Optional Equipment Selection; Protection; Indication - GE SecoGear Application Manual

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current element (51G) to be connected to the neutral
current transformer of a local power transformer feeding
the incoming line.
• SSIL-2: Use this type of incoming line for an impedance or
solidly grounded system fed from a remote wye-
connected transformer, or a local wye-connected
transformer with no current transformer in the
transformer neutral connection.
This type of incoming line would include three-phase
time-overcurrent protection (51) and residually
connected ground-over-current relay (51N).
• SSIL-3: Use this type of incoming line for ungrounded or
solidly grounded systems for which no ground relays are
desired.
This type of incoming line would include three-phase
time-overcurrent protection (51), and no ground relays.

Optional Equipment Selection

Protection

• Overcurrent Relay Characteristics: Time-current
characteristics for overcurrent relays are determined by
system studies. After the time-current characteristic has
been established, ensure the relays selected offer the
required time current characteristics that satisfy the
application.
• Current Summation Connection: For lineups containing
bus-tie breakers, specify that the incoming line
overcurrent relays be wired for current summation (also
known as partial differential). Add a lockout relay (86) and
a set of three CTs, mounted on the tie breaker, for each
set of relays to be wired this way.
• Open-phase Protection: For incoming lines fed from
transformers with fused primaries or sources subject to
single-phase operation, add negative-sequence voltage
protection (60/47) and time delay (62). This function is
available in multifunction relay protection packages, such
as GE Type 850 and F650, or as a single function relay
Type NBV or other.
• Transformer Differential Protection: Add differential
protection for incoming lines fed from transformers with
a means to trip a primary breaker. Differential protection
can be in the form of separate relays, such as GE Type
STD single-phase transformer differential relays (87T), or
as part of a complete multifunction transformer
protection package, like GE 845, T35 or T60 relays. In
addition, add one Type GE Series 95 lockout relay (86T),
one Type HAA fault pressure auxiliary target relay
(63FPX), and a set of three current transformers.
For impedance grounded systems with larger
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SecoGear Medium-voltage Switchgear Application and Technical Guide
transformers and for which three-phase transformer
differential relaying is not sensitive enough to detect
secondary ground faults, include ground differential relay
protection (87TG) with a single function GE Type IFD relay,
or as part of a complete multifunction transformer
protection package.
• Bus Differential Protection: For systems requiring bus
differential protection, add a GE B30 or B90 three-phase
solid state differential protection relay (87B) and one Type
GE Series 95 hand reset lockout relay (86B). Bus
differential requires a dedicated set of three CTs on the
incoming line.
• Current Transformers for Remotely Located
Differential Relays: For incoming lines included in bus or
transformer differential zones for which relays are not
mounted on the incoming line equipment, add a separate
set of three current transformers for each differential
function.
• Directional Power, Underfrequency, and Undervoltage
Protection: To detect utility tie circuit fault conditions
prior to automatic reclosing and to initiate programmed
load shedding, add, either singly or in combination, a
power directional relay (32), underfrequency relay (81),
undervoltge relay (27) and timer (62). This applies for
systems with local generation or large motors. These
features are included in GE Multilin 850 and F650 relays.
A study of each system is required to assure proper
selection and circuit location of these relays.
• Automatic Throwover: For lineups with a normally open
tie breaker or a normally open alternate incoming line
breaker, add automatic primary throwover equipment if
desired. This consists of two undervoltage relays (27), two
multicontact auxiliary relays (27X), two timers (2 and 62),
two auxiliary relays (2X and 62X), and one manual-
automatic selector switch (43).
Automatic throwover equipment requires an empty
auxiliary compartment for mounting, custom designed
for each application. If using GE 850 multifunction relays
on the incoming line and tie breakers, only two timers (2
and 62), two auxiliary relays (2X and 62X), and one
manual-automatic switch (43) are required.

Indication

• Instrumentation and Metering: For incoming lines for
which voltage indication and relay voltage source are not
required, omit the voltmeter, voltmeter switch, and two
voltage transformers. For circuits requiring the indication
or metering of additional electrical quantities, add
indicating analog meters as appropriate or a
multifunction meter, such as GE EPM6000. Some relays
include extensive metering functions such as Amps, Volts,
SecoGear Switchgear Applications
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