Transmission and Distribution MCQs 2026

When ambient temperature rises, conductor sag generally

1. A decreases always ✓
2. B remains unchanged always ✓
3. C increases because thermal expansion lengthens the conductor ✓
4. D becomes zero ✓

Maximum conductor tension under worst loading usually occurs at

1. A hottest day only ✓
2. B minimum temperature with maximum wind and/or ice loading ✓
3. C no wind condition only ✓
4. D average annual temperature only ✓

Ruling span in sag-tension calculations is defined as

1. A shortest span in the section only ✓
2. B average tower height ✓
3. C equivalent span that gives the same maximum tension as the actual supports ✓
4. D ground clearance distance ✓

Wind pressure on conductors increases effective weight and therefore

1. A reduces sag ✓
2. B increases sag and reduces ground clearance ✓
3. C eliminates tension variation ✓
4. D removes aeolian vibration ✓

Ice loading on transmission conductors

1. A reduces conductor weight ✓
2. B eliminates need for dampers ✓
3. C lowers tower height requirements ✓
4. D increases mechanical load and sag significantly ✓

Stringing chart for overhead lines relates

1. A sag and tension to temperature and span ✓
2. B only voltage regulation ✓
3. C only fault level ✓
4. D only relay settings ✓

For supports at different elevations, sag calculation must account for

1. A only span length ignoring height difference ✓
2. B only insulator type ✓
3. C only bundle spacing ✓
4. D unequal support heights and horizontal tension component ✓

Aeolian vibration of conductors is caused by

1. A vortex shedding in steady wind across the cylindrical conductor ✓
2. B only short-circuit forces ✓
3. C only ice melting ✓
4. D only transformer inrush ✓

Stockbridge dampers on transmission lines are used to mitigate

1. A voltage regulation only ✓
2. B aeolian vibration and fatigue of conductors ✓
3. C fault current magnitude ✓
4. D transformer magnetizing inrush ✓

Spacer dampers in bundled conductors prevent

1. A sub-conductor clashing and control bundle oscillation ✓
2. B increase of line voltage to infinity ✓
3. C elimination of series impedance ✓
4. D blocking of zero-sequence current ✓

Ground clearance of an overhead line is minimum at

1. A support/tower location ✓
2. B only during faults ✓
3. C transformer terminals ✓
4. D mid-span where sag is maximum ✓

Higher erection tension during stringing results in

1. A higher sag always ✓
2. B zero tension at supports ✓
3. C lower sag at operating conditions ✓
4. D infinite span capability ✓

Pin type insulators are commonly used on

1. A 400 kV EHV long strings only ✓
2. B underground cables only ✓
3. C SF6 switchgear tanks only ✓
4. D distribution lines up to about 33 kV ✓

Suspension insulator strings on transmission towers are used because

1. A they provide flexibility and mechanical strength for higher voltages ✓
2. B they eliminate the need for conductors ✓
3. C they replace transformers ✓
4. D they conduct load current ✓

Strain insulators are employed at

1. A dead ends, sharp corners and long spans where tension is high ✓
2. B transformer bushings only ✓
3. C motor terminals only ✓
4. D neutral grounding resistors only ✓

String efficiency of an insulator disc string is less than 100% when

1. A all discs share equal voltage always ✓
2. B line frequency is zero ✓
3. C conductor is perfectly smooth ✓
4. D capacitance to earth causes unequal voltage distribution across discs ✓

Flashover of an insulator refers to

1. A puncture through the solid insulator body only ✓
2. B melting of conductor only ✓
3. C tripping of distance relay only ✓
4. D discharge over the insulator surface between electrodes ✓

Puncture of a porcelain insulator means

1. A recoverable surface flashover only ✓
2. B permanent breakdown through the insulator material ✓
3. C corona without discharge ✓
4. D harmonic resonance only ✓

Guard rings on insulator strings help by

1. A increasing line inductance ✓
2. B carrying load current ✓
3. C improving voltage distribution and reducing stress on lower discs ✓
4. D replacing earth wire ✓

Number of insulator discs in a string depends on

1. A conductor material only ✓
2. B power factor of load only ✓
3. C line voltage, insulation coordination and pollution level ✓
4. D motor slip only ✓

Composite polymeric insulators compared to porcelain offer

1. A always lower creepage requirement regardless of site ✓
2. B zero need for maintenance ever ✓
3. C lighter weight and better pollution performance in many cases ✓
4. D inability to used outdoors ✓

Fog-type or anti-fog insulator profiles are designed for

1. A indoor switchboards only ✓
2. B coastal and polluted environments with longer creepage paths ✓
3. C DC machines only ✓
4. D underground joints only ✓

Transformer per unit impedance referred to a common MVA base is

1. A always higher on LV by turns ratio squared only without MVA change ✓
2. B zero on one side always ✓
3. C the same on HV and LV sides ✓
4. D dependent only on frequency ✓

Per unit admittance Ypu equals

1. A actual admittance divided by MVA only ✓
2. B line SIL only ✓
3. C actual admittance multiplied by base impedance ✓
4. D reciprocal of sag ✓

A common system study base MVA is

1. A always 1 kVA only ✓
2. B 100 MVA or a value matching the largest plant rating ✓
3. C always equal to line length in km ✓
4. D always zero ✓

Per unit active power Ppu is computed as

1. A actual MW divided by base MVA ✓
2. B MW multiplied by kV only ✓
3. C MVAR divided by frequency ✓
4. D kA times ohm only ✓

Per unit current Ipu equals

1. A actual current times voltage only ✓
2. B fault level only ✓
3. C actual current divided by base current Ibase ✓
4. D charging current only ✓

Nominal voltage kV chosen as base is typically

1. A minimum sag voltage only ✓
2. B corona onset voltage only ✓
3. C rotor bar voltage only ✓
4. D rated or nominal system voltage of the bus ✓

Advantage of per unit values near 1.0 is

1. A elimination of all fault currents ✓
2. B improved numerical conditioning in calculations ✓
3. C zero need for symmetrical components ✓
4. D automatic relay coordination ✓

Line charging susceptance in per unit is often small compared to

1. A short-circuit impedance magnitudes in transmission studies ✓
2. B transformer nameplate MVA only ✓
3. C motor slip values ✓
4. D fuse cut-off ratings ✓

Voltage regulation of a line approximated at lagging power factor is

1. A (|Vr| − |Vs|)/|Vs| only at leading pf always ✓
2. B zero for all loads always ✓
3. C (|Vs| − |Vr|) / |Vr| × 100% for comparable angles ✓
4. D equal to SIL always ✓

Ferranti effect occurs when

1. A heavy lagging load at short line only ✓
2. B fault at transformer only ✓
3. C receiving end voltage exceeds sending end voltage at light load on long lines ✓
4. D motor starting only ✓

Ferranti effect is most pronounced on

1. A short distribution feeders at full load ✓
2. B DC resistive loads only ✓
3. C long EHV lines at light or no load ✓
4. D synchronous motor full load ✓

At light load on a long overhead line, receiving end power factor tends to be

1. A leading due to line charging ✓
2. B always unity only ✓
3. C always lagging only ✓
4. D zero always ✓

Open-circuit receiving end of a long line may show voltage

1. A always zero ✓
2. B always equal to short-circuit level ✓
3. C equal to DC battery voltage only ✓
4. D higher than sending end due to capacitive Ferranti rise ✓

Positive voltage regulation at lagging load means

1. A receiving voltage is always higher ✓
2. B sending end voltage magnitude exceeds receiving end under load ✓
3. C line has zero impedance ✓
4. D power flows from load to source only ✓

Load power factor strongly affects voltage regulation because

1. A resistance becomes zero ✓
2. B frequency doubles ✓
3. C reactive component of current causes additional voltage drop in line impedance ✓
4. D SIL becomes negative ✓

Shunt capacitors installed at load buses improve voltage profile by

1. A increasing line charging on EHV only ✓
2. B increasing series impedance ✓
3. C supplying reactive power locally and reducing line VAR flow ✓
4. D blocking positive-sequence faults ✓

Series capacitors on transmission lines reduce voltage regulation by

1. A increasing Ferranti rise only ✓
2. B partially compensating line inductive reactance ✓
3. C eliminating the need for conductors ✓
4. D replacing distance protection ✓

On-load tap changers on transformers regulate voltage by

1. A changing transformer turns ratio under load ✓
2. B changing line length physically ✓
3. C inserting fuses in series ✓
4. D opening circuit breaker contacts only ✓

Shunt reactors on long EHV lines at light load are used to

1. A increase Ferranti effect ✓
2. B raise receiving voltage further ✓
3. C replace series impedance completely ✓
4. D absorb excess reactive power and limit voltage rise ✓

ABCD parameters of a transmission line are used to compute

1. A sending end voltage and current from receiving end conditions ✓
2. B only transformer copper loss ✓
3. C only motor slip ✓
4. D only fuse melting time only ✓

Critical loading for voltage support on uncompensated lines relates to

1. A motor starting current only ✓
2. B SIL and line length where reactive power balance changes character ✓
3. C Buchholz trip level only ✓
4. D PID derivative time only ✓

Characteristic impedance Zc of a lossless overhead line equals

1. A R/L only ✓
2. B sqrt(L/C) where L is series inductance and C is shunt capacitance per unit length ✓
3. C C/R only ✓
4. D sqrt(RG) only ✓

Surge impedance loading (SIL) of a transmission line is given by

1. A V/Zc only ✓
2. B Zc/V² ✓
3. C V×Zc×√3 only ✓
4. D V²/Zc in MW for line-to-line voltage V ✓

In the nominal π model of a medium-length line, shunt capacitance is placed

1. A only at the receiving end ✓
2. B at both sending and receiving ends as half the total line capacitance each ✓
3. C only at the sending end ✓
4. D entirely in the middle as a lump ✓

Series impedance per unit length of an overhead line includes

1. A only shunt capacitance ✓
2. B only corona loss resistance alone ✓
3. C only transformer leakage ✓
4. D resistance and inductive reactance of conductors ✓

Geometric mean distance (GMD) in inductance formula refers to

1. A resistance of earth wire only ✓
2. B insulator string length ✓
3. C tower footing resistance ✓
4. D equivalent spacing among bundled or multi-conductor arrangements ✓

Geometric mean radius (GMR) of a conductor bundle is used to compute

1. A only corona onset voltage ✓
2. B equivalent inductance per phase lower than single conductor ✓
3. C only sag at maximum tension ✓
4. D only zero-sequence resistance only ✓

Skin effect in AC transmission conductors causes

1. A uniform current across the cross-section always ✓
2. B reduction of resistance at higher frequency ✓
3. C current concentration near the surface increasing effective resistance ✓
4. D zero inductance change ✓

Proximity effect in parallel conductors results in

1. A non-uniform current distribution and increased effective resistance ✓
2. B increased shunt capacitance only ✓
3. C elimination of inductive reactance ✓
4. D infinite surge impedance ✓

Bundled conductors on EHV lines primarily reduce

1. A corona loss and line inductance ✓
2. B series resistance to zero ✓
3. C shunt capacitance to zero ✓
4. D surge impedance below 1 ohm always ✓

A short transmission line model neglects

1. A shunt capacitance and uses only series impedance ✓
2. B series resistance only ✓
3. C both series and shunt completely ✓
4. D transformer magnetizing branch ✓

Propagation constant γ of a uniform line is

1. A only jωL ✓
2. B only R/L ✓
3. C only G/C without imaginary part ✓
4. D γ = sqrt((R+jωL)(G+jωC)) = α + jβ ✓

Nominal T equivalent of a line places

1. A all impedance at one end only ✓
2. B capacitance only at sending end ✓
3. C no shunt branch ✓
4. D half the series impedance at each end and total shunt admittance at the centre ✓

Charging current in an unloaded long overhead line is due to

1. A shunt capacitance of the line ✓
2. B series resistance only ✓
3. C transformer no-load current only ✓
4. D fault current only ✓

Resistance of a conductor per km increases with temperature because

1. A inductance falls to zero ✓
2. B resistivity of metal increases with temperature ✓
3. C capacitance doubles always ✓
4. D GMR becomes infinite ✓

Sag of a conductor on a level span with uniform loading is approximately

1. A s = wL/T ✓
2. B s = 8T/(wL²) ✓
3. C s = wL²/(8T) where w is weight per unit length and T is tension ✓
4. D s = w/T only ✓

Arcing horns on insulator fittings protect by

1. A increasing series impedance of line ✓
2. B measuring fault distance ✓
3. C providing a path for flashover away from critical metal parts ✓
4. D turning on SCR ✓

Corona on insulators in wet weather can lead to

1. A improved string efficiency above 100% ✓
2. B power loss, audible noise and eventual flashover ✓
3. C zero charging current ✓
4. D automatic voltage boost without load ✓

Creepage distance of an insulator is

1. A direct straight-line distance through air only ✓
2. B surface path length between live and earth electrodes ✓
3. C conductor cross-section area ✓
4. D tower footing resistance ✓

Underground cables compared with overhead lines have

1. A higher capacitance and charging current per km ✓
2. B negligible shunt capacitance always ✓
3. C no insulation requirement ✓
4. D lower voltage rating always ✓

In belted type paper-insulated cables, insulation layers are

1. A always individually metal screened ✓
2. B immersed in SF6 gas ✓
3. C replaced by air gaps only ✓
4. D laid helically without metallic screens between phases ✓

Screened or shielded cables reduce electric stress by

1. A eliminating the need for conductor ✓
2. B using only one phase in a duct ✓
3. C removing the sheath ✓
4. D keeping uniform radial field within each core insulation ✓

Capacitance grading of high-voltage cables uses

1. A layers of different permittivity to equalize radial stress ✓
2. B only thicker conductor without insulation change ✓
3. C air gaps between cores only ✓
4. D open delta connection ✓

Charging current in a long underground cable at no load is

1. A purely resistive always ✓
2. B leading current due to cable capacitance ✓
3. C zero because cable is short ✓
4. D same as fault current ✓

Dielectric loss in cable insulation contributes to

1. A increased surge impedance only ✓
2. B heating of insulation and reduced transmission efficiency ✓
3. C negative sequence currents only ✓
4. D motor starting torque ✓

XLPE insulated cables are preferred today because

1. A they have good dielectric strength and easier jointing than PILC ✓
2. B they require only paper oil impregnation ✓
3. C they cannot be used underground ✓
4. D they have no thermal limit ✓

Cable ampacity is primarily limited by

1. A only skin effect at DC ✓
2. B only corona on sheath ✓
3. C only relay pickup current ✓
4. D conductor temperature rise under load ✓

Sheath bonding in cable systems is done to

1. A control sheath circulating currents and voltage rise ✓
2. B increase line inductance to infinity ✓
3. C replace the conductor ✓
4. D eliminate the need for earthing ✓

Murray loop test on cables is used for

1. A locating earth faults in cable cores ✓
2. B measuring power factor of motor ✓
3. C setting distance relay zones ✓
4. D calibrating PID controller ✓

Minimum bending radius during cable installation must be observed to avoid

1. A increase of surge impedance only ✓
2. B damage to insulation and conductors ✓
3. C automatic voltage regulation ✓
4. D symmetrical component unbalance only ✓

Paper-oil impregnated (PILC) cables require

1. A no sealing against moisture ever ✓
2. B careful handling of oil impregnation and jointing skill ✓
3. C operation only at DC voltage ✓
4. D absence of any metallic sheath ✓

Direct burial of cables requires consideration of

1. A only tower height ✓
2. B only insulator string length ✓
3. C soil thermal resistivity and mechanical protection ✓
4. D only excitation reactance of alternator ✓

Cable joints and terminations must control

1. A electric stress concentration at insulation interfaces ✓
2. B only rotor slip ✓
3. C only prime mover governor gain ✓
4. D only Buchholz gas volume only ✓

Per unit impedance is defined as

1. A actual impedance multiplied by base voltage only ✓
2. B fault MVA divided by load MVA only ✓
3. C line length in km divided by SIL ✓
4. D actual impedance divided by base impedance ✓

Base impedance on a three-phase system is Zbase =

1. A MVA_base / kV ✓
2. B kV / MVA_base only ✓
3. C sqrt(kV×MVA) only ✓
4. D (kV_line-line)² / MVA_base ✓

When changing per unit base, impedance transforms as

1. A Zpu_new = Zpu_old only regardless of base ✓
2. B multiply by kV_new only ✓
3. C Zpu_new = Zpu_old × (MVA_new/MVA_old) × (kV_old/kV_new)² ✓
4. D divide by frequency ✓

Per unit system simplifies fault calculations because

1. A it eliminates all resistances ✓
2. B it removes the need for sequence networks ✓
3. C it sets all voltages to zero ✓
4. D transformer turns ratios need not be explicitly applied in the network ✓

For three-phase analysis, voltage base is usually

1. A phase-to-neutral only always ✓
2. B peak phase voltage only ✓
3. C line-to-line nominal kV ✓
4. D DC link voltage only ✓