Siemens SIMPRO-100 - SIMPRO-100 Relay Settings Sheets; Relay Settings: General Data; General Data Parameters

SIMPRO-100
Motor Thermal Element
E
PRIM-2400C 211
E.7 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 SIMPRO-100 Relay 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 relay adds a 10% safety margin to
this setting, thus if you set Thermal Capacity
Used to Start equal to 65%, the relay requires the
% Thermal Capacity to fall below 25%
(100% – 65% – 10% = 25%) when the motor is
stopped before another start is permitted. The
relay asserts the Thermal Lockout until the motor
is cool.
In addition, the relay 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 relay 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 relay
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
SIMPRO-100 Relay.