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Monday, August 1, 2022

What happens when frequency and voltage change?

In AC electrical system, there are voltage and frequency which are always fluctuating in nature by small or large difference because in a power system. There are many loads and among them, some loads are connected and disconnected at any time due to this reason system voltage and frequency is fluctuating in nature.  For small difference, there is not much affect on the system as well as load.

when frequency and voltage of a system change?


When frequency and voltage of a system change

Generally in a power system, there is theoretically constant voltage and frequency but which is not possible because in a system, there will be load variation. The load in a system is variable all time so that much more fluctuation in load and the generator need to generate only required amount of energy for that governor will help by close or open the valve of water to the turbine and also AVR (automatic voltage regulator) helps to maintain the voltage level. Generally, governor helps to maintain frequency and AVR helps to maintain voltage level. Their value should not change much more, otherwise system may collapse or get damaged or system equipment get damaged. 

Frequency & voltage fluctuation on system

For a system, the voltage level may be varied by ∓ 10% but its value change according to system provider (electricity provider). Similarly, the frequency level may be varied by ∓ (1 - 3)% but also its value may change for different electricity provider. Generally, higher value fluctuation should be prevented for system safety. For example, a system of 220V with 50 HZ frequency is present in a city. Then, its maximum fluctuation value of voltage is (198 - 242) V and frequency is (49.5 - 50.5) HZ for 10% voltage and 1% frequency.

In a power system, change in voltage and frequency may effect the system loads like lights, heater, transformer, motors etc. That's why, in a power system, change is voltage is 10% (less or greater) and frequency is 1 - 3% (less or greater, generally greater). For that value, all electrical equipment will works goodly. We are going to describe about effect of voltage and frequency for lights, heaters, transformers, motors. 

Sensitivity of frequency fluctuation on loads are as follows:-

  • Lights ( incandescent lamp) :- no effect much more
  • Heaters ( heating element) :- no effect much more
  • Transformers :- For low frequency, transformer will heat up and increase losses. For high frequency, voltage increases ( can go up to 20% high of frequency for transformers without causing dangerous fault).
  • Motors :- For low frequency, motors will heat up and increase losses. For high frequency, voltage increases ( can go up  to(5 - 10)% high of frequency for motors without causing dangerous fault). And AC motors go to wrong speed for fluctuation in frequency.

Sensitivity of voltage fluctuation on loads are as follows:-

  • Lights ( incandescent lamp) :- For high voltage, lamps will more glow and bright but it will decrease its life time. For low voltage, lamps will less glow and dim but it will increase its life time.
  • Heaters ( heating element) :- no effect much more
  • Transformers :- For low voltage, there is not much problem with that but for high voltage, heat up the transformer and increase losses (can go up to 20% high voltage without damage).
  • Motors :- For low voltage, motor's torque will reduce but for high voltage, high heat and losses occurs. For DC motors, it will go wrong speed for fluctuation in voltage.
Generally change in frequency will affect the load that are inductance i.e. reactive load such as motor, transformer. Similarly, the change in voltage will affect the resistive load i.e. load with resistance such as heater, incandescent lamp. 

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