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, McGraw Hill 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 DC charge 1 mA

parts which need NOT to be touch function by personal during

Magnitude of current, when it is not possible to release hand.

Current suffocation causes paralysis,

3,5 mA

>25 mA 3 mA 10 mA 0,5 m C 5O m C >100 mA ----

AC

15-100Hz DC Limited constant current parts which have to be touch by personal during function

Parts which need NOT to be touch by personal during function

Magnitude of current, when it is not possible to release hand.

Current paralysis, suffocation causes 1 mA

3,5 mA

>25 mA 3 mA 10 mA >100 mA Charge 0,5 mC 5O mC ----

Contact voltage U

d

Safety voltage

Area Normal Dangerous Extra dangerous In contact ( during handling ) Safety voltage of living (hot) parts [ V ] living non living living non living living non living AC [V]

50 50

25

50

12

25

DC [V] 100 120 60 120 25 60

Protection against dangerous voltage 1.

2.

3.

4.

   Using isolation of living parts 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