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Punjab PSEB Sr. Sec. NSQF Power (Distribution Lineman) study materials
Punjab PSEB Sr. Sec. NSQF Power (Distribution Lineman) study resources

Punjab PSEB Sr. Sec. NSQF Power (Distribution Lineman) practice questions

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Question 1Electrical Fundamentals and Basic Science

A distribution lineman needs to know the standard frequency of the AC supply used on Punjab low-tension distribution feeders. What is that frequency?

  1. 100 Hz
  2. 50 Hz Correct answer.
  3. 25 Hz
  4. 60 Hz

Explanation

India generates and distributes alternating current at a standard frequency of 50 Hz, so every LT and HT feeder in Punjab is operated at this value. The frequency is set nationally by grid policy, and equipment such as transformers and meters is rated for it.

Question 2Electrical Fundamentals and Basic Science

On a 400 V three-phase four-wire LT distribution main, what is the nominal voltage between any one phase conductor and the neutral?

  1. 11 kV
  2. 110 V
  3. 400 V
  4. 230 V Correct answer.

Explanation

The declared LT supply is 400 V between phases and 230 V between any phase and neutral, because the phase-to-neutral value equals the phase-to-phase value divided by the square root of three. Domestic single-phase consumers are therefore connected phase-to-neutral at about 230 V.

Question 3Electrical Fundamentals and Basic Science

A copper conductor of a service line has resistance R. If the lineman replaces it with a copper conductor of the same material and length but twice the cross-sectional area, the new resistance is:

  1. 4R
  2. R divided by 4
  3. R divided by 2 Correct answer.
  4. 2R

Explanation

Resistance varies inversely with cross-sectional area when resistivity and length are unchanged, so doubling the area halves the resistance. This is why thicker service conductors carry the same current with lower voltage drop and less heating.

Question 4Electrical Fundamentals and Basic Science

A single-phase domestic load draws 10 A at 230 V with a power factor of 1. What is the active power consumed?

  1. 2300 W Correct answer.
  2. 230 W
  3. 23 W
  4. 23000 W

Explanation

Active power in a single-phase circuit equals voltage multiplied by current multiplied by power factor. With unity power factor the calculation is simply 230 V times 10 A, giving 2300 W.

Question 5Electrical Fundamentals and Basic Science

A consumer's installation shows a power factor of 0.8 lagging. What does this indicate about the load current relative to the supply voltage?

  1. The current leads the voltage by about 37 degrees
  2. The current lags the voltage by about 37 degrees Correct answer.
  3. The current is 180 degrees out of phase with the voltage
  4. The current is exactly in phase with the voltage

Explanation

A lagging power factor means the current waveform reaches its peak after the voltage, which happens with inductive loads such as motors and chokes. The angle whose cosine is 0.8 is about 37 degrees, so the current lags by that amount.

Question 6Electrical Fundamentals and Basic Science

Why is a capacitor bank sometimes installed at an LT distribution substation in a rural feeder?

  1. To increase the resistance of the feeder conductors
  2. To raise the system frequency from 50 Hz to 60 Hz
  3. To convert the supply from AC to DC for the consumers
  4. To reduce the line current for a given active power and improve voltage regulation Correct answer.

Explanation

Capacitors supply reactive power locally, so the inductive reactive demand drawn through the feeder falls. The total current therefore drops for the same active power, cutting losses and improving the voltage at the far end of the line.

Question 7Electrical Fundamentals and Basic Science

A 100 kVA distribution transformer supplies a load of 80 kW at a power factor of 0.8. What is the apparent power drawn, and is the transformer loaded within rating?

  1. 80 kVA, within rating
  2. 100 kVA, exactly at rating Correct answer.
  3. 64 kVA, well within rating
  4. 125 kVA, overloaded

Explanation

Apparent power equals active power divided by power factor, so 80 kW divided by 0.8 gives 100 kVA. That equals the transformer rating, meaning it is fully loaded but not overloaded, leaving no margin for additional load.

Question 8Electrical Fundamentals and Basic Science

In a star-connected three-phase, four-wire LT system, what is the current in the neutral conductor when the three phase loads are perfectly balanced and sinusoidal?

  1. Zero Correct answer.
  2. Equal to the phase current
  3. Twice the phase current
  4. The arithmetic sum of the three phase currents

Explanation

In a balanced three-phase system the three phase currents are equal in magnitude and displaced by 120 degrees, so their phasor sum is zero. The neutral therefore carries no current under perfect balance, and it carries current only when the phases are unbalanced.

Question 9Electrical Fundamentals and Basic Science

A lineman measures the voltage at a consumer's terminal as 200 V while the declared supply is 230 V. Which statement about this condition is correct?

  1. The consumer is receiving a higher-than-declared voltage
  2. The consumer's equipment may draw higher current, and the low voltage indicates excessive drop or overload Correct answer.
  3. The frequency of the supply has fallen below 50 Hz
  4. The power factor of the installation has become zero

Explanation

A terminal voltage well below the declared value points to excessive voltage drop along the service or feeder, often from overload or a poor connection. Constant-power loads such as motors then draw more current at the lower voltage, worsening heating and drop.

Question 10Electrical Fundamentals and Basic Science

Which material property makes copper preferred over aluminium for many LT service connections of the same current rating?

  1. Lower melting point than aluminium
  2. Higher resistivity for the same cross-section
  3. Lower resistivity, allowing a smaller cross-section for the same resistance Correct answer.
  4. Greater susceptibility to corrosion in normal atmospheres

Explanation

Copper has lower resistivity than aluminium, so a copper conductor of a given length needs less cross-sectional area to achieve the same resistance. That is why copper is common in service connections and jointing where space and contact quality matter.

Question 11Electrical Fundamentals and Basic Science

A 1 kW immersion heater runs for 3 hours each day. What energy does it consume in one day?

  1. 300 kWh
  2. 0.33 kWh
  3. 30 kWh
  4. 3 kWh Correct answer.

Explanation

Electrical energy in kilowatt-hours equals power in kilowatts multiplied by time in hours. One kilowatt for three hours therefore gives 3 kWh, which is the unit basis used for consumer billing.

Question 12Electrical Fundamentals and Basic Science

A current transformer of ratio 100/5 A is used with an ammeter on a distribution feeder. If the ammeter reads 3 A, what is the approximate line current?

  1. 300 A
  2. 60 A Correct answer.
  3. 15 A
  4. 500 A

Explanation

The CT ratio means the primary current is twenty times the secondary current, since 100 divided by 5 is 20. Multiplying the 3 A secondary reading by 20 gives about 60 A in the feeder.

Question 13Electrical Fundamentals and Basic Science

In a distribution system, what is the main purpose of an earthing system at a pole-mounted substation?

  1. To increase the line voltage for better regulation
  2. To provide a low-resistance path so fault current operates protective devices and to limit touch voltage Correct answer.
  3. To reduce the frequency of the supply
  4. To store reactive energy for peak loads

Explanation

Earthing gives fault current a defined low-resistance return path so that fuses or breakers clear the fault quickly. It also holds exposed metalwork near earth potential, limiting the touch and step voltages a person could experience.

Question 14Electrical Fundamentals and Basic Science

A fuse protecting a distribution transformer secondary is rated 100 A. A sustained fault current of 400 A flows. What is the expected behaviour and the reason?

  1. The fuse will operate only after the voltage falls to zero
  2. The fuse will not operate because the current is below the rating
  3. The fuse will operate only if the power factor exceeds unity
  4. The fuse element melts and clears the circuit because the current greatly exceeds its rating Correct answer.

Explanation

A fuse element melts when the current through it exceeds its rating for sufficient time, and a fault current of four times the rating heats it rapidly. The element then ruptures and interrupts the circuit, protecting the downstream equipment.

Question 15Electrical Fundamentals and Basic Science

Which statement correctly describes the relationship between line voltage and phase voltage in a star-connected three-phase transformer secondary?

  1. Line voltage equals phase voltage
  2. Line voltage equals phase voltage divided by the square root of three
  3. Line voltage equals phase voltage multiplied by the square root of three Correct answer.
  4. Line voltage equals three times the phase voltage

Explanation

In a star connection the line voltage is the phasor difference of two phase voltages displaced by 120 degrees, which gives a factor of the square root of three. Thus a 230 V phase winding produces about 400 V between lines.

Question 16Electrical Fundamentals and Basic Science

A lineman needs to check whether a joint in an LT line is heating under load. Which instrument is most suitable for a quick, non-contact check?

  1. A megger
  2. A phase sequence indicator
  3. An earth tester
  4. An infrared thermometer Correct answer.

Explanation

An infrared thermometer measures surface temperature without contact, so a hot joint can be detected safely while the line is energised. High resistance at a joint causes local heating that shows up as an abnormal temperature rise.

Question 17Electrical Fundamentals and Basic Science

A megger is used on a de-energised LT circuit and shows a very low insulation resistance to earth. What does this most probably indicate?

  1. The conductor cross-section is too large
  2. The insulation has deteriorated or there is a leakage path to earth Correct answer.
  3. The circuit is healthy and ready for energisation
  4. The supply frequency is incorrect

Explanation

An insulation resistance test applies a DC voltage and measures leakage; a very low reading means current is passing through deteriorated insulation or a damp path to earth. The circuit should be investigated and not energised until the reading recovers.

Question 18Electrical Fundamentals and Basic Science

Two identical 100 W lamps are connected in series across a 230 V supply. Assuming equal and constant resistance, what is the approximate power dissipated by each lamp?

  1. 200 W
  2. 25 W Correct answer.
  3. 50 W
  4. 100 W

Explanation

In series the two lamps share the supply voltage equally, so each receives about 115 V, half its rated voltage. Since power varies with the square of voltage for a fixed resistance, each lamp dissipates about one quarter of its rated power, roughly 25 W.

Question 19Electrical Fundamentals and Basic Science

Why is alternating current, rather than direct current, used for LT distribution in Punjab villages?

  1. AC eliminates the need for earthing
  2. AC conductors have zero resistance
  3. AC allows voltage to be changed easily by transformers, reducing transmission and distribution losses Correct answer.
  4. AC cannot produce magnetic fields, so it is safer

Explanation

Transformers work on alternating flux, so AC voltage can be stepped up for efficient bulk transfer and stepped down for safe consumer use. This ability to change voltage levels with simple static equipment is the main reason AC dominates distribution.

Question 20Electrical Fundamentals and Basic Science

A three-phase balanced load draws a line current of 10 A at 400 V line voltage with a power factor of 0.8. What is the approximate active power?

  1. 16.0 kW
  2. 8.0 kW
  3. 3.2 kW
  4. 5.5 kW Correct answer.

Explanation

Three-phase power equals the square root of three times line voltage times line current times power factor. Using 1.732 times 400 times 10 times 0.8 gives about 5540 W, or roughly 5.5 kW.

Question 21Electrical Fundamentals and Basic Science

A conductor carrying a steady current of 50 A has a resistance of 0.02 ohm per span of the line. What is the power lost as heat in that span?

  1. 1000 W
  2. 50 W Correct answer.
  3. 1 W
  4. 100 W

Explanation

Copper loss equals the square of the current multiplied by resistance. Fifty amperes squared is 2500, and multiplying by 0.02 ohm gives 50 W dissipated in the span.

Question 22Electrical Fundamentals and Basic Science

Why is the skin effect more significant at high voltage distribution than at LT, and what does it do to effective conductor resistance?

  1. It changes the supply frequency itself
  2. It has no effect on resistance at any frequency
  3. It forces current to the conductor centre and lowers effective resistance
  4. It forces current to the conductor surface at higher frequencies and raises effective resistance Correct answer.

Explanation

Skin effect concentrates alternating current toward the outer surface of a conductor, reducing the useful cross-section and raising effective AC resistance. The effect grows with frequency, so it matters more where high-frequency components or large conductors are involved.

Question 23Electrical Fundamentals and Basic Science

A consumer complains that his single-phase meter runs fast. Which check is most relevant before concluding that the meter is faulty?

  1. Verify the meter constant and time a known load against the meter disc revolutions Correct answer.
  2. Measure the earth electrode resistance at the substation
  3. Check the phase sequence of the LT feeder
  4. Test the transformer oil dielectric strength

Explanation

Meter accuracy is verified by comparing the energy registered for a known load with the expected value derived from the meter constant. Timing disc revolutions against a controlled load shows whether the meter is registering correctly.

Question 24Electrical Fundamentals and Basic Science

Which of the following best explains why bundled or larger cross-section conductors are used on long LT feeders with heavy load?

  1. To reduce voltage drop and copper loss for a given current Correct answer.
  2. To raise the supply frequency at the load end
  3. To increase the reactance of the line
  4. To increase the voltage drop along the feeder

Explanation

Voltage drop and copper loss both fall as conductor resistance decreases, and resistance falls as cross-sectional area increases. Larger conductors therefore keep the far-end voltage within limits and reduce energy wasted as heat.

Question 25Power Distribution System Overview and Layout

In a typical Punjab urban 11 kV distribution feeder, which conductor arrangement is most commonly used for the three-phase main line on overhead poles?

  1. Single-core XLPE cable laid directly in the soil
  2. Bare copper conductors suspended on shackle insulators at the pole top
  3. Bare ACSR conductors on pin insulators in a horizontal or triangular formation Correct answer.
  4. Insulated ABC bunched cable strung between stay wires

Explanation

Overhead 11 kV feeders in Punjab are normally built with bare ACSR conductors carried on pin insulators, arranged either horizontally on cross-arms or in a triangular formation at the pole top. This gives adequate phase-to-phase and phase-to-earth clearance at minimum cost. Insulated bunched cable is used mainly for LT or for congested narrow lanes, not for the standard 11 kV main line.

Question 26Power Distribution System Overview and Layout

A distribution system is described as a 'radial' system. What is the defining operational characteristic of this layout?

  1. Power flows from the substation to the load along a single path with no alternative feed Correct answer.
  2. Loads are connected in a closed ring that is switched at both ends
  3. Every consumer is fed from two independent substations simultaneously
  4. The feeder is energised only from the consumer end during peak hours

Explanation

In a radial layout each load point has only one electrical path back to the source, so a fault anywhere on the feeder interrupts all consumers downstream of it. This is the simplest and cheapest distribution arrangement and is widely used for LT and many 11 kV feeders. Reliability is improved only by adding sectionalising or later converting to a ring or interconnected arrangement.

Question 27Power Distribution System Overview and Layout

Why is a ring main arrangement adopted for some 11 kV distribution feeders in dense urban areas?

  1. It eliminates the requirement of earthing at the distribution transformer
  2. It allows the faulty section to be isolated and supply restored from the other end Correct answer.
  3. It removes the need for any protective relays on the feeder
  4. It permits the use of a lower system voltage for the same load

Explanation

A ring main gives two paths to each load point, so when a section faults, the isolators on either side of the fault are opened and the healthy sections can be re-energised from the opposite end. This shortens outage duration and improves supply reliability. It does not remove protection or earthing requirements, nor does it change the system voltage.

Question 28Power Distribution System Overview and Layout

What is the principal reason for keeping the length of an LT distribution main short in a Punjab village or mohalla network?

  1. To limit voltage drop and line losses on the low-voltage side Correct answer.
  2. To increase the short-circuit level at the consumer terminals
  3. To reduce the number of distribution transformers required
  4. To allow the use of thinner conductors for the same current

Explanation

At low voltage a given current produces a much larger percentage voltage drop and I-squared-R loss, so LT mains are kept short and the distribution transformer is placed near the load centre. This keeps consumer terminal voltage within permissible limits. Shortening the main does not raise fault level or permit thinner conductors.

Question 29Power Distribution System Overview and Layout

In a three-phase four-wire LT distribution system, which conductor is deliberately earthed at the distribution transformer neutral?

  1. The blue phase conductor
  2. The neutral conductor Correct answer.
  3. The red phase conductor
  4. The yellow phase conductor

Explanation

The neutral of the LT winding is solidly earthed at the distribution transformer and the neutral conductor is run along the line to carry unbalanced current and provide a return path for single-phase loads. Earthing the neutral also keeps phase-to-earth voltage stable. Phase conductors are never earthed in normal operation.

Question 30Power Distribution System Overview and Layout

A distribution transformer is to be sited in a mixed urban locality. Which consideration most directly governs its location in the distribution layout?

  1. Placing it near the load centre to minimise LT feeder length and voltage drop Correct answer.
  2. Placing it at the far end of the area so that LT mains run back towards the substation
  3. Placing it wherever the 11 kV line happens to end, irrespective of load
  4. Placing it at the highest available pole top to reduce insulation cost

Explanation

The transformer should sit at the load centre so that the low-voltage mains radiating from it are as short as possible, which limits voltage drop and copper loss. The 11 kV extension is comparatively cheap to run to that point. Siting purely by the end of the existing 11 kV line ignores the load distribution.

Question 31Power Distribution System Overview and Layout

What is the function of a sectionalisor installed on an 11 kV feeder?

  1. To isolate a faulty section so that healthy sections upstream remain energised Correct answer.
  2. To step down 11 kV to 400 V for distribution
  3. To improve the power factor of the feeder
  4. To convert three-phase supply into single-phase supply

Explanation

A sectionalisor divides a long feeder into manageable sections so that a fault in one section can be isolated and the healthy upstream section re-energised. This reduces the number of consumers affected by a single fault. Voltage transformation, power-factor correction and phase conversion are done by other equipment.

Question 32Power Distribution System Overview and Layout

In the standard layout of an LT distribution network, what does an ABC (aerial bunched cable) system replace?

  1. Bare overhead LT conductors on poles Correct answer.
  2. The energy meter at the consumer premises
  3. The earthing electrode at the transformer
  4. The distribution transformer itself

Explanation

Aerial bunched cable is an insulated overhead LT construction in which the phase and neutral conductors are twisted together and supported on poles. It replaces bare LT conductors, reducing accidental contact, pilferage and clearance problems in congested areas. It does not replace transformers, meters or earthing.

Question 33Power Distribution System Overview and Layout

Why are distribution transformers in a Punjab urban network often connected in a bank or provided with a spare unit at the same location?

  1. To eliminate the need for a neutral conductor
  2. To reduce the number of LT circuits required
  3. To allow load transfer and quick restoration when one transformer is taken out for repair Correct answer.
  4. To increase the system frequency during peak load

Explanation

Providing two or more transformer units at a load centre lets the operator transfer load to the healthy unit when one is isolated for maintenance or repair, keeping supply continuous. It is an operational reliability measure. It has no effect on frequency, LT circuit count or the need for a neutral.

Question 34Power Distribution System Overview and Layout

Which of these describes the correct sequence of the distribution chain from the transmission system down to the LT consumer?

  1. Distribution transformer, transmission substation, LT main, 11 kV feeder, service connection
  2. 11 kV feeder, transmission substation, service connection, distribution transformer, LT main
  3. Transmission substation, 11 kV feeder, distribution transformer, LT main, service connection Correct answer.
  4. LT main, distribution transformer, service connection, 11 kV feeder, transmission substation

Explanation

Power leaves the transmission substation at 11 kV (or 33 kV then 11 kV), travels along the feeder to the distribution transformer, is stepped down to 400 V, flows through the LT main and finally reaches the consumer through the service connection. Following this order correctly traces the voltage transformation at each stage.

Question 35Power Distribution System Overview and Layout

A 33/11 kV substation feeds four radial 11 kV feeders. If one feeder faults near the substation busbar, what is the expected effect on the other three feeders?

  1. They supply at reduced frequency until repairs are completed
  2. They are energised at 33 kV until the fault is cleared
  3. They are all automatically de-energised along with the faulty feeder
  4. They continue to supply, provided the faulty feeder breaker clears the fault Correct answer.

Explanation

Each radial feeder has its own circuit breaker at the substation, so a fault on one feeder trips only that breaker while the busbar and the other feeders remain energised. Selectivity of protection is what limits the outage. The other feeders are neither de-energised nor operated at a different voltage or frequency.

Question 36Power Distribution System Overview and Layout

What is the main purpose of providing a guard or barbed-wire fencing around an outdoor distribution transformer installed at ground level in a public area?

  1. To prevent unauthorised persons from approaching live parts Correct answer.
  2. To improve the earth resistance of the transformer
  3. To increase the transformer cooling efficiency
  4. To support the LT service connections mechanically

Explanation

Ground-mounted transformers in public places must be enclosed so that unauthorised persons cannot come near live terminals or climb the structure. This is a safety requirement of the distribution layout. Fencing does not affect earthing, cooling or the mechanical support of service lines.

Question 37Power Distribution System Overview and Layout

In a double-pole or H-pole structure used for an LT distribution line, what is the main structural advantage over a single pole?

  1. It reduces the number of insulators required per phase
  2. It provides greater transverse strength and a wider base for heavier conductors and cross-arms Correct answer.
  3. It allows the line to be operated at a higher voltage class
  4. It removes the need for stay wires at angle points

Explanation

Two poles braced together give a wider base and greater resistance to transverse wind and conductor tension loads, which suits heavier LT mains and larger cross-arms. The insulator count per phase is unchanged. Voltage class is fixed by insulation design, and stays may still be needed at angle points.

Question 38Power Distribution System Overview and Layout

A lineman observes that the LT neutral conductor on a four-wire main has been broken near a pole. What is the immediate consequence for single-phase consumers downstream of the break?

  1. Their supply voltage falls to exactly zero and nothing is damaged
  2. Their phase conductors become earthed through the broken neutral
  3. Their neutral return is lost, so phase-to-neutral voltages become abnormal and equipment may be damaged Correct answer.
  4. Their supply frequency drops in proportion to the load

Explanation

With the neutral broken, single-phase loads downstream lose their return path and the neutral point floats, so the voltage across individual consumers depends on the imbalance of connected loads. Some consumers see overvoltage and others undervoltage, which can damage appliances. Frequency is unaffected and phase conductors do not become earthed.

Question 39Power Distribution System Overview and Layout

Which layout feature most directly reduces the length of LT service mains in a planned residential colony?

  1. Providing more stay wires on the LT poles
  2. Locating distribution transformers at the centre of each load block Correct answer.
  3. Increasing the height of the LT poles
  4. Using a larger conductor size for the 11 kV feeder

Explanation

Placing a transformer at the centre of each block means service mains radiate outwards in all directions, so each consumer is close to the source. This minimises LT service length and voltage drop. Pole height, 11 kV conductor size and stays affect other aspects of the design, not service-main length.

Question 40Power Distribution System Overview and Layout

What is the purpose of a stay wire and anchor provided at an angle or terminal pole of an overhead distribution line?

  1. To provide an additional earth connection for the line
  2. To support the insulators on the cross-arm
  3. To carry the neutral current back to the transformer
  4. To resist the unbalanced pull of conductors and keep the pole vertical Correct answer.

Explanation

At angle and terminal poles the conductor tension is not balanced, so a stay wire transfers the resultant pull to an anchor in the ground and prevents the pole from leaning or failing. Stays are mechanical supports only. They do not carry load current, provide earthing or hold insulators.

Question 41Power Distribution System Overview and Layout

In an interconnected distribution arrangement, what is the role of a normally open point (NOP) between two feeders?

  1. It continuously carries load current between the two feeders in normal operation
  2. It steps down the voltage between the two feeders
  3. It earths both feeders whenever a fault occurs
  4. It allows load to be transferred from one feeder to the other during an outage by closing the point Correct answer.

Explanation

The normally open point keeps the two feeders electrically separate during normal operation, but it can be closed after isolating the fault so that healthy load is picked up by the adjacent feeder. This is the basis of interconnected distribution. In normal operation no current flows through the NOP and it does not earth or transform anything.

Question 42Power Distribution System Overview and Layout

Why is the distribution transformer neutral earthed at more than one point along the LT line in some networks?

  1. To increase the phase-to-phase voltage supplied to consumers
  2. To reduce the number of poles required for the LT line
  3. To allow the LT line to be operated without a neutral conductor
  4. To keep the neutral near earth potential along the run and limit voltage rise on the neutral during unbalanced loading Correct answer.

Explanation

Repeated neutral earthing holds the neutral close to earth potential along the length of the LT main, so touch voltage on the neutral and voltage rise from unbalanced current are limited. It is a safety and voltage-regulation measure. It does not change phase-to-phase voltage, pole count or the need for a neutral.

Question 43Power Distribution System Overview and Layout

Which type of distribution substation is typically installed on a single pole or H-pole structure in a rural 11 kV feeder?

  1. Indoor metal-clad switchgear substation
  2. Underground vault substation
  3. Gas-insulated 66 kV substation
  4. Pole-mounted distribution transformer substation Correct answer.

Explanation

Rural 11 kV distribution commonly uses a pole-mounted transformer with a small platform, drop-out fuses and an LT distribution box. It is cheap, quick to install and needs no building. Indoor, underground-vault and gas-insulated substations are used at higher voltages or in dense urban locations.

Question 44Power Distribution System Overview and Layout

A 11 kV feeder is 15 km long and serves scattered rural loads. Which layout measure best improves voltage regulation at the tail end without changing the conductor?

  1. Adding a step-type or capacitor-based voltage regulator or switched shunt capacitors along the feeder Correct answer.
  2. Increasing the length of the LT mains at the tail end
  3. Lowering the sending-end voltage at the substation
  4. Reducing the number of distribution transformers on the feeder

Explanation

On a long rural feeder the voltage falls progressively towards the tail end. Switched shunt capacitors or a feeder voltage regulator raise and hold the voltage without changing the conductor. Lengthening LT mains, cutting transformer numbers or lowering the sending voltage would all worsen tail-end voltage.

Question 45Power Distribution System Overview and Layout

What is a service connection in the distribution layout?

  1. The earthing strip buried below the transformer
  2. The busbar inside the 33/11 kV substation
  3. The 11 kV line between two substations
  4. The conductors and fittings that connect a consumer's premises to the LT distribution main Correct answer.

Explanation

The service connection is the final link between the LT main and the consumer's installation, usually a short insulated service cable with a fuse and meter. It is the boundary between utility and consumer equipment. Substation busbars and 11 kV interconnection lines belong to the upstream network.

Question 46Power Distribution System Overview and Layout

Why are drop-out expulsion fuses mounted on the cross-arm ahead of a pole-mounted distribution transformer?

  1. To clear transformer faults and allow the transformer to be isolated visibly from the feeder Correct answer.
  2. To earth the transformer tank during maintenance
  3. To regulate the LT voltage supplied to consumers
  4. To measure the energy consumed by the transformer

Explanation

Drop-out fuses protect the transformer against overcurrent and faults and provide a visible isolating gap when opened, so the transformer can be worked on safely. They do not regulate voltage, earth the tank or meter energy. Earthing is done separately with an earth switch and electrode.

Question 47Power Distribution System Overview and Layout

In an LT distribution network, what does a 'balanced' distribution of single-phase loads across the three phases achieve?

  1. Increased neutral current and higher line loss
  2. Reduced neutral current and lower voltage unbalance at consumer terminals Correct answer.
  3. A higher phase-to-phase voltage at the far end of the main
  4. Elimination of the need for a neutral conductor

Explanation

Spreading single-phase consumers evenly over the three phases keeps the vector sum of phase currents small, so neutral current and neutral-to-earth voltage rise are reduced. This improves voltage balance at consumer terminals and lowers losses. It does not remove the neutral or raise the phase-to-phase voltage.

Question 48Power Distribution System Overview and Layout

A colony has a 400 V LT main fed from a 250 kVA distribution transformer. The lineman notes that the voltage at the far end of the main is low only during evening peak. Which explanation is most consistent with this observation?

  1. The neutral earthing has been removed from the transformer
  2. The LT conductors have changed their material at peak hours
  3. Voltage drop along the LT main increases with the higher peak load current Correct answer.
  4. The transformer secondary voltage is permanently set too low

Explanation

Voltage drop equals current times impedance, so it grows as the evening load current rises, producing a low far-end voltage only at peak. A permanently low transformer tap would cause low voltage at all times, not only at peak. Earthing and conductor material do not change with time of day.

Question 49Transmission and Distribution Lines, Conductors and Insulators

In an 11 kV three-phase overhead distribution line, what is the approximate phase-to-phase voltage between any two conductors?

  1. 230 V
  2. 33 kV
  3. 11 kV Correct answer.
  4. 1.1 kV

Explanation

The declared system voltage of a distribution feeder is expressed as the phase-to-phase (line) voltage, so an 11 kV line has roughly 11 kV between any two phase conductors. The phase-to-neutral value is about 6.35 kV, obtained by dividing by √3. The 230 V figure is a single-phase domestic supply, not the line voltage.

Question 50Transmission and Distribution Lines, Conductors and Insulators

A 66 kV line is strung with a conductor whose cross-section is stated as 100 mm² ACSR. What does the 'A' in ACSR indicate?

  1. Aluminium Correct answer.
  2. Aerial
  3. Annealed
  4. Armoured

Explanation

ACSR stands for Aluminium Conductor Steel Reinforced, where the outer strands are aluminium to carry current and the core strands are steel for mechanical strength. The 'A' therefore denotes aluminium, not a heat treatment or a construction class. Armouring and aerial are unrelated descriptors.