Maharashtra HSC Power Distribution Lineman (NSQF) key terms

The fixed relationship in a circuit where voltage equals current multiplied by resistance (V = I × R). It lets a lineman predict how current changes when resistance or supply voltage changes.

A circuit where components connect end to end so the same current flows through each one and the total resistance is the sum of the individual resistances.

A circuit where components connect across the same two points, so each receives the full supply voltage and the total current is the sum of branch currents.

An AC supply using three conductors whose voltages are equal in magnitude and displaced by 120 electrical degrees, giving constant power delivery and two useful voltage levels from one transformer.

A transformer or motor winding arrangement where one end of each of the three phases joins at a common neutral point, so line voltage is 1.732 times phase voltage.

A winding arrangement where the three phases connect end to end in a closed loop, so line voltage equals phase voltage and line current is 1.732 times phase current.

The ratio of real power in watts to apparent power in volt-amperes in an AC circuit. A low value means more current flows for the same useful work, increasing losses and voltage drop.

The reduction in voltage along a conductor caused by current flowing through its resistance and reactance. Excessive drop at the consumer end causes dim lights and motor starting problems.

The stage where mechanical or other energy is converted into electrical energy at power stations, typically at 11 kV to 25 kV, before being stepped up for bulk transport.

Bulk movement of electrical power at high voltage, commonly 66 kV and above, over long distances between generating stations and load centres to keep losses low.

The final stage of the power system that carries electricity from substations at 33 kV, 11 kV and 400/230 V to individual consumers through feeders, distributors and service mains.

A conductor or line that carries power from a substation to a distribution point or another substation. It is designed on current-carrying capacity, not on voltage drop at its far end.

A line from which consumers are tapped at intervals along its length. It is designed mainly to keep voltage variation within limits at every tapping point, not just at its end.

Aluminium Conductor Steel Reinforced: stranded aluminium wires around a galvanised steel core. The steel carries tension and the aluminium carries current, giving a strong, economical overhead conductor.

The vertical dip of a conductor between two supports caused by its own weight and tension. Correct sag keeps tension within limits and maintains the required ground clearance.

The minimum vertical distance between the lowest conductor and the ground, road or building below, laid down in the supply code for each voltage and location.

A galvanised steel guy wire anchored to the ground or a structure to resist the unbalanced pull of conductors at a pole, especially at angles, terminations and crossings.

A porcelain or polymer insulator fixed on a pin on the cross-arm of a pole, used to support conductors on distribution lines up to about 33 kV.

A string of ceramic or glass discs linked together to support and insulate high-voltage conductors. More discs are added for higher voltages to give the needed creepage and withstand.

The shortest path along the surface of an insulator between its live and earthed ends. It must be long enough to prevent surface flashover in polluted or wet conditions.

A transformer that steps 11 kV or 33 kV down to 400/230 V for consumers. It is rated by kVA, has ONAN cooling and a tap changer for adjusting secondary voltage.

A tapping switch on a distribution transformer that changes the turns ratio to correct secondary voltage. It must only be operated when the transformer is isolated and dead.

An instrument transformer that reduces line current to a standard low value for metering and protection. Its secondary must never be open-circuited while primary current flows.

An instrument transformer that reduces high voltage to a standard low value for meters and relays. Its secondary must never be short-circuited while energised.

An instrument that integrates power over time and records energy consumed in kilowatt-hours. It is the basis for consumer billing and for energy accounting on feeders.

Fixing tamper-evident seals on the meter cover, terminal cover and meter board so that any attempt to open, bypass or reverse the meter can be detected during inspection.

The complete arrangement from the distributor or pole to the consumer's premises, including service cable, meter board, meter, main switch and earthing, done after the load demand is sanctioned.

Making a permanent electrical and mechanical connection between two cable ends or conductor lengths, using ferrules, insulation and heat-shrink or tape to restore insulation strength.

Preparing a cable end to connect to equipment or an overhead line, using a cable lug, pot end or stress-relief kit so the insulation withstands the applied voltage.

A metal fitting crimped or soldered onto a conductor end to provide a flat bolted connection to a terminal. Its size must match the conductor and the terminal bolt.

A hand or hydraulic tool that compresses a lug or ferrule onto a conductor with a controlled die pressure, giving a low-resistance joint without heat or solder.

Deliberately connecting the non-current-carrying metal parts of equipment and the neutral point to the general mass of earth to keep touch voltage safe and clear faults quickly.

The resistance between an earth electrode and the surrounding soil, measured with an earth tester. It must be low enough for protective devices to operate within the required time.

A protective device that trips when the current difference between live and neutral conductors exceeds a set value, such as 30 mA, protecting people from electric shock.

Opening and locking off all sources of supply to a circuit or apparatus so that it is dead and cannot be re-energised until the lock and tag are removed by the authorised person.

A written authorisation issued by an authorised person that names the work, the isolation points, the safety precautions and the time limit before work on electrical apparatus may begin.

Proving an isolated circuit is de-energised by testing with a proven voltage detector on all conductors and phases, then applying an earth before touching the conductors.

A personal fall-arrest device of straps worn around the shoulders, chest, waist and legs, attached by a lanyard to a sound anchor point while working at height.

Planned recovery of a person who has fallen or is suspended in a harness, or has been shocked on a pole, using trained personnel, rescue kit and a controlled lowering method.

Chest compressions with rescue breaths given to a person who is unresponsive and not breathing normally, continued until trained help arrives after an electrical shock.

A test using a megger to apply a high DC voltage and measure leakage across insulation, proving that a transformer, cable or motor is dry and safe to energise.

A portable instrument that applies a high DC test voltage, commonly 500 V or 1000 V, to measure insulation resistance in megohms and detect moisture, dirt or damaged insulation.