Found 1006 Articles for Electronics & Electrical

An electrical transformer is tested at the transformer manufacturer premises and at the consumer’s site and also periodically in regular and emergency basis during its service life to confirm its specifications and performance.Types of Transformer TestsTests of transformer done at the manufacturer’s premises −Type testsRoutine testsSpecial testsTests of transformer done at the consumer’s site −Pre-commissioning testsPeriodic testsEmergency testsType Tests of TransformerThe type tests of a transformer are performed at the manufacturer’s premises to prove the design expectations and consumer’s specifications. The type tests are performed in a prototype unit, not in all manufactured units and these tests confirm the basic ... Read More

The star-star connection of transformer is shown in the figure. Here, the one terminal of three windings on each of the primary and the secondary sides being connected at a common point (called neutral point) and the other end of each winding is taken out as the line terminal.In the case of star-star connection, the phase current is equal to the line current and they are in phase. The line voltage is √3 times of the phase voltage. Also, there is a phase difference of 30° between the line voltages and phase voltages.For an ideal transformer the voltage ratios are ... Read More

In case of the star-delta connection of a transformer, the primary winding of the transformer is connected in star while the secondary winding is connected in delta (see the figure).Primary Winding – Since the primary winding is connected star fashion. Therefore, the primary line voltage is equal to the √3 times of the primary phase voltage and the primary line current is same as the primary phase current.Secondary Winding – The secondary winding is connected in delta manner. Therefore, on the secondary side of the transformer, the line voltage will be the same as the phase voltage whereas the line ... 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

Short-circuit and open-circuit tests are to be performed on a 3-winding transformer to determine the parameters of the equivalent circuits of it.Short-Circuit TestThe equivalent impedances Z1, Z2 and Z3 referred to a common base can be determined by performing three short-circuit tests as follows −Test 1In the first test, the secondary winding is short circuited, the tertiary winding is kept open circuited and a low voltage being applied to the primary winding so that full-load current flows in the secondary winding (see the figure above). Then, the voltage, current and power input to the primary winding is to be measured.Let ... Read More

A potential transformer (P.T.) is an instrument transformer which is used for the protection and measurement purposes in the power systems. A potential transformer is mainly used to measure high alternating voltage in a power system.Potential transformers are step-down transformers, i.e., they have many turns in the primary winding while the secondary has few turns. The figure shows a typical potential transformer for the measurement of high alternating voltage. From the figure, it is clear that a P.T. is a well designed step down transformer.The stepped down voltage by the Potential transformer can be measure using a low range AC ... Read More

When the primary windings of two or more transformers are connected to a common voltage supply and their secondary windings are connected to a common load. Then, the transformers are said to be connected in parallel, i.e., parallel operation of the transformers. The figure shows two transformers T1 and T2 connected in parallel.Reasons for Parallel Operation of TransformersThe primary reasons for operating transformers in parallel are as follows −For large loads, it may be impractical or uneconomical to have a single large transformer so that many small transformers are paralleled to meet the load demand.By operating the transformers of standard ... Read More

If one transformer of delta-delta connected transformer bank is damaged or opened, then rest of the system will continue to supply the 3-phase power. If this damaged transformer is isolated, the remaining two transformers will function as a 3-phase bank with rating reduced to about 58 % that of the original delta-delta bank. This type of arrangement is known as open-delta or V-V connection.Therefore, in the case of open-delta or V-V connection, two instead of three 1-phase transformers are used for three-phase operation.Now, let VRY, VYB and VBR be the applied voltages to the primary winding. The voltage induced in ... Read More

There are four main types of transformers viz.Distribution TransformersPower TransformersAutotransformersInstrument TransformersDistribution TransformersThe transformers which are used to step down the transmission voltage to the distribution voltage or the distribution voltage to a standard service voltage are known as distribution transformers. These transformers have variable load which is considerably less than the full load rating of the transformer. Hence, the distribution transformers are designed to have their maximum efficiency at between ½ and ¾ of the full load.These transformers are kept in operation 24 hours a day whether they are carrying any load or not. The distribution transformers have a good ... Read More

When the load is connected to a DC generator, the load current flows through the armature conductors and set up a magnetic flux called armature flux. This armature flux is always 180° phase apart from the main field flux and distorts or opposes it. This opposition of armature flux on the main field flux is known as armature reaction.The armature reaction has two undesirable effects. The first is it reduces the main field flux called as demagnetising effect and the second is it distorts the main field flux called as cross magnetising effect.ExplanationIn order to calculate the demagnetising and cross-magnetising ... Read More