bt 224 resistance and capacitive ccts Flashcards
what do sine wave diagrams do
help visulize the relationships between AC voltages and currents
what do phasor diagrams represent
quantities and phase relationships
what is one cycle of a sine wave
360 degrees
current through a pure inductance _______ rhe voltage across it by 90 degrees in ac ccts
lags
current in a capacitance _______ the voltage across it by 90 degrees in ac ccts
leads
what is impedance
The total opposition to current flow. (Z)
equation for impedance
Z= E divided by I
Energy is the ability to ____________
do work
What is power
The rate at witch energy is transferred from one system to another.
What is the SI unit of energy and power
-joules
-watts (joules/second)
In AC systems how often does current change directions
every half cycle
How are AC loads classified as and what do they do.
-Active loads do real work
-reactive loads store the energy they recieve and return it within the same AC current cycle
What is Active power
-called true power
-the rate of net energy transfer through the cct.
-measured in Watts
What is reactive power
-rate energy is circulated betweeb the reactive load and the supply
-Measured in VARS
-doesnt do “work” so cant be in watts
-inductive or capacitive
what is apparent power
-measured in volt-amps (VA)
-indicates how close a cct is operating capacity without considering how much load is active or reactive.
- = volts x amps
what is power factor. how to calculate
- ratio of active power to apparent power
-cct capacity being used to do work compared to total cct capacity in use. - PF= Watts divided by VA
Define energy and power
energy-ablity to do work
power- rate work is being done
What is the SI unit for energy?
Joules
What is the SI unit for power?
Watts
What unit is used for energy by North American electrical suppliers?
kW/hr
In what basic way is a reactive load different from an active load?
circulating energy not doing any actual work
Equation for watts
W= voltage x IR
equation for VARS
E x I xl
E x I x sin<0
Equations for VA
E x It
E x I
when inductors and capacitors are connected in // their ccts are _________ degrees out of phase
180
When a // cct contains both inductive and capacitive loads, each load draws the same _________ as if was alone on the RLC cct
current
The ac current that ciculates between the coil and the source __________ 90 degrees. as a result these ccts are ________ degrees out of phase
lags
180 degrees
can you connect a coil in series with a capacitor
no
When inductive and capacitive current are equal what will happen to the current
all the reactive power will circulate within the cct and there is no reactive demand on the suppy
In AC systems how often does the current change directions
every half cycle
A capacitive power wave is _______- degrees out of phase with the inductive power wave
180
A capacitor that is out of phase with an inductor takes in energy at the exact same time the inductor is ______________ to the cct and vise versa
returning it
What happens when voltage and current are in phase
-power wave is all positive
-All enrgy carries by the cct is used by active power loads
-when the current is 90 degrees out of phase the cct carries the energy that circulates between a reactive load and its source of current
what happens when the phase angle falls between 0-90 degrees
-positive portion of the power wave is larger then the negative portion
-cct carries active and reactive power
-active power is = to the difference between the positive and negative waves
-the reactive power is the negative side of the wave plus a matching portion of the positive side
What does the power wave represent
the rate that energy is delivered through the cct and thr direction the enrgy is moving
when a cct contains resistance, inductive and capacitance in // the opposite side of the current trangle is the _________________________
total reactive current
What does an impedance triangle do
summarizes the relationships between series resistance and reactance and provides a method for calculating impedance and phase angle
Where does the oposition to current come from in a cct
volt drop that is across the loads
When 2 or more loads are connected in // across a supply how does each load draw current
independantly
when 2 or more loads are connected in series across a supply when will the current rise
-rises until the total volt drop is equal to the applied voltage and 180 degrees out of phase
what happens when you connect coils and capacitors in series
its dangerous
When inductors and capacitors are connected in // their current are _______ out of phase
180 degrees
what is parallel resonance
if the capacitance or inductance can be adjusted, the cct current will be minimum when the 2 reactances are perfectly matched
what happens in a cct at parallel reasonance
-supply provides only in-phase resistive current
-phase angle is 0
-cct current is at a minimum
-impedance is at a maximum
What is series reasonance
-if the inductive and capacitive reactances can be adjusted, the current will be at maximum when they are perfectly matched.
What happens in a series cct at series reasonance
-impencance is low
-current and volt drops are high
-phase angle is 0
