LOAD SHARING BY TWO TRANSFORMERS
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Let us consider the following two cases: Equal voltage ratios. Unequal voltage ratios. 1.39.1 Equal Voltage Ratios Assume no-load voltages EA and EB are identical and in phase. Under these conditions if the primary and secondary are connected in parallel, there will be no circulating current between them on no load. Figure 1.48 Equal Voltage Ratios Figure 1.48 shows two impedances in...
PARALLEL OPERATION OF SINGLE-PHASE TRANSFORMER
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It is required to connect a second transformer in parallel with the first transformer if the load exceeds the rating of the transformer shown in Figure 1.46. The primary windings are connected to the supply bus bars while the secondary windings are connected to the load bus bars. During paralleling of the transformer, similar polarities of the transformers should be connected to the same bus...
SUMPNER’S TEST
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To determine the rise of maximum temperature of a transformer, its load test is of utmost importance. Using suitable load impedance, small transformers can be put on full load. The full-load test of large transformers is not possible because considerable wastage of energy occurs and it is difficult to get a suitable load for absorbing full-load power. Sumpner’s test is used to put large transformer...
ALL-DAY EFFICIENCY
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The ratio of output in watts to input in watts is called commercial efficiency of a transformer. Distribution transformers are used for supplying lighting and general networks. Distributiontransformers are energized throughout the day. Their secondaries are at no load most of the time in a day except during the hours of lighting period. Core loss occurs throughout the day. Copper loss occurs...
POLARITY TEST OF A SINGLE-PHASE TRANSFORMER
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Polarity testing of transformers is vital before connecting them in parallel. Otherwise, with incorrect polarity, it is not possible to connect them in parallel. The rated voltage is applied to the primary and its two terminals are marked as A1 and A2, respectively, as shown in Figures 1.44(a) and 1.45(b), respectively. The secondary winding terminals are also marked as a1 and a2, shown in Figures...
EFFICIENCY OF A TRANSFORMER
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Due to the losses in a transformer, its output power is less than the input power.∴ Power output = Power input – Total losses∴ Power input = Power output + Total losses = Power output + Pi + PCuThe ratio of power output to power input of any device is called its efficiency (η). Output power of a transformer at full-load = V2I2ftcosθ, where cosθ is the power factor...
LOSSES IN A TRANSFORMER
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Two types of losses occur in a transformer:Core loss or iron loss occurs in a transformerbecause it is subjected to an alternating flux.The windings carry current due to loading and hence copper losses occur.1.32.1 Core or Iron LossThe separation of core losses has already been introduced. The alternating flux gets set up in the core and it undergoes a cycle of magnetization and demagnetization....
KAPP’S REGULATION
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Kapp had designed a diagram shown in Figure 1.42 to determine the regulation at any power factor. The description of the construction of the diagram is shown below.Figure 1.42 Kapp’s DiagramLoad current (I2) is taken as a reference phasor. OA representing V2 is drawn at angle θ2 with I2. AB represents I2R02 drawn parallel to I2, whereas BC represents I2X02 drawn perpendicular to AB, i.e., I2. Here...
CALCULATION FOR VOLTAGE REGULATION
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The voltage regulation up is expressed mathematically byPositive sign is for lagging power factor and negative sign is for leading power factor.1.31.1 Zero Voltage RegulationFor lagging power factor and unity power factor, 0V2 > V2. Therefore, we get positive voltage regulation. For leading power factor, V2 starts increasing. At a certain leading power factor, 0V2 = V2 and hence regulation becomes...
PER UNIT RESISTANCE, LEAKAGE REACTANCE AND IMPEDANCE VOLTAGE DROP
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Full-load voltage of a transformer can be expressed as a fraction of the full-load terminal voltage.Let I1fl be the full-load primary current, I2fl be the full-load secondary current, V1 be the rated pri-mary voltage and V2 be the rated secondary voltage.Per unit resistance drop of atransformer∴ Per unit reactance drop of a transformerPer unit reactance drop of...
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