Voltage increase in transformer

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fjrivera

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Greetings to all,

During the past few weeks, the voltage in the secondary side of a transformer 8320V-480/277V was around 509V (each phase) with the different loads connected. It was decided to increase the transformer turn ratio. After this change, the voltage in the secondary side of a transformer without any load connected was around 482V (each phase). After the load was connected, the voltage increases to around 492V. So, any theory of why the voltage increased after load was connected.

Thanks!
 
Have you installed anything with a capacitive load? For example, some VFDs have cap banks on the front end.

carl
 
fjrivera said:
Greetings to all,

During the past few weeks, the voltage in the secondary side of a transformer 8320V-480/277V was around 509V (each phase) with the different loads connected. It was decided to increase the transformer turn ratio. After this change, the voltage in the secondary side of a transformer without any load connected was around 482V (each phase). After the load was connected, the voltage increases to around 492V. So, any theory of why the voltage increased after load was connected.

Thanks!
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The capacitors you have on the secondary will cause a voltage rise on the
secondary. Check and see what you have. You may want to remove them
temporarily and check the voltage again.
 
-I'd think some resonant effect, like with capacitors resonating with the transformer inductance, is necessary for this voltage rise. If so, it would be a tuned RLC circuit and depending on the component values you'd see a huge rise in voltage at the resonant peak. Since the change caused more voltage, you are heading toward, and not away from, the peak.
-With no resistance in the circuit, the simple formula for resonance is f = 1/(2pi)[(LC)^0.5]. F is the resonant frequency, Pi = 3.14 and you probably know the C value.
-If you know the transformer inductance you could find the resonant frequency. There's a different formula for parallel resonant and series resonant circuits.
-Same with an "8 ohm" loudspeaker. At resonance the impedance goes way above 8 ohms.
 
Double post, still struggling with HughesNet due to incompetence of Verizon. They installed over 700 yards of fiber to my house but ran it down the wrong right of way to a telco box with no fiber connection. Now they have to re-run the fiber, this will take weeks to get completed due to their scheduling.
 
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And while all this is more than possible there is also a change in primary voltage, other users on the line and their changing power usage or automatic tap changers changing due to changes in loads on the distribution system.


Did you monitor the voltage on the transformer secondary over a long period of time or did someone notice the higher voltage at possibly a time of small loads and decide to change the tap setting without looking at the WHOLE picture.
 
ferro-resonance

ferro-resonance

I Googled the term above and also looked at your reference (which had a formula for resonant circuits). Unfortunately I have already chucked my ancient text on magnetic circuits.

I do think regulation is a different physical concept than resonance.

I suppose you could have a constant voltage transformer inadvertently connected to a resonant circuit. I don't know if this would be stable; system stability criteria is a whole 'nother thing. And some regulators overcompensate, raising the voltage in face of increasing load, instead of keeping the voltage constant or slightly dropping it.

What the heck. . .I plead "no comprende."
 
ferro-resonance

ferro-resonance

Scratch that, I found "magnetic circuits and transformers".

They talked about a problem with 3rd harmonic resonance in Y-Y banks of transformers. I don't know if this is relevant to the problem at hand; I did mostly electronics after I got out of school.

I think the generic term for all these components, including transformers and saturable reactors, used to be "iron core reactors."
 
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