Quiz 1 Flashcards
What is impedance? + formula
Reactance (X) together with resistance (R) with help of complex number (j) “forms” impedance (Z)
Z = R + jX
Unit: Ohm
What is reactance? + formula
The capacitance and inductance in a component can be
modelled as reactance (X_C or X_L) is like a resistance equivalent
and can be handled like a resistance but with a shift in time (the shift can be seen as 90º)
X = X_L + X_C
Unit: Ohm
What is capacitance? + formula
A capacitance is a property that is working against changes in the
voltage (u-kurvan hamnar efter i-kurvan => -j)
C, unit: F (Farad)
X_C = 1 / (2pif*C)
(this formula => unit Ohm)
What is inductance?
An inductance is a property that is working against changes in the
current (u-kurvan hamnar före i-kurvan => +j)
L, unit: H (Henry)
X_L = 2* pi * f * L
(this formula => unit Ohm)
Från rektangulär till polär form:
sqrt(Re^2 + Im^2) < atan(Im/Re)
What is power factor?
cos(𝜑), where 𝜑 is the angle between voltage and current (angle always positive)
What does it mean if PF leading?
capacitive
What does it mean if PF lagging?
inductive
Which motor is better for low rpm?
Synchronous
Which motor is not self-starting?
Synchronous
Which motor is best when not running all the time?
Asynchronous
How to calculate apparent power with power factor?
S_ph = P_ph/cos(p)
(in a phase for example)
unit: VA
Q unit?
VAr
Reactive power
How to calculate current magnitude from power?
I_ph = S_ph/V_ph
