The instrument that measures the low value of power factor accurately is known as the Low Power Factor Wattmeter (LPFW). The low power factor meter is used for measuring the power of the highly inductive circuit.
Application:
As the LPF is most suitable for inductive loads, it is suitable for the measurement of power in inductive loads, open circuit test on single phase transformer, and load test on an induction motor.
It is not suitable for the measurement of power in resistive loads.
22. A dynamometer wattmeter is almost universally used for the measurement of _______
AC Power Only
DC Power Only
Both AC and DC Power
Frequency
Answer.3. Both AC and DC Power
Explanation:
A dynamometer wattmeter is almost universally used for the measurement of d.c. as well as a.c. power. It works on the dynamometer principle i.e. mechanical force exists between two current-carrying conductors or coils.
23. In A.C. circuits, power consumed is ________
Product of voltage and current
It depends on the p.f. of the circuit in addition to voltage and current
It depends on the supply voltage
It depends on the magnitude of the circuit current
Answer.2. It depends on the p.f. of the circuit in addition to voltage and current
Explanation:
Power developed in an ac circuit can be expressed as P=VI cos ∅.
where
V is the voltage across the circuit
I is the current flowing through the circuit
cos∅ is the power factor of the circuit.
Hence in AC circuit power consumed depends on the p.f. of the circuit in addition to voltage and current.
24. When the moving coil in a Dynamometer type wattmeter deflects ________
Pointer moves
Pointer doesn’t move
Current flows
Voltage is generated
Answer.1. Pointer moves
Explanation:
In a Dynamometer type wattmeter, the current coil carries the load current and the potential coil carries current proportional to the load voltage. Due to currents in the coils, mechanical force exists between them. The result is that the movable coil moves the pointer over the scale. The pointer comes to rest at a position where deflecting torque is equal to the controlling torque.
25. In D.C. circuits, power is measured using ________
Ohmmeter and galvanometer
Ohmmeter and voltmeter
Ammeter and voltmeter
Ammeter and galvanometer
Answer.3. Ammeter and voltmeter
Explanation:
A voltmeter is an instrument used for measuring the electrical potential difference between two points in an electric circuit.
An ammeter is a measuring device used to measure the electric current in a circuit.
From Ohm’s Law
R = V/I and P = VI
So we can measure resistance and power from the voltmeter and ammeter used together. Resistance is proportional to voltage and inversely proportional to current but power is directly proportional to both voltage and current.
A dynamometer wattmeter is almost universally used for the measurement of d.c. as well as a.c. power. It works on the dynamometer principle i.e. mechanical force exists between two current-carrying conductors or coils.
26. When a current-carrying coil in Dynamometer type wattmeter is placed in the magnetic field?
No force is exerted
Voltage is produced
Power is generated
A force is exerted
Answer.4. A force is exerted
Explanation:
In a Dynamometer type wattmeter, the current coil carries the load current and the potential coil carries current proportional to the load voltage. Due to currents in the coils, mechanical force exists between them. As a result, a deflection torque is generated and the moving coil undergoes deflection. The result is that the movable coil moves the pointer over the scale. The pointer comes to rest at a position where deflecting torque is equal to the controlling torque.
27. A dynamometer type wattmeter consists of ________
Only potential coil
Potential and current coils
Only current coil
No coils
Answer.2. Potential and current coils
Explanation:
When a dynamometer instrument is used as a wattmeter, the fixed coils are connected in series with the load and carry the load current while the moving coil is connected across the load through a series multiplier R and carries a current proportional to the load voltage. The fixed coil (or coils) is called the current coil and the movable coil is known as the potential coil.
28. In a Dynamometer type wattmeter, the fixed coil is split into ________ Parts.
4
3
2
1
Answer.2. Potential and current coils
Explanation:
The dynamometer-type wattmeter essentially consists of two coils called fixed coil and moving coil. The fixed coil is split into two equal parts that are placed parallel to each other. The two fixed coils are air-cored to avoid hysteresis effects when used on AC. moving coil. The fixed coil is also called the current coil as it is connected in series with the load.
29. Controlling torque in Dynamometer type wattmeter is provided by _____
Spiral Spring
Hair Spring
Gold Spring
Control Spring
Answer.1. Spiral Spring
Explanation:
In Dynamometer type wattmeter the controlling torque is provided by a pair of spiral type hair springs fixed on the spindle. These hairs prings also provide the path for the current flow into and out of the moving coil, M.
30. The controlling torque in Dynamometer type wattmeter is provided by the
Eddy current Damping
Air Friction Damping
Fluid Friction Damping
Electromagnetic Damping
Answer.2. Air Friction Damping
Explanation:
In Dynamometer type wattmeter for controlling torque the damping of the moving system is provided using an air friction damping mechanism. Here, the moving system carries a light aluminum vane that moves in a sector-shaped enclosure providing damping.
