Transmission and Distribution MCQs 2026

Ferranti effect occurs when

1. Aheavy lagging load at short line only✓
2. Bfault at transformer only✓
3. Creceiving end voltage exceeds sending end voltage at light load on long lines✓
4. Dmotor starting only✓

Ferranti effect is most pronounced on

1. Ashort distribution feeders at full load✓
2. BDC resistive loads only✓
3. Clong EHV lines at light or no load✓
4. Dsynchronous motor full load✓

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

1. Aleading due to line charging✓
2. Balways unity only✓
3. Calways lagging only✓
4. Dzero always✓

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

1. Aalways zero✓
2. Balways equal to short-circuit level✓
3. Cequal to DC battery voltage only✓
4. Dhigher than sending end due to capacitive Ferranti rise✓

Positive voltage regulation at lagging load means

1. Areceiving voltage is always higher✓
2. Bsending end voltage magnitude exceeds receiving end under load✓
3. Cline has zero impedance✓
4. Dpower flows from load to source only✓

Load power factor strongly affects voltage regulation because

1. Aresistance becomes zero✓
2. Bfrequency doubles✓
3. Creactive component of current causes additional voltage drop in line impedance✓
4. DSIL becomes negative✓

Shunt capacitors installed at load buses improve voltage profile by

1. Aincreasing line charging on EHV only✓
2. Bincreasing series impedance✓
3. Csupplying reactive power locally and reducing line VAR flow✓
4. Dblocking positive-sequence faults✓

Series capacitors on transmission lines reduce voltage regulation by

1. Aincreasing Ferranti rise only✓
2. Bpartially compensating line inductive reactance✓
3. Celiminating the need for conductors✓
4. Dreplacing distance protection✓

On-load tap changers on transformers regulate voltage by

1. Achanging transformer turns ratio under load✓
2. Bchanging line length physically✓
3. Cinserting fuses in series✓
4. Dopening circuit breaker contacts only✓

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

1. Aincrease Ferranti effect✓
2. Braise receiving voltage further✓
3. Creplace series impedance completely✓
4. Dabsorb excess reactive power and limit voltage rise✓

ABCD parameters of a transmission line are used to compute

1. Asending end voltage and current from receiving end conditions✓
2. Bonly transformer copper loss✓
3. Conly motor slip✓
4. Donly fuse melting time only✓

Critical loading for voltage support on uncompensated lines relates to

1. Amotor starting current only✓
2. BSIL and line length where reactive power balance changes character✓
3. CBuchholz trip level only✓
4. DPID derivative time only✓

Characteristic impedance Zc of a lossless overhead line equals

1. AR/L only✓
2. Bsqrt(L/C) where L is series inductance and C is shunt capacitance per unit length✓
3. CC/R only✓
4. Dsqrt(RG) only✓

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

1. AV/Zc only✓
2. BZc/V²✓
3. CV×Zc×√3 only✓
4. DV²/Zc in MW for line-to-line voltage V✓

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

1. Aonly at the receiving end✓
2. Bat both sending and receiving ends as half the total line capacitance each✓
3. Conly at the sending end✓
4. Dentirely in the middle as a lump✓

Series impedance per unit length of an overhead line includes

1. Aonly shunt capacitance✓
2. Bonly corona loss resistance alone✓
3. Conly transformer leakage✓
4. Dresistance and inductive reactance of conductors✓

Geometric mean distance (GMD) in inductance formula refers to

1. Aresistance of earth wire only✓
2. Binsulator string length✓
3. Ctower footing resistance✓
4. Dequivalent spacing among bundled or multi-conductor arrangements✓

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

1. Aonly corona onset voltage✓
2. Bequivalent inductance per phase lower than single conductor✓
3. Conly sag at maximum tension✓
4. Donly zero-sequence resistance only✓

Skin effect in AC transmission conductors causes

1. Auniform current across the cross-section always✓
2. Breduction of resistance at higher frequency✓
3. Ccurrent concentration near the surface increasing effective resistance✓
4. Dzero inductance change✓

Proximity effect in parallel conductors results in

1. Anon-uniform current distribution and increased effective resistance✓
2. Bincreased shunt capacitance only✓
3. Celimination of inductive reactance✓
4. Dinfinite surge impedance✓

Bundled conductors on EHV lines primarily reduce

1. Acorona loss and line inductance✓
2. Bseries resistance to zero✓
3. Cshunt capacitance to zero✓
4. Dsurge impedance below 1 ohm always✓

A short transmission line model neglects

1. Ashunt capacitance and uses only series impedance✓
2. Bseries resistance only✓
3. Cboth series and shunt completely✓
4. Dtransformer magnetizing branch✓

Propagation constant γ of a uniform line is

1. Aonly jωL✓
2. Bonly R/L✓
3. Conly G/C without imaginary part✓
4. Dγ = sqrt((R+jωL)(G+jωC)) = α + jβ✓

Nominal T equivalent of a line places

1. Aall impedance at one end only✓
2. Bcapacitance only at sending end✓
3. Cno shunt branch✓
4. Dhalf 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. Ashunt capacitance of the line✓
2. Bseries resistance only✓
3. Ctransformer no-load current only✓
4. Dfault current only✓

Resistance of a conductor per km increases with temperature because

1. Ainductance falls to zero✓
2. Bresistivity of metal increases with temperature✓
3. Ccapacitance doubles always✓
4. DGMR becomes infinite✓

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

1. As = wL/T✓
2. Bs = 8T/(wL²)✓
3. Cs = wL²/(8T) where w is weight per unit length and T is tension✓
4. Ds = w/T only✓

When ambient temperature rises, conductor sag generally

1. Adecreases always✓
2. Bremains unchanged always✓
3. Cincreases because thermal expansion lengthens the conductor✓
4. Dbecomes zero✓

Maximum conductor tension under worst loading usually occurs at

1. Ahottest day only✓
2. Bminimum temperature with maximum wind and/or ice loading✓
3. Cno wind condition only✓
4. Daverage annual temperature only✓

Ruling span in sag-tension calculations is defined as

1. Ashortest span in the section only✓
2. Baverage tower height✓
3. Cequivalent span that gives the same maximum tension as the actual supports✓
4. Dground clearance distance✓

Wind pressure on conductors increases effective weight and therefore

1. Areduces sag✓
2. Bincreases sag and reduces ground clearance✓
3. Celiminates tension variation✓
4. Dremoves aeolian vibration✓

Ice loading on transmission conductors

1. Areduces conductor weight✓
2. Beliminates need for dampers✓
3. Clowers tower height requirements✓
4. Dincreases mechanical load and sag significantly✓

Stringing chart for overhead lines relates

1. Asag and tension to temperature and span✓
2. Bonly voltage regulation✓
3. Conly fault level✓
4. Donly relay settings✓

For supports at different elevations, sag calculation must account for

1. Aonly span length ignoring height difference✓
2. Bonly insulator type✓
3. Conly bundle spacing✓
4. Dunequal support heights and horizontal tension component✓

Aeolian vibration of conductors is caused by

1. Avortex shedding in steady wind across the cylindrical conductor✓
2. Bonly short-circuit forces✓
3. Conly ice melting✓
4. Donly transformer inrush✓

Stockbridge dampers on transmission lines are used to mitigate

1. Avoltage regulation only✓
2. Baeolian vibration and fatigue of conductors✓
3. Cfault current magnitude✓
4. Dtransformer magnetizing inrush✓

Spacer dampers in bundled conductors prevent

1. Asub-conductor clashing and control bundle oscillation✓
2. Bincrease of line voltage to infinity✓
3. Celimination of series impedance✓
4. Dblocking of zero-sequence current✓

Ground clearance of an overhead line is minimum at

1. Asupport/tower location✓
2. Bonly during faults✓
3. Ctransformer terminals✓
4. Dmid-span where sag is maximum✓

Higher erection tension during stringing results in

1. Ahigher sag always✓
2. Bzero tension at supports✓
3. Clower sag at operating conditions✓
4. Dinfinite span capability✓

Pin type insulators are commonly used on

1. A400 kV EHV long strings only✓
2. Bunderground cables only✓
3. CSF6 switchgear tanks only✓
4. Ddistribution lines up to about 33 kV✓

Suspension insulator strings on transmission towers are used because

1. Athey provide flexibility and mechanical strength for higher voltages✓
2. Bthey eliminate the need for conductors✓
3. Cthey replace transformers✓
4. Dthey conduct load current✓

Strain insulators are employed at

1. Adead ends, sharp corners and long spans where tension is high✓
2. Btransformer bushings only✓
3. Cmotor terminals only✓
4. Dneutral grounding resistors only✓

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

1. Aall discs share equal voltage always✓
2. Bline frequency is zero✓
3. Cconductor is perfectly smooth✓
4. Dcapacitance to earth causes unequal voltage distribution across discs✓

Flashover of an insulator refers to

1. Apuncture through the solid insulator body only✓
2. Bmelting of conductor only✓
3. Ctripping of distance relay only✓
4. Ddischarge over the insulator surface between electrodes✓

Puncture of a porcelain insulator means

1. Arecoverable surface flashover only✓
2. Bpermanent breakdown through the insulator material✓
3. Ccorona without discharge✓
4. Dharmonic resonance only✓

Guard rings on insulator strings help by

1. Aincreasing line inductance✓
2. Bcarrying load current✓
3. Cimproving voltage distribution and reducing stress on lower discs✓
4. Dreplacing earth wire✓

Number of insulator discs in a string depends on

1. Aconductor material only✓
2. Bpower factor of load only✓
3. Cline voltage, insulation coordination and pollution level✓
4. Dmotor slip only✓

Composite polymeric insulators compared to porcelain offer

1. Aalways lower creepage requirement regardless of site✓
2. Bzero need for maintenance ever✓
3. Clighter weight and better pollution performance in many cases✓
4. Dinability to used outdoors✓

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

1. Aindoor switchboards only✓
2. Bcoastal and polluted environments with longer creepage paths✓
3. CDC machines only✓
4. Dunderground joints only✓

Arcing horns on insulator fittings protect by

1. Aincreasing series impedance of line✓
2. Bmeasuring fault distance✓
3. Cproviding a path for flashover away from critical metal parts✓
4. Dturning on SCR✓

Corona on insulators in wet weather can lead to

1. Aimproved string efficiency above 100%✓
2. Bpower loss, audible noise and eventual flashover✓
3. Czero charging current✓
4. Dautomatic voltage boost without load✓

Creepage distance of an insulator is

1. Adirect straight-line distance through air only✓
2. Bsurface path length between live and earth electrodes✓
3. Cconductor cross-section area✓
4. Dtower footing resistance✓

Underground cables compared with overhead lines have

1. Ahigher capacitance and charging current per km✓
2. Bnegligible shunt capacitance always✓
3. Cno insulation requirement✓
4. Dlower voltage rating always✓

In belted type paper-insulated cables, insulation layers are

1. Aalways individually metal screened✓
2. Bimmersed in SF6 gas✓
3. Creplaced by air gaps only✓
4. Dlaid helically without metallic screens between phases✓

Screened or shielded cables reduce electric stress by

1. Aeliminating the need for conductor✓
2. Busing only one phase in a duct✓
3. Cremoving the sheath✓
4. Dkeeping uniform radial field within each core insulation✓

Capacitance grading of high-voltage cables uses

1. Alayers of different permittivity to equalize radial stress✓
2. Bonly thicker conductor without insulation change✓
3. Cair gaps between cores only✓
4. Dopen delta connection✓

Charging current in a long underground cable at no load is

1. Apurely resistive always✓
2. Bleading current due to cable capacitance✓
3. Czero because cable is short✓
4. Dsame as fault current✓

Dielectric loss in cable insulation contributes to

1. Aincreased surge impedance only✓
2. Bheating of insulation and reduced transmission efficiency✓
3. Cnegative sequence currents only✓
4. Dmotor starting torque✓

XLPE insulated cables are preferred today because

1. Athey have good dielectric strength and easier jointing than PILC✓
2. Bthey require only paper oil impregnation✓
3. Cthey cannot be used underground✓
4. Dthey have no thermal limit✓

Cable ampacity is primarily limited by

1. Aonly skin effect at DC✓
2. Bonly corona on sheath✓
3. Conly relay pickup current✓
4. Dconductor temperature rise under load✓

Sheath bonding in cable systems is done to

1. Acontrol sheath circulating currents and voltage rise✓
2. Bincrease line inductance to infinity✓
3. Creplace the conductor✓
4. Deliminate the need for earthing✓

Murray loop test on cables is used for

1. Alocating earth faults in cable cores✓
2. Bmeasuring power factor of motor✓
3. Csetting distance relay zones✓
4. Dcalibrating PID controller✓

Minimum bending radius during cable installation must be observed to avoid

1. Aincrease of surge impedance only✓
2. Bdamage to insulation and conductors✓
3. Cautomatic voltage regulation✓
4. Dsymmetrical component unbalance only✓

Paper-oil impregnated (PILC) cables require

1. Ano sealing against moisture ever✓
2. Bcareful handling of oil impregnation and jointing skill✓
3. Coperation only at DC voltage✓
4. Dabsence of any metallic sheath✓

Direct burial of cables requires consideration of

1. Aonly tower height✓
2. Bonly insulator string length✓
3. Csoil thermal resistivity and mechanical protection✓
4. Donly excitation reactance of alternator✓

Cable joints and terminations must control

1. Aelectric stress concentration at insulation interfaces✓
2. Bonly rotor slip✓
3. Conly prime mover governor gain✓
4. Donly Buchholz gas volume only✓

Per unit impedance is defined as

1. Aactual impedance multiplied by base voltage only✓
2. Bfault MVA divided by load MVA only✓
3. Cline length in km divided by SIL✓
4. Dactual impedance divided by base impedance✓

Base impedance on a three-phase system is Zbase =

1. AMVA_base / kV✓
2. BkV / MVA_base only✓
3. Csqrt(kV×MVA) only✓
4. D(kV_line-line)² / MVA_base✓

When changing per unit base, impedance transforms as

1. AZpu_new = Zpu_old only regardless of base✓
2. Bmultiply by kV_new only✓
3. CZpu_new = Zpu_old × (MVA_new/MVA_old) × (kV_old/kV_new)²✓
4. Ddivide by frequency✓

Per unit system simplifies fault calculations because

1. Ait eliminates all resistances✓
2. Bit removes the need for sequence networks✓
3. Cit sets all voltages to zero✓
4. Dtransformer turns ratios need not be explicitly applied in the network✓

For three-phase analysis, voltage base is usually

1. Aphase-to-neutral only always✓
2. Bpeak phase voltage only✓
3. Cline-to-line nominal kV✓
4. DDC link voltage only✓

Transformer per unit impedance referred to a common MVA base is

1. Aalways higher on LV by turns ratio squared only without MVA change✓
2. Bzero on one side always✓
3. Cthe same on HV and LV sides✓
4. Ddependent only on frequency✓

Per unit admittance Ypu equals

1. Aactual admittance divided by MVA only✓
2. Bline SIL only✓
3. Cactual admittance multiplied by base impedance✓
4. Dreciprocal of sag✓

A common system study base MVA is

1. Aalways 1 kVA only✓
2. B100 MVA or a value matching the largest plant rating✓
3. Calways equal to line length in km✓
4. Dalways zero✓

Per unit active power Ppu is computed as

1. Aactual MW divided by base MVA✓
2. BMW multiplied by kV only✓
3. CMVAR divided by frequency✓
4. DkA times ohm only✓

Per unit current Ipu equals

1. Aactual current times voltage only✓
2. Bfault level only✓
3. Cactual current divided by base current Ibase✓
4. Dcharging current only✓

Nominal voltage kV chosen as base is typically

1. Aminimum sag voltage only✓
2. Bcorona onset voltage only✓
3. Crotor bar voltage only✓
4. Drated or nominal system voltage of the bus✓

Advantage of per unit values near 1.0 is

1. Aelimination of all fault currents✓
2. Bimproved numerical conditioning in calculations✓
3. Czero need for symmetrical components✓
4. Dautomatic relay coordination✓

Line charging susceptance in per unit is often small compared to

1. Ashort-circuit impedance magnitudes in transmission studies✓
2. Btransformer nameplate MVA only✓
3. Cmotor slip values✓
4. Dfuse 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. Bzero for all loads always✓
3. C(|Vs| − |Vr|) / |Vr| × 100% for comparable angles✓
4. Dequal to SIL always✓