MV Motor Start Duty

Status
Not open for further replies.
D

dy11

Member
Location
PA
Occupation
Plant Electrical Engineer
We have a 2000HP 4160V motor. Below is an excerpt of the starting duty, as labeled on the motor.

Motor cold 2 consecutive starts
Motor at operating temp. 1 consecutive start
Subsequent starts with motor running between starts 20 minutes apart
Subsequent starts with motor standing between starts 45 minutes apart
Starts should NOT average more than 6 per day throughout the life of the motor

When does the transition between standing and running occur? For example, assuming there is no protective device supervising starts, if the motor has been running for a day and is stopped by an operator for a normal shutdown, at what point would the operator need to wait 45 mins instead of 20 mins in order to start the motor again?

Could a start be attempted immediately since there is 1 consecutive start allowed after running at temp?

Is "standing between starts" referring to a failed start attempt where the contactor closes but the motor doesn't stay online?

Thank you
 
You can immediately restart a motor that was previously at running temp.

But, heat begins to build up in a motor that has stopped after having been running. This is why you need to wait 45 minutes before a restart unless the restart occurs within 20 minutes.
 
dy11 said:
We have a 2000HP 4160V motor. Below is an excerpt of the starting duty, as labeled on the motor.

Motor cold 2 consecutive starts
Motor at operating temp. 1 consecutive start
Subsequent starts with motor running between starts 20 minutes apart
Subsequent starts with motor standing between starts 45 minutes apart
Starts should NOT average more than 6 per day throughout the life of the motor

When does the transition between standing and running occur? For example, assuming there is no protective device supervising starts, if the motor has been running for a day and is stopped by an operator for a normal shutdown, at what point would the operator need to wait 45 mins instead of 20 mins in order to start the motor again?

Could a start be attempted immediately since there is 1 consecutive start allowed after running at temp?

Is "standing between starts" referring to a failed start attempt where the contactor closes but the motor doesn't stay online?

Thank you
Click to expand...

“Standing Between Starts” means a locked rotor condition or failing to get up to rated speed. The problem is that self cooling and adequate airflow depends on the motor getting up to speed. Without being able to remove the heat generated when starting, the thermal capacity can be exceeded with additional starts. Also, is this an induction or synchronous motor?


Sent from my iPhone using Tapatalk
 
Understood thank you. This is an across the line started induction motor driving a refrigerant compressor for a chiller.
 
dy11 said:
Understood thank you. This is an across the line started induction motor driving a refrigerant compressor for a chiller.
Click to expand...
Just a side note: Ensuring the line voltage is adequately boosted (above nominal) prior starting will greatly reduce the chances of stalling the motor.
 
The 45 minute delay seems like it contradicts with the 2 cold consecutive starts allowed. If it's been offline for an extended time and the first start attempt fails to reach rated speed, shouldn't I be able to immediate retry without waiting 45 mins?
 
dy11 said:
The 45 minute delay seems like it contradicts with the 2 cold consecutive starts allowed. If it's been offline for an extended time and the first start attempt fails to reach rated speed, shouldn't I be able to immediate retry without waiting 45 mins?
Click to expand...

There is a significant amount of heat generated with starting alone. If you go for a restart, you are adding the heat associated with starting the motor to the already present operating temperature of the motor, which could run hotter than doing two consecutive cold starts.

By the way, RTD's are sometimes used with protective relays to adjust the thermal capacity of the motor based on ambient temperature conditions and allow for a restart sooner.
 
Status
Not open for further replies.
Top