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Electrical Level 3 and 4 > High Voltage > Flashcards

High Voltage Flashcards

1
Q

CEC Extra Low Voltage

A

≤ 30V AC

≤ 42.4 V DC

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2
Q

CEC Low Voltage

A

> 30V AC ≤ 1000V AC

> 42.4V DC ≤1060V DC

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3
Q

CEC High Voltage

A

> 1000V AC

> 1060V DC

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4
Q

IEEE/ANSI Medium Voltage

A

100V to 69,000V

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5
Q

IEEE/ANSI High Voltage

A

69KV to 230KV

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6
Q

IEEE/ANSI Extra High Voltage

A

230KV to 800KV

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7
Q

IEEE/ANSI Ultra high voltage

A

> 800KV

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8
Q

IEEE stands for?

A

Institute of Electrical and Electronic Engineers

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9
Q

ANSI stands for ?

A

American National Standards Institute

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10
Q

The 2 main factors in determining transmission line voltage is?

A

Load and Distance

also existing infrastructure

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11
Q

Generated voltage is less than transmission voltage due to?

A

Insulation contraint in the alternators

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12
Q

Gen Station typical voltage

A

10KV to 30KV

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13
Q

Transmission line voltage?

A

60kv to 800kv

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14
Q

Distribution Line voltage

A

`2.4kv to 69kv

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15
Q

Utilization line voltage

A

600V or less

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16
Q

For transmission voltages a general rule is ?

A

1000V per mile

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17
Q

Three classifications for HV networks?

A

Radial
Ring or Loop
Network or Grid

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18
Q

AC Transmission system types of overhead conductors

A

Stranded bare copper
Solid copper
Aluminum conductor steel reinforced (ACSR)
All aluminum conductor (AAC)

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19
Q

AC Transmission insulator materials

A

Porcelain
Glass
Polymer Resins (ie. silicon)

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20
Q

Insulators have _______ or ________ to increase ______ _______.

A

Skirts
Petticoats
Creepage distance

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21
Q

Types of insulators

A

Pin
Post
Suspension
Strain

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22
Q

Pin insulator characteristics

A

< 35 KV

Conductor fastened with a binding

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23
Q

Post insulator charac.

A

Like pin but stronger
Higher voltages
Conductor fastened with clamp

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24
Q

Suspension insulator charac.

A

Conductor hangs on the bottom

Modular (individual skirts are stacked for higher voltages)

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25
Q

Strain insulator charac.

A

used where line dead-ends or turns
strong tensile strength
individual skirts are stacked for higher voltage

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26
Q

Max distance of an underwater/underground cable?

A

40-50 km typically

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27
Q

Underground and underwater cable charc.

A

Expensive (high initial cost)

On going power losses with AC

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28
Q

High voltage DC cable charac.

A

No shred (DC has no hysteresis or eddy current losses)(no skin effect)
No capacitive losses
Expensive
Requires rectifier (at source) and inverter (at load)

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29
Q

What does ESF stand for?

A

Electrostatic Field

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30
Q

Electrostatic field charac.

A
  • a voltage AC or DC produces an electrostatic field
  • the size of the field depends only on voltage, not current nor AWG
  • ESF is constantly changing in AC, steady in DC
  • ESF forces may be concentrated or dispersed by conductor shapes
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31
Q

Voltage Gradient

A

ESF strength with respect to distance

Voltage density

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32
Q

Dielectric Strength

A

the voltage an insulator can withstand before breaking down
-in high voltage this is called “flashover”
- V/mm or V/in
Air = 3MV/m or 3000V/mm
Vacuum = 10 to the 12 V/M

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33
Q

Dielectric Constant

A
  • how good an insulating material is as a capacitive medium

dielectric strength relative to a vacuum
vacuum is assigned “1”
air = 1.0006
mica = 3

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34
Q

Striking distance v.s. Creepage Distance

A

“flashover” vs “tracking”

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35
Q

Corona

A
  • ionization (breakdown) of air caused by ESF

- Symptoms - RFI, hissing/crackling sound, violet/blue light, ozone.

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36
Q

What does BIL stand for?

A

Basic Impulse Insulation Level

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37
Q

BIL ratings can be __ to __ times the system voltage

A

5 to 30

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38
Q

Equipment over ___kv must be BIL rated

A

2.5

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39
Q

What is a Vault?

A

Fire resistant construction for housing HV elec equipment ie. tranformers etc.

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40
Q

Lightning Rods

A
  • protect structures
  • not connected to equipment
  • electrode on top of a structure wired as short and straight as possible to an isolated ground electrode
  • CEC 10-108, App. B and G
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41
Q

Series Reactors

A
  • used to limit fault currents
  • very little effect under normal conditions
  • if a fault occurs, short circuit current is ‘choked’
  • can allow for less expensive CBs having a lower interrupting rating
  • also impedance grounding can achieve similar goals
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42
Q

2 types of instrument transformers used in HV

A 
Voltage transformers (VTs and PTs)
Current transformers (CTs)
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43
Q

Voltage transformers

A
  • low VA rating
  • 120 V secondary rating usually
  • primary 3 A typical
  • ground secondary
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44
Q

Current transformers

A
  • in series with the primary
  • 5 A secondary
  • 1A secondary emerging
  • ground secondary
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45
Q

Radial HV system charac.

A 
Least expensive
Simplest 
Only one supply
Least reliable 
Least likely to backfeed
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46
Q

Ring/Loop HV system charc.

A 
Requires 2 feeds
Costs more
More reliable
May use auto transfer switch
Subject to back feeds
Allows maintenance via isolation
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47
Q

Network/Grid HV system charc.

A 
Greatest reliability 
Most expensive 
Requires complex switching 
Used for hospitals, airports, penetentiaries 
Most danger of back feed
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48
Q

Methods of isolating AC transmission systems

A

Elevation (poles, towers)
Substations (fences)
Vaults

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49
Q

The WCB specifies that only persons who are _____ and _____ are allowed to work on HV.

A

Trained and qualified

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50
Q

Rural distribution systems primarily use?

A

Overhead lines

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51
Q

What effect does electric stress have on insulation?

A

Weakens insulation

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52
Q

Why is creepage distance kept relatively long?

A

to keep creepage current/leakage to a very low value

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53
Q

What is the function of a surge arrestor?

A

to divert a high voltage surge to ground by providing an easy conducting path (overvoltage)

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54
Q

What are the main parts of a surge arrestor?

A

Air gap

Thyrite material

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55
Q

What are the 5 general steps to be taken in a safe switching sequence?

A
  1. Disconnect
  2. Lock out
  3. Test for absent voltage
  4. Ground and short circuit
  5. Screen off neighbouring live parts
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56
Q

Single strand HV cable

A
  • used for termination where flexibility is not required

- #2 or smaller, usually #10 or smaller

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57
Q

Concentric Stranding HV cable

A
  • typical strandings are 7, 19, 37 etc.
  • large undesirable air voids
  • flexible
  • difficult to remove insulation
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58
Q

Compressed stranding HV cable

A
  • 97% of the concentric stranding cross section
  • smaller air voids
  • improves on concentric
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59
Q

Compact stranding HV cable

A
  • 90% of the size of concentric

- preferred for HV

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60
Q

Bare overhead aluminum HV conductors

A
  • OK for bends
  • light
  • not strong enough for long spans
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61
Q

Bare overhead aluminum conductor steel reinforced (ACSR)

A
  • center strand is steel for strength
  • steel center is called the “messenger”
  • outer strands are aluminum
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62
Q

Bare overhead aluminum conductor composite reinforced (ACCR)

A
  • strong and light
  • carbon fibre or fibreglass messenger
  • alumina fibers
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63
Q

Are bare conductors or insulated conductors preferred for HV?

A

Bare, due to lack of continuous capacitive charging and discharging losses associated with insulation

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64
Q

Types of HV cable

A

Armoured cable - (TECK)(ACWU), MI
Wire Armoured - Submarine cable
Tape Armoured - steel tape armoured (STA)
Paper Insulated Lead Covered (PILC) - underground
Concentric Neutral - underground

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65
Q

Another name for a concentric neutral cable?

A

Underground Residential Distribution (URD)

66
Q

Concentric neutral cable (URD) characteristics

A
  • cable has shielding which also serves as a neutral
  • neutral has 100% of ampacity of center conductor
  • 3 Ø 4W uses 33% concentric neutral
  • connect all 3 neutrals = 100% ampacity
67
Q

Purpose of cable jackets?

A
  • provide mechanical protection
  • seal out contaminants
  • reduce friction
  • identify cable specs
68
Q

Cable dielectrics =

A

Insulation

69
Q

Types of cable insulation (dielectrics)

A
  • Rubber
  • Thermoplastic
  • Thermoset
  • Paper insulated lead covered (PILC)
70
Q

Rubber insulation charc.

A
  • 600V to 15KV

- moisture resistant

71
Q

Thermoplastic insulation charac.

A
  • 5KV to 15KV
  • tends to soften at higher temps and get brittle at lower temps
  • Polyvinyl chloride (PVC)
  • Polyethylene (PE)
72
Q

Thermoset insulation charac.

A
  • 5KV to 69KV
  • does not tend to soften with increase in temp
  • cross linked polyethylene (XLPE)
  • ethylene propylene rubber (EPR)
  • silicon
73
Q

Paper insulated lead covered insulation charc.

A
  • Paper insulated

- Lead covered

74
Q

Concentrated ESF can lead too?

A

Corona which will compromise the insulation and lead to flashover

75
Q

What will even out the ESF surrounding the entire conductor?

A

“strand shield” of semiconductor material

76
Q

The stranded shield layer is often referred to as?

A

Semi-con layer

77
Q

What causes the ESF to be evenly distributed throughout the insulation?

A

“Insulation shield” which is at ground potential

78
Q

The insulation shield is usually bonded?

A

At both ends but not always

79
Q

B/C the insulation shield is not an ideal conductor, a _________ surround it so that it’s entire length is bonded as well.

A

Conductive layer (copper or aluminum tape)
or
Conductive neutral

80
Q

Cables are rated ____ ____?

A

Line voltage ( 15KV, 28KV, 35KV )

81
Q

HV cable insulation are rated by?

A

Percentage (100%, 133% or 173%)

82
Q

100% insulation

A

cables in grounded wye system or ungrounded system where faults cleared in 1 minute or less

83
Q

133% insulation

A
  • cables in ungrounded systems where faults are cleared in 1 hour or less
  • most common
84
Q

173% insulation

A
  • cables in ungrounded systems where faults are cleared in more than 1 hour
  • not common
85
Q

Percentages represent _______ ?

A

Thickness

86
Q

The thicker the insulation, the more _____ ______ it can withstand before electrical breakdown.

A

Voltage stress

87
Q

Dielectric strength is

A
  • the ability of the dielectric to withstand electrical breakdown under the influence of voltage
  • voltage per unit thickness
88
Q

What is the most commonly used insulation for medium voltage cables?

A

XLPE (cross-linked polyethylene)

89
Q

Cables rated over ______ V require a strand shield?

A

1000V

90
Q

Sheath voltage depends on?

A

Current magnitude
Cable length
Insulation thickness

91
Q

What is sheath voltage?

A

an induced voltage in the shield caused by AC current flowing in the conductor

92
Q

Which cable shield must be grounded?

A

Insulation shield

93
Q

A concentric neutral cable is?

A
  • One whose metallic insulation shield has as much ampacity as the current-carrying conductor
  • A group of bare or tin-coated copper wires wound helically over the insulation shield
94
Q

What factor determines the minimum available AWG size of a HV cable?

A

Voltage

95
Q

The ampacity of a non-shielded cables is based on an ambient temp. of?

A

30 degrees

96
Q

The ampacity of a shielded cable is based on an ambient temp. of?

A

40 degrees

97
Q

What are the 2 most common voltage ratings of medium-voltage cables used for power applications?

A

15KV and 25KV

98
Q

Where will there be a high concentration of stress lines when removing the insulation shield?

A

at the point where the insulation shield is discontinued

99
Q

The 2 most common types of stress relief are?

A

Geometric (Stress cone)

Capacitive (Hi-K)

100
Q

Geometric stress relief

A

A factory made stress cone is used to build up the thickness of the insulation in the region of high electric stress.

101
Q

Termination Classifications

A

Class 1 - requires stress relief, anti-tracking and a seal to the environment.
Class 2 - requires stress relief and anti-tracking
Class 3 - only requires stress relief

102
Q

All cables rated over ____KV require an insulation shield?

A

5KV

103
Q

Switchgear includes

A 
Circuit breakers
Fuses
Load break switches
Disconnect/Isolation switches
Protective relay circuitry 
Instrument Transformers
104
Q

Metal Clad switchgear

A

Gear “racks out”
Insulated bus bars
Shutters close
Dont rack under load

105
Q

Metal enclosed switchgear

A 
Bare bus bars
Fixed switches and CBs
Viewing window to see contacts
Louvers for ventilation
Sections may or may not be divided
106
Q

Arc interruption methods

A

Fast separation of contacts using compress springs
Auxiliary “flicker” contacts and “arc chutes”
Magnetic force
Temperature rise
Compressed air
Oil immersed contacts

107
Q

Horn gap switch

A

Can interrupt small currents, 15A max

Air break

108
Q

Load break switch

A 
Can make and interrupt current
Compressed spring opens contacts fast
Main contact opens
Aux contact opens in arc chute
Arc is extinguished
109
Q

LBS/Fuse Combo

A 
Cheaper than CBs
Current limiting fuses interrupt faults
Striker pin of fuse trips load break
All 3 lines are opened 
Prevents single phasing
110
Q

2 purposes of the striker pin?

A

Trips load break switch

Visual indicator of blown fuse

111
Q

Isolation switches

A

Carry rated load
Cannot make or break any current flow
Isolated after circuit is de-energized
Provides visual verification of contacts

112
Q

Disconnect switches

A

Carry rated current
Can switch minimal current <0.5A
IE. magnetizing current
Used to isolate equipment

113
Q

Circuit Breakers types

A 
Air/air magnetic
Oil (bulk oil/dead tank or minimum oil/oil poor)
Inert gas 
Vacuum
Air blast
114
Q

Air/air magnetic CB

A

Maximum ratings - 15KV, 3000A
Arc chutes
blow out coils
puffer

115
Q

Bulk Oil CB

A

Oil is a good dielectric
Older style
Indoor or outdoor
All poles within a common oil chamber

116
Q

Minimum Oil CB

A

One oil vessel per pole
Sight gauges for checking oil
Containment curbs

117
Q

Inert Gas CB

A

Sulphur Hexaflouride
Maintained at a low positive pressure
Very high dielectric strength
Used in all voltage ranges

118
Q

Vacuum CB

A 
Typically up to 35kv
Uses a motor charged spring
Vacuum is an excellent dielectric 
The fast action may cause voltage spikes
Real estate friendly
119
Q

Air blast CB

A 
Compressed air extinguishes the arc
Compressed air also may operate switches
May be up to 800 PSI
All voltage ranges especially extra high voltage (800KV)
Silencers may be required
120
Q

CB Reclosers

A 
Used exclusively for overhead lines
Burns branches off bare conductors
May attempt reclosure 3 or 4 times 
10 - 20 second delay after each trip
Lock out if unsuccessful
Part of a coordinated system
121
Q

Distribution Fuses

A

Pole top “distribution cut out”
Tensioned inner fuse link blows releasing cartridge
Cartridge swings down
Can be used indoors with a muffler/condenser

122
Q

Power fuses

A 
Current limiting similiar to HRC fuses
One time use
Very fast
May cause voltage transients 
Non expulsion type
Striker pin operates LBS
123
Q

Solid material fuse

A

Not current limiting - may take several cycles to open
Expulsion type - boric crystals surround fuse link, during fault boric acid forms steam and water, pressure helps extinguish the arc
Some may have replaceable cartridge

124
Q

Liquid Fuse

A

Mostly obsolete
Oil filled
Non renewable

125
Q

Why must the shielding be removed for an adequate distance when terminating a cable?

A

to minimize leakage currents

126
Q

Why are outdoor terminations of the skirting type?

A

to increase creepage distance

127
Q

Cable Insulation specs

A

Prevents ground faults and short circuits line to line
Leakage currents exist in all insulators except a perfect vacuum
Resistance - In M ohms range, tested with high DC voltage, negative temp coefficient.

128
Q

Dielectric Absorption

A

Dangerous effect of cable capacitance after DC (Megger) is removed
In AC circuits the capacitive effect is power loss

129
Q

Megger Testing specs

A
  • Generally non-destructive
  • H.V. DC applied for some time
  • DC values = 500V - 15KV typically
  • Applied time depends on the capacitance of cable or equipment
  • Readings are taken after they stabilize
  • Isolate equipment/cable from ALL sensitive loads
  • Isolate the cable ends from ground and “corona proof”
130
Q

How should you connect the megger for HV testing?

A
  • positive lead to ground (return/path/tape shield)
  • negative lead to test conductor/equipment
  • guard lead to dielectric
131
Q

Reverse polarity megger test is preferred due to?

A

Electroendosmosis

132
Q

Guard lead specs

A

Also a return path but it bypasses the meter

May connect to the dielectric to shunt surface current around the meter

133
Q

Capacitive charging current

A

Initial “inrush”
Varies depending on cable/equipment
May last for several seconds

134
Q

Absorption Current

A

Charge is building in the cable/equipment
Bare bus bars = short duration
Long cables = long duration

135
Q

Proof Test

A

Test the cable after it is pulled in to prove it is good

Before terminating so time and materials may be saved

136
Q

Short time test

A

60 second duration

137
Q

Polarization Index Test

A

Two readings - 1 minute duration and 10 minute duration

1 min reading

Ratio below 1.5 indicates a problem

138
Q

Step voltage test

A
  • Voltage is stepped up in 60 second intervals
  • Current should increase in linear pattern and resistance should remain constant
  • If M ohms decreases with increasing voltage, insulation may be bad.
139
Q

Dielectric Absorption Tests (Megger test)

A

Readings are taken over a 10 minute period

The shape of the curve is interpreted

140
Q

Hi-Pot Testing

A
  • DC or AC
  • Possibly destructive
  • More specialized than megger
  • May use voltages of 30KV, 60KV or higher
  • Highly trained personnel
141
Q

Hi-Pot Thumping

A
  • Hi-Pots may be used to find underground cable faults
  • A spark gap is connected in parallel to the cable
  • Hi-Pot is connected and the gap sparks
  • Increasing the gap space eventually cause the sparking to stop
  • The cable fault begins sparking/thumping
  • A ground microphone and headset can usually locate the fault location
142
Q

Voltage classifications for rubber gloves Beige

A

Class 00
Proof - 2500V AC/10,000V DC
Max Usage - 500V AC/ 750V DC

143
Q

Voltage classifications for rubber gloves Red

A

Class 0
Proof - 5000/20000V
Max use - 1000/1500V

144
Q

Voltage classifications for rubber gloves White

A

Class 1
Proof - 10,000/40,000V
Max use - 7500/11250V

145
Q

Voltage classifications for rubber gloves Yellow

A

Class 2
Proof - 20KV/50KV
Max use - 17kv/25.5kv

146
Q

Voltage classifications for rubber gloves Green

A

Class 3
Proof - 30kv/60kv
Max use - 26.5kv/39.75kv

147
Q

Voltage classifications for rubber gloves Orange

A

Class 4
Proof - 40kv/70kv
Max use - 36kv/54kv

148
Q

Runway lighting circuits can be loaded to a maximum of ___KW for an operating voltage of _____ V AC.

A

20kw
3030V AC
6.6A

149
Q

What HV measuring tool is used for non contact voltage testing?

A

Modiewark

150
Q

What voltages do the primary and secondary wires typically carry for runway lighting?

A

Primary 5000V +

Secondary less than 50V

151
Q

What does SCADA stand for?

A

Supervisory Control And Data Aquisition

152
Q

What does ASLC stand for?

A

Airport series lighting cable

153
Q

Most common failure for runway lighting?

A

Isolation transformer

154
Q

What is the purpose of the strand shield on HV cables?

A

prevents the corona from developing in the air pockets that might be between the conductor and insulation by bonding the outer strands together

155
Q

What is the main difference between concentric neutral cables and shielded cables?

A

Concentric neutral has the ability to use its insulation shield as a return path or neutral, tape does not.

156
Q

A DC Hi-Pot tester measures 3 types of current?

A

Leakage
Capacitive
Absorption

157
Q

Name the three most common HV switches used today?

A

Load break
Disconnect/Isolation
Horn gap

158
Q

Name the fastest acting HV fuse and a unique feature it has?

A

Current limiting

Striker pin to open the load break to prevent single phasing

159
Q

What two functions does a distribution cut out offer when it drops out?

A

Large re striking distance

Visual indictation

160
Q

What three things are required in order from tracking to occur?

A

Moisture
Contamination
HV

Electrical Level 3 and 4 (10 decks)

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