Electrical

What is an energy meter?

The energy meter is a measuring device that can be used to measure the quantity of electricity or energy according to a period of time. This measurement can also be described as the total electrical energy consumed for a certain time period. The electrical equipment works by consuming electric power and so this meter would measure the electrical energy used by the instruments in a home or in an industry for a period of time. The energy meters are used in domestic and also in industrial applications. The Kilowatt-hour meter is widely used, it is the major electric meter that can be seen in many places and its measurement will be in kilowatt-hour.

What are the major functions of an energy meter?

  • The energy meter would act as an indicating meter, it would indicate the amount of electrical energy consumed
  • This meter would act as an integrating instrument
  • The energy meter would record the amount of energy consumed
  • This meter is an absolute instrument

What is energy?

Energy can be explained as a product of power and time

Energy = Power × time

The energy unit is watt and it is defined over time which will be in seconds

What is the difference between energy meter and watt-hour meter?

Both of these meters would measure the electrical power consumption. The watt-hour meter would indicate the value at a certain instant when the reading is done. The energy meter has recording or registration ability so it can combine all the instantaneous readings of power over a period of time.

What are the required characteristics of the energy meter?

  • The readings in this meter must be quickly given by dials and also the multiplier factors should be removed
  • The meter design must be simple and it shouldn’t have any parts that would easily deteriorate, all the parts should have a long life
  • The meter casing should be dust and waterproof
  • The friction loss should be low and should remain constant for a long period of time. In order to achieve this the moving parts should be light and also the parts should have good quality
  • The counter device should only have minimum friction and the meter needs to have good torque so that there won’t be any accuracies due to friction
  • The energy loss in the meter should be less
  • The energy meter must be able to operate properly during varying voltage and current conditions

What are the factors that must be considered while selecting an energy meter?

  • Accuracy
  • Quality of the parts
  • Temperature and pressure range
  • Resolution
  • Repeatability
  • uncertainty

How does an energy meter work?

The most common type of energy meter is induction type energy meter, it can also be called electromechanical meters. This type of energy meter can be widely seen in domestic and industrial AC circuits. This type of meter has less friction and also has high torque to weight ratio. This type of energy meter is very economical and accurate, the induction meter can be used for a wide range of loads and temperature conditions. The operating principle of this type of energy meter is electromagnetic induction. So if a current-carrying conductor is acted on by a magnetic field, then the force it would experience would be proportional to the current and the field.

We can see two electromagnets in the meter and they are shunt electromagnet and series electromagnet and it can be seen in the above image. The series electromagnet will be excited due to the current coil power flow. The shunt electromagnetic coil is directly connected to the supply and hence it would carry the current which is proportional to the shunt voltage and this coil is the pressure coil. The magnet is connected to the copper band and they are adjustable. The flux which is produced by the shunt magnet will be aligned by the copper band. The flux alignment will be in a way that it will be perpendicular to the supplied voltage.

Construction of induction meter (parts of induction meter)

Driving system

This system has two electromagnets and they are the series and shunt electromagnets that we discussed above. The energizing of the series electromagnet takes place by the load current. There would be a current coil that is connected to the load and this coil would take the load current to the electromagnet. So the magnet would produce a flux that will be proportional to the load current. The other electromagnet is the shunt magnet and it has a large number of coil turns wound on the middle limp. This coil is known as the pressure or voltage coil and it is connected to the mains and this coil will be highly inductive. Due to this, the current would lag the supply voltage.

Moving system

This section consists of an aluminum disc and it would be mounted on a spindle. The aluminum disc is placed between the two magnets and the disc would rotate continuously due to the deflecting torque.

Braking system

There is a permanent magnet which is situated near to the aluminum disc and this acts as the braking system. So when the movement of the disc occurs in the braking magnet field then eddy current will be induced in the disc. The current which is created by this is in a way that it would restrict the rotation and hence the braking torque created. The braking torque will be proportional to the disc speed because the induced current is proportional to the disc speed.

Recording system

This system is for the continuous recording of the number on a dial and this number will be proportional to the revolution of the disc. The disc revolution number is the amount of electrical energy that passes through the meter.

What is an electronic energy meter and how does it work?

The electronic meter doesn’t have any moving parts and because of it, these meters are called static energy meters. This meter is controlled by an integrated circuit and the IC which is used for this purpose is ASIC. The IC which is used in this meter is application specified integrated circuit. The electronic energy meter is composed of a voltage converter, current converter, multiplier, counter, etc. The sampling of the current and voltage will be done by the current and voltage transformer. The meter would use a reference voltage to compare it with the input voltage after that the voltage value will be transferred to the output section. The AD converters would convert this output to digital format.

What are the advantages of electronic meters over electromechanical meters?

  • Reliability and ruggedness
  • Good accuracy
  • Easy calibration
  • Security
  • Automated meter reading
  • Anti-tampering protection
  • It would support non-linear and low power factor loads
  • It can record power factor and also the used reactive power

How to improve the performance of the energy meter?

We need to consider certain limitations and they should be taken care of

Instrumental errors

This type of error could happen during the construction of the meter. It could also happen during the calibration of the meter too. Friction or hysteresis could also cause this type of error, these errors can be caused due to the loading effect and also because of the misuse of the meter.

Environmental errors

The meter operation would be affected by its environment too, the operation of the energy meter would be affected by the temperature, pressure, humidity, and also because of the magnetic field

Observational errors

This type of error would happen due to improper observation, the major reason for this type of error is parallax and inaccurate reading measurements.

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