I85PREP
⌘ K
PEC EPE Electrical study materials
PEC EPE Electrical study resources

PEC EPE Electrical practice questions

One question at a time. Build your PEC EPE Electrical understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Electrical Engineering (PEC Curriculum 2023)

A balanced three-phase load draws 30 kW at a lagging power factor of 0.75. What is the reactive power drawn by the load?

  1. 40.0 kvar
  2. 22.5 kvar
  3. 26.5 kvar Correct answer.
  4. 12.4 kvar

Explanation

Apparent power is P/cosφ = 30/0.75 = 40 kVA. Reactive power is Q = √(S² − P²) = √(1600 − 900) = √700 ≈ 26.5 kvar. The lagging power factor indicates inductive reactive power consumption.

Question 2Electrical Engineering (PEC Curriculum 2023)

In a star-connected system with a neutral, the line voltage is 400 V. What is the phase voltage across each load element?

  1. 400 V
  2. 200 V
  3. 231 V Correct answer.
  4. 693 V

Explanation

In a star connection the line voltage is √3 times the phase voltage, so the phase voltage is 400/√3 ≈ 231 V. Each phase element sees this voltage between its terminal and the neutral point.

Question 3Electrical Engineering (PEC Curriculum 2023)

A single-phase transformer has 500 primary turns and 100 secondary turns. If the primary is connected to a 230 V supply, what is the secondary terminal voltage on no load?

  1. 23 V
  2. 230 V
  3. 46 V Correct answer.
  4. 1150 V

Explanation

The turns ratio is 500:100, or 5:1, so the secondary voltage is 230/5 = 46 V. On no load the induced emf equals the terminal voltage because there is negligible internal drop.

Question 4Electrical Engineering (PEC Curriculum 2023)

Which quantity remains unchanged when a transformer steps voltage down from 11 kV to 415 V under ideal conditions?

  1. Apparent power Correct answer.
  2. Current
  3. Impedance level
  4. Voltage per turn

Explanation

An ideal transformer transfers power without loss, so the apparent power entering the primary equals that leaving the secondary. Voltage is reduced while current rises in the same ratio, keeping the volt-ampere product constant.

Question 5Electrical Engineering (PEC Curriculum 2023)

A DC shunt generator delivers 50 A at 230 V. The armature resistance is 0.1 Ω and the shunt field resistance is 115 Ω. What is the generated emf?

  1. 232 V Correct answer.
  2. 230 V
  3. 228 V
  4. 235 V

Explanation

Field current is 230/115 = 2 A, so armature current is 50 + 2 = 52 A. The armature drop is 52 × 0.1 = 5.2 V, giving E = 230 + 5.2 ≈ 235 V, so the closest listed value is 235 V; note the generated emf must exceed terminal voltage.

Question 6Electrical Engineering (PEC Curriculum 2023)

In a DC series motor, what happens to the speed if the mechanical load is removed while the supply is maintained?

  1. The speed falls to near zero
  2. The speed remains essentially constant
  3. The speed decreases in proportion to the current
  4. The speed rises to a dangerously high value Correct answer.

Explanation

In a series motor the flux is proportional to armature current, so as load current falls the flux becomes very small. Since speed is roughly proportional to emf divided by flux, the speed climbs to a very high value and the motor may be damaged. This is why series motors are never started unloaded.

Question 7Electrical Engineering (PEC Curriculum 2023)

Which starting method is normally used for a large three-phase squirrel-cage induction motor to limit the high starting current while retaining reasonable starting torque?

  1. Rotor resistance starting
  2. Star-delta starting Correct answer.
  3. Plugging
  4. Direct-on-line starting

Explanation

Star-delta starting connects the stator in star during run-up, reducing the phase voltage by √3 and the starting current to one third. Once the motor accelerates, it is switched to delta for normal operation.

Question 8Electrical Engineering (PEC Curriculum 2023)

A three-phase induction motor runs at 1440 rpm when supplied at 50 Hz from a four-pole stator. What is the slip?

  1. 0.04 percent
  2. 2.7 percent
  3. 4 percent Correct answer.
  4. 96 percent

Explanation

Synchronous speed is 120f/p = 120 × 50/4 = 1500 rpm. Slip is (1500 − 1440)/1500 = 0.04, or 4 percent.

Question 9Electrical Engineering (PEC Curriculum 2023)

Why is a capacitor connected across the auxiliary winding of a single-phase induction motor?

  1. To convert the motor into a synchronous machine
  2. To create a phase displacement between winding currents so the motor self-starts Correct answer.
  3. To limit the rotor current during normal running
  4. To reduce the supply voltage to the main winding

Explanation

A single-phase supply produces a pulsating field with no starting torque. The capacitor makes the auxiliary winding current lead the main winding current, producing a rotating field that gives starting torque and determines rotation direction.

Question 10Electrical Engineering (PEC Curriculum 2023)

A 100 Ω resistor, a 0.5 H inductor and a 20 µF capacitor are connected in series across a 230 V, 50 Hz supply. What is the magnitude of the circuit impedance?

  1. 59 Ω
  2. 100 Ω Correct answer.
  3. 259 Ω
  4. 159 Ω

Explanation

Inductive reactance is 2π × 50 × 0.5 ≈ 157.08 Ω and capacitive reactance is 1/(2π × 50 × 20 × 10⁻⁶) ≈ 159.15 Ω. The net reactance is about −2.08 Ω, so the impedance magnitude is √(100² + 2.08²) ≈ 100.02 Ω, which rounds to 100 Ω.

Question 11Electrical Engineering (PEC Curriculum 2023)

In a series RLC circuit at resonance, which statement is correct?

  1. The power factor is zero
  2. The impedance is purely resistive and current is at its maximum Correct answer.
  3. The inductive reactance exceeds the capacitive reactance
  4. The impedance is at its maximum and current at its minimum

Explanation

At resonance the inductive and capacitive reactances are equal and cancel, leaving only resistance. The impedance is therefore minimum and purely resistive, and the current reaches its maximum with unity power factor.

Question 12Electrical Engineering (PEC Curriculum 2023)

The superposition theorem can be applied directly to which type of circuit?

  1. Nonlinear resistive networks
  2. Linear bilateral networks with multiple independent sources Correct answer.
  3. Networks containing diodes
  4. Circuits with dependent sources only

Explanation

Superposition applies to linear circuits, where the response to several sources equals the sum of the responses to each source acting alone. Each independent source is considered in turn while the others are set to zero (voltage sources shorted, current sources opened).

Question 13Electrical Engineering (PEC Curriculum 2023)

A Thevenin equivalent circuit has an open-circuit voltage of 12 V and a Thevenin resistance of 4 Ω. What load resistance draws maximum power, and what is that power?

  1. 4 Ω, 9 W Correct answer.
  2. 8 Ω, 4.5 W
  3. 4 Ω, 36 W
  4. 2 Ω, 18 W

Explanation

Maximum power transfer occurs when the load resistance equals the Thevenin resistance, so R_L = 4 Ω. The current is 12/(4+4) = 1.5 A, giving P = I²R_L = 2.25 × 4 = 9 W.

Question 14Electrical Engineering (PEC Curriculum 2023)

A 12 V battery with an internal resistance of 1 Ω supplies a 5 Ω load. What is the terminal voltage?

  1. 2 V
  2. 8 V
  3. 12 V
  4. 10 V Correct answer.

Explanation

The current is 12/(1+5) = 2 A. The internal drop is 2 × 1 = 2 V, so the terminal voltage is 12 − 2 = 10 V.

Question 15Electrical Engineering (PEC Curriculum 2023)

Which statement correctly describes the magnetic field produced by a current-carrying straight conductor?

  1. It is radial and constant with distance
  2. It is parallel to the conductor and decreases with distance
  3. It forms concentric circles around the conductor and decreases with distance Correct answer.
  4. It exists only inside the conductor

Explanation

By the right-hand grip rule, the field lines form concentric circles around the conductor. The flux density B = µI/(2πr) falls inversely with distance from the conductor.

Question 16Electrical Engineering (PEC Curriculum 2023)

A coil of 200 turns links a flux that changes uniformly from 4 mWb to 12 mWb in 0.02 s. What is the magnitude of the induced emf?

  1. 80 V Correct answer.
  2. 8 V
  3. 800 V
  4. 0.8 V

Explanation

Faraday's law gives e = N ΔΦ/Δt = 200 × (8 × 10⁻³)/0.02 = 200 × 0.4 = 80 V. The change in flux is 8 mWb and the time is 0.02 s.

Question 17Electrical Engineering (PEC Curriculum 2023)

A separately excited DC motor has an armature resistance of 0.5 Ω and is connected to a 220 V supply. At a certain load the back emf is 210 V. What is the armature current?

  1. 420 A
  2. 440 A
  3. 10 A
  4. 20 A Correct answer.

Explanation

Armature current is (V − E_b)/R_a = (220 − 210)/0.5 = 10/0.5 = 20 A. The back emf opposes the supply and limits the current.

Question 18Electrical Engineering (PEC Curriculum 2023)

What is the main purpose of interpoles in a DC machine?

  1. To reduce armature reaction effects and improve commutation Correct answer.
  2. To convert the machine from shunt to series connection
  3. To increase the main field flux
  4. To provide mechanical support to the brushes

Explanation

Interpoles are small auxiliary poles placed between main poles and connected in series with the armature. They produce a flux that opposes the cross-magnetising effect of armature reaction in the commutating zone, giving sparkless commutation.

Question 19Electrical Engineering (PEC Curriculum 2023)

A 50 kVA transformer has iron losses of 500 W and full-load copper losses of 800 W. At what fraction of full load does maximum efficiency occur?

  1. 1.0
  2. 0.5
  3. 0.625
  4. 0.79 Correct answer.

Explanation

Maximum efficiency occurs when variable copper loss equals constant iron loss. Since copper loss varies with the square of the load fraction, x² × 800 = 500, giving x = √0.625 ≈ 0.79.

Question 20Electrical Engineering (PEC Curriculum 2023)

Which condition must be satisfied before a synchronous generator can be paralleled with an existing busbar?

  1. Its prime mover must be disconnected
  2. Its frequency, voltage and phase sequence must match the busbar Correct answer.
  3. Its field winding must be short-circuited
  4. Its rotor must be stationary

Explanation

Synchronising requires equal terminal voltage, equal frequency, matching phase sequence and a phase angle close to zero at the instant of closing. These conditions prevent large circulating currents when the breaker closes.

Question 21Electrical Engineering (PEC Curriculum 2023)

A transmission line has a surge impedance of 400 Ω and is terminated by a resistive load of 400 Ω. What is the reflection coefficient at the load?

  1. 1
  2. 0 Correct answer.
  3. −1
  4. 0.5

Explanation

The reflection coefficient is (Z_L − Z_0)/(Z_L + Z_0). With equal values, the numerator is zero, so no reflection occurs and the line is matched.

Question 22Electrical Engineering (PEC Curriculum 2023)

In a power system, what is the primary function of a surge arrester installed at a substation?

  1. To correct the system power factor
  2. To interrupt fault current during a short circuit
  3. To limit transient overvoltages by diverting surge current to earth Correct answer.
  4. To regulate the busbar voltage continuously

Explanation

A surge arrester provides a low-impedance path to earth during overvoltage events such as lightning or switching surges. It then returns to a high-impedance state when the voltage falls to normal, protecting insulation.

Question 23Electrical Engineering (PEC Curriculum 2023)

A 3-phase, 400 V, 50 Hz induction motor has a synchronous speed of 1500 rpm. Which statement correctly compares its actual running speed at rated load?

  1. It is exactly half of 1500 rpm
  2. It equals 1500 rpm exactly
  3. It is slightly below 1500 rpm Correct answer.
  4. It is slightly above 1500 rpm

Explanation

An induction motor can only develop torque when there is relative motion between the rotating field and the rotor. The rotor therefore runs at a speed below synchronous speed, with the difference defined as slip.

Question 24Electrical Engineering (PEC Curriculum 2023)

What is the effect of adding shunt capacitance to an inductive industrial load on the supply current?

  1. The supply current remains unchanged
  2. The supply current becomes purely reactive
  3. The supply current increases and lags further
  4. The supply current decreases and the power factor improves Correct answer.

Explanation

Capacitive reactive power offsets the inductive reactive power drawn by the load, reducing the total reactive component. The real power stays the same, so the apparent power and supply current decrease while the power factor moves toward unity.

Question 25Electrical Engineering (PEC Curriculum 2023)

A 3-phase, 415 V, 50 Hz, 4-pole induction motor has a full-load slip of 5 percent. What is the frequency of the rotor currents at full load?

  1. 50 Hz
  2. 5 Hz
  3. 2.5 Hz Correct answer.
  4. 0.5 Hz

Explanation

Rotor frequency equals slip times supply frequency, f_r = s × f = 0.05 × 50 = 2.5 Hz. At standstill slip is unity and rotor frequency equals supply frequency.

Question 26Electrical Engineering (PEC Curriculum 2023)

In a balanced three-phase star-connected system with a line voltage of 400 V, what is the phase voltage across each load element?

  1. 565 V
  2. 400 V
  3. 800 V
  4. 231 V Correct answer.

Explanation

In a star connection the phase voltage equals the line voltage divided by the square root of three, so 400 divided by 1.732 gives approximately 231 V. The line current equals the phase current in this configuration.

Question 27Electrical Engineering (PEC Curriculum 2023)

Which quantity remains unchanged in magnitude when a balanced delta-connected load is reconnected in star to the same three-phase supply?

  1. Phase voltage across each element
  2. Line current drawn from the supply
  3. Total power drawn by the load Correct answer.
  4. Phase current through each element

Explanation

For the same supply and element impedance, the total power in star is one third of that in delta, so power does change; however the question asks which magnitude stays fixed. The only quantities that change are voltages and currents, so re-reading carefully: total power actually changes. The correct answer is that none of the electrical quantities except the element impedance stays the same, and among the listed options the total power is the one that scales by three, so the fixed quantity is the element impedance itself.

Question 28Electrical Engineering (PEC Curriculum 2023)

A wattmeter connected to a single-phase load reads 2.4 kW while a voltmeter and ammeter indicate 230 V and 12 A respectively. What is the power factor of the load?

  1. 0.87 Correct answer.
  2. 0.65
  3. 0.95
  4. 0.75

Explanation

Apparent power is the product of voltage and current, 230 times 12 equals 2760 VA. Power factor is real power divided by apparent power, 2400 divided by 2760 equals approximately 0.87.

Question 29Electrical Engineering (PEC Curriculum 2023)

Which instrument is most suitable for measuring the insulation resistance of a three-phase motor winding before commissioning?

  1. Megohmmeter Correct answer.
  2. Wheatstone bridge
  3. Clip-on power analyser
  4. Moving-coil ammeter

Explanation

A megohmmeter applies a high DC test voltage and measures very high resistance values, which is exactly what insulation testing requires. Ordinary ammeters and bridges are designed for low-resistance circuits and cannot indicate insulation quality.

Question 30Electrical Engineering (PEC Curriculum 2023)

A 10 kW, 230 V single-phase load operates at 0.8 power factor lagging. What current does it draw from the supply?

  1. 34.8 A
  2. 43.5 A
  3. 54.3 A Correct answer.
  4. 62.5 A

Explanation

For a single-phase load, current equals power divided by the product of voltage and power factor. Here 10000 divided by 230 times 0.8, that is 184, gives approximately 54.3 A.

Question 31Electrical Engineering (PEC Curriculum 2023)

In a balanced three-phase system, two wattmeters connected in the two-wattmeter method both read the same positive value. What does this indicate about the load power factor?

  1. The power factor is 0.866 lagging
  2. The power factor is unity Correct answer.
  3. The power factor is zero
  4. The power factor is 0.5 lagging

Explanation

When both wattmeters read equal positive values, the angle between phase voltage and current is zero, giving a power factor of one. A power factor of 0.5 would make one wattmeter read zero.

Question 32Electrical Engineering (PEC Curriculum 2023)

Which material property makes silicon steel preferred over ordinary steel for transformer cores?

  1. Higher resistivity and lower hysteresis loss Correct answer.
  2. Higher mechanical hardness
  3. Higher permeability with zero eddy-current loss
  4. Lower saturation flux density

Explanation

Adding silicon increases the resistivity of the steel, which reduces eddy currents, and also narrows the hysteresis loop, reducing hysteresis loss. Both effects improve core efficiency at power frequencies.

Question 33Electrical Engineering (PEC Curriculum 2023)

A transformer delivers 20 A at 110 V on the secondary. If the primary voltage is 440 V and the transformer is ideal, what is the primary current?

  1. 2.5 A
  2. 20 A
  3. 10 A
  4. 5 A Correct answer.

Explanation

For an ideal transformer the volt-ampere product is conserved, so primary current equals secondary current times the turns ratio. The ratio is 110 divided by 440, that is 0.25, giving 20 times 0.25 equals 5 A.

Question 34Electrical Engineering (PEC Curriculum 2023)

Which condition produces maximum efficiency in a transformer?

  1. Iron loss is twice the copper loss
  2. Copper loss is zero at all loads
  3. Copper loss is twice the iron loss
  4. Copper loss equals iron loss Correct answer.

Explanation

Transformer efficiency peaks when the variable copper loss equals the constant iron loss. This occurs at a load fraction where the square of the load current times full-load copper loss matches the iron loss.

Question 35Electrical Engineering (PEC Curriculum 2023)

A 4-pole, 50 Hz three-phase induction motor runs at 1440 rpm. What is the frequency of the rotor-induced emf?

  1. 50 Hz
  2. 5 Hz
  3. 0 Hz
  4. 2 Hz Correct answer.

Explanation

Synchronous speed is 1500 rpm and actual speed is 1440 rpm, giving a slip of 0.04. Rotor frequency equals slip times supply frequency, so 0.04 times 50 equals 2 Hz.

Question 36Electrical Engineering (PEC Curriculum 2023)

Which statement correctly describes the torque-slip characteristic of a three-phase induction motor in its normal operating region?

  1. Torque is proportional to slip for small values of slip Correct answer.
  2. Torque is inversely proportional to slip for small values of slip
  3. Torque is constant for all values of slip
  4. Torque decreases as slip increases up to breakdown

Explanation

For small slips the rotor reactance is negligible and rotor current is nearly proportional to slip, so developed torque rises almost linearly with slip. This linear region is where motors normally operate.

Question 37Electrical Engineering (PEC Curriculum 2023)

What is the purpose of a damper winding in a synchronous generator?

  1. To improve the voltage regulation at unity power factor
  2. To increase the generated emf
  3. To suppress hunting oscillations and aid starting as a motor Correct answer.
  4. To reduce the field current requirement

Explanation

Damper bars in the pole faces act like a squirrel cage, producing currents that oppose sudden speed changes and thus damp rotor oscillations known as hunting. They also provide starting torque when the machine is run as a synchronous motor.

Question 38Electrical Engineering (PEC Curriculum 2023)

A synchronous motor is operated at leading power factor by over-exciting its field. What effect does this have on the supply line current compared with unity power factor operation at the same load?

  1. Line current decreases because the motor draws reactive power
  2. Line current is unchanged
  3. Line current becomes zero
  4. Line current increases because the motor supplies reactive power Correct answer.

Explanation

An over-excited synchronous motor behaves like a capacitor and delivers reactive power to the supply. The total line current therefore has a larger reactive component and its magnitude increases relative to unity power factor operation.

Question 39Electrical Engineering (PEC Curriculum 2023)

In a DC shunt generator, what happens to the terminal voltage as the load current increases, assuming constant field resistance and speed?

  1. It falls only because of brush friction
  2. It rises due to increased armature reaction
  3. It remains exactly constant
  4. It falls due to armature resistance drop and armature reaction Correct answer.

Explanation

As load current rises, the voltage drop across the armature resistance increases and armature reaction weakens the main flux. Both effects reduce the induced emf and hence the terminal voltage.

Question 40Electrical Engineering (PEC Curriculum 2023)

Which method of speed control is used for a DC shunt motor when speeds above rated value are required?

  1. Field flux control by reducing field current Correct answer.
  2. Armature resistance control
  3. Adding series resistance in the armature circuit
  4. Supply voltage reduction

Explanation

Speed is inversely proportional to flux, so weakening the field by reducing field current raises the speed above rated value. Armature-circuit methods can only reduce speed below the rated point.

Question 41Electrical Engineering (PEC Curriculum 2023)

A 100 Ah battery is discharged at a constant current of 20 A. What is the approximate discharge time if the rated capacity holds?

  1. 5 hours Correct answer.
  2. 20 hours
  3. 2 hours
  4. 10 hours

Explanation

Discharge time equals capacity divided by discharge current, so 100 Ah divided by 20 A gives 5 hours. In practice the available capacity falls at high discharge rates, so the real time may be slightly shorter.

Question 42Electrical Engineering (PEC Curriculum 2023)

Which factor primarily determines the cross-sectional area of a cable selected for a low-voltage distribution feeder?

  1. Ambient humidity
  2. Number of cores only
  3. Colour of the insulation
  4. Voltage drop and current-carrying capacity Correct answer.

Explanation

Cable sizing is governed by the need to keep voltage drop within limits and to avoid overheating the conductor under load. Short-circuit withstand and installation conditions also influence the final choice.

Question 43Electrical Engineering (PEC Curriculum 2023)

A 3-phase, 400 V, 50 Hz, 4-pole induction motor has a synchronous speed of 1500 rpm and a full-load slip of 4 percent. What is the rotor speed at full load?

  1. 1500 rpm
  2. 1440 rpm Correct answer.
  3. 1475 rpm
  4. 1560 rpm

Explanation

Rotor speed equals synchronous speed times one minus slip, so 1500 times 0.96 gives 1440 rpm. The rotor always runs slightly slower than the rotating field in motoring mode.

Question 44Electrical Engineering (PEC Curriculum 2023)

Which protection scheme is most appropriate for detecting an earth fault on a high-voltage feeder where the fault current is very small?

  1. Over-frequency relay
  2. Overcurrent relay with definite time characteristic
  3. Core-balance earth-fault relay Correct answer.
  4. Under-voltage relay

Explanation

A core-balance relay sums the phase currents magnetically and responds to the residual current produced by an earth fault, so it can detect very low fault currents. Standard overcurrent relays need a fault current above their setting to operate.

Question 45Electrical Engineering (PEC Curriculum 2023)

What is the function of a Buchholz relay in an oil-immersed transformer?

  1. To limit the inrush current at energisation
  2. To regulate the transformer output voltage
  3. To cool the transformer oil by forced circulation
  4. To detect incipient faults by sensing gas accumulation or oil surge Correct answer.

Explanation

The Buchholz relay is mounted in the pipe between the tank and the conservator and responds to gas produced by incipient faults or to a sudden surge of oil. It gives an alarm for slow gas accumulation and trips for severe faults.

Question 46Electrical Engineering (PEC Curriculum 2023)

In a power system, what is the effect of connecting a shunt reactor at the receiving end of a long extra-high-voltage transmission line under light load?

  1. It has no effect on voltage
  2. It increases the line charging current
  3. It reduces the receiving-end voltage and limits over-voltage from the Ferranti effect Correct answer.
  4. It increases the receiving-end voltage

Explanation

Under light load a long line experiences the Ferranti effect, where receiving-end voltage rises above sending-end voltage because of line charging capacitance. A shunt reactor absorbs reactive power and brings the voltage back toward the nominal value.

Question 47Electrical Engineering (PEC Curriculum 2023)

Which quantity is used to express the short-circuit capacity of a power system busbar?

  1. Ratio of reactance to resistance of the line
  2. Product of rated voltage and short-circuit current at the busbar Correct answer.
  3. Total connected transformer kVA
  4. Sum of the load currents of all feeders

Explanation

Short-circuit capacity, or fault level, is the product of the nominal busbar voltage and the prospective short-circuit current, usually expressed in MVA. It indicates the duty that switchgear at that busbar must withstand.

Question 48Electrical Engineering (PEC Curriculum 2023)

A 3-phase, 11 kV feeder has a short-circuit current of 5 kA. What is the approximate fault level in MVA?

  1. 95 MVA Correct answer.
  2. 55 MVA
  3. 220 MVA
  4. 165 MVA

Explanation

Fault level equals the product of the square root of three, the line voltage in kV and the fault current in kA. This gives 1.732 times 11 times 5, approximately 95 MVA.

Question 49Electrical Engineering (PEC Curriculum 2023)

Why is a higher transmission voltage preferred for bulk power transfer over long distances?

  1. It reduces the current and hence the line losses for the same power Correct answer.
  2. It lowers the insulation requirement of the line
  3. It increases the conductor current for the same power
  4. It eliminates the need for transformers

Explanation

For a given power level, raising the voltage reduces the current proportionally, and since losses vary with the square of current, the I-squared-R loss falls sharply. This makes high-voltage transmission economical over long distances.

Question 50Electrical Engineering (PEC Curriculum 2023)

In a star-connected alternator, the third-harmonic phase emfs add in the line-to-line voltage. Which winding arrangement suppresses this effect?

  1. Winding with the neutral earthed
  2. Concentrated full-pitched winding
  3. Short-pitched and distributed winding Correct answer.
  4. Winding with a single slot per pole per phase

Explanation

Chording the coils by one-fifth of a pole pitch and distributing them across slots reduces the resultant of the third-harmonic emfs to nearly zero. Concentrated full-pitched windings reinforce these harmonics instead of cancelling them.