Inside a substation, transformers raise or lower voltage using electromagnetic induction. Circuit breakers, switches, relays, busbars, and insulators control the path of current and isolate faults before equipment is damaged. A step-up substation near a wind or solar farm may raise voltage from about 34.5 kV to 115 kV or higher for transmission.
A distribution substation later steps voltage down so neighborhoods, schools, and businesses can use the electricity safely.
Key Facts
- Transformer voltage ratio: Vp / Vs = Np / Ns
- Ideal transformer power: VpIp = VsIs
- Electrical power: P = VI for direct current or simplified single-phase circuits
- Three-phase power: P = sqrt(3) V I power factor
- Higher voltage reduces current for the same power, which lowers heating losses.
- Power loss in wires is P_loss = I^2R, so cutting current greatly reduces wasted energy.
Vocabulary
- Substation
- A substation is a grid facility that changes voltage, switches power routes, and protects electrical equipment.
- Transformer
- A transformer is a device that uses electromagnetic induction to increase or decrease AC voltage.
- Busbar
- A busbar is a thick metal conductor that connects multiple circuits inside a substation.
- Circuit breaker
- A circuit breaker is a switch that opens automatically to stop current during a fault or overload.
- Insulator
- An insulator is a material or support that prevents electric current from flowing where it should not.
Common Mistakes to Avoid
- Thinking a substation generates electricity is wrong because it mainly changes voltage, routes power, and protects the grid.
- Ignoring current when voltage changes is wrong because in an ideal transformer, raising voltage lowers current for the same power.
- Using P = VI for every grid problem without checking conditions is wrong because real AC systems often require power factor and three-phase relationships.
- Assuming circuit breakers only protect people is wrong because they also protect transformers, lines, and other grid equipment from fault currents.
Practice Questions
- 1 A wind farm sends 20 MW of power to a step-up transformer. If the transmission voltage is 100 kV and power factor is ignored, what current flows in the line using P = VI?
- 2 A transformer has 500 turns on the primary coil and 5000 turns on the secondary coil. If the primary voltage is 13.8 kV, what is the secondary voltage?
- 3 Explain why a renewable energy substation often raises voltage before sending electricity over long transmission lines, and name two devices in the substation that help protect or route the power.