P&B MPC2000+ Technical Manual page 39

MPC2000+ Technical Manual
( )
p 2 - (1-H/C)(I L ) 2
t c = 32.a.log e
--------------------
p 2 - s 2
Where 'I L' is the steady state load prior to overload condition divided by motor FLC, e.g. if motor is running at FLC,
I L =1.
'H/C' is the hot/cold ratio in per unit value e.g. 40% hot to cold ratio = 0.40.
The Cool Time Factor is factory set at 5 unless specific information is available from the motor manufacturer to
calculate the actual setting it is recommended that the default setting is used.
With regard to current unbalance protection the pick up default setting is 15% and trip time is 30 seconds. These
figures should be set to the motor requirements if the Negative Phase Sequence withstand can be obtained. Formula
for calculating the unbalance setting can be obtained from P & B Engineering on request.
Further help on the application of thermal overload protection by ringing P & B Engineering at Manchester on 0161
230 6363.
P&B Engineering ISSUE 7 28/9/99 Page 35