Understanding Electrical Measurements in Mechanics and Electricity

1. Anglicky v odborných předmětech"Support ofteachingtechnicalsubjects in English“ Tutorial :Mechanic - electrician Topic: Electricalmeasurements the 2nd. Year Performance measurementDC, AC 1f Prepared by: Ing. Jiří Smílek Projekt Anglicky v odborných předmětech, CZ.1.07/1.3.09/04.0002 je spolufinancován Evropským sociálním fondem a státním rozpočtem České republiky.

2. Power Output • Work is a physical quantity. • Designation – W- el. work (energy) - A –mechanical work • Unit - 1J = 1 W.s(electrical ) joule (symbolJ) - other • Power outputequals work done in one second. • Designation - P • Unit - watt (symbolW). • Power outputequals work done in one second P=W/t (W;Ws,s) • Electrical power output– electrical power current I at a voltage U • P=U.I • Unit- watt (symbolW).

3. Types of power • Direct current power output- DConly active • P=U*I, Unit- W - watt • Using Ohm’s law I=U/R (U=RI, R=U/I) • P=RI2 • P=U2/R • Alternating current power output- AC • 1 f - single-phase • apparent S=U*I , • unit – V.A – volt-ampere • active P=U*I*cos φ, • unit- W - watt • idle Q=U*I*sin φ, • unit- var – volt-ampere • reactive

4. Types of power • 3 f - three-phase • apparent S=√3U*I • active P=√3U U*I*cos φ • idle Q=√3U U*I*sin φ

5. Types of power • Power output P – common name • Powerappliances P1 – power output, which the appliance consumes – the motor voltage and current • Power outputappliancesP2– power output, which the appliance puts out – the motor speed and torque Powerinput(100 %) Power output(85 %) • Supplied power power put out • P1 = P2 + ΔP P2= P1 - ΔP

6. Types of power • Loss of power- ΔP=P1-P2 - Unit W • The engine heat • Efficiency η=P2/P1 . 100 - Unit% Powerinput(100 %) Power output (85 %) • Supplied powerpower put out • P1 = P2 + ΔP P2 = P1 - ΔP • Loss of power (15 %) • ΔP = P1 – P2

7. Measurement of DC power output • DC – direct current power output • Measurements using the method: • indirect – voltmeter and ammmeter • RV – internal resistance of the voltmeter • RA – internal resistance of the ammeter a) I = IA , U = UV – UA = UV - RA . IA b) U=UV , I = IA – IV = IA - UV / RV P = U . I = UV . IA - RA . IA2 P = U . I = UV . IA - UV2 / RV RA << R RV >> R

8. Measurement of AC power output1 f • AC – Alternating current power output • Measurements using the method : • direct – wattmeter, • To check using a voltmeter and ammeter • With the current coil voltage • Actual power output Ps • PS = P – RAI2 – RWAI2 • RWA – coil current resistance meter

9. Measurement of AC power output1f • AC – Alternating • Measurements using the method: • direct – wattmeter, • To check using a voltmeter and ammeter • With the current coil voltage • Actual power output Ps • PS = P – U2/ RV– U2RWU • RWU – coil resistance voltage meter

10. Activities for students - questions • Name the types of power output: • d) • e) • f) • Explain what power input is • Explain how you prove a loss of power • Write how to calculate the motor efficiency

11. Activities for students - questions • How can you overload: • A current coil wattmeter, • A voltage coil wattmeter • Two coils, • Even when the hand shows deflection within the scale?

12. Bibliography • Mužík, J. Management ve vzdělávání dospělých. Praha: EUROLEX BOHEMIA, 2000. ISBN 80-7361-269-7. • Wikipedie • Příručka elektrotechnika, Europa 2000 • Elektrické měření - E. Viteček, Vl.HOS - SNTL 1978 • Elektřina kolem nás – Zdeněk Opava – Albatros 1981 • Operační program Vzdělávání pro konkurenceschopnost, ESF 2007 – 2013. • Available at: http://www.msmt.cz/eu/provadeci-dokument-k-op-vzdelavani-pro-konkurenceschopnost