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Worksheets264_Revision
Total questions: 78
Worksheet time: 39mins
What does the cable abbreviation PILCSTA stand for?
Paper insulated lead covered steel wire armoured
Plastic insulated lead covered steel wire armoured
Paper insulated lead covered steel tape armoured
Paper insulated laminated copper steel tape armoured
What joint would be used to connect an XLPE main to an existing PILC main?
Service breach joint
Mains loop joint
Heavy duty termination
Mains transition breach joint
The amount of current that can be passed down a conductor is:
Proportional to the thickness of the insulation
Inversely proportional to the cross-sectional area
Proportional to the cross-sectional area
Inversely proportional to the number of cores
The most highly stressed part of the insulation on a high voltage cable is:
Adjacent to the conductor
Adjacent to the dielectric screen
Adjacent to the outer sheath
The stresses are all equal
Cables laid in ducts may need to be:
De-rated because of the cables’ inability to dissipate heat
Rated higher due to better heat dissipation
Increased in size to ensure clearance with the duct
De-rated because of voltage drop
When laying a new LV Mains cable the following must be recorded on the mains records:
Length of the cable run
Maximum continuous current ratings
Substation fed from
Cable voltage
What is the correct interpretation of the following information taken from a cable record? 3c 300 S4C XLPE 11kV
3 Core 300mm2 Copper unsheathed 11kV
3 x 1 core 300mm2 Aluminum lead sheathed 11kV
3 Core 300mm2 Solid Aluminum conductor 11kV
3 Core 300mm2 Stranded Copper conductor 11kV
What precautions should be taken when mixing polyurethane resin?
Wear breathing apparatus and gloves
Wear eye protection, overalls and gloves
Wear breathing apparatus and overalls
Wear overalls and gloves
What does the symbol indicate?
Link box
Open point
Bottle end
Straight joint
What is used to ensure continuity of cable sheaths when live jointing?
Insulated tools
Temporary earth bonds
Supplementary bonding
Phase to earth bonds
The type of fault where conductors are disconnected is known as:
Earth Fault
High Resistance Fault
Short Circuit Fault
Open Circuit Fault
Before proving a low voltage cable is dead what must be done with the tester?
Battery check
Proved on a known supply before and after use
Tested on an adjacent dead cable
Internally PAT tested
What can the existence of voids in compound filled cable joint boxes cause?
High resistance connections
Burning of insulation
Earth tracking faults
Ionisation
How is a HV Cable proved dead at the point of work?
Test lamps
Spiking
Pressure test
Earthing live cores
Which device would be used to open a circuit on no load only?
Isolator
Circuit breaker
Transformer
Earthing switch
Which device is used to capture and discharge over voltages?
IDMT relay
Lightning arrestor
Buchholz relay
Circuit breaker
A tap changer has the ability to alter:
The outgoing voltage
The incoming voltage
The outgoing current
The incoming current
What is the purpose of a fault thrower switch?
To stabilize the load voltage
To ensure transformer losses are reduced
To enable upstream protection devices to operate
To protect against lightning strikes
Which of the following two attributes does Sulphur Hexafluoride have?
High dielectric strength and low arc interruption properties
Low dielectric strength and high arc interruption properties
High dielectric strength and high arc interruption properties
Low dielectric strength and low arc interruption properties
An earth electrode must have which of the following attributes?
High electrical resistance
High voltage gradient
Carry fault current for 6 mins
Low electrical resistance
What is the main reason for earthing a neutral point on a low voltage 4 wire system?
Voltage Stabilisation
Overcurrnet Protection
Limits currents at houses
Prevents electrocution
What devices are designed to ensure the correct sequence of operations on substation equipment?
Safety locks
Safety documents
Interlocks
Fuses
Which device would be used to connect two busbars to allow maintenance?
Insulated busbar
Isolator
Bus section
Bus coupler
The impedance in on-load tap changers is to prevent:
Open circuiting taps
Excessive voltage rises
Short circuiting taps
Excessive voltage drop
Why is all metalwork in substations bonded and earthed?
To ensure transformer tap changers operate correctly
To ensure voltage is stabilised
To create an equi-potential zone
To create a direct path from conductors to earth
What is the reason for introducing resistors on a HV system?
To minimise the heating effects of oil in transformers
To ensure interlocks can be operated on circuit breakers
To allow transformers to work more efficiently
To limit the amount of fault current in the system
When a transformer reaches a critical temperature which form of protection will initiate a trip?
Winding temperature indicator
Buchholtz
Overcurrent temperature indicator
Earth fault
A Buchholtz relay is used for the protection of:
Circuit breakers
Transformers
Cables
Generators
By which principles does a Buchholtz relay operate?
It detects the amount of water contained in oil
It detects the amount of Hydrogen gas generated by oil
It detects the amount of oxygen gas generated by oil
It monitors the dielectric strength of oil
Which type of transformer protection will automatically operate oil pumps and cooling fans?
ONAN
XLPE
WTI
DOEF
When would a circuit breaker be most likely to require maintenance?
Post fault
Every 3 months
After every operation
Every 10 operations
What documents allow network owners to site overhead lines on private land by paying yearly rent?
Easement
Lease
Wayleave
Section 39
Which conductor would most likely be used for transmission overhead lines?
AAAC
ACSR
Copper
AAC
Electrolytic action is:
Where dissimilar metal conductors are used
A reaction inside an overhead line transformer
The amount of current a conductor can hold
A low resistance joint
What is the minimum open ground clearance for an LV overhead line?
6.4m
5.2m
2.8m
4.2m
Why are stockbridge dampers used on overhead line steel towers?
To reduce damage due to lightning
To increase conductor strength
To increase insulator resistance
To reduce damage due to vibration
When is a circuit main earth applied to an overhead line?
a) After the issue of a safety documents
b) Before the issue of a safety document
c) Before the line is isolated
d) After the additional earths have been applied
What effect does ice loading have on conductors?
a) Decreases tension
b) Increases the effect of wind loading
c) Reduces current carrying capacity
d) Decreases the effect of wind loading
The sag of a conductor is inversely proportional to:
a) The support height
b) The tension of the conductor
c) Span length
d) Conductor type
Which fault would cause the most damage to a porcelain insulator?
a) Flashover
b) Puncture
c) Surface leakage
d) Tracking
What type of gas is used in a gas filled cable?
Carbon dioxide.
Oxygen.
Helium.
Nitrogen.
What type of cable is XLPE?
Plain lead covered earth cable.
Mineral insulated cable.
Cross linked polyethylene insulated cable.
Steel wired armoured cable.
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.
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.
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? - BUT NOT TRIDENT ONES
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.
