HP Vs Brake HP
HP Vs Brake HP
(OP)
Should we use HP or BHP for the calculation of loads? For example a 20HP load has a BHP=18. We have to size transformer for eight 20HP motors.
If we take HP of motors then: 8*20*0.746 = 119.36 kVA (150kVA transformer required)
But if we take BHP of motors, then: 8*18*0.746 = 107.42 kVA (112.5kVA transformer required)
Please let me know commenst.
If we take HP of motors then: 8*20*0.746 = 119.36 kVA (150kVA transformer required)
But if we take BHP of motors, then: 8*18*0.746 = 107.42 kVA (112.5kVA transformer required)
Please let me know commenst.






RE: HP Vs Brake HP
Mike Halloran
Pembroke Pines, FL, USA
RE: HP Vs Brake HP
The mechanical load does not matter. You could have a motor with nothing connected to it and you'd size the motor feeders and electrical supply the same way.
And your formula is wrong. You've left our motor power factor and motor efficiency.
RE: HP Vs Brake HP
As of motor starting, if the full load current of the transformer is at least six times larger than the FLA of the largest motor, then motor starting should not be a problem and motor starting study should not be required. Is it correct?
RE: HP Vs Brake HP
RE: HP Vs Brake HP
But as David said, you can't use logic or the laws of physics - you have to comply with the NEC. That's why we have codes - to prevent people lacking basic understanding from cutting so many corners that they burn down the building.
RE: HP Vs Brake HP
You cannot use the BHP to size the transformer.The BHP is given by the pump performance curve.Then you should assume a reasonable coupling efficiency and then get the motor HP.Then you have to go the next available motor HP rating to get the actual motor HP.Then you have to see how many are running contineously,or as stand-by or as intermittent to size the transformer.Finally you have to see whether the transformer is enough to start the motors depending on your operation requirements.As dpc pointed out the motor rated voltage is 460 on a 480 V network and your transformer is having 480V no-load sec voltage.