Introduction; Application - GE CEY51A Instructions Manual

GEl-I27S
MHO DISTANCE RELAY
TYPE CEY5IA
INTRODUCTION
The CEY51A relay is an extended-range, three-phase, high-speed, single-zone,
mho directional distance relay. It is constructed of three single-phase units in
one L2-0 case with provisions for single-phase testing. One target and seal-in unit
provides indication of operation for all three units. The transient overreach of
this relay is limited by design so that it is suitable for use as a first-zone
device. One CEY51A relay will provide complete one-zone protection for three-phase,
phase-to-phase and double phase-to-ground faults.
APPLICATION
The CEY51A relay, because of its low transient overreach (maximum of six
percent) and its memory action, is primarily a first-zone tripping relay. As such,
it is applicable as a high-speed tripping unit in direct and permissive
underreaching transferred tripping schemes, as well as a first-zone tripping relay
in straight distance and carrier schemes.
When applying this relay for the protection of a given circuit, it is
advantageous to set the relay on the highest basic-minimum-reach tap that will
accomodate the desired reach setting. This will ensure the highest possible
operating torque level. For first-zone applications, the relay may be set for as
much as 90% of the distance to the remote terminal.
Since all forms of the CEY51A relay have adjustable maximum-torque angle
available, a consideration of which angle to use may arise. It is suggested that
arc resistance for faults near the relay should be considered in this regard. The
smaller the angle of maximum torque, the greater the arc resistance that the unit
will accommodate.
The basic sensitivity of the CEY51A relay will depend on the basic mlnlmum tap
that is used. Figure 2 gives the steady-state and dynamic sensitivity of the relay.
In order to be sure that the relay will reach no less than 90% of its setting, the
minimum three-phase fault current flowing in the relay for a fault at the remote end
of the line should be at least those values given in table I.
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