2B: The relays of type ID_MT on The Feeders circuit breakers have a current setting of 125% CT ratio yoo/5 and atime multiplier setting of 400/5 0.5A three phase fault current of 5000A Flows through feeders, The characteristics of The relay given in atable for PS_M=1 calculate: Ⓒ Feeders relay current RSM and The actual operating time IF The Feeder supplied by transformer Find The TSM For The trans former overcurrent relay Take The discrimination time 0.5 sec. CT ratio 1000/ and CS-100% 10621.7 PSM: Time sec 2.2 20 16 12 2.5 2.75 3 3.8 10 12

2B: The relays of type ID_MT on The Feeders circuit breakers have a current setting of 125% CT ratio yoo/5 and atime multiplier setting of 400/5 0.5A three phase fault current of 5000A Flows through feeders, The characteristics of The relay given in atable for PS_M=1 calculate: Ⓒ Feeders relay current RSM and The actual operating time IF The Feeder supplied by transformer Find The TSM For The trans former overcurrent relay Take The discrimination time 0.5 sec. CT ratio 1000/ and CS-100% 10621.7 PSM: Time sec 2.2 20 16 12 2.5 2.75 3 3.8 10 12

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 3.47P: Consider the oneline diagram shown in Figure 3.40. The three-phase transformer bank is made up of...

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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.
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.
Q2: A generator supplies motor through a star-delta transformer. The generator is connected to the star side of transformer. A fault occurs between the motor terminals and the transformer. The symmetrical components of the rubtransient current in motor and transformer toward the fault as table below laz(per unit) j2.0 lao(per unit) j3.0 las (per unit) Motof toward the fault Transformer toward the -0.8-j2.6 0.8-j0.4 j1.0 fault Assume X-X,- X2 for both the motor and gencrator. Describe the type of fault. Find (a) the prefault current, in line a, (b) the subtransient fault current in per unit and (c) the subtransient current in each phase of the gencrator in per unit. Gén. Motor
2. What type of potential transformer would you use for a 362-kV grounded-neutral metering application on an interconnection system? A. Bar-type B. Cascade-type C. Window-type D. Phase-shift-type
Q2 Figure Q2 shows a single line diagram of a power system and the associated data of this system are given in Table Q2. The pre-fault load current and A-Y transformer phase shift are neglected. (a) (b) If a Single Line-to-Ground (S-L-G) fault occurs at Bus 5 and the pre-fault voltage is 1.0 pu, calculate the subtransient fault current in Ampere. (c) (d) (e) Using base of 100 MVA and 11 kV at generator G₁, construct the positive sequence, negative sequence and zero sequence networks with their corresponding component values indicated. G₁ Recalculate (b) if the neutral on HV side of T3 is solidly grounded. Repeat part (b) with Line-to-line (L-L) fault. What will happen to L-L fault current in (d) if the neutral on the HV side of T3 is solidly grounded? Bus 1 T₁ Bus 4 Line 1 Line 2 Figure Q2 Bus 5 T2 T3 Bus 2 Bus 3 G₂ G3
Problem #2: A transformer is fed from a 100 MVA, 18 kV generator via a 5-cycle breaker. Generator reactance are: X"F18%, X'=25%, Xe=120%. A three-phase fault occurs at the load side of the breaker when the transformer was unloaded. Find: A)The sustained short circuit current in the breaker. B) Initial symmetrical rms current in the breaker. C) Maximum de short circuit component in the breaker.
Problem #2: A transformer is fed from a generator via a 5-cycle breaker. Generator reactance are: X"=18%, X'=25%, Xe=120%. A three-phase fault occurs at the load side of the breaker when the transformer was unloaded. Find: A)The sustained short circuit current in the breaker. B) Initial symmetrical rms current in the breaker. C) Maximum dc short circuit component in the breaker.
QUESTION TWOo A three-phase 50 Hz, 200 MVA, 220/66 kV transformer has a clock number of Yd11. The transformer winding resistances are 2.0 N and 0.12 N, and the leakage reactances are 10 N and 0.6 N for the high voltage side and low voltage side respectively. (a) Sketch the phase voltage phasor diagrams for the high-voltage side and low-voltage side of the transformer and from the phasor diagrams obtain its connection diagram. (b) Calculate the per-unit impedance of the transformer referred to the high-voltage side. (c) Calculate the full-load copper losses of this transformer. (d) Calculate the efficiency of the transformer when it supplies 90% of full-load at a power factor of 0.85 lagging, if the core losses are equal to 1.6 MW. (e) Suggest the most suitable method of cooling this transformer and explain how the suggested method works. () Why are most power transformers and distribution transformers' tanks oil-filled? To increase the supply capacity, the transformer described above…
8. A three-phase 50 Hz, 200 MVA, 220/66 kV transformer has a clock number of Yd11. The transformer winding resistances are 2.0 N and 0.12 A, and the leakage reactances are 10 0 and 0.6 N for the high voltage side and low voltage side respectively. (a) Sketch the phase voltage phasor diagrams for the high-voltage side and low-voltage side of the transformer and from the phasor diagrams obtain its connection diagram. (b) Calculate the per-unit impedance of the transformer referred to the high-voltage side. (c) Calculate the full-load copper losses of this transformer. (d) Calculate the efficiency of the transformer when it supplies 90% of full-load at a power factor of 0.85 lagging, if the core losses are equal to 3 MW.
b) A fault occurs at bus 4 of the network shown in Figure Q3. Pre-fault nodal voltages throughout the network are of 1 p.u. and the impedance of the electric arc is neglected. Sequence impedance parameters of the generator, transmission lines, and transformer are given in Figure Q3, where X and Y are the last two digits of your student number. V₁ = 120° p.u. V₂ = 120° p.u. jX(1) j0.1Y p.u. jX2)= j0.1Y p.u. jXko) j0.1X p.u. - 0 jX(1) = j0.2 p.u. 1JX(2) = 0.2 p.u. 2 jX1(0) = j0.25 p.u. jX2(1) j0.2 p.u. V₁=1/0° p.u. jX(2(2) = j0.2Y p.u. jX2(0) = j0.3X p.u. = V₂ = 120° p.u. jXT(1) j0.1X p.u. jXT(2) j0.1X p.u. JX3(1) j0.1Y p.u. JX3(2)=j0.1Y p.u. jXT(0) j0.1X p.u. JX3(0)=j0.15 p.u. 0- = 3 = Figure Q3. Circuit for problem 3b). For example, if your student number is c1700123, then: jXa(n) = j0.13 p. u., jXa(z) = j0.13 p. u., and jXa(o) = j0.12 p. u. 4 (i) Assuming a balanced excitation, draw the positive, negative and zero sequence Thévenin equivalent circuits as seen from bus 4. (ii)…
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Voltage unbalance is the unbalance that occurs when the voltages at different motor terminals are not equal. This is a big problem for power companies generating, and other facilities using three phase power. If left in this condition this can cause transformer and motor windings to prematurely burn open. Using a DMM you are troubleshooting a 480 volt, 3 phase power feeding a fused disconnect connected to a 3 phase, 1 H.P. motor. Your findings are as follows: Phase A/B = 441 volts, Phase A/C = 479 volts and Phase B/C = 457 volts Find the voltage unbalance and determine if this is acceptable.