Maharashtra HSC Power Distribution Lineman (NSQF) cheat sheet

Ohm's law: V = I × R; power P = V × I = I²R = V²/R. In a purely resistive DC circuit these three power forms are interchangeable.

Series circuit: same current through all elements, R_total = R1 + R2 + …, voltage divides in proportion to resistance.

Parallel circuit: same voltage across all branches, 1/R_total = 1/R1 + 1/R2 + …, current divides inversely with branch resistance.

Three-phase power: P = √3 × V_L × I_L × cos φ for balanced loads; V_L = √3 × V_phase in star connection, I_L = √3 × I_phase in delta.

AC impedance: Z = √(R² + X²), where X_L = 2πfL and X_C = 1/(2πfC); current and voltage are in phase only when X = 0.

Power factor = cos φ = kW/kVA; a low power factor raises current for the same kW, increasing line loss (I²R) and voltage drop.

RMS and peak: for a sine wave, V_rms = V_peak/√2 ≈ 0.707 V_peak and V_avg (half cycle) = 0.637 V_peak.

Energy: 1 kWh = 1 unit = 3.6 × 10⁶ J; energy billed = power (kW) × time (h).

Kirchhoff's rules: sum of currents at a node = 0; sum of voltages around a closed loop = 0.

Chain: generation (11–25 kV at alternator terminals) → step-up transmission (132/220/400 kV) → step-down substation (33/11 kV) → distribution (11 kV, 415 V) → consumer.

Transmission at high voltage reduces current for a given power, so I²R loss and conductor cross-section both fall; loss ∝ 1/V² at constant power.

India's standard LV three-phase distribution is 415 V line-to-line, 240 V line-to-neutral, 50 Hz; 11 kV is the common primary distribution voltage.

Distribution is classified as primary (11/33 kV feeder) and secondary (415/240 V), and by layout as radial, ring-main, or interconnected.

Radial system: cheapest and simplest, one supply path, so a feeder fault interrupts all downstream consumers.

Ring-main system: feeder loops back to the source, allowing supply from either side; isolators at each end of a section permit fault isolation.

Interconnected system: multiple sources feed the network, improving reliability and load sharing but requiring protection coordination.

Voltage drop in a distributor is limited by statute/practice (commonly about ±6% at the consumer terminal for LV), so feeder length and load density govern conductor choice.

Load factor = average load / maximum demand; diversity factor = sum of individual maximum demands / maximum demand on the system.

Common overhead distribution conductors: ACSR, AAAC, and copper; ACSR uses a steel core for tensile strength with aluminium outer strands for conductivity.

Standard sizes are designated by nominal aluminium area in mm² (e.g., Rabbit 6, Weasel 20, Rabbit/Squirrel 12.5, Dog 100, Panther 200 in ACSR).

Sag formula for level supports: S = wL²/(8T), where w = weight per unit length, L = span, T = tension; sag increases as tension falls.

Supports: steel tubular or rail poles, RCC/PCC poles, and wooden poles; stay wires and struts resist unbalanced pull at angles and terminations.

Insulators: pin type for LV/11 kV, suspension or disc type for higher voltages, shackle and stay insulators for tension and anchoring.

Creepage distance must suit pollution level; in coastal or industrial areas longer creepage or anti-fog insulators are used to prevent flashover.

Hardware: cross-arms, back-clamps, top clamps, suspension clamps, guy grips, AB switches, and drop-out fuses; all must be galvanised to resist corrosion.

Minimum ground clearance for 11 kV overhead lines is about 5.2 m across roads and higher across railways; LV lines need about 5.0 m over roads as per CEA practice.

Conductor spacing on the cross-arm must maintain the specified phase-to-phase clearance and avoid clashing under wind-induced swing.

Distribution transformer standard ratings: 10, 16, 25, 63, 100, 160, 250, 400, 630 kVA; typical 11 kV/433–415 V, Dyn11 vector group.

Turns ratio: V1/V2 = N1/N2; for an 11 kV/415 V transformer the ratio is about 26.5:1.

Transformer losses: no-load (iron) loss is constant and present whenever energised; load (copper) loss varies as the square of load current.

Efficiency is maximum when copper loss equals iron loss; all-day efficiency weights losses over 24 hours and favours distribution transformers lightly loaded off-peak.

Dyn11 means delta-connected HV, star-connected LV with neutral brought out, and LV lags HV by 30°; it handles unbalanced LV loads and third harmonics well.

Substation equipment: transformer, HT fuse or circuit breaker, lightning arresters, isolators, CTs/PTs, busbars, earthing, and LT distribution board.

Drop-out (horn-gap) fuses protect distribution transformers; expulsion-type fuse links are rated to carry normal load and clear transformer faults.

Oil in the transformer serves insulation and cooling; BDV (breakdown voltage) of oil is tested and should be high (typically ≥ 30 kV/2.5 mm gap) before energisation.

Buchholz relay on oil-immersed transformers detects gas accumulation and oil surge, giving alarm and trip for internal faults.

Sequence: route survey and marking → pit excavation → pole erection and alignment → cross-arm and insulator fitting → conductor pay-out → stringing and tensioning → sag adjustment → binding/clamping.

Pole depth rule of thumb: about 1/6 of pole length is buried (e.g., 9 m pole set about 1.5 m deep), with a concrete or stone foundation and earth backfill.

Pits must be offset in the direction of the line pull so the pole stands plumb after backfilling; stays are set at about 45° where possible.

Stringing uses a pilot wire or draw wire pulled over rollers; conductors must not be dragged on the ground or over sharp edges.

Sag is checked against a sag template or calculated value at the prevailing conductor temperature; too little sag overstresses the conductor, too much reduces clearance.

Binding on pin insulators is done with the same conductor or aluminium binding wire, with the conductor on the correct groove and the tie wrapped in the specified direction.

Jointing in mid-span is avoided; joints are made at the pole with proper jointing ferrules or compression splices and then tensioned correctly.

Guard wires, danger plates, anti-climbing devices and phase plates are installed before the line is energised; jumpers are formed with adequate clearance.

LV service connection uses insulated cable from the pole to the consumer, with a service bracket, fuse/MCB, and an energy meter in a sealed meter box.

Service cable size is selected for the consumer's sanctioned load and for voltage drop; the neutral must never be smaller than required and must not be fused.

Straight-through joints in LV cables are made with compression ferrules or mechanical connectors, then insulated with heat-shrink or self-amalgamating tape to restore insulation.

HT terminations use cable-end kits (stress control, insulation, rain sheds) matched to the cable type; a poor termination causes tracking and flashover.

Cable preparation: correct stripping length, no nicked conductor, no moisture ingress, and phase identification by colour or ferrule before jointing.

Crimping is preferred over twisting; the correct die and lug size must match the conductor, and the crimp is pull-tested or visually checked.

Service connection must be made with the line isolated and earthed; the consumer's installation is checked for polarity, insulation resistance, and earthing before energisation.

For a three-phase service, phase sequence is verified and the neutral is connected first and disconnected last to avoid floating neutrals.

Single-phase domestic supply is 240 V, 50 Hz; three-phase supply is 415 V, 50 Hz; sanctioned load determines the meter and service rating.

Energy meter records kWh; a 1-phase meter has phase and neutral connections with the load side downstream of the meter, and the meter is sealed by the utility.

Meter constant = revolutions per kWh; for a meter marked 600 rev/kWh, one revolution corresponds to 1/600 kWh.

Meter accuracy test: connect a known load, time a known number of revolutions, and compare calculated energy with recorded energy; error beyond limits requires replacement.

CT-operated (LT/HT) metering multiplies meter reading by the CT ratio (and PT ratio) to get actual energy; a 200/5 CT gives a multiplier of 40.

Consumer installation checks: insulation resistance, earth continuity, polarity, MCB/RCCB rating, and no unauthorised load or tampering.

Tariff components commonly include energy charge, fixed/demand charge, and duty; power factor penalty or rebate applies where specified.

Theft and tampering detection includes meter seal checks, abnormal consumption patterns, and bypass or shunt inspection.

Earthing types: plate, pipe, rod, and strip electrodes; earth resistance should be low (commonly ≤ 1 Ω for substations and ≤ 5–8 Ω for consumer installations, per applicable standard).

Earthing system parts: earth electrode, earth conductor, earth continuity conductor, and bonding of all metalwork to the earth grid.

Protective devices: fuse, MCB, MCCB, ELCB, and RCCB; an RCCB rated 30 mA is used for personal protection in wet or domestic circuits.

RCCB/ELCB trips on earth leakage current, not on overload; an MCB trips on overload and short circuit but does not sense earth leakage.

Fuse selection: rated current above normal load but below the cable's current-carrying capacity, with the correct breaking capacity for the fault level.

Safe isolation: identify the circuit, open the breaker, lock and tag, prove the tester on a known live source, test for dead on all phases, and earth the conductors.

First aid for electric shock: isolate the supply, do not touch the casualty until isolated, call for help, and start CPR if breathing has stopped.

Fire class for electrical equipment is Class C (or E in some classifications); use CO₂ or dry powder, never water on live electrical fires.

Personal protective equipment: rubber gloves, insulated tools, safety shoes, helmet, and arc-rated clothing for live or near-live work.

Permit-to-work types: line clear permit, hot-line permit, and shutdown permit; the permit is issued by an authorised person and returned only after work completion and restoration.

Line clear procedure: isolate, lock and tag, prove dead, earth at the work site on all sides, and display 'Men at Work' boards.

Earths must be applied on the side of the work towards every possible source of supply, and removed only after the work is completed and personnel withdrawn.

Working at height: use a full-body harness with double lanyard, anchor above shoulder level, and inspect the harness before each use.

Ladder rule: 1 in 4 (75°) angle, tied off at the top, three points of contact, and no metal ladder near live lines.

Bucket truck or elevated platform work requires a trained operator, outriggers on firm ground, and a spotter at ground level.

Emergency response: raise alarm, isolate supply, give first aid, and inform the control room; record the incident and preserve the scene.

Rescue from a live line: do not touch the casualty until the supply is isolated or the casualty is cleared with an insulated device.

Insulation resistance test: use a megger (500 V DC for LV, 1000/2500 V for HT); acceptable LV insulation is typically ≥ 1 MΩ, and a low reading indicates moisture or damage.

Earth resistance test: use a three-terminal fall-of-potential method with two auxiliary spikes; spacing about 20–30 m apart, and take readings in dry conditions.

Continuity test: use a low-resistance ohmmeter or multimeter; a good earth continuity conductor reads close to zero ohms.

Polarity and phase sequence: check with a phase sequence meter before paralleling or commissioning a three-phase installation.

Transformer oil testing: BDV, moisture content, acidity, and dissolved gas analysis; oil filtration or replacement is done when BDV falls below limits.

Preventive maintenance: tightening of connections, cleaning of insulators, checking fuse and relay settings, and thermographic scanning of joints for hot spots.

Clamp meter measures current without breaking the circuit; a tong tester on a live conductor must be rated for the voltage and used with insulated gloves.

Cable fault location: Murray loop or Varley loop for low-resistance faults, and time-domain reflectometer (TDR) for open or high-resistance faults.