A Single-phase induction type energy meter is also known as a watt-hour meter. This name is given to him. This article focuses only on its construction features and operation. The induction type energy meter essentially comprises the following components:
1. Driving system
2. Moving system
3. Brake system and
4. Recording system
It consists of two electromagnets, called “Shunt” Magnet and “Series” Magnet, of laminated construction. A coil comprising a large number of turns of fine wire is wound on the middle branch of the shunt magnet.
This coil is called a ” pressure or voltage ” coil and is connected to the power supply network. This voltage coil has several turns and is designed to be as highly inductive as possible. In other words, the voltage coil produces a high inductance/resistance ratio.
This causes the current, and therefore the flux, to retard the supply voltage by almost 90 degrees.
Adjustable copper shading rings are provided on the center leg of the shunt magnet to affect the angular shift between the magnetic field created by the shunt magnet and the supply voltage is approximately 90 degrees.
Copper shading strips are also referred to as a power factor compensator or compensation loop. The series electromagnet is powered by a coil, called the “current” coil which is connected in series with the load so as to carry the load current. The flux produced by this
The moving system basically consists of a rotating aluminum disc light mounted on a spindle or vertical shaft. The shaft that supports the aluminum disc is connected by a gear mechanism to the clock mechanism on the front of the meter to provide information consuming power by the load.
The time-varying (sinusoidal) fluxes produced by the shunt and the magnet in series induce eddy currents in the aluminum disc.
The interaction between these two magnetic fields and the eddy currents creates a motor torque in the disk.
The number of rotations of the disc is therefore proportional to the energy consumed by the load in a certain time interval and is commonly measured kilowatt-hours (Kwh).
The damping of the disc is provided by a small permanent magnet, located diametrically opposite the ac magnets. The disc passes between the magnetic voids. The movement of the rotating disc through the magnetic field passing through the air gap creates eddy currents in the disc which react with the magnetic field and exert a braking torque.
By changing the position of the brake magnet or diverting part of the flow there, it is possible to control the speed of the rotating disc.
Recording or counting system
The recording or counting system essentially consists of a gear train, driven either by a worm gear or by a pinion gear on the disc shaft.
The energy meter thus determines and adds or integrates all the instantaneous power values so that the total energy used during a period is therefore known.
Therefore, this type of meter is also referred to as an “integral” meter.
Operation of the single-phase induction energy meter
The basic operation of the single-phase induction type Energy Meter is based on only two mechanisms:
- Rotation mechanism of an aluminum disc that rotates at a speed proportional to the power.
- The mechanism for counting and displaying the amount of energy transferred.
Let’s look at these mechanisms in a few words:
Rotation mechanism of an aluminum disc
What is made to rotate at a speed proportional to the power?
The metal disc is powered by two coils. One coil is connected so as to produce a magnetic flux proportional to the voltage and the other produces a magnetic flux proportional to the current. The field of the voltage coil is delayed 90 degrees using a delay coil.
This produces eddy currents in the disk and the effect is such that a force is exerted on the disk in proportion to the product of the instantaneous current and voltage.
A permanent magnet exerts an opposite force proportional to the speed of the disc’s rotation – it acts as a brake that stops spinning the disc when the current stops drawing, instead of allowing it to spin faster and faster. This causes the disc to spin at a speed proportional to the power used.
The mechanism for displaying the amount of energy transferred
Based on the number of rotations of the aluminum disc.
The aluminum disc is supported by a spindle that has a worm gear that drives the register. The register is a series of dials that record the amount of energy used.
The dials can be of the cyclometer type, an easy-to-read odometer-like display where, for each numbering, a single digit is displayed through a window on the face of the meter or of the pointer type, with a pointer indicating each digit.
It should be noted that with the dial pointer type, adjacent pointers usually rotate in opposite directions due to the gear mechanism.