METHOD FOR DETERMINATION OF IMPREGNATION COEFFICIENT FOR ELECTRICAL MACHINES COILS Russian patent published in 2014 - IPC H02K15/12 

FIELD: electricity.

SUBSTANCE: invention is related to the field of electric engineering, and namely to non-destructive quality control procedures for electrical products, in particular, to impregnation of windings of electrical machines. According to the suggested method for determination of impregnation coefficient for electrical machine windings impregnated by cured polymer composition capacitance values C_cbi and C_cui in regard to the ground are measured for each electrical machine winding in the batch before and upon impregnation by the polymer composition and drying. Then, upon impregnation and drying of windings temperature of each winding T_1ui is measured and through the wire of each tested winding stabilised direct current I₀ is passed and its values is selected depending on section area S of the winding wire strand within the range of maximum current density permitted for the material of the winding wire from j_min up to j_max within the range of values j_minS ≤I₀≤j_maxS. At that the above selected current I₀ is passed through the winding during a certain period of time t₀ and voltage drop is measured at the winding U_1i at the moment of stabilised current delivery to it and voltage drop at the winding U_2i at the above period of time t₀. Upon the above operations according to measurement results the impregnation coefficient K_ic is determined for each tested winding in the near-body cavities and impregnation coefficient K_tt of turn-to-turn cavities in the windings as per the following formulas: $${К}_{ic}=\frac{1}{\ln {\epsilon }_{is}}\times \ln \frac{{С}_{cui}({С}_{eq}-{С}_{cbi})}{{С}_{cbi}({С}_{eq}-{С}_{cui})},(4)$$ (4), $${К}_{tt}=\frac{1}{m_{0tt}{с}_{с}}\{I_0\times t_{о}[\frac{U_{1i}(U_{1i}+U_{2i})\alpha }{2(U_{2i}-U_{1i})[1+\alpha ({Т}_1-20]}]-[1+\alpha ({Т}_1-20)]\frac{B_2}{U_{1i}}+B_1\},(5)$$ (5), where $${С}_{eq}=\frac{рS_a{\epsilon }_0{\epsilon }_{э}{\epsilon }_{fi}}{(d_e{\epsilon }_{fi}+d_{fi}{\epsilon }_e)}$$ is equivalent capacity of in-series capacitance of enamel and frame insulation of the winding; p is a number of slots in the magnet core to which the tested part of the winding is placed; S_a is an area of the slot surface; ε₀=8.854187·10^-12 is the electrical constant; ε_e is dielectric capacitivity of enamel film at the winding wire; ε_fi is dielectric capacitivity of frame insulation; d_ei is thickness of enamel insulation of the wire; d_fi is thickness of frame insulation at the wire; c_c is specific heat capacity of the dried impregnation composition; $$m_{0tt}=d_c{S}_c{l}_w(1-\frac{р}{4}{К}_f)\times \frac{р}{2}-рS_a^2{\epsilon }_0(\frac{{С}_{eq}-{С}_{dc}}{{С}_{dc}{С}_{eq}})$$ is a limit mass of dry impregnation composition which can be placed in turn-to-turn cavities of the winding at 100% of their filling; d_c is density of dried impregnation composition; S_cs is cross-sectional area of the slot; l_w is length of the winding turn; K_f is the slot filling coefficient; α is temperature coefficient of the winding wire resistance; B₁ = C_eehc + C_fiech is equivalent heat capacity of enamel $${С}_{eehc}={с}_e\frac{\pi (D_e^2-D_w^2)}{4}{1}_w{\rho }_e$$ and frame insulation C_ei = C_fi × P × d_fi × L × p × c_fi; c_e is specific heat capacity of enamel; D_e is the diameter of enamelled wire of the winding; D_w is the diameter of the winding wire strand; l_tw is rated length of the wire in the tested winding part; ρ_e is enamel density; c_fi is specific heat capacity of the frame insulation; P is the slot perimeter; d_fi is thickness of the frame insulation; L is the slot length; ρ_fi is density of the frame insulation; $${В}_2={с}_w\times {\rho }_{20}\times I_0^2{\rho }_w{l}_w^2$$ is the constant rate; c_tw is specific heat capacity of the material used for the winding wire strand; ρ₂₀ is specific resistivity of the material used for the winding wire at 20°C.

EFFECT: simplification of the method due to avoidance of measuring capacity in regard to the ground for one random winding and self-capacitance before impregnation, dipping of the above winding into impregnating liquid with the known dielectric capacitivity and measuring of this winding capacity in regard to the ground and self-capacitance again with the winding placed in the impregnating liquid as well as die to avoidance of double measurements of self-capacitance for each of the tested winding before and upon impregnation, improvement of accuracy because the value of impregnation coefficient does not depend on relative position of turns in the slot, as well as increase in information content of control because this method allows to determine distribution of the impregnation composition inside the winding and impregnation coefficients for near-body and turn-to-turn cavities of windings.

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