Product Description - GE 735 Instruction Manual

1.1 OVERVIEW
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The 735/737 is a microprocessor based relay used to perform primary circuit protection on distribution networks at any volt-
age level. Instantaneous and time overcurrent phase and ground protection features replace the equivalent of 8 separate
protection devices. Each protection element can be selectively enabled by front panel dial settings. Flexible settings and
selectable curve shapes enable accurate coordination with other devices. Cause of trip indications and a bar graph load
monitor are provided on the front panel.
A momentary dry contact closure from the 735/737 relay is used to activate the breaker trip coil in the event of a fault. To
help determine the cause of a trip, separate indicators are provided for phase instantaneous, phase time overcurrent,
ground fault instantaneous, and ground fault time overcurrent. These latched indicators remain set after a breaker trip.
They can be reset by the front panel CLEAR button.
A special feature of the 735/737 named "Trip Record" is the ability of the relay to sequentially display the last five causes of
trips. To display the trips, press and hold the reset key. After 2 seconds, the front panel indicators will display the last 5 trips
starting with the most recent.
The 735/737 has separately adjustable instantaneous and time overcurrent pickup levels. No intentional delay is added to
the instantaneous trip. Five separate time overcurrent curve shapes can be selected: definite time, moderately inverse, nor-
mal inverse, very inverse, and extremely inverse. For each curve shape, 40 different curves to produce different time delay
levels can be selected using the time multiplier settings and curve shift. These allow selection of optimum coordination with
fuses, feeders, motors, trans-formers, etc. To monitor load current, a front panel bar graph indicator is provided. It gives an
indication of 10% of CT rating to 100% of CT in steps of 10%. This is useful for monitoring breaker loading and during test-
ing.
Ground level and time delay can be selected for coordination with upstream devices. The ground signal is normally derived
as the residual sum of the 3 phase CTs, eliminating the need for an additional ground sensor. Alternatively, for more sensi-
tive detection, an additional core balance (zero sequence) ground sensor, encircling the 3 phase conductors, can be used.
Like time overcurrent phase protection, 5 separate curve shapes and 40 curves for each shape are available for ground
fault protection.
To accommodate more complex control schemes the 737 has 8 additional output relays to provide a separate dry contact
output for each different protection element. That is, in addition to the 2 common trip contacts, the 737 has contacts for trip
from:
51A, 51B, 51C, 51N, 50A, 50B, 50C, and 50N
These eight additional outputs can be programmed to activate:
• as a separate trip output for each 50/51 protection element
• as a latched cause of trip output for fault diagnosis interface to a SCADA
• when phase/ground current exceeds the pickup setting to warn of an impending trip
Internal monitoring of the relay is continuous. When control power is applied and the relay is operating normally, the
"RELAY IN SERVICE" LED is on. Should a fault be detected, the "SERVICE REQUIRED" LED will light to indicate a prob-
lem. In addition, the failsafe SERVICE relay output will change state signalling a malfunction to a remote monitoring device
such as a programmable controller. In this case the 735/737 relay should be replaced and sent in for service. As long as the
"SERVICE" LED is off and the "RELAY IN SERVICE" LED is on the relay is operating normally. If the test switch is on, the
RELAY IN SERVICE LED will flash. When either the phase or ground time/overcurrent threshold is exceeded, a separate
pickup indicator flashes which is useful for testing, and to warn of an impending trip.
Relay states can be monitored via the RS485 communication port. This allows relays to be linked together over a simple
twisted pair wire to communicate with a PLC or computer using the Modbus protocol. Baud rate and a unique slave
address are set via the front panel communications switches.
1-2 735/737 Feeder Protection Relay
1 INTRODUCTION

1.1.2 PRODUCT DESCRIPTION

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