# Overvoltage limiting

A

#### Anonymous

Hi,

In our plant, when the production stop for one day, there's less charge on the electrical system. That cause the voltage to go up to about 520Vac (normally 480Vac) at the end of the plant (the cable run is maximum).

The problem is we got some drives that doesn't support that overvoltage and blow out.

Is there a way to keep the voltage to 480Vac even if we stop the production??

C

#### Curt Wuollet

Better wiring and transformers with better load regulation. This is typical when voltages decrease with load and taps are changed to compensate rather than using larger conductors to avoid the voltage drops. When the load decreases and the voltage drops go away, the transformer ratios are wrong for the higher voltage and you fry stuff. Or if the transformers are loaded too heavily and tapped to make up for it, when the transformer is unloaded, the voltage goes high. You can get conditioners and regulators, but these tend to be point solutions and more expensive than correcting the problem. Hopefully the problem is in your plant. If your service is changing a lot with load, you have to have a chat with the local utility. It's fairly easy to find out where the drops are occurring.

Regards

cww

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#### uday rajhansa

When the cable length is high the voltage at the end of unloaded lines may become higher. First measure the volatge at the time when the line is loaded and note down. See what is the difference between the loaded and unloaded line voltages. Set the transformer tap position in such away that the voltage is 480 V in unloaded condition. Voltage drop will take place when the line is loaded, if the loads are resistive or inductive in nature. For improving the voltage use capacitors of appropriate ratings, which can be made to switch on or off automatically as the voltage drops/rises up to certain level.

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#### Phil Corso, PE

Posted on 1x-Aug-07 (X:X) by Phil Corso, PE
Responding to Anonymous’ 09-Aug (19:04) query, technically speaking, it is not an “overvoltage problem”, but instead a “voltage-spread” problem. Before, corrective action can be taken, or ecommendations for such made, please provide the following information:

1) What is the actual LV-bus measurement at the time of normal load?
2) What is the actual LV-bus measurement at the time of maximum voltage?
3) What is the primary voltage, presuming there is a utility-fed stepdown transformer, for 1)?
4) What is the primary voltage, presuming there is a utility-fed stepdown transformer, for 2)?
5) Is most of the utilization apparatus rated at 460-V or 480-V?
6) Who has responsibility for the transformer?
7) Can you provide the type of electrical load, i.e., mostly heaters, motors, or if both, do you know the ratio?
8) Does electrical load contain capacitor-banks for power-factor compensation?