Rlc Flashcards
Only use R ( resistance ) in DC circuit when calculating current
Yes!!!!!! I = E/R
Current = volts divide resistance
Only use (z) impedance in AC CIRCUIT when calculating current
I=E/Z
Current = volts divide impedance
Power factor equation
Pf= watts/VA
Watts(true power) divide by apparent power (VA)
What is AC effective resistance
Dc ohmic value plus shred effects on conductor = AC EFFECTIVE
How to test AC EFFECTIVE RESISTANCE
Wattmetre and ammetre
Bc hydro adds surcharge for anything that operates under what % power factor
90%
Impedance = AC OR DC?
Impedance ONLY in AC!
Impedance (z)
I = e/z
Resistance AC or DC?
Both but when calculating current only in DC use resistance
I = E/R
On right triangle what goes on hypotenuse (3 values )
Voltage
Apparent power
Impedance
On triangle what goes on adjacent ( 3 values)
Resistance (ohms)
True power (watts)
Er (volts resistance)
On triangle what goes on opposite (3 values)
Reactance (XL)
Reactive power (RP)
Volts across Reactance (Exl)
What do we not use in AC when calculating current?
Do not use resistance! Only impedance (z)
Point in sin wave where rate of change is greatest?
0 and 180 degrees
Point in sinwave where rate of change is least?
90 and 270 degrees
Inductance only effects cct when magnitude of _______ is changing
Current
In DC current only changed when what?
Switch open or closed
In AC current changes when
It’s always changing magnitude and direction through fill sinewave
It’s always changing magnitude and direction through fill sine wave
What is pure inductive circuit?
Only quantity in circuit is inductance (no resistance)
Triangle is straight line = opp/hyp are equal
What is pure resistive cct?
Only resistance and all power and voltage is dissipated by resistor (light/heater/toaster)
Triangle is straight horizontal line = adj and hyp are equal
Phase angle between current and voltage in resistive cct
0 (both in phase with each other)
Phase angle between current and voltage in inductive cct?
90 degrees ( current lags voltage by 90)
Phase angle if cct has resistance and inductive reactance?
Between 0-90 degrees. Needs to be calculated
Opposition to current in purely resistive cct?
Resistance
Opposition to current in purely inductive cct?
Inductive reactance
What is inductive reactance directly proportional to?
Frequency and inductance
More resistance in a cct what happens
More resistance = current and voltage come more in phase with each other
Impedance (Z) is a combination of what?
Resistance (R) and inductive reactance (XL)
What types of power to practical inductors produce?
True power and reactive power = 90degree out of phase
Apparent power (VA) combination of ..?
True power (watts) and reactive power (VAR)
Another name for Q factor?
Figure of merit
What is Q factor measurement of
Energy wasted- rate of dissipation
Q factor is directly proportional to what?
Frequency of ac supply
When voltage is POSITIVE and current is NEGATIVE power will be?
NEGATIVE POWER
When voltage and current are both positive or negative we get what power?
POSITIVE power
Another term for reactive power?
Wattless power
Why are VAR’s called lagging VAR’s
VAR lags behind voltage inductive cct
What does wattmeasure measure
True power in watts. It’s a combination of voltmeter and ammeter p= I X E
Voltage coil connected in_______
Ammetre connected in __________
Volt = parallel with load
Ammetre = series with load
What power factor will purely resistive cct have?
100% power factor and phase angle of 0
What power factor will purely inductive cct have?
Power factor 0% and phase angle of 90
Heat loss is a form of what power?
True power and can be measured in watts
1hp =
1hp =746 watts
1hp =0.746 kW
Inductance in series in parallel =
Same as resistance. Adds in series/ adds inversely in parallel
Capacitance in series and parallel?
Opposite of resistance = series adds inversely / parallel = adds up
As inductance decreases what happens to current?
It increases! Inversely proportional
Inductance decreased what happens reactance ?
It decreased also ( directly proportional)
Inductance and inductive reactance are directly proportional T/F
True!
Current and impedance are inversely proportional T/F?
True
What two factors vary change in inductive reactance?
Frequency and inductance of coil
Adding inductors in parallel = what happens to total inductance?
Total inductance halves
Reactance halves
Adding inductors in series= what happens to inductance?
Total inductance doubles
Reactance doubles
Inductor ELI means?
Voltage leads the current
E leads I
Capacitor ICE means
Current leads voltage
I leads E
Inductive reactance is directly proportional to frequency T /F
True as frequency goes up, inductance goes up
Capacitive reactance is Directly or inversely proportional to frequency?
Inversely proportional. As frequency increases, capacitance decreases
What is resonant frequency?
The point on sine wave in a AC series circuit where inductive reactance and capacitive reactance cancel each other out
In a purely capacitive cct voltage lags current by what angle?
90 degrees
In purely inductive cct current lags voltage by what angle
90 degree
Voltage has no effect on reactance true or false?
True!
Capacitance in farads ‘c’ add inversely BUT XC add straight up in series… T/F
True! Only add farads inversely use XC to add straight up
True power and frequency are
