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

A full-load test on the large transformer is to be conducted to determine the maximum temperature rise of the transformer which is called as back-to-back test. The back-to-back test is also known as Sumpner’s test or regenerative test.In case of small transformers, the full-load test is conveniently possible, but for large transformers, full load test is very difficult. It is because, a suitable load to consume full-load power of a large transformer may not be available. It will also be very expensive as a large amount of energy will be wasted in the load during the test.The figure shows the ... Read More

Approximate Voltage Drop in a TransformerThe figure shows the approximate equivalent circuit of a practical transformer referred to secondary side.At no-load i.e. with I2= 0, the secondary terminal voltage is, $$\mathrm{V_{2}=KV_{1} .....(1)}$$When an inductive load of power factor cosφ2 (lagging) is connected across the secondary winding of the transformer, the secondary winding carries a current I2 and hence the voltage drops occur in $(R_{2} + K^2R_{1})$ and $(X_{2} + K^2X_{1})$. As a result, the secondary voltage drops from KV1 to V2 across the load terminals.By applying KVL to the circuit, we get, $$\mathrm{V_{2}=KV_{1}-I_{2}[(R_{2} + K^2R_{1})+J(X_{2} + K^2X_{1})]}$$$$\mathrm{⇒ V_{2}=KV_{1}-I_{2}(R_{02} +jX_{02}) = ... Read More

There are different types of DC generators are available for the various types of applications. The applications of various types of DC generators based on their characteristics are as follows −Applications of Separately Excited DC GeneratorsA separately excited DC generator requires an independent external DC source for the excitation of field winding. Thus, it is expensive and being rarely used. Following are some application of separately excited DC generators −These are able to produce a wide range of voltage output, they are primarily used in laboratory and commercial testing.These are used in speed regulation tests.These generators operate in a stable ... Read More

The currents induced in the armature winding of a DC generator are alternating in nature. The action of commutator (called commutation) involves the change from a generated alternating current to a direct current.ExplanationConsider a commutator consisting of a cylindrical metal ring cut into two segments C1 and C2 respectively separated by a thin sheet of mica. The commutator is mounted on the rotor shaft and insulated from it. The ends of the armature coil sides AB and CD are connected to the segments C1 and C2 respectively. Two stationary carbon brushes are placed on the commutator and carry current to ... Read More

Magnetic Leakage or Leakage FluxThe part of magnetic flux that does not follow the desired path in a magnetic circuit is known as leakage flux.In most of practical magnetic circuits, the path of a large part of the magnetic flux is through iron part of the magnetic circuit and the rest part of magnetic flux flows through air. The magnetic flux in the air gap is known as useful flux $(\varphi_{g})$ since it can be used for various useful purposes.Consider a magnetic circuit having an iron core with a coil wound on it and having a narrow air gap. The ... Read More