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BE1-67N General Information
1-1
SECTION 1
•
GENERAL INFORMATION
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 (3
I
0
) 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.
Figure 1-1. Zero Sequence Polarizing (Two-Winding Transformer)
Summary of Contents for BE1-67N
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