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EE135 - Power System Protection > LE3 > Flashcards

LE3 Flashcards

1
Q

What are the design considerations for transmission lines?

A

Conductors, insulators, and support structures

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2
Q

What are the considerations for designing the conductors?

A

Type and size of conductor, Sag of conductor, Span between conductors, Whether or not the atmosphere is corrosive, Voltage drop, Climate at the line location,
Thermal capacity, and Economic consideration

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3
Q

What are the types of conductors?

A

ACSR, AAC, AAAC, ACAR, Alumoweld

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4
Q

What do ACSR stands for?

A

Aluminum clad steel reinforced

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5
Q

What do AAC stands for?

A

All aluminum conductor

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6
Q

What do AAAC stands for?

A

All aluminum alloy conductor

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7
Q

What do ACAR stands for?

A

Aluminum conductor alloy reinforced

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8
Q

What is the other term for alumoweld?

A

Aluminum clad steel conductor

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9
Q

This is done to reduce the tension in the line and to compensate for the stretching and compression of the line.

A

Sag

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10
Q

The voltage drop of the transmission line must be a maximum of ___ of the supplied power

A

5%

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11
Q

The Conductor is assumed to withstand a temperature of _______ without a decrease in strength

A

75 degrees celsius

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12
Q

What are the types of insulators?

A

Pin, suspension, strain, and shackle type

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13
Q

Pin type insulators are used for voltages up to ______.

A

33kV

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14
Q

Suspension type insulators are used for voltages greater than ______.

A

33kV

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15
Q

Where does the strain type insulators are applied?

A

At dead ends or sharp corner.

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16
Q

This type of insulator was used before the development of strain type insulators

A

Shackle type

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17
Q

What are the design considerations of support structures?

A

Type of supports, terrain, workspace, location of poles, and whether or not guy wire is required

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18
Q

What are the types of support structures for the overhead transmission line?

A

Wooden poles, steel poles, reinforce concrete poles, and steel towers

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19
Q

What is the maximum line span and materials that wooden poles are made up of?

A

50m line span ; sal or ehir

20
Q

What are the different types of the steel poles?

A

Rail, tubular, and rolled steel joints

21
Q

What are the different support structures for the underground transmission line?

A

Solid dielectric cross-linked polyethylene, self-contained, fluid-filled, and high pressure, fluid-filled

22
Q

Are power outages are less frequent with underground transmission lines?

A

Yes

23
Q

Do repairs take longer with underground transmission lines, usually up to six weeks?

A

Yes

24
Q

Do repair in overhead transmission line can be made in one day?

A

Yes

25
Q

Do overhead transmission lines have longer life span compared with underground?

A

Yes

26
Q

Do corona discharge happens in underground transmission lines?

A

No

27
Q

What are the purposes of underground transmission system?

A

Aesthetic, property increase of 5%-10%, protection from storms, and reliability of power supply

28
Q

Most distribution voltages are between what range of kV?

A

4 and 35kV

29
Q

Voltages are always given as line-to-line.

True or False?

A

True

30
Q

What are the four major voltage classes?

A

5, 15, 25, and 35kV

31
Q

What are the advantages of higher-voltage distribution?

A

Small voltage drop and losses, higher capacity, longer reach or distance of transmission, fewer substation

32
Q

What are the disadvantages of higher voltage distribution?

A

Low reliability, dangerous to handle, higher equipment cost

33
Q

Most of the three-phase distribution feeders and transformers connections use the ______.

A

Wye system. It offers more advantages than disadvantages

34
Q

Most systems use grounded-wye connections and current is usually present in the neutral line because the three phase currents are not normally balanced.

True or False?

A

True

35
Q

Delta connected feeders are more vulnerable to stray currents and voltages through the earth as the earth tries to balance the current flow.

True or False?

A

True

36
Q

What are the advantages of wye connection?

A 
Common Ground Reference
, Better Voltage Stability
, Lower Operating Voltage
, Smaller Equipment Size
, Can Use Single Bushing Transformers
, Easier to Detect Line-to Ground Faults
, Better Single-Phase Protection with Fuses
37
Q

What is the disadvantage of wye connection?

A

It requires 4 conductors

38
Q

What are the advantages of delta connection?

A

It only requires 3 conductors, power quality is enhanced, lighting performance

39
Q

What are the disadvantages of delta connection?

A

No ground reference, stray currents, unbalanced circuit

40
Q

Grounded wye systems have voltages of line-to-line and line-to-neutral.

True of False

A

True

41
Q

What are the different transformer connections?

A

gY-gY, D-gY, fY-D, D-D, oY-oD

42
Q

What is the most common three-phase transformer supply connection?

A

gY-gY

43
Q

What is the advantage and disadvantages of gY-gY

A

Reduced ferroresonance ; Tank Heating, Cannot supply 120 and 240v

44
Q

What is the advantage and disadvantages of D-gY?

A

No tank heating ; susceptible to ferroresonance, cant supply 120 and 240v, cant act as a grounding source

45
Q

What are the advantages and disadvantages of fY-D?

A

can supply ungrounded service, can supply 4-wire with 240/120v ; voltage unbalance, susceptible to ferroresonance

46
Q

What are the advantages and disadvantages of D-D?

A

can supply ungrounded service, can supply 4-wire service with 240/120V ; ferrorresonance, circulating current

47
Q

What are the advantages and disadvantages of oY-oD

A

Can supply 3-phase load from 2-phase supply, immune to ferroresonance ; high secondary voltage unbalance, primary ground current

EE135 - Power System Protection (3 decks)

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