Course 07001

Where can power factor correction can be done?

• Load or service

• Lowering the voltage

• Start of a circuit

• Using a serge protector

Answer explanation

Power factor correction can be effectively done at the load or service level, where the reactive power is generated or consumed. This helps improve the overall efficiency of the electrical system.

Power factor is the relationship between

• ST and PT

• ST and QT

• VAR and VA

• Power consumed and power wasted

Answer explanation

Power factor is defined as the ratio of real power (ST) to apparent power (PT). It indicates how effectively electrical power is being converted into useful work output.

A motor load produces what type of power

• Apparent power

• True power

• Wasted power

• Heat power

Answer explanation

A motor load primarily converts electrical energy into mechanical energy, which is considered true power. Apparent power includes both true power and reactive power, while wasted power and heat power are not the main outputs of a motor load.

When a motor load increases the inductive part.

• Stays constant

• Increases

• Decreases

• Magnetic field

Answer explanation

When a motor load increases, the inductive part of the load stays constant because the inductance is a property of the motor's windings, which does not change with the load applied.

In power factor correction the capacitor is connected_________________ with the motor

• Parallel

• Series

• Series parallel

• In phase with the motor voltage

Answer explanation

In power factor correction, capacitors are connected in parallel with the motor to improve the power factor by compensating for reactive power, thus reducing the overall current drawn from the supply.

Calculate the capacitor branch circuit current where the capacitance is 100uf connected to a 120V 60hz supply.

• 4.7A

• 47A

• 4.7 ohms

• 4.7 W

Methods of power factor correction

• Using a capacitor

• Using a synchronous motor

• Using a capacitor bank

• All of the above

Answer explanation

All the listed methods—using a capacitor, a synchronous motor, and a capacitor bank—are effective for power factor correction. Therefore, the correct answer is 'All of the above'.

When Inductive reactance is equal to capacitive reactance

• The current will increase

• The current decreases

• Voltage decrease

• The capacitor will explode

Answer explanation

When inductive reactance equals capacitive reactance, the circuit is at resonance, allowing maximum current to flow. Thus, the correct answer is that the current will increase.

There is a 10 ohm , 20 ohm and 40 ohm resistors connected in series. Find Rt

• 15 ohms

• 70 Amps

• 70ohms

• 7.5 ohms

Answer explanation

To find the total resistance (Rt) in a series circuit, sum the individual resistances: Rt = 10 ohm + 20 ohm + 40 ohm = 70 ohm. Therefore, the correct answer is 75 ohms.

In the diagram above fin the power factor of the motor.

• 0.414

• 1

• 0.7

• 2

Answer explanation

The power factor is calculated as the cosine of the phase angle between voltage and current. In this case, the given value of 0.414 indicates a lagging power factor, which is typical for motors, confirming it as the correct choice.