Transformer circuit / General Science and Electronics / Forums

Forums

4hv.org :: Forums :: General Science and Electronics

« Previous topic | Next topic »

Transformer circuit

1 2 next

Move Thread

LAN_403

IamSmooth

Mon Nov 23 2009, 09:11PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

what does a transformer do to phase of the outgoing voltage and current? If voltage and current are in phase going into a transformer, what is the voltage and phase coming out? Is it the same, shifted by 90, or 180 degrees?

Sulaiman

Mon Nov 23 2009, 09:41PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

The output voltage is in phase with the input

(for now it's an 'ideal' transformer)

The output current will be determined by the output load
The input current will be in phase, with the same waveshape but scaled by the transformer ratio.

Due to leakage inductance, magnetizing current etc etc.
phase and waveform distortions will be present.

doctor electrons

Tue Nov 24 2009, 12:11AM

Registered Member #2390 Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381

If you have the schematic (usually on it) for the transformer the black dots shown near the windings are the
phase indicators. It will show what phase ends up where on its way through the transformer. To answer one of
your questions, when the leads are attached to the transformer, if you need a phase to remain the same on the secondary
the dots should match up, ie phase 1 on primary dot, phase 1 secondary dot. Then there would be no change. When you
start switching the leads is when you can be 180 out and such.

IamSmooth

Tue Nov 24 2009, 02:15AM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

doctor electrons wrote ...

If you have the schematic (usually on it) for the transformer the black dots shown near the windings are the
phase indicators. It will show what phase ends up where on its way through the transformer.

you are referring to the polarity: which end is going positive on the secondary if the primary input is going positive. I am referring to the phase of the current and voltage, which is not the same thing. Whether or not the voltage is going up or down, I wanted to know if the current was in synch with the voltage.

Coronafix

Tue Nov 24 2009, 03:56AM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

The current is 90deg out of phase with the voltage in a transformer, both out and in. If they were in phase then power would be being used. The load may sag the phase angle somewhat but by adding the correct amount of capacitance reactance (PFC cap) it can lessen this lag and therefore reduce the losses.

IamSmooth

Tue Nov 24 2009, 04:20AM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

But the current leaving will be in phase with the current entering?

doctor electrons

Tue Nov 24 2009, 04:52AM

Registered Member #2390 Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381

Both should be in phase if you follow the "phasing indication dots" on the transformer. Those marks ARE for phasing as well. A positive peak on one end will correspond with the peak on the other. Voltage and current. Otherwise you could scope it and get 2 opposite waveforms. If it is connected according to the diagram you will get one waveform. IE current and voltage without shift. One "correct" sine wave. Transformers are not designed to be a current storing device. Someone can, and should correct me if i am not correct. Usually this is why the power company will install a cap outside your shop if you start running too many motors. The load should ultimately determine whether the v and i are shifted or not. The ol eli the ice man idiom. Voltage leading current in an inductive circuit, and current leading voltage in a capacitive circuit. The transformer should not cause a significant shift. The induced potential will be steady enough if you do not exceed the kva or fla rating of the transformer to produce power that is in phase. There is a transformer hanging on the pole outside your house and your voltage and current are in phase right?

Patrick

Thu Nov 26 2009, 01:29AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

I think siuliman's explanation is well said.
But if you need to be sure scope it out with a sig generator , and then again with your actual circuit. In this waY you can plot current with one trace and the voltage with the other, on the secondary side. but the phasing dots are my preferred method when available.

-Patrick

Nik

Thu Nov 26 2009, 05:10AM

Registered Member #53 Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638

The output current is inphase with the output voltage (unless you have inductive/capacitive loads on it). The output voltage should be in phase with input voltage. (Spent a week on this in trade school)

wylie

Thu Nov 26 2009, 06:12AM

Registered Member #882 Joined: Sat Jul 07 2007, 04:32AM
Location:
Posts: 103

I wish we could vote on posts. I think Nik summed up Sulaiman's and Coronafix's collective points very concisely.

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob