GE SecoGear Application Guide

DET-882 SecoGear Medium-voltage Switchgear Application and Technical Guide
SecoGear Switchgear Applications
©2017 General Electric All Rights Reserved 49
REDUCED VOLTAGE STARTING
Power distribution system voltage regulation requirements
sometimes mandate reduced current starting to minimize
the current inrush and voltage sag when starting large
motors.
Inserting a reactor and then bypassing it as the motor
comes up to speed is one method of accomplishing this
objective.
An auto transformer connection is an alternate method of
reduced voltage starting. This method applies a reduced
voltage via the autotransformer, which is shorted out as the
motor comes up to speed. Figure 5-8 through Figure 5-9
illustrate the typical SecoGear circuits and arrangements for
these special motor starting requirements.
Figure 5-8: Reduced Voltage Reactor Start
SYNCHRONOUS MOTOR FEEDERS (SMF)
Synchronous motor feeders are used to control and protect
full-voltage-start synchronous motors and are designated
as motor “branch circuit” protective equipment. Economics
usually preclude protecting a motor smaller than 1500 HP
(SMF1) with a device package as complete as one used for
larger motors (SMF2). Also see IEEE C37.96-2012 IEEE Guide
for AC Motor Protection for relaying recommendations.
Protective Scheme Selection
• SMF1: Basic equipment for an SMF-1 (1500 HP and less)
includes three-phase running overload, locked rotor, and
short-circuit protection (49/50); undervoltage protection
with time delay (27, 62) (only one required per lineup);
zero sequence ground-fault protection (50GS); load
current indication. The overcurrent relays operate from
three CTs, one in each phase, and a ground-sensor CT.
A complete economical motor protection package is
available in the GE Multilin 869 digital motor protection
relay. The equipment is specified for use on impedance
grounded or solidly grounded systems. See “Optional
Equipment Selection (for SMF1 and SMF2)” for
modifications of this equipment for use on systems with
other types of grounding or having motors with other
types of excitation.
• SMF2: Basic equipment for an SMF2 (greater than 1500
HP) is a GE Multilin 869 digital motor protection relay,
which includes three-phase running overload, locked
rotor, and short-circuit protection (49/50); undervoltage

GE SecoGear Specifications

General

Brand	GE
Model	SecoGear
Category	Switch
Language	English