1. Induction type instruments are used for ____________
Explain:-
2. Driving system in an induction type single phase energy meter consists of _________
Explain:-
3.Moving system of the induction type single phase energy meter has _________
Explain:- Aluminium disc is provided in the air gap between the series and shunt magnets. Jewel bearings support the spindle. Hence the moving system in an induction type single phase energy meter consists of light aluminium disc.
4.Braking system consists of _________
Explain:- In an induction type single phase energy meter, edge of the aluminium disc consists of a permanent magnet also known as a brake magnet. E.m.f is induced in the aluminium disc when it rotates as a result of the magnetic field produced by the brake magnet
5. What is the effect of eddy currents in the aluminium disc?
Explain:- The eddy currents induced in an aluminium disc vary in proportion to the speed of the disc. As a result the braking torque exerted on the disc varies in proportion to the speed.
6. Obtaining correct reading from the energy meter requires ______________
Explain:- In order to obtain an exact reading for the energy consumed by a load using an energy meter, we require the pressure coil to have a low value of resistance and low iron losses.
7.Phase angle can be made 90 degrees using ____________
8. Copper shading bands are _________
Explain:-
9. As copper shading bands move up ________
Explain:-
10.Shunt flux is made to lag the applied voltage using ________
Explain:- We make use of shading coil on the central limb of a shunt magnet and shading bands in order to make the shunt flux to lag the applied voltage by almost 90 degrees. Lag adjustment:
In the induction type energy meters, in order to maintain the speed of rotation proportional to power The phase angle between the supply voltage and pressure coil flux should be equal to 90 degree .
However, in actual practice, the angle between the supply voltage and pressure coil flux is exactly not 90 degree but few degrees less. Therefore, some lag adjustments require.
Lag adjustment adjusts the angle between current in pressure coil and supply voltage equal to 90othat means Current lags behind 90 degrees than the supply voltage.
Lag adjustment can be done by adjusting shading bands on shunt magnet.
11.At overloads, magnetic shunt ________
Explain:- As the magnetic shunt reaches saturation at overloads, magnetic shunt diverts the flux due to series magnet. As a result a large portion of the flux appears in the gap of the air disc. This compensates the self braking torque.
12.Energy meter reads correctly when the ___________
13. Small torque for energy meter is provided __________
Explain:-
14. Friction torque is eliminated by _________
15.Self braking torque is _________
Explain:- In an energy meter, the self braking torque is dependent on the square of the load current. As a result the disc rotates at a slightly slower speed at high value of loads.
16. Self braking action is minimised by _________
Explain:- In an energy meter we can minimise or eliminate the self braking action by keeping the disc speed as low as possible at full load condition. This is achieved by maintaining the flux due to the current coil smaller than that due to the shunt coil.
17. Overload compensating devices is _________
Explain:- Magnetic shunt reaches saturation at overloads. As a result, its permeability reduces. Hence the overload compensating device takes the form of a magnetic shunt.
18. Magnitude of flux in an energy meter varies __________
Explain:- In the driving system of an energy meter, magnitude of flux can be incorrect as a result of abnormal values of currents and voltages. This occurs due to a change in the resistance of the pressure coil circuit.
19. Energy meter creeps __________
Explain:- In an energy meter, when the magnetic circuit is asymmetrical, a driving torque is produced. As a result of this driving torque, the energy meter creeps.
20. Supply voltage in an energy meter is __________
Explain:- Generally the supply voltage is constant in an energy meter. It can fluctuate as a result of unavoidable reasons leading to errors in the reading of the energy meter.