My question is very simple
Why low voltage or voltage fluctuation cause non motor load to burn like filament bulbs , energy saver bulbs?
In low voltage how does we the current increases for non motor load as power is not constant because the light of bulbs get dimmer it means the bulbs is not receiving its required power so how does the it burns.
In motor at low voltage the motor speed becomes slow so why does its winding burn out ? why the current increases in low voltage while the speed also falls down?
Hi Ahmed,
I am afraid the first part of your question (the part on non-motor loads) is not too clear. Would you like to restate that part ?
The second part (about motor loads) is easily answered. At low voltage the motor loads do slow down, but that brings them closer to blocked-rotor (or stalled) condition. And we know that the blocked rotor current is much higher than rated current. So as the rotor slows down, the current becomes progressively high leading to occasional winding burn-outs.
-Sanjay
W=VICos(phi)=loss+mechanical load, hence if voltage is reduced than the permissible limit, for same mechanical loading, the excess current would over heat the motor, and damaged on long run.
Motor current = (motor voltage applied - motor back emf) / winding resistance.
As the motor slows the motor back emf drops so the numerator increases and the ohmic loss in the winding increases. Ultimately it burns out.
Winding power = motor current ^2 x winding resistance.
Sir thank you for clearing motor load query but why low voltage or voltage fluctuation burns bulbs
If there is a surge of voltage then it can burn a bulb, because the filament is operating near its maximum temperature to get the greatest efficiency possible from a thermal lamp. Low voltage won't normally destroy a bulb - but with tungsten halogen bulbs, they work by combining the tungsten evaporated from the filament with the halogen, then if they are not operated at full voltage the filament won't get hot enough to decompose the tungsten halide back to tungsten and maintain the filament thickness, and their life will shorten - a little.
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