3 Cold starts and 2 hot start

[kssschsekhar]

Hi all,

Recently I come across following technical specification clause for MV or LV motor (LV motors can be considered as > 100 kW rating)
The clause details are as follows

....Electric motors shall be suitable for two (2) successive starts with the motor already at full load working temperature, subject to motor being permitted to decelerate to rest under operating conditions between successive starts.
After a cooling period of 30 minutes at rest another starting sequence of two (2) successive starts shall be permissible…..


Can I say above clause means Three (3) Cold starts and Two (2) Hot Starts of motor?

Till date I heard only 3 Cold / 2 Hot starts of motor only. Is there any other meaning for above clause?

Next...
Is 3 Cold/2 hot starts applicable for small motors like 0.37 kW? Till now I am assuming number of starts should be for large motors like > 100 kW due to Motor winding's insulation thermal rating (Class F insulation and Class B temperature rise).

 

[itsmoked]

Big motors.. I'll let someone else comment on that.

Direct relationship the smaller the motor the more starts per hour. At 0.37kW probably 120 starts an hour.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

That looks like an end user spec for a specific project or engineering standard, not a manufacturing spec.
The spec does not adequately define cold starts.
One cold start and then the time interval between hot starts.
How do you get 3 cold starts?
After one cold start, you are making hot starts.
The motor must cool for an undetermined amount of time greater than 30 minutes before it is ready for another cold start.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[krisys]

The hot start and cold starts can be defined in various manner, as long as the concept is clear. This is effectively like four (4) hot starts at an interval of 30 minutes.

 

[RRaghunath]

This seems like 4-starts in one hour, with 30min cooling time after two successive starts.
Thus, it seems to be a specific project requirement.

 

[waross]

The spec may be a bid spec:
Ths is what the motor must be capable of.
Versus
This is what the motor is capable of.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LionelHutz]

3 cold starts really means 3 starts beginning with a cold or ambient temperature motor. And no, the starting duty listed doesn't match 3 starts from a cold condition.