Pengantar Teknik Elektro

Kuliah 2 : Basic Electrical Quantities

Why Are There Three Conductors in Power Transmissions Lines?

Most AC power transmission systems have three conductors.The voltage on each phase (referenced with respect to earth ground) is a sinusoid with a phase difference of 120° from the voltages in the other two phases.

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Three Phase

A three conductor transmission system is called a three-phase system.The power delivered by a three phase system (assuming a balanced load) is constant, even though the voltages in each phase vary sinusoidally.Three phase systems are more efficient than single systems due to reduced power losses.

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Topics

Introduction (1 session)Basic Electrical Quantities (1 session)Circuit Analysis (2 sessions)Introduction to Electromagnetism (1 session)Introduction to Electronics (1 session)Introduction to Digital Logic Circuits (1 session)Introduction to Digital Information (1 session)Introduction to Computer (1 session)Introduction to Telecommunication (1 session)Introduction to Control (1 session)Introduction to Power Systems (1 session)Introduction to Photonics (1 session)Review (1 session)

Basic Concepts

System of Units

System of Units

More Units

Charge and Current

Basic Quantities

Basic quantities are voltage, current, and power.The sign convention is important in computing power supplied by or dissipated by a circuit element.Circuit elements can be active or passive; active elements are called sources.

Current

Types of Current

AC versus DC

AC is alternating currentAC quantities always vary sinusoidally in timeUsually, we will know the frequency and solve for the amplitude and phase.

DC is direct currentDC quantities are always constant in time.DC can not be directly transformed to lower or higher voltages.

Current Range

Voltage

Voltage Range

Representation

Example

Sign Convention

Power

Passive Sign Convention

Positive Power

Negative Power

Example

Energy

Example

Which circuit element is supplying power?Which is dissipating power?How much is supplied/dissipated?

Power plant

+

-220V

10A

What is inaccurate about this example?

Example

How much power is supplied/dissipated?

Power plant

+

-

14.14 cos(50 2πt) A

311.13 cos(50 2πt) V

Let’s Use MATLAB!

Start MATLAB

t=0:0.0005:0.1;v=311.13*cos(2*pi*50*t);plot(t,v)i=14.14*cos(2*pi*50*t);plot(t,i)p=v.*i;plot(t,p)sum(p)/201