Earthing of Power Supply Installations

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Questions and Answers

What size of MS flat is used to connect one terminal of the secondary winding of a traction power transformer directly to the earthing grid?

75 mm x 8 mm (correct)
100 mm x 10 mm
25 mm x 4 mm
50 mm x 6 mm

Which connections are required for the designated terminal of the secondary of each potential, current, and auxiliary transformer?

One connection of 100 mm x 10 mm
One connection of 75 mm x 8 mm
One connection of 50 mm x 6 mm and one of 75 mm x 8 mm
Two separate connections of 50 mm x 6 mm (correct)

What is the minimum size of MS flat used to connect the metallic framework of outdoor equipment to the earthing grid for equipment on the primary side of traction power transformers rated between 66 kV up to 3000 MVA?

25 mm x 4 mm
75 mm x 8 mm
100 mm x 10 mm
50 mm x 6 mm (correct)

For equipment rated at 220 kV up to 10000 MVA, which ground conductor size must be used?

75 mm x 8 mm (A) Signup and view all the answers

How many separate and distinct connections are required for all outdoor equipment's metallic framework?

Two connections (B) Signup and view all the answers

What is the material of the flat used for earthing connections as specified in the guidelines?

Mild Steel (C) Signup and view all the answers

What is the maximum voltage rating discussed for equipment connections on the primary side of traction power transformers?

220 kV (D) Signup and view all the answers

What is the required size of the MS flat for connecting masts and structures to the earthing ring?

50 mm x 6 mm (C) Signup and view all the answers

What type of wire is used to connect fencing panels to the supporting uprights?

6 SWG G.I. wire (B) Signup and view all the answers

How should the ground terminal of the lightning arrester be connected?

Directly to the earth electrode with two connections (D) Signup and view all the answers

Where should the earthing ring inside the remote control cubicle be positioned?

300 mm from the floor level (B) Signup and view all the answers

How are connections of earth strips to each other made?

Using welding (B) Signup and view all the answers

What type of electrical systems are excluded from the scope of this code of practice?

Low voltage (LT) electrical power distribution systems (A) Signup and view all the answers

What does 'Earth' refer to in this context?

A conductive mass of the earth with zero electrical potential (A) Signup and view all the answers

Which term describes the resistance of an earth electrode with respect to the earth?

Combined Earth Resistance (B) Signup and view all the answers

What is meant by 'Equipment earthing'?

Earthing all metal work of electrical equipment not carrying current (C) Signup and view all the answers

What components make up an 'Earthing grid'?

Interconnected, horizontal bare conductors buried in the earth (C) Signup and view all the answers

What does 'Mesh Voltage (E mesh)' refer to?

The maximum touch voltage within a mesh of an earthing grid (A) Signup and view all the answers

Which of the following is not included in the power supply installation as defined in the content?

Signal and telecommunication equipment (A) Signup and view all the answers

What is the purpose of equipment earthing?

To ensure effective operation of protective gear during leakage (B) Signup and view all the answers

Which voltage levels are specified in the code for traction sub-stations?

220/25 kV, 132/25 kV, 110/25 kV, or 66/25 kV (A) Signup and view all the answers

What is a key drawback of using coke treated electrodes?

They lead to rapid corrosion of electrodes and steel frameworks. (D) Signup and view all the answers

Where should coke treated electrodes not be located?

Within 6.0 m of other metal work. (C) Signup and view all the answers

What is recommended in high embankments if the specified earth resistance cannot be achieved?

Use electrodes longer than 4 m to reach the parent soil. (A) Signup and view all the answers

What is the minimum depth at which the earthing grid should be buried?

600 mm (C) Signup and view all the answers

What type of material is recommended for making connections between the earth electrode and the grid?

75 mm x 8 mm MS flat (B) Signup and view all the answers

What technique is advised for joining longitudinal and transverse conductors in the earthing grid?

Welding (D) Signup and view all the answers

How should the spacing of earthing grid conductors be managed?

They should be spaced to maintain acceptable step and touch potentials. (B) Signup and view all the answers

What requires consideration when determining the size of the earthing grid conductor?

Incoming system voltage and fault level (C) Signup and view all the answers

Which of the following is NOT a characteristic of an effective earthing grid?

Uniform installation at ground level (C) Signup and view all the answers

What is the main purpose of earthing electrodes in traction substations?

To ensure safety and minimize earth resistance. (C) Signup and view all the answers

What is the minimum height at which the earth screen wires should be strung above the live conductors?

2.5 m (A) Signup and view all the answers

How many separate and distinct connections are required for each metallic fencing upright to the main earthing grid?

Two (D) Signup and view all the answers

What type of wire is used to connect the metallic fencing panels to the uprights?

6 SWG G.I. wire (D) Signup and view all the answers

Which of the following statements about the earthing arrangement at a switching station is correct?

Three earth electrodes must be interconnected to form a closed loop. (B) Signup and view all the answers

What is the function of the earth screen in outdoor substations?

To shield against direct lightning strikes. (D) Signup and view all the answers

What should the earthing arrangement for the 240 V ac supply to the oil filtration plant consist of?

Two separate distinct connections (B) Signup and view all the answers

Which type of flat is required for making distinct connections in an earthing system?

50 mm x 6 mm MS flat (B) Signup and view all the answers

What is the purpose of connecting to the traction rail in earthing arrangements?

To limit potential gradient during faults. (B) Signup and view all the answers

What material is specified for the earth screen wires used in substations?

Galvanized steel (A) Signup and view all the answers

How are the secondary terminals of transformers connected in the earthing arrangement?

By two separate and distinct connections. (D) Signup and view all the answers

Which connection method is specified for the metallic door panels to supporting uprights?

Two separate and distinct connections using 6 SWG G.I. wire. (B) Signup and view all the answers

What is the purpose of the earthing ring inside the remote control cubicle?

To ensure safe grounding for all electrical equipment in the cubicle. (B) Signup and view all the answers

Which material is specified for connecting the metal casing of transformers to the mast/structures?

50 mm x 6 mm MS flat. (D) Signup and view all the answers

How should connections of earth strips to each other be made according to standard practice?

By welding. (B) Signup and view all the answers

Where should the earthing leads from the lightning arrester be positioned in relation to the earth electrode?

They must be brought to the earth electrode as short and straight as possible. (D) Signup and view all the answers

What is the primary aim of conducting equipment earthing in electrical installations?

To maintain an effective operation of protective gear (D) Signup and view all the answers

Which term specifically refers to the interconnected, horizontal bare conductors buried in the earth?

Earthing grid (C) Signup and view all the answers

In the context of this code, how is the term 'Earth' defined?

The conductive mass of the earth with a potential taken as zero (B) Signup and view all the answers

What does the term 'Combined Earth Resistance' specifically exclude from its definition?

The traction rail (D) Signup and view all the answers

Which aspect of equipment does the earthing code primarily cater to?

Earthing at specific traction substations and switching stations (C) Signup and view all the answers

What is the significance of 'Mesh Voltage (E mesh)' in the earthing context?

It represents the maximum touch voltage within an earthing grid mesh (A) Signup and view all the answers

What type of electrical system is specifically excluded from the purview of this code?

Low voltage (LT) electrical power distribution systems (D) Signup and view all the answers

What is a critical reason for limiting the use of coke treated electrodes in earthing systems?

They can cause rapid corrosion of nearby metal structures. (A) Signup and view all the answers

How deep should the earthing grid be buried according to the guidelines?

600 mm (A) Signup and view all the answers

Which of the following is recommended for difficult locations such as high embankments?

Using electrodes longer than 4 m to reach the parent soil. (B) Signup and view all the answers

What is the connection method used between the MS flat and the MS rod in the earthing grid?

Welding (D) Signup and view all the answers

What is the primary consideration when determining the size of the earthing grid conductor?

The incoming system voltage and fault level (A) Signup and view all the answers

How should the connections between longitudinal and transverse conductors of the earthing grid be handled?

By welding (B) Signup and view all the answers

What is essential for ensuring a low resistance and adequate current-carrying capacity in large sites?

A reasonable distribution of electrodes (A) Signup and view all the answers

What joint method is specified for connecting an earth electrode to the grid?

Through MS links by bolted joints (C) Signup and view all the answers

What spacing strategy is emphasized for earthing grid conductors?

Conductors should be spaced to maintain safe step and touch potentials (A) Signup and view all the answers

Where should earth electrodes ideally be located in a traction substation?

Within and adjacent to the perimeter fence (A) Signup and view all the answers

What is the main objective of an earthing system in a traction environment?

To provide a uniform potential around the station (B) Signup and view all the answers

Which of the following does NOT represent a requirement of a good earthing system?

Provide high resistance path for fault currents (D) Signup and view all the answers

In the context of earthing, what does 'Step Voltage' refer to?

Potential difference over one meter on earth's surface (D) Signup and view all the answers

What is meant by 'Touch Voltage' in earthing terminology?

Voltage difference experienced by a person reaching towards a grounded structure (D) Signup and view all the answers

Which of the following characteristics is crucial for an earthing system to ensure safety during faults?

Uniform potential surface around the station (D) Signup and view all the answers

How does an effective earthing system contribute to protecting personnel?

By maintaining low impedance paths that minimize voltage differences (B) Signup and view all the answers

What would likely happen if the maximum voltage gradient during earth faults exceeds safe limits?

Increased risk of shock or injury to personnel (D) Signup and view all the answers

Which term describes the potential difference resulting from electrical potential variances on the earth's surface?

Step Voltage (B) Signup and view all the answers

What is the assumed distance between two points when measuring Step Voltage?

One meter (D) Signup and view all the answers

What is the minimum number of earth electrodes required at each switching station?

Three (A) Signup and view all the answers

Which connection method is used for earthing the fencing panels?

Two separate connections with 6 SWG G.I. wire (D) Signup and view all the answers

What is the purpose of the overhead earth screen in outdoor substations?

To limit lightning strikes on the equipment (D) Signup and view all the answers

Which of the following materials is used as an earthing conductor for the main earthing grid connections?

Galvanized steel (B) Signup and view all the answers

How should the earth electrodes at a switching station be interconnected?

Using 50 mm x 6 mm MS flat to form a closed loop (B) Signup and view all the answers

What type of steel is specified for the earth screen wires in outdoor substations?

Galvanized steel (A) Signup and view all the answers

What is the height requirement for the overhead earth screen above the live conductors?

At least 2.5 m (A) Signup and view all the answers

What is the minimum requirement for connections to the 240 V AC supply for the oil filtration plant?

Two separate and distinct connections with 50 mm x 6 mm MS flat (A) Signup and view all the answers

Which configuration is used for the earthing connections of each potential and current transformer?

Two distinct connections to the main earthing ring (B) Signup and view all the answers

What connection technique is used for earthing the metallic door panels at the substation?

Two distinct connections with 6 SWG G.I. wire (D) Signup and view all the answers

Flashcards

Earthing of traction power transformer secondary

One terminal of the 25 kV secondary winding of each traction power transformer is directly connected to the earthing grid using a 75 mm x 8 mm MS flat. An additional connection is made to the buried rail using a similar size MS flat.

Earthing of potential, current, and auxiliary transformers

A designated terminal on the secondary side of each potential, current, and auxiliary transformer is connected to the earthing grid using two separate and distinct earth connections. Each connection uses a 50 mm x 6 mm MS flat.

Outdoor equipment earthing method

Metallic frames of outdoor equipment (transformers, circuit breakers, etc.) and steel structures are connected to the earthing grid via two separate connections. One connection is made to the nearest longitudinal conductor, the other to the nearest transverse conductor of the grid.

Ground conductor size (primary side)

The size of the MS flat used for grounding equipment on the primary side of a traction power transformer depends upon the system voltage and fault level. Sizes range from 50mm x 6mm to 75mm x 8mm. Refer to the table for specific sizes.