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4th year electrical > High Voltage > Flashcards

High Voltage Flashcards

1
Q

The alternator at a large hydro dam will probably generate power at the 138kV level. (T/F)

A

False
10-20kV
Most common 13.8kV

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2
Q

Name the invisible field of force surrounding energized conductors

A

Electrostatic field

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3
Q

What does BIL stand for?

A

Basic impulse insulation level

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4
Q

What is the significance of the BIL with regards to the insulation on HV equipment?

A

Must be rated higher than nominal system voltage

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5
Q

What are the three general classifications on HV distribution systems?

A

Radial - cheap, least reliable
Loop
Network - most reliable

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6
Q

Which of the three general classifications of HV distribution is the simplest and cheapest?

A

Radial

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7
Q

Which of the three general classifications of HV distribution would be typically used to supply a major airport or hospital?

A

Network/grid

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8
Q

What is the primary purpose of a series reactor in a HV system?

A

Limit fault currents

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9
Q

Give two advantages of utilizing high voltage/low current for transmission purposes

A

Smaller conductors
Less line drop/loss

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10
Q

Which is more likely to be higher:
a. Step voltage
b. Touch voltage

A

Touch voltage

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11
Q

Give the four steps, in order, for a high voltage fuse disconnect

A
  1. Open disconnect
  2. Remove key
  3. Open fuse compartment
  4. Change fuse
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12
Q

What type of grounding system can be installed in order to overcome the dangers of step voltage/touch voltage?

A

Ground matt or grid

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13
Q

What is this?

A

A lightning arrestor

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14
Q

What is the minimum safe distance (limit of approach) for voltages up to 75kV?

A

3m/10ft

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15
Q

What are two major physical differences between LV cables and HV cables?

A

HV cables have shielding
HV cables have thicker insulation

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16
Q

What material do most ‘medium voltage’ cables use for their insulation?

A

Thermoset
XLPE (cross linked polyethlene)

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17
Q

Name three (of the six) most common types of medium voltage cables

A

Teck
Mining
Concentric neutral
Submarine
Shielded power cables
PILC

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18
Q

Define dielectric strength

A

The ability of a material to withstand break down when subjected to a voltage

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19
Q

What are two types of shielding for HV cables?

A

Strand/conductor shield
Insulation shield

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20
Q

Which of the two shielding methods is used in order to overcome the problem of ionized air between stranded conductors?

A

Strand/conductor shield

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21
Q

Would a HV cable have its shield grounded at one end or both ends?

A

Both ends, in order to avoid having a potentially dangerous voltage appear on the shield

22
Q

A dielectric is more commonly known as an……

A

Insulator

23
Q

What percent voltage does a cable connected to a grounded system use?

A

100%

24
Q

What percent voltage does a cable connected to an ungrounded system use?

A

133%

25
Q

Not a question. Study this bitch

A

Yaga

26
Q

Why are the ampacities of tables 1,3 higher than 2,4?

A

Better heat dissipation when run in free air

27
Q

When referring to HV cable installation, the term ‘stress relief’ refers to a device that relieves a physical strain due to gravitational stresses. (T/F)

A

False

28
Q

What are two types of stress relief?

A

Geometric
Capacitive

29
Q

Why is a conductor shield required?

A

To avoid ionisation of free air

30
Q

Why is an insulation shield required?

A

To avoid concentration of electrostatic flux

31
Q

A stress relief device is required if the cable is not of the shielded type. (T/F)

A

False

32
Q

A circuit breaker can be readily removed from….

A

Metal-clad switchgear

33
Q

What is the name used for the long fibreglass tube used for opening and closing distribution cutouts?

A

Hot stick

34
Q

What is a fuses current rating?

A

The continuous current rating (max normal current)

35
Q

What is a fuses interrupting rating?

A

The max fault current it can handle

36
Q

What is the main function of the horns on a horn-gap switch?

A

Spare the main contacts from arcing

37
Q

List the three main ratings for a HV fuse

A

Voltage
Continuous current
Interrupting current

38
Q

A 25kV URD cable will have strand and insulation shielding in its construction. (T/F)

A

True

39
Q

Extra high voltage cables will likely use a thermoplastic insulation. (T/F)

A

False

40
Q

Dielectric strength of a material is the ability of the dielectric to withstand electrical breakdown under the influence of frequency. (T/F)

A

False

41
Q

Dielectric strength will increase if a dielectric becomes heated. (T/F)

A

False

42
Q

XLPE is a thermoset plastic. (T/F)

A

True

43
Q

Most HV alternators generate electrical power at voltages between 20kV and 40kV to reduce line loss. (T/F)

A

False
10kV-20kV

44
Q

An AC test of insulation integrity is achieved by comparing the watts of the cable to the VA of the cable. The insulation under test is considered good when the power factor of the cable is closest to zero. (T/F)

A

True

45
Q

The conductor shield overcomes the problem of ionized air between the conductor strands. (T/F)

A

True

46
Q

The insulation shield creates an equidistant radial flux in the insulation. (T/F)

A

True

47
Q

If the insulation shield was constructed of lead, it would also prevent the ingress of moisture into the cable. (T/F)

A

True

48
Q

A pothead is a termination method that has been traditionally used on shielded power cables. (T/F)

A

False

49
Q

How are lightning arrestors connected to the load?

A

In parallel

50
Q

How are reactors connected to the load?

A

In series

4th year electrical (7 decks)

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