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What is Megger? Types, Uses, Construction & Working Principle of Megger

Hello Engineers, Welcome to our today’s headline, “What is Megger? Types, Uses, Construction & working principle of megger” The topics we will discuss today are: – What is Megger? How many types of megger and what? The structure and function of the megger? Uses of megger. How is Megger tested for good or bad? How to measure high resistance by megger? Etc.

What is Megger?

Megger is a permanent magnet moving coil type instrument used to measure the insulation resistance of electrical circuits, machines, transformers, etc.

Megger is also called a hand-operated generator. Megger has been in use since 1889. However, its use and popularity has been increasing since 1920. In continuation of this, various versions of Megger are being marketed with many modern options which have made its application and use much easier.

How many types of megger and what?

Megger can be divided into 2 parts based on usage.

(A) Electronic Megar Meter

(B) Manual Megger Meter

(A) Electronic Megger: – Electronic Megger meters consist of a battery-powered digital display. There are also two knobs or leads for measuring insulation. And there may be a selection switch, with which the range can be selected. There are many modern meggers that act as auto select. So they do not have a separate switch for selection.

(B) Manual Megger Meter: – This device has a DC generator and an ohm meter. DC generators are usually manual. There is also a clutch system so that the hand-driven generator can produce a specific testing current. There is a selector switch for selecting different ranges and two knobs or leads for measuring insulation.

What is Megger? How many types of megger and what? Hope you got the answers to these questions. Let’s now come to know about the construction and working principles of Megger.

Construction & Working Principle of Megger

Construction of a Megger

মেগারের গঠনপ্রণালী

The Megger is a permanent magnet moving coil type instrument with pole pieces of permanent magnet projected horn type and central iron core. The deflecting coil is located at right angles to the control coil and can rotate freely in the field of the permanent magnet. Both coils are connected to the landscape of a hand-operated DC generator. The control coils are connected in series with another coil (compensating coil) and they are again connected in series with a constant value of resistance (R).

The resistance that needs to be measured has to be connected in series with the deflecting coil. The control coils and compensating coils are connected in series so that the currents flowing through them are reversed. Which is denoted by ‘cross’ and ‘dot’ in Figure (A).

deflecting coil of a Megger

The directions of the currents on the adjacent sides of the two coils are shown in the same direction. This causes a rotation when these sides enter the air pap field between the South Pole peak and the central iron core. (See Figure B). I hope you understand the structure of the megger.

compensating coil of a Megger

Working principle of a Megger

Since the control coil of the megger and the compensating coil is connected across the horizontal end of the generator with series resistance. Therefore the current flowing through these coils is directly proportional to the voltage applied to the test circuit. When no current flows through the deflecting coil (Figure A), the control coil assumes a neutral position. In this case, the torque is zero. In this case, the position of the pointer is at one end of the scale and then its torque is zero. In this case, the pointer position is at one end of the scale and it is marked by the ‘∞’ (infinite) sign. Which indicates the infinite resistance of the tested circuit.

When current flows through the deflecting coil, a rotation occurs. Which rotates the coil and pointer clockwise. This rotation causes the control coil to enter the South Pole field. This results in a controlling torque in the anticlockwise direction. Equilibrium is obtained when deflecting torque is equal to controlling torque. I hope you understand the working principles of Meggers.

Uses of Megger

Megger is a portable resistance measuring instrument used to measure the resistance of various insulators used in electrical work. The effects of moisture, heat, pressure, and dust tend to damage the insulation of various electrical equipment. Megger is therefore used to measure insulation regularly to avoid major accidents.

Although all resistances from zero to infinite values can be measured with the help of a megger, it is a high-quality resistance measuring instrument. Because the first spot on its scale is zero and the second spot is 1 kilohm. As a result, it is impossible to measure low-resistance by megger. 

The use of Megar is mentioned below:-

(A) Megger is used to measure insulation resistance.

(B) Megger is used for the continuity tests.

(C) Meggers are used to testing short circuits.

(D) Megger is used for the polarity of switch or fuse.

How is Megger tested for good or bad?

The continuity test is used to check whether the megger is good or bad. This continuity test can be used to determine if a cable or cable conductor has any gaps or gaps in any circuit.

If the two ends of a cable or cable conductor are connected to the two ends of the megger and the handle of the megger is rotated, it shows zero text, but it must be understood that there is no break or gap anywhere in the conductor.

If infinite or shows a text, the conductor is broken or empty somewhere. If the meter cut does not give zero or infinite readings even after turning the handle of the meter, then the mega meter is lost.

What is the function of guard ring in Megger?

When the megger is used in a damp and dusty environment, leakage paths are formed through the dust accumulated on the outside of the instrument. This can cause ‘earth leakage current’ to flow, from where it enters the deflecting coil. As a result, the distraction is interrupted and gives wrong lessons.

To avoid this, a metal guard ring is placed around the edge of the line, which is directly connected to the ‘negative’ edge of the generator. If a current ‘leaks’, the ‘line’ will return directly to the generator by means of a ‘guard ring’ instead of passing through the edge, so that the interference of the instrument will be uninterrupted.

How to measure high resistance by Megger?

The voltage generated by turning the handle of the DC generator on the meter is applied to the horizontal of the voltage coil (control coil) through a constant value resistance (R) and to the horizontal of the declector coil through a current regulating resistance (R). The measured resistance is connected across the horizontal (E&L) of the testing end.

In fact, two coils are nothing more than a moving coil voltmeter and an ammeter in an instrument.

(A) Suppose, (E & L) the recipients are open circuit. Now the voltage that will be generated by turning the handle of the generator is applied to the landscape of coil B. As a result, current will flow through coil B, but no current will flow through coil A. The resulting torque will rotate the moving coil of the megger until the pointer reaches the ‘∞’ (infinite) point of the scale. This indicates that the resistance of the external circuit is too high for measuring the instrument.

(B) If the testing ends (E & L.) are closed by a very low-quality resistance or short-circuited. However, too much current will flow through the directing coil A. The declaring torque caused by coil A will be opposite to the torque generated by coil B. The resulting torque will rotate the moving coil in such a way that the pointer reaches the ‘zero’ point of the scale. This indicates that the resistance of the external circuit is too small to measure the instrument. So far today. Let me know in the comments if you have any questions.

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