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Megger | Working Principle Types History Uses of Megger

Published on 24/2/2012 & updated on Wednesday 18th of July 2018 at 07:51:42 PM

History of Megger

The device is being used since 1889, popularity raised during 1920s since the long back device is same in its uses and purpose of testing, few real improvements appeared in recent years with its design and quality of tester. Now high-quality options are available which are easy to use and quite safe.

What is Megger?

Insulation resistance IR quality of an electrical system degrades with time, environment condition, i.e., temperature, humidity, moisture and dust particles. It also gets impacted negatively due to the presence of electrical and mechanical stress, so it’s become very necessary to check the IR (Insulation resistance) of equipment at a constant regular interval to avoid any measure fatal or electrical shock.

electronics megger

Uses of Megger

The device enable us to measure electrical leakage in wire, results are very reliable as we shall be passing electric current through device while we are testing. The equipment basically uses for verifying the electrical insulation level of any device such as motors, cables, generators, windings, etc. This is a very popular test being carried out since very long back. Not necessary it shows us exact area of electrical puncture but shows the amount of leakage current and level of moisture within electrical equipment/winding/system.

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Megger | Working Principle Types History Uses of Megger

Types of Megger

This can be separated into mainly two categories:-
  1. Electronic Type (Battery Operated)
  2. Manual Type (Hand Operated)
But there is another types of megger which is motor operated type which does not use battery to produce voltage it requires external source to rotate a electrical motor which in turn rotates the generator of the megger.

electronics megger

Electronic Type Megger

Important parts:-
  1. Digital Display :- A digital display to show IR value in digital form.
  2. Wire Leads :- Two nos of wire leads for connecting megger with electrical external system to be tested.
  3. Selection Switches :- Switches use to select electrical parameters ranges.
  4. Indicators :- To indicates various parameters status i.e. On-Off. For Example Power, hold, Warning, etc.
Note: - Above construction is not similar for every megger, it difference appears manufacture to manufacture but basic construction and operation are same for all.

Advantages of Electronic Type Megger

Disadvantages of Electronic Type Megger

Hand Operated Megger

hand operated megger Important parts:- Analog display:- Analog display provided on front face of tester for IR value recording. Hand Crank:- Hand crank used to rotate helps to achieve desired RPM required generate voltage which runs through electrical system. Wire Leads:- Used same as in electronic tester i.e. For connecting tester with electrical system.

Advantages of Hand Operated Megger

  1. Still keeps important in such high-tech world as it’s an oldest method for IR value determination.
  2. No external source required to operate.
  3. Cheaper available in market.

Disadvantages of Hand Operated Megger

  1. At least 2 person required to operate i.e. one for rotation of crank other to connect megger with electrical system to be tested.
  2. Accuracy is not up to the level as it’s varies with rotation of crank.
  3. Require very stable placement for operation which is a little hard to find at working sites.
  4. Unstable placement of tester may impact the result of tester.
  5. Provides an analog display result.
  6. Require very high care and safety during use of the same.

Construction of Megger

Circuit Construction features :- megger principle
  1. Deflecting and Control coil : Connected parallel to the generator, mounted at right angle to each other and maintain polarities in such a way to produced torque in opposite direction.
  2. Permanent Magnets : Produce magnetic field to deflect pointer with North-South pole magnet.
  3. Pointer : One end of the pointer connected with coil another end deflects on scale from infinity to zero.
  4. Scale : A scale is provided in front-top of the megger from range ‘zero’ to ‘infinity’, enable us to read the value.
  5. D.C generator or Battery connection : Testing voltage is produced by hand operated DC generator for manual operated Megger. Battery / electronic voltage charger is provided for automatic type Megger for same purpose.
  6. Pressure Coil Resistance and Current Coil Resistance : Protect instrument from any damage because of low external electrical resistance under test.

Working Principle of Megger

Work philosophy based on ohm-meter or ratio-meter. The deflection torque is produced with megger tester due to the magnetic field produced by voltage and current, similarly like ‘Ohm's Law’. The torque of the megger varies in a ration with V/I, (Ohm's Law:- V = IR or R = V/I). Electrical resistance to be measured is connected across the generator and in series with deflecting coil. Produced torque shall be in opposite direction if current supplied to the coil.
  1. High Resistance = No Current :- No current shall flow through deflecting coil, if resistance is very high i.e. infinity position of pointer.
  2. Small Resistance = High Current :- If circuit measures small resistance allows a high electric current to pass through deflecting coil, i.e. produced torque make the pointer to set at ‘ZERO’.
  3. Intermediate Resistance = Varied Current :- If measured resistance is intermediate, produced torque align or set the pointer between the range of ‘ZERO to INIFINITY’.

Connection Diagram of Megger for Testing

megger megger

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