Study of Electro-Dynamic Type Instruments. Meter Accuracy. The meter is mechanically damped by means of aluminum vanes that move in enclosed air chambers. Although very accurate, electrodynamometer-type meters do not have the sensitivity of the D'Arsonval-type meter movement. For this reason, you will not find them used outside of the laboratory environment to a large extent. The primary advantage of the electrodynamometer-type meter movement is that it can be used to measure alternating as well as direct current. If you apply alternating current to the standard galvanometer-type meter, it will not produce a usable reading. Q.29 What is the primary advantage of the electrodynamometer-type meter over the D'Arsonval-type meter? When an electrodynamometer is used as a voltmeter, no problems in construction are encountered because the current required is not more than 0.1 ampere. Figure 3-17. - Circuit arrangement of electrodynamometer for use as a voltmeter and an ammeter.
Electric power is measured by means of a wattmeter. Wattmeter Connection. How to become an Electrician | SparkyFacts.co.uk. Updated for the 2012-2013 qualification changes! How to become an electrician? Well, it is not a short or easy process. There are many different paths to your qualifications. It can be very confusing since you might easily receive contradictory answers from different colleges or course providers. The old City & Guilds Technical Certificate in Electrotechnical Technology (2330) is replaced by the new C&G 2365 level 2 and C&G 2365 level 3 Diploma in Electrical Installations (Buildings and Structures). The C&G 2357-13 NVQ Level 3 Diploma in Installing Electrotechnical Systems and Equipment is still kept for now and is still the best qualification to get in order to become an electrician in the UK. This means that in order to become an electrician you will have to gain the following qualifications: Or Form September 2012 you will need to gain the C&G 2365 Level 2 and C&G 2365 Level 3 Diploma in Electrical Installations (Buildings and Structures) in order to become an electrician.
Complicated?
AC inductor circuits : Reactance And Impedance -- Inductive. Inductors do not behave the same as resistors. Whereas resistors simply oppose the flow of electrons through them (by dropping a voltage directly proportional to the current), inductors oppose changes in current through them, by dropping a voltage directly proportional to the rate of change of current. In accordance with Lenz's Law, this induced voltage is always of such a polarity as to try to maintain current at its present value. That is, if current is increasing in magnitude, the induced voltage will “push against” the electron flow; if current is decreasing, the polarity will reverse and “push with” the electron flow to oppose the decrease. This opposition to current change is called reactance, rather than resistance. Expressed mathematically, the relationship between the voltage dropped across the inductor and rate of current change through the inductor is as such: Pure inductive circuit: Inductor current lags inductor voltage by 90o.
Pure inductive circuit, waveforms. AC capacitor circuits : Reactance And Impedance -- Capacitive. Capacitors do not behave the same as resistors. Whereas resistors allow a flow of electrons through them directly proportional to the voltage drop, capacitors oppose changes in voltage by drawing or supplying current as they charge or discharge to the new voltage level. The flow of electrons “through” a capacitor is directly proportional to the rate of change of voltage across the capacitor.
This opposition to voltage change is another form of reactance, but one that is precisely opposite to the kind exhibited by inductors. Expressed mathematically, the relationship between the current “through” the capacitor and rate of voltage change across the capacitor is as such: The expression de/dt is one from calculus, meaning the rate of change of instantaneous voltage (e) over time, in volts per second. The capacitance (C) is in Farads, and the instantaneous current (i), of course, is in amps.
Pure capacitive circuit: capacitor voltage lags capacitor current by 90o Capacitive reactance. The Power Factor Triangle...the vector representation explained. Power Factor Formulas and the Power Factor Triangle, now that you understand the terminology, are easily within your grasp. The key to the Power Factor Triangle is understanding vectors. I'll make vectors easy and in a few minutes you'll have it. Vector AnalysisVectors are simply another way to draw sine waves. You'll see its not difficult and actually makes things easier. Vectors, as used in this discussion, are representations of a sine wave of current relative to a sine wave of voltage.
Instead of showing the current as a sine wave, the vector shows it as a straight line that points in a direction. The direction of the arrow is simple. Lets look at cases where the currents leads or lags voltage by 45 degrees. Current B lags the voltage by 45 degrees so the vector points down and to the right (see below). Adding VectorsThis is almost as fun as connecting the dots (an EE's childhood pastime).
Hopefully that makes sense to you. Good news! Yup! Apparent Power x PF = Real Power. True, Reactive, and Apparent power : Power Factor. We know that reactive loads such as inductors and capacitors dissipate zero power, yet the fact that they drop voltage and draw current gives the deceptive impression that they actually do dissipate power. This “phantom power” is called reactive power, and it is measured in a unit called Volt-Amps-Reactive (VAR), rather than watts. The mathematical symbol for reactive power is (unfortunately) the capital letter Q. The actual amount of power being used, or dissipated, in a circuit is called true power, and it is measured in watts (symbolized by the capital letter P, as always).
The combination of reactive power and true power is called apparent power, and it is the product of a circuit's voltage and current, without reference to phase angle. Apparent power is measured in the unit of Volt-Amps (VA) and is symbolized by the capital letter S. As a rule, true power is a function of a circuit's dissipative elements, usually resistances (R). Resistive load only: Reactive load only: Phasor Diagrams. Phasor Diagrams In AC electrical theory every power source supplies a voltage that is either a sine wave of one particular frequency or can be considered as a sum of sine waves of differing frequencies. The neat thing about a sine wave such as V(t) = Asin(ωt + δ) is that it can be considered to be directly related to a vector of length A revolving in a circle with angular velocity ω - in fact just the y component of the vector.
The phase constant δ is the starting angle at t = 0. In Figure 1, an animated GIF shows this relation [you may need to click on the image for it to animate]. Since a pen and paper drawing cannot be animated so easily, a 2D drawing of a rotating vector shows the vector inscribed in the centre of a circle as indicated in Figure 2 below. The angular frequency ω may or may not be indicated. When two sine waves are produced on the same display, one wave is often said to be leading or lagging the other. Asin(ωt + φ) = 5sin(ωt + 30°) + 4sin(ωt + 140°) ; For capacitors and.