21. Which type of measuring instrument widely used in power systems for measuring energy?
Rectification type
Induction type
Moving coil or iron-type
Electrostatic type
Answer.3. Induction type
Explanation:
Induction-type instruments can be used as an ammeter, voltmeter, or wattmeter.
Induction-type single-phase energy meter is used invariably to measure the energy consumed in any AC circuit in a prescribed period where supply voltage and frequency are constant.
The energy meter is an integrating instrument that measures the total quantity of electrical energy supplied to the circuit in a given period.
22. What is the main function of the registering system of the Energy meter?
Record the number of rotations of an aluminum disc
Record the energy consumed in the aluminum disc
Record the torque in the aluminum disc
Record the frequency of rotation of the aluminium disc
Answer.1. Record the number of rotations of an aluminum disc
Explanation:
The main function of registering system is to record the number of rotations of the Aluminium disk.
Rotation/Revolution is proportional to the energy consumed directly in kilowatt-hour.
The reading in kWh is obtained by multiplying the number of rotations of the disc with the meter constant.
R ∝ E
R = kmE
R = Revolution
E = Energy consumed in kWh
km = Meter constant
23. Boards on which various control accessories like energy meter, iron-clad switch, fuses, etc. are housed are called ______ boards.
Panel
Control
Standard
Switch
Answer.1. Panel
Explanation:
The boards on which various control accessories like energy meters, iron-clad switches, fuses, etc. are housed are known as panel boards.
A panel board is a component of an electrical distribution system that divides an electrical power feed into branch circuits, while providing a protective circuit breaker or fuse for each circuit, in a common enclosure.
24. A 3 phase 3 element energy meter of 415V, 50 Hz has its pressure coil rated for
200 V
240 V
415 V
440 V
Answer.3. 415 V
Explanation:
When the energy meter is connected in the circuit, the current coil carries the load current and the pressure coil carries the current proportional to the supply voltage.
Since pressure coil is rated at line voltage i.e. VRY, VBR etc. So that pressure coil of 415V, 50 Hz 3-ϕ 3 element energy meter is rated at 415V.
25. Adjusting the position of the braking magnet and moving it closer to the center of the disc in energy meter _____ speed.
Increase
Decrease
Unaffected
Any of the above
Answer.2. Decrease
Explanation:
The main part of this system is a permanent magnet called a brake magnet.
It is located near the disk so that eddy currents are induced in it due to the movement of the rotating disk through the magnetic field.
This eddy current reacts with the flux and exerts a braking torque which opposes the motion of the disk. The speed of the disk can be controlled by changing flux.
The speed(N) of the energy meter is inversely proportional to the distance(d) between the spindle and the permanent magnet.
Hence, to compensate slow down of the speed of the disc can be done by adjusting the position of the braking magnet and moving it closer to the center of the disc.
26. An energy meter connected to an immersion heater (resistive) operating on an AC 230 V, 50 Hz AC single-phase source reads 2.3 units in 1 hour. The heater is removed from the supply and now connected to a 400 V peak to peak square wave source of 150 Hz. The power in kW dissipated by the heater will be.
3.478
1.739
1.540
0.870
Answer.2. 1.739
Explanation:
For square waveform
Peak value = RMS value = Average value
Peak to peak value = 2 × peak value
VP = 200 V
2.3 units for one hour at 230 V energy consumed = KWh
2.3 = V2t/R
2.3 = (230)2 × 1/R
R = 23 Ω
P = V2/R = (200)2/23
P = 1.739 kW
27. A 230 V, 1-phase watt-hour meter records a constant load of 10 A for 10 hours at unity p.f. If the meter disc makes 2300 revolutions during this period, what is the meter constant in revolutions/kWh?
300 rev/kWh
200 rev/kWh
100 rev/kWh
400 rev/kWh
Answer.3. 100 rev/kWh
Explanation:
Given
V = 230 volt
I = 10 amp at unity power factor
Power = VI cosϕ = 230 × 10 × 1 = 2300 watt = 2.3 kW
No of revolution in 1 hr = 2300/10 = 230 revolution
Meter Constant = No of revolution in 1 hr/No of kW in 1 hr
Meter Constant = 230/2.3 = 100 Revolution/kWh
28. The series magnets in the Induction type energy meter are wound with
Large turns of wire
Small turns of wire
Medium turns of wire
No turns or wires
Answer.2. Small turns of wire
Explanation:
Series magnet in induction type energy meter consists of a number of U-shaped laminations of silicon steel staggered together to form a core.
A coil of thick wire having a few turns is wound on both the legs of a U-shaped magnet. This coil is connected in series with the load. Thus, it is excited by the circuit current or load current and is known as the current coil.
This magnet is placed below the aluminum disc and produces the magnetic field φse proportional to and in phase with line current.
29. In an Energy Meter the Driving System ________ Registering System and ________ form the basic construction parts.
Moving System, Parallel System
Series System, Braking System
Moving System, Braking System
Magnetic Flux System, Shunt System
Answer.3. Moving System, Braking System
Explanation:
The four essential components of the Induction type energy meter
Driving system
Moving system
Registering system
Braking system
Moving system:- In this system, a thin aluminum disk is placed in the gap between the two electromagnets and mounted on a vertical shaft that is free to rotate.
Driving system:- In this system, there are two silicon steel laminated electromagnets. Upper magnet→ Shunt magnet→ behaves as the potential coil. Lower magnet→ series magnet→ behave as current coil
Registering system:- It registers the number of rotations of the disk which is proportional to the energy consumed directly in kilowatt-hour.
Braking system:- This system has a permanent magnet called a brake magnet. It is located near the disk so that eddy currents are induced and braking toque to the disk.
30. _____ magnet also acts as a braking magnet in an induction type energy meter.
Series Magnet
Shunt Magnet
Electromagnet
Both series and Shunt Magnet
Answer.1. Series Magnet
Explanation:
In an induction type energy meter the series magnet also acts as a braking magnet, since it opposes the main torque producing flux generated by the shunt magnet.
