Schweitzer Engineering Laboratories SEL-701-1, Инструкция по эксплуатации

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Date Code 20011009
SEL-701-1 Monitor
Motor Thermal Element
Motor Starting Thermal Capacity
E.13
Motor Starting Thermal Capacity
A normal motor start is expected to use a significant percentage of the available
starting thermal capacity. After a motor start, it is generally necessary for the motor to
cool for a time before another start is permitted. The cooling can usually take place
while the motor is stopped or running.
If a motor usually requires 70% of the available thermal capacity to start and if a
start is attempted while the present % Thermal Capacity exceeds 30%, a locked rotor
trip is likely because the motor is still too hot.
The SEL-701-1 Monitor provides two facilities to help ensure that a motor start is
not attempted while the motor is still too hot to be started safely. The Thermal Capacity
Used to Start (TCSTART) setting allows you to define a fixed value of thermal capacity
that you expect the motor to use on a start. The monitor adds a 10% safety margin to
this setting, thus if you set Thermal Capacity Used to Start equal to 65%, the monitor
requires the % Thermal Capacity to fall below 25% (100% – 65% – 10% = 25%) when
the motor is stopped before another start is permitted. The monitor asserts the Thermal
Lockout until the motor is cool.
In addition, the monitor learns a thermal capacity used to start by recording the
thermal capacity used during each of the past five successful motor starts. This learned
parameter is reported in the motor operating statistics report. When you set Use
Learned Starting Thermal Capacity (TCLRNEN) equal to Y, the monitor uses the
largest of the last five starting percentages in place of the TCSTART value to determine
when to release the thermal lockout.
NOTE:
Since the Thermal Capacity Used to Start percentage is
based on the starting thermal element trip threshold, the
monitor automatically switches to that threshold for %
Thermal Capacity calculation as soon as the motor stops. You
may observe this as a large drop in the % Thermal Capacity
value when you stop the motor. This is normal operation for
the SEL-701-1 Monitor.