Synchronous motor

mary20 · Mar 4, 2011

HI im an apprentice and im studying for my exam was just looking for a bit of help on a few questions please..

If the d.c. supply in a three phase synchronous motor is increased what effect will it have on the operation of the motor
Help Please Thanks

where is the best place to post my questions?

RogertheBodger · Mar 4, 2011

Synchronous motors show some interesting properties, which finds applications in power factor correction. The synchronous motor can be run at lagging, unity or leading power factor. The control is with the field excitation, as described below:

When the field excitation voltage is decreased, the motor runs in lagging power factor. The power factor by which the motor lags varies directly with the drop in excitation voltage. This condition is called under-excitation.
When the field excitation voltage is made equal to the rated voltage, the motor runs at unity power factor.
When the field excitation voltage is increased above the rated voltage, the motor runs at leading power factor. And the power factor by which the motor leads varies directly with the increase in field excitation voltage. This condition is called over-excitation.
The most basic property of synchro motor is that it can be use both as a capacitor or inductor. Hence in turn it improves the power factor of system.

Wish I could claim Authorship of this, found it on the net,
Hope it answers your question.

Steve1412 · Mar 4, 2011

Thats a blast from the past question....did remember though it affected the PF and not the speed!!!!

pushrod · Mar 4, 2011

Was just about to say something similar and then checked if there had been any replies! It would not have been as good as the above!

Steve1412 · Mar 4, 2011

hey Wiki ur so fine ur so fine u blow my mind hey WIKI!!!!!!!!!!!!!!!

RogertheBodger · Mar 4, 2011

Steve1412 said:
hey Wiki ur so fine ur so fine u blow my mind hey WIKI!!!!!!!!!!!!!!!

I already said in my post that I got the information off the net!
Trying to help the OP - what are you trying to do?

Steve1412 · Mar 4, 2011

Chill out!!!!! we could tell it was c & p from some site....just commented that wiki is a good source of information....just in a light hearted manner!!!!!!!

IQ Electrical · Mar 4, 2011

Is anyone noticing problems with the site today?

I replied to this thread and it's disappeared, another thread I replied to has posted twice!

Steve1412 · Mar 4, 2011

IQ Electrical said:
Is anyone noticing problems with the site today?

I replied to this thread and it's disappeared, another thread I replied to has posted twice!

Glad its not just me...thought my laptop had a problem!!!!

RogertheBodger · Mar 4, 2011

Yes IQ the site is very slow today, my posts are coming on twice.

pushrod · Mar 4, 2011

Yeah was getting worried about my laptop as well lol!

Geordie Spark · Mar 4, 2011

IQ Electrical said:
Is anyone noticing problems with the site today?

I replied to this thread and it's disappeared, another thread I replied to has posted twice!

It's running very slow for me today.

Knobhead · Apr 3, 2011

Under excitation you run the risk of phase slip with the danger of sever mechanical damage
Normal or unity excitation the rotor is locked to the synchronous speed. Overload can wreck the motor or drive.
Over excitation causes leading power factor, used on large sites for overall power factor correction. Overload will virtually wreck everything.
When I say overload it’s when the rotor is forced out synchronous and slips one pole. The smallest synchronous motor I’ve come across was 1500HP, imagine that getting hick-ups while running.

Have a look at http://www.lmphotonics.com/ you will find it very useful, I still do.