- 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 defined as a device that measures and records the electrical power passing through a circuit over time. It helps determine the electrical energy used by homes, businesses, or devices. 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 referred to as an energy meter or electric meter or electricity meter, or electrical meter.
Mainly the watt-hour meter comprises a tiny motor and a counter. The motor will operate by diverting the exact fraction of current flowing in the circuit to be measured.
The motor’s speed is directly proportional to the amount of current flowing through the circuit.
Each revolution of the motor’s rotor corresponds to a specific amount of current flow. A counter attached to the rotor tracks these revolutions, displaying the total energy usage.
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 reduce the rotor speed.
The most modern meter can store up the previous value with time and date. So the tampering is avoided. Utilities install remote reporting meters to detect tampering.
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
A non-magnetic and electrically conductive aluminum metal disc is made to revolve in a magnetic field in this type of meter. The rotation is made possible with the power passing through it. The rotation speed is proportional to the power flow 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 is connected in series with the line, which comprises a coil of few turns with thick wire. A shunt magnet is connected in shunt with the supply and comprises a large number of turns with 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.
A flux is produced by the series magnet that is directly proportional to the current flow, and the shunt magnet corresponding produces another flux to the voltage. Because of the inductive nature, these two fluxes lag each other by 90o.
An eddy current is developed in the disc, which is the interface of the two fields. A force corresponding produces this current to the product of instantaneous current, voltage, and phase angle.
A break torque is developed on the disc by the braking magnet positioned over one side of the disc. The speed of the disc becomes constant when the following condition is achieved, Braking torque = 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 main three types of matt 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. | 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 |
