- Watt-Hour Meter Definition: A watt-hour meter is defined as a device that measures and records the electrical power passing through a circuit over a period of time.
- Components and Function: The watt-hour meter includes a motor and a counter, where the motor’s speed is proportional to the current flow, and the counter tracks energy usage based on motor revolutions.
- Types of Watt-Hour Meters: There are three main types: electromechanical induction meters, electronic energy meters, and smart energy meters.
- Modern Features: Modern meters prevent tampering by storing previous readings and using remote reporting.
- Advantages of Different Types: Electromechanical meters are simple and low-cost, electronic meters are accurate and robust, and smart meters offer advanced features like tamper prevention and enhanced accuracy.
What is a Watt Hour Meter?
A watt-hour meter is a device that measures and records the electrical energy passing through a circuit over time. It shows the energy used by homes, businesses or devices, and utilities install watt-hour meters at consumers’ premises for billing purposes.
Readings are taken during each billing period. The common billing unit is kilowatt-hour (kWh), which equals the use of one kilowatt of power for one hour or 3,600,000 joules.
The watt-hour meter is often called an energy meter, electric meter, electricity meter or electrical meter.
At its core, a watt-hour meter comprises a small motor and a counter. The motor runs on a small fraction of the current flowing through the measured circuit.
The motor’s speed is directly proportional to the power flowing through the circuit, that is, the rate at which the circuit uses energy.
Each revolution of the rotor corresponds to a fixed amount of current-driven energy use. A counter attached to the rotor tracks these revolutions, displaying the total energy consumption.
Tampering and Security
A common tampering method involves attaching a magnet to the outside of old energy meters. Using capacitance and inductive loads can also slow the rotor.
The most modern meters store previous readings with time and date stamps, which discourages tampering. Utilities also install remote-reporting meters to detect it.
Types of Watt Hour Meter
Basically, the watt-hour meter is classified into three different types as follows:
- Electromechanical type induction meter
- Electronic energy meter
- Smart energy meters
Electromechanical Type Induction Meter
In this meter type, a non-magnetic, electrically conductive aluminium disc revolves in a magnetic field. The passing power drives the rotation, and the rotation speed is proportional to the power flowing through the meter.
Gear trains and counter mechanisms are incorporated to integrate this power. This meter works by counting the total number of revolutions, and it is relative to the usage of energy.
A series magnet sits in series with the line and carries a coil of a few turns of thick wire. A shunt magnet connects in shunt across the supply and carries many turns of thin wire.
A braking magnet, a permanent magnet, is included for stopping the disc at the time of power failure and placing the disc in position. This is done by applying a force opposite to the rotation of the disc.
The series magnet produces a flux directly proportional to the current flow, and the shunt magnet correspondingly produces a flux proportional to the voltage. Because of the inductive nature, these two fluxes lag each other by 90o.
An eddy current develops in the disc where the two fields interact. The resulting force is proportional to the product of the instantaneous voltage, current and the phase angle between them.
The braking magnet, positioned over one side of the disc, develops a braking torque on it. The disc speed settles when the braking torque equals the driving torque.
The gear arrangement linked with the shaft of the disc is implemented for recording the number of revolutions. This is for single-phase AC measurement. An additional number of coils can be implemented for different phase configurations.
Electronic Energy Meter
The major feature of the electronic meter other than power usage measurement is that it can display the energy usage on a LED or LCD. In some advanced meters, the readings can be transmitted to remote areas.
It can also record the amount of usable energy in on-peak hours and off-peak hours. In addition, this meter can record the parameters of supply and load like voltages, reactive power used, the instantaneous rate of usage demand, power factor, maximum demand, etc.
Smart Energy Meter
In this type of meter, communication in both directions (Utility to the customer and customer to the utility) is possible.
Customer to utility communication includes parameter values, consumption of energy, alarms, etc. The utility to consumer communication includes disconnect/reconnect instructions, automatic meter reading system, upgrading of the software of the meter, etc.
Modems are implemented in this meter to make communications easy. The communication system includes fiber cable, power line communication, wireless, telephone, etc.
Advantages of Different Types of Watt Hour Meter
The three main types of watt-hour meters are:
- Electromechanical Energy Meters
- Electronic Energy Meters
- Smart Energy Meter
The advantages of each of these types of watt-hour meters are listed below:
| Electromechanical Energy Meter | Electronic Energy Meter | Smart Energy Meter |
| Simple construction. | Handles non-linear loads. | Reduction in need of visits for reading/taking monthly bills. |
| Accurate and precise measurement. | More robust. | Tampering of meters can be avoided. |
| Reliable. | Improvement in quality of electrical distribution. | Better accuracy. |
| The cost is low. | Highly accurate | High Efficiency |
