What is the principle of operation of dynamometer-type instruments?
B
Electrostatic attraction
C
Electromagnetic interaction between fixed and moving coils
Analysis & Theory
Dynamometer-type instruments operate on the principle of electromagnetic interaction (mutual force) between current-carrying fixed and moving coils.
Which of the following instruments is typically made using a dynamometer mechanism?
Analysis & Theory
Dynamometer-type instruments are commonly used as wattmeters to measure power in both AC and DC systems.
Dynamometer-type instruments can be used for:
Analysis & Theory
They can measure power in both AC and DC circuits since their operation is based on instantaneous values of current and voltage.
The deflecting torque in a dynamometer-type instrument is proportional to:
B
Product of currents in fixed and moving coils
Analysis & Theory
Deflecting torque ∝ If × Im, where If is current in fixed coil and Im is current in moving coil.
In a dynamometer-type wattmeter, which coil is connected in series with the load?
Analysis & Theory
The fixed coil (current coil) is connected in series with the load to carry full load current.
Which coil in a dynamometer-type wattmeter is connected across the supply (parallel to load)?
Analysis & Theory
The moving coil (voltage coil) is connected across the load through a high resistance to measure voltage.
Which damping method is used in dynamometer-type instruments?
Analysis & Theory
Air friction damping is used because eddy current damping is not suitable with non-magnetic coils.
What is the major disadvantage of dynamometer-type instruments?
A
They are expensive and delicate
B
They cannot measure AC power
C
They are inaccurate for DC circuits
D
They generate excessive heat
Analysis & Theory
Dynamometer-type instruments are expensive and delicate due to their complex construction.
The scale of a dynamometer-type instrument is:
Analysis & Theory
The scale is generally non-uniform because the deflecting torque depends on the product of two currents.
Which of the following errors is common in dynamometer-type wattmeters at low power factor?
B
Inductive reactance error
C
Pressure coil inductance error
Analysis & Theory
At low power factor, the inductance of the voltage coil causes phase shift errors in measurement.