Introduction to Earthing in Power Systems
Earthing is a hair-trigger feature of electrical systems, which refers to the process of connecting non-current distribution parts or the neutral point of the power supply system to the earth. The primary goal is to facilitate the direct discharge of electrical energy in a manner that ensures safety. It involves connecting various components of installations to electrical conductors or electrodes that are in uncontrolled contact with the soil, usually located high above ground level. This entire voltage turnout is called an “earthing system”, with metallic conductors connecting installation parts to earth in what is called “electrical connections”.
Objectives of Earthing:
1. Personnel Protection: The most important objective is to protect persons from electric shock. This is achieved by ensuring that non-current distributing parts, such as equipment frames, remain continuously at ground potential, even in situations where insulation fails.
2. Lightning and surge protection: Earthing provides a specified venting path for the surge arrester and protects both equipment and personnel from the potentially hazardous effects of lightning and voltage surges.
3. Grounding Neutral System: This establishes the ground connection required for systems that use a grounded neutral configuration.
4. Equipment Maintenance: Earthing serves as a way to positively vent and de-energize the feeder or equipment better than performing any maintenance activities.
Importance of Power System Earthing:
The importance of a strong earthing system cannot be underestimated. It is important to have an adequate and constructive ground that can withstand unwanted conditions without causing immediate shutdown or dangerous voltage surges. Inadequate grounding can lead to massive earthings and dangerous situations that underline the hair-triggering role of a well-designed earthing system. In this context, it is often considered desirable to have multiple grounds and connections to increase ground protection.
Types of Earthing:
1. Neutral earthing: It involves connecting the neutral points of 3-phase windings to low-resistance earthing, which is synonymous with ensuring system safety and security.
2. Equipment Earthing: Primarily earthing focuses on non-current distribution parts, it addresses concerns related to personnel safety, lightning vs. safety, and contributes to earth fault protection.
Definitions in Power System Earthing:
1. Earth electrode: A blanket term encompassing any wire, rod, plate or conductors of various types embedded in the ground horizontally or vertically to provide constructive earthing. In distribution systems, this may be a rod driven vertically into the ground, while in generating stations and substations, grounding mats are increasingly used.
2. Resistance-to-Earth or Earth Resistance: It refers to the resistance offered by the earth electrode to the splash of current in the ground. It is important to note that this term primarily refers to the resistance of the soil between the electrode and the point of zero potential rather than the contact resistance between the earthing electrode and the soil.
3. Earthing Lead: The wire responsible for connecting the earth wire or any other workings to the earth electrode is known as earthing lead.
4. Earth Current: The current flowing through the earth electrode into the ground is called earthing current.
5. Step Potential: It shows the potential difference between the feet of a person standing on the floor of the substation, during the splashing of earth fault current through the grounding system, with a gap of 0.5 m between the two feet (one step) .
6. Touch potential: Touch potential refers to the potential difference between the fingers of a raised hand touching a faulted structure and the feet of a person standing on the floor of the substation. The goal is to pay alimony to minimize the blow to this potential difference.
7. Trap Potential: The maximum touch potential within the trap of the grounding grid is called trap potential.
8. Transferred Potential: A special specimen of touch potential where a potential is transferred into or out of the substation is known as transferred potential.
Effects of Electric Currents on the Human Body:
It is important to understand the effects of electrical currents on the human soul in order to design earthing systems that prioritize safety.
• Threshold of perception: At approximately 1 mA, individuals begin to feel a tingling sensation when exposed to an electrified object through intact skin.
• Let go current: This is the imbalance level at which individuals can release their grip on the conductor, approximately 9 mA for men and 6 mA for women.
• Hold-on-type accident: Currents in the range of 20-100 mA can cause severe pain and possible physical injury.
• Ventricular fibrillation: With Vilom 100 mA, there is a risk of a serious cardiac emergency known as ventricular fibrillation, which can be fatal if not corrected within minutes.
• High currents (6 A and above): These pose a risk of temporary respiratory paralysis and severe burns.
It is important to understand these effects to design earthing systems that ensure safety in various electrical installations. By comprehensively addressing the principles and applications of earthing, we can promote a safe electrical environment for both equipment and personnel.
BRIEF SUMMARY
Definition: Earthing is the process of connecting the non-current distribution parts or neutral point of the power supply system to earth.
Purpose: To ensure the safe discharge of electrical energy by connecting electrodes to components in the soil.
Objectives of Earthing:
1. Personnel Safety: Prevent electric shock by grounding non-current distribution parts.
2. Lightning and surge protection: Build a path to surge arresters to protect equipment and personnel from lightning and voltage surges.
3. Grounding Neutral Systems: Establish a ground connection for systems with a grounded neutral configuration.
4. Equipment Maintenance: To facilitate safe venting and de-energizing of equipment during maintenance.
Importance of Power System Earthing:
A strong earthing system is important to withstand adverse conditions without shutdown or dangerous voltage surges. Inadequate grounding can cause critical earthing and dangerous situations.
Types of Earthing:
1. Neutral Earthing: Connect the neutral points of the 3-phase windings to low-resistance earthing for system protection.
2. Equipment Earthing: Focus on non-current distribution parts, addressing personnel safety, lightning and earth fault protection.
Definitions in Power System Earthing:
1. Earth electrode: A wire, rod, plate or conductor buried in the ground for constructive earthing.
2. Resistance-to-earth or earth resistance: The resistance of the soil between the electrode and the point of zero potential.
3. Earthing lead: A wire connecting the earth wire or other workings to the earth electrode.
4. Earth current: The current flowing through the earth electrode into the ground.
Effect of electric currents on the human body:
• Understanding these effects is important to design safe earthing systems.
• Range of perception: Individuals feel a tingling sensation at approximately 1 mA through intact skin.
• Let go current: The level of imbalance that causes loosening of the grip, about 9 mA for men and 6 mA for women.
• Hold-on-type accident: Currents of 20–100 mA can cause severe pain and possible physical injury.
• Ventricular fibrillation: Risk of serious cardiac emergency at 100 mA, potentially fatal if not corrected promptly.
• High currents (6 A and above): Create a risk of temporary respiratory paralysis and severe burns.
A comprehensive understanding of these effects assists in designing earthing systems for safety in various electrical installations, promoting a safe electrical environment for equipment and personnel.