1. Shunt Capacitor
Connection: In parallel (shunt) with the system.
Purpose: Improve power factor and support voltage.
Why: Many loads (motors, transformers, fluorescent lights) are inductive and draw lagging current, causing poor power factor, higher line losses and lower efficiency.
How it works: A capacitor draws leading current which cancels part of the inductive current when placed in parallel with the load. This reduces total current from the supply and improves efficiency and voltage.
Benefits:
- Improves power factor (reduces utility penalties).
- Reduces line losses.
- Supports voltage under heavy load.
Analogy: The inductive load leans backwards while walking — the capacitor pulls them slightly forward so both walk upright.
2. Series Reactor
Connection: In series with the circuit (feeder, transformer, or capacitor bank).
Purpose: Limit short-circuit current and filter harmonics.
Why: Faults create huge current; some loads (motors, arc furnaces) draw non-sinusoidal currents (harmonics) that distort the waveform. Without added impedance, harmonics flow freely and cause problems.
How it works: The reactor (coil) adds inductive reactance in series. This opposes sudden changes in current and filters high-frequency harmonics. In capacitor banks it prevents resonance with the network.
Benefits:
- Limits fault current to protect breakers and transformers.
- Reduces harmonic distortion.
- Increases system stability.
Analogy: A speed bump — it slows down excessive current spikes while allowing normal traffic.
3. Series Capacitor
Connection: In series with the transmission line.
Purpose: Reduce line reactance and improve power transfer capability.
Why: Transmission lines have inductive reactance (XL) which limits active power transfer and causes voltage drop—especially over long distances.
How it works: A series capacitor provides capacitive reactance (negative reactance) that cancels part of the line's inductive reactance. The net effect is lower total reactance, better voltage profile and higher power transfer.
Benefits:
- Increases maximum transmittable power.
- Improves voltage stability over long distances.
- Reduces need for constructing new transmission lines.
Analogy: Making a hilly road less steep so cars (power) can travel faster and easier.
4. Shunt Inductor (Shunt Reactor)
Connection: In parallel (shunt) with the line or network.
Purpose: Absorb excess reactive power and control overvoltage (Ferranti effect) under light-load conditions.
Why: Long transmission lines behave capacitively when lightly loaded, which can raise the receiving-end voltage (the Ferranti effect). Overvoltage can damage equipment.
How it works: The shunt inductor draws lagging current to cancel the line's capacitive effect, bringing voltage down to safe limits.
Benefits:
- Controls overvoltage during low-load or no-load conditions.
- Protects equipment and insulation.
- Maintains stable voltage profile.
Analogy: Putting a weight on a floating balloon to keep it from rising — the inductor pulls the voltage back down.
Summary Table
| Device | Connection | Main Purpose | Cancels | Typical Use Case |
|---|---|---|---|---|
| Shunt Capacitor | Parallel | Improve power factor, support voltage | Inductive reactive power | Factories, distribution networks |
| Series Reactor | Series | Limit fault current, filter harmonics | — | Capacitor banks, arc furnaces, feeders |
| Series Capacitor | Series | Reduce line reactance, increase power transfer | Inductive reactance of line | Long transmission lines |
| Shunt Inductor | Parallel | Absorb excess reactive power, reduce overvoltage | Capacitive reactive power of line | Long EHV lines during light load |