In a corner of the distribution substation stand rows of clustered metal cylinders: the capacitor bank. They don't transform voltage or interrupt current, but they spare the network wasted capacity and support its sagging voltage — a hidden function worth understanding.
Construction of a Capacitor
At its core, a capacitor is two conductive metal plates separated by an insulating material (dielectric). In actual manufacturing, layers of metal and dielectric are wound together, and the two metal ends are brought out of the cylinder for connection — in series or parallel depending on the required voltage and capacitance. Its capacitance is measured in farads (F), and in practice in microfarads (µF).
Its fundamental property is storing electrical energy, retaining it, and then discharging it on demand in a fast, orderly manner — and this same property is the source of its danger during maintenance, as you'll see in Capacitor Discharge.
Why Are They Installed in Distribution Substations?
- Improving power factor: inductive loads (motors, air conditioners) draw reactive power that burdens the network; capacitors compensate for it locally, reducing the total current — details in Power Factor Improvement.
- Raising voltage and compensating for voltage drop: the reactive current flowing through line impedance causes a voltage drop; compensation recovers part of this drop at the line ends.
- Freeing up capacity: reducing reactive current frees up capacity in transformers and cables to serve additional real loads.
Where and How Are They Installed?
- Units are grouped into banks inside cabinets or open-frame structures, with bushings similar to those used on transformers.
- Installed in three-phase systems: near substations, on poles in overhead networks, and in factory panels.
- Protected by circuit breakers or fuses, just like transformers.
Sample answer: Their primary function is to improve power factor by compensating for the reactive power drawn by inductive loads, which leads to raising voltage and compensating for voltage drop along the lines, and freeing up capacity in transformers and cables. A capacitor consists of two conductive plates separated by an insulating material, wound in layers with their ends brought out for connection, with capacitance measured in microfarads, and its key property is storing energy and discharging it quickly and in an orderly manner when needed.
Assuming that capacitors "generate" real power that directly saves on the bill. A capacitor doesn't generate kilowatts; it compensates for kilovars (reactive power), which reduces current, losses, and low-power-factor charges — the savings are real, but the mechanism must be correctly understood.
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