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Calibrate a single-phase energy meter by phantom loading at different power factor by Phase shifting transformer

 

 

Objective: -  Calibrate a single-phase energy meter by phantom loading at different power factor by    

                         (i) Phase shifting transformer.

Apparatus Required:

Sr. No.

Name of the Equipment

Range

Type

Quantity

1.

Energy Meter

240V,(5-20)A, 50Hz

1- ф, MI

1

2.

Phase Shift  Transformer

440V/440, 500VA

1- ф

1

3.

U.P.F Wattmeter

(150/300/600)V,(0-10)A

Dynamometer Type

1

4.

Voltmeter

(0-300)V

MI

1

5.

Ammeter

(0-10)A

MI

1

6.

Resistive Load

230V,(0-10)A

1- ф

1

7.

Stop Watch

-

Digital

1

8.

Connecting Wires

-

-

As Required

9.

Single-Phase Variac

240V / (0-270)V

-

1

Theory:

Induction type of energy meters are universally used for measurement of energy in domestic and industrial a.c. circuits. Induction type of meters possesses lower friction and higher torque/weight ratio. Also they are inexpensive and accurate, and retain their accuracy over a wide range of loads and temperature conditions. There are four main parts of the operating mechanism:

  1. Driving system
  2. Moving system
  3. Braking system and
  4. Registering system.

Driving System: The driving system of the meter consists of two electro-magnets. The core of these electromagnets is made up of silicon steel laminations. The coil of one of the electromagnets is excited bythe load current. This coil is called the ‘current coil’. The coil of second electromagnet is connected across the supply and, therefore, carries a current proportional to the supply voltage. This coil is called the ‘pressure coil’. Consequently the two electromagnets are known as series and shunt magnets respectively.Copper shading bands are provided on the central limb. The position of these banks is adjustable. The function of these bands is to bring the flux produced by the shunt magnet exactly in quadrature with the applied voltage.

Moving System: This consists of an aluminum disc mounted on a light alloy shaft. This disc is positioned in the air gap between series and shunt magnets.

Braking System: A permanent magnet positioned near the edge of the aluminum disc forms the braking system. The aluminum disc moves in the field of this magnet and thus provides a braking torque. The position of the permanent magnet is adjustable, and therefore, braking torque can be adjusted by shifting the permanent magnet to different radial positions as explained earlier.

Registering (counting) Mechanism: The function of a registering or counting mechanism is to record continuously a number which is proportional to the revolutions made by the moving system. In all induction instruments we have two fluxes produced by currents flowing in the windings of the instrument. These fluxes are alternating in nature and so they produce emf s in a metallic disc or a drum provided for the purpose. These emfs in turn circulate eddy currents in the metallic disc or the drum. The breaking torque is produced by the interaction of eddy current and the field of permanent magnet. This torque is directly proportional to the product of flux of the magnet, magnitude of eddy current and effective radius ‘R’ from axis of disc. The moving system attains a steady speed when the driving torque equals braking torque. The term testing includes the checking of the actual registration of the meter as well as the adjustments done to bring the errors of the meter with in prescribed limits. AC energy meters should be tested for the following conditions:1.At 5% of marked current with unity pf.2.At 100% (or) 125% of marked current.3.At one intermediate load with unity pf.4.At marked current and 0.5 lagging pf.

The supply voltage is applied across the pressure coil. The pressure coil winding is highly inductive as it has very large number of turns and the reluctance of its magnetic circuit is very small owing to presence of air gaps of very small length. Thus the current Ip through the pressure coil is proportional to the supply voltage and lag it by a few degrees less the 90 degrees. This is because the winding has a small resistance and there are iron losses in the magnetic circuit. Current input produces a flux. This flux divides itself into two parsфg and фp. The major portion фg flows across the side gaps as reluctance of this path is small. The reluctance to the path of flux фp is large and hence its magnitude is small. This flux фp goes across aluminium disc and hence is responsible for production of driving torque. Flux фp is in phase with current Ip and is proportional to it. Therefore flux фp is proportional to voltage V and lags it by an angle a few degrees less than 90 degrees since flux фp is alternating in nature, it induces an eddy emf in the disc which in turn produces eddy current,The load current I flows through he current coil and produces a flux фg. This flux is proportional to the load current and is in phase with it. This flux produces eddy current is in disc. Now the eddy current is interacts with flux фp to produce a torques and eddy current is interacts with фg to produce another torque. Here two torques are in the opposite direction and the net torque is the different of these.

Circuit Diagram:

Fig 5.1 -phase energy meter by phantom loading

Procedure :-

  1. Give the connections as per the circuit diagram above.
  2. Apply 220V A.C to the pressure coil circuit by means of phase shifting transformer.
  3. Apply a load of 2 Amps by switching on the load.
  4. Note down the reading of two meters in a given period of time, say 2 minutes.
  5. Find out the percentage error at this load.
  6. Now rotate the rotor of phase shifting transformer so that the working power factor (p.f) of the meter is varied.
  7. For this power factor repeat steps 4 and 5.
  8. Now increase the load current in suitable steps and repeat the steps 4,5,6 and tabulate the results. The expected example results are given in the table below:

Observation Table:

Sr. No.

Current I(A)

Power Factor

Wattmeter (w)x2

Time (T) in Hours

Measured Power (Whr)

(E1)

Actual

Energy

(E2) = W X T

% Error =

E1-E2/E2 x 100

1

 

 

 

 

 

 

 

2.

 

 

 

 

 

 

 

3.

 

 

 

 

 

 

 

4.

 

 

 

 

 

 

 

5.

 

 

 

 

 

 

 

CALCULATION:

E1=wt/3600 wh (practical or measured)

for E2

k=900 rev/kwh

900 rev à1000wh

0.9 rev à1wh

19 rev à19/0.9 = 11.11 wh

Energy consumed measured by meter for 10 rev is e2=11.1 (theoretical or actual).

Result:

The given single phase energy meter is tested at different loads and calibration curve is plotted.

Precautions:

1. There should not be any loose connections.

2. Meter readings should not be exceeded beyond their ratings

3. Observe the ammeter reading. Apply the voltage slowly so that the current is Within the limited range of ammeters, wattmeter and energy meter.

4. If the energy meter rotate in reverse direction, change either its current coil terminals or pressure coil terminal or pressure coil terminal but not both

Experiment No. – 05 (ii)

Objective:-To Calibrate a single-phase energy meter by phantom loading at different power factor

                       by (ii) Auto transformer.

Apparatus Required:

Sr. No.

Name of the Equipment

Range

Type

Quantity

1.

Energy Meter

240V,(5-20)A, 50Hz

1- ф, MI

1

2.

Auto Transformer

230/(0-270)V, (0-10)A

1- ф

1

3.

U.P.F Wattmeter

(150/300/600)V,(0-10)A

Dynamometer Type

1

4.

Voltmeter

(0-300)V

MI

1

5.

Ammeter

(0-10)A

MI

1

6.

Resistive Load

230V,(0-10)A

1- ф

1

7.

Stop Watch

-

Digital

1

8.

Connecting Wires

-

-

As Required

Theory:

Induction type of energy meters are universally used for measurement of energy in domestic and industrial a.c. circuits. Induction type of meters possesses lower friction and higher torque/weight ratio. Also they are inexpensive and accurate, and retain their accuracy over a wide range of loads and temperature conditions. There are four main parts of the operating mechanism:

  1. Driving system
  2. Moving system
  3. Braking system and
  4. Registering system.

Driving System: The driving system of the meter consists of two electro-magnets. The core of these electromagnets is made up of silicon steel laminations. The coil of one of the electromagnets is excited by the load current. This coil is called the ‘current coil’. The coil of second electromagnet is connected across the supply and, therefore, carries a current proportional to the supply voltage. This coil is called the ‘pressure coil’. Consequently the two electromagnets are known as series and shunt magnets respectively. Copper shading bands are provided on the central limb. The position of these banks is adjustable. The function of these bands is to bring the flux produced by the shunt magnet exactly in quadrature with the applied voltage.

Moving System: This consists of an aluminum disc mounted on a light alloy shaft. This disc is positioned in the air gap between series and shunt magnets.

Braking System: A permanent magnet positioned near the edge of the aluminum disc forms the braking system. The aluminum disc moves in the field of this magnet and thus provides a braking torque. The position of the permanent magnet is adjustable, and therefore, braking torque can be adjusted by shifting the permanent magnet to different radial positions as explained earlier.

Registering (counting) Mechanism: The function of a registering or counting mechanism is to record continuously a number which is proportional to the revolutions made by the moving system. In all induction instruments we have two fluxes produced by currents flowing in the windings of the instrument. These fluxes are alternating in nature and so they produce emf s in a metallic disc or a drum provided for the purpose. These emfs in turn circulate eddy currents in the metallic disc or the drum. The breaking torque is produced by the interaction of eddy current and the field of permanent magnet. This torque is directly proportional to the product of flux of the magnet, magnitude of eddy current and effective radius ‘R’ from axis of disc. The moving system attains a steady speed when the driving torque equals braking torque. The term testing includes the checking of the actual registration of the meter as well as the adjustments done to bring the errors of the meter with in prescribed limits. AC energy meters should be tested for the following conditions:1.At 5% of marked current with unity pf.2.At 100% (or) 125% of marked current.3.At one intermediate load with unity pf.4.At marked current and 0.5 lagging pf.

The supply voltage is applied across the pressure coil. The pressure coil winding is highly inductive as it has very large number of turns and the reluctance of its magnetic circuit is very small owing to presence of air gaps of very small length. Thus the current Ip through the pressure coil is proportional to the supply voltage and lag it by a few degrees less the 90 degrees. This is because the winding has a small resistance and there are iron losses in the magnetic circuit. Current input produces a flux. This flux divides itself into two pars фg and фp. The major portion фg flows across the side gaps as reluctance of this path is small. The reluctance to the path of flux фp is large and hence its magnitude is small. This flux фp goes across aluminum disc and hence is responsible for production of driving torque. Flux фp is in phase with current Ip and is proportional to it. Therefore flux фp is proportional to voltage V and lags it by an angle a few degrees less than 90 degrees since flux фp is alternating in nature, it induces an eddy emf in the disc which in turn produces eddy current, T he load current I flows through he current coil and produces a flux фg. This flux is proportional to the load current and is in phase with it. This flux produces eddy current is in disc. Now the eddy current is interacts with flux фp to produce a torques and eddy current is interacts with фg to produce another torque. Here two torques are in the opposite direction and the net torque is the different of these.

Circuit Diagram:

Procedure:

1. Connections are made as per the circuit diagram.

2. Set Auto Transformer at zero voltage position before switching on the supply.

3. Gradually increase the voltage using the auto-transformer till the voltmeter reads 230V.

4. Now apply the Load at certain value (i.e. 2A )

5. Time taken for 25 rev. of the disc of the energy meter in the forward direction is noted

6. Record the Voltmeter, Ammeter, & Watt-meters are noted.

7. The experiment is repeated for different values of current (i.e. 4A, 6A,8A) at constant voltage.

8. After noting the values slowly decrease the auto transformer till Voltmeter comes to zero voltage position and switch off the supply.

Observation Table:

Sr.

No.

Voltage

(V)

(Volts)

Load

Current

(IL)

(Amps)

Wattmeter

Reading

W (Watts)

Time

for

10 rev

T(Sec)

Energy

meter

Reading

(E1)

Actual

Energy

(E2) = W X T

% Error =

E1-E2/E2 x 100

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CALCULATION:

E1=wt/3600 wh (practical or measured)

for E2

k=900 rev/kwh

900 rev à1000wh

0.9 rev à1wh

19 rev à19/0.9 = 11.11 wh

Energy consumed measured by meter for 10 rev is e2=11.1 (theoretical or actual).

 

Result:-

The given single phase energy meter is tested at different loads and calibration curve is plotted.

Precautions:

1. There should not be any loose connections.

2. Meter readings should not be exceeded beyond their ratings

3. Observe the ammeter reading. Apply the voltage slowly so that the current is Within the limited range of ammeters, wattmeter and energy meter.

4. If the energy meter rotates in reverse direction, change either its current coil terminals or pressure coil terminal or pressure coil terminal but not both

Viva Voce Questions

1. What is a phantom Load?

2. What is creeping?

3. What is Braking?

4. Define meter constant?

5. What is Friction? What are the different types of Friction, explain it?

6. Write short notes on driving system, Moving system, Braking systems, registering systems?

7. What are the errors occurred by the driving system?

8. How do you prevent the creeping?

9. What are the errors occurs in the energy meter?

10. What is the principle of 1-Phase energy meter?

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