6. The relation between the field current and the armature current in an alternator with the armature short- circuited can be shown by A. a rated-current 80% pf saturation curve. B. a synchronous impedance curve. C. an open-circuit saturation curve. D. a zero-power-factor regulation curve.
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6. The relation between the field current and the armature current in an alternator with the armature short-
circuited can be shown by
A. a rated-current 80% pf saturation curve.
B. a synchronous impedance curve.
C. an open-circuit saturation curve.
D. a zero-power-factor regulation curve.
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- Determine the efficiency of a 1500kVA, 2300 V, 3 –phase, Y – connected alternator which operates at rated output with a power factor of 80%. The DC armature resistance at 70º C between terminals is 0.08 ohm. The field takes 70 A at 120 V from the exciter equipment. Friction and windage losses are 15kW, iron loss is 35kW and stray load losses is 15 kW. Assume the effective armature winding resistance is 1.5 times the DC value. a. 94.56 % b. 90.31 % b. 93.35 % d. 92.62 %(12) An alternator which is operating in parallel with other alternators at rated terminal voltage has an armature resistance of 0.015 pu and synchronous reactance of 0.35 pu. It delivers a power output in kW equal to 0.8 of its rated kVA and the voltage regulation is equal to 15%. The power factor at which the machine is operating approximately equal to .........4. Determine the voltage regulation of a 2,000-V, 1-phase alternator giving a current of 100 A at 0.8 p.f. leading from the test results. Full-load current of 100 A is produced on short-circuit by a field excitation of 2.5 A. An e.m.f. of 500 V is produced on open-circuit by the same excitation. The armature resistance is 0.8 Q. Draw the vector diagram. |- 8,9%]
- A three-phase, 4-pole, 1,500 rpm alternating having a double layer-windings with 18 turns per coil. The slots per pole per phase are 10 and the coil span is 22 slots. The spread phase is 60 degrees and the flux per pole is 0.0625 Weber. If the armature windings are wye connected. a) Determine the generated voltage per phase and the line to line voltages. b) If the alternator is delivering a three - phase load of 1,200KW at 0.8 lagging power factor what is the line current of the alternatorDetermine the efficiency of a 1500kVA, 2300-V, 3-phase, Wye connected alternator, which operates at a rated output, with a power factor of 80%, The DC armature resistance at 0.08-ohm. The field takes a 70-Aat 120-V from the exciter equipment. Friction and windage losses are 35-kW, iron losses is 15-kW and stray power losses is 1.2-kW. The effective armature winding resistance is 1.8 times the DC value.Kindly solve the problem with step by step complete solution. Also, put the given and formula used so that I can understand. Thank you. A 2200V, 60 Hz, three-phase, Y-connected alternator has an effective resistance per phase of 0.5 ohm. A field current of 30A produces a full load current of 200A on short circuit and a line-to-line emf of 1100 V on open circuit. Determine the power angle of the alternator when it delivers full load at .80 lagging pf.
- Discussion:- 1. What do you understand by "armature- reaction"? Discuss the effect of armature reaction in an alternator when it is loaded with resistive, inductive and capacitive loads. 2. Give the value of voltage regulation for different power factors at full load current and interpret their values.First question) Choose the correct a nswer for all characters a) In an alternator, the armature reaction influences the magnitude of Wave form of generated voltage. O Flux Terminal voltage per phase Speed of the machine No load loss b) Brushless excitation system consisting stator and rotor field winding and power diodes Stator field winding and power diodes stator and rotor field winding and capacitor Everything mentioned in the options O c) If input mech. Power of SG constant, :the functionality of AVR is Control terminal voltage O Control Load angle O Control flux and terminal voltage O Control flux of rotor d) What will happen if a stationary alternator (off) is connected to a live ?power system It is likely to run as a synchronous motor :of It will decrease bus bar voltage O It will get short circuited It will disturb generated e.m.f. of other paralleled alternators. e) The winding of a 4-pole alternator having 36 slots and a coil span of 1 to 8 .is short-pitched by.............…A three-phase star-connected alternator working at 1400 KVA,50 Hz, 2300 V, has an armature dc resistance of 0.15 2. Assume the ac resistance is 1.4 times the dc resistance. A field current of 75 A produces a short circuit current of 360 A and for the same field current the open circuit voltage is 1000 V. Determine a) Synchronous reactance of the machine b) Full load regulation at 0.9 leading c) Power angle a) b)
- 1. A three-phase, 318.75-kVA, 2300-V alternator has an armature resistance of 0.35 /phase and a synchronous reactance of 1.2 2/phase. Determine the no-load line-to-line generated voltage and the voltage regulation at (a) Full-load kVA, 0.8 power factor lagging, and rated voltage. (b) Full-load kVA, 0.6 power factor leading, and rated voltage.Two identical 2,000 kW alternator operates in parallel. The governor of the first machine is such that the frequency drops uniformly from 50 Hz at no-load to 48 Hz at full-load. The corresponding uniform speed drop of the second machine is 50 Hz to 47.5 Hz. What is the maximum load that can be delivered without overloading either machine?1. i)What are the different ways to supply DC power to rotor of an alternator? Which method is superior and why? ii)How do you define ‘static stability limit’ of an alternator?