-current restraint. % IOP display. Tap scaling covers the range of to amperes in in 5 Ampere CT models, and to amperes ampere increments in 1 Ampere CT models. Low sensing burden. Maintains proper operation when tested for interference in accordance withIECC , Trial-Use Standard Withstand Capability of Relay systemsto Radiated electromagnetic Interference from Transceivers.

3 Five year MANUALR equest publication 9171300990P. O. BOX 269 HIGHLAND, ILLINOIS 62249, PHONE 618-654-2341 FAX 618-654-2351 ADDITIONAL INFORMATIONBE1-87 TFUNCTIONAL DESCRIPTION2A fault would be indicated by a nonzero IOP. However,saturation caused by heavy through-currents, mag-netic inrush or overexcitation can cause IOP to bepresent even though no fault has occurred. To preventfalse tripping under such conditions, various types ofrestraint are TRIP OUTPUTThe restrained trip output is subject to three typesof restraint signals developed within the Relay inresponse to external conditions: Percentage restraint Second-harmonic restraint Fifth-harmonic restraintThe calculate max individual current circuit deter-mines which scaled input is receiving the greatestcurrent.

4 The resulting signal, %IMAX (figure 2) repre-sents the percentage of through-current and isextended to the trip comparator, where it is comparedto the operating the operating current is greater than %IMAX andthere is no inhibit signal present, a restrained trip isproduced; also an auxiliary output will occur (depend-ing on Relay configuration).Harmonic RestraintsThe restrained trip output may be inhibited by eitherof two harmonic restraints. These are generated byfilters tuned to the second- and fifth-harmonic contentof the operate current.

5 Comparators monitor thesesignals. When the fifth-harmonic content exceeds35% of the operate current (indicating overexcitationof the Transformer ), or when the 2nd-harmoniccontent exceeds 12% (single-phase) or 18% (three-phase) of the operating current (indicating a mag-netic inrush condition), an inhibit signal blocksoperation of the Restrained output Relay . The three-phase mode uses summing of the second harmonicsignal to provide secure Speed Applications (Option)On some applications, overall fault clearing time canbe a major issue.

6 The 87T can optionally be config-ured with a faster overall operating speed for BE1-87T is a solid-state Relay to protect powertransformers by providing an output contact closurewhen the scaled currrent into the protected trans-former does not equal the scaled current out (withindefined limits). The Relay is harmonically restrained toprevent tripping during intial energization andoverexcitation conditions. A through-current restraintalso provides security against tripping for externalfaults. An unrestrained tripping element is included toprovide high speed tripping in the event of a severeinternal functional block diagram in Figure 1 illustrates theoverall operation of the BE1-87T .

7 Since the Relay isavailable as either a single-phase or three-phasedevice, only phase A is shown in detail. Phases B andC, when present, are functionally similar to phase TRANSFORMERSA standard current Transformer with a 5A or 1A sec-ondary winding supplies sensing current for eachinput. These current transformers may be shared withother protective relays due to the isolation of individualinputs. The sensed currents are, in turn, applied to theinternal input transformers of the currents are scaled by rotary switches thatintroduce resitances to the internal CT switches are calibrated in ampere incrementsfrom to amperes (5 ampere CT models) ampere increments from to amperes(1 ampere CT models).

8 The many graduations ofadjustment are provided to allow each input to ap-proach an ideal representation of its actual operatingper unit analog signals representing each input s contribu-tion are electronically sound. This process producesthe operating current (IOP), which is the algebraic sumof the input , with perfectly matched CTs, a transformerwithout an internal fault would have an IOP of DESCRIPTION, Continued3 Unbalance DisplayThe 87T can be optionally configured with a frontpanel indication of system unbalance, to permitverification of proper Relay connections.

9 The displayconsists of 8 LEDs, which show the unbalance as apercent of trip. IOP% IMAX ()UNRESTRAINED TRIP OUTPUTThe IOP signal is also compared against a referenceestablished by the front panel UNRESTRAINED TRIP setting. When this reference is exceeded, the unre-strained trip output Relay is energized. The unre-strained trip is not affected by through-current orharmonic SHIFT AND ZERO SEQUENCE FILTER(Available only in three-phase relays)In three-phase relays, the phase-shift jumpers may beplaced to provide +30 degrees, -30 degrees or nocompensation for delta-wye or wye-delta transformerconfigurations.

10 The 30 degree phase shift will accom-plish the corresponding zero sequence single-phase relays, the internal phase shift is notavailable and the phase shift compensation and zerosequence filtering must be provided by the external Relay (Option)The auxiliary Relay is controlled by two switches, S1and S2, which allow it to respond to a restrained trip,or to an unrestrained trip, or both. The S1 and S2switches are located on the mother SUPPLYThe solid-state power supply is a low burden, flybackswitching design which delivers a nominal 12 Vdc tointernal circuitry.