Found 1006 Articles for Electronics & Electrical

Armature ReactionThe current flowing through the armature conductors creates a magnetic field, which is called as armature flux. This armature flux distorts and weakens the magnetic flux produced by the main poles. This effect of armature flux on the main flux is known as armature reaction.Case 1Consider a two pole generator on no-load. Thus, the current in the armature conductors is zero. Under this condition, there is only the main flux (φm) in the machine which is produced by the main poles. This main flux is distributed symmetrically with respect to the polar axis (i.e. centre line of field poles).The ... Read More

The open-circuit test and the short-circuit test being performed on a transformer to determine the circuit parameters, efficiency and the voltage regulation without actual loaded of the transformer. The open-circuit and short-circuit tests give more accurate results than those are obtained by performing the measurements on a fully loaded transformer. The principle of advantage of these tests is the power consumption is very small as compared to the full-load output of the transformer.Open-Circuit Test of TransformerThe circuit arrangement for the open-circuit test of a transformer is shown in the figure. In this test the high voltage side of the transformer ... Read More

Working of AutotransformerThe connection diagram of an ideal step-down autotransformer is shown in the figure. In which the winding ab is the primary winding having N1 turns and the winding bc is the secondary winding having N2 turns. Here, the current I1 is the input primary current and the current I2 is the output secondary current or load current.Now, the number of turns in the 'ac' portion of the winding is N1 – N2 turns and the voltage across this portion is V1 – V2. The current in the common portion (winding 'bc') of the winding is I2 – I1.Consider ... Read More

A three-phase star-connected autotransformer is shown in the figure. The three-phase autotransformers are used for small ratios of transformation.In practice, the star connected three-phase autotransformers are used and the delta connected autotransformers are avoided. The primary application of three phase autotransformers is for interconnecting two power systems of different voltage levels such as 66 kV to 132 kV power systems, 110 kV to 220 kV power systems, 220 kV to 400 kV power systems etc.Numerical ExampleA three-phase star-connected autotransformer supplies a balanced three-phase load of 100 kW at 380 V and at 0.85 power factor lagging. If the supply voltage ... Read More

The non-sinusoidal nature of the magnetising current in a three phase transformer produces some undesirable phenomena. The phase magnetising current should contain third and higher order harmonics which is necessary to produce a sinusoidal flux.If the phase voltage across each phase is sinusoidal, then the phase magnetising currents are given as follows −$$\mathrm{𝐼_{𝑅𝑁} = 𝐼_{𝑚}\:sin\:𝜔𝑡\:+\:𝐼_{3𝑚 }sin(3𝜔𝑡\:+\:φ_{3})\:+\:𝐼_{5𝑚}\:sin(5𝜔𝑡\:+\: φ_{5})\:+\:… (1)}$$$$\mathrm{𝐼_{𝑌𝑁} = 𝐼_{1𝑚}\:sin(𝜔𝑡 − 120°)\:+ \:𝐼_{3𝑚}\:sin[3(𝜔𝑡 − 120°)\:+\:φ_{3}]\:+\:𝐼_{5𝑚} \:sin[5(𝜔𝑡 − 120°)\:+\:φ_{5}] +....}$$$$\mathrm{\Rightarrow\:𝐼_{𝑌𝑁} = 𝐼_{1𝑚}\:sin(𝜔𝑡 − 120°)\:+\:𝐼_{3𝑚}\:sin(3𝜔𝑡\:+\:φ_{3})\:+\:𝐼_{5𝑚}\:sin(5𝜔𝑡\:+\:120°\:+\:φ_{5}) +..…\:(2)}$$And$$\mathrm{𝐼_{𝐵𝑁} = 𝐼_{1𝑚}\:sin(𝜔𝑡 − 240°)\:+ \:𝐼_{3𝑚}\:sin[3(𝜔𝑡 − 240°)\:+\:φ_{3}]\:+\:𝐼_{5𝑚}\:sin[5(𝜔𝑡 − 240°)\:+\:φ_{5}] +...}$$$$\mathrm{\Rightarrow\:𝐼_{𝐵𝑁}= 𝐼_{1𝑚}\:sin(𝜔𝑡 − 240°)\:+\:𝐼_{3𝑚}\:sin(3𝜔𝑡\:+\:φ_{3})\:+\:𝐼_{5𝑚}\:sin(5𝜔𝑡\:+\:240°\:+\:φ_{5}) +\:… (3)}$$Hence, from the eqns. (1), (2) and (3), it is clear that ... Read More

The rectifiers are used to convert alternating current (AC) to direct current (DC). The advantages of increased number of phases of the AC supply are given as follows −A smoother waveform is obtained on the DC side as the number of phases of the AC supply is increased.The objectionable harmonics in the AC being reduced with the increase in the number of phases.With the increase in the number of phases, the efficiency of the converter unit (rectifier) is also increased.Therefore, because of these advantages 6-phase is preferred instead of 3-phase for rectification. In order to obtain three to six phase ... Read More

The rectifiers are used to convert alternating current (AC) to direct current (DC). The advantages of increased number of phases of the AC supply are given as follows −A smoother waveform is obtained on the DC side as the number of phases of the AC supply is increased.The objectionable harmonics in the AC being reduced with the increase in the number of phases.With the increase in the number of phases, the efficiency of the converter unit (rectifier) is also increased.Therefore, because of these advantages 6-phase is preferred instead of 3-phase for rectification. In order to obtain three to six phase ... Read More

The procedure for determining the voltage regulation of a 3-winding transformer is given as follows −Step 1Determine the kVA in each winding (primary, secondary and tertiary) for the given load. Determine x for each winding. Where, x is the ratio of actual kVA loading of the winding to the base kVA used in determining the network parameters. Hence, $$\mathrm{For\:primary\:winding, \:𝑥_{1 }=\frac{Primary\:kVA\:loading}{Base\:kVA}}$$$$\mathrm{For\:secondary\:winding, \:𝑥_{2 }=\frac{Secondary\:kVA\:loading}{Base\:kVA}}$$$$\mathrm{For\:tertiary\:winding, \:𝑥_{3 }=\frac{Tertiary\:kVA\:loading}{Base\:kVA}}$$Step 2Calculate the voltage regulation for each winding at its operating power factor.Let cosφ1, cosφ2 and cosφ3 are the operating power factors of primary winding, secondary winding and tertiary winding respectively. If vr1, vr2 and vr3 ... Read More

In case of the delta-star connection of a 3-phase transformer, the primary winding is connected in delta while the secondary winding is connected in star (see the figure).Primary Winding − As the primary winding is connected in delta. Hence, the line voltage and the phase voltage on the primary side are the same and the line current is √3 times of the phase current.Secondary Winding − The secondary winding is connected in star fashion. Thus, the secondary line voltage is √3 times of the phase voltage and the line current is equal to the phase current.The delta-star connected 3-phase transformers ... Read More

A conventional two-winding transformer can be converted into an autotransformer as shown in the figures given below. It can be converted into a step-up autotransformer by connecting the two windings electrically in series with additive polarities. If the windings are connected electrically in series with subtractive polarities, then a step-down autotransformer is obtained.To understand the conversion of a two winding transformer into an autotransformer, consider a conventional two-winding transformer of 20 kVA, 11000/400 V. This transformer has to be connected in autotransformer.Case 1 – With Additive PolarityThe figure shows the series connections of the winding with additive polarity. As the ... Read More