Electrical Basics:

This site(www.completepowerelectronics.com) is mainly for discussing about various power electronics topics. Various power electronics topics are discussed in detail in various posts & pages. But it is highly important and essential to be strong in fundamentals. This page and following pages will serve as a reference guide while reading advanced topics. Say for an example, after completing your masters in Power Electronics and Drives if you are going for an interview then you can not expect questions only related to power electronics topics. You may be face electrical basics questions like electrical laws also.

In addition to the fundamentals of electrical, we had given sets of interview questions and Objective questions related to the power electronics field. These self test materials will indicate our familiarity with the topics.

Electricity:

Electricity is a very convenient form of energy. It is relatively easy to produce

in bulk in power stations whether they be coal-fired, oil-fired or nuclear (using

steam turbines to drive the generators) or hydro (using water turbines to drive

the generators).

Energy sources

There are two basic variables in electric circuits, namely electric current and electric potential difference (which we will often call voltage for short). A source of energy is required to cause a current to flow and thereby to produce electric voltages in various parts of the circuit.

Voltage source

An ideal voltage source is independent of the current through it. Its electromotive force (emf) or voltage is a function of time only. If a thick copper wire were connected across its ends the current through it would be infinite. The symbol for an ideal voltage source is shown

Current source

An ideal current source is independent of the voltage across it and if its two

ends are not connected to an external circuit the potential difference across it

would be infinite. The symbol for a current generator is shown

Resistivity

The resistance of a conductor is directly proportional to its length (l) and

inversely proportional to its cross-sectional area (A). Mathematically then

R ≈ l/A. This may also be written as

R = ρl/A

where ρ is the constant of proportionality and is called the resistivity of the material of the conductor. The unit of ρ is therefore the ohm-metre. Sometimes it is convenient to use the reciprocal of resistance which is called conductance (G) for which the unit is the siemens (S).

conductance (G): It is measure of material's ability to allow the flow of charge.

Alternating Current: It is the current in which the magnitude and direction vary periodically.

Cycle: One complete set of change in value and direction of alternating quantities is called as cycle

Period: It is the time taken to complete one cycle. The symbol is T

Frequency: The number of cycles completed per second is known as frequency of the alternating current. The unit is Hertz (Hz). f=1/T

Instantaneous value: The value of an alternating quantity at a particular instant in a cycle is called instantaneous value.

Peak value: The maximum value of an alternating quantity during a cycle is called its peak value

Phase: The developement of an ac quantity through different stages as known as phase

In-phase: When two alternating quantities reach their maximum and minimum value simultaneously, then these quantities are said to be in-phase

Out-of-Phase: When two alternating quantities do not attain their maximum and minimum values simultaneously then they are at out of phase. It is also known as phase difference.

Phase angle: It is an angular displacement between two alternating quantities.

Average Value: The arithmetical average of all the values of an alternating quantity over one cycle is called average value.

Average Value = Area under the curve/ Base (period)

Root Mean Square Value (RMS Value)

The rms value of an alternating current is defined as that steady current which when flowing through a given resistance for a given time produces the same amount of heat as produced by the alternating current when flowing through the same resistance for the same time. It is also known as effective value of an alternating current.

I_{RMS} = √[Area under the squared wave/ Period]

Form Factor:

The ratio of RMS value to average value of an alternating quantity is called form factor

Form factor = RMS value/ Average value

Peak Factor:

The ratio of maximum value to the RMS value of an alternating quantity is called as peak factor

Peak factor = Maximum value/ RMS value