Basler Electric BE1-67N Ground Directional Overcurrent Relay

PURPOSE

BE1-67N Ground Directional Overcurrent Relays provide ground fault protection for transmission and

distribution lines by sensing the flow of ground (zero sequence) current into or out of protected zones.

Zero sequence quantities provide a secure reference for the directional element because these quantities

are defined by the total source impedance of the power system.

APPLICATION

BE1-67N Ground Directional Overcurrent Relays are recommended for multi-grounded systems to

provide coordination necessary to selectively trip the faulted line. A directional overcurrent relay operates

by comparing the measured current to a reference quantity to determine whether current is flowing into or

out of the protected zone. Reference quantity is also referred to as polarizing quantity.

BE1-67N relays use one of the following quantities for polarization:

• Zero sequence current

• Zero sequence voltage

• Dual zero sequence current and voltage

The polarizing quantity is field selectable using a switch mounted on the analog circuit board. When the

selected polarizing quantities are less than the minimum threshold, relay operation will be inhibited. When

using dual polarization, the relay will operate if either polarizing quantity is above minimum threshold.

Zero Sequence Current

Zero sequence current polarization is preferred for applications with low ground source impedance.

Figure 1-1 illustrates relay connections that obtain zero sequence current (3I0

) from a separate current

transformer in the grounded neutral of a two winding wye-delta power transformer. Figure 1-2 illustrates

relay connections that obtain zero sequence current from a current transformer(s) in the grounded

neutral(s) of a three winding transformer. The magnitude of the zero sequence current used for polarizing

may be different from that of the ground current seen by the measuring element(s) of the relay.

Zero Sequence Voltage

Zero sequence voltage polarization is preferred for higher ground source impedances. Refer to Figures 1

1 and 1-2 for relay connections that obtain zero sequence voltage (3V0

) from a set of grounded wye

broken delta voltage transformers. The voltage polarized relay has a directional polarization adjustment to

match the impedance angle of the protected line to the characteristic angle of the relay. This is the angle

about which the directional angle is centered. A choice of line angles allows the relay to be adjusted to

include the resistance component of the ground fault.

Dual Zero Sequence Current and Voltage

Dual polarization is preferred where ground source impedance varies, or to provide redundant

polarization. Dual polarization is achieved using a polarizing signal that is the phasor sum of the current

and voltage polarizing signals.

OUTPUT CONTACTS

BE1-67N relays have the following output contacts: relay status alarm (relay fail), tripping, and auxiliary

(optional).

Relay Status Alarm

A relay status alarm output contact (relay fail) indicates that proper voltages are not being supplied to the

internal relay circuitry or that the microprocessor self-diagnostics has detected an error. This alarm output

contact is normally closed.

Tripping

Normally open or normally closed tripping contacts are included for each function within the relay.

Configuration of these contacts is defined by the relay style number. These output contacts are used with

optionally selected target indicator circuits.

Auxiliary

Normally open, normally closed, or single pole double throw (SPDT) auxiliary contact configurations are

provided to act in parallel with the tripping function(s) of the relay. Configuration of the auxiliary output

contacts are also defined by the relay style chart.

An auxiliary contact can be configured (via internal switches) to operate in parallel with any combination

of tripping outputs. Configurable auxiliary outputs permit use of the BE1-67N relay in various carrier

schemes.

PUSH-TO-ENERGIZE OUTPUTS

A push-to-energize pushbutton is included for each tripping output contact. These pushbuttons can be

used to verify correct operation of external control circuit wiring without the need to supply test signals to