Induction Watt Hour Meter

Posted on  by admin

Induction-type meters measure power in alternating-current circuits and are the type commonly seen on the outside of houses. Specialized watt-hour meters include totalizing meters, which record the power used in more than one circuit, and highly accurate portable meters, which are used for testing installed…. 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.

Why are induction energy meters preferred?

What is induction energy meter?

The monitor can be as simple as a $14 “plug load” monitor that plugs into an outlet; then you plug the device/appliance into the monitor. Typically, an LED screen shows you the consumption. The energy meter measures the total energy consumed by the load while the wattmeter measures the power in a circuit. The energy meter measures the energy in joules but wattmeter the measure the power in watts. It is also used for determining the power rating of the homes and industrial appliances.


How many watts does a fridge use?

Following are the advantages of induction type meters: They are inexpensive as compared to moving iron type instruments. They have high torque is to weight ratio as compared to other instruments. They retain their accuracy over wide range of temperature as well as loads.

Definition: The meter which is used for measuring the power of three phase supply is known as the three phase energy meter. The three phase meter is constructed by connecting the two single phase meter through the shaft. The total energy is the sum of the reading of both the elements. The average home refrigerator uses 350-780 watts. Refrigerator power usage depends on different factors, such as what kind of fridge you own, its size and age, the kitchen’s ambient temperature, the type of refrigerator, and where you place it.


Different types of fridges have different power requirements. A single-phase power meter requires the electrical power calculation that measures accurate power consumption from current, voltage and clock information, and the clock function that operates on a battery when there is a power outage.


Induction disc relays are of two types. They are,
  • The power meter must have stable operation during a specified period of time.
  • There is a prominent difference between current coil and pressure coil The current coil is always connected in series.

induction watthour meter

While the pressure coil is connected in parallel with the load. Moreover, the current coil measures the current while the pressure coil measures the voltage. Following are the disadvantage of the induction type instruments: a) Change in temperature causes variation in the resistance of the moving element, affects the eddy currents therein, and so the operating torque.

The error due to this is in part offset by a balancing effect due to change in temperature of the windings.


What is the disadvantage of induction type wattmeter?

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

The two windings produce an alternating flux when they are energized. Let the fluxes be Φ1 and Φ2 respectively. The phase angle θ between the fluxes can be adjusted by using reactance in parallel with the secondary winding. The resultant torque produced by the interaction of flux of one of the magnets with the eddy currents of the other in the disc is proportional to Φ1 Φ2 sinθ.


What is single phase energy meter?

  • Induction disc relays are robust in construction.
  • The operation of the induction disc relay can be easily controlled under abnormal conditions just by opening the secondary coil.
  • By using induction disc relays, the current setting and the time settings can be obtained easily.
  • Induction disc type relays are reliable and accurate.
  • They can be used for overcurrent protection.

What is the difference between an energy meter and watt meter?

  • Induction disc type relays are used where reliability and robustness are needed.
  • These types of relays find wide applications where slow-speed relays are required.
  • Induction disc type relays are employed where adjustable operating time and time-delay feature is required.
  • This type of relay is used where a high reset to pick-up ratio is needed.

What is the difference between current coil and pressure coil in an energy meter?

The construction of an induction cup relay is similar to an induction motor. The below shows the construction of the induction cup relay. The induction cup relay consists of the following parts,

  • Stationary iron core (stator),
  • Hollow cylindrical cup (rotor),
  • Electromagnet, and
  • Coils.

The stationary iron core acts as a stator which consists of two, four, or more poles. Nowadays it is constructed for 4 or more poles. The hollow cylindrical cup acts as a rotor similar to a disc in the other two relays. It is free to rotate in the air gap between electromagnets and stationary iron core.


Electromagnets create a magnetic field. It consists of two pairs of coils, when these coils are energized, flux is produced in the coils. These fluxes will have the same frequency but are displaced by an angle α from each other. These coils will then energize the iron core thus producing a rotating flux in the air gap.


Due to these fluxes, eddy currents are made to circulate in the rotor. Thus it will give rise to a force that acts on the rotor. So, the hollow cup rotates in the direction of the magnetic field between magnets and stationary iron core as the rotor of the induction motor. This makes the fixed contacts of the trip circuit close and sends a trip signal to the breaker to open the circuit. There is a control spring backstop attached to the spindle of the cup to avoid rotation of the rotor continuously.


How can I monitor my home power consumption?

  • In induction cup relays, the inertia of the cup is much lesser than that of the disc in induction disc relays.
  • Induction cup structures have a very high torque to weight ratio and are therefore very sensitive.
  • They are very fast in operation due to the light rotor (the operating time is less than 0.10 seconds) and are therefore suitable for high-speed operation.
  • The leakage in the magnetic circuit is minimum in induction cup relays due to more efficient magnetic systems. This also reduces the resistance to the induced current path in the rotor.
  • Because of the efficient magnetic system and light-weighted rotor, Volt-Ampere (VA) burden is greatly reduced in induction cup relays. The torque per VA is about three times that of induction disc relays.
  • Induction cup relays can be made to have linear characteristics by proper design. They can be made to operate accurately over a wide range with a high ratio of reset to pick-up value.
  • They produce steady non-vibrating torques.
  • The parasitic torque due to current or voltage alone is small in the induction cup relay.
  • They are inherently less sensitive to dc transients.
  • These relays are best suited for protection where the normal abnormal conditions differ marginally.