For some electrical machines, taking into account their features, other calculation stages may be used, and the dependencies of the main dimensions may be written in a different form.
1. Design power P′. First, based on the rated power of the machine, the calculated power P′ is determined using formulas (1)–(5).
Then, according to P′ and n - synchronous speed for AC machines or rated speed for DC machines - taking into account the characteristics of the machine being designed, electromagnetic loads A and Bδ are selected according to the recommended data or curves. Substitution into formula (6) allows you to determine the volume of the anchor D2Lef. For a single-layer AC winding with a full step, you can first take Kdp = 0.96; for a two-layer shortened winding with a coil pitch y=5ι/6 - Kdp=0.92.
P’=KEPN/ηNcosψN………………(1)
Formula (1) is applied to asynchronous machines and synchronous generators. The unit of P′ is kilovolt-ampere.
P’=KEPN/cosψN………………(2)
Formula (2) applies to synchronous generators. The unit of P′ is kilovolt-ampere.
P’=KEPN………………(3)
Formula (3) applies to synchronous compensators. The unit of P′ is kilovolt-ampere.
P’=KgPN………………(4)
Formula (4) is applied to DC generators with parallel excitation. The unit of P′ is kilowatt.
P’=KmPN/ηN………………(5)
Formula (5) is applied to DC motors with parallel excitation. The unit of P′ is kilowatt.
In formulas (1)–(5):
KE is the ratio of the induced EMF to the voltage at the terminals at rated load;
ηN and cosψN - efficiency and power factor at rated load;
Kg is a coefficient that takes into account the voltage drop in the generator armature and the machine with parallel excitation;
Km is a coefficient that takes into account the voltage drop in the generator armature and the machine with parallel excitation.
nD2Lef/P’=CA………………(6)
2. Calculation of D and Lef
Based on the recommended data, a suitable λ is selected, after which the main dimensions D and Lef are determined separately using the calculated volume of the anchor D2Lef.
For asynchronous and synchronous machines, the outer diameter of the stator D1 is also determined. To effectively use electrical steel, reduce the number of standard sizes of dies and other equipment, increase unification and ensure a consistent increase in power in the series in China, standard outer diameters of stator cores for AC machines D1 and armatures for DC machines Da have been established.
For D1 or Da greater than 99 cm, segmented sheets should be used.
It should be noted that the standard diameters were established taking into account the level of production of that time and are not constant. Some new series also use other diameters.
3. Method of empirical analogy
Considerable practical experience has been accumulated in production, so the main dimensions are often determined by analogy.
Taking into account the specific conditions of the designed machine - design, materials, technical and economic indicators and technology - the main dimensions and other parameters are preliminarily selected based on the design and test data of previously produced machines of the same type and similar sizes. For example, for an induction machine, it is common to directly select the outer diameter of the stator and the corresponding dimension or height of the axle, inner diameter, length, air gap, inner diameter of the rotor and the number of stator and rotor slots.
If the designed machine I and the previously produced machine II of the same type have the same number of poles, but different rated power, using formula (6), the armature length, conductor cross-section and number of turns are approximately determined by the ratio PNI/PNII.
The material is not an official publication and reflects the personal opinion of the author.