Energy Meter

Energy meters play a crucial role in measuring and monitoring electrical energy consumption, enabling fair billing, promoting energy efficiency, and supporting the management of power distribution networks. These meters come in different forms, including analog, digital, smart meters, and advanced metering infrastructure (AMI). There are various types of energy meters, which have several functions. It is used for household or domestic purposes for measuring electricity bills. In this article, we will go through what is energy meter?, construction with its operations, Then we will go through its types and finally, we will conclude our article with its Advantages, Disadvantages, and characteristics.

An energy meter is a type of device used to measure the amount of energy measured in a specified period of time. It is a type of meter that measures electrical engineering. By the measurement of electricity, it becomes possible to measure the cost of electricity. Induction type of energy meters are universally used for the measurement of energy in domestic and industrial ac. circuits. Induction types of meters possess lower friction and a higher torque/weight ratio. Also, induction-type meters are inexpensive and accurate and retain their accuracy over a wide range of loads and temperature conditions.

There are four main parts of the operating mechanism:

• Driving system.
• Moving system.
• Braking system.
• Registering system.

Driving system

• The driving system of the meter consists of two electromagnets. The core of these electromagnets is made up of silicon steel laminations. The coil of one of the electromagnets is excited by the load current. This coil is called the current coil. The coil of the second electromagnet is connected across the supply and therefore, carries a current proportional to the supply voltage. This coil is called the pressure coil. Consequently, the two electromagnets are known as series and shunt magnets respectively.
• Copper shading bands are provided on the central limb. The position of these bands is adjustable. The function of these bands is to bring the flux produced by the shunt magnet exactly in quadrature with the applied voltage.

Moving system

• This consists of an aluminum disc mounted on a light alloy shaft. This disc is positioned in the air gap between series and shunt magnets. The upper bearing of the rotor (moving system) is a steel pin located in a hole in the bearing cap fixed to the top of the shaft. The rotor runs on a hardened steel pivot, screwed to the foot of the shaft. The pivot is supported by a jewel bearing. A pinion engages the shaft with the counting or registering mechanism.
• A unique design for the suspension of the disc is used in the floating-shaft energy meter. Here the rotating shaft has a small magnet at each end, where the upper magnet of the shaft is attracted to a magnet in the upper bearing and the lower magnet of the shaft is to a magnet in the lower bearing. The c-moving system thus floats without touching either h-bearing surface, and the only contact with the movement is that of the gear connecting the shaft with the o gear of the train, thus the friction is drastically reduced.

Braking system

• A permanent magnet positioned near the edge of the aluminum disc forms the braking system. The aluminum disc moves in the field of this magnet and thus provides a braking torque. The position of the permanent magnet is adjustable, and therefore, braking torque can be adjusted by shifting the permanent magnet to different radial positions.

Registering (counting) mechanism

• The function of a registering or counting mechanism is to record continuously a number that is proportional to the revolutions made by the moving system. By a suitable system, a train of reduction gears the pinion on the rotor shaft drives a series of five or six-pointers. The energy used by the loads in a kilowatt-hour is directly correlated with their rotation.

The supply voltage is applied across the pressure coil. The pressure coil winding is highly inductive as it has a very large number of turns and the reluctance of its magnetic circuit is very small owing to the presence of air gaps of very small length. Thus the current I, through the pressure coil is proportional to the supply voltage and lags it by a few degrees less than 90°. This is because the winding has a small resistance and there are iron losses in the magnetic circuit.

Current I produce a flux. This flux divides itself into two parts, and. The major portion flows across the side gaps reluctance of this path is small. The reluctance to the path of flux is large and hence its magnitude is This flux, goes across the aluminum disc and hence is responsible for the production of driving torque. Flux is in phase with current I, and is proportional to it. Therefore flux is proportional to voltage V and lags it by an angle a few degrees less than 90°. Since flux o, is alternating in P nature, it induces an eddy emf in the disc which in turn produces an eddy current.

The load current I flow through the current coil and produces a flux ₁. This flux is proportional to the load current and is in phase with it. This flux produces eddy current I in the disc. Now the eddy current interacts with flux o, to produce a torque, and eddy current interacts with it to produce another ep torque. These two torques are in the opposite direction and the net torque is the difference.

Phasor Diagram of Energy Meter

Let,

V = applied voltage

I = load current

Φ = phase angle of load

I_p = pressure coil current

del = phase angle between supply voltage and pressure coil flux

f = frequency.

Z = impedance of eddy current paths

α = phase angle of eddy current paths

E_ep = eddy emf induced by flux Φ_p

I_ep = eddy current due to flux Φ_p

E_ev = eddy emf induced by flux Ф_s

I_es = eddy current due to flux Фs

T_d ∝ Ф₁ x Ф₂ x f / Z x sinß x cosα = K₁ x Ф1 Ф2 f / Z sinßcosα

where K₁ = a constant

Now ß = phase angle between fluxes Ф₁ and Φ₂

In our case, the two fluxes are Φ_p and Φ_s

ß = Phase angle between fluxes, Φ_p and Φ_s = (Delta – Ф)

Driving torque, T_d = K₁ Φ_p Φ_s f/Z sin(del – Φ) cos α

But Φ_p ∝ V and Φ_s ∝ Ι.

T_d = K₂ Φ_p Φ_s f/Z sin(del – Φ) cos α

If f, Z, and α are constants,

T_d = K₃ VI sin( del – Φ )

If N is the steady speed, braking torque

T_B = K₄ x N

At steady speed, the driving torque must equal the braking torque

K₄ N = K₃ VI sin( del – Φ )

or

N = KVI sin( del – Φ )

If Delta = 90°

Speed, N = KVI x sin(90 deg – Ф) = KVI x cosФ = K x (power)

The Speed of the rotation is directly Proportional to the power.

Thus so that the speed of rotation is proportional to power, angle del should be equal to 90°. Hence the flux Φ_p’ must be made to lag the supply voltage to be exactly 90°.

Total Number of revolution=[Tex]\int N dt=k\int VI sin(\Delta-\phi) [/Tex]

taking del=90°,total number of revolutions

=[Tex]k\int VI cos\phi dt [/Tex]

[Tex]=k\int power dt=k \times energy [/Tex]

So the three phase energy meter is used for measuring the large power Consumption.

Generally some types of energy meter are as follows:

• Single Phase Energy Meter
• Three Phase Energy Meter
• Analogue Energy Meter
• Digital Electric Energy Meter
• Time of use Energy Meter

Single Phase Energy Meter

Single phase energy meter is used for home appliances. The single phase energy meter is directly connected between the line and load. It consists of two electromagnets one is the shunt magnet and other is the series magnet and in between these two magnets we are having the aluminium disk. So this aluminium disk is rotating in the magnetic field. The speed of this disk is proportional to the part which is consumed by the appliance. Read my article on the Electrical House wiring, in this article you will learn how energy meter is connected, and also explains the complete house wiring.

Three Phase Energy Meter

Three phase energy meter is used for commercial or industrial application. As in the industries we have huge amount of current so to protect it we will use current transformer. It will step down the current to isolate energy meters from high current. The three phase energy meters have three phase wires and one neutral wire. The output three wires go to the main db. One unit means 1000 watt hour.

Analogue Energy Meter

Also known as electromechanical meter, these are among the oldest meter in Indian history. They do not have a display or connectivity facility. These meters read the electricity and display it on circular scales. The operator reads the electricity meter on the scale and analyses the total electricity consumed.

Digital Energy Meter

These meters offer easier readings than analogue electric meters. Besides, they provide an LED or LCD display and have a connectivity feature. The operators do not need to calculate the readings on the scale as the LED or LCD screen provides an accurate reading.

Time-of-Use Energy Meter

This is the third type and can either be digital or analogue. The primary difference is that it is for people who register for the time-of-use plan. In this plan, the electricity is charged considering the peak and off-hours. Two separate meters are used for this purpose, one for calculating the electricity during peak hours and the other for off-peak hours.

In some meters, a slow but continuous rotation is obtained even when no current is flowing through the current coil and only the pressure coil is energized. This is called creeping. The major cause for creeping is over-compensation for friction. If the friction compensating device is adjusted to give a driving torque to compensate for starting friction which is bigger than the running friction there is a tendency for the disc to run even when there is no current through the current coils because the friction compensating torque is independent of the load current as the compensating device is voltage actuated. The other causes of creeping are excessive voltage across the potential coil (which is responsible for the production of excessive torque by the friction compensating device), vibrations, and stray magnetic fields.

To prevent this creeping two diametrically holes are drilled in the disc; the disc will come to rest with one of the holes under the edge of a pole of the shunt magnet the rotation being thus limited to a maximum of half a revolution. If a hole is under the edge of a pole, the circular eddy-current paths in the disc will be distorted as shown. The effective center of the eddy-current paths is then at A’ and this point is the central point of the equivalent magnetic pole produced by the currents. Examination of polarities shows that there is a resulting force on the disc, tending to move A’ away from the pole axis A. Thus the disc may creep until the by-hole reaches a position near the edge of a pole, but further movement is opposed by the torque produced in the manner just described. The magnitude of this torque is not sufficient to affect the action of the meter on load.

Note:- In order to measure energy we have to measure power which is measured by the current coil and potential coil.
Therefore, we require two coils in the energy meter.

There are some list of Advantages and Disadvantages of Energy Meter given below :

Advantages of Energy Meter

• The Energy Meter gives accurate readings.
• Energy meters require very little maintenance.
• The energy consumption of an energy meter is very low.

Disadvantages of Energy Meter

• Installing a meter is very time-consuming.
• Electromagnetic interference changes the sensitivity of the energy meter.
• Installation cost of energy meters is very high.

• Powerful and easy to expand
• The accuracy level is high and stable.
• The starting current is small and the error curve is flat.
• Wide frequency response range.
• Little affected by external magnetic field.
• Convenient for installation and use.
• Large overload capacity.
• Stronger anti stealing ability.

Note:- The key characteristics of energy meters include accuracy, metering type (electromechanical, electronic, or digital), measurement units (such as kilowatt-hours), voltage and current ratings, type of connection (single-phase or three-phase), tariff structures, display type (analog or digital), communication capabilities (especially in the case of smart meters), data logging, tamper detection, prepayment features, environmental conditions, installation type, and regulatory compliance.

The evolution of energy metering technology has led to a variety of meter types, each with its own set of characteristics tailored to specific applications and user needs. They provide accurate measurements of electricity or gas usage, facilitating precise billing based on actual consumption. Smart meters, in particular, offer additional functionalities such as real-time data transmission and two-way communication, enabling better energy management and efficiency. They empower consumers to track their usage, encouraging more responsible resource utilization and cost-saving measures. Moreover, these meters aid utility companies in grid optimization by providing crucial data on demand and usage patterns.

Can energy meters be tampered with to reduce electricity bills?

Yes, it can be tampered to reduce electricity bill.

In what unit does energy meter measures energy?

Energy meter measures energy in kilo watt hour ( kWh).

Can energy meter measures power factor?

Yes, some advanced energy meters can measure power factor which provides valuable data on the efficiency of electrical systems.

What is the difference between an analog and a digital energy meter?

Analog energy meters have rotating dials, while digital energy meters display consumption in numerical form. Digital meters are more accurate and easier to read.