Nowadays, modern societies are highly dependent on electrical power supply. To live & make our life comfortable, we use a number of appliances or gadgets at our residences or offices.
Electrocution, Electrical fire and Lightning kill 15,000 people every year. Also 75000 (approx.) suffer because of these deaths, there is loss of property and assets, dreams of many people associated with deceased shatter.
The news of electric shock or electric fire killing people gives pain and forces everyone to find the solution. But in a day or two, we again forget and wait for another accident to happen. (Refer figure 1)
There are too many tales that different parts of the country have to tell each day without fail (many cases are even not reported or recorded).
Keeping the figure for the injured aside, the numbers for the electrocution deaths in the country tell a story of their own. According to the National Crime Records Bureau, around one lakh people lost their lives because of electrocution in the last decade alone. The annual average of fatalities rose to 12,500 per year or 30 fatalities every day. Calling the 30 electrocution deaths per day in India ‘accidents’ is something which is not justified as it tends to insulate all stake holders from accountabilities.
Around 1 lakh people died due to electrocution in the last decade, as per NCRB data. The detail of deaths due to electrocution & fire for last three years in given below in table 1.
Main causes of electrocution & electrical fire hazard
Electrocution & Electrical Fires in Electrical Installation may be broadly caused by:
- Over currents (overloads and short circuits)
- Harmonics
- Earth fault
- Electric arcs in cables and loose Connections
- Failure of protection device or Wrong selection of protection device
- Wrong selection of cables or wires
- Mismatch of illumination fittings rating and lamps used
- Use of extension cord for heaters or any other heavy loads
- Use of outlived (outdated) or damaged equipments
- Over voltages (lightning) & arcing ground
- Consumer has become prosumer
- Inadequate design for earthing / grounding
- Improper or no verification and testing (commissioning or periodical)
Basic of over current in the electrical system
Electrical systems are designed to safely handle currents within specified limits. However, various conditions can lead to overcurrent situations, each with distinct causes, effects, and protective measures. This discussion will delve into overcurrent, overload, short-circuit, and earth fault currents, providing a comprehensive understanding of their characteristics and implications in electrical engineering.
Overcurrent: Overcurrent refers to any current in an electrical circuit that exceeds the rated or intended value. Its causes:
- Normal operational conditions: Momentary increases in current due to changes in load.
- Abnormal conditions: Faults such as short circuits or ground faults.
Component failure: Malfunctioning equipment or aging components.
Overload: This occurs when the current in a circuit exceeds the rated load current for an extended period.
- Causes: Excessive connected load, sustained high-demand periods, or inadequate circuit capacity. (Refer figure 2)
- Effects: Overheating of conductors, insulation degradation, and potential damage to equipment.
- Protection: Circuit breakers, fuses, and thermal overload relays designed to trip at predetermined overload thresholds.
Short-Circuit: A direct low-resistance path between conductors of different phases or between a phase and ground.
- Causes: Insulation failure, accidental contact between conductors, or equipment faults. (Refer figure 3)
- Effects: Rapid rise in current, magnetic forces, and potential mechanical damage to conductors and equipment.
- Protection: High-current rated fuses, circuit breakers with instantaneous trip settings, and protective relays designed to detect short circuits.
Earth Fault: This occurs when a live conductor unintentionally contacts earth or a conductive part connected to earth.
- Causes: Insulation breakdown, equipment faults, or accidental contact with grounded surfaces. (Refer figure 4)
- Effects: Current flows from the phase conductor to ground, potentially causing equipment damage and safety hazards.
- Protection: Differential relays, residual current devices (RCDs), and ground fault detectors designed to detect small leakage currents indicative of earth faults.
Characteristics and Implications
- Overload: Typically exceeds nominal operating current by 110% to 150%.
- Short-Circuit: Can be several times higher than normal operating current, limited only by system impedance.
- Earth Fault: Generally lower in magnitude compared to short-circuit currents, but significant enough to cause damage if not promptly detected and isolated.
Short circuit in the electrical system
Electrical fires very often take place in residential sector. This is because most of the people do not account for the rating of the appliances while placing or connecting them. Being an individual, most of us are not aware about the parameters we need to consider while purchasing the product. The only thing that people look for is the cost effectiveness, which in turn leads to extreme situation resulting in electrical fires. Major reason for electrical fire in LV system is Short Circuiting i.e. flowing of current through unintended path.
A short circuit is an abnormal connection between two nodes of an electric circuit intended to be at different voltages. This results in an electric current limited only by the equivalent resistance of the rest of the network which can cause circuit damage, overheating, fire or explosion (Refer figure 5).This high current generates high heat and presence of fuel or any other flammable materials may result in the fire hazard as governed by fire triangle in figure 6.
Short circuit happens mainly due to degradation of insulation. As the wire gets old, the insulation gets degraded, due to which there is a chance of short circuiting (Refer figure 7) & this may lead to fire.
Over voltage in the electrical system
Understanding the internal and external causes of overvoltage in power systems is essential for implementing effective protection and mitigation strategies. Internal factors like switching operations, capacitor switching, faults, and resonance require careful design and use of protective devices to minimize transient overvoltages.
External influences such as lightning strikes, electromagnetic interference, and grid switching necessitate robust grounding, surge protection, and system resilience measures. By addressing these causes comprehensively, power systems can maintain reliability, protect equipment, and ensure safe operation in diverse operational conditions. (Refer figure 8)
Theory of arcing ground-ungrounded system
Ungrounded system is one where the neutral is not connected to earth. Thus, neutral of ungrounded system is isolated. Arcing Ground is an electrical phenomenon in which the voltage of faulty phase fluctuates due to capacitive charging current. This arcing ground phenomenon is prevalent in three phase ungrounded neutral system.
To be continued…
Dr. Rajesh Kumar Arora obtained his B. Tech. and M.E. degrees in Electrical Engineering from Delhi College of Engineering, University of Delhi. He completed his PhD in grounding system design from UPES, Dehradun. He is also a certified Energy Manager and Auditor and has worked in 400kV and 220kV Substations for more than 14 years in Delhi Transco Limited (DTL). He has also worked as Deputy Director (Transmission and Distribution) in Delhi Electricity Regulatory Commission (DERC). Presently he is working in D&E (Design and Engineering) department of DTL.
