RU2024147C1 - Method of current protection of motor with dependent characteristic of operation - Google Patents

Abstract

FIELD: electrical engineering. SUBSTANCE: temperature of cooling air is measured or set. Heat condition of motor is simulated mathematically using ratio of root-mean-square value of current to long-duration permissible current of stator in second power as value reflecting amount of heat recovered per time unit. In this case constants of times of heating and cooling are set separately for winding and magnetic core with account of operational condition of motor. Long-duration permissible multiplicity of current is determined with account of ambient air temperature and for multiplicities of current lesser than long-duration permissible one-temperature of heat balance of winding. Adiabatic character of heating process of winding is simulated in function of the square of multiplicity of stator current limiting it by temperature of heat balance with current multiplicities not exceeding permissible one for long duration. Process of heating of magnetic core is simulated by exponential law in function of difference of temperatures of winding and of winding heat balance or magnetic core temperature if it exceeds the latter. Motor is switched off with fall of voltage in system below threshold one if winding temperature exceeds maximum pre-start one. When simulating process of heating of winding upper level of limiting of multiplicity of stator current is specified. EFFECT: improved reliability of current protection. 3 cl, 1 dwg

Description

 The invention relates to the electric power industry, in particular to methods of protecting engines, in which the load current of the protected motor is controlled, the processes of its heating and cooling are modeled, and the shutdown is acted upon with a time delay depending on the intensity of these processes in the event that the motor overheats exceed the permissible ones.

 In relay protection, methods of current protection of motors based on modeling of processes of their heating are known. There is a method in which the stator current is measured, the thermal state of the motor is mathematically modeled using, as a value reflecting the amount of heat generated per unit time, the multiplicity of the current value in relation to the rated stator current in the second degree [1]. Engine cooling is modeled exponentially as a function of the temperature rise of the engine. The heating and cooling processes are combined in time, and the cooling time constant is selected depending on the fact of rotation of the rotor. The output signal is formed when the temperature reaches the superheat.

 The disadvantage of this method is that there is no control of the temperature of the cooling air, in addition, the engine is considered as a homogeneous body, which is permissible only at small multiples of the overload current. These shortcomings predetermine a low coefficient of sensitivity of protection at low multiples of the overload current and do not allow the use of overload capabilities of the motor.

1 - e

, (1) где Θ - температура двигателя;
ΔΘ_доп - превышение температуры, соответствующее установившемуся тепловому режиму при кратности тока, равной 1;
I - ток статора;
I_доп - длительно допустимый ток статора;
t - время;
Т - постоянная времени нагрева;
Θ_о - температура охлаждающего воздуха.There is also a known method of protecting engines from overloads with continuous monitoring of the thermal regime taking into account the changing conditions of the cooling medium, in which the stator current is measured, the temperature of the cooling air is measured or set, and the thermal state of the engine is mathematically modeled using, as a value, reflecting the amount of heat released per unit time , the multiplicity of the current value in relation to the rated current of the stator in the second degree, the cooling of the engine is modeled exponentially in the functions of exceeding the engine temperature combine the heating and cooling processes in time, summarize the excess of the engine temperature with the temperature of the cooling air, and the output signal is generated when the sum of the temperatures reaches the limit value Θ _max [2]. The method [2] allows you to simulate the thermal process in an electric motor according to the expression
θ = θ ₀ + Δθ _add

1 - e

, (1) where Θ is the engine temperature;
ΔΘ _add - excess temperature corresponding to the steady-state thermal regime at a current multiplicity of 1;
I is the stator current;
I _add - long-term permissible stator current;
t is the time;
T is the heating time constant;
Θ _о - cooling air temperature.

= Δθ·K $\genfrac{}{}{0ex}{}{\text{2}}{\text{I}}$ (2)
Известно, что допустимое кратковременное превышение температуры по отношению к длительно допустимой принимается равной 1,3, а согласно ГОСТ 183-74
Θ_макс = ΔΘ_доп + Θ_о = ΔΘ_доп + 40^oС=
= 120^оС . (3)
Отсюда очевидно, что, моделируя тепловой процесс согласно способу [1], в зоне кратностей тока от 1 до 1,14 I_доп образуется зона нечувствительности, т. е. не обеспечивается защита двигателя при этих кратностях тока в то время, когда в качестве длительно допустимого рекомендуется принимать ток, равный 1,05 I_н.From the expression (1) it is obvious that a certain amount of excess of temperature corresponds to a different amount of current ΔΘ _dop at a steady-state thermal regime, which is described by the equation
Δθ _∞ = Δθ _add

= ΔθK $\genfrac{}{}{0ex}{}{\text{2}}{\text{I}}$ (2)
It is known that the permissible short-term temperature rise in relation to the long-term permissible is assumed to be 1.3, and according to GOST 183-74
Θ _max = ΔΘ _add + Θ _o = ΔΘ _add + 40 ^o С =
= 120 ^about C. (3)
From this it is obvious that, simulating the thermal process according to the method [1], in the zone of current multiplicities from 1 to 1.14 I, a _{deadband is} formed, that is, motor protection is not provided at these current multiplicities at a time when allowable, it is recommended to take a current equal to 1.05 I _n .

Using in the expression (1) as the term the cooling air temperature allows you to adjust the protection parameters both in terms of the heat balance temperature and in response time. If the temperature of the gaseous cooling medium is different from 40 ^o C, the maximum allowable temperature is exceeded parts converted electric machine, wherein the recalculation is only valid within 30-60 ^C. This requirement not implement protection, operating according to the method [2].

 A significant disadvantage of the method [1] and [2] is that the engine is considered as a homogeneous body having a generalized heating time constant. In this case, either protection is not provided at large multiples of current, or the overload capacity of the motor at low multiples of the overload current is underutilized. If the time constant is chosen for small multiples of the overload current, then for large multiples, for example, with a prolonged start-up or jamming of the rotor, the overheating of the winding will exceed the limit values. If the time constant is chosen for high currents, then at low multiples of the overload current, the protection will falsely shut off the motor.

 In addition, the methods [1] and [2] do not provide a lock-up on the motor or its self-start when the winding overheats and do not provide a delay time from the current at high current multiplicities, which is necessary for motors with difficult starting conditions.

 The purpose of the invention is to improve the protective characteristics of devices for implementing the proposed method.

 This is achieved by the fact that with the method of current protection of the motor with a dependent response characteristic, in which the stator current is measured, the ambient temperature is measured or set, the thermal state of the motor is mathematically modeled, using the multiplicity of the effective value as a value reflecting the amount of heat generated per unit time the stator current with respect to its nominal value in the second degree, form the output signal when the limit temperature is reached, and the engine cooling is modeled by exponential law. According to the invention, the heating time constants and the cooling time constants are set separately for both the stator winding and the magnetic circuit, the long-term permissible current multiplicity is determined taking into account the temperature of the cooling air, the thermal balance temperature of the winding is determined for the current multiplicities less than the permissible, the adiabatic nature of the heating process of the winding is simulated the functions of the multiplicity of the stator current to the second degree, limiting it to the temperature of the heat balance or the limit at the multiplicity of current, exceeding boiling long allowable, the process of heating of the magnetic circuit model exponentially as a function of the temperature difference between the winding and the magnetic circuit, winding the cooling process is modeled by an exponential function to the winding temperature and temperature difference of the heat balance of the magnetic circuit or temperature, if it exceeds the latter. The cooling process of the magnetic circuit is modeled exponentially as a function of the temperature difference of the magnetic circuit and cooling air. Moreover, the heating or cooling process of the winding is combined in time with the heating and cooling processes of the magnetic circuit.

 In addition, in particular in particular cases, the following is carried out: when determining the temperature of the heat balance of the winding, the lower level of the ambient temperature is limited, the temperature exceeds the starting current of the protected motor and the maximum starting temperature of the winding is ensured at which it starts or self-starts without exceeding the maximum permissible temperature of the winding , when the maximum starting temperature is reached, the engine start is blocked, and while the voltage decreases at networks below a predetermined value turn off the engine, for which an additional voltage is measured. When modeling the process of heating the windings, the upper level of the stator current ratio is set.

+ θ_м.нач , (4) где Θ_м - температура обмотки (медь);
Θ_м.нач. - температура обмотки в начале процесса;
Θ_о ^ж - температура охлаждающего воздуха (не менее 30^оС);
τ_м.н. - постоянная времени нагрева обмотки (меди).The proposed method differs from the prototype in the presence of these essential features and thereby meets the criterion of "novelty." A distinctive feature of the method is that the heating and cooling time constants are set separately for the winding and the magnetic circuit, taking into account the operating mode of the motor. It is known that the heating time constant is equal to the cooling time constant when the engine is running and differs when it is turned off. Setting various time constants for the winding and for the magnetic circuit allows you to more accurately simulate the heating and cooling processes of both the winding and the entire motor. The heating of the winding is modeled as adiabatic, as a function of the multiplicity of the stator current with respect to its long-term permissible value in the second degree, and its temperature is determined by the equation
θ _m =

+ θ _m.nach , (4) where Θ _m is the temperature of the winding (copper);
Θ _m. - winding temperature at the beginning of the process;
Θ _о ^ж - temperature of cooling air (not less than 30 ^о С);
τ _m - constant heating time of the winding (copper).

. (5)
Тогда время срабатывания защиты в функции кратности тока статора во второй степени можно получить из формулы (5) с учетом коэффициента запаса
t_с.з. = t_доп ^. К_з. (6)
При выполнении защиты в соответствии с выражением (6) отключение двигателя должно происходит при выполнении условия

I²dt >

. (7)
Так как интегрирование в течение достаточно большого промежутка времени любого значения тока приводит к срабатыванию защиты, то процесс интегрирования ограничивают во времени. Ограничение времени интегрирования тока осуществляют для кратностей тока менее длительно допустимых значений при нагреве обмотки до температуры теплового баланса, которую определяют по формуле
θ_М∞= θ $\genfrac{}{}{0ex}{}{\text{*}}{\text{0}}$ +(θ_м.доп-40^°C)·K $\genfrac{}{}{0ex}{}{\text{2}}{\text{I}}$ , (8) где Θ_м.доп - длительно допустимая температура обмотки.The solution of equation (4) with respect to t gives an expression of the permissible motor operating time with current overload:
t _add =

. (5)
Then the response time of the protection as a function of the multiplicity of the stator current to the second degree can be obtained from formula (5) taking into account the safety factor
t _s.z. = t _add ^. To _s . (6)
When performing protection in accordance with expression (6), the engine must be switched off when the condition

I ² dt>

. (7)
Since integration over a sufficiently long period of time of any current value leads to a trip of the protection, the integration process is limited in time. The time integration of the current is limited for current multiplicities of shorter permissible values when the winding is heated to the temperature of the heat balance, which is determined by the formula
θ _M∞ = θ $\genfrac{}{}{0ex}{}{\text{*}}{\text{0}}$ + (θ _mdop -40 ^° C) · K $\genfrac{}{}{0ex}{}{\text{2}}{\text{I}}$ , (8) where Θ _m.dop is the long-term permissible temperature of the winding.

(9)
Если температура обмотки меньше температуры теплового баланса, моделируют нагрев обмотки согласно выражению (4) до достижения ею температуры теплового баланса. Если температура обмотки выше температуры теплового баланса, определенной согласно выражению (8), то моделируют процесс охлаждения обмотки. Охлаждение обмотки при условии, что Θ_m∞больше Θ_ст, моделируют по экспоненциальному закону
θ_м= (θ_м.нач-θ_м∞)

+ θ_м∞ , (10) где Θ_м.нач. - температура обмотки в начале процесса;
τ_м.охл. - постоянная времени охлаждения обмотки ( τ_м.охл. равна τ_м.н, при работающем двигателе и τ_м.охл. больше τ_м.н. при отключенном двигателе).From (8) we see that if the cooling air temperature other than 40 ^{° C,} produce heat balance correction coil temperature limiting a minimum value _of Θ ^x, thus prolonged allowable multiplicity of stator current with the cooling air temperature is determined by the formula:
K _idop =

(9)
If the temperature of the winding is less than the temperature of the heat balance, they model the heating of the winding according to expression (4) until it reaches the temperature of heat balance. If the temperature of the winding is higher than the temperature of the heat balance determined according to expression (8), then the process of cooling the winding is simulated. The cooling of the winding, provided that Θ _{m∞ is} greater than Θ _{st, is} modeled exponentially
θ _m = (θ _{m.start -θ m∞} )

+ θ _m∞ , (10) where Θ _m . - winding temperature at the beginning of the process;
τ _m. - time constant of the cooling coil (τ τ _{Cand m.ohl} equal, with the engine running and longer τ τ _{m.ohl Cand} engine _{disconnected...).}

, (11) где Θ_ст - температура магнитопровода (стали).If the temperature of the heat balance of the winding is lower than the temperature of the magnetic circuit, for example, when the motor is turned off or the load is relieved, that the process of cooling the winding is described by the equation
θ _m = θ _st + (θ _{m.start -θ st} )

, (11) where Θ _st is the temperature of the magnetic circuit (steel).

1-

, (12) где Θ_ст.нач, - температура магнитопровода в начале процесса;
τ_ст.н - постоянная времени нагрева магнитопровода.As soon as the temperature of the winding exceeds the temperature of the magnetic circuit, the heating process begins. This process is modeled exponentially as a function of the temperature difference of the winding and the magnetic circuit according to the expression
θ _st = θ _st. + + (θ _{m -θ st.} )

1-

, (12) where Θ _st.nach , is the temperature of the magnetic circuit at the beginning of the process;
τ _st.n - time constant of heating the magnetic circuit.

, (13) где τ_ст.охл. - постоянная времени охлаждения магнитопровода ( τ_ст.охл.равна τ_ст.н при работающем двигателе и τ_ст.охл больше τ_ст.н при отключенном двигателе).If the temperature of the magnetic circuit exceeds the temperature of the cooling air, the process of cooling the magnetic circuit begins. This process is described by the equation
θ _st = θ ₀ + (θ _{st.-start -θ 0} )

, (13) where τ _st . - the time constant of cooling the magnetic circuit (τ _{st. cool.} equals τ _{st. n} when the engine is running and τ _{st. cool is} greater than τ _{st. n} when the engine is off).

 Elimination of the time simulation of heating and cooling processes of the winding. The heating and cooling processes of the magnetic circuit are simulated simultaneously and combined in time with the heating or cooling processes of the winding.

, (14) где К_э - кратность эквивалентного пускового тока;
К_з - коэффициент запаса больший 1.For engines operating in the mode of frequent starts, it is relevant to block the start when the maximum starting temperature of the winding is exceeded. The maximum starting temperature is determined by the formula
θ _bl = θ _max -

, (14) where K _e is the multiplicity of the equivalent starting current;
To _s - safety factor greater than 1.

 When the voltage in the network is lower than the value characterizing a power failure, the motor, the temperature of the winding of which exceeds the maximum pre-start, is turned off, which prevents their obviously unsuccessful self-start. For engines with severe starting conditions, a limitation of the upper level of the stator current multiplicity is set, thereby providing an independent part of the time-current characteristic in the zone of high current multiplicities.

 The drawing shows a functional diagram of a device for implementing the proposed method.

 The device comprises an input current to voltage converter 1, a cooling air temperature signal setter 2, a scaling organ 3, a lower level limiter 4, upper level limiters 5 and 15, a max selector 6, analog signal adders 7, 10 and 16, a quadrator 8, threshold organs 9 12.0 14 and 19 of the maximum level, driver of module 11, threshold organ 13 of the minimum level, voltage-frequency converters 17, 18 and 21, logic element 2I 20, comparator 22, frequency dividers 23 and 24, delay element 25, multiplier 26 logical elem nt OR 27, AND gate 28, OR-2I, reversible binary counters 29 and 30, digital to analog converters 31 and 32 as well as the output signal conditioners 33 and 34.

 The method is as follows.

The value of the winding temperature simulated by the device Θ _m is stored in the counter 29, and the temperature of the magnetic circuit Θ _st is stored in the counter 30. Heating is modeled by the implementation of direct counting, and cooling by the reverse counting. Digital-to-analog converters 31 and 32 are connected to the outputs of the counters 29 and 30. A voltage proportional to the temperature of the winding is formed at the output of the converter 31
U ₃₁ = f (Θ _m ), (15) and a voltage proportional to the temperature of the magnetic circuit is formed at the output of the converter 32
U ₃₂ = f (Θ _st ), (16) The voltage U _{31 is} supplied to the inputs of the limiter 5, threshold organs 12 and 14 and to the input B of the adder 10. The voltage U _{32 is} supplied to the input B of the max selector 6 and to the input A of the adder 7. Converter 1 converts the stator current of the protected motor into a unipolar voltage proportional to the input current and equal to
U ₁ = a ^. I, (17) where a is the coefficient of proportionality.

; (18) где I_н.тт. - номинальный ток трансформатора тока;
I_доп - длительно допустимый ток статора защищаемого двигателя.This voltage is supplied to the input of the scaling organ 3, the transmission coefficient of which is determined by the formula
K _p =

; (18) where I _nt - rated current of the current transformer;
I _add - long-term permissible stator current of the protected motor.

The output signal of block 3 is supplied to the inputs of the analog quadrator 8 and threshold organ 9. The setpoint 2 of the cooling air temperature signal generates a voltage proportional to the temperature of the cooling air at its output, directly measuring it or setting it. Voltage
U ₂ = f (Θ _o ) (19) enters the input C of the adder 7 and through the lower limiter 4 to the input B of the adder 16. The restriction level in block 4 is determined by the lower temperature limit Θ _о , at which correction of the long-term permissible motor current is allowed . The output voltage of the quadrator 8 is supplied to the input A of the adder 16 and through the limiter 15 of the upper level to the input of the Converter 21 voltage - frequency. Voltage equal
U ₁₆ = b ^. U ₈ + U ₄ , (20) where U ₁₆ is the voltage at the output of the adder 16;
b is the coefficient of proportionality;
U ₈ is the voltage of the quadrator, directly proportional to the input current of the stator to the second degree;
U ₄ is a voltage proportional to the temperature Θ _{о of} cooling air with a lower level restriction, is fed to the input A of the comparator 22 and the max selector 6. The voltage U ₅ , proportional to the temperature of the winding with the upper level limitation implemented by the limiter 5, is supplied to the input of the comparator. limitation is determined by the value of the long-term allowable temperature of the winding Θ _m.dop . Comparator 22 with equal input voltages fixes the thermal balance of the winding. Moreover, at the outputs of the comparator there are logic signals of the zero level, blocking the operation of the counter 29 through the logic element 28. If the voltage at the input A of element 22 exceeds the voltage at the input B, the signal of the logic unit at the output A> B switches the counter 29 to the direct counting mode (heating windings) and rectangular pulses from the output of the converter 21 through the logic element 28 are fed to the counting input of the counter 29. The voltage supplied to the input of the converter 21 is limited, if necessary, to the upper level for the purpose of independent of the radiation response characteristics at high rates of current. The conversion coefficient of the element 21 is set taking into account the constant heating time of the winding. Elements 6, 10, 17, 23, and 26, together with element 28 form a channel for modeling the cooling of the winding. The max selector 6 supplies the input A of the adder 10 the maximum of the voltage values supplied to the input of the max selector 6. The adder 10 generates at its output a voltage U ₁₀ proportional to the difference between the temperature of the winding and the temperature of the thermal balance of the winding or the temperature of the magnetic circuit, if it exceeds the last:
U ₁₀ = U ₃₁ - U ₁₆ if U ₁₆ > U ₃₂ (21) or
U ₁₀ = U ₃₁ - U ₃₂ if U ₁₆ <U ₃₂ , where U ₁₀ is the voltage at the output of the adder 10;
U ₃₁ - voltage proportional to the temperature of the winding from the output of the Converter 31;
U ₁₆ is the voltage from the output of the adder 16 corresponding to the temperature of the thermal balance of the winding;
U ₃₂ - voltage from the output of the Converter 32, proportional to the temperature of the magnetic circuit.

The voltage from the output of the adder 10 is supplied to the input of the Converter 17 voltage-frequency. The conversion coefficient of the Converter 17 is set taking into account the constant cooling time of the running engine. Rectangular pulses from the output of the converter 17 are fed to the input of the frequency divider 23 and, when the engine is running, through the element 26, to the fourth inputs of the logic element 28. If the winding temperature is higher than the temperature of the thermal balance of the winding, a logic signal of a single level appears at the output A <B of the comparator 22, and at the output A> B - zero. The counter 29 at the same time switches to the countdown mode (winding cooling). The multiplexer 26 is controlled by a signal from the output of the threshold organ 9, which detects the presence of stator current. Thus, when the engine is running, the fourth input of element 28 receives pulses from the output of the converter 17, and when the engine is off, from the output of the frequency divider 23. The division ratio is determined by the ratio of the cooling time constant of the winding of the disconnected motor to the cooling time constant of the winding of the running motor. Interacting in this way, elements 1-4, 5, 6, 10, 10, 15-17, 21-23, 26, 28-32 provide modeling of the thermal state of the winding, either realizing or modeling the process of its heating according to expressions (4), (8 ) and (9), or cooling according to expressions (10) or (11). Elements 7, 11, 18, 19, 24 together with multiplexer 26 form a channel for modeling heating and cooling of the magnetic circuit. The inputs of the adder 7 receive voltage proportional to the temperatures of the winding, magnetic circuit and cooling air. The output of the adder 7, the voltage value is determined by the expression
U ₇ = U ₃₁ + U ₂ - 2 ^. U ₃₂ , (22) where U ₃₁ is the voltage from the output of the converter 31, proportional to the temperature of the winding;
U ₂ - voltage from the output of the Converter 2, proportional to the temperature of the cooling air,
U ₃₂ - voltage from the output of the Converter 32, proportional to the temperature of the magnetic circuit.

If the voltage U _{7 is} positive, the heating of the magnetic circuit is simulated, and if it is negative, then cooling. Switching the counting direction of the counter 30 is carried out by a threshold organ 19, at the output of which a logic signal of a single level corresponds to a positive input voltage, and an output signal of a zero level corresponds to a negative input voltage. At the same time, the voltage from the output of the adder 7 through the shaper module 11 is supplied to the Converter 18 voltage-frequency. The conversion coefficient of the Converter 18 is selected taking into account the time constant of heating the magnetic circuit. Rectangular pulses from the output of the converter 18 are fed to the input of the frequency divider 24 and when the engine is running through the element 26 they are fed to the counting input of the counter 30. When the engine is off, the counting input of the counter 30 is connected using the multiplexer 26 to the output of the frequency divider 24. The division ratio of element 24 is determined by the ratio the time constant of cooling the magnetic circuit of the switched off motor to the constant time of heating the magnetic circuit. Interacting in this way, elements 2, 7, 11, 18, 19, 24, 26, 30, 31, and 32 provide modeling of the thermal state of the magnetic circuit, while simultaneously simulating the heating of the magnetic circuit according to expression (12) and cooling according to expression (13). The inputs of the threshold organs 12 and 14 receives a voltage proportional to the temperature of the winding. When this voltage reaches the value corresponding to the maximum permissible temperature of the winding, a threshold organ 14 is triggered, at the output of which a logic signal of a unit level appears, which, through a logic element 24, acts on the output shutter 34. When the element 12 is triggered, a single signal from its output acts on the blocker of the output signal 33. The response setting of element 12 is determined according to expression (14). At the input of the threshold element 13 serves the mains voltage. When the mains voltage drops below a value characterizing a power failure (for example, below 0.6 U _nom ), a logical unit signal appears at the output of element 13. While reducing the mains voltage and reaching the maximum pre-starting temperature of the winding through the logic element 20, a delay element 25 is triggered, which, with a time delay detuned, for example, from high-speed protection against short circuits, acts sequentially on the logic element 2 and on the output driver 34 "

 The method allows with greater accuracy to simulate the processes of heating and cooling the engine and improve the protective characteristics of devices that implement the method.

Claims (4)

 1. METHOD OF CURRENT PROTECTION OF THE MOTOR WITH DEPENDENT CHARACTERISTIC OF OPERATION, in which the stator current is measured, the temperature of the cooling air is measured or set, the thermal state of the motor is mathematically simulated using, as a quantity characterizing the amount of heat generated per unit time, the multiplicity of the effective current value with respect to long-term permissible stator current in the second degree, an output signal is formed upon reaching the limit temperature, and the engine cooling is modeled exponentially law, characterized in that the time constants are set separately for both the stator winding and the magnetic circuit, the long-term permissible current multiplicity is determined taking into account the temperature of the cooling air, the temperature of the thermal balance of the winding is determined for current multiplicities less than the permissible, the adiabatic nature of the process of heating the winding is simulated in the function of the multiplicity of the stator current to the second degree, limiting it to the temperature of the heat balance or the limiting temperature at current multiplicities exceeding the duration as permissible, the heating process of the magnetic circuit is modeled exponentially as a function of the difference in temperature of the winding and the temperature of the magnetic circuit, the cooling process of the coil is modeled exponentially as a function of the difference of temperature of the winding and the temperature of the heat balance of the winding or the temperature of the magnetic circuit, if it exceeds the latter, the cooling process of the magnetic circuit is modeled by exponential law as a function of the temperature difference of the magnetic circuit and the cooling air, moreover, the heating or cooling process REPRESENTATIONS winding aligned in time with the heating and cooling processes of the magnetic circuit.  2. The method according to p. 1, characterized in that when determining the temperature of the heat balance of the windings limit the lower temperature level of the cooling air.  3. The method according to claim 1, characterized in that they determine the temperature rise from the starting current of the protected motor and the maximum starting temperature of the winding, at which the motor starts or starts without exceeding the limiting temperature of the winding, when the maximum starting temperature is reached, the engine is blocked, and when at the same time lowering the mains voltage below a predetermined value, the engine is turned off, for which an additional voltage is measured.  4. The method according to claim 1, characterized in that when simulating the heating process of the winding, the upper level of the stator current ratio is set.

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