List different methods of developing damping torque.
Ans:
Methods of developing Damping Torque:
1) Air friction damping.
2) Fluid friction damping.
3) Eddy current damping.
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Define:
(i) Precision (ii) Accuracy
Ans:
(i) Precision: It is the measure of consistency or repeatability of the measurements; it is also known as degree of exactness.
(ii) Accuracy: It is the closeness with which an instrument reading approaches the true value of the quantity being measured.
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Name the material used for:
(i) Moving coil
(ii) Spring of PMMC instrument
Ans:
(i) Material used for Moving Coil: Copper
(ii) Material used for Spring of PMMC Instrument: Phospher bronze
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List one method of range extension of D.C ammeter and a.c. ammeter.
Ans:
Method of Range Extension of D.C Ammeter:
i) By using shunt resistance.
Method of Range Extension of A.C Ammeter:
i) By using CT.
ii) By using shunt resistance.
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State the function of control spring.
Ans:
Function of Control Spring:
i) To produce control torque or force.
ii) To lead current to the moving coil.
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Enlist any four errors that occur in dynamometer type wattmeter.
Ans:
Errors in Dynamometer Type Wattmeter:
1) Errors due to method of connection.
2) Error due to pressure coil inductance.
3) Error due to pressure coil capacitance.
4) Error due to mutual inductance effect.
5) Error due to stray magnetic fields.
6) Error due to eddy currents.
7) Temperature error.
8) Error due to vibration of moving system.
9) Error due to friction.
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State two advantages of two-watt meter method.
Ans:
Advantages of Two Wattmeter Method for 3-Phsae Power Measurement:
1) It is used for balanced as well as unbalanced load.
2) For the star type load, it is not necessary to connect the neutral point for connection of wattmeter.
3) Delta load need not to be opened to connect the wattmeter.
4) For balanced loads, it possible to measure power factor along with the power.
5) Only two watt meters are required which reduces cost of instruments
6) It is possible to measure reactive volt-amperes for balanced loads also.
7) The circuit connections are independent of load connection.
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