ELECTRICAL SERVICES - Lecture -1
Topics to be Discussed
Basic Principles and Laws :
OHM’S LAW-
V=IR
(If the physical conditions remains same )
CONCEPT OF RESISTANCE –
R= Գ ( l / a )
Effect of Temperature on Resistance …?
(Գ- Specific resistance of the material )
BASIC SERIES AND PARALLEL CIRCUITS.
Series circuits - R= r1 + r2 + r3+ r4+…………
( current remains constant in the circuit )
Parallel circuits – 1/R = 1/r1 + 1/r2 + 1/r3
+……..
( Voltage remains constant in the circuit )
CONCEPT OF VOLTAGE DROP.
Ohm's Law can be used to verify voltage drop. In a DC
circuit, voltage equals current multiplied by
resistance. V = I R. Also, Kirchhoff's circuit laws state that
in any DC circuit, the sum of the voltage drops across
each component of the circuit is equal to the supply
voltage.
VOLTAGE, POWER, AND ENERGY
RELATIONSHIP.
E= P t
( Unit of energy – Watt Hour)
For electrical energy consumption measurement
One Unit energy = 1000watt x 1 hour = 1Kwh
VOLTAGE, POWER RELATIONSHIP.
P= VI ( for DC circuits )
P= VI Cos Ø ( for AC circuits )
P= I² R
(we consider it to calculate heating effect in
conductors)
CONCEPT OF DC & AC
Faraday's law of induction is a basic law of
electromagnetism that predicts how a magnetic
field will interact with an electric circuit to produce
an electromotive force. This relationship is known
as Faraday's law of induction. The units for EMF
are volts
????
- Induced EMF
N - Number of turns in coil
Ø - Change in magnetic flux
t - Change in Time
Classification of voltage
Upto 250 volts
–
Low voltage or LT
251 – 650 volts
-
Medium voltage
651- 33 kv
-
High voltage or HT
Above 33 kv
-
Extra high voltage
Concept of Single Phase and 3 phase
Generation
Transmission and
distribution of electrical
power

Generation at 11 kv

Transmission up to 800 kv

Distribution 33 kv – 11 kv

Distribution in our colonies –
3 ø, 415 v, 4wire 50 hz
1 ø, 230 v, 2 wire 50 hz

Tolerance in voltage up to ± 5%
228 – 252 volts 1 ø
394.25 – 435.7 volts 3 ø

Voltage of 3 ø = √3 x voltage of 1 ø

Wires used for distribution lines
ACSR - Aluminium conductor steel
reinforcement
ABC - Arial bunch conductor
Assignments for Today1. Write down the basic Laws of Electricity mentioned Below in your own Hand
writing with neat sketches on A-4 paper.
1. OHM’S LAW
2. CONCEPT OF RESISTANCE.
3. BASIC SERIES AND PARALLEL CIRCUITS.
4. CONCEPT OF VOLTAGE DROP.
5. VOLTAGE, POWER, AND ENERGY RELATIONSHIP.
6. FARADAY’S LAW OF ELECTROMAGNETIC INDUCTION.
1. Draw the electrical symbols provided in pdf form on Half cartridge sheet or
A-3 paper. ( Symbols of article-1.2.13- 1.2.19 and similar symbols from
National Building Code or Indian Electricity Code )
THANK YOU.