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EE135 - Power System Protection > LE2 > Flashcards

LE2 Flashcards

(69 cards)

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1
Q

What type of lightning stroke is shown?

A

Direct stroke

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1
Q

This lightning arrester consists of two 1.5cm rods which are bent at right angle with a gap between

A

Rod gap arrester

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2
Q

Class F insulation is made of …

A

Mica, glass fibres, or asbestos built up mica, glass fibres laminates

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2
Q

What kind of feeder is shown?

A

Parallel Feeder

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2
Q

It is the most common failure in the grounding of conductor

A

Insulation failure

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2
Q

It starts from the cloud towards the earth and carries charge as soon as the air near the cloud breaks down

A

Leader streamer

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2
Q

This lightning protection consist of a network of copper conductors mounted all over the electrical equipment in the substation and properly connected with low impedance

A

Earthing screen

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3
Q

What are the two common bus bar protection scheme?

A
  • Differential protection
  • Fault bus protection
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4
Q

This lightning protection is also called as protector tube and on the occurrence of an overvoltage, the series gap is panned and an arc struck between the electrodes in the tube then gas builds up and carries away ionized air around the arc

A

Expulsion type arrester

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5
Q

What type of bus bar protection scheme is shown?

A

Fault bus protection

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5
Q

The action depends on the distance between the point where the relay is installed and the point of fault

A

Distance protection

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5
Q

In this type of lightning stroke, the lightning discharge directly from the cloud to the subject equipment

A

Direct stroke

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5
Q

This lightning arrester consists of two horn shaped metal rods separated by a small air gap

A

Horn gap arrester

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6
Q

SPDs used at the line side. It is connected between the secondary of the service transformer and the LINE side of the service disconnect over current devices, as well as the LOAD side, including watt-hour meter socket enclosures

A

Type 1 SPD

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7
Q

What are the two types of lightning strokes?

A
  • Direct stroke
  • Indirect stroke
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8
Q

This type of line protection is typically used in radial feeder and it uses a definite time relays and inverse time relays

A

Time-graded Overcurrent Protection

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9
Q

State the maximum allowable temperature for each insulation classes

  • Y
  • A
  • E
  • B
  • F
  • H
  • C
A

↵

  • Y - 90ºC
  • A - 105ºC
  • E - 120ºC
  • B - 130ºC
  • F - 155ºC
  • H - 180ºC
  • C - 180+ ºC
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10
Q

What type of relay is shown?

A

Definite time relay

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12
Q

Class E insulation is made of …

A

Synthetic resin enamels, cotton and paper laminates with formaldehyde bonding

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13
Q

Example of _______ insulation classification is the air or SF6.

A

Gas insulation classification

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13
Q

Class A insulation is made of …

A

Cotton, silk, or paper impregnated with varnish or insulation oil

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13
Q

Class B insulation is typically made of …

A

Mica, glass fibers, and asbestos built up mica, glass fibres, asbestos

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13
Q

This type of SPD is installed on the load side of the service disconnect over-current devices.

A

Type 2 SPD

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14
Q

What composes the external disturbances in surges?

A

↵

  • Utility load switching
    • Smart grid
  • Lightning strikes
    • cloud to cloud
    • cloud to ground
    • cloud to man-made objects
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15
Point of utilization SPDs, installed a minimum of 10 meters (30 feet) from the electrical service panel.
Type 3 SPD
16
The rolling spheres in lightning protection system must overlap to provide maximum protection from lightning. TRUE or FALSE
FALSE Overlapping of rolling spheres cancels out each other, thus, creating a dead spot between the lightning protection system
17
In order for an electrostatic discharge to occur, two things are necessary:
1. a sufficiently high electric potential between two regions of space must exist; and 2. a high-resistance medium must obstruct the free, unimpeded equalization of the opposite charges.
18
Various power stations or substations are interconnected by alternate routes.
Ring main system
20
What is the average distance in miles between the lightning strikes?
2 - 3 miles
22
Surges originate from ...
80% internal disturbances 20% external disturbances
24
Why ground electrical power system?
↵ * For safety related to electrical shock hazard * Bonding of non-current carrying conductive materials to the mass of Earth fixes their potential to “*Zero potential*”
25
What type of lightning stroke is shown?
Indirect stroke
26
It resist current and keep the current in its path along the conductor
Insulation
27
Class Y insulation is typically made of ...
Cotton, silk, paper,or wood
28
This bus bar protection scheme compares or totalize the currents entering and leaving the bus bar. When fault current enters the system, it will disturb the balance in the system and produces differential current to operate the relay
Differential protection
28
This lightning stroke results from the electrostatically induced charges on the conductors due to the presence of charged clouds
Indirect stroke
29
How much current and voltage is associated with lightning?
120 kA and 100MV
30
This lightning protection is used on transmission lines
Overhead ground wires
30
It consists of an air cored inductor connected in series with the line
Ferranti surge absorber
31
These are designed to reduce and divert potentially damaging short-duration voltage spikes safely out of the system to Ground.
Surge protective devices (SPD) or Transient voltage surge suppressors (TVSS)
32
What are the causes of overvoltage?
* Internal Causes * Switching surges * Insulation Failure * Arcing ground * Resonance * External Cause * Lightning
33
This lightning arrester consists of a series of metallic cylinders insulated from one another and separated by small intervals of air gaps
Multigap arrester
35
It forms an important link between the incoming and outgoing circuits
Bus bars
35
In the event of short circuit, which CB would open first?
The CB that is closest to the fault
37
This bus bar protection scheme uses earthed metal barrier surrounding each conductor throughout its entire length in the bus structure
Fault bus protection
38
This type of lightning arrester incorporates non-linear resistors and extensively used on systems operating at high voltages. Consists of two assemblies 1. Series spark gaps 2. Non-linear resistor disk
Valve type arrester
39
Electrical discharge due to lightning results in electrical current from the ground to clouds
Return stroke
40
What are the 3 protection against lightning?
* Earthing screen * Overhead ground wire * Lightning arrester of surge diverters
42
What is the temperature of lightning?
30,000 ºC or 54,000ºF
44
Component SPDs, including discrete components as well as component assemblies
Type 4 SPD
45
What are the two types of lightning?
Negative downward lightning and Positive upward lightning
46
What are the different line protections?
* Time graded over current protection * Differential protection * Distance protection
47
It includes isolating switches, circuit breakers, and associated connection
Bus bar zone
48
State some of the types of cable insulations.
* PVC (Polyvinyl Chloride) * PE (Polyethylene) * XLPE (Cross-link Polyethylene) * EPR (Ethylene Propylene Rubber) * Paper Based
50
This insulation classification is divided into two major categories: organic and inorganic.
Solid insulation classification
51
In the event of short circuit, the closest CB opens and all other CB will also open. TRUE or FALSE
FALSE
52
Lightning protection system follows what method?
Rolling sphere method
54
What is the speed of lightning?
60 km/s
56
Damages to insulations are commonly caused by... ## Footnote (8 answers)
* Mechanical Damage * Vibration * Excessive heat and cold * Dirt * Oil * Corrosive vapours * Moisture from processes * Humidity
58
SPDs and TVSSs are made of what component?
Metal oxide varistor (MOV)
59
What composes the internal disturbances in surges?
* Load switching * Variable frequency drives * Lightning and air handlers
61
Insulation oil is an insulation classification of what type?
Liquid insulation classification
62
It is the overvoltage produced on the power system due to switching operations
Switching surges
63
What type of relay is shown?
Inverse time relay
64
What are the five types of lightning arrester?
* Rod gap arrester * Horn gap arrester * Multigap arrester * Expulsion type arrester * Valve type arrester
65
A sudden rise in voltage for a very short duration in the power system
Voltage surge
66
# Take a rest What are the four main features of lightning protection?
1. Air terminal 2. Conductors 3. Ground termination 4. Surge protection
68
A _______ connected between the line and earth can act as a surge absorber. Since its reactance is inversely proportional to frequency, it will be low at high frequency and high at low frequency. It acts as short circuit at high frequency and passes them directly to earth
Capacitor or condenser
69
What type of bus bar protection scheme is shown?
Differential Protection

EE135 - Power System Protection (3 decks)

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