GE Industrial Solutions AF-650 GP General Purpose Drive - Manual (Page 19)

6.1.5 Calculation of the Brake Resistor Average Power
The average power is determined by the process period time, i.e. the length of the braking time in relation to the process period time.
If the amount of kinetic energy (Eb) transferred to the resistor in each braking sequence (see examples 1 and 2 in the chapter Application Examples) is known, the
average power of the resistor can be calculated as follows:
Pavg =
Eb
TP
W
T
p
= period time in seconds.
If the amount of kinetic energy transferred to the resistor in each braking sequence is not known, the average power can be calculated on the basis of the process
period time and the braking time.
The duty-cycle for the braking sequence is calculated as follows:
Duty cycle =
Tb × 100
TP
%
T
p
= process period time in seconds.
T
b
= braking time in seconds.
GE offers brake resistors with a duty-cycle of max. 10% and 40%, respectively (some drives are only available with a duty-cycle of max. 10%). If a 10% duty-cycle
is applied, the brake resistors are able to absorb Ppeak for 10% of the period time. The remaining 90% of the period time will be used on deflecting excess heat.
The average power with 10% duty-cycle can be calculated as follows: Pavg = Ppeak × 10 % W
The average power with 40% duty-cycle can be calculated as follows: Pavg = Ppeak × 40 % W
The calculations apply to intermittent braking using a period time of 120/300/600 seconds.
NB!
Longer time than the specified intermittent braking period time may result in overheating of the resistor.
AF-650 GP Brake Resistor Design Guide
18
6