Duty
For duty which is less than continuous, a shunt need not be rated as high as a straight calculation based on resistance and voltage or current would indicate.
If, for instance the shunt is repeatedly energized for a short period (not to exceed 5 minutes)… a conservative rating may be obtained as follows:
K1 = √D
Pplus = Pmax / K1
Pmax = Prated x 0.66
Pmax = maximum continous power
Prated = catalog rated power
Pplus = maximum pulsating power
where D is the ratio of ON time to the total period.
Example:
A 800 Amp 50mV shunt is energized for 15 seconds of each minute.
D = 15 /60 = 0.25 and K1 = √0.25 = 0.5 thus,
Prated = 800 x 0.05 = 40 watts
Pmax = Prated x 0.66 = 40 x 0.66 = 26.4 watts
Pplus = Pmax / K1 = 26.40 / 0.5 = 52.8 watts
therefore this shunt can be loaded up to 1056 Amps.
For surge and pulse service a different approach must be used. In these cases it is necessary to provide enough thermal mass to absorb the energy to be dissipated and be sure that the construction of the shunt is adequate to accommodate the peak power. Therefore, it is recommended that a complete description of the pulse / surge wave shape or circuit constants and operating conditions be submitted to the CSI Engineering Department for the selection of a suitable shunt.
Canadian Shunt Industries Ltd
80 Bullock Drive, Unit 1
Markham, ON L3P 3P7
Canada
1.800.433.5604
T 905.294.5274
F 905.294.5096
