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EPS > EPS Revision II. > Flashcards

EPS Revision II. Flashcards

1
Q

*State two advantages of neutral earthing .

A

1) Star point is always at earth point and will not float thus the voltage will maintain nearly constant .
2) Simple protective system based on the earth leakage current can be used .
3) An arcing ground fault cannot occur .

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2
Q

**Name three/four methods of neutral earthing .

A

1) Solid earthing
2) Resistance earthing
3) Reactance earthing
4) Peterson coil

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3
Q

**List two essential loads that require supply when main fails .

A

1) Fireman lift
2) Emergency lighting system
3) PA system

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4
Q

**State the main function of the inverter when the mains fails .

A

It converts the DC power back to clean AC power for the load supply .

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5
Q

*State two reasons for providing an emergency and standby power supply .

A

1) To provide continuity of supply to essential loads within the building .
2) For fire-fighting and safety, since there is a danger when the supply fails .

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6
Q

*State three functions of booster transformer .

A

1) To increase the voltage only at the far end .
2) It is not worth while to install a tap changing transformer .
3) If the distributor is very long, increasing substation voltage to bring the far point within limit may result in voltages at the near point exceeding the limit .

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7
Q

**State two methods of power factor correction .

A

1) Use of capacitor
2) Use of synchronous motor
3) Use of phase modifier

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8
Q

*List three types of HV circuit breakers .

A

1) Oil circuit breakers
2) Air circuit breakers
3) Vacuum circuit breakers
4) Sf6 circuit breakers

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9
Q

**Name two methods of differential feeder protection .

A

1) Circulating current

2) Balanced voltage

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10
Q

**Briefly state the term ·Essential Load

A

Loads that require supply even when the mains fail, to ensure continuity of production and safety to personnel

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11
Q

List four components that are found in standby generator.

A

1) Prime mover
2) Brushless generator
3) Mechanical governor
4) Automatic voltage regulation

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12
Q

**State three effects for having poor power factor in an electrical system

A

1) Effect on transmission lines
2) Effect on switch gears and busbars
3) Effect on generator
4) Effect on prime movers

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13
Q

**State two kinds of pilot wire differential feeder protection scheme.

A

1) Circulating current

2) Balanced current

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14
Q

**State 3 factors that need to be considered for an effective differential protection .

A

1) CT mismatch, power
2) Transformer winding
3) Tap changing facility

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15
Q

**State four methods that are employed in earthing the neutral conductor.

A

1) Solid earthing
2) Resistance earthing
3) Reactance earthing
4) Peterson coil

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16
Q

**List out two types of tap changing transformer.

A

1) Off load tap

2) On load tap

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17
Q

**In a pilot wire differential feeder protection, two principles are employed. Name the two principles adopted.

A

1) Circulating current

2) Balanced current

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18
Q

**Name three modular power sub-assemblies employed in the uninterruptible power supply system

A

1) Rectifier
2) Battery
3) Inverter

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19
Q

*Name two starters that can provide a reduced voltage starting.

A

1) Star-delta starter

2) Soft starter

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20
Q

*Name the starter that can provide a full voltage starting.

A

Direct on line starter

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21
Q

*State the use of CTs (current transformers) in the switchboard system.

A

Isolate high primary voltage of the system from the protection and measuring equipment and transform the primary high current to small secondary current of 1A or 5A

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22
Q

*State two advantages of using air circuit breaker.

A

1) No fire hazard caused by oil

2) High speed operation

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23
Q

*State the percentage voltage variation that is approved for the consumer’s incoming supply.

A

+-6%

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24
Q

*Name 3 motors that can be operated using a star-delta starter and 2motors that cannot be operated using a star-delta starter.

A

Can be operated using Star-delta:
Delta connect motors
Light loaded motors

Cannot be operated using Star-delta:
Applications with a load torque higher than 50 % of the motor rated torque

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25
Q

*State the rated operational voltage supply in the 3-phase supply system.

A

400V

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26
Q

*Name 2 methods that are employed in a combined-cycle system.

A

Gas turbines and steam turbines.

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27
Q

*State briefly what is Harmonic distortion.

A

Harmonic distortion is caused by nonlinear devices in the power system. A nonlinear is one in which the current is not proportional to the applied voltage.

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28
Q

*Name 3 devices that can cause harmonic distortion and 1 device that will not harmonic distortion

A

Causes of harmonic distortion:
Fluorescent Lighting;
Adjustable Speed Drives; and
Personal Computer and Monitor.

Will not:
UPS

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29
Q

*State the limitation of a circuit breaker rating per circuit allowed in a substation.

A

2000A

30
Q

*State the purpose of introducing Energy Market in Singapore.

A

1) To promote the efficient supply of competitively priced electricity
2) To open electricity to retail market
3) To allow certain government assets to be privatised
4) To encourage private investment in Singapore power system

31
Q

*State the function of Energy Market Company

A

1) To protect the interest of consumers with regard to price, reliability and quality of services.
2) Operate wholesale market
3) Settle accounts of market participants
4) Facilitate planning and augmentation of the transmission.

32
Q

*State the secondary transmission voltage in Singapore.

A

(66 kV)

33
Q
  • State the primary transmission voltage in Singapore.
A

(230 kV & 400kV)

34
Q
  • Name 3 circuit breakers that are suitable for high voltage operation.
A

1) Oil circuit breakers
2) Air circuit breakers
3) Vacuum circuit breakers
4) Sf6 circuit breakers

35
Q

*Name 2 circuit breakers that are not suitable for high voltage operation but only for use in low voltage operation instead

A

1) Miniature circuit breaker

2) Moulded case circuit breaker

36
Q

*State the 4_ sequential stages of energy conversion in generation of electricity using steam turbine

A

Fossil fuel>Steam>Mechanical>Electrical energy

37
Q

*State the purpose of using a Voltage Transformer.

A

Voltage transformer is a low voltage transformer , its function is to provide lower output voltage in fixed proportion to input voltage in primary side.

38
Q
  • State which level of harmonic distortion generates zero phase sequence
A

3,6,9,12,15,18,21

39
Q
  • State the function of the carrier current equipment used in a sub-station.
A

used for communication, relaying, tele-marketing or for supervisory control.

40
Q

*State the power limitation for a 3 phase induction when incorporates a DOL starter for its operation.

A

2.2 kW (found in EMD module notes)

41
Q

**List any three functions of a substation.

A

1) They provide facilities for regulating the voltage on the outgoing distribution feeders.
2) They provide points where safety devices maybe be installed to disconnect circuit or equipment in the event of trouble.
3) They provide a convenient place to take measurement to check the operation of various parts of the system.

42
Q

** What is the rated secondary current of a 600/5A current transformer?

A

5A

43
Q

**State the difference between a rated operational voltage and a rated insulation voltage as found in a switchgear catalogue.

A

Rated operational voltage :
The rated operational voltage (Uc) is the voltage at which the switchboard is to be used

Rated insulation voltage :
The rated insulation voltage (Ui) of switchgear is the voltage at which dielectric tests, clearances and cree page distances of the switchgear are referred.

44
Q

**List-any three types of emergency power source.

A

1) Batteries
2) Standby
3) Generator
4) Uninterruptible power supply (UPS)

45
Q

**Name 2 earth electrodes used in Singapore.

A

1) Earth Rods

2) Earth Tapes

46
Q

**Name 2 primary distribution voltages and 2 secondary distribution voltages.

A

Primary: 22k and 230kV

Secondary: 400V and 230V

47
Q

**Name 2 secondary distribution phases.

A

Single Phase & 3-Phase

48
Q

**Name 2 current transformer(CT) commonly used in low voltage switchgear panel.

A

Protection current transformers and measuring current transformers.

49
Q

*The fundamental frequency in Singapore is ?

A

The Fundamental Frequency In Singapore is: 50HZ

50
Q

*Name the 4 components of UPS

A

1) Rectifier
2) Batter
3) Inverter
4) Static Switch

51
Q

*Direct on line starter has one _____and one·____ unit.

A

Direct Online Starter Has One: Main Contractor And One: Thermal Unit

52
Q

*Name 4 components use in switchboard.

A

1) Circuit Breaker
2) Control Circuits
3) Busbar
4) Cable Connecting Terminals

53
Q

*TT system is used in ____consumer.

A

LV

54
Q

*TNS system is used in _____consumer.

A

HV

55
Q

*Name one circuit breaker which is chemically inert, non toxic and non-inflammable.

A

SF6 circuit breaker

56
Q

*Annual cost of running power station has parts

A

3 Parts

57
Q

*When requires to increase voltage at far end of a distributor a____ is used

A

Booster transformer

58
Q

*Medium line T transmission has its line capacitance connected in the ______of its network.

A

Mid

59
Q

*State the advantages of building indoor substation.

A

1) Maintenance cost because of cleaner environment, 2)Switching operation is not affected by weather.
3) Less space required

60
Q

*Name the medium used to turn the turbine blade for an hydro-electric power station.

A

Water at high level.

61
Q

*Which member of EMA supplies power to non-contestable consumers?

A

MSSL for electricity consumed.

62
Q

*Which cables or lines connect the main substation to distribution substation?

A

Feeder conductors

63
Q

*State application of voltage or potential transformer?

A

Steps down the high voltage to suitable value for monitoring, only used in high voltage switch gears.

64
Q

*Name the type of relay used for a non-unit protection?

A

Directional relay

65
Q

*Name one common unit protection device that can operate at high speed to isolate faulty feeder.

A

Pilot wire differential protection

66
Q

*Name an overload protection device with operating element that can operate to isolate non dangerously high current.

A

Protective relays(A protective relay is electrical devices which responds to abnormal conditions in an electrical power system , and controls a circuit breaker so as to isolate the faulty section or the system, with minimum interruptions to service.

67
Q

*An audio-frequency signal is transmitted along the cable path via ______

A

Detection coil

68
Q

*Define the term known as ‘skin effect’

A

Current flowing in a cable produces I (square) R losses. When load current contains harmonic content, additional losses are introduced. To compound the problem, the effective resistance of the cable increases with frequency because of the phenomenon known as “skin effect”.

69
Q

*Given: cost of static loss-free capacitor :;: $12 per kVAR. depreciation on capital ;;; 15%
annual tariff;;; $4 per kVA m.d.
find the most economical power factor.

A

cos sin-1(C/A)
=cos sin-1[(0.15x12)/4]
=0.89

70
Q

*Briefly explain what is motor control centres.

A

Motor Control centres are simply physical groupings of combination starters in one assembly. A combination starter is a single enclosure containing the motor starter and the fuses or circuit breaker.

71
Q

*Given: load power = 2000kW at 0.85p.f. lagging is to be corrected to most economical p.f.
Find €1; angle before p.f. correction

A

cos-1(0.85)=25.9

EPS (2 decks)

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