Tutorial: Mechanic - electrician Topic: Basics of electrical engineering the 2nd. year Measuring the capacity Prepared by: Ing. Jiří Smílek Projekt Anglicky v odborných předmětech, CZ.1.07/1.3.09/ je spolufinancován Evropským sociálním fondem a státním rozpočtem České republiky.

 Definition of units of capacity The basic unit - 1 F (farad) 1 farad is the capacity of an electric capacitor, which has a voltage of 1V and holds a charge of 1C. Capacitance is: Directly proportional to: the active area S permittivity ε Inversely proportional to: the distance between the plates d C= ε S/d

 The used method: Volt-ampere (Ohm’s) method – applied to the measurements of large impedances Supply voltage must have a known and constant frequency a)Involvement of a small C b)Involvement of a large C

We must know: current voltage When we don’t know the value of the capacity C X we calculate it from basic data from an A-metre and a V-metre Capacitive reactance Of which we don’t know the capacity, the angular frequency – ω will help Or the help of frequency f  Calculation 1 – when an AC current:

When measuring it is important that there is an AC current flowing through the circuit If not, you should make a re-count on a replacement scheme Phasor diagram  Calculation 2:

 The used method: Measuring capacity distribution of an electric charge  The measurement procedure: The capacity of the capacitor C is known and the position I of switch p is charged with a voltage U and a charge Q. Switch the switch to position 2; by an unknown capacity C X connected in parallel to capacity C. The charge is divided into two capacitors and the voltage U is subtracted again from the voltmeter. For the switch applies In position 1 - Q = U.C In position 2 - Q = U.Cx + U x C x. Unknown capacity of a capacitor

 Describe how to define a unit of capacity ◦  Name for what is the proportional capacity of the capacitor ◦  Write what are the requirements for power voltage ◦  Draw a circuit for measuring ◦ small C ◦ large C

 Calculate an example:  A block capacitor has an unreadable data capacity; we can find out about the circuit with an ammeter. The ammeter showed a current I = 2.76A at a voltage of 230V, 50 Hz  Capacitive reactance ◦ X C =  Capacitance ◦ C X =

 Mužík, J. Management ve vzdělávání dospělých. Praha: EUROLEX BOHEMIA, ISBN  Operační program Vzdělávání pro konkurenceschopnost, ESF 2007 –  Dostupné na: konkurenceschopnosthttp:// konkurenceschopnost  Učebnice Elektrická měření – Ing. Pavel Vylegala, SŠE Ostrava, 2006  Učebnice Elektrické měření – SNTL, 1981  Elektrotechnika - Laboratorní cvičení pro bakalářské studium - Doc. Ing. Miloš Hammer, CSc.