Basler Electric BE1-87T - Manual (Page 15)

9171300990 Rev V BE1-87T General Information 1-3
Three-phase BE1-87T relays use second-harmonic sharing. The second-harmonic content of all three
phases is summed together to derive the restraint for each phase. As a result, the second-harmonic
inhibit range and the associated factory setting, is higher than on single-phase relays.
Fifth-Harmonic Restraint
Power transformer overexcitation causes additional exciting current to flow into one set of terminals. This
presents an apparent differential (or operating) current not attributable to an internal fault. Although
potentially damaging, overexcitation is not an internal fault and, therefore, is not an appropriate condition
for transformer differential relay operation. One of the principal components in the complex waveform
produced during overexcitation is the fifth harmonic. BE1-87T relays use fifth-harmonic restraint to inhibit
the differential relay operation.
Unrestrained Trip
Severe internal transformer faults may cause CT saturation. Under such circumstances, harmonic-
restraint transformer differential relays may fail to trip because of the extremely high harmonic content in
the waveform. Lack of operation can result in severe transformer damage.
BE1-87T relays provide an independent unrestrained tripping function. When set above the possible
inrush current magnitude, this function provides high-speed protection for the most severe internal faults.
Options
Push-To-Energize Output Pushbuttons
Two PUSH-TO-ENERGIZE OUTPUT switches are available as a means to verify external output wiring
without the inconvenience of having to test the entire relay. Option 2-S provides a small pushbutton switch
for each isolated output function (Restrained and Unrestrained) and may be actuated by inserting a thin,
non-conducting rod through access holes in the front panel. Refer to Figures 2-1 through 2-4 for location.
Appropriate power must be applied to Power Supply terminals 3 and 4 (shown in Figures 4-7 through 4-
10) for these pushbuttons to operate the output relays. However, it is not necessary to apply currents to
the sensing inputs of the relay for these switches to function.
Auxiliary Output Contacts
Three types of auxiliary output contacts are available: Normally open, normally closed and SPDT. The
contacts can be made to respond to a restrained trip, an unrestrained trip, or both. Refer to the Functional
Description: Auxiliary Relay Option for further information.
Power Supply
Various power supply options are available to allow the BE1-87T to be used with standard supply
voltages. See the Style Number Identification Chart, Figure 1-1, for details.