Relay Assignment Practices - GE 469 Instruction Manual

469
Motor Management Relay
Relay Assignment
Practices
5–6
programmed as latched or unlatched. Once a latched alarm feature becomes
active, the reset key must be pressed to reset that alarm. If the condition that
has caused the alarm is still present (e.g. hot RTD) the Alarm relay(s) will not
reset until the condition is no longer present. If on the other hand, an unlatched
alarm feature becomes active, that alarm will reset itself (and associated output
relay(s)) as soon as the condition that caused the alarm ceases. As soon as an
alarm occurs, the alarms messages are updated to reflect the alarm and the
469 display defaults to that message. Since it may not be desirable to log all
alarms as events, each alarm feature may be programmed to log as an event or
not. If an alarm is programmed to log as an event, when it becomes active, it is
automatically logged as a date and time stamped event.
• BLOCK START: A 469 Block Start prevents or inhibits the start of the motor
based on some logic or algorithm. The Block Start feature is always assigned to
the Block Start relay. In addition to the Trip relay(s), a trip always operates the
Block Start relay. If the condition that has caused the trip is still present (e.g.
hot RTD), or there is a lockout time when the RESET key is pressed, the Block
Start relay will not reset until the condition is no longer present or the lockout
time has expired. Blocking features are always unlatched and reset immediately
when conditions that caused the block cease. In addition to becoming active in
conjunction with trips, a block may become active once the motor stops. There
are several features that operate as such: Starts/Hour, Time Between Starts,
Start Inhibit, Restart Block, and 469 Not Programmed. Block messages are
updated to reflect the block when it becomes active (complete with lockout time
if required) and the screen defaults to that message. Blocks are normally not
logged as events. If however, a motor start or start attempt is detected when a
block is active, it is automatically logged as a date and time stamped event.
This scenario might occur if someone shorts across the block terminals and
overrides the 469 protection to start the motor.
There are six output relays. Five of the relays are always non-failsafe, the other
(Service) is failsafe and dedicated to enunciate internal 469 faults (these faults
include Setpoint Corruption, failed hardware components, loss of control power,
etc.). One of the output relays is dedicated as the Block Start relay; it is dedicated
to features that are intended to block motor starting. The four remaining relays may
be programmed for different types of features depending on what is required. One
of the relays, 1 TRIP, is intended to be used as the main trip relay. Another relay,
4 ALARM, is intended to be used as the main alarm relay. The two relays that are
left, 2 AUXILIARY and 3 AUXILIARY, are intended for special requirements.
When assigning features to Auxiliary Relays 2 and 3, it is a good idea to decide early
on what is required since features that may be assigned may conflict. For example,
if 2 AUXILIARY is to be used for upstream trips, it cannot also be used for the
control of a Reduced Voltage Start. Similarly, if 3 AUXILIARY is to be dedicated as a
relay to echo all alarm conditions to a PLC, it cannot also be used strictly to
enunciate a specific alarm such as Undercurrent.
In order to ensure that conflicts in relay assignment do not occur, several
precautions have been taken. All trips with the exception of the Short Circuit Backup
Trip default to the 1 TRIP output relay. All alarms default to the 4 ALARM relay. Only
special control functions are defaulted to Auxiliary Relays 2 and 3. It is
recommended that these assignments be reviewed once all the setpoints have been
programmed.
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