B) Recursive short-time mode

Conclusions, similar to given above, determine next correlations for the electromagnets of this type:

F = 2p²_cr∙ε²∙d⁵_c / (C₁∙δ₀²) (1.48) d_c = ⁵√[C₁∙F∙δ₀² / (2p²_cr∙ε²)] (1.49)

F / δ₀³ = 2p²_cr∙ε²χ⁵ / C₁ (1.50)

w∙I = (9∙10³∙p_cr∙d_c / φ∙χ∙τ)∙√(d_c / C₁) (1.51)

S_m = [2.82∙ρ∙(1 + n)∙p_cr∙d_c² / (φ∙χ∙τ∙U)]∙√(d_c / C₁) (1.52)

w = (U/ p_cr)∙√{10³∙f_ap∙n / [ρ∙(1 + n)∙(1 + 2n + α)∙h∙Θ_per∙d_c)]} (1.53)

The coefficient of overcurrent p_cr can be defined under the set size of relative duty ratio DR_%: p_cr = √100 / DR_%.

C) Short-time duty

In this mode, ignoring heat emission from a surface, they accept, that all radiated heat in a coil goes to heating of active material. For electromagnets with external forward armature travel and two coils it is got a like § 1.1:

permissible current density in the cross-section of wire

j = I / S_m = w∙I / (2f_ap∙m∙n∙d²_c),

MMF of electromagnet

w∙I = 2f_ap∙m∙n∙j∙d²_c,

induction in a basic air-gap

B₀ = μ₀∙φ∙χ∙ w∙I / 2δ₀,

full electromagnetic force

F = 5,1π∙μ₀∙φ²∙χ²∙j²∙f²_ap∙m²∙n²∙ε²∙τ²∙d⁶_c / δ₀².

If to enter denotation

C₃ = √[2∙10³∙ρ / c∙γ_m∙Θ_per∙ φ²∙χ²∙f²_ap∙m²∙n²∙τ²] ≈ 0,14 / (φ∙χ∙f_ap∙m∙n∙τ), (1.54)

that we will get

F = 2ε²∙d⁶_c / C²₃∙ δ₀²∙t_on.. (1.55)

The key size of examined electromagnetic core in short-time duty is determined by a formula

d_c = ³√ [(C₃∙ δ₀ / 1,41∙ε)∙√(F∙t_on) (1.56)

Dependence of F = F(χ) is determined by correlation

√F / δ₀² = 1,41∙ε∙x³ / (C₃∙√t_on) (1.57)

from which it is determined by a method, considered before:

d_c = χ∙δ₀

and accordingly cross-section of wire metal

S_m = 2π∙ρ∙(1 + n)∙f_ap∙m∙n∙d³_c / (U∙√t_on)

and number of loops of two coils

w = U∙C₄∙√t_on / d_c ≈ U∙√t_on / (π∙ρ∙(1 + n)∙d_c) (1.58)

Induction in a working air-gap is calculated under the found values of d_c, χ, ε or approximately by a formula:

B₀ ≈ (3,8∙10^-5 / τ∙ ³√C₃)∙ ³√[F / (δ₀∙√ t_on)]

Design of asynchronous machines

Last years asynchronous machines, operating in motor and generator modes, find application in the independent systems of electrical equipment. Asynchronous generator of three-phase current with the rotor winding, executed as a squirrel cage, has a series of advantages : it is simple by a design, does not have sliding contacts, possesses high reliability. High mechanical durability of rotor allows to use a generator for large angular speed of rotation. The power consumption on voltage control at the use of bias method of armature back is small (in 5÷10 times less, than at magnetoelectric generators).

An asynchronous machine, being combined motor-generating unit in the independent systems of electrical equipment, can operate in two modes − motor and generator. In the motor mode there is an acceleration of machine with a turbine to nominal speed, i. е. it operates in the starter mode. At working substance supply to a turbine and disconnecting of external feed an asynchronous machine passes into the generator mode, here the process of passing into the independent system does not require an interruption in the users feed. Starting time of plant is reduced.

The lack of asynchronous generators, limiting their application, are a necessity of application of excitation capacitors and complication of voltage control.