SecoGear Medium-voltage Switchgear Application and Technical Guide
DET-882
SecoGear Switchgear Applications
38
©2017 General Electric All Rights Reserved
Induction motor feeders, full-voltage start
Induction motor feeder (IMF) is similar to a general-
purpose feeder, except it is used for controlling and
protecting full-voltage-start motors and is designated as
motor “branch circuit” protective equipment. For motors
greater than 1500 HP, motor differential protection is
typically required.
Motor feeders, reduced-voltage start
Reduced-voltage-start applications, utilizing reactors or
autotransformers, are available. Contact your GE Sales
Representative for additional information.
Synchronous motor feeders, full-voltage start
Synchronous motor feeder (SMF) is similar to an induction
motor feeder, except it is used for controlling and
protecting full-voltage-start synchronous motors and is
designated as motor “branch circuit” protective
equipment. For motors greater than 1500 HP, motor
differential protection is typically required.
Future unit
The metal-clad future unit (FU) compartments are a basic
mechanically prepared circuit breaker unit, except the
breaker is to be provided at a future date. Provisions are
made to receive a breaker of specified rating. It is
recommended to equip these base units with the breaker
stationary auxiliary switch and breaker position switch, if
the active feeders are so equipped, and install current
transformers (possibly multiratio). This minimizes field
installation, downtime and adjustment procedures when
the application of this base unit is determined. The
selected relays may be added to the door when the
circuit application is determined, or a new door may be
purchased with relays and devices completely wired.
GENERAL-PURPOSE FEEDERS (GPF)
A general-purpose feeder (GPF) is metal-clad equipment
controlling and protecting a set of conductors supplying one
or more branch circuit distribution centers, one or more
branch circuit distribution centers, or any combination of
these centers.
Protective Scheme Selection
•
GPF-1: Use this type of feeder for systems that are
impedance or solidly grounded and for which selectivity
is not required with downstream residually connected
ground relays.
GPF-1 feeders include three-phase overcurrent
protection (50/51) and one instantaneous overcurrent
element (50GS) connected to a ground-sensor CT (GSCT).
•
GPF-2: Use this type of feeder for systems that are
impedance or solidly grounded and for which selectivity
is required with downstream residually connected
ground relays.
GPF-2 feeders include three-phase overcurrent
protection (50/51) and residually connected time over
current ground element (51N).
•
GPF-3: Use this type of feeder for ungrounded or solidly
grounded systems for which no ground relays are
desired.
GPF-3 feeders include three-phase overcurrent
protection (50/51) and no ground fault element.
Optional Equipment Selection
Protection
•
Automatic Reclosing: For open-wire overhead
distribution circuits on which this feature is desired, use
the GE MIF II, F650 or 850 relay, which includes
automatic-reclosing (79) and cutoff switch (79CO)
functionality.
Current Transformers for Differential Circuits
For a feeder included in a bus-differential-protected zone,
add a separate set of three current transformers located on
the outgoing side of the feeder.
For a transformer-differential-protected zone, add a
separate set of three current transformers located so that
the feeder circuit breaker is included in the zone.
Indication
•
Instrumentation and Metering: Most solid-state
protective relays today offer basic load current indication
(such as GE 350). Some relays include extensive metering
functions such as Amps, Volts, Watts, Vars, PF, and
demand functions (such as GE 850, F650, F35 &, F60, 3
Series, 8 Series, UR family)
•
Test Blocks: For circuits that require the provisions for
insertion of portable recording meters or other similar
devices, add current and voltage test blocks. The basic
current test block is wired to maintain the circuit when
the test plug is removed.
•
Indicating Lamp: Additional indicating lamps can be
provided, such as for circuits requiring a circuit breaker
disagreement or spring-charged indication function.