Q2. Consider a 40MVA, 132/11kV transformer with a reactance of 15% on its rating, (a) shown in Figure Q2. It is equipped with an on-load tap-changer that is used to maintain constant voltage at the 11kV busbar by compensating for variations in the voltage of the 132kV network, and for the voltage drop across the transformer. The variation of the network voltage at 132KV transformer busbar for heavy loading conditions is shown in the table below. Active power losses in the transformer are ignored, and it is assumed that the value of the reactance of the transformer is not influenced by the change in the turn ratio. Calculate t, the tap ratio, and the actual voltage at bus 2 in this case. (Note: For instance, a nominal ratio of the transformer is 132/11, when tapped to give 144/11 ratio, therefore t is 144/132=1.09). Load Power factor Voltage at 132kV Desired voltage at busbar (Bus 1) 11kV busbar (Bus 2) 5MVA 0.9 185kV 11kV Bus 2 Bus 1 X=15% t:1 Figure Q2

Q2. Consider a 40MVA, 132/11kV transformer with a reactance of 15% on its rating, (a) shown in Figure Q2. It is equipped with an on-load tap-changer that is used to maintain constant voltage at the 11kV busbar by compensating for variations in the voltage of the 132kV network, and for the voltage drop across the transformer. The variation of the network voltage at 132KV transformer busbar for heavy loading conditions is shown in the table below. Active power losses in the transformer are ignored, and it is assumed that the value of the reactance of the transformer is not influenced by the change in the turn ratio. Calculate t, the tap ratio, and the actual voltage at bus 2 in this case. (Note: For instance, a nominal ratio of the transformer is 132/11, when tapped to give 144/11 ratio, therefore t is 144/132=1.09). Load Power factor Voltage at 132kV Desired voltage at busbar (Bus 1) 11kV busbar (Bus 2) 5MVA 0.9 185kV 11kV Bus 2 Bus 1 X=15% t:1 Figure Q2

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 3.17P: The transformer of Problem 3.16 is supplying a rated load of 50 kVA at a rated secondary voltage of...

See similar textbooks

Similar questions

Consider two interconnected voltage sources connected by a line of impedance Z=jX, as shown in Figure 2.27. (a) Obtain expressions for P12 and Q12. (b) Determine the maximum power transfer and the condition for it to
A single-phase two-winding transformer rated 90MVA,80/120kV is to be connected as an autotransformer rated 80/200kV. Assume that the transformer is ideal. (a) Draw a schematic diagram of the ideal transformer connected as an autotransformer. showing the voltages, currents, and dot notation for polarity. (b) Determine the permissible kVA rating of the autotransformer if the winding currents and voltages are not to exceed the rated values as a two-winding transformer. How much of the kA rating is transferred by magnetic induction?
In developing per-unit circuits of systems such as the one shown in Figure 3.10. when moving across a transformer, the voltage base is changed in proportion to the transformer voltage ratings. (a) True (b) False
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.
A three-phase transformer is rated 1000MVA,220Y/22kV. The Y-equivalent short-circuit impedance, considered equal to the leakage reactance, measured on the low-voltage side is 0.1. Compute the per-unit reactance of the transformer. In a system in which the base on the high-voltage side of the transformer is 100MVA,230kV what value of the per-unit reactance should be used to represent this transformer?
Consider Figure 3.4. For an ideal phase-shifting transformer, the imda nce is unchanged when it is referred from one side to the other. (a) True (b) False
Consider an ideal transformer with N1=3000andN2=1000 turns. Let winding 1 be connected to a source whose voltage is e1(t)=100(1| t |)volts for 1t1ande1(t)=0 for | t |1 second. A2- farad capacitor is connected across winding 2. Sketch e1(t),e2(t),i1(t),andi2(t) versus time t.
Three single-phase, two-winding transformers, each rated 450MVA,20kV/288.7kV, with leakage reactance Xeq=0.10perunit, are connected to form a three-phase bank. The high-voltage windings are connected in Y with a solidly grounded neutral. Draw the per-unit equivalent circuit if the low-voltage windings are connected (a) in with American standard phase shift or (b) in Y with an open neutral. Use the transformer ratings as base quantities. Winding resistances and exciting current are neglected.
For the transformer in Problem 3.10. The open-circuit test with 11.5 kV applied results in a power input of 65 kW and a current of 30 A. Compute the values for GcandBm in siemens referred to the high-voltage winding. Compute the efficiency of the transformer for a load of 10 MW at 0.8 p.f. lagging at rated voltage.
A two-winding single-phase transformer rated 60kVA,240/1200V,60Hz, has an efficiency of 0.96 when operated at rated load, 0.8 power factor lagging. This transformer is to be utilized as a 1440/1200-V step-down autotransformer in a power distribution system. (a) Find the permissible kVA rating of the autotransformer if the winding currents and voltages are not to exceed the ratings as a two-winding transformer. Assume an ideal transformer. (b) Determine the efficiency of the autotransformer with the kVA loading of part (a) and 0.8 power factor leading.
Consider the oneline diagram shown in Figure 3.40. The three-phase transformer bank is made up of three identical single-phase transformers, each specified by X1=0.24 (on the low-voltage side), negligible resistance and magnetizing current, and turns ratio =N2/N1=10. The transformer bank is delivering 100 MW at 0.8 p.f. lagging to a substation bus whose voltage is 230 kV. (a) Determine the primary current magnitude, primary voltage (line-to-line) magnitude, and the three-phase complex power supplied by the generator. Choose the line-to-neutral voltage at the bus, Va as the reference Account for the phase shift, and assume positive-sequence operation. (b) Find the phase shift between the primary and secondary voltages.
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.