The other problem that you would have, is that while the motor is spinning and the rotor field has not decayed, there will be voltage across the terminals preventing you from making DC measurments. The generated voltage drops away with time and this dcay dpends on the time constant of the rotor circuit, but typically, you need to disconnect the motor for more than 0.5 seconds to eliminate it. When the motor is reconnected, the generated voltage will not be synchronised to the supply, so effectively, you can be closing on to a much higher voltage than is usual. The voltage and frequency are dependent on the motor speed. When the stator is disconnected, the motor behaves like a generator, generating voltage out its terminals. The problem is that while the motor is being driven, there is a rotating magnetic field in the stator which is where the torque is derived from. This can break rotor bars, couplings and do a lot of damage to the driven load. Open transition switching causes very high current and torque transients at reconnection. Your idea of turning off the power to the motor for a cycle or so in order to make a measurement could result in major problems and damage. RE: Calculating motor winding temperature charlierod (Electrical) /Precise motor feeder leads impedance calculations are suggested, either by hand or by computer.\\\ Any comments about this?, Does anyone have experience in applying the resistance method? Second, motor terminals are not readily available so most of measurements will have to be performed in the motor control center (corrections to be made to account for feeder resistance). /The ohmmeter that is more accurate is called:ĭigital Low Resistance Ohm (DLRO) meter. Until i show the method works at least for smaller motors). /Normally, it is tacitly assumed that whoever has 200HP motor and associated hardware or production means will have a smaller amount of money reserved for the necessary maintenance, testing, measurements, etc.\\\ First, we got motors with nominal powers up to 200 HP and this implies the use of a special kind of ohmmeter (wich i'm afraid is not available at the company and they won't be willing to buy one I'm thinking about applying the resistance method but i got two problems. RE: Calculating motor winding temperature charlierod (Electrical)Ĭomment on charlierod (Electrical) marked ///\\\ I find really interesting all these motor thermal issues. Any comments about this?, Does anyone have experience in applying the resistance method?Īgain, thanks for your help.
First, we got motors with nominal powers up to 200 HP and this implies the use of a special kind of ohmmeter (wich i'm afraid is not available at the company and they won't be willing to buy one until i show the method works at least for smaller motors).
I think those estimations are valid for the motor they use in the calculations but are not standard values.
Can anyone explain it?Īlso in the document "INDUCTION MOTORS: PARTI-Analysis", the authors made some aproximations that i cannot realize (Rs = Ro/5, Xs = X1/2 and the way they find the value for Xo). I still don't understand the model wich uses R1/Ro as a capacitance value.
Before reading your posts i've already obtained such on line papers which i have found really helpful.