Principles of AC Circuits #1
The iron losses in an AC circuit are made up of what 2 elements
Eddy currents and hysteresis effects
A circuit property that has the ability to oppose a change in current is known as?
Inductance
What type of power is calculated as work divided by time? True, reactive or apparent?
True power
What is the definition of power?
The rate at which work is being done OR the rate at which energy is converted from one form to another
eg. when heat, light or mechanical motion is being produced
A resistor is doing 6000W of work when connected to a 120V AC. What is the current flowing through the circuit?
I = P/V = 6000/120 = 50A
What 3 factors affect impedance?
Resistance, inductive reactance, capacitive reactance
What circuit property is calculated by dividing the AC circuit voltage by the circuit current?
Impedance
What circuit property results in heat dissipation?
Resistance
Name 2 other terms that can be used when referring to real power
Active power, in-phase power, true power, power
What are the 3 types of power in an inductive circuit?
True power, reactive power, apparent power
You are given a right angle triangle. The opposite and adjacent sides measure 6 and 8. What is the length of the hypotenuse?
6^2 + 8^2 = 36 + 64 = 100
Square root of 100 = 10
In a phasor diagram, what does the length of the line indicate?
Magnitude of the phasor
What is power factor a ratio between?
P/S
Power to apparent power
In what type of field is reactive power due to inductance stored?
Electromagnetic
In what type of field is reactor power due to capacitance stored?
Electrostatic
In what 2 forms can phasors be expressed?
Polar form eg. 5V @ 36.9 degs
Rectangular form eg. (4V, 3V)
If V1 is at 280 degrees and V2 is at 200 degrees, which phasor is leading and by how many degrees?
V1 leads by 80 degrees
What is the phase angle in a purely resistance circuit?
0
What is the relationship between power factor and theta?
PF = cos theta
If the VARS of a motor is greater than its power dissipation, would the PF be greater or less than 0.707?
Less since theta is more than 45 degrees
Describe the steps you would take to add 2 phasors
Break each phasor into X and Y components. Add the X components together and the Y components together. With the cumulative X and Y values, calculate the new resultant phasor using Pythagoras.
What must be the same between 2 AC voltages (from 2 different sources) for the phase displacement between them to remain constant?
Frequency
In a power triangle, Q = 100 and P = 75. Is the phase angle more or less than 45 degrees?
More
A coil is connected to an AC supply and has a resistive volt drop of 65V while the reactive volt drop is 40V. What is the applied voltage and the phase angle in degrees.
Pythagoras - applied voltage is 76.32V
Theta = 31.61 degrees
A single-phase motor is operating on a 240VAC circuit. When the motor is fully loaded, it draws a current of 3.2A at a PF of 0.8 lag. Calculate S, P and Q.
S = E x I = 240x3.2 = 768 VA
P = S x PF = 768 x 0.8 = 614.4 W
Q^2 = S^2 - P^2 = 460.8 VAR