Smart meters for mitigating electrical accidents

A load switch in a smart meter is a relay or circuit breaker that controls the flow of electricity through the meter. It can be remotely operated and is designed to disconnect the electrical load if certain conditions are met. This capability enhances safety by enabling immediate response to dangerous situations.

Abstract: Nowadays, modern society is highly dependent on electrical power supply. To live & make our life comfortable, we use a number of appliances/gadgets at our residence/office. Every day we get up with the news of electrocution or electrical fires in residential or commercial buildings or public locations or distribution transformers for substations. This forces us to ponder over the reasons/ causes of such accidents which lead to loss of lives as well as assets/properties. In today’s evolving energy sector, smart metering is ready to become a game-changer in optimizing electricity management. Smart meters provide real-time data that allows utilities to do monitoring, manage & control the electricity usage patterns. Further this ensures accurate billing and reduces operational costs. Above all for consumers, it offers greater transparency and control over their energy consumption, leading to potential cost savings and more informed decision-making.

This paper provides insight about optimal use of smart energy meters in mitigation of electrical accidents and fire hazards for all locations. 

Key Words:  Electrocution, Electrical Fire, Insulation Failure, Short Circuit, Heating Effect, Arcing (Loose Connection), Grounding System & Smart Meter

Fig. 1 ELECTROCUTION ACCIDENTS

1. INTRODUCTION

Nowadays, modern society is highly dependent on electrical power supply. To live & make our life comfortable, we use a number of appliances/gadgets at our residence/office. 

Electrocution, Electrical fire and Lightning kill 15,000 a year. Also 75000 (approx.) suffer because of these deaths, there is loss of property and assets, and the dreams of many people associated with the 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&2)

                 

Fig. 2 ELECTRICAL FIRE ACCIDENTS

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 stakeholders from accountabilities.

Around 1 lakh people died due to electrocution in the last decade, as per NCRB data. The details of deaths due to electrocution & fire for the last three years are given below in table 1.

TABLE 1 NCRB DATA OF DEATHS DUE TO LIGHTNING ELECTROCUTION AND SC FIRE 2020-222

2. MAIN CAUSES OF ELECTROCUTION & ELECTRICAL FIRE HAZARD 

Electrocution & Electrical Fires in Electrical Installation may be broadly caused by

1. Over currents (overloads and short circuits) 
2. Harmonics
3. Earth fault 
4. Electric arcs in cables and loose Connections
5. Failure of protection device or Wrong selection of protection device
6. Wrong selection of cables or wires
7. Mismatch of illumination fittings rating and lamps used
8. Use of extension cord for heaters or any other heavy loads
9. Use of outlived (outdated) or damaged equipments
10. Over voltages (Lightning ) & arcing ground
11. Consumer has become prosumer
12. Inadequate design for earthing / grounding
13. Improper or No verification and testing (commissioning or periodical)

2.1 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.

1. Overcurrent: Overcurrent refers to any current in an electrical circuit that exceeds the rated or intended value.

   Causes: A. Normal operational conditions: Momentary increases in current due to changes in load.

2. Abnormal conditions: Faults such as short circuits or ground faults.
3. Component failure: Malfunctioning equipment or aging components.

Fig. 3 OVERLOADING OF EXTENSION BOARD

2. Overload: 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 3)
• 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.

Fig. 4 SHORT CIRCUIT IN ELECTRICAL SYSTEM

3. 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 4)
• 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.

Fig. 5 EXAMPLE OF EARTH (GROUND) FAULT 

4. Earth Fault: 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 5)
• 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.

2.1.1 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.

2.2 SHORT CIRCUIT IN THE ELECTRICAL SYSTEM

Electrical fires very often take place in the 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 situations resulting in electrical fires. Major reason for electrical fire in the LV system is Short Circuiting i.e. flowing of current through unintended paths.

                           Fig.6 CONCEPT OF SHORT CIRCUIT

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 (please refer figure 6).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 7.

                                          Fig.7 FIRE TRIANGLE

Short circuits happen 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 (figure 8) & this may lead to fire.

                             Fig.8 FIRE DUE TO INSULATION FAILURE

2.3 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 9)

Fig. 9 LIGHTNING AND ITS IMPACT ON BUILDING

2.3.1 Theory of Arcing Ground-Ungrounded System

Ungrounded System is one where the neutral is not connected to earth. Thus, the neutral of the 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 a three phase ungrounded neutral system. 

Let us now consider a fault condition. Suppose a single line to ground fault takes place in C phase as shown in figure 10 below.

Fig. 10 IMPACT OF SLG FAULT ON UNGROUNDED SYSTEM

The fault current in this case will complete its circuit as shown in figure above. Fault current I_C will be equal to the vector sum of I_A and I_B. Therefore,

I_C = I_A + I_B

Please note that, I_C in C phase will flow toward the neutral. Therefore we can say that, phase voltage of the C phase has reversed its direction. This in turn means that the voltage of the neutral point has shifted from ground potential to phase voltage.

Because of this shifting of neutral voltage, the voltage of the healthy phase will become equal to the line voltage. Due to this raised voltage of healthy phases, charging currents will increase i.e. charging current in faulted phase is three times that of the normal charging current. Due to this heavy arcing will take place in the faulted phase. This phenomenon of arcing is known as Arcing Ground. 

3.0 ROLE OF ADEQUATE EARTHING/GROUNDING

Grounding/ Earthing means making a connection to the general mass of earth. The use of grounding is so widespread in an electric system that at practically every point in the system, from the generators to the consumers’ equipment, earth connections are made.

There are two types grounding (Refer figure 11):

1. Neutral Grounding
2. General (Equipment) Grounding

Fig.11 EQUIPMENT AND NEUTRAL EARTHING

The objectives of General Grounding system include:

1. To provide a low resistance return path for fault current which further protects both working staff and equipment installed in the premises (Refer figure 12).
2. To prevent dangerous GPR with respect to remote ground during fault condition.
3. To provide a low resistance path for power system transients such as lightning and over voltages in the system.
4. To provide uniform potential bonding /zone of conductive objects within substation to the grounding system to avoid development of any dangerous potential between objects (and earth).
5. To prevent building up of electrostatic charge and discharge within the substation, which may result in sparks.
6. To allow sufficient current to flow safely for satisfactory operation of the protection system.

Fig.12 UNEARTH SYSTEM AND SHOCK HAZARD

The main objective of grounding electrical systems is to provide a suitably low resistance path for the discharge of fault current which ultimately provides safety to working personnel and costly installed equipment by providing sufficient current to safety devices. 

Fig. 13 PROVISION OF EARTH TERMINAL AT METER BOX

In India, the use of earthing terminals in switchboards is often inconsistent, and this has serious safety implications. Earthing, or grounding, is a crucial electrical safety measure designed to prevent electric shocks and fires by directing stray currents safely into the ground. Despite its importance, many people in India neglect or fail to implement proper earthing in their electrical systems. Understanding the reasons behind this and the associated dangers can shed light on why this issue is so critical. (Refer figure 13)

1. Lack of Awareness and Understanding

2. Inadequate Implementation and Enforcement of Standards

3. Economic Constraints

4. Unqualified or Undertrained Electricians

Dangers Associated with Lack of Earthing : The dangers of neglecting earthing are severe and multifaceted. Without proper earthing, electrical faults such as short circuits or insulation failures can lead to electric shocks, which can cause injury or even death. Electrical appliances and wiring can become live with stray currents, posing a constant risk to anyone in contact with them. Additionally, the absence of earthing increases the risk of electrical fires, which can result in property damage, loss of life, and financial losses.

The basic concept of smart meter

A smart meter is an AC static watt-hour meter with time-of-use registers and internal connect and disconnect switches with two-way communication capability. It is designed to measure the flow of forward (import) or both forward (import) and reverse (export), store and communicate the same along with other parameters defined in the standard. It shall be remotely accessed for collecting data/events and programming for select parameters.

The smart meter is a component of Advanced Metering Infrastructure. For  this standard, the smart meter is conceived as a single unit comprising the following functional zones:

a)    Metering,

b)   Load switch,

c)    Metering protocol, and

d)   Communication modules.

The smart meters may be widely used, and the buyer may choose desired features to meet the objectives of their overall system and site conditions.  The smart meter architecture is categorised into two variants to facilitate such a flexible approach. The two variants are diagrammatically represented in the figures below respectively. These variants apply to both built-in and pluggable types of smart meters. The main components are described below:

Fig: Variant -1 of smart meter

Fig: Variant -2 of smart meter

NOTE:-1.Neighbourhood Area Network [NAN] 2. Data Concentrator Unit [DCU] 3. Head End System [HES] 4.In-Home Display [IHD]

5. Hand Held Unit [HHU]

Smart meter functional requirements

The smart meter developed as per the standard is required to support the handling of the following operational requirements:

Disconnection mechanism

The smart meter shall support disconnection (all the switches shall operate) under the following conditions:

a)       Over current (minimum 105% of Imax in any phase for predefined persistence time),

b)      Load control limit (programmable and set by utility),

c)       Pre-programmed event conditions (factory set),

d)      Disconnect signal from utility control centre, and

e)       In case of pre-paid facility under defined/ agreed conditions.

It must be noted that as per the relevant Indian Standard

1  Persistence time value to be provided by the utility.

2  The utility shall provide a list of events for  pre-programmed disconnection.

Reconnection mechanism

The local reconnection due to disconnection under over current and load control limit shall be as follows:

1. The switch re-connection is decided by meter locally. It will try to reconnect the load up to a predefined time with a predefined interval (time and interval are programmable by utility). The meter shall remain in normal connect mode if the consumption is within limits.

2. If the consumption exceeds the programmed limits, it will lock out and wait for 30 min (lock-out period). After this period, the meter shall reconnect the load, and if the consumption is still above the limit, the procedure as defined above in (a) shall be repeated with a status update to HES.

3. In all conditions other than ‘Over current and load control limit, ’ reconnection shall normally be done from HES. In case of communication failure with HES, reconnection shall be made through a local optical port with specified security.

Reconnection mechanism for prepayment meter

As per the agreed prepayment structure with utility.

Status of load switch: Indication of the status of the load switch (that is connected/ disconnected) shall be available on display as well as at HES.

Load switches for protection against fire and electrocution.

Smart meters are sophisticated devices crucial in modern energy management, offering enhanced capabilities beyond traditional meters. One of their most critical functions is improving safety, particularly in preventing fire and electrocution risks. A key component in achieving this is the load switch, an integral feature in many smart meters. Here, we will explore how load switches in smart meters contribute to safety by preventing fire and electrocution and provide guidelines for their effective use.

Understanding load switches in smart meters

A load switch in a smart meter is a relay or circuit breaker that controls the flow of electricity through the meter. It can be remotely operated and is designed to disconnect the electrical load if certain conditions are met. This capability enhances safety by enabling immediate response to dangerous situations.

1.  Protection against fire

a)  Overcurrent protection: One of the primary functions of a load switch is to provide overcurrent protection. Excessive current can cause overheating in electrical wiring, potentially leading to fires. Smart meters with load switches can detect when the current exceeds a safe threshold. When this happens, the load switch can automatically disconnect the circuit, preventing overheating and reducing fire risk.

b) Overvoltage protection: In addition to overcurrent, overvoltage conditions can pose a fire risk. Smart meters with load switches can protect against this by disconnecting the circuit when voltage levels exceed safe limits. Overvoltage conditions may result from issues such as lightning strikes or power surges. By disconnecting the load, the smart meter helps to prevent potential damage and fire hazards associated with these conditions.

2.  Protection against electrocution

a)  Ground fault detection: Ground faults occur when electrical current unintentionally flows to the ground, often through a person or conductive material. This can result in electric shock or electrocution. Smart meters with load switches can incorporate ground fault detection features that monitor for abnormal current paths. If a ground fault is detected, the load switch can quickly disconnect the circuit, significantly reducing the risk of electrocution.

Detection mechanisms: The load switch in a smart meter can be equipped with ground fault sensors that measure the difference in current between the live and neutral wires. Any imbalance, indicating a potential ground fault, triggers the switch to disconnect the load, protecting individuals from electric shock.

b)  Residual current protection: Residual Current Devices (RCDs) protect against electrocution. Some smart meters integrate RCD functionality into their load switches. These devices detect residual currents that may indicate leakage or faults in the system. When an unsafe residual current is detected, the load switch disconnects the circuit, thus preventing potential electric shock.

Sensitivity settings: Load switches with RCD capabilities can be adjusted for sensitivity, ensuring they react appropriately to varying levels of residual current. Proper calibration is essential to balance sensitivity and minimise false tripping while providing effective protection.

3.   Healthiness of earthing (grounding) connection

How it works:

• Monitoring voltage levels: Smart meters can measure the voltage between different points in the electrical system, including between live and earth. If there is an open earth connection, the voltage between the live wire and the earth might significantly differ from normal values.
• Detection of abnormalities: Significant deviations in voltage readings can indicate a problem with the earthing system.

Practical guidelines for effective use

To maximise the benefits of load switches in smart meters for fire and electrocution protection, users and installers should adhere to several practical guidelines:

1. Proper installation: Proper installation is critical for operating safety features effectively. Incorrect installation can lead to malfunctions and reduce the effectiveness of protection mechanisms.
2. Regular maintenance: Regularly check the smart meter and its load switch. This includes verifying that the load switch operates correctly, inspecting for signs of wear or damage, and ensuring that safety features are functional.
3. Configuration and calibration: Properly configure and calibrate the load switch settings according to the electrical system’s specific requirements. This includes setting appropriate thresholds for overcurrent and overvoltage protection and calibrating RCD sensitivity.
4. User education: Educate users about the importance of smart meter load switches and safety features. Information on recognising signs of electrical problems and what actions to take in case of a safety alert can further enhance overall safety.
5. Emergency procedures: Establish clear emergency procedures in the event of a fault or safety alert. Users should know how to disconnect the power supply safely and seek professional assistance if needed.

Thus, smart meters are crucial in safeguarding against fire accidents and electrocution. Load switches in smart meters play a pivotal role in enhancing electrical safety. Through features such as overcurrent protection, overvoltage protection, ground fault detection, and residual current protection, these devices help prevent dangerous situations that could lead to significant harm. Effective use of load switches involves proper installation, regular maintenance, accurate configuration, and user education. By adhering to these practices, the benefits of smart meters in safeguarding against electrical hazards can be fully realised, contributing to a safer and more reliable electrical environment.

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References

[1]

IS 3043-2018, Indian Standard Code of Practice for Grounding.

[2] CEA ‘Measures Relating to Safety and Electric Supply’ Regulations 2023.

[3] CEA ’Installation and Operation of Meters’ (Amendment) Regulations, 2019.

[4]

IS 16444 A.C. Static Direct Connected Watt-hour Smart Meter Class 1 and 2— Specification.

Author: 

Dr. RAJESH KUMAR ARORA obtained the B. Tech. & Master of Engineering (ME) degrees in Electrical Engineering from Delhi College of Engineering, University of Delhi, India in 1999 and 2003 respectively. He completed his PhD in grounding system design from UPES, Dehradun. He is also certified Energy Manager and Auditor and has worked in 400kV and 220kV Substation for more than 14 years in Delhi Transco Limited (DTL). He has also been Deputy Director (Transmission and Distribution) in Delhi Electricity Regulatory Commission (DERC) for 03 years and 06 months. He has also contributed to DTL’s OS department for more than 2 years and rendered his services in the SLDC of Delhi Transco Limited (DTL). Presently he is working in D&E (Design and Engineering) department of DTL.