In India we normally have 220V to 240V AC supply, but we have some problems in our area. The normal voltage normal is 260V to 290V, the service provider company is irresponsible, so I am handling it with servo stabilizer and reduce it to a safe range of 220-240V. During the night (11:30 PM to morning 5:00AM,) the voltages surges up to 310V and it is beyond my stabilizer range.

There is an automatic relay controller that cuts the main supply if the voltage is more than 300V. Then it monitors the voltage for some time. If it is unsafe, the main supply remains disconnected permanently (and then relay has to be reset manually, even if supply goes safe it does not start automatically.) Due to this, the UPS remains active and the battery goes down by 5AM.

Due to 300+ voltage, when the main supply is disconnected by the relay, some reverse current continues, resulting in LED and tube lights corners to glow slightly, even though they are switched off. There is an RCCB after the rlay. When it is switched off manually, LED and tube lights corners does not glow.


  1. First the supply comes to the relay that has a range of 145V to 300V. The upper limit is set to 16 amperes, which is sufficient.
  2. Then, there is 63ampere RCCB for shock protection, current leakage (30mA protection)
  3. Then there is the servo stabilizer 3KVA range 145V to 300V
  4. Then there is the UPS 1.5KVA

I want some solution that will reduce extra voltage from 290V to 335V with addition of some circuit.


2 Answers 2


My sympathy with you about your situation.

The servo stabilizer seems to be a mechanical AVR (automatic voltage regulator), or a motor driven Variac (variable transformer).

Since your problem occurs due to the stabilizer limit at high side, this would be the simplest solution:

  1. Step down the line using a transformer, 310V to 240V.
  2. Connect the stabilizer to 240V winding.

This solution will cover as high voltage as up to 310V. Meantime, when the line voltage dips to the lowest voltage, of 220V, the transformer will produce: (220V x (240/310)) = 170V.

Thus, your stabilizer should be able to boost 170V to 220V or higher.

All the best,


In North America, we have no need for servo conditioners as the grid must be regulated within 10% and is usually 5% in Toronto.

These devices when used by many on a poor regulated grid actually makes the grid more unstable by drawing more current when the grid is low.

I suggest you buy a 3kVA Variac and set it to 80%. That should be less than $80usd.

A Servo conditioner is just a servo controlled Variac or perhaps a relay controlled tap-changer.


Someone with the necessary skills could possibly modify the Conditioner with more windings on the primary input to drop the voltage 20%.


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