- #1

Loz30

- 2

- 0

A Synchronous motor is coupled to a DC Compound Motor.

The DC Machine is rated for 220 V DC. Its Armature Resistance is 1.0 Ω .

The Synchronous Machine is a 4 pole 400 V 50 Hz 3 Phase AC Machine with an efficiency of 80%.

Since Synchronous Motor is not self starting , the DC Machine is run as a Motor first with a Terminal Voltage of 220 V DC. When both the Machines are up to speed AC Power and DC Power (For Field ) are switched on to the AC Machine to Run as Synchronous Motor.

Now the DC Machine starts to run as DC Generator and delivers power at a current of 20 Amps.

1) Determine the input Active power to the Synchronous Motor

2) Determine the Efficiency of DC Generator

I know I can calculate the nominal speed of the AC machine given the frequency and number of poles N=(120f)/p which works out to be 1500RPM but I don't have the torque so I can't calculate the power from that.

I've also tried starting from the DC machine side when acting as a generator, but I'm only able to calculate the armature power from it's resistance and the output current which is P=I

I know I can calculate the nominal speed of the AC machine given the frequency and number of poles N=(120f)/p which works out to be 1500RPM but I don't have the torque so I can't calculate the power from that.

I've also tried starting from the DC machine side when acting as a generator, but I'm only able to calculate the armature power from it's resistance and the output current which is P=I

^{2}R=20^{2}X1=400W..I'm not looking for the whole solution, but I would greatly appreciate a little help to get me on the right track so I can work it out on my own.

Thankyou very much!