1. A 3-phase, 30 MVA, 33 kV alternator has internal reactance of 4% and negligible resistance. Find theexternal reactance per phase to be connected in series with the alternator so that steady current on short-circuit does not exceed 10 times the full load current.[2-178 Q]2. A 3-phase transmission line operating at 33 kV and having a resistance of 5 2 and reactance of 20 Q isconnected to the generating station through 15,000 kVA step-up transformer. Connected to the bus-barare two alternators, one of 10,000 kVA with 10% reactance and another of 5000 kVA with 7:5% reac-tance. Calculate the short-circuit kVA fed to the symmetrical fault between phases if it occurs(1) at the load end of transmission line(ii) at the high voltage teminals of the transformer[(1) 44,500 kVA (ii) 100,000 kVA]3. The plant capacity of a 3-phase generating station consists of two 8 MVA generators of reactance 14-5%each and one 4 MVA generator of reactance 9-5%. These are connected to a common bus-bar fromwhich loads are taken through a number of 3 MVA step-up transformers each having 4% reactance.Determine the MVA rating of the circuit breakers on (1) L.V. side and (ií) H.V. side. Reactances given[1) 15-24 MVA (i) 50-25 MVA]are based on the MVA of each equipment.4. The 33 kV bus-bar of a station are in two sections A and B separated by a reactor. Section A is fed fromfour 10 MVA generators each having 20% reactance and section B is fed from the grid through 50 MVAtransformer of 10% reactance. The circuit breakers have rupturing capacity of 500 MVA. Find thereactance of the reactor to prevent the circuit breakers being overloaded if a symmetrical short-circuit[145 Q]occurs on an outgoing feeder connected to it.5. A generating station has five section bus-bar connected with a tie-bar through 7-5% reactors rated at3000 kVA. Each generator is of 3000 kVA with 10% reactance and is connected to one section of thebus-bar. Find the total steady input to a dead short-circuit between the lines on one of the sections of the[(1) 55-3 MVA (ii 150 MVA]bus-bars (1) with and (iî) without reactors.

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1. A 3-phase, 30 MVA, 33 kV alternator has intemal reactance of 4% and negligible resistance. Find the external reactance per phase to be connected in series with the altemator so that steady current on short- circuit does not exceed 10 times the full load current. [2-178 Q] 2. A3-phase transmission line operating at 33 kV and having a resistance of 5 Q and reactance of 20 N is

1. A 3-phase, 30 MVA, 33 kV alternator has intemal reactance of 4% and negligible resistance. Find the external reactance per phase to be connected in series with the altemator so that steady current on short- circuit does not exceed 10 times the full load current. [2-178 Q] 2. A3-phase transmission line operating at 33 kV and having a resistance of 5 Q and reactance of 20 N is

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 3.43P: Three single-phase transformers, each rated 10MVA,66.4/12.5kV,60Hz, with an equivalent series...

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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.
Consider the single-Line diagram of a power system shown in Figure 3.42 with equipment ratings given: Generator G1: 50MVA,13.2kV,x=0.15p.u. Generator G2: 20MVA,13.8kV,x=0.15p.u. Three-phase -Y transformer T1: 80MVA,13.2/165YkV,X=0.1p.u. Three-phase Y- transformer T2: 40MVA,165Y/13.8kV,X=0.1p.u. Load: 40MVA,0.8PFlagging,operatingat150kV Choose a base of 100 MVA for the system and 132-kV base in the transmission-line circuit. Let the load be modeled as a parallel combination of resistance and inductance. Neglect transformer phase shifts. Draw a per-phase equivalent circuit of the system showing all impedances in per unit.
Three single-phase transformers, each rated 10MVA,66.4/12.5kV,60Hz, with an equivalent series reactance of 0.1 per unit divided equally between primary and secondary, are connected in a three-phase bank. The high-voltage windings are V-connected and their terminals are directly connected to a 115-kV three-phase bus. The secondary terminals are all shorted together. Find the currents entering the high-voltage terminals and leaving the low-voltage terminals if the low-voltage windings are (a) Y-connected and (b) - connected.
The motors M1andM2 of Problem 3.45 have inputs of 120 and 60 MW, respectively, at 13.2 kV, and both operate at unity power factor. Determine the generator terminal voltage and voltage regulation of the line. Neglect transformer phase shifts.
A 3-ph transmission line operating at 10 kV and having a resistance of 1 ohm and a reactance of 4 ohms is connected to the generating station bus-bars through a 5 MVA step-up transformer having a reactance of 5%. The busbars are supplied by a 10-MVA alternator having 10% reactance. Calculate the symmetrical short-circuit current if it occurs (a) at the receiving end of the line and (b) at the HV terminals of the transformer.
A 15kVA, 440V, single-phase alternator draws a field current of 5A at rated load. With the same field current, the open circuit emf and short-circuit current are 100V and 80A respectively. The ohmic resistance of the armature between terminals is 0.12 ohm. The ratio of effective to ohmic resistance maybe taken as 1.1. Determine the voltage regulation (in %) when the load is purely resistive.
The figure below shows a radial transmission system with a generator having a terminalvoltage of 95 KV at angle of10.5°. The load demand is 50 MW at a power factor of 0.88 lagging.Use a base of 128.4MVA . Instructions :round of to 2 decimal places. Calculate the following : 1.Load current (A) and Base current (A) 2Per unit impedance of transformer 2 and Per unit impedance of transformer 1.3.Per unit voltage of the generator. And Per unit voltage of the line. 4.Per unit voltage of the transformer 1 5.Per unit impedance of the line.6.Resistance of the transmission line when the load consumes full-load (Ω).
(i) at the load end of transmission line (ii) at the high voltage terminals of the transformer Q.5 A 3-phase transmission line operating at 33 kV and having a resistance of 5 ohm and reactance of 20 ohm is connected to the generating station through 5, 00 KVA step-up transformer.Connected to the bus-bar are two alternators,one of 10, 00 KVA with 10% reactance and another of 5000 kVA with 7.5% reactance.Calculate the short-circuit kVA fed to the symmetrical fault between phases if it occurs
A 50 MVA, 15 kV three phase generator has a subtransient reactance of 0.2 p.u. The generator supplies two motors over a transmission line having transformers at both ends as shown in Fig. The motors have rated inputs of 30 MVA and 20 MVA both 30 kV with 0.15 p.u. subtransient reactance. The rating of the sending end transformer, Tr1 is 50 MVA, 11 kV / 132 kV with leakage reactance of 0.1 p.u. Transformer Tr2 at the receiving end has three single phase transformers and the rating of each individual transformer is 20 MVA , 33 / 76 kV with leakage reactance of 0.12 p.u. Series reactance of the line is 25 ohms. Draw the reactance diagram with all reactance marked in p.u. Select the generator rating as the base in the generator circuit.
2. A 3Ø, 2000KW, 480V ∆-connected alternator is short-circuited and is operated at ratedspeed to produce rated current at 4A excitation. With the short-circuit remove andwith the excitation adjusted to 5A, the voltage between stator terminal is 330V. Theeffective resistance between terminal as measured with dc is 2Ω. Determine the %V.R.of the alternator at half-load and pf of 0.8 leading without changing any given values.
A 3Ø, Y-connected alternator is rated at 1,600KVA, 13.5KV. The armature effective AC resistance per phase is 1.5Ω. The percentage regulation for a load of 1,280kW at unity power factor is 3.5%. Determine:(a) synchronous reactance of the alternator(b) %VR at full-load 0.8pf leading(c) What is the effect on %VR value if taken at half-load lagging pf? Justify andexplain briefly your answer on one(1) sentence.
A 3-phase transmission line operating at 33 kV and having a resistance of 5 Ω and reactance of 20 Ω isconnected to the generating station through 15,000 kVA step-up transformer. Connected to the bus-barare two alternators, one of 10,000 kVA with 10% reactance and another of 5000 kVA with 7·5% reactance.Calculate the short-circuit kVA fed to the symmetrical fault between phases if it occurs(i) at the load end of transmission line(ii) at the high voltage terminals of the transformer[(i) 44,500 kVA (ii) 100,000 kVA]