Can transformers withstand 300V ?

I am using a 220V AC primary and 12-0V secondary for power supply in a circuit. I want to know whether these transformers can withstand 300V at primary side because voltage sometimes increase here to 300V and comeback to normal in 30 minutes or 1 hour. So, during this time will the transformer burn out ?

The secondary of trf is rated at 12V 500 mA.

Only the transformer manufacturer can tell you that for certain.

I would *guess* that if you are running it at under say 50% load current it would be OK. A relatively small increase of input voltage would not cause physical damage but the heat produced will increase and if it is already under strain it may be enough to overheat it and cause permanent failure.

Brian.

Standard transformers are designed for the expectable voltage variations according to international standards. The positive tolerance is +10 or even +15% maximum. I would expect partial saturation and respective high magnetizing currents for most transformers at 300 V. Depending on the transformer type, it could overheat even with no load.

The current rating of secondary is 500 mA and my circuit will draw a max current of 250 mA when the relay is ON and 150 mA less current than this when relay is OFF. Is it better to use a 12V 500 mA buck power supply instead ? will that handle the high voltage which appear sometimes ? I just want to make my system fail proof.

I am talking about these power supplies.

**broken link removed**

https://www.aliexpress.com/w/wholesale-switching-power-supply-220v-12v-500ma.html

Are these better than ordinary transformer based power supplies ?

I feel that the transformer will overheat during a 300V overload, so might only last 500 Hrs at this voltage. The only true test is to run it and measure the input voltage and input current. Plotting these will give a straight line up to the core saturation point. If the graph curves upwards, you are taking more current then required for a given voltage. So the difference between your straight bit and the curved bit will give you the excess current, times this by the voltage, will give you the amount of excess power being dissipated in the core. A PTC in series with the feed might work.
Frank

just use two transformer in series if u r a hobbyist n not want spend much... hihi
if u r manufacture.. go n order transformer with primary 300 v n secondary in ratioed of that 300..
next design good regulation
simple as best.... i.ve done this in a village of my neighbour

Under conditions like yours, I would find a transformer rated to 350V primary to be on a safe side. You can also put two 240V transformers in series, then use a regulator on the secondary DC output to stabilize the output voltage.
The situation is bad and solving it may not be easy. Even commercial AC voltage regulators usually cannot handle input voltages exceeding 250-280 V.
Another solution is to find a switcher type AC/DC converter, and use a series resistor to drop any input voltage to 240 V max. Such AC/DC converters operate well from 95 to 240 V AC input,so with an overvoltage protection resistor they will work well for wide AC input variations.
How other utilities survive your AC mains going to 300 V? Motors, refrigerators, microwave ovens must die soon! Maybe it is time to switch AC power provider as he makes the situation dangerous.

To keep costs low, steel core transformers operate at a flux density of around 1.5 Tesla at nominal voltage, with a 15% overvoltage rating which takes it to about 1.7 Tesla.

What you are proposing is to operate the core above 2 Tesla. This condition will severely overheat the core and draw a lot of current, even without any load.

You don't mention if your power is either 50 or 60 Hz.
If by any chance you live in a 60 Hz area, you could buy a transformer rated for 220V, 50 Hz, because operating a 50 Hz transformer with 60 Hz allows a 20% higher voltage, while maintaining the same flux density.