EPS Flashcards
(2) Function of singapore electricity market
1) To promote efficient supply of the competitively priced electricity.
2) To open up the electricity retail market.
3) To allow certain government assest to be privatised.
4) To encourage private investment in Singapore’s power system.
(2) Function of energy market authority ?
1) To protect the interests of consumers.
2) To ensure that the electricity licensees provide an efficient service.
3) To ensure security of supply of electricity to consumers.
4) To protect the public from dangers arising from electricity related activities.
(2) Function of energy market company ?
1) Operate wholesale market.
2) Prepare schedules for generating units.
3) Settle accounts of market participants.
4) Facilitate the planning
(2) Function of power system operator ?
1) Maintain reliability of the power system.
2) Forecasting and reporting on the conditions.
3) Coordinating actions.
4) Dispatch facilities,
(2) Function of market support services licensee ?
1) Reading electricity meters.
2) Facilitate the access.
3) Facilitate the transfer.
4) Supplying electricity.
(3) Saving in conductor material is not offset by ?
1) Increased in cost of the insulating line.
2) Increase in size of transmission line structures.
3) Increase in size of generating stations and substations.
(3) Advantages of overhead lines ?
1) Cheaper.
2) Cost of overhead lines does not increase much.
3) Available for high voltage.
4) Can be easily repaired and put back into service.
(3) Advantages of underground lines ?
1) Underground system does not interfere with amenity.
2) In densely populated areas.
3) Maintenance is very low.
4) Cable is useful for suppressing line surges.
(3) Function of feeders ?
Connect the mains substation to various distributions substations.
(4) Types of power stations ?
1) Thermal power stations
2) Hydo-electric power station
3) Nuclear power station
4) Diesel power station
5) Wind electric generator
6) Solar plant
7) Tidal plant
(4) Types of thermal power stations in Singapore ?
1) Steam turbines
2) Gas turbines
3) Combined cycle system
(4) Which power station has the most efficient power station ?
Combined cycle system
(4) Choice of site for thermal power station ?
1) The power station should be located near coal mine to reduce transportation cost.
2) it should be located near continuous supply of water foe cooling purposes.
(4) Advantages for thermal power station ?
1) It is not affected by weather conditions.
2) It can be installed at any places if transportation for fuel are available.
(4) Disadvantages for thermal power station ?
1) High initial cost.
2) High maintenance cost.
3) High running cost due to fuel cost.
4) Fumes pollute the atmosphere.
(4) Choice of site for hydro power station ?
1) Sufficient quantity of water at a reasonable hight.
2) Reservoir should have a large catchment area.
(4) Advantages for hydro power station ?
1) Construction is simple.
2) It can be started up instantly.
3) Running charges are very low.
4) It does not cause pollution.
(4) Disadvantages for hydro power station ?
1) Initial cost is very high because of enormous civil engineering work.
2) High cost of power.
3) Long dry seasons may affect the water supply.
(4) Choice of site for nuclear power station ?
1) It must be located away from densely populated.
2) It must have adequate water supply for cooling purposes.
(4) Advantages for nuclear power station ?
1) It requires less space as compared to other power stations of similar capacity.
2) The transmission and distribution cost are lower as it can be located near industrial load center.
(4) Disadvantages for nuclear power station ?
1) High initial cost due to sophisticated advance technology and safety features.
2) High salaries are paid for specialised personnel to operate the plant.
3) Harmful radioactive wave leakage is a potential danger.
4) Nuclear waste disposal is a sensitive issue.
(4) Choice of site for diesel power station ?
It can be located any where.
(4) Advantages for diesel power station ?
1) It can be located any where.
2) it occupies little space .
3) It can be started up very quickly.
4) Design layout is simple.
5) Requires little operating staff.
(4) Disadvantages for diesel power station ?
1) Fuel cost is high.
2) Lubrication cost is high.
3) Maintenance cost is high.
4) It is only suitable for small power generation as operation cost is high.
(5) What is the function of substation ?
It is to transform elcetrical energy from one form to another (E.g. AC to AC or from one voltage level to another)
(5) Additional functions provided by the substation ?
1) Provide switching between transmission lines.
2) Regulate voltage on the outgoing distribution feeders.
3) Provide points for safety devices to be installed.
4) Provide a place to make measurement.
(5) Types of substations ?
1) Transmission substations
2) Distribution substations
3) Industrial substations
(5) Requirements for substations ?
1) Power cable should be separated from control cable.
2) Oil handling arrangement should be adequate.
3) Means of extinguishing should be available.
4) Fire proof switchroom and cable room should be provided to avoid fire hazard.
(5) Equipments in the substation.
1) Insulators
2) Busbar
3) Circuit breakers and reclosers
4) Air break disconnect switch
5) Transformer
6) Voltage regulators
7) Protective fuses and relays
8) Switchboard
9) Control, cables and conduit system
10) Carrier current system equipment
11) Control room
(5) Insulators
- Used for supporting live conductors and busbars.
- Voltages up to 66kV
(5) Busbars
Main bar or conductor carrying electric current
(5) Circuit breakers and reclosers
- Making and breaking high voltage circuit when they carry the normal load current.
- Pneumatic or hydraulic or mechanically operated breaker is used.
(5) Air break disconnect switch
Opened only after the circuit breaker had opened the circuit. Installed on both end of equipment to de-energise it effectively for maintenance.
(5) Transformer
Tap changing mechanism on low voltage side.
(5) Voltage regulators
It is a transformer with a variable ratio. When outgoing voltage becomes too high or too low the regulator will automatically adjust the ration of the transformation to bring the voltage to the predetermined value.
(5) Protective fuse and relays
Commonly provided on the high voltage side along wit the other protective devices.
(5) Switchboard
Consist of meters, relays and control equipments.
(5) Carrier current equipment
Used for communications, relaying, tele-metering or for supervisory control.
(5) Control room
houses all equipment such as switchboard, carrier current equipment, batteries.
(5) Selection of busbar depends on ?
1) Flexibility during operation.
2) Immunity during total shut-down.
3) Initial cost of installation.
4) Load handled by the busbar.
(5) Types of busbar system ?
1) Single busbar system
2) Sectionalised busbar system
3) Double busbar system
4) A breaker and a half arrangement
5) Ring mains
(5) Single busbar system
- Cheapest arrangement
- Total shut dow of the station where is a busbar fault
- Necessary to de-energies the system for maintenance
- Normally used in distribution system
(5) Sectionalised busbar system
- Either section can be isolated from the other under fault or maintenance condition.
- Supply will be shut down for the entire section in case of fault or work on the entire section.
- Normally used in distribution system.
(5) Double busbar system
Maintenance without disturbance to any of the circuit.
(5) A breaker and a half arrangement
- Economical compared to the double bus system.
- Normally used in generating system.
(5) Ring main
- Greater flexibility as the generators connected to any one busbar can be used to supply load to feeder on any section.
- Normally used in transmission or important distribution switching station.
(5) Outdoor substations advantages ?
1) Smaller construction works needed.
2) Lesser building materials requires.
3) Lower installation cost.
4) Shorter installation time.
5) Extension of the scheme is easier.
(5) Indoor substations advantages
1) Less space is required.
2) Less maintenance cost is cheaper.
3) Switching operation is not affected by weather.
(6) Requirement of a good distribution system.
1) Reliable, that is, there should be no power failure.
2) Cost of the system should not be unduly excessive.
3) Incoming voltage to the consumers premises must be maintained within +-6% of the declared voltage.
4) The system should not be overload.
5) The power loss should be at minimum.
(6) Typical network consist of ?
1) Feeder
2) Distributors
3) Servie mains
(6) Types of feeders ?
1) Radial feeders
2) Ring feeders
(6) Radial feeders
Cheap and simple
(6) Ring feeders
- Close circuit
- Costly but the supple is fed from both direction.
- Can be transformed into a double ring circuit by the addition of an interconnector.
(6) Feeding patterns of a distributor ?
1) Distributor fed from one end
2) Distributor fed from both end with unequal voltage
3) distributor fed from both end with equal voltage
(7) What is the distance for a short line transmission ?
60 Km
(7) What is the distance for a medium line transmission ?
Between 60 Km and 70 Km
(8) What is the purpose of voltage control ?
1) To keep the consumer’s voltage at the required supply.
2) To maintain a stable supply system with minimum interruption to load.
3) To step up/down voltage to the required consumer’s voltage level.
(8) Types of tap changing transformer ?
1) Off-load tap-changer
2) On load tap changer
(8) Process to change off-load tap-changer ?
- De-energising the transformer
- Changing the tap position
- Re-energising it back to service
(8) Advantages of on load tap changer ?
1) Less wearing of tapping.
2) Ease of maintenance and inspection.
(8) Disadvantages of on load tap changers ?
1) During switching there is a chance of transformer impedance which causes a voltage surge.
2) There are twice as many switching as voltage steps.
3) Complicated in design if a high reactance between the parallel windings is to be introduce.
(8) Advantages of auto-regulated boosted transformer ?
1) Any failure in booster will not throw the main transformer out of service.
2) The booster can be cut out for inspections or overhaul while the main transformer remains in service.
3) The main transformer has no tapping and no working parts.
(8) Disadvantages of auto-regulated boosted transformer ?
1) It is more expensive when the distributor already regulated by a tap changer.
2) Together with the main transformer, they increase the losses thereby affecting transmission efficiency.
3) They take up more space.
(9) Annual cost of power station can be decided into three parts.
1) Fixed cost
2) Semi-Fixed cost
3) Running cost
(9) Fixed cost
Comprises of the cost of the central administrative organization and the capital cost of the station site.
(9) Semi-fixed cost
Comprises of the cost of buildings, plants, salaries
(9) Running cost
Fuel and water
(10) Consumers have to pay the following charges .
1) Contracted capacity charge (kW)
2) Uncontracted capacity charge (kW)
3) Usage charge
4) Reactive power charge
(11) Effects of low power factors ?
1) Larger cables will increase capital cost, also voltage drop and line loss will increase.
2) Increase in cross sectional area of conductors and the material cost.
3) Increase in copper loss and decrease in generator efficiency.
(11) Methods of improving power factor ?
1) Use of capacitors
2) Use of synchronous motor
3) Use of phase modifier
(12) Application of motor control ?
Application on cooling, heating, lighting, motor driven machinery.
(12) Basic motor control is made up of ?
Contactor and overload relay
(12) What does MCC stand for ?
Motor control centers
(12) Advantages of MCC ?
1) Faster and easier installation and wiring
2) Centralised motor control
3) Less total space required
4) Neat, attractive
(12) Types of motor starters ?
1) Direct on-line (DOL) starter
2) Forward revers DOL starter
3) Star-delta starter
4) Soft starter
(12) Direct on-line (DOL) starter
- Most common starting method available on the market.
- Consist of main contactor, thermal of eletromagetic. overload relay
- Highest possible starting current.
(12) Star-delta starter
- Consist of three contactor, overload relay and a timer.
- Starting current is 30% of direct on-line starter.
- Starting torque is 25% of direct on-line starter.
(12) Soft starter
- Has thyristors in the main circuit.
- Motor voltage is regulated with a printed circuit board.
(13) Equipments installed in a switchboard ?
1) Circuit breaker
2) Control circuit
3) Measuring instruments
4) Protective relays
5) Busbar
6) Cable connecting terminals
(13) Types of switch boards ?
1) Open type
2) Dead front type
3) Cubical type
4) Multi-cubical type
5) Desk type
6) Box type/Multi-box type
(13) Rated insulation voltage
It is the voltage at which dielectric test of the switch gear are referred.
(13) Rated current
The rated current must be carried without exceeding temperature limits specified.
(13) Rated short-time withstand current
The amount of current a circuit can carry during a specified short time under specific condition
(13) Function of a transformer ?
1) Isolate the high primary voltage side from the protection and measurement equipment.
2) Transform the high primary current to a small secondary current of 1A to 5A.
(13) Types of current transformers ?
1) Protection current transformers
2) Measurement current transformers
(13) Rated primary current
The maximum amount of primary current the transformer is designed for.
(13) Rated secondary current
The maximum amount of secondary current the transformer is designed for.
(13) Burden
The maximum amount of load which can be connected on the secondary side.
(13) Accuracy class
Accuracy of the CT under prescribed condition of use.
(14) Function of current limiting reactor
1) It limits the fault current and protect equipments.
2) It protects circuit breakers with inadequate breaking capacity.
3) it localizes the fault by limiting fault currents flowing from healthy parts of the system.
(14) Types of current limiting reactors ?
1) Ironed cored magnetically shield reactor
2) Air cored non-shield reactor
3) Air cored ring shield reactor
(14) Air cored non-shield reactor
- Mounted on ceramic pedestal type insulator
- Not suitable for outdoor
- Cannot be placed near metallic object
(14) Generator reactor
Has large reactance to protect themselves against fault
(14) Disadvantages of generator reactor ?
1) There is a constant voltage drop and power loss in reactor.
2) If fault occurs in any of the feeders, the continuity of the supply will be affected.
3) If fault occurs near alternator busbar, the busbar voltage drop will drop to a very low value.
(14) Advantages of feeder reactors ?
1) If fault occurs, the voltage drop in the reactors will not affect the alternator busbar voltage.
2) If fault occurs in the feeder, fault current is reduced by the reactor and other feeders are not affected.
(14) Disadvantages of feeder reactor ?
1) There is a constant voltage drop and power loss in the reactor.
2) If fault occurs before reactors, there is no protection for the generators.
(14) Methods of connecting busbar reactor ?
1) Ring busbar reactor system
2) Tie bar reactor system
(14) Advantages of tie bar system ?
1) During fault, there are alway two reactors in series between each generator and the fault.
2) When additional generators are installed, there is no need to change the size of the existing reactors.
(14) Disadvantages of tie bar system ?
Additional bar is required
(15) Advantages of earthing the neutral ?
1) Star point is always at earth potential and will not float thus the voltage will maintain nearly constant.
2) Simple protective system based on the detection of the earth leakage current can be used .
3) An arcing ground fault cannot occur .
(15) Disadvantages of earthing the neutral ?
1) The earth fault current is very much heavier than in an unearthed system.
2) The earth fault current must be isolated immediately .
3) Earth connection must be made at all vulnerable point in the system .
(15) Earthing neutral that can be classified under earth neutral system ?
1) Solid earthing system
2) Resistance earthing system
3) Reactance earthing system
4) Peterson coil
(15) What earthing system is used for low voltage earthing system
TT System
(15) What earthing system is used for high voltage earthing system
TNS System
(15) Earthing installation consist of ?
1) Earthing electrode
2) Earthing conductor
3) Circuit protective conductor
4) Main equipotential bonding conductor
5) Supplementary equipotential bonding conductor
(15) Recognised earth electrodes ?
1) Earth rods or pipes
2) Earth tap or wires
3) Earth plates
4) Underground structural metalwork
(15) Protective conductors ?
1) Earthing conductor
2) Circuit protective conductor
3) Main equipotential bonding conductor
