ns. 1. Iron los..........varies approximately as V². 2. Cu loss..........it also varies as but decreases with an increase in voltage if constant kVA output is assumed. 3. Efficiency...........for distribution transformers, efficiency at fractional loads decreases with in- crease in voltage while at full load or overload it increases with increase in voltage and vice- versa. 4. Regulation..........it varies as but decreases with increase in voltage if constant kVA output is assumed. hamas Cutemperatures

ns. 1. Iron los..........varies approximately as V². 2. Cu loss..........it also varies as but decreases with an increase in voltage if constant kVA output is assumed. 3. Efficiency...........for distribution transformers, efficiency at fractional loads decreases with in- crease in voltage while at full load or overload it increases with increase in voltage and vice- versa. 4. Regulation..........it varies as but decreases with increase in voltage if constant kVA output is assumed. hamas Cutemperatures

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 3.29P: Consider three ideal single-phase transformers (with a voltage gain of ) put together as ...

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Consider three ideal single-phase transformers (with a voltage gain of ) put together as three-phase bank as shown in Figure 3.35. Assuming positive-sequence voltages for Va,Vb, and Vc find Va,Vb, and VC. in terms of Va,Vb, and Vc, respectively. (a) Would such relationships hold for the line voltages as well? (b) Looking into the current relationships, express IaIb and Ic in terms of IaIb and Ic respectively. (C) Let S and S be the per-phase complex power output and input. respectively. Find S in terms of S.
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.
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
In developing per-unit equivalent circuits for three-phase transformers. under balanced three-phase operation. (i) A common Sbase is selected for both the H and X terminals. (ii) The ratio of the voltage bases Vbase/VbaseX is selected to be equal to the ratio of the rated line-to-line voltages VratedHLL/VratedXLL. (a) Only one of the above is true. (b) Neither is true. (C) Both statements are true.
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 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
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?
The per-unit equivalent circuit of two transformers Ta and Tb connected in parallel, with the same nominal voltage ratio and the same reactan of 0.1 per unit on the same base, is shown in Figure 3.43. Transformer Tb has a voltage-magnitude step-up toward the load of 1.05 times that of Ta (that is, the tap on the secondary winding of Tb is set to 1.05). The load is represented by 0.8+j0.6 per unit at a voltage V2=1.0/0 per unit. Determine the complex power in per unit transmitted to the load through each transformer, comment on how the transformers share the real and reactive powers.
The direct electrical connection of the windings allows transient over voltages to pass through the auto transfonner more easily, and that is an important disadvantage of the autotransformer. (a) True (b) False
Explain the concept of distributed energy resources (DERs) and their impact on the modern power grid.
Construct the circuit in Figure 1 in the Circuit JS simulator. Note that the voltage source is given in RMS. Within Circuit JS while defining the max voltage of the voltage source include “rms” after the number to tell Circuit JS that this is a rms value. Also note that there are additional parameters when instantiating a transformer in Circuit JS. Leave these at the default values. Additionally, transformers may have problems simulating in Circuit JS. Answer the following: 1. From the simulation results, determine the power dissipated in R2 and compare to the expected value from the previous section.2. Change the transformer ratio (“Ratio” as a fraction when you “Edit…” the transformer component) to the value calculated in the previous section to provide maximum power transfer in R2. Note: In Circuit JS, Transformer Ratio = Primary/Secondary.3. Rerun the simulation, calculate the power dissipated in R2 and compare to the expected value from the previous section.4. Change the…
Describe the concept of power system harmonics and their impact on the quality of electrical supply.