start voltage current relationship
start voltage current relationship
(OP)
Start voltage / amprage relation ship was given to me by one of our engineers as
Arated/Ameasured = Vrated/Vmeasured
so that if you see a V drop at the motor you will also see a decrease in Ampreres.
Is this correct????
Arated/Ameasured = Vrated/Vmeasured
so that if you see a V drop at the motor you will also see a decrease in Ampreres.
Is this correct????





RE: start voltage current relationship
RE: start voltage current relationship
During the starting condition yes, the voltage drop will reduce the inrush current proportional to the line voltage drop.
Under a steady HP load condition, the current will increase with a drop in voltage.
IL = HP*746/(1.73*VLL*EFF*PF)
Were
IL = Line current under load
HP= shaft load in Horse power.
VLL= Line to line voltage
EFF = motor efficiency ( regularly it will drop a while with lower voltage)
PF = motor power factor.
RE: start voltage current relationship
The software that we use calculates the start current from the Irms, Irms/Vrms X Vrated = Istart is that also correct if we have a correct voltage. The motor start I is estimated by the manufacturer because they do not manufacture or assemble the whole motor we do.
RE: start voltage current relationship
The start current reduction is independent of load, but if the current / voltage is reduced too far, there will be insufficient torque to accellerate the load to full speed.
The start torque reduces with the squaare of the voltage or current reduction.
Best regards,
Mark Empson
http://www.lmphotonics.com