Alternators

Problem 591: A three-phase, 11-kV wye connected synchronous alternator has a synchronous reactance of 8 ohms per phase but negligible resistance. If the excitation is such that the open circuit voltage is 14 kV, determine the power factor at the maximum output.

Problem 592: A three-phase AC generator is supplying power to a load of 3200 kW at 2300 volts and a power factor of 60%. Assume that the loss of the line, the generator armature and the load is equal to 10% of the load, what would be the savings in watts if the power factor were raised to 80%?

Problem 593: A 3-phase 50 MVA, 13.8 kV, 3600 rpm, 60 Hz grid connected generator with a synchronous reactance of 3.8 ohms per phase operating with a lagging power factor of 0.88 at rated voltage and current. Determine new power factor if the rotor current is decreased by 5%.

Problem 594: A 3-phase 50 MVA, 13.8 kV, 3600 rpm, 60 Hz grid connected generator with a synchronous reactance of 3.8 ohms per phase operating with a lagging pf of 0.88 at rated voltage and current. If the load decreases such that its prime mover power is decreased by 25% and the rotor current decreases by the same percentage, what will be the new pf?

Problem 595: A 3-phase 50 MVA, 13.8 kV, 3600 rpm, 60 Hz grid connected generator with a synchronous reactance of 3.8 ohms per phase operating with a lagging pf of 0.88 at rated voltage and current. If the machine is to provide a lagging reactive power of 40 MVAR and still operating at its rated current, what percent change in the rotor current is required?

Problem 596: A three-phase turbo alternator has a reactance of 15 ohms and negligible resistance, the machine draws an armature current of 250 amperes at 0.8 pf lagging when running on 12,000 volts infinite busbars. If the steam admission is constant but the emf is raised by 20%, calculate the new operating pf.

Problem 597: A three-phase, 20 kV, synchronous alternator has a reactance of 10 ohms and a negligible resistance. The machine draws an armature current of 150 A, 0.80 pf lagging. If the steam admission is constant and field current is adjusted raising the induced the emf by 25%, determine the value of the new armature current.

Problem 598: A standby Diesel generator set will have the following loads: Inductive load drawing 50 kVA at 0.8 power factor; Lighting load drawing 20 kVA at 1.0 power factor. At what power factor will the generator operate?

Problem 599: A 250 V, 30 Hz generator supplies power to a parallel circuit consisting of a 20 hp motor whose efficiency is 90% at 0.80 pf lagging and a second load that draws an apparent power of 7 kVA at unity pf. Determine the system reactive power.

Problem 600: Two 3-\(\phi\), 4160 V, 60 Hz alternators are operated in parallel. The total load of the system is 1050 W at 75% lagging pf. If alternator A is carrying 700 kW at 80% pf lagging, determine kVAR of alternator B.

Problem 601: Two alternators A and B are operating in parallel supplying a load drawing 1000 kVA at 0.80 power factor lagging. If alternator A contributes 500 kVA at 0.60 power factor lagging, determine the power factor of alternator B.

Problem 602: Two identical three-phase Y-connected alternators A and B share equally a load of 10 MW at 33 kV and 80% lagging pf. The synchronous reactance of each machine is 4 ohms per phase and the armature resistance is negligible. Alternator A has its field excitation adjusted to carry 125 A lagging current, what is the current supplied by alternator B?

Problem 603: Alternator A (100 kVA, 3-\(\phi\), 240 V, 60 Hz, 1800 rpm) is operating in parallel with alternator B (125 kVA, 3-\(\phi\), 240 V, 60 Hz, 1800 rpm). The load of alternator A is 60 kW at 90% pf lagging and the load of alternator B is 80 kW at 70% pf lagging. Determine pf of load.

Problem 604: Two 3-phase, Y-connected turbo alternators supply a load of 3000 kW at 6.6 kV and at 0.8 pf lagging. The excitation of machine A is adjusted so that it delivers 150 A at a lagging power factor, and the governors are so set that the load is shared equally between the machines. Determine the operating power factor of machine B.

Problem 605: Two alternators are operating in parallel supplying a common load of 4250 kW at 0.85 power factor lagging. Alternator A contributes 600 kVAR at 0.92 power factor lagging. Solve for the power factor of alternator B

Problem 606: Two Y-connected alternators A and B running in parallel supply the following loads at 3.3 kV: Load 1: 800 kW at unity pf; Load 2: 600 kW at 0.8 pf lagging; Load 3: 400 kW at 0.707 pf lagging. If alternator A is adjusted to carry an armature current of 150 A at 0.85 pf lagging, what is the armature current of alternator B?

Problem 607: Two AC generators running in parallel supply the following loads: 400 kW at unity pf; 500 kW at 0.9 pf lagging; 600 kW at 0.866 pf lagging. One machine is loaded to 1000 kW at a pf of 0.92 lagging, what is the operating power factor of the second machine.

Problem 608: Two alternators are connected in parallel. The total load is 4250 kW at 0.85 pf lagging. Alternator A operates with a load of 2125 kW at 0.707 pf lagging. Determine the kVA load of alternator B.

Problem 609: Sipalay Mines, has two 3-phase, 60 Hz AC generators operating in parallel. The first unit has a capacity of 1000 kVA and the second unit has a capacity of 1500 kVA. The first is driven by a prime mover so adjusted that the frequency fall from 61 Hz at no-load to 59.6 Hz at full load. The second has a different speed-load characteristics, the frequency fall from 61.4 Hz at no-load to 59.2 Hz at full load. When these alternators are jointly delivering 2000 kW, what is the load of each generator?

Problem 610: Two alternators are driven by shunt motors. The shunt motors have speed-load droop characteristics of 3% and 4% respectively. The alternators are in parallel and each carrying 50 kW. There is no automatic speed-load control. An additional 50 kW is switched on. What are the resulting loads of the alternators assuming that the speed-load control of each is not adjusted?