Three single-phase distribution transformers, each rated for 18kVA, 20000/220 volts, are connected in a Dy three-phase bank.For convenience, at the factory, the OCT and the SCT were per-formed as per standards with the whole three-phase bank alreadyconnected and the measured values were as follows:Vline 381.051V, line 1.78436A, P30 = 372.414 W.Vline = 5656.85 V, Iline = 1.55885 A, P30 = 2160 W.Three phase bank of single phase transformer on a utility pole.37.5 K(a) Find the single phase equivalent circuit referred to the low volt-age side.(b) Find the transformer regulation at the rated load and voltageand a power factor of 0.45 lagging (Neglect the excitation current).(c) Using the "load" model, what is the approximate transformer-bank's efficiency, n, under these conditions of load?(a) R2 X=2Rsc=mXsc = mS(b) Vreg=(c) n = %

Three single-phase distribution transformers are connected in a Dy three-phase bank. Rated power…

Three single-phase distribution transformers, each rated for 18 kVA, 20000/220 volts, are connected in a Dy three-phase bank. For convenience, at the factory, the OCT and the SCT were per- formed as per standards with the whole three-phase bank already connected and the measured values were as follows: Vline 381.051V, line = 1.78436A, P30 = 372.414 W. Vline = 5656.85 V, pline = 1.55885 A, P3 =2160 W. Three phase bank of single phase transformer on a utility pole. 37.5 K (a) Find the single phase equivalent circuit referred to the low volt- age side. (b) Find the transformer regulation at the rated load and voltage and a power factor of 0.45 lagging (Neglect the excitation current). (c) Using the "load" model, what is the approximate transformer- bank's efficiency, n, under these conditions of load?

Three single-phase distribution transformers, each rated for 18 kVA, 20000/220 volts, are connected in a Dy three-phase bank. For convenience, at the factory, the OCT and the SCT were per- formed as per standards with the whole three-phase bank already connected and the measured values were as follows: Vline 381.051V, line = 1.78436A, P30 = 372.414 W. Vline = 5656.85 V, pline = 1.55885 A, P3 =2160 W. Three phase bank of single phase transformer on a utility pole. 37.5 K (a) Find the single phase equivalent circuit referred to the low volt- age side. (b) Find the transformer regulation at the rated load and voltage and a power factor of 0.45 lagging (Neglect the excitation current). (c) Using the "load" model, what is the approximate transformer- bank's efficiency, n, under these conditions of load?

Power System Analysis and Design (MindTap Course List)

6th Edition

ISBN:9781305632134

Author:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma

Publisher:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma

Chapter3: Power Transformers

Section: Chapter Questions

Problem 3.37P: Three single-phase two-winding transformers, each rated 25MVA,54.2/5.42kV, are connected to form a...

See similar textbooks

Similar questions

Three single-phase two-winding transformers, each rated 3kVA,220/110volts,60Hz, with a 0.10 per-unit leakage reactance, are connected as a three-phase extended autotransformer bank, as shown in Figure 3.36(c). The low-voltage winding has a 110 volt rating. (a) Draw the positive-sequence phasor diagram and show that the high-voltage winding has a 479.5 volt rating. (b) A three-phase load connected to the low-voltage terminals absorbs 6 kW at 110 volts and at 0.8 power factor lagging. Draw the per-unit impedance diagram and calculate the voltage and current at the high-voltage terminals. Assume positive-sequence operation.
Three single-phase two-winding transformers, each rated 25MVA,34.5/13.8kV, are connected to form a three-phase bank. Balanced positive-suence voltages are applied to the high-voltage terminals, and a balanced, resistive Y load connected to the low-voltage terminals absorbs 75 MW at 13.8 kV. If one of the single-phase transformers is removed (resulting in an open connection) and the balanced load is simultaneously reduced to 43.3 MW (57.7 of the original value), determine (a) the load voltages Va,Vb, and Vc; (b) load currents Ia,Ib, and Ic; and (c) the MVA supplied by each of the remaining two transformers. Are balanced voltages still applied to the load? Is the open transformer overloaded?
In per-unit equivalent circuits of practical three-phase transformers, under balanced thr-phase operation, in which of the following connect ions would a phase-shifting transformer come up? (a) Y-Y (b) Y- (c) -
Three single-phase two-winding transformers, each rated 25MVA,54.2/5.42kV, are connected to form a three-phase Y- bank with a balanced Y-connected resistive load of 0.6 per phase on the low-voltage side. By choosing a base of 75 MVA (three phase) and 94 kV (line-to-line) for the high-voltage side of the transformer bank, specify the base quantities for the low-voltage side. Determine the per-unit resistance of the load on the base for the low-voltage side. Then determine the load resistance RL in ohms referred to the high-voltage side and the per-unit value of this load resistance on the chosen base.
Consider the three single-phase two-winding transformers shown in Figure 3.37. The high-voltage windings are connected in Y. (a) For the low-voltage side, connect the windings in , place the polarity marks, and label the terminals a, b, and c in accordance with the American standard. (b) Relabel the terminals a, b, and c such that VAN is 90 out of phase with Va for positive sequence.
A bank of three single-phase transformers, each rated 30MVA,38.1/3.81kV, are connected in Y- with a balanced load of three 1, Y-connected resistors. Choosing a base of 90MVA,66kV for the high-voltage side of the three-phase transformer. spify the base for the low-voltage side. Compute the per-unit resistance of the load on the base for the low-voltage side. Also, determine the load resistance in ohms referred to the high-voltage side and the per-unit value on the chosen base.
Consider a single-phase electric system shown in Figure 3.33. Transformers are rated as follows: XY15MVA,13.8/138kV, leakage reactance 10 YZ15MVA,138/69kV, leakage reactance 8 With the base in circuit Y chosen as 15MVA,138kV determine the per-unit impedance of the 500 resistive load in circuit Z, referred to circuits Z, Y, and X. Neglecting magnetizing currents, transformer resistances, and line impedances, draw the impedance diagram in per unit.
Connect three single-phase transformers in Y-Y, with subtractive polarity, so that the line-to-line voltages on the primary are 30 degrees delayed to their respective line-to-line voltages on the secondary. It should show each step that is needed to make this connection (example: the phasor diagram) and should show the final connection of the three transformers including the polarity markings. Assume phase A on the primary is terminal "H1".
A 10 MVA three phase load is to be served by a three phase transformer at aline voltage of 13.8 kV. The supply side voltage(line-line) is 138 kV. Varioussingle phase transformers are available in the warehouse but all havewindings with voltage ratings under 100 kV and current ratings under 250 A.Is it possible to serve the load using only three single phase transformers? Ifso, specify the three phase connections and the low and high voltage ratingsof the single phase transformers.
Three single-phase transformers, each rated 10 MVA , 66.4/12.5 kV, 60 Hz , with an equivalent series reactance of 0.1 per unit divided equally between primary and secondary, are connected in a three-phase bank. The high-voltage windings are Y-connected and their terminals are directly connected to a 115-kV three-phase bus. The secondary terminals are all shorted together. Find the currents entering the high-voltage terminals and leaving the low-voltage terminals if the low-voltage windings are (a) Y-connected and (b) Δ- connected.
1. How do you measure three phase line currents by using two current transformers? Draw the connection scheme.
a)Why are transformers generally connected in parallel at a substation?b)What conditions must be met for two transformers to be paralleled?c)Draw the phase relationship and connection diagram for Dd0 connection andYy6