What is a Wattmeter

In this article, we will discuss the wattmeter, a measuring instrument used in electrical and electronic circuits to measure the amount of active power in watts. Here, we will cover the definition of a wattmeter, its circuit symbol, types, and applications. So, let’s begin with the basic definition of the wattmeter.

Definition of Wattmeter

A wattmeter is an electrical measuring instrument used to measure the amount of electrical power consumed in an electric circuit.

A typical wattmeter consists of two types of coils namely, current coil and potential coil. The current coil is designed to carry the full load current and it is connected in series with the load in the circuit. Whereas, the potential coil is designed to carry the full load voltage and is connected in parallel with the load.

Wattmeter Symbol

The symbol of the wattmeter is shown in the following figure.

Wattmeter Formula

Wattmeter is used to measure the amount of active power in an electric circuit. It measures the electric power in watts. The formula of the power measured by the wattmeter is given below.

The power measured in a DC circuit using a wattmeter is given by,

P = V × I

The power measured in an AC circuit using a wattmeter is given by,

P = V × I × cos ϕ

Where V is the line voltage, I is the line current, and cosϕ is the power factor of the load. In the case of a DC circuit, the value of the power factor is unity, i.e. 1.

Wattmeter Accuracy

The wattmeters available in the market can measure electrical power with an accuracy ranging from 1% to 5% and it depends on the type of the wattmeter and manufacturer.

For example, a wattmeter which has a 3% error in measurement will give a power reading of 100 watts as 97 watts.

Wattmeter Connection Diagram

The following figure shows the connection diagram of a wattmeter in an electric circuit to measure the power consumed by the load.

From the circuit diagram, it can be seen that the current coil of the wattmeter is connected in series with the load and carries the full load current, whereas the potential coil is connected in parallel with the load and carries full load voltage.

Types of Wattmeters

Based on the construction, the following two main types of wattmeters are available:

• Induction Type Wattmeter
• Dynamometer Type Wattmeter

(1). Induction Type Wattmeter:

Induction type wattmeter is a type of wattmeter that can be used only for AC power measurement. This wattmeter works on the principle of electromagnetic induction. 

An induction-type wattmeter typically consists of two electromagnets namely, a series magnet and a shunt magnet. It also has a thin disc made of aluminium and a pointer attached to this disc. The disc of the wattmeter rotates on the flow of an electric current through the electromagnet coils by the action of electromagnetic induction.

(2). Electrodynamometer Type Wattmeter:

An electrodynamometer-type wattmeter is another type of wattmeter that can be used for measuring both AC and DC electric power. 

This type of wattmeter consists of a fixed coil divided into two equal halves and a moving coil. The electrodynamometer type wattmeter works on the principle of dynamometer which is two current-carrying conductors placed near to each other experience a mechanical force.

Applications of Wattmeters

A wattmeter is mainly used for measuring the electric power consumed in an electric circuit. A few examples of Wattmeter applications are listed below:

• In power-generating stations
• In distribution and transmission substations
• In laboratories to perform experiments
• In electrical manufacturing companies determine the amount of electricity consumed by devices.
• In the maintenance of electrical devices.
• In electric panels to show power readings.

Hence, this is all about Wattmeter and its applications. In conclusion, a wattmeter is a device widely used in electrical industries to record the amount of power consumed in an electric circuit.