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CONTROL
4–324
The Thermal Lockout Time calculation is based on the values of TCU, TC
Time Constant Stopped (CTCS). The latter is set in
. The formula is shown in on the Thermal Start Inhibit logic diagram:
> Thermal Model
If, for the example above, the Cool Time Constant Stopped = 30 Minutes and the motor TCU
= 90%, the lockout time is: 30 x ln (90% / 66%) = 9.3 minutes
If the start history is not available, the inhibit time is: 30 x ln (90% / 15%) = 54 minutes
The 869 constantly displays the Thermal Lockout Time in
motor is neither stopped nor tripped.
If the Emergency Restart input is asserted during a Thermal Start lockout, the TCU is set to
zero and the Thermal Trip OP is reset. This causes resetting of Thermal Lockout Time to
zero and dropout of the Start Inhibit and Thermal Inhibit OP and allows a new start.
In the event of a real emergency, the Emergency Restart input operand must remain
asserted at logic 1 until the emergency is over. The Thermal Inhibit OP and Start Inhibit
operands will remain reset until the Emergency Restart Input is de-asserted. However,
calculation of Thermal Lockout Time continues after resetting to zero regardless of the
duration of the Emergency Restart input.
Path:
Setpoints > Control > Motor Starting > Start Supervision > Thermal Inhibit
FUNCTION
Range: Disabled, Enabled
Default: Disabled
The element works as described at the beginning of this chapter if the Function is set to
Enabled. If the Function is set to Disabled, the element is not functional unless the motor
thermal capacity has reached 100% and the thermal model trip function is enabled. In
that case, the Thermal Start Inhibit operates and the lockout time is approximately 190%
of the Cool Time Constant Stopped. After the lockout time expires, the TCU will decay to
15% and a new start will be allowed.
TC USED MARGIN
Range: 0 to 25% in steps of 1%
Default: 25%
Setpoint values in the range of 0 to 25% specify the margin to be included in the
calculation of the adjusted Thermal Capacity Used at start value.
Figure 4-129: Thermal Start Inhibit logic diagram
Setpoints > Protection > Group 1 > Motor
Status > Motor
869 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 4: SETPOINTS
and the Cool
ADJ
menu even if the
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