Answer.1. To indicate resistance

Explanation:-

The megger is used for the measurement of high resistance and insulation resistance.  The high resistance to be tested is connected between terminals of megger. The opposing torques of the coils balance each other so that pointer attains a stationary position at some intermediate point on the scale. The scale is calibrated in megaohms so that the resistance is directly indicated by the pointer.

Answer.3. Megger

Explanation:-

The continuity test is a procedure that is often used for the detection of faults in an electrical circuit. This test indicates whether there is an electrical connection between two locations within a circuit.

The megger can also be used to test continuity between any two points, if the pointer shows full deflection then there Is an electrical continuity between them.

The megger is an excellent continuity tester. Connect the ohmmeter across the circuit or component to be tested. If there is continuity through the circuit or component, the needle will move. A reading of zero generally indicates a short circuit. A reading of infinity indicates an open circuit.

Answer.3. Friction clutch slippage

Explanation:-

Now meggers are usually rated at 500 volts. To avoid excessive test voltages, most meggers are equipped with friction clutches. When the generator is cranked faster than its rated speed, the clutch slips, and the generator speed and output voltage are not permitted to exceed their rated values.

Answer.2. 500 volts

Explanation:-

Now meggers are usually rated at 500 volts. To avoid excessive test voltages, most meggers are equipped with friction clutches. When the generator is cranked faster than its rated speed, the clutch slips, and the generator speed and output voltage are not permitted to exceed their rated values.

Answer.3. The generator is not operating

Explanation:-

There are no restraining springs on the movable member of the instrument portion of the megger. Therefore, when the generator is not operated, the pointer floats freely and may come to rest at any position on the scale.

Answer.4. Reversely calibrated based on the pointer position

Explanation:-

The scale of megger is calibrated reversely means the normal position of pointer indicates infinity when full-scale deflection indicates zero resistance.

Answer.2. Device such as motor, cable, etc

Explanation:-

The Megger or Meg-ohmmeter is a portable deflection instrument used to check the insulation resistance of electrical cables or equipment such as transformer winding, motor winding, transmission line cables, etc. This instrument also measures the insulation resistance of the electric circuit relative to the earth.

The megger can be used to determine whether there is sufficiently high resistance between the conducting part of a circuit and the ground. This resistance is called insulation resistance.

Answer 1. No effect

Explanation:-

A megger is an ohm- meter-type instrument by means of which the value of resistance can be measured and directly indicated by the position of a pointer on a scale. The resistance indicated in an ohm- meter-type instrument is independent of the voltage applied for a test.

Since changes in voltage affect both coils is in the same proportion, the position of the moving element is independent of the voltage. In the event that the instrument is short-circuited, the ballast resistance is sufficient to protect the current coil.

Answer.4. Pointer show Deflection

Explanation:-

The megger can also be used to test continuity between any two points, if the pointer shows full deflection then there is electrical continuity between them.

Answer.4. All of the above

Explanation:-

The advantages of the megger include the following.

• It can produce an accurate result. The accuracy of measurement is unaffected by variations in the speed of the generator between 60 and 180 r.p.m.
• It is very handy and easy to operate
• It can be used anywhere as it is a portable instrument
• It can produce very quick results
• It is robust and safe to use

Answer.2. Only statement 2 is correct

Explanation:-

The disadvantages of the megger include the following.

• The hand-driven type is difficult to operate. The result produced is also not quite accurate.
• An electronic type would require an external power supply
• The electronic type is quite expensive

Answer.1. C-B-A-D

Explanation:-

Using the Megger

To use a megger to check wiring insulation, connect one test lead to the insulation and the other test lead to the conductor, after isolating the wiring from the equipment. Turn the hand crank until the slip clutch just begins to slip and note the meter reading. Normal insulations should read infinity. Any small resistance reading indicates the insulation is breaking down.

Answer.4. All of the above

Explanation:-

Megger Safety Precautions

When you use a megger, you could be injured or damage equipment you are working on if the following MINIMUM safety precautions are not observed.

• Use meggers on high-resistance measurements only (such as insulation measurements or to check two separate conductors on a cable).
• Never touch the test leads while the handle is being cranked.
• Deenergize and discharge the circuit completely before connecting a megger.
• Disconnect the item being checked from other circuitry, if possible, before using a megger.

Answer.4. Anyone of the terminal touching with the body

Explanation:-

An insulation resistance test is a correct term for this form of testing, not a megger test, as megger is a manufacturer’s trade name, not the name of the test.

Types of Cable Faults

Cables are generally laid directly in the ground or in ducts in the underground distribution system. For this reason, there are little chances of faults in underground cables. However, if a fault does occur, it is difficult to locate and repair the fault because conductors are not visible. Nevertheless, the following are the faults most likely to occur in underground cables

Open-circuit fault. When there is a break in the conductor of a cable, it is called an open-circuit fault. The open-circuit fault can be checked by a megger. For this purpose, the three conductors of the three-core cable at the far end are shorted and earthed. Then resistance between each conductor and earth is measured by a megger. The megger will indicate zero resistance in the circuit of the conductor that is not broken. However, if the conductor is broken, the megger will indicate infinite resistance in its circuit.

Short-circuit fault. When two conductors of a multi-core cable come in electrical contact with each other due to insulation failure, it is called a short-circuit fault. Again, we can seek help or a megger to check this fault. For this purpose, the two terminals of the megger are connected to any two conductors. If the megger gives zero reading, it indicates a short circuit fault between these conductors. The same step is repeated for other conductors taking two at a time.

Earth fault: When the conductor of a cable comes in contact with the earth, it is called earth fault or ground fault. To identify this fault, one terminal of the megger is connected to the conductor and the other terminal is connected to the earth. If the megger indicates zero reading, it means the conductor is earthed. The same procedure is repeated for other conductors of the cable.

Answer.2. 50 MΩ ⁄ Number of outlets(points + switches)

Explanation:-

Testing of Insulation Resistance of Complete Installation to Earth

The principal purpose of testing the insulation is to verify that there are no inadvertent connections between live conductors and between live and Earth before the installation is energized. Tests are required between live conductors (e.g. between phases and between phase(s) and neutral) and between all live conductors and Earth.

Insulation resistance of the installation depends on many factors such as atmospheric conditions, humidity, dirt, etc. As such its calculation is not possible, but it can be readily measured. Normally the insulation resistance is quite high and can be measured by an instrument called megger; usually used for the measurement of high resistance. The main object in performing this test is to ascertain whether the complete wiring is sound enough to avoid leakage current.

As per the Indian electricity rules, the leakage current of an installation should not exceed 1/5000 of the maximum supply-demand of the consumer. As such the insulation resistance of the complete installation to earth should not be less than 1 MΩ. Insulation resistance test must be conducted on dc voltage of value not less than twice the standard supply voltage. However, it need not exceed  500 V for medium voltage circuits.

Insulation resistance of the installation to earth is measured by a megger generating dc voltage of about 500 V. Insulation resistance is measured under the following conditions.

(i) Main switch in off position.

(ii) The main fuse to be taken out.

(iii) All other fuses to be provided.

(iv) All lamps must be put in the on position.

(v) All switches must be made on.

(vi) Live and neutral wire to be shorted together.

Testing of Insulation Resistance Between Conductors

After testing the insulation resistance of installation to earth, the insulation resistance between line and neutral should be measured. The major object in conducting this test is again to ensure that the insulation is quite sound between the conductors and there are no chances of any appreciable leakage current between them.

This test should be carried out under the following conditions of installation

(i) Main switch off.

(ii) the Main fuse is withdrawn.

(iii) All other fuses in their position.

(iv) All switches in on position.

(v) All lamps from the holders were removed.

(vi) Two terminals of the meager are connected to the line and neutral wire.

Insulation resistance measured under the above condition by a megger should not be less than 50 MΩ divided by the number of outlets(points + switches). However, it need not be more than 1 MΩ.

Answer.1. Megger

Explanation:-

A null method of measurement is a simple, accurate and widely used method that depends on an instrument reading being adjusted to read zero current only. The method assumes:

(i) If there is any deflection at all, then some current is flowing;

(ii) If there is no deflection, then no current flows (i.e. a null condition).

E.g of null detection method is DC potentiometer, Kelvin double bridge, AC potentiometer, Wheatstone bridge