Contents
What is the pitch factor of an alternator?
The pitch factor is the measure of resultant emf of a short-pitched coil in comparison with resultant emf of a full pitched coil. Hence, it must be the ratio of phasor sum of induced emfs per coil to the arithmetic sum of induced emfs per coil.
How do you reduce the harmonics in the emf generated in the alternator?
As a result, harmonic emf is always generated in the Alternator. These harmonics can however be eliminated / suppressed by the following methods: The distribution of armature winding along the air gap periphery tends to make the generated emf waveform sinusoidal.
What factors do the generated emf in an alternator depend upon?
Due to relative motion between armature conductors and the main field, an emf is induced in the armature windings whose magnitude depends upon the relative speed and as well as the magnetic flux.
What is synchronizing power of an alternator?
Synchronizing Power is defined as the difference between input power to alternator at power angle 𝛿 and input power to alternator at power angle 𝛿 + 𝛿’. Synchronizing Power is denoted by PSY. Let V be the bus bar voltage and E be the EMF induced in the alternator.
How are slot angles calculated?
Calculation of Distribution Factor These slots are distributed along the periphery of stator in 2 pole pitches. Therefore the angle between any two consecutive slots will be equal to 20 degree (2×180 / 18 = 20). This angle between two consecutive slots is called Angular Slot Pitch.
How many windings does an alternator have?
Three-phase alternators have three sets of windings; they’re more efficient than a single-phase alternator, which produce a single-phase AC current. When working properly, the three windings produce three currents that make up the three phases. Adding all three together produces the total AC output of the stator.
How do I reduce the harmonics of my alternator?
The different ways to eliminate the harmonics from generated voltage are,
- Distribution of armature windings : Instead of having concentrated type of windings, they should be distributed in different slots.
- Chording :
- Fractional slot windings:
- Skewing:
- Large length of air gap:
Which prime mover is used for high speed alternator?
The prime movers used for salient pole alternators are water wheels like Kaplan turbine, Francis turbine, Pelton wheel etc., and diesel or petrol engines. The prime movers used for non-salient pole alternators are steam turbines and gas turbines. 7. Salient pole machines are not suitable for high speed operations, why?
Which kind of motor is most suitable for turbo alternator which are designed to run at high speed?
Non-salient pole type or cylindrical type rotors are used in high-speed alternators or turbo-alternators having speed between 1500 rpm to 3000 rpm.
Which is the best chording angle for an alternator?
A chording angle of 30° is most useful in an Alternator as it gives the following pitch factors, 0.966 for fundamental, 0.707 for 3rd harmonic, 0.259 for 5th and 7th harmonics and 0.7.7 for 9th harmonics.
Why is the chording angle 30 degrees in synchronous generator?
Chording angle in Synchronous Generator/ Alternator is introduced to tackle the problem of harmonics that couldn’t be taken care of during the design either in – Cylindrical Pole Rotor : As we can’t achieve a stepped sinusoidal mmf in the air gap, given that the manufacturers are reluctant to cut the slots with different dye’s as they are costly.
How to calculate the pitch factor of an alternator?
Calculate the pitch factor for the under-given windings : (a) 36 stator slots, 4-poles, coil-span, 1 to 8 (b) 72 stator slots, 6 poles, coils span 1 to 10 and (c) 96 stator slots, 6 poles, coil span 1 to 12. Sketch the three coil spans.
How is the 3 rd harmonic suppressed in 3 phase alternator?
In 3 phase alternator, the 3 rd harmonic is suppressed by star or delta connection as in the case of 3 phase transformer. Total attention is given for designing a 3 phase alternator winding design, for 5 th and 7 th harmonics.