DC machines

· DC machine:

General arrangement of 4- pole motor or generator is as follows.

Each pole core has its own pole tips to support field windings & it will also reduce the reluctance of the air gap.

Here each winding in each pole alternatively stimulate N & S. In the middle there is a iron lamination which used as armature. Laminations are used to reduce the eddy current.

Short transmission lines phaser diagrams

Here sending current is equal to receiving current .But sending & receiving voltages are not equal to due to impedance voltage drop in the transmission line.

Vs=Vr+IZ

Receiving end voltage lag by  angle with respect to sending end voltage. In practical situation step-up and step –down transformer is used at sending end and receiving end of the transmission line as below.

Therefore total impedance can be implemented as Z=Z_T1+Z_L+Z_T2

This can be equivalent to single phase circuit as below and transformer impedance can be assumed as series impedance.

Morderately long lines:

*Transmission lines between 80km and 240km can be assumed under this category.

*These transmission lines represented by T or π.

T-method

Vs=Sending end voltage for single phase

Vr=Receiving end voltage for single phase

Is=Sending end current

Ir=Receiving end current for single phase

Z=R+jX

Y=G+jB

G=leakage conductance per phase

B=Capacitive susceptance

π-method

Normally moderately long lines leakage may also be ignored. Therefore Y=G+jB=jwc0

W=Radian frequency of the power supply

C0=Capacitance to neutral of the transmission line.

Long lines:

*Te lines beyond 240km can be named as long lines.

*In Sri lanka, long lines cannot be seen yet!

*In long lines impedance & admittance assumed uniformly distributed.

Basics of power systems

Short lines:

*Transmission lines which are up to , 80km can be classified as short lines.

*Here capacitance & leakage may be ignored !

*This transmission can be 1ø or 3ø .

Introdution to power systems

Electrical Power Systems

Power system engineering is special branch of electrical engineering. Power engineering can be mostly touch with transmission, distribution &technology.

The special responsibility of a power system is that, in addition to maintain the generation of electrical power at adequate level, the power has to be transmitted to the various load levels.

Power system engineer should have a knowledge regarding the operation & control of inter connected power systems, specially when inter connecting the local grid to form an integrated power pool.

Power engineering never falls down, because of energy crises all over the world. But lots of connecting problems , energy (voltage) converting problems , & planning operation problems may occur in the field while working.

There are three major classification in transmission lines.

1. Short lines
2. Moderately long lines
3. long lines