Electro-Mechanical Energy Meters

Electro-Mechanical Energy Meters

Electro-Mechanical Energy Meters are obsolete now but some countries are still using it due to its cheapness and robustness. Other name of these Energy Meters are Disk meters.

3 Phase Electro-Mechanical Energy Meter
Figure 1: 3-Phase Electro-Mechanical Energy Meter

Working Principle of Electro-Mechanical Energy Meters

As their name suggest, Electro-Mechanical Energy Meters are the combination of Mechanical and Electrical Technology. A mechanical disk present inside the meter rotates when the load applied. The speed of disk is directly proportional to the amount of load applied. With the rotation of disk, dial of the Energy Meter increase its value.

Equivalent Circuit of Energy meters
Figure 2: Equivalent Circuit of Energy meters

The above image is giving idea about the working principle of disk meters. There are two coils present in the diagram and in between these two coils a rotating disk is present. One coil is current coil which is connected in series with load, that’s why it is also called as series coil as well. Other coil is voltage coil connected in parallel, that’s why it is called as shunt coil as well. When both coils are energized they will induce eddy current in the disk. There is a copper shading band present above the disk which gives 90 degrees’ phase shift eddy currents, which results in the rotation of disk.

There will be no rotation of the disk, if the switch is open. As soon as the switch will close, current will start to flow which results in the voltage induction and hence the rotation of the disk. The speed of the disk depends on the load applied. As heavy load requires large current, thus when large current passes through the current coil, large amount of eddy current will produce which will rotate the disk fast.

Side Note: If you short the Live and neutral of load side disk will start to rotate at its full speed or may be burn out. AC fans work on this principle but with a controlled speed.

Advantages and Disadvantages of Electro-Mechanical Meters

Advantages of Electro-Mechanical Meters

Robustness: These meters are strong meters with respect to new energy meters. As Digital Energy Meters have small and sensitive components, they can burn easily with any stray jerk of voltage. On the other hand, Disk meters can endure those voltage fluctuations. Moreover, coils present in disk meters are tough and cannot easily be destroyed.

Mechanical Dial of Energy Meter: Readings of the dial of Electro-mechanical Energy Meter is pretty hard to alter. So, its dial can be also taken as advantage of Electro-mechanical meters.

No use of battery: Whenever battery of the digital meter dies or power turns off due to any reason, reading of meter will be vanished. But readings of disk meter will be always present due to Mechanical dial present on it.

Disadvantages of Electro-Mechanical Meters

Future up-gradation: There is no chance of future enhancement in these kinds of Energy Meters. They are what they are, you cannot improve it or include anymore innovation in it.

Accuracy limits: Disk meters mostly gives class 2 accuracy.

Read an article on class accuracies.

It is not possible to get more accuracy through disk method. It is mandatory to change the technology to get more accuracy.

Limited measurements: As disk meters have only one dial so they only measure active or reactive power at a time. Moreover, they cannot measure MDIs, instantaneous power, voltage, current or other important factors.

Highly exposed to electricity stealers: Yes, these meters are easy to manipulate because meter reversing or disk blocking techniques are really easy to implement on it.

Summary: Electro-Mechanical meters were a great breakthrough in energy measuring world. But with the advancement of technology, advanced smart energy meters are going to take their place completely.

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Electrical engineering is my profession, my hobby and my passion. I completed bachelors of electrical engineering in 2015. Currently I am working with an Electric Utility Company. Power Electronics, Embedded Systems and Energy Metering are my fields of specialization. In free time I listen music and watch movies.

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