Figure Qu. 1 below shows a simple Single Line Diagram (SLD) for a power system where a Utility supplies a 66 kV Customer. - 13.8 kV The 'PG Bus' is a 13.8 kV Power Generation Bus, to which Generators G1, G2, G3 & G4 are connected. The 'T Bus' is a 66 kV Transmission bus, which connects Transformers TF1 and TF2, to two lines L1 and L2. These two lines supply power to the 66 kV 'Customer Bus'. G1 YG 100MW 0.8 p.f. 13.8 kV Zpu=2% TF1 66 kV 66 kV L1 Zone 1 G2 G 350 MVA 13.8/66 kV Zpu = 0.28 YND11 50 MVA 0.8 p.f. 13.8 kV Zpu=1% Z actual =j2.1780 Bus 1 Customer Bus * BSCB CB1 X Figure Qu. 1 G3 G Equipment 66 kV Customer Busbars 66 kV Bus Section Circuit Breaker - BSCB 66 kV Circuit Breaker - CB1 66 kV Circuit Breaker - CB2 CB2 50 MVA 0.8 p.f. 13.8 kV Zpu=1% TF2 Bus 2 Z actual =j2.1780 L2 F 350 MVA 13.8/66 kV Zpu = 28% YND11 Zone 2 G4 YG T Bus 40 20 20 20 Maximum Short Circuit Rating (KA) The Utility's equipment data are indicated on the SLD in Figure Qu. 1, while the 66 kV Customer has provided the data in Table 1 below, for the equipment which they own. Table 1: Customer's Equipment Data As an engineer at the Utility, you are required to prepare the following. 100MW 0.8 p.f. 13.8 kV Zpu=2% PG Bus Page 1 of 7 Note: (1) You must use a base MVA of 100 MVA and a base Voltage of 66 kV for all of your calculations (2) You are to assume that all busbar, conductors, and circuit breakers have negligible impedance, unless otherwise specified (3) You are to assume that all circuit breakers indicated are operated in the closed state i. Draw and simplify the per unit impedance diagram (to its Thevenin equivalent) for the power system shown in Figure Qu. 1. (5 marks) ii. Determine the per unit and actual short circuit level at 'Bus 2' for a 3 phase bolted fault, F. (2 marks) iii. Determine the actual short circuit fault current at 'Bus 2' for the 3-phase bolted fault, F. (1 mark) Tragedy has struck There has been a major fire at the Power Generation Station and G4 was damaged beyond repair. Executives at the Utility decide that moving forward, they can reduce network losses (save money) by commissioning the replacement generator closer to the Load. These Utility Executives somehow manage to persuade the Customer to provide accommodation (at no cost) for the replacement generator. The new generator will therefore inject power via a 100 MVA, 13.8/66 kV Transformer (TF3), directly onto Zone 1 of the 66 kV Customer Bus. iv. Describe briefly, one engineering consideration you may have with respect to the proposed electrical location of the replacement generator, and how it may affect the Customer's Equipment. (2 marks) Page 2 of 7 The Utility has a 100MVA, 13.8/66 kV Transformer in stock and readily available for use as TF3, however it is also possible for a new custom built 100 MVA, 13.8/66 kV Transformer to be quickly procured, if the need arises. The nameplate information for the 'in-stock' transformer is detailed as follows; - MVA Rating - 100 MVA Voltage Ratio - 13.8/66 kV p.u. Impedance - 10% Vector Group - YNd11 A manufacturer catalogue has three possible options for the replacement generator, GT_A, GT_B or GT_C, and their specifications are detailed in Table 2 below. Terminal Voltage 100 MVA 13.8 kV 80 MW 13.8 kV 100 MVA 13.8 kV Table 2: Replacement Generator Options The Utility's Executive is inclined to procure GT_B since it is the cheapest. V. Generator ID Rating/Capacity GT_A GT_B GT_C p.f. 0.8 80% 0.8 p.u. Impedance 1% 0.03 5% As an Engineer at the Utility, determine the feasibility, using calculations to support your argument, of replacing G4 with GT_B. Give special consideration to the existing customer equipment Hints a. Draw the per unit representation for all equipment in the proposed power system. (Remove any non-functional equipment, and insert GT_B generator, with the 'in-stock' transformer as the associated step up transformer). (3 marks) C. b. Simplify the per unit diagram in (a) and determine the actual short circuit current for a 3-phase bolted fault F, on 'Bus 2' (5 marks) Comment on the suitability of procuring GT_B to be used with the 'in- stock' transformer. (2 marks) d. Determine the per unit and actual fault current contribution from GT_B (at the generator terminals) for a 3-phase bolted fault F, on 'Bus 2'. (3 marks) e. Suggest three (3) recommendations which will theoretically ensure that the Customer can safely clear any 3-phase bolted fault at their facility. Give consideration to all the information detailed above as well as any other engineering method which you may be aware of. (3 marks) Page Limit- 4 pages (single sided)