Blondel’s Theorem states that if a network is supplied through N conductors, the total power is measured by summing the readings of N wattmeters so arranged that a current element of a wattmeter is in each line and the corresponding voltage element is connected between that line and a common point.
Similar to wattmeters, Blondel’s theorem is applicable to energy meters as well. Thus, a three-element energy meter is required for a three-phase four-wire system, and for a three-phase three-wire system, a two-element energy meter is required.
2. The type of arrangement used to measure the power through the energy meter is
Three-phase Four-wire system
Three-phase Three-wire System
Both 1 and 2
DC System
Answer.3. Both 1 and 2
Explanation:
Similar to wattmeters, Blondel’s theorem is applicable to energy meters as well. Thus, a three-element energy meter is required for a three-phase four-wire system, and for a three-phase three-wire system, a two-element energy meter is required.
Therefore, these meters are categorized as three-element energy meters and two-element energy meter
3. A three-element energy meter is used for _______
Three-phase Four-wire system
Three-phase Three-wire System
Both 1 and 2
DC System
Answer.1. Three-phase Four-wire system
Explanation:
A three-element energy meter is used for the three-phase four-wire system. The fourth wire is a neutral wire. The construction of an individual element is similar to that of a single-phase energy meter.
One unit of three-element, the three-phase element is always cheaper than three units of a single-phase energy meter.
4. The additional wire i.e fourth wire in the three-element energy meter is known as
Ground Wire
Neutral Wire
Phase Wire
Supply wire
Answer.2. Neutral Wire
Explanation:
A three-element energy meter is used for the three-phase four-wire system. The fourth wire is a neutral wire. Each element has the same constructional details as that of a single-phase energy meter. Three discs are provided for each element, thus, it is a multi-disc type wattmeter.
5. The pressure coil in the three-element energy meter is connected in _____
Series with Neutral only
Parallel with Neutral only
Series with Neutral and Line
Parallel with Neutral and Line
Answer.4. Parallel with Neutral and Line
Explanation:
A three-element energy meter is used for the three-phase four-wire system. The fourth wire is a neutral wire. Each element has the same constructional details as that of a single-phase energy meter. Three discs are provided for each element, thus, it is a multi-disc type wattmeter.
The pressure and current coils are labeled as P1, P2, P3, and C1, C2, C3, respectively.
The pressure coils are connected across a neutral and a line whereas the current coils are connected in series with the lines.
The coils are connected in such a manner that the net torque produced is the sum of the torques due to all three elements.
6. One unit of three-element, the three-phase element is always _____ than three units of single-phase energy meter.
Cheaper
Costlier
Beneficial
Harder
Answer.1. Cheaper
Explanation:
A three-element energy meter is used for the three-phase four-wire system. The fourth wire is a neutral wire. The construction of an individual element is similar to that of a single-phase energy meter.
One unit of three-element, the three-phase element is always cheaper than three units of a single-phase energy meter. But due to the interaction between eddy currents produced by one element with the flux produced by another element, there may be errors in the measurement by the three-phase energy meter. Such errors may be reduced by suitable adjustments.
7. The pressure coil in the three-element energy meter is connected in _____
Series with Neutral only
Parallel with Neutral only
Series with Line
Parallel with Neutral and Line
Answer.3. Series with Line
Explanation:
A three-element energy meter is used for the three-phase four-wire system. The fourth wire is a neutral wire. Each element has the same constructional details as that of a single-phase energy meter. Three discs are provided for each element, thus, it is a multi-disc type wattmeter.
The pressure and current coils are labeled as P1, P2, P3, and C1, C2, C3, respectively.
The pressure coils are connected across a neutral and a line whereas the current coils are connected in series with the lines.
The coils are connected in such a manner that the net torque produced is the sum of the torques due to all three elements.
8. Two element energy meter is also known as _______
Single Disc type wattmeter
Multi-Disc type wattmeter
Single Disc type Voltmeter
Multi-Disc type Ammeter
Answer.2. Multi-Disc type wattmeter
Explanation:
Two element energy meter is also called a multi-disc type wattmeter as two separate discs are provided for each element. It is used to measure energy for a three-phase three-wire system.
The connections of the meter are similar to that of two wattmeter method of power measurement. The pressure coils, carried by the shunt magnet are connected in parallel and the current coils, carried by the series magnet are connected in series.
The total torque generated is equal to the sum of the torques generated by each element and the method of torque generation is similar to the single-phase energy meter.
9. A two-element energy meter is used for _______
Three-phase Four-wire system
Three-phase Three-wire System
Both 1 and 2
DC System
Answer.2. Three-phase Three-wire System
Explanation:
Two element energy meter is also called a multi-disc type wattmeter as two separate discs are provided for each element. It is used to measure energy for a three-phase three-wire system.
The connections of the meter are similar to that of two wattmeter method of power measurement. The pressure coils, carried by the shunt magnet are connected in parallel and the current coils, carried by the series magnet are connected in series.
10. In a two-element energy meter the pressure coil Is carried by ____
Shunt Magnet
Series Magnet
Both shunt and Series Magnet
None of the above
Answer.1. Shunt Magnet
Explanation:
Two element energy meter is also called a multi-disc type wattmeter as two separate discs are provided for each element. It is used to measure energy for a three-phase three-wire system.
The connections of the meter are similar to that of two wattmeter method of power measurement. The pressure coils, carried by the shunt magnet are connected in parallel and the current coils, carried by the series magnet are connected in series.
11. In a two-element energy meter, the current coil Is carried by ____
Shunt Magnet
Series Magnet
Both shunt and Series Magnet
None of the above
Answer.2. Series Magnet
Explanation:
Two element energy meter is also called a multi-disc type wattmeter as two separate discs are provided for each element. It is used to measure energy for a three-phase three-wire system.
The connections of the meter are similar to that of two wattmeter method of power measurement. The pressure coils, carried by the shunt magnet are connected in parallel and the current coils, carried by the series magnet are connected in series.
12. The conditions for which energy meters are tested are _____
Power factor Testing
Starting Test
Creep test
All of the above
Answer.4. All of the above
Explanation:
Before energy meters are released for measuring purposes, their actual registration is checked. Also, the errors are kept within reasonable limits by doing some adjustments. This is known as testing the energy meter. Some of the conditions for which energy meters are tested are given below.
The power factor is unity and the current is 5% of the marked value.
Power factor is unity and the current is 100% or 125% of marked value.
Current is equal to the marked value and 0.5 lagging power factor.
Power factor is unity with one intermediate load.
Starting test: This test does not check the accuracy of the meter, rather it is performed to check if the meter starts and runs properly. According to this test, the meter should start and run with normal voltage and a current of 0.5% of the marked value.
Creep test: This test states that the meter should not creep, that is, it must not undergo more than one revolution for a voltage of 110% of its marked value and open current circuit.
