Woodward MRM4, Руководство пользователя

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Protective Elements
The long acceleration time (LAT) function can block the critical LRC-LRT
rotor thermal protection during a start and destroy the motor. Turn LAT
OFF unless absolutely needed and the motor's suitability for this starting
duty has been confirmed. Use only with zero speed switch function ZSS
ON and switch input connected to protect a stalled motor.
The User can temporarily defeat the I2t thermal protection limit after a start by setting a Long Acceleration Time
delay. This can be a dangerous setting that blocks thermal tripping and holds the bucket at a 100% level if the
load takes a long time to reach running speed. An example is a motor spinning a large centrifuge. In using LAT,
the User can take advantage of the partial cooling from airflow produced by the motor spinning at below-normal
speed, as compared to unfanned heating of a locked rotor. The motor must be rated for this severe starting
duty. Also, the User must ensure that the motor actually has begun to spin well before the locked-rotor time has
expired. This is accomplished by connecting a zero-speed switch to a Digital Input and turning on ZSS function.
The zero-speed switch is a contact that is closed when the motor is at rest, and opens as the motor begins to
spin, usually at 5-10% of running speed. If ZSS is set to ON and the protective device relay does not sense the
contact open in one-half the locked-rotor time setting, it trips the motor.
Turn OFF LAT unless the application specifically demands it. Use a zero
speed switch with LAT. Using an LAT setting greater than locked rotor time
without a zero speed switch temporarily defeats thermal protection and
damages the motor if the rotor actually is locked.
If » LAT« is used, check the settings of transition time » TRNT« and jam start delay to be sure they are
coordinated with the prolonged starting cycle.
Anti-Backspin Delay Time (ABS)
»ABS« sets the time in seconds before a motor restart is permitted after a trip or stop condition. This function
can be set to » inactive« .
This function is used with a motor driving a pump working into a head, or any other load that tends to spin in a
reverse direction (backspin) when the motor is de-energized. It blocks starting during the time when the motor
might be rotating in reverse following a trip. Also, this function may be used simply to set idle time (time between
stop and start) before a restart is permitted.
Motor Cold Warm Detection
The motor will be considered as cold (»C
OLD SEQU
=
TRUE
«) after being in the »stop« mode for more than one hour
if the time between starts timer is set to a lower value than 1 hour.
Else, the motor will fall back into the »cold« state if the time between starts timer is elapsed. By means of the
Emergency Override function, the motor can be forced to switch to the cold state.
EN MRM4 01/11 Page 271