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Which of the following quantity is changed at substations?
Voltage
Current
Frequency
All of above
Voltage
An electrical substation is a subsidiary station of an electricity generation, transmission, and distribution system where voltage is transformed from high to low, or the reverse, using transformers. The primary purpose is to adjust the voltage level to suit long-distance transmission, distribution, or end-user consumption requirements.
An electrical substation is a subsidiary station of an electricity generation, transmission, and distribution system where voltage is transformed from high to low, or the reverse, using transformers. The primary purpose is to adjust the voltage level to suit long-distance transmission, distribution, or end-user consumption requirements.
VsтАЛVpтАЛтАЛ=NsтАЛNpтАЛтАЛ тАФ Transformer turns ratio determining voltage change
P=3тАЛVLтАЛILтАЛcos╧Х тАФ Relationship between voltage, current, and power
The principle of operation is based on electromagnetic induction within power transformers. By changing the number of turns in the primary and secondary windings, the substation alters the voltage level while keeping the frequency constant. Since power (P=VIcos╧Х) remains relatively constant (ignoring losses), a step-up in voltage results in a step-down in current, minimizing I2R transmission losses.
Substations use transformers to step up voltage for transmission to reduce I2R losses.
Frequency is strictly maintained at 50 Hz (in India) and is not changed at substations.
Current varies inversely with voltage to maintain power equilibrium.
Substations also house switchgear, protection equipment, and busbars for network control.
Reduction in transmission line losses
Voltage regulation for stable consumer supply
High capital investment
Requires significant land and maintenance
Power transmission from generation plants
Distribution to industrial and domestic grids
Transmission lines operate at high voltage (e.g., 400kV, 765kV) to minimize current and conductor cross-sectional area.
Frequency (50 Hz) is a grid-wide parameter controlled by generators, not by standard transformers in substations.
Option B is incorrect because current changes as a consequence of voltage transformation, not as a primary control parameter.
Option C is incorrect because transformers are constant-frequency devices.
A is correct тАФ Substations primarily utilize transformers to step up or step down voltage levels to optimize power transmission and distribution.
Always remember the relation V├ЧI=constant; when substations change voltage, current must change to keep power balanced, but frequency remains constant.