Download Electrical Engineering 1

Electrical Circuits and Electronics
Reading (Tu 8:00) – Doc. Ing. Jan Chyský, CSc
Lab. Exercises (Tu 16:00) – Ing. Josef Vlček, CSc
http://elektro.fsid.cvut.cz/en/
Literature:
Chapman Stephen J., Electric Machinery Fundamentals, McGraw-Hill Publishing
Company, 1985, ISBN 0-07-010662-2
Crecraft D.I., Gorham D.A., Sparkes J.J., Electronics, Chapman&Hall 1993,
ISBN 0-412-41320-5
Rizzoni Giorgio, Principles and Applications of electrical Engineering, McGrawHill Publishing Company ISBN 0-256-26116-4
Roadstrum William H., Wolaver Dan H., Electrical Engineering for All Engineers,
John Wiley&Sons, Inc., ISBN 0-471-51043-2
First Part
 Analysis
of Electrical Circuits
(Ohm’s law, Kirchhoff’s laws, loop and
nodal analysis, principle of superposition.
Thevenin’s and Norton theorems. Circuits
supplied by DC and AC. Transient states in
electrical circuits.
Second Part
 Electronics
(Semiconductors, diodes, transistors,
thyristors, operating amplifiers.
Basic analogue and digital circuits)
Electricity at work
National Grid
Serves for distribution of electrical energy
from powerplants to consumers
Distribution Systém
AC and DC electricity
Voltage from batery is in one direction.
Current flows from + lead to – lead
 Voltage on coils terminal when the coil is
turned in magnetic field.

Single and 3 Phase Generator
Delta connection
Star connection
One end of each phase coils
is commonly linked to form
a star or neutral point
Voltage between any phase
line and neutral is 1/sqrt(3)
times that between any two
phases
phase/phase = 400 V
phase/line = 230 V
1
3
Distribution
Circuit protection
Means of isolating supply
Means of protection against
axcess current
Means of protection against
earth leakage
Circuit protection (2)
Fuses and beakers must be
accomodated to load.
For motors should be used
other fuses than for bulbs
Personal protection

Preserve persons to injury by electric
current.
The injury causes current not voltage, but
the voltage causes the current (Ohms law)
I = V/R
System earthing
Earth electrode
 Earthing
conductor
 Protective
conductor

System earthing (2)
System earthing (3)

TN-S systém
Uses separate protective
PE and neutral N
conductor
System earthing (4)

TN-C-S systém
Uses common
protective PE and
Neutral conductor
System earthing (5)

Earth leakage
protection
Safety of work
Basic prescript - Law 50/1978 Sb
Divides persons according their qualification
§3 - Introduced workers
§4 – Instructed workers (students in
universities labotarory)
Both paragraphs are valid for workers without
electrotechnical educations
Safety of work (2)
Terminology
Living parts (hot) serves for current
conducting, or aro under voltage or parts are
conected vith voltage
Non-living are construction parts regulary
without any voltage or current. Due to
concern some voltage or current
may be there there
Safety of work (3)
Incidence of electric curent on body
Safety current
AC 15-100Hz
1 mA
DC
charge
3 mA
0,5 mC
parts which need NOT to be
touch by personal during
function
3,5 mA
10 mA
5O mC
Magnitude of current, when it is
not possible to release hand.
Current
causes
paralysis,
suffocation
>25 mA
>100 mA
----
AC 15-100Hz
DC
Charge
Limited constant current
parts which have to be touch
by personal during function
1 mA
3 mA
0,5 mC
Parts which need NOT to
be touch by personal during
function
3,5 mA
10 mA
5O mC
Magnitude of current, when it
is not possible to release
hand.
Current
causes
paralysis, suffocation
>25 mA
>100 mA
----
Contact voltage Ud
Safety voltage
Area
Normal
Dangerous
Extra dangerous
In contact ( during
handling )
Safety voltage of living (hot) parts [ V ]
AC [V]
DC [V]
living
50
100
non living
50
120
living
25
60
non living
50
120
living
12
25
non living
25
60
Protection against dangerous voltage
1.
Using isolation of living parts



2.
3.
4.
Basic isolation
Suplementary isolation
Double isolation
Using covering
Using barrier
Using position
Protection against dangerous voltage
5.
6.
Additional protection with current
protector
Additional isolation (insulated pads,
glove, etc.)
Protection using automatic
disconnection in TN system

Uses fuse or circuit breaker for
disconnecting power supply