# Efficiency of a synchronous machine.

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1. Jan 30, 2016

### Sharples049

1. The problem statement, all variables and given/known data
The armature resistance per phase is given as 24.7ohms.
Delta configured machine.
Open circuit voltage is 220v, short circuit current is 1.1A at 3000rpm.
Rpm is dropped to 1500rpm and no load line voltage is 100.
Find power and efficiency if an inductive load of 1.4H is applied at the load.

2. Relevant equations
As per synchronous machines electrical theory.

3. The attempt at a solution
Still working on it but simulation results aren't the same. Any help will be appreciated thankyou.

2. Jan 30, 2016

### cnh1995

You need to show your attempt. You can start by calculating the synchronous impedance (Zs) from OC and SC data given.

3. Jan 30, 2016

### Sharples049

ok so far i have Zs to be 200ohms from the OC and SC data. By substituting the armature resistance to find the synchronous reactance Xs, I have Xs to be 198.5ohms. This is where i'm becomming stuck, it is a delta configured machine so i'm unsure of what the equivalent circuit values will be in order to calculate power.

4. Jan 30, 2016

### cnh1995

Since this is delta configuration, VL=Vph=100V.

5. Jan 30, 2016

### Sharples049

I'm stuck after that mate. Haven't done much on synchronous machines. Will the equivalent circuit be made up of the 24.7ohms and inductance calculated from Xs, then the load? Or will the Ra and Xs values be different due to the delta formation?
Any help will be much appreciated.

6. Jan 30, 2016

### cnh1995

The values will not change in delta. You can use them as they are.