RU2791293C1 - Method for determining the response time of the protection of current-carrying contact connections of switching devices against overheating - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: method includes monitoring the deviation from the maximum allowable temperature value of the contact surface of the current-carrying contact connection most susceptible to overheating as a part of the switching device and generating a signal when the contact surface reaches the maximum allowable temperature. In the monitoring mode, the value of a rectangular current pulse is measured and compared with a predetermined threshold value, while taking into account the value of the conditionally contact dynamic resistance. If the current exceeds its threshold value, the temperature control of the contact surface is carried out in the dynamic monitoring mode at the heating time interval of the contact connection according to a linear law, then the temperature values measured during dynamic monitoring of the external surface of the contact part available for direct measurements are recalculated, then the mathematical expectation of the values of the conditionally contact dynamic resistance is calculated and the moment of time before switching off the switching device is determined.

EFFECT: increase in the accuracy and speed of determining the response time of the protection.

1 cl, 5 dwg, 5 tbl

Description

The invention relates to the field of electrical engineering, in particular to means of protecting switching equipment from unacceptable temperature rises, namely, from reaching the melting point of the material of contact parts of contact connections (CC) of live parts in power supply circuits that directly respond to an unacceptable temperature rise during operational or test rectangular current pulse. It can be used in power supply systems of residential, administrative and industrial facilities with a voltage of 0.4 kV, at manufacturers of switching devices and in organizations specializing in testing contact connections of current-carrying parts of electrical equipment for thermal resistance by short-circuit through current.

A known method for protecting switching equipment and contact threaded connections of current-carrying parts (RU No. 2264682, November 20, 2005), including maintaining the temperature of the switching equipment clamps within acceptable limits by tightening the clamps. The disadvantage of this method is the lack of the possibility of on-line control of the heating process directly of the contact surfaces of the contact joints, on which, first of all, the maximum temperature of the contact-piece material is reached under the operational or test effect of a rectangular current pulse in order to prevent the fusion of the contact-pieces.

до t₂=t₁+nΔt, где t₁ - время начала нагрева по линейному закону; l - толщина контакт-детали; с, λ - удельная теплоемкость и теплопроводность материала контакт-детали; Δt - шаг измерений; n - число измерений; t₂ - время завершения температурного контроля в режиме динамического мониторинга, затем осуществляют пересчет измеренных в ходе динамического мониторинга значений температуры, доступной для прямых измерений внешней поверхности контакт-детали T₁(τ⁽ⁱ⁾), i=1, 2, …, n в соответствующие значения температуры, недоступной для прямых измерений контактной поверхности контактного соединения T₂(τ⁽ⁱ⁾), i=1, 2, …, n по формуле:A known method for determining the response time of the protection of current-carrying contact connections of switching devices from overheating (RU No. 2635385 dated November 13, 2017), including monitoring the deviation from the maximum allowable temperature value of the contact surface of the current-carrying contact connection in the composition of the switching device and generating a signal, according to which determines the time for the contact surface to reach the maximum allowable temperature, characterized in that in the monitoring mode the value of a rectangular current pulse is measured and the measured value is compared with a given threshold value of the test or operational rectangular current pulse, in case the current exceeds its threshold value, temperature control of the contact surface is carried out in dynamic monitoring mode on the heating time interval of the contact connection according to the linear law: from

up to t ₂ =t ₁ +nΔt, where t ₁ is the start time of heating according to a linear law; l is the thickness of the contact piece; c, λ - specific heat capacity and thermal conductivity of the contact-piece material; Δt - measurement step; n is the number of measurements; t ₂ - time to complete the temperature control in the dynamic monitoring mode, then recalculate the temperature values measured during dynamic monitoring, available for direct measurements of the outer surface of the contact part T ₁ (τ ⁽ⁱ⁾ ), i=1, 2, ..., n into the corresponding temperature values, inaccessible for direct measurements of the contact surface of the contact connection T ₂ (τ ⁽ⁱ⁾ ), i=1, 2, ..., n according to the formula:

where τ ⁽ⁱ⁾ - time count; i is the serial number of the measurement; n is the number of the last measurement; k ₁ - multiplicative calibration factor; k ₂ - additive calibration factor; T ₂ (0) - the initial value of the temperature of the contact surface; T _max - the maximum allowable temperature for a given contact connection; I _max - the measured value of the test or operational rectangular current pulse; ρ ₂₀ - electrical resistivity of the contact-piece material at a temperature of 20°C; c is the specific heat capacity of the contact-piece material; α - temperature coefficient of resistivity; S ₁ - cross-sectional area of the contact part; S ₂ - overlap area of the contact parts (conditional area of the contact surface); Ф(τ ⁽ⁱ⁾ ) - dynamic coefficient, depending on the measurement time

, и по зарегистрированным косвенным измерениям температуры контактной поверхности строят уравнение:

, and according to the registered indirect measurements of the temperature of the contact surface, the following equation is constructed:

where A and B are the coefficients of the linear regression equation, substituting into which the value of the maximum allowable heating temperature T _max of the contact surface of the COP determines τ _max - the time before switching off the switching device.

The disadvantage of this method is not sufficient for practical purposes, the speed of determining the time during which it is possible to operate protection COP switching device from overheating.

The problem solved by the present invention is to improve the quality (reliability, speed) of determining the time during which the protection of the COP of the switching device from overheating is possible.

The technical essence is achieved by the fact that the quantitative value of measurements of conditionally contact dynamic resistance is introduced into the determination procedure.

до t₂=t₁+mΔt,This problem is solved by the fact that in the method for determining the response time of the protection of current-carrying contact connections of switching devices from overheating, composition of the switching device and the generation of a signal by which the time of reaching the maximum allowable temperature by the contact surface is determined; if the current exceeds its threshold value, the temperature control of the contact surface is carried out in the dynamic mode monitoring on the time interval of heating the contact connection according to the linear law from

up to t ₂ \u003d t ₁ + mΔt,

where t ₁ is the start time of heating according to a linear law,

l is the thickness of the contact piece,

c, λ - specific heat capacity and thermal conductivity of the contact-piece material,

Δt - measurement step,

m - the number of measurements of the value of conditionally contact dynamic resistance

- условно-контактного динамического сопротивления (УКДС), одновременно учитывающего как изменение переходного контактного сопротивления R_К, так и эффективной площади контактной поверхности S_ЭФ=k_ПРS₂ (S=S₂ - площадь нахлестки контакт-деталей (условная площадь контактной поверхности), k_ПР - коэффициент приведения), как функции прямоугольного импульса тока I_max, по формуле:t ₂ - the time of completion of temperature control in the dynamic monitoring mode, then recalculate the temperature values measured during dynamic monitoring of the outer surface of the contact part available for direct measurements T ₁ (τ ⁽ⁱ⁾ ), i=1, 2, ..., m ( τ ⁽ⁱ⁾ - measurement time count) into the corresponding values

- conditionally contact dynamic resistance (UKDS), simultaneously taking into account both the change in the transient contact resistance R _K and the effective area of the contact surface S _EF =k _PR S ₂ (S=S ₂ - overlap area of contact parts (conditional area of the contact surface) , k _PR - reduction coefficient), as a function of a rectangular current pulse I _max , according to the formula:

, равноеwhere T ₀ is the temperature value of the open surface of the contact part at the moment the pulse starts, then the mathematical expectation of the UKDS value at the moment of time is calculated

equal to

до t₂=t₁+mΔt по формуле:since when calculating the temperature of the contact surface in the time interval of heating the CS according to the linear law from

up to t ₂ \u003d t ₁ + mΔt according to the formula:

в момент времени τ⁽ⁱ⁾, а вместе с ней и величина

от времени не зависят, т.е. являются постоянными, а величина

представляет собой надежное косвенное измерение УКДС, после чего, подставляя в формулу (5) t=τ_max и T₁(t)=T_max (такая подстановка фактически обеспечивает контроль отклонения от максимально допустимого значения температуры наиболее подверженной перегреву контактной поверхности токоведущего контактного соединения) определяют τ_max - момент времени до отключения коммутационного аппарата.derivative of the temperature of the contact surface with respect to time

at the moment of time τ ⁽ⁱ⁾ , and together with it the value

do not depend on time, i.e. are constant, and the value

represents a reliable indirect measurement of the UKDS, after which, substituting in the formula (5) t=τ _max and T ₁ (t)=T _max (such a substitution actually provides control of the deviation from the maximum allowable temperature value of the most overheated contact surface of the current-carrying contact connection) determine τ _max - the time before switching off the switching device.

The invention is aimed at preventing failure of the contact connections of switching devices.

The technical result of the invention is to improve the quality (reliability, speed) of determining the time during which the protection of the switching device from overheating is possible, which prevents the melting of the material of the contact - details of the contact connection by obtaining operational and reliable information about the thermal state of the contact surface most susceptible to overheating KS.

In FIG. 1 is a diagram of a bolted connection with points of direct measurement of the temperature of the outer surface of the contact part T ₁ (t) and indirect measurement of the temperature of the contact surface T ₂ (t).

In FIG. 2 - stages of heating of the bolted contact connection under the influence of a rectangular current pulse.

In FIG. 3(a) and 3(b) - a diagram of a bolted connection with the conditional dimensions of the surfaces to be joined.

In FIG. 4 - heating with a rectangular current pulse of 20 kA open T ₁ (t) and contact T ₂ (t) surfaces of the COP according to a linear law at the stage of dynamic monitoring (formula (1) at ρ ₂₀ =0).

The method is carried out as follows. In the time interval before the start of the pulse (Fig. 2) under the influence of the rated current I _n the process of heating the COP is set: T ₁ (t)=T _1.0 ; T ₂ (t)=T _2.0 . The remaining heating interval is divided into three stages: 1) the initial stage of adiabatic heating (0<t<t ₁ ) exponentially; 2) the stage of transition of the CC heating process to a linear dependence of temperature on time (t ₁ <t<t ₂ ) and 3) the stage of heating the CC according to a linear law to the maximum allowable temperature T _max (t ₂ <t<τ _max ). The beginning of the second and third stages of heating is determined according to the data on the thermophysical characteristics and the thickness of the contact part.

At the first stage, the value of the operational or test rectangular current pulse I _max is measured. If it exceeds a predetermined threshold value I _p (this condition ensures the presence of an adiabatic mode of heating the COP), then measurements of the heating temperature of the outer surface of the contact part are started.

At the second stage, the temperature of the outer surface of the contact part is measured and the measured values are converted into conditionally contact dynamic resistance according to formula (3).

At the third stage, according to the formula (6), τ _max is determined - the time of onset of overheating of the COP.

и t₂=t₁+mΔt. Осредненные на интервале измерения данные о теплофизических характеристиках электрокерамики с, λ и толщине контакт-детали l приведены в таблице 1.The beginning of the second and third stages is determined from the ratios

and t ₂ \u003d t ₁ + mΔt. The data on the thermophysical characteristics of the electroceramics c, λ and thickness of the contact piece l are averaged over the measurement interval in Table 1.

The technical result is achieved by the fact that in the method of protecting the contact connections of the current-carrying parts of the switching equipment of electrical equipment from overheating, a signal is given according to the predicted time for the contact surface to reach the maximum allowable temperature, after which the switching device is switched off using the load switch, which prevents the melting of the contact parts.

i=1, 2, …, m (фактически это m-кратное косвенное измерение постоянной величины

, повышающее достоверность и скорость получения результата измерений) и вычислению по формуле (6) времени срабатывания защиты КС от перегрева τ_{max, 2} был рассмотрен нагрев болтового контактного соединения двух контакт-деталей из электрокерамики (фиг. 3) прямоугольным импульсом тока 20 кА.Example. As an example of improving the quality of determining the response time of protection against overheating by switching according to the invention from n indirect measurements of the temperature of the contact surface of the COP T ₂ (τ ⁽ⁱ⁾ ), i=1, 2, ..., n at the initial stage of adiabatic heating of the COP according to a linear law , building on the measured values of the equation of linear regression and forecasting on the constructed equation of time τ _{max, 1} reaching the maximum allowable temperature value T _max by the contact surface to m (m<n) measurements of the temperature of the open surface of the contact part T ₁ (τ ⁽ⁱ⁾ ), i=1, 2, …, m with subsequent recalculation of the measured values into conditionally contact dynamic resistance

i=1, 2, …, m (in fact, this is an m-fold indirect measurement of a constant value

, which increases the reliability and speed of obtaining the measurement result) and the calculation according to the formula (6) of the response time of the protection of the COP against overheating τ _{max, 2,} heating of the bolted contact connection of two electroceramic contact parts (Fig. 3) with a rectangular current pulse of 20 kA was considered.

First, the values of the measured temperature of the open surface of the contact connection T ₁ (τ ⁽ⁱ⁾ ) (Fig. 4), obtained at a value of a rectangular current pulse of 20 kA, are set. As the maximum allowable heating temperature _Tmax , a temperature of 1000°C was taken, the step of measurements carried out at the second stage was taken equal to 0.1 seconds, the thermophysical properties are given in table 1, in table 2 - the geometric characteristics of the COP and calibration coefficients.

Since formulas (3)-(6) are valid only for sufficiently large values of I _max (I _max is several times greater than I _H , i.e. calculations are performed without taking into account the direct heating of the contact part by a rectangular current pulse, only heating by the heat released on the transient contact resistance), then the calculation formula (1) is also used without taking into account direct heating, i.e. at ρ ₂₀ =0.

Calculation by the method of the prototype. First, in the dynamic monitoring mode on the time interval (t ₁ <t<t ₂ ), the temperature of the open surface of the contact part T ₁ (τ ⁽ⁱ⁾ ), i=1, 2, ..., n is measured (Fig. 4, Table 3 ), then according to the formula (1) at ρ ₂₀ =0 and calibration coefficients k1=0.99 and k2=0.05 (Table 2) calculate the temperature of the contact surface of the COP T ₂ (τ ⁽ⁱ⁾ ), i=1, 2, …, n (Fig. 4, Table 3).

Then, according to the calculated values of the contact surface temperature T ₂ (τ ⁽ⁱ⁾ ), the linear regression coefficients A=244 and B=268 are calculated, and according to equation (2), the response time of the overheating protection τ _{max, 1} =3s is calculated using the prototype method.

.Calculation by the new method. In the dynamic monitoring mode on the time interval (t ₁ <t<t ₂ ) measure the temperature of the open surface of the contact part T ₁ (τ ⁽ⁱ⁾ ), i=1, 2, ..., m (m<n) (Fig. 4 , Table 4), then according to formula (3) for given in Table. 2, 3 parameters and T ₀ \u003d 90 ° C, I _max \u003d 20 kA calculate the corresponding values of UKDS

.

Then, according to formula (6), the operation time of the COP overheating protection τ _max , ₂ = 3 s is calculated using the new method for all τ ⁽ⁱ⁾ (Table 4). The response times of protection against overheating of the COP according to the prototype method and the proposed new method τ _{max, 1} and τ _{max, 2} turned out to be equal, because in the table. 4 to calculate the UKDS, accurate measurements of the temperature of the open surface of the contact part T ₁ (τ ⁽ⁱ⁾ ), i=3, 4, 5 (see Table 3) were used.

Table 5 shows the results of calculating the operation time of the COP overheating protection according to the proposed method τ _{max, 2} for all τ ⁽ⁱ⁾ , i=3, 4, 5, obtained from the temperatures of the open surface of the contact part, measured with an error of 2°C. They differ from the exact value of τ _{max, 2} =3 s by 0.04 s; 0.03 s and 0.02 s, respectively.

, равное в данном случае

подставляя которое в (6), снова получают τ_{max, 2}=3с.To increase the reliability of the result of calculating the response time of the COP protection against overheating, formula (6) uses the mathematical expectation of the UKDS value at the time

, equal in this case

substituting which in (6), again get τ _{max, 2} =3s.

среднего арифметического значения этой величины, вычисленных по температуре открытой поверхности T₁(τ⁽ⁱ⁾), измеренной в моменты времени t=τ⁽ⁱ⁾, i=3, 4, 5; скорость определения времени срабатывания защиты от перегрева КС повышается за счет уменьшения количества точек измерения температуры и упрощения расчетных формул (объема вычислений в формулах (4), (6) значительно меньше, чем в формулах (1), (2) совместно с формулами для расчета коэффициентов линейной регрессии).This example shows the improvement in the quality of determining the response time of the protection of a symmetrical bolted connection of rectangular busbars from overheating by a rectangular current pulse due to the transition to the method proposed in the invention: reliability is increased by calculating the constant value of the UKDS of a given contact connection with three repetitions (three measurements of the temperature of the open surface of the contact -details are made with an error of 2°C) and taken as the measured value of UKDS at the time

the arithmetic mean of this value, calculated from the temperature of the open surface T ₁ (τ ⁽ⁱ⁾ ), measured at times t=τ ⁽ⁱ⁾ , i=3, 4, 5; the speed of determining the response time of protection against overheating of the compressor station is increased by reducing the number of temperature measurement points and simplifying the calculation formulas (the amount of calculations in formulas (4), (6) is much less than in formulas (1), (2) together with the formulas for calculating linear regression coefficients).

Claims (18)

A method for determining the response time of the protection of current-carrying contact connections of switching devices against overheating, including monitoring the deviation from the maximum allowable temperature value of the contact surface of the contact surface most susceptible to overheating in the composition of the switching device and generating a signal that determines the time the contact surface reaches the maximum allowable temperature, in the mode monitoring measure the value of a rectangular current pulse and compare the measured value with a predetermined threshold value of the test or operational rectangular current pulse, characterized in that the value of the conditionally contact dynamic resistance is taken into account and, if the current exceeds its threshold value, the temperature control of the contact surface is carried out in the dynamic monitoring mode on time interval of contact connection heating according to the linear law from

up to t ₂ \u003d t ₁ + mΔt, where t ₁ is the start time of heating according to a linear law, l is the thickness of the contact piece, c, λ - specific heat capacity and thermal conductivity of the contact-piece material, Δt - measurement step, m - the number of measurements of the value of conditionally contact dynamic resistance, t ₂ - time to complete the temperature control in the dynamic monitoring mode, then recalculate the temperature values measured in the course of dynamic monitoring that are available for direct measurements of the outer surface of the contact part

into the corresponding values of the conditionally contact dynamic resistance (UKDS), which simultaneously takes into account both the change in the transitional contact resistance R _K and the effective area of the contact surface S _EF =k _PR S _PR (k _PR <1) - the coefficient of reduction of the conditional area to the effective (actual) area of the contact connection), as a function of a rectangular current pulse I _max , according to the formula:

where T ₀ is the temperature value of the open surface of the contact part at the moment the pulse starts, τ ⁽ⁱ⁾ - time count, T _max - the maximum allowable temperature for a given contact connection; I _max - the measured value of the test or operational rectangular current pulse; l is the thickness of the contact piece, S - overlap area of contact parts (conditional area of the contact surface); c, λ - specific heat capacity and thermal conductivity of the material of the contact part, then calculate the mathematical expectation of the value of UKDS at the moment of time

equal to

, and determine τ _max - the moment of time before switching off the switching device

Images