What is the Function of an Earthing or Grounding Transformer?

 Earthing or Grounding Transformer

Generally, an Earthing or Grounding Transformer is not a three-phase transformer, but a single-phase transformer with the primary (HV end) rated voltage equal to the system phase-to-neutral voltage and the secondary (LV end) rated voltage of either 240V or 11oV.

To avoid any switching transient in the Transformer primary of the transmission system, or a big noise may damage the Transformer. To avoid such spurious signal, grounding is provided in the primary. The grounding also affects third harmonics from the switching transient.

Electrical Substation Equipment: Grounding Network and Its Functions

Fig-Electrical Grid Substation

Substation equipment grounding is a crucial aspect of electrical power systems to ensure safety and proper functioning. The main purpose of grounding is to provide a low-resistance path for fault currents, stray currents, and lightning surges, allowing them to flow to the ground rather than damaging equipment or posing a safety hazard to people.

Electrical Substation Equipment Grounding Networks Details

What do we need to know to understand the substation grounding properly, following the local and international standards? The Basics of Substation Grounding must be known to any person who works in the substation area.

Method of Tower Grounding | Electrical Transmission Line

What is the purpose of a tower grounding?

Not only is tower grounding, but it is also fundamental and essential in an electrical system for both the safety and reliability of the system. 

The most important part of grounding is to protect people, structures, and equipment since damage can cause outages or malfunction and result in economic losses of great value. 

Allowable Earthing Resistance for Link Box Earthing

The allowable earthing resistance for a link box depends heavily on the type of bonding system (solid vs. cross-bonded) and the location of the link box (at a termination vs. along the cable route).

There is no single "universal" value, but standard industry specifications and practices typically require the following limits:

1. Typical Allowable Resistance Values

Why Does Single-Phase Require a Neutral Conductor but not in Three-Phase?

Do you think about why single-phase electricity requires a neutral conductor while three-phase electricity does not?

In a single-phase electrical system, power is transmitted using two conductors: the live conductor (carrying current) and the neutral conductor (completing the circuit). The neutral conductor is necessary to complete the circuit and provide a return path for the current back to the source.

Grounding, Earthing and Protection Against Lightning Procedure as Bangladesh Electricity Distribution Code

If you do not follow the electricity safety code it's may danger anytime

Why is Earthing Necessary in Electrical Systems?

The main purpose of the earthing of any electrical appliance is to protect it from carrying current due to accidental contact with the live wire or what is called the phase wire of the power supply system. It is a good practice to provide two parallel connections of the earth conductor to any electrical installation whether it is for domestic or industrial use. Normally Copper wire or strip is used as an earthing conductor but nowadays it is replaced by Galvanized Iron or Aluminum conductor is also used since Copper is costly and chances of theft or pilferage are high.

Why We put Salt and Charcoal into Earth-pit while Earthing?

What is Earthing Resistance?

Earthing resistance is not the resistance of the electrode. The earthing resistance is not same all over the area. The value of earting resistance is depends upon the soil resistivity of the particular area. Actually the measured earth resistance is not only the resistance of the electrode, it is the combined resistance of conductor and the associated soil. During fault, if the soil resistance is higher the fault current cannot dissipate to associate soil.

To improve the conductivity of poor soil during fault current, salt and charcoal around the conductor is used to dissipate. Regarding this, IEEE 80–2013 clause 14.5 (a), (b), (c), (d) tells us about soil treatment for better conductivity.

Using Salt & Charcoal has its own demerits. Salt & Charcoal are leaching compounds so it required frequent application. 

Charcoal is used to retain the moisture for long duration because it is an adsorbent and salt is added to increase the conductivity both these products help to pass the leakage current through earth wire as early as possible to remove the chances of shock.

We can practice permanent earthing compounds which are moisture independent as per IEEE 80–2013 clause 14.5(d).

You may read about:

01. What is the Function of Earthing or Grounding Transformer?

02. Equipment Grounding for De-energized Construction and Maintenance.

How salt and charcoal works to improve earthing resistance?

Coal or Charcoal is made of carbon which is good conductor that can minimize the earth resistant. The salt use as electrolyte to form conductivity between earth electrode (generally GI pipe or plate) Coal and Earth with humidity. Sand has used to form porosity to cycle water & humidity around the mixture.

The whole purpose of providing earthing is to discharge the leakage current or fault current safely to the ground. Means better the conductivity of the soil or lesser its resistance. Adding charcoal and water in earthing pit decreases soil resistivity. 

The layer of charcoal and salt helps to maintain low resistance for earth fault currents. Because of ionic behavior of salt and charcoal they will maintain moisture content around the earth pit. 

Why Earthing Switch or Disconnector is Used in Transmission Line?

How Earthing or Disconnector Switch Play Rule to Personnel Safety Even in a Isolated Disconnected Line? 

The function of earth or disconnector switch is to discharge the capacitive voltage that stored in generator side or long transmission line conductors in the isolated system just after opening the CB (Circuit Breaker) and Isolator.

So, we understand that the main purpose of earth switch is to ground the isolated bus/conductor. Generally earth switch is mechanically interlinked with isolator. Means when isolator opens the circuit then earth-switch closes & vice-vars.

When earth switch is connected to the isolated but charged system it discharges the stored energy to earth, so that maintenance work can be carried out either in line on generator side.

So earth switch provides extra safety to the working personnel during transmission line maintenance.

You may interrelated to read:

01. What is the Function of Earthing or Grounding Transformer?

02. Equipment Grounding for De-energized Construction and Maintenance.

In my practical experiences I found three cases regarding the necessity of earthing in dead line too.

Case-1:

When the line crews working a dead line where parallel another line is alive. The line crews experienced the voltage exist and they felt some electrical shook.

Case-2:

When we construct parallel two circuits high voltage transmission line and energized a single circuit first. We found that other circuit also experiencing around 1kV in control panel metering system. This happened due to induced voltage.

Case-3:

When we construct a long overhead transmission and it was causing electric shook before touching with any energized line. Finally we discovered the voltage developed in it due to conductor capacitive behavior.

When Earthing Switch or Disconnector Should be Operated?

Operating the earth switch in an energized line may causes sever accident. The condition of earth switch operation is as below;

1. Earth switches should be operated only when the isolators are in open;
2. All earth switches can be operated manually. Semaphore indicator can be seen for position feedback (on/off) in switch yard control panel.

Latest Earth Switch or Dis-connector

What we discussed is for maintenance purpose earth switch mainly, but in latest GIS (Gas Insulated Switch) system switch-gear used automatic high speed earth switch. In this system when any fault occurred the faulty part automatically isolated and earthed by high speed auto earth switch and protect the equipment immediately.