Maharashtra HSC Power Distribution Lineman (NSQF) flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Ohm's law

For a resistive circuit, voltage equals current multiplied by resistance (V = I × R). Power equals V × I, and can also be written as I²R or V²/R.

Parallel circuit resistance

Branches share the same voltage, and total resistance is found from the reciprocal sum of branch resistances. Total resistance is always lower than the smallest branch.

Three-phase power formula

For a balanced load, power equals √3 times line voltage times line current times power factor. Line voltage is √3 times phase voltage in a star connection.

Power factor

Cosine of the phase angle between voltage and current. A low value means higher current for the same real power, raising line loss and voltage drop.

kWh unit

One kilowatt-hour equals 3.6 million joules and is one billing unit. Energy consumed equals power in kilowatts multiplied by time in hours.

Transmission voltage advantage

Raising transmission voltage reduces current for the same power, so resistive line loss falls in proportion to the square of the voltage ratio.

Radial distribution system

A single supply path from source to consumer. It is the simplest and cheapest layout, but any feeder fault interrupts every downstream consumer.

Ring main system

The feeder loops back to the source so a section can be supplied from either end. Isolators at section ends allow fault isolation without full shutdown.

Load factor

Average load divided by maximum demand over a period. A high load factor means plant is used efficiently and fixed costs are spread over more units.

ACSR conductor

Aluminium conductor steel reinforced. Aluminium outer strands carry current while the central steel core provides tensile strength, allowing longer spans with less sag.

Sag formula

For level supports, sag equals weight per unit length times span squared, divided by eight times tension. Sag rises when tension falls or span increases.

Pin insulator

A single-piece insulator fixed on a pin or spigot, used on low and medium voltage lines. The conductor sits in a groove and is tied with binding wire.

Creepage distance

The shortest path along the insulator surface between phase and earth. It must be longer in polluted coastal or industrial areas to prevent surface flashover.

Dyn11 vector group

Delta-connected high voltage winding and star-connected low voltage winding with neutral brought out. Low voltage lags high voltage by 30 degrees.

Transformer all-day efficiency

Efficiency calculated over 24 hours, weighting iron loss for the whole period and copper loss only during loaded hours. It matters for distribution transformers with light night loads.

Buchholz relay

A gas-operated relay fitted in the pipe between transformer tank and conservator. It alarms on gas accumulation and trips on sudden oil surge from internal faults.

Drop-out fuse

A horn-gap expulsion fuse on the transformer pole. The fuse carrier drops open visibly after operation, giving clear isolation and easy replacement.

Pole setting depth

A common rule is to bury about one-sixth of the pole length, for example 1.5 metres of a 9 metre pole, with proper foundation and compacted backfill.

Stringing rollers

Pulley blocks suspended from supports that carry the conductor during pay-out. They prevent abrasion and allow the conductor to be pulled and tensioned freely.

Stay wire

A guy wire anchored in the ground to resist unbalanced pull at angle, termination, and section poles. It is set at roughly 45 degrees where space permits.

Service connection

The insulated cable and fittings linking the utility pole to the consumer's premises, including service bracket, protective fuse or MCB, and sealed energy meter.

Heat-shrink joint insulation

Tubing that shrinks on heating to wrap the joint tightly, restoring insulation and moisture sealing. Correct size and even heating are essential for a sound joint.

Crimping versus twisting

Compression crimping with the correct die and lug gives a low-resistance, mechanically sound joint. Twisting is not accepted for service or line connections.

Energy meter constant

The number of disc revolutions per kilowatt-hour, marked on the meter. It is used to calculate energy during accuracy testing against a known load.

CT multiplier

For current-transformer metering, actual energy equals meter reading multiplied by the CT ratio. A 200/5 CT gives a multiplier of forty.

Sanctioned load

The load in kilowatts or kVA approved by the utility for a consumer. It fixes the service cable, meter rating, and fixed charges.

Earth resistance limit

Substation earthing is kept near one ohm, while consumer installations commonly need about five to eight ohms, depending on the applicable standard.

RCCB

A residual current circuit breaker that trips when earth leakage current exceeds its setting, typically 30 milliamperes for personal protection. It does not sense overload.

Prove-test-prove

Safety sequence for proving dead: test the voltage detector on a known live source, test the isolated conductors, then test the detector again to confirm it works.

Line clear permit

A written authorisation issued after a line is isolated, locked, proved dead, and earthed. It is returned only when work is finished and the line is restored.

Safety earths at work site

Temporary earths applied on every side of the work towards any possible supply source. They are removed only after all personnel and tools are withdrawn.

Insulation resistance test

A megger applies DC voltage, commonly 500 volts for low voltage, to measure insulation resistance. A very low reading indicates moisture, damage, or contamination.