High Voltage

Question 1

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

Answer 1

False
10-20kV
Most common 13.8kV

Question 2

Name the invisible field of force surrounding energized conductors

Answer 2

Electrostatic field

Question 3

What does BIL stand for?

Answer 3

Basic impulse insulation level

Question 4

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

Answer 4

Must be rated higher than nominal system voltage

Question 5

What are the three general classifications on HV distribution systems?

Answer 5

Radial - cheap, least reliable
Loop
Network - most reliable

Question 6

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

Answer 6

Radial

Question 7

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

Answer 7

Network/grid

Question 8

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

Answer 8

Limit fault currents

Question 9

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

Answer 9

Smaller conductors
Less line drop/loss

Question 10

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

Answer 10

Touch voltage

Question 11

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

Answer 11

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

Question 12

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

Answer 12

Ground matt or grid

Question 13

What is this?

Answer 13

A lightning arrestor

Question 14

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

Answer 14

3m/10ft

Question 15

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

Answer 15

HV cables have shielding
HV cables have thicker insulation

Question 16

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

Answer 16

Thermoset
XLPE (cross linked polyethlene)

Question 17

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

Answer 17

Teck
Mining
Concentric neutral
Submarine
Shielded power cables
PILC

Question 18

Define dielectric strength

Answer 18

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

Question 19

What are two types of shielding for HV cables?

Answer 19

Strand/conductor shield
Insulation shield

Question 20

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

Answer 20

Strand/conductor shield

Question 21

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

Answer 21

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

Question 22

A dielectric is more commonly known as an……

Answer 22

Insulator

Question 23

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

Answer 23

100%

Question 24

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

Answer 24

133%

Question 25

Not a question. Study this bitch

Answer 25

Yaga

Question 26

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

Answer 26

Better heat dissipation when run in free air

Question 27

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)

Answer 27

False

Question 28

What are two types of stress relief?

Answer 28

Geometric Capacitive

Question 29

Why is a conductor shield required?

Answer 29

To avoid ionisation of free air

Question 30

Why is an insulation shield required?

Answer 30

To avoid concentration of electrostatic flux

Question 31

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

Answer 31

False

Question 32

A circuit breaker can be readily removed from….

Answer 32

Metal-clad switchgear

Question 33

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

Answer 33

Hot stick

Question 34

What is a fuses current rating?

Answer 34

The continuous current rating (max normal current)

Question 35

What is a fuses interrupting rating?

Answer 35

The max fault current it can handle

Question 36

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

Answer 36

Spare the main contacts from arcing

Question 37

List the three main ratings for a HV fuse

Answer 37

Voltage Continuous current Interrupting current

Question 38

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

Answer 38

True

Question 39

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

Answer 39

False

Question 40

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

Answer 40

False

Question 41

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

Answer 41

False

Question 42

XLPE is a thermoset plastic. (T/F)

Answer 42

True

Question 43

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

Answer 43

False 10kV-20kV

Question 44

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)

Answer 44

True

Question 45

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

Answer 45

True

Question 46

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

Answer 46

True

Question 47

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

Answer 47

True

Question 48

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

Answer 48

False

Question 49

How are lightning arrestors connected to the load?

Answer 49

In parallel

Question 50

How are reactors connected to the load?

Answer 50

In series