Induction Type Energy Meter MCQ Quiz in मल्याळम - Objective Question with Answer for Induction Type Energy Meter - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

Concept:

Induction type energy meter:

• The basic principle of induction type energy meter is electromagnetic induction.
• When alternating current flow through two suitably located coils produces a rotating magnetic field which is cut by the metallic disc suspended near to the coils thus emf induce in the disc which is circulated eddy current in it.
• With the interaction of the rotating magnetic field and eddy currents, torque is developed and causes the disc to rotate.

Meter constant(K):

\(K = \frac{{No.\;of\;revolutions}}{{Energy\;in\;kWh}}\)

Explanation:

Energy of meter in kWh (E) = (V I cosϕ) × 10^-3

E = 240 × 10 × 0.8 × 10^-3 

E = 1.92 kWh

\(K = \frac{{No.\;of\;revolutions}}{{Energy\;in\;kWh}}\)

Number of revolution = meter constant(K) × kWh

Number of revolution = 600 × 1.92 = 1152 

Speed of disc (N) =\(\frac{{Revolution}}{{60}}\)

N = \(\frac{{1152}}{{60}}\)

N = 19.2 rpm

• Sometimes the disc of the energy meter makes slow but continuous rotation at no load i.e. when the potential coil is excited but with no current flowing in the load; This is called creeping.
• This error may be caused due to overcompensation for friction, excessive supply voltage, vibrations, stray magnetic fields, etc
• In order to prevent this creeping on no-load two holes or slots are drilled in the disc on opposite sides of the spindle.
• This causes sufficient distortion of the field; The result is that the disc tends to remain stationary when one of the holes comes under one of the shunt magnets.

Rating of electrical instruments

The electrical ratings such as current, voltage, power, or phase are the rated values of the instruments.

The rated values are the maximum values of the instruments at which it can operate.

Above this value, if the instrument is operated then it will get damaged.

Explanation

The rating of the pressure coil of 3ϕ energy meter is 3ϕ, 415 V, 50 Hz.

Hence, the pressure coil of the energy meter has a maximum capacity of 415 V.

Creep :

• In energy meters, when the pressure coil is energized, a slow, but the continuous rotation of the disc is observed even when there is no current in the current coil. This is called Creeping.
• This can be due to several reasons such as overcompensation for friction, vibrations, stray field effects, and excessive pressure coil voltage.
• To prevent creeping, two diametrically opposite holes are drilled on the disc.
• The disc will stall when one of the holes comes under one of the poles of the shunt magnet. Thus the rotation is restricted to a maximum of half a revolution.

How to reduce creep: 

• To prevent creeping, two diametrically opposite holes are drilled in the disc of energy meters. 
• Due to this hole, the disc will come to rest when the hole comes under the edge of the pole of the shunt magnet. Thus creeping is limited to a maximum of half of the rotation

Energy meter: 

• Energy meter measures electrical energy in a kilowatt hour.
• It is also known as kilowatt-hour meter or Induction type watt-hour meter.
• It is a type of integrating instruments

Construction of Energy meter: The four essential components of the meter

• Driving system
• Moving system
• Registering system
• Braking system

The principle of working of all electrical measuring instruments depends upon various effects of electric current or voltage as shown in the table given below.

Concept:

• The number of revolutions made by the energy meter per kilowatt-hour is known as the meter constant of an energy meter.
• Unit of meter constant is revolution per kilowatt-hour (rev / kWh)
• It is constant for a particular energy meter.

Meter constant (K) = No. of revolution by meter / Energy consumed (E)

E (in kWh) = voltage x current x cos ϕ × time x 10-3 = Load × time x 10-3

Where, cos ϕ = power factor

Calculation:

Load power = 450 W, time = 100 sec, Number of revolutions = 10

Energy supplied in 100 seconds \(= 450 \times \frac{{100}}{{3600}} \times {10^{ - 3}} = 12.5 \times {10^{ - 3}}\;kWh\)

Number of revolutions in 100 seconds = 10

Meter constant = number of revolutions / kWh

Meter constant \( = \frac{10}{{12.5 \times {{10}^{ - 3}}}} = 800\;rev/kWh\)

Concept:

Based on the nature of the operation, instruments can be classified into three types.

Indicating Instruments: These indicate the quantity being measured by means of a pointer that moves on a scale. These instruments indicate the instantaneous value of the electrical quantity being measured at the time at which it is being measured.

Example: Ammeter, Voltmeter

Recording Instruments: These instruments record continuously the variation of any electrical quantity with respect to time. In principle, these are indicating instruments but so arranged that a permanent continuous record of the indication is made on a chart or dial.

Any electrical quantity like current, and voltage can be recorded by a suitable recording mechanism.

Example: A potentiometric type of recorder used for monitoring temperature records the instantaneous temperatures on a strip chart recorder.

Integrating Instruments: These instruments record the consumption of the total quantity of electricity, energy, etc. during a particular period of time. These instruments give reading for a specific period of time but no indication of reading for a particular instant of time.

Example: Ampere-hour meter, Energy meter, kilovolt ampere-hour meter.

The correct answer is option 4):(two torques would be equal and opposite)

Concept:

• The meter which is used for measuring the power of three phase supply is known as the three phase energy meter. The three phase meter is constructed by connecting the two single phase meter through the shaft. The total energy is the sum of the reading of both the elements.
• The three phase energy meter has two discs mounted on the common shaft. Both the disc has its braking magnet, copper ring, shading band and the compensator for getting the correct reading. The two elements are used for measuring the three phase power. The construction of the three phase meter is shown in the figure below.

• For three phase meter, the driving torque of both the elements is equal. This can be done by adjusting the torque. The torque is adjusted by connecting the current coils of both the elements in the series and their potential coils in parallel. The full load current is passed through the coil due to which the two opposite torque is set up in the coilThe adjustment made with the magnetic shunt in three-phase, two-element energy meter for the rotation of aluminum disc to be zero istwo torques would be equal and opposite
• For three phase meter, the driving torque of both the elements is equal. This can be done by adjusting the torque. The torque is adjusted by connecting the current coils of both the elements in the series and their potential coils in parallel. The full load current is passed through the coil due to which the two opposite torque is set up in the coil

Concept:

Meter constant, \(k = \frac{{number\;of\;revolutions}}{{measured\;value \;in \;kWh}}\)

Energy consumed or measured value = (VI cosϕ) (Time in hr)

Where, V = Voltage

I = current

cos ϕ = Power factor

Calculation:

Given meter constant, (k) = 500 revolution/kWh

When testing, 50 revolutions in 86 seconds.

i.e., \(K_{measured} = \frac{50 \times 3600}{4.4 \times 86}\)

= 475.68

∴ \(\rm \% \ error = \frac{K_{(measured)} - K_{(true)}}{K_{(true)}}\)

\(= \frac{475.68 - 500}{500} \times 100 \%\)

= - 4.86%

Therefore, the correct option is (b).