- •V.S. Martynjuk, I.I. Popovska
- •Study of the electromechanics energy converters design Aim of work
- •Theoretical positions
- •Design of direct current electromechanics converters
- •Design of synchronous electromechanic converters
- •Designs of asynchronous electromechanics converters
- •Order of work performance
- •Contents of a report
- •Control questions
- •Research of single-phase transformer Aim of work
- •Order of work implementation
- •Table of report contents
- •Control questions
- •Research of dc generator of parallel excitation Aim of work
- •Order of work implementation
- •Control questions
- •Research of direct current мотоrs Aim of work
- •Report content
- •Control questions
- •Research of three-phase asynchronous motor with squirrel-cage rotor Aim of work
- •Order of work performance
- •Table of report contents
- •Control questions
- •Calculation of electromagnets of direct-current а. Preliminary calculation of electromagnet. Calculation of key size of core
- •1.1. Electromagnets with external turning armature
- •B) Recursive short-time mode
- •C) Short-time duty
- •1.2. Electromagnets with external forward armature travel
- •B) Recursive short-time mode
- •C) Short-time duty
- •Design of asynchronous machines
- •Features of asynchronous generators operation
- •2. Determination of main sizes and calculation of asynchronous machine
- •Choice of number of stator and rotor slots
- •4. Active and inductive resistances of stator and rotor winding
- •5. Choice of excitation capacitor
- •6. A calculation of magnetic circuit and determination of o.C. Current of asynchronous machine in traction mode
- •7. Calculation and plotting of magnetic characteristic (b-h curve) of asynchronous machine
- •8. Plotting of operating characteristics of asynchronous motor
- •9. Losses of energy and efficiency of asynchronous machine
- •Home work (by discipline “Aviation electric machines and devices”)
1.2. Electromagnets with external forward armature travel
The most widespread forms of electromagnets of this type are electromagnets, presented on fig 1.3. As it follows from pictures, in examined cases there are two identical basic air-gap, in this connection a full electromagnetic force F is determined by a formula
F = 2F0 = 2∙5,1∙B02∙ S0 / μ0,
Fig. 1.3, a where В0 − induction in a basic air-gap, Wb/сm2; S0 − equivalence cross-section of each of basic gaps, сm2.
So, MMF, being on both gaps, determined so:
(w∙I)0 = φ (w∙I)П = 2∙δ0∙B0 / μ0,
where φ − coefficient, taking into account of MMF drop in steel and non-working gaps.
Induction В0 with a glance of possible in exploitation lowering of MMF (w∙I)п = χ∙w∙I, where χ ≤ 1, equals to: B0 = μ0∙φ∙χ∙w∙I / 2δ0
Permissible MMF w∙I of electromagnet coils is determined coming from its operation mode, terms of heating and presence of two coils, having a cooling surface 2Scl.
a) Continuous running duty of Fig. 1.3, b electromagnet
For this mode next correlations, similar to got before, are correct. Resistance of one coil :
R = 10-4∙ρ∙π∙(1 + n)∙dc∙w / 2Sm
where w − total number of loops of both coils; Sm – cross-section of wire metal, equals to :
Sm = 2fap∙m∙n∙ dc2 / w.
So, general losses in resistance of electromagnet are equal to:
P = 2R∙I2 = 10-4∙ρ∙π∙(1 + n)∙w2∙I2 / fap∙m∙n∙dc
On the other hand, Р is determined from correlation
Θper = P / 2h∙Scl = P / [2h∙(Sex + α∙Sin)].
Substituted Р and Scl from (1.5) into the formula Θper, we will define the value of MMF of electromagnet:
w∙I = 2√[104∙fap∙m2∙n∙(1 + 2n + α)∙h∙Θper∙dc3 / ρ(1 + n)]
the value of electromagnetic force
F = 8∙104∙μ0∙φ2∙ε2∙χ2∙fap ∙τ2∙m2∙n∙(1+ 2n + α)∙h∙Θper∙dc5/ [ρ(1 + n) δ02],
and key size of a core
dс = 5√{[103∙ρ∙(1 + n)∙F∙δ02 / [φ2∙ε2∙χ2∙fap∙τ2∙m2∙n∙(1+ 2n + α)∙h∙Θper]}
Designating, as well as before,
C1 = [2∙103∙ρ(1+n)] / [φ2∙χ2∙fap∙τ2∙m2∙n∙(1+2n+α)∙h∙Θper], we will get accordingly:
F = 2ε2∙dc5 / (C1∙ δ02) (1.42)
and dc = 5√[C1∙F∙δ02 / 2ε2] (1.43)
Transformation of the last formula gives dependence
F / δ03 = 2ε2∙χ5 / C1, (1.44)
facilitating, as it was explained before, determination of dc = χ∙δ0. Thus under F they understand full force of electromagnet. In this case we determine:
MMF of coils
w∙I = (9∙103∙dc / φ∙χ∙τ)∙√(dc / C1) (1.45)
2) cross-section of wire
Sm = [2.82∙ρ∙(1 + n)∙dc2 / (φ∙χ∙τ∙U)]∙√(dc / C1) (1.46)
3) number of coil loops
w = U∙√[103∙fap∙n / ρ∙(1 + n)∙(1 + 2n + α)∙h∙Θper∙dc) ] = C2∙U∙√(C1 /dc) (1.47)
4) induction in a working air-gap
B0 = (0,396∙10-4√F) / (τ∙ε∙dc)
approximately by a formula
B0 ≈ (4∙10-5 / τ∙ 5√C1) ∙√(F3/ δ04)