Motor Theory

[DM7.ENG]

Thats why I wrote V/Z rather than V/R to consider losses as a result if R+JXL-JXC I.e capacitive & inductive reactances.

 

[Besoeker]

This is the circuit I use to model motors for performance calculations.

It's the Stienmetz equivalent circuit. All values are referred to the stator side.
You are not normally given component values but I have developed an interactive spreadsheet where I can estimate them from fixed speed data. I've needed to do this to provide guaranteed efficiency figures for VSD applications.

I don't know if this will work......

Power Rating (kW)	(kW)	500
X1	(W)	0.0531
R1	(W)	0.0071
Xm	(W)	2.00
Rm	(W)	121
X2'	(W)	0.075
R2'	(W)	0.00723
Windage & Frict	(kW) 8

If it does, you will see that the X component of each branch exceeds the R by about an order of magnitude.
I perhaps ought to add that this was for an actual motor that was installed in a pumping station.

The "W" is omega for ohms.

 

[shanky887614]

A bit loose in my explanation, I meant the generation of the magnetic field and its interation with the rotor to create a turning force limits the current flow, remove the rotor and you have just got 3 windings with very little resistance and then ohms law will take over - very high current which will either burn out the winding and/or take out the fusing.

I was keeping it simple so as not to let it get confusing, motor theory can get very complex very quickly so was just expressing the resistance of the windings may not have a calculating factor on the current drawn by the motor.

is there any books or anything that go more indepth into motor theory than say the standard this is an induction motor etc

 

[DM7.ENG]

Just 1 last thing to add to this conversation. Can anyone clarify why the current drops by a third when in star in comparison to delta. The impedance doubles as there is 2 windings between phases so why does the current not half?

is there any books or anything that go more indepth into motor theory than say the standard this is an induction motor etc

 

[UKMeterman]

Have a read Electric Motors and Drives: Fundamentals, Types and Applications: Amazon.co.uk: Austin Hughes: 9780080983325: Books ask your college library to get it in.