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WorksheetsElectrical Power Engineering - Distribution and Transmission
Total questions: 40
Worksheet time: 20mins
What type of cable is XLPE?
Plain lead covered earth cable.
Mineral insulated cable.
Cross linked polyethylene insulated cable.
Steel wired armoured cable.
What type of gas is used in a gas filled cable?
Carbon dioxide.
Oxygen.
Helium.
Nitrogen.
What does not affect the rating of a cable?
Being drawn into a cable duct.
Being installed using cable cleats.
The type of soil in which it is laid.
A number of cables grouped together.
What is the purpose of screening 3-phase high voltage cables?
Stops electrolytic action.
Controls tangential stresses.
Provides a good earth continuity.
Gives extra mechanical protection.
What should happen to un-armoured lead sheathed cables laid in the ground?
Be encased in concrete.
Always be drawn in ducts.
Surrounded by sand or similar graded material.
Backfilled with the excavated soil with no specific precautions taken.
What must happen to cables being pulled into a draw-in system?
Supported on rollers throughout their length.
Supported at the duct entrance.
Pulled in by means of a winch.
Pulled in by hand.
What is the main advantage of keeping cable records and data?
Makes fault predictions much quicker.
Makes sense to untrained individuals.
Makes excellent use of I.T. equipment.
Makes system maintenance more efficient.
What do the letters ABSD refer to for an item on a cable plan?
An aerial bundled steel distributer.
An air blast system disengage.
An air break switch disconnector.
An aerial balanced safety distancer.
What should be reviewed regarding all buried services in the area before any excavation work starts?
Correct tools and equipment.
Permission from the owner.
Programme of work.
Plans or other suitable information.
What is the reason for bonding underground cables before jointing?
To ensure all live conductors are separated.
To ensure the neutral conductor is floating at 25 V.
To ensure continuity of the earth.
To ensure spiking can be undertaken.
Why are high resistance joints in electrical connections unacceptable?
A voltage is produced at the joint.
Heat is produced at the joint.
They cause electrolytic corrosion.
They cause a large increase in current.
Why is ionisation undesirable in a cable dielectric?
It affects the current rating.
It produces waxing.
It results in deterioration.
It gives rise to tangential stress.
What does cable spiking minimise the risk of?
Moisture.
Flashover.
Corona.
Puncture.
Why are capacitors installed on the main supply in a substation?
To provide a regulated power supply.
To improve the power factor correction.
To protect transformer windings.
To reduce the stress impact on cables.
What is the main purpose of multi-break construction for HV-circuit breakers?
Divide the total interrupting duty between several breaks.
Divide the open-circuit current between several breaks.
Obtain a greatly increased speed of contact separation.
Allow the circuit to be interrupted in a sequence of successive breaks.
What are off-load tap changers in distribution transformers designed to do?
Control input voltage at full load.
Allow for future increases in load.
Reduce output voltage at periods of light load.
Permit nominal output voltage to be maintained.
Why is the common or star point of the secondary winding in a three-phase four-wire distribution transformer connected to earth?
Obtain the line voltage.
Maintain the neutral at earth potential.
Enable the transformer core to be earthed.
Provide a tapping point for the neutral conductor.
What is the main reason for Earthing?
To provide a low-impedance fault path.
To eliminate voltage differences.
To allow for the use of metallic equipment.
To limit the current to earth.
What is not an example of an open circuit fault?
A broken cable.
A blown fuse.
A tripped breaker.
A closed switch.
What is the reason for bonding metal work?
To create an equipotential zone.
To create a potential equidistant zone.
To equalise potential between phases.
To create equilibrium potential between phases.
Which type of switch is used for remote tripping of a circuit breaker?
Fused.
Isolator.
Fault thrower.
Bus sectionaliser.
What is the purpose of a low earth fault loop impedance?
It ensures a good earth fault path and load current.
It ensures the earth path is a complete loop circuit.
It ensures sufficient current will flow to operate protective devices.
It ensures protective multiple earthing is effective in event of earth fault.
Which connection arrangement represents a delta connected transformer winding?
1.
2.
3.
4.
Why are substation interlock systems used?
So that one master key will open the substation.
So that the correct sequence of operations are followed.
So that the transformer can operate under wireless control.
So that all transformers on the ring are connected together.
What is the purpose of bus section switches?
To sectionalise the busbars to limit fault levels.
To effectively operate at voltages less than 120 V.
To allow for remote operation of attached equipment.
To facilitate sections of the busbar to be removed live.
Why is mineral oil used in electrical plant such as transformers and industrial switchgear?
It ensures it remains fireproof.
It requires no maintenance.
It has good dielectric strength.
It cannot be contaminated by impurities.
What should insulating oil be tested for prior to filling HV switchgear?
Viscosity.
Specific gravity.
Carbon deposit.
Dielectric strength.
What does a Buchholz relay protect when used in a circuit?
A transformer.
A motor.
An instrument.
A cable.
What initiates the operation of automatic cooling fans on an ONAF transformer?
Measurement of the transformer load current.
Measurement of the winding temperature.
Measurement of the ambient temperature.
Measurement of the wind speed.
Figure 1 represents a 33/11 kV delta-star transformer. What is resistor R used for?
To operate the relay.
To limit the earth fault current.
To limit the switching-in current.
To neutralise transformer reactance.
What is the purpose of preventative maintenance?
To make sure all faults will occur at a certain time.
To allow new transformers to be purchased on time.
To ensure there will never be any faults on the system.
To maximise uptime and continuity of the service.
With reference to regulations, which system is it not essential to earth all the associated metal work?
Underground cables.
Outdoor type substations.
Overhead lines.
Indoor type substations.
Wood pole supports are typically used for overhead voltages ranging from which of the following?
11 kV-33 kV.
11 kV-66 kV.
230 V-230 kV.
230 V-66 kV.
How many strands are there in a standard 132 kV overhead line conductor?
7.
19.
37.
59.
Why are compression type joints connected to a tension insulator filled with graphite grease?
To allow the conductor to move more easily.
To improve the insulation of the joint.
To improve holding capacity.
To prevent corrosion.
Where should the spacers holding the conductors of each phase be positioned on the 275 kV grid system of overhead lines?
Located on the ground.
Just clear of the ground.
At normal height using a man hoist.
At normal height using a trolley car.
What effect does ice have on an overhead conductor?
Has no effect on the conductor.
Reduces the tension in the conductor.
Decreases the effect of wind pressure.
Increases the effect of wind pressure.
Why are insulators provided with sheds?
To lengthen the tracking surface.
To prevent puncture.
To protect against lightning.
To reduce the risk of corrosion.
What is a simple form of lightning protection for a supply system mounted on steel towers?
A surge diverter.
An expulsion gap.
A surge inverter.
An over-running earth wire.
What would be an indication of excessive corona on a 275 kV overhead transmission?
Broken strands or spacers.
Interference caused by a kite string.
Exceptionally dry weather conditions.
A frozen cable.
