Energy meter

What is Energy meter???

The energy meter is nothing but a device or instrument which is used to measure the amount of electrical energy consumed by the consumer or the load. This load can be domestic, commercial or industrial. SI unit of electrical power is watt. So, this meter is also known as watt-hour (Wh) meter. If an electric load is consumed one kilo-watt power in one hour, it is considered as one kWh consumption or one unit of energy is consumed. These meters are installed at every place where utility is supplying electrical energy. 

The energy meter is always connected in series with the load. The load will be single phase or three phase and according to the type of load, energy meter is classified as a single-phase meter or three phase meter. For single phase or lower load, energy meter can directly connect with load but in case of higher load (industrial-3-Φ), step down current transformer is used to reduce current.

Basically, these meters are measuring an instantaneous voltage and current, and calculate instantaneous power by multiplying the voltage and current. To find final energy utilization, instantaneous power is integrated over a period of time.

According to working principle, energy meter is classified into three types;

               1)      Electro-magnetic induction type energy meter

               2)     Electronic energy meter

               3)     Smart energy meter

Electro-magnetic induction type energy meter

Construction: This energy meter works on the principle of electromagnetic induction. These meters are not used in present system. This energy meter consists of two electromagnets and one aluminum disc. These two electromagnets are made up of laminated silicon steel. Both electromagnets are carried two windings. The upper electromagnet has M-shaped core and consists of a coil, which is known as pressure coil or voltage coil. The upper electromagnet is known as shunt magnet. The lower electromagnet is known as a series magnet (U-shaped) and carries two coils, which is known as current coils. The pressure coil is directly connected to the supply. So, current passes through this coil is proportional to the shunt voltage. The pressure coil consisting of many turns of thin wire and the current coil consisting of few turns of thick wire. In the lower part of shunt magnet, the copper band is placed, which provides frictional compensation and the shunt magnet flux.

The Al disc is mounted on a spindle between two electromagnets. This disc can easily rotate on the vertical shaft without any friction. The permeant magnet is placed near the Al disc. This magnet is known as break magnet.

The registering system is used to record the number of rotations of Al disc. Their rotation is directly proportional to the electrical energy consumed by the load.

Working: The Al disc is placed between the two electromagnets. The voltage coil is connected to supply voltage. The magnetic field induced in the voltage coil is proportional to system voltage and the magnetic field induced in current coil is proportional to current flow to the load. These both fields are perpendicular to each other and because of the magnetic fields, the eddy current is produced in the Al disc. The torque is produced due to the interaction of the eddy current and magnetic field, which creates a force on the disc and disc starts rotating. This torque is directly proportional to the product of the voltage and current.

Advantages:

          1)      Cost of this meter is less compared to electronic energy meter.

          2)     Simple in construction and maintenance is easy.

          3)     High torque to weight ratio.

Disadvantages:

          1)      Less accurate

          2)     Easy to tamper and less secure

Electronic energy meter:

Electronics energy meter is classified into two parts;

               1)      Analog energy meter

               2)     Digital energy meter.

In analog energy meter, the magnitude of voltage and current is obtained from the potential transformer and current transformer respectively. These analog values are converted into digital samples with the help of analog to digital converter (ADC). These samples are converted into frequency signals by a frequency converter. It is used to drive counter system, which integrates this samples over time and results in the reading of power consumption. Analog energy meter is more accurate compared to electromechanical energy meter but less accurate compared to digital energy meter.

In digital energy meter, microprocessor or digital signal processor is used. Similar to an analog energy meter, voltage and current transducers are connected to an analog to digital converter and it is connected with the microprocessor. The voltage and current samples are multiplied in the microprocessor. The phase angle between voltage and current is measured by a microprocessor which is used to calculate reactive power and power factor. To perform this tasks in a microprocessor, it is programmed and it is able to calculate parameters like; electrical power consumption, power factor, reactive power, voltage, current, date & time and charges according to the tariff. Digital energy meter has an LCD or LED display, which is used to display parameters.

The digital energy meter is more accurate compared to analog and electromechanical energy meter and lesser chances of tampering and energy theft in a digital energy meter. But the installation cost of digital energy meter is high compared to analog and electromechanical energy meter. The performance of digital energy meter is depending on the microprocessor.

Smart energy meter:

The smart energy meter is the next generation of an electric meter. The smart meters are installed in developed countries.

Advantages of the smart energy meter,

             1)      It can detect outage

             2)     It can limit the demand

             3)     Record consumer consumption

             4)     Remote disconnection and reconnection

             5)     It can monitor quality of supply

             6)     Advanced Communication system

The smart has the ability to measure the power in both directions; utility to load and load to the utility. For example, the smart meter is installed at a home and a solar rooftop is also installed. Let us assume that, in present condition, generation of solar is higher than a load, in this condition power will transfer from load (home) to utility and if generation is less than the demand, in this condition, power will transfer from utility to load. In this case, the meter can measure the power in both directions.

The smart meter has an advanced communication system for data transfer. It can transfer data to the utility like energy consumption, voltage, and current value, power factor etc. The power theft is not possible in case of a smart meter. The consumer can directly pay money through the meter and not need to visit the consumer for meter reading. It can connect to your smartphone also so, you can get details of all parameter from your phone.

The smart meter has only one disadvantage that is cost. The cost of this meter is very high and to develop and install the smart meter advance technology is required.