Inductors and Capacitors in Circuits #1
How many time constants does it take for an inductor to reach maximum steady state value of current?
5
By what percentage does capacitor voltage increase every time constant when a constant voltage is applied to it?
63.2%
The iron losses in an AC circuit are made up of what 2 elements
Eddy currents and hysteresis effects
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 is the formula to calculate a time constant for an inductor?
T = L/R
What is the formula to calculate a time constant for an capacitor?
T = RC
What 3 factors affect impedance?
Resistance, inductive reactance, capacitive reactance
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
What device can be connected in an inductive circuit to mitigate damage due to voltage spikes when the circuit is opened?
Discharge resistor
What is the phase relationship between I and V in a capacitor?
I LEADS V by 90 degrees
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 what type of field is reactor power due to inductance stored?
Electromagnetic
In what type of field is reactor power due to capacitance stored?
Electrostatic
What is the phase relationship between I and V in an inductor?
I LAGS V by 90 degrees
What do the open and closed arrowheads represent in a phasor diagram?
Closed - current
Open - voltage
In what 2 forms can phasors be expressed?
Polar form eg. 5V @ 36.9 degs
Rectangular form eg. (4V, 3V)
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
What is the inductive reactance of a 450mH coil if it is connected to a 100Hz supply?
2(pi)(f)(L) = 2(3.14)(100)(0.45) = 282.74 ohms
What value of capacitor has a capacitive reactance of 10 ohms when connected to a 60Hz supply?
C = 1/[2(pi)(f)(Xc)] = 1/[2(3.14)(60)(10)]
= 0.000265F OR 265 uF
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.
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