TUTORIAL PROBLEMS 1. A 3-phase, 30 MVA, 33 kV alternator has internal reactance of 4% and negligible resistance. Find the external reactance per phase to be connected in series with the alternator so...

A 3-phase, 30 MVA, 33 kV alternator has internal reactance of 4% and negligible resistance. Find the
external reactance per phase to be connected in series with the alternator so that steady current on shortcircuit does not exceed 10 times the full load current. [2·178 Ω]

Extracted text: TUTORIAL PROBLEMS 1. A 3-phase, 30 MVA, 33 kV alternator has internal reactance of 4% and negligible resistance. Find the external 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 and reactance of 20Q is connected to the generating station through 15,000 kVA step-up transformer. Connected to the bus-bar are 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 (i) at the load end of transmission line (ii) at the high voltage terminals 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 from which 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 (i) L.V. side and (ii) H.V. side. Reactances given |(1) 15-24 MVA (ii) 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 from four 10 MVA generators each having 20% reactance and section B is fed from the grid through 50 MVA transformer of 10% reactance. The circuit breakers have rupturing capacity of 500 MVA. Find the reactance of the reactor to prevent the circuit breakers being overloaded if a symmetrical short-circuit 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 at 3000 kVA. Each generator is of 3000 kVA with 10% reactance and is connected to one section of the bus-bar. Find the total steady input to a dead short-circuit between the lines on one of the sections of the bus-bars (i) with and (ii) without reactors. [1-45 Q| |() 55-3 MVA (ii) 150 MVA] 6. A generating station has four bus-bar sections. Each section is connected to tie-bar though 20% reactors rated at 200 MVA. Generators of total capacity 100 MVA and 20% reactance are connected to each bus- bar section. Calculate the MVA fed to a fault under short-circuit condition one one of the bus-bars. [1000 MVA]