How Voltage drop makes Bill hike? Fact File 16


Voltage drop in the power line is known as Brown out since it causes the bulb to dim. Brown out is a serious condition which can cause poor performance of electrical or electronic equipments or it may permanently damage them. Voltage drop in the domestic power supply increases power consumption, especially in high current devices using motor and heating element. The increase in current consumption is meant for compensating the voltage loss. This is the reason why the Incandescent bulb becomes too hot in low voltage.

Power consumption of the appliance and the supply voltage are related. As per the equation, I= W/V . Here I is the current consumed in Amperes, W the wattage of the appliance and V is the voltage in the domestic supply. For example, a Fridge rated 300 watts working in  230 volts AC, consumes 300 / 230 = 1.3 Amps current. If the same Fridge operates in 180 volts, its power consumption is 300/180 = 1.6 Amps. That is, an extra 0.3 ampere current is used when there is 50 volts drop in the power line. But if the appliance is a high current device like a 1000 watts heater, the extra current consumed will be large. That is why, the power companies advice to switch off high current devices during the peak hours in the evening if there is voltage drop. When the voltage is too low, the power companies introduce Load shedding which is known as Rolling Black Out.

The major problems related to Voltage drop are
1. Brown Out can cause heating of Motors, Compressors in AC or Fridge. Low voltage also increases the current consumption in these devices to compensate the decreased voltage. Incandescent bulbs generate much heat in low voltage.

2. The mechanical power of Motors will run at low speed and torque in Brown out conditions. Motor will draw more current due to reduced back e.m.f that develops at low armature speed. This may result in permanent damage of the armature by burn out.

3. In CRT monitors, brown out causes shrinking of screen size, dimming etc.

4. In DC power supply, brown out causes the appearance of ripples at the output.

5. In digital circuits, brown out brings the control signals below the threshold at which the logic state is detected. When the input voltage returns normal, the logic state sometimes latch and show incorrect states.

6. In DC power supplies, the output voltage drops when the input voltage drops.

Rolling Black Out

This is commonly called as Load shedding which is the intentionally doing power outage in areas to conserve power. In Rolling Black out, power supply is stopped for non overlapping periods and resume the power after the predetermined time. This done when the demands for the power exceeds the production or power distribution.


Power outage can cause many problems in electric and electronic devices which can be reduced by providing adequate protection systems. These includes, Spike protectors, ELCB, MCB, Surge breakers etc. In computer system, power outage affects data loss and hardware damage etc. So UPS is used in computer systems to avoid this.UPS provides well regulated output free from spikes and transients. If power fails or voltage drops, UPS will instantly takes over the system through back up.

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