EXAMPLE 9.1 Power-system sequence networks and their Thévenin equivalents A single-line diagram of the power system considered in Example 7.3 is shown in Figure 9.3, where negative- and zero-sequence reactances are also given. The neutrals of the generator and A-Y transformers are solidly grounded. The motor neutral is grounded through a reactance X, = 0.05 per unit on the motor base. (a) Draw the per-unit zero-, positive-, and negative- sequence networks on a 100-MVA, 13.8-kV base in the zone of the generator. (b) Reduce the sequence networks to their Thévenin equivalents, as viewed from bus 2. Prefault voltage is VF = 1.05/0° per unit. Prefault load current and A-Y transformer phase shift are neglected. FIGURE 9.3 т, 2 M Line Single-line diagram for Example 9.1 X2 - 20 0 X, = 60 N X, 100 MVA 13.8 kV 100 MVA 100 MVA X" - 0.15 13.8-kVA/138-kVY 138-kV Y/13.8-kVA 100 MVA X, = 0.17 X = 0.10 per unit X = 0.10 per unit 13.8 kV Xo = 0.05 per unit X" = 0.20 %3D X2 = 0.21 Xo = 0.10 X, = 0.05 per unit

EXAMPLE 9.1 Power-system sequence networks and their Thévenin equivalents A single-line diagram of the power system considered in Example 7.3 is shown in Figure 9.3, where negative- and zero-sequence reactances are also given. The neutrals of the generator and A-Y transformers are solidly grounded. The motor neutral is grounded through a reactance X, = 0.05 per unit on the motor base. (a) Draw the per-unit zero-, positive-, and negative- sequence networks on a 100-MVA, 13.8-kV base in the zone of the generator. (b) Reduce the sequence networks to their Thévenin equivalents, as viewed from bus 2. Prefault voltage is VF = 1.05/0° per unit. Prefault load current and A-Y transformer phase shift are neglected. FIGURE 9.3 т, 2 M Line Single-line diagram for Example 9.1 X2 - 20 0 X, = 60 N X, 100 MVA 13.8 kV 100 MVA 100 MVA X" - 0.15 13.8-kVA/138-kVY 138-kV Y/13.8-kVA 100 MVA X, = 0.17 X = 0.10 per unit X = 0.10 per unit 13.8 kV Xo = 0.05 per unit X" = 0.20 %3D X2 = 0.21 Xo = 0.10 X, = 0.05 per unit

Introductory Circuit Analysis (13th Edition)

13th Edition

ISBN:9780133923605

Author:Robert L. Boylestad

Publisher:Robert L. Boylestad

Chapter1: Introduction

Section: Chapter Questions

Problem 1P: Visit your local library (at school or home) and describe the extent to which it provides literature...

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What is the definition of zero sequence impedance in transformer? What is the benefit of zero sequence impedance in transformers?
Describe the process of fault current analysis in power systems and its significance in protecting electrical equipment from damage.
Figure below shows the single-line diagram of three-bus power system with generation at bus 1 and bus 3. The voltage at bus 1 is V₁ = 1.025/0° per unit. The voltage magnitude at bus 3 is fixed at 1.05 per unit with a real power generation of 250 MW. The scheduled load on bus 2 is marked on the diagram. Line impedances are marked in per unit on a 100 MVA base. Line resistances and line charging susceptances are neglected. By using Gauss-Seidel method and initial estimates of V₂(0) = 1.020° and V3(0) = 1.0520°, determine V₂ and V3. Perform calculation for one iteration. V₁ = 1.025/0° j0.1 Slack Bus j0.2 j0.4 j0.2 3 j0.1 250 MW 150 Mvar |V3|=1.05 P3 = 250 MW
A hydro powered 50 MVA generator, with a synchronous reactance 0.33 p.u., delivers 40 MW over a transmission line of 0.15 p.u. reactance to an infinite system. A 3-phase short circuit transient fault occurs on the busbar between the generator and transmission line. Given that the generator emf is 1.4 p.u. prior to and during the fault and all reactances are to a 50 MVA base: Sketch the single line schematic diagram of the system. Determine the maximum load angle the generator can swing to without losing stability. i) ii) iii) iv) Sketch the corresponding power-angle curve for the system showing the accelerating and decelerating areas. Calculate the critical clearing angle of the system to keep its stability.
Q2\ The one-line diagram of a simple power system is shown in figure below. All impedances are expressed in per unit (pu) on a common MVA base. All resistances and shunt capacitances are neglected. The generators are operating on no load at their rated voltage. A three-phase fault occurs at bus 1 through a fault impedance of Zf = j0.08 per unit. Using Thevenin's theorem obtain the impedance to the point of fault and the fault current in per unit. Determine the bus voltages and line currents of generators during fault. X₁ = = 0.1 XT-0.1 3 1 to ojo XL=0.2 2 040 X₁ = 0.1
-The symmetrical fault occurs in the terminals of the synchronous generator. Find the direct axis transient reactance of the synchronous generator under the transient period for the data given below, Leakage reactance(Xl)= 1.3 ohm, Armature reactance (Xad)= 1.6 ohm and field reactance (Xf)=5.4 ohm. 2.10 2.53 1.23 4.00 -The existing condition of the power system can be determined by _____________ analysis. Short Circuit Stability Power Flow Transient
For the following single line diagram of a three-phase system, a three-phase fault occurs at point P and just before the fault the line voltage is 18 kV at P. Find out the transient fault current in pu and original value at point P. Take, the given kVA and kV of the G1 as the new base. [hint: the transient and sub-transient reactances of the synchronous generators are assumed to be same. But for the motors, assume that the transient one is 1.7 times of the sub-transient reactance.] 20,000 KV A 6.9KV 15% G1 7000 KVA 5KV Tz 14% 11/33KV 33/6.9 AV 5+j8 s2 (G2 load 20000 KVA 15000 KVA 10% 12%0 25,000 KVA 6.9KV 8% as orebtsansient [Au tue mpedanmees are given per-unit values)
Discussion : 1- What are the advantages and disadvantages of this test ? 2- Why it's imporctical carry out actual load test on large rating transformers ? 3- What will be the current in the primary windings? i) When secondaries are not loaded ? ii) When secondaries are loaded ?
Contribution of fault analysis in power system netwrok?
Only need answers for the second question(9.16) at bus 1.
Describe the concept of fault analysis in power systems. What types of faults can occur, and how are they mitigated?