ČVUT FEL Praha – Katedra elektrických pohonů a trakce ESEM1/ 1 ELECTRIC CURRENT AND ITS EFFECTS ELECTRIC CHARGE AND CURRENT VOLTAGE, CURRENT, RESISTANCE MATERIALS DIRECT CURRENT AND ALTERNATING CURRENT CURRENT EFFECTS IN HUMAN BODY SAFETY AND FIRST AID

ČVUT FEL Praha – Katedra elektrických pohonů a trakce ESEM1/ 2 CHARGE AND CURRENT atoms can lose and accept electrons elementary charge = - 1, C ampere – A; coulomb – C; second - s THE MASS IS ELECTRICALLY NEUTRAL ELECTRIC CURRENT IS THE MOVEMENT OF CHARGE

ČVUT FEL Praha – Katedra elektrických pohonů a trakce ESEM1/ 3 DIRECT CURRENT - DC CHARACTERISTICS: sense of current flow is constant CONVENTION: positive sense is from + to - Instantaneous value i(t i ) Mean value I

ČVUT FEL Praha – Katedra elektrických pohonů a trakce ESEM1/ 4 ALTERNATING CURRENT - AC CHARACTERISTICS: sense of current flow changes mean value during T = zero changes repeat periodically CONVENTION: positive sense is from + to - Instantaneous value i(t i ) Peak value (amplitude) I max RMS (root-mean-square) value I

ČVUT FEL Praha – Katedra elektrických pohonů a trakce ESEM1/ 5 MEAN VALUES - average hertz – Hz; second - s

ČVUT FEL Praha – Katedra elektrických pohonů a trakce ESEM1/ 6 MEAN VALUES – equivalent DC hertz – Hz; second - s

ČVUT FEL Praha – Katedra elektrických pohonů a trakce ESEM1/ 7 MEAN VALUES – harmonic current hertz – Hz; second – s

ČVUT FEL Praha – Katedra elektrických pohonů a trakce ESEM1/ 8 RMS VALUES

ČVUT FEL Praha – Katedra elektrických pohonů a trakce ESEM1/ 9 VOLTAGE,CURRENT,RESISTANCE voltage U – volt – V current I – ampere – A resistance R – ohm –   = resistivity (also in  cm or  mm 2 /m) (  ;  m,m,m 2 ) TCR = temperature coefficient (former  )

ČVUT FEL Praha – Katedra elektrických pohonů a trakce ESEM1/ 10 MATERIALS INSULANTS (dielectric) –  >  m Ideal = vacuum. In industry for example mica, glass, silk, transformer oil, nitrogen etc. SEMI-CONDUCTORS –  = 10 to  m Several chemical compounds and elements - Se, Ge, Si. With increasing decreases R. CONTUCTORS –  = to 10  m Mostly used = metals. With increasing rises R. ACCORDING TO FREE CHARGES TRANSFER:

ČVUT FEL Praha – Katedra elektrických pohonů a trakce ESEM1/ 11 EFFECTS OF CURRENT THERMIC LIGHTING CHEMICAL MAGNETIC FORCE PHYSIOLOGICAL COOKERS TUBES ELECTROLYSI S MOTORS THERAPY COILS

ČVUT FEL Praha – Katedra elektrických pohonů a trakce ESEM1/ 12 PHYSIOLOGICAL EFFETCS Effects of current flow through living organism, especially human body. Medical treatment Electric current accidents DC current decomposes body cells, causes heavy body burns, can also harm heart activity. AC current – depends on frequency – 50 to 60 Hz causes muscle contraction and heart spasm.

ČVUT FEL Praha – Katedra elektrických pohonů a trakce ESEM1/ 13 ACCIDENTS HAZARD IS ALWAYS CAUSED BY CURRENT FREQUENT ACCIDENTS: shock burns cramps stopped breathing stopped heart activity FACTORS: touch voltage and environment conditions time of duration body resistance – over skin  Treshold of perception: 1 – 3 mA, let-go limit: 10 mA, fibrillation limit: 35 mA

ČVUT FEL Praha – Katedra elektrických pohonů a trakce ESEM1/ 14 PROTECTION KNOWLEDGE (rules, standards …) and CAUTION INJURY IS NOT CAUSED BY: Safe current (according ČSN IEC 479 ( )) PERMISSIBLE TOUCH VOLTAGE ČSN (usual condition – DC 120 V, AC 50 V permanent) TECHNICAL MEASURES: INSULATION PROTECTIVE MEANS CONNECTION, CONSTRUCTION, PLACEMENT

ČVUT FEL Praha – Katedra elektrických pohonů a trakce ESEM1/ 15 BASIC FIRST AID SET AFFLICTED PERSON FROM THE RANGE OF CURRENT TREATMENT OF SECONDARY INJURIES ARTIFICIAL RESPIRATION INDIRECT HEART MASSAGE ALWAYS CALL DOCTOR RENDER FIRST AID TREATMENT TILL THE DOCTOR COMES

ČVUT FEL Praha – Katedra elektrických pohonů a trakce ESEM1/ 16 Example 1a SINE WAVE CURRENT FIND PEAK VALUE MEASURE RMS VALUE ? RELATION BETWEEN PEAK AND RMS VALUES ? INFLUENCE OF FREQUENCY signal generator osc. measuting instrument

ČVUT FEL Praha – Katedra elektrických pohonů a trakce ESEM1/ 17 Example 1b RECTANGULAR WAVE CURRENT FIND MEAN VALUE FIND RMS VALUE ? EFFECT OF THE FORM OF RECTANGLE

ČVUT FEL Praha – Katedra elektrických pohonů a trakce ESEM1/ 18 Example 1c RECTANGULAR CURRENT WITH DC OFFSET FIND MEAN VALUE FIND RMS VALUE ? ARE THERE SOME DIFFERENCES IN VALUES CALCULATED BY MEANS OF DISCUSSED EQUATIONS