RU2437109C2 - Control method of electrical resistance of insulation and protective disconnection of electrical equipment - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: method is based on measurement of leakage current from auxiliary source of measuring voltage in the form of periodic sequence of pulses; measurement of leakage current I₁ in time range T<t≤2T and leakage current I₂ in range 3T<t≤4T by integration of voltage drop on reference resistance over a period of supply mains, calculation of insulation resistance by formula

recording of n last values of insulation resistance; calculation as per these values of expected values of insulation resistance in the current measurement range r_e and further range

comparison of values r_ins, r_e,

with allowable range R₀ and in case r_ins<R₀; r_e<R₀ disconnection of electrical equipment; in case r_ins<R₀; r_e>R₀ repeated comparison in the next range and in case of repetition of the case r_ins<R₀ the disconnection of electrical equipment.

EFFECT: increasing quick action of monitoring of insulation and reliability of protection of electrical equipment.

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Description

The invention relates to electrical engineering and relay protection of power supply systems and is intended for use in electrical AC networks containing semiconductor rectifier installations.

Known methods for monitoring electrical insulation resistance and protective shutdown of electrical equipment, based on measuring the leakage current from an auxiliary source of measuring voltage, in which a monitored jump in the measured DC voltage is applied to the controlled network during the transition process of establishing the measuring voltage at the network insulation impedance at a given time from the beginning of this process, the first instantaneous value of the measuring voltage on it is measured and stored the isolation isolation of the network, after interrupting the process of charging the network capacitance and storing the instantaneous value of the measuring voltage in the transient during isolation of the insulation impedance, record the second instantaneous value of the measuring voltage in the transition process of discharging the network capacity after a time equal to the specified time of charging the network capacity, and calculate the resistance isolation (A.S. No. 1707569 (USSR), MKI G01R 27/18, 1992; A.S. No. 1541533 (USSR), MKI G01R 27/18, 1990).

When implementing the known methods, the insulation resistance of the network is determined by calculating the instantaneous values of the voltage drop across the insulation resistance at certain times of the transient processes of charge and discharge of the network capacity. When connecting or disconnecting additional network sections during these transients, the measurement results are distorted and, as a consequence, false protection trips are possible.

Therefore, the disadvantages of the known method of controlling the insulation resistance and protecting the electrical network is the low reliability of protection.

Of the known methods, the closest to the achieved result to the proposed one is a method of monitoring the insulation resistance and protecting the electrical network, based on measuring the leakage current from an auxiliary source of measuring voltage, at which the measuring voltage is formed in the form of a periodic pulse train of the form

where U (t) is the measuring voltage; U ₁ , U ₂ - constant voltage, U ₁ > U ₂ ; τ is the time interval, T is the period of the power supply network, τ <T; measure the leakage current I ₁ in the time interval T <t≤2T and the leakage current I ₂ in the interval 3T <t≤4T by integrating the voltage drop across the reference resistance over the period of the supply network, calculate the insulation resistance by the formula

,

,

where r _t is the internal resistance of the source, compare the obtained value with the two settings R ₁ and R ₂ , R ₁ <R ₂ , when r _from <R ₁ repeat the measurements n ₁ times, and when R ₁ <r _from <R ₂ repeat the measurements n ₂ times (n ₁ ≤n ₂ ), and when sequentially confirming the fact that the insulation resistance decreases n ₁ or n ₂ times, the network is disconnected (RF Patent No. 2144679, MKI G01R 27/18, H02H 3/16 - Publ. 20.01.2000 . Bull. No. 2).

The method is based on measuring the leakage current from an auxiliary measuring voltage source in the form of a periodic sequence of pulses of the form

and includes measuring the leakage current I ₁ in the time interval T <t≤2T and the leakage current I ₂ in the interval 3T <t≤4T by integrating the voltage drop across the reference resistance for the period of the supply network, calculating the insulation resistance by the formula

,

,

comparing the obtained value with the two settings R ₁ and R ₂ , R ₁ <R ₂ , for r _of <R ₁ repeat measurements n ₁ times, and for R ₁ <r _of <R ₂ repeat measurements n ₂ times and disconnect the network in series confirmation of the fact of reducing the insulation resistance n ₁ or n ₂ times.

In the known method, in order to make a decision to turn off electrical equipment, it is necessary to repeat the fact of reducing the insulation resistance n ₁ or n ₂ times, therefore, the speed of protection is wired, and therefore the reliability is low.

Therefore, the known method does not provide high-speed control of insulation resistance and reliable protection of electrical equipment.

Thus, the disadvantages of the known method of monitoring the insulation resistance are the low speed of monitoring the insulation resistance and the reliability of the protection of electrical equipment.

The purpose of the invention is to increase the speed of monitoring the insulation resistance and the reliability of the protection of electrical equipment.

This goal is achieved by the fact that in the known method of controlling the electrical insulation resistance and protective shutdown of electrical equipment, which form the measuring voltage in the form of a periodic sequence of pulses of the form

where u (t) is the measuring voltage; U ₁ , U ₂ - constant voltage, U ₁ > U ₂ , τ - time interval, T - the period of the power supply network, τ <T; measure the leakage current I ₁ in the time interval T <t≤2T and the leakage current I ₂ in the interval 3T <t≤4T by integrating the voltage drop across the reference resistance over the period of the supply network, calculate the insulation resistance by the formula

,

,

, сравнивают значения r_из, r_п,

с допустимым значением R₀ иwhere r _t is the internal resistance of the source, compare the obtained value with the setpoint R ₀ , repeat the measurements and in the case of an unacceptable decrease in the insulation resistance, turn off the electrical equipment, additionally remember the n last values of the insulation resistance, calculate the predicted values of the insulation resistance over the current measurement interval r _n and the subsequent interval

, compare the values of r _from , r _p ,

with a valid value of R ₀ and

- in the case r _of <R ₀ ; r _p <R ₀ turn off the electrical equipment;

- in the case r _of <R ₀ ; r _p > R ₀ make a repeated comparison on the subsequent interval, and in case of a repeat of the event r _from <R ₀ , the electrical equipment is switched off;

производят повторное сравнение на последующем интервале и в случае события r_из<R₀ производят отключение электрооборудования, а при r_из>R₀; r_п<R₀;

производят третье измерение и при повторении события r_из>R₀; r_п<R₀;

или при r_из<R₀ производят отключение электрооборудования.- in the case r _of > R ₀ ; r _p <R ₀ ;

make a repeated comparison on the subsequent interval and in the event of an event r _from <R ₀ , the electrical equipment is switched off, and when r _from > R ₀ ; r _p <R ₀ ;

make the third measurement and when repeating the event r _from > R ₀ ; r _p <R ₀ ;

or when r _from <R ₀ , the electrical equipment is switched off.

Compared with the closest similar solution, the proposed technical solution has the following new features (operations):

- additionally remember n last values of insulation resistance;

;- the stored n sequential values of the insulation resistance calculate the predicted values of the insulation resistance in the current measurement interval r _p and the subsequent interval

;

с допустимым значением R₀ и- compare the values of r _from , r _p ,

with a valid value of R ₀ and

- in the case r _of <R ₀ ; r _p > R ₀ disable the electrical equipment;

- in the case r _of <R ₀ ; r _p > R ₀ make a repeated comparison on the subsequent interval, and in case of a repeat of the event r _from <R ₀ , the electrical equipment is switched off;

производят повторное сравнение на последующем интервале и в случае события r_из<R₀ производят отключение электрооборудования, а при r_из>R₀; r_п<R₀;

производят третье измерение и при повторении события r_из>R₀; r_п<R₀;

или при r_из<R₀ производят отключение электрооборудования.- in the case r _of > R ₀ ; r _p <R ₀ ;

make a repeated comparison on the subsequent interval and in the event of an event r _from <R ₀ , the electrical equipment is switched off, and when r _from > R ₀ ; r _p <R ₀ ;

make the third measurement and when repeating the event r _from > R ₀ ; r _p <R ₀ ;

or when r _from <R ₀ , the electrical equipment is switched off.

Therefore, the claimed technical solution meets the requirement of "novelty."

When implementing the invention, the speed of monitoring the insulation resistance and the reliability of the protection of electrical equipment are increased. This is ensured by a combination of the following technical solutions implemented in the proposed method:

- remembering the n last values of the insulation resistance;

по запомненным n последовательным значениям сопротивления изоляции;- calculation of forecast values of insulation resistance in the current measurement interval r _p and the subsequent interval

by stored n sequential values of insulation resistance;

с допустимым значением R₀ и в зависимости от результатов сравнения выполнением следующих действий:- comparing the values of r _from , r _p ,

with a valid value of R ₀ and depending on the comparison results by performing the following steps:

- in the case r _of <R ₀ ; r _p <R ₀ : shutdown of electrical equipment;

- in the case r _of <R ₀ ; r _p > R ₀ : repeated comparison at a subsequent interval and in case of a repeat of event r _from <R ₀ , the electrical equipment is switched off;

: повторное сравнение на последующем интервале и в случае события r_из<R₀ производят отключение электрооборудования, а при r_из>R₀; r_п<R₀;

производят третье измерение и при повторении события r_из>R₀; r_п<R₀;

или при r_из<R₀ производят отключение электрооборудования.- in the case r _of > R ₀ ; r _p <R ₀ ;

: repeated comparison on the subsequent interval and in the event of an event r _from <R ₀ , the electrical equipment is switched off, and when r _from > R ₀ ; r _p <R ₀ ;

make the third measurement and when repeating the event r _from > R ₀ ; r _p <R ₀ ;

or when r _from <R ₀ , the electrical equipment is switched off.

Therefore, the claimed technical solution meets the requirement of "positive effect".

For each distinguishing feature, a search is made for well-known technical solutions in the field of measurement technology and relay protection.

Operations:

- remembering the n last values of the insulation resistance;

;- from the stored n sequential values of the insulation resistance, the calculation of the predicted values of the insulation resistance in the current measurement interval r _p and the subsequent interval

;

с допустимым значением R₀ и- comparison of the values of r _from , r _p ,

with a valid value of R ₀ and

- in the case r _of <R ₀ ; r _p <R ₀ shutdown of electrical equipment;

- in the case r _of <R ₀ ; r _p > R ₀ repeated comparison at a subsequent interval and in the event of a repeat of the event r _from <R _{0 the} shutdown of electrical equipment;

повторное сравнение на последующем интервале и в случае события r_из<R₀ отключение электрооборудования, а при r_из>R₀; r_п<R₀;

третье измерение и при повторении события r_из>R₀; r_п<R₀;

или при r_из<R₀ отключение электрооборудования, в известных способах аналогичного назначения не обнаружены.- in the case r _of > R ₀ ; r _p <R ₀ ;

repeated comparison at a subsequent interval and in the event of an event r _from <R _0, disconnection of electrical equipment, and when r _from > R ₀ ; r _p <R ₀ ;

the third dimension and when repeating the event r _from > R ₀ ; r _p <R ₀ ;

or when r _of <R _{0, the} disconnection of electrical equipment in known methods of similar purpose were not detected.

Thus, these features provide the claimed technical solution according to the requirement of "significant differences".

The essence of the invention is illustrated by drawings. Figure 1 shows a simplified schematic diagram of a three-phase electrical network, explaining the method of monitoring the insulation resistance of the network in the presence of a valve converter P in the network, figure 2 shows the equivalent single-line circuit of the electrical network, figure 3 shows a diagram of the measuring voltage, figure 4 a diagram of the process of measuring insulation resistance is given.

Figure 1 indicates: e _A , e _B , e _C - phase voltage of the controlled network; U _t - voltage of the source of the test signal; r _t2 , r _t3 - resistance of additional resistors, r _and - reference measuring resistor; r _A , r _B , r _C - insulation resistance of the phases, respectively A, B and C of the controlled network; C _A , C _B , C _C - capacitance of phases A, B and C; P - valve converter; r _p1 , r _p2 - insulation resistance of the DC network (for feeders connected to the positive and negative poles of rectifier P); C _p1 , C _p2 - DC network capacitance; Z _p - the integrated load resistance of the Converter; MK - microcontroller; KA - switching apparatus.

; сравнении r_из, r_п и

заданным допустимым значением сопротивления изоляции R₀ и принятии решения о защитном отключении электрооборудования производится с помощью микроконтроллера МК. Коммутационный аппарат КА, управляющий вход которого соединен с выходом микроконтроллера МК, предназначен для отключения защищаемого участка сети.The voltage from the source U _t through the star of additional resistors r _m1 , r _m2, r _m3 enters a controlled three-phase network. The current flowing in the circuit: "test signal source" U _t - additional resistors r _m1 , r _m2, r _m3 - insulation resistance - ground, is controlled by the magnitude of the voltage drop across the measuring resistor r _and . The value of the insulation resistance is calculated depending on the measured current and the known test voltage. Processing of measurement information, consisting in calculating the insulation resistance r _from , storing n successive values of the insulation resistance, calculating from these values the predicted values of the insulation resistance in the current measurement interval r _p and the subsequent interval

; comparing r _from , r _p and

the specified permissible value of the insulation resistance R ₀ and the decision on the protective shutdown of electrical equipment is performed using the microcontroller MK. The switching apparatus of the spacecraft, the control input of which is connected to the output of the microcontroller MK, is designed to disconnect the protected section of the network.

The resistance identification algorithm is explained using the equivalent single-line circuit shown in figure 2, where it is indicated: C _E , r _e - equivalent capacitance and insulation resistance of the controlled network; C _n , r _p - equivalent capacitance and insulation resistance in a direct current network; U _p - the constant component of the voltage.

The source of the test signal during the time interval τ <t≤2T generates a constant voltage U _t = U ₂ . In steady state, the current of this source is

.where r _of is the equivalent insulation resistance of the network,

.

During the time interval 2T + τ <t≤4T, the source of the test signal generates a voltage U _t = U ₂ . In this case, the source current is

The solution of the system of equations (1) and (2) with respect to r _from gives the formula

invariant with respect to the constant voltage U _p under the assumption U _t = const in the measurement interval.

The waveform of the test signal is shown in FIG. Test voltage is a sequence of bipolar pulses of a special shape. In the time interval 0≤t≤τ voltage U _t = U ₁ and provides an accelerated process of transition of the electrical system to the steady state (forced charge of capacitors C and C _p ). To exclude the influence on the measurement results of the variable component due to the flow through the measuring resistor r _and currents caused by sources e _A , e _B , e _C , measurements of currents I ₁ and I _{2 are} carried out in steady state by integrating the voltage drop across the resistance r _and for the period supply voltage.

The emergency shutdown signal generation algorithm provides for:

- calculation of the equivalent insulation resistance r _from ;

- storing and storing in the memory of the controller n, for example, the last four measured values of insulation resistance;

измерения;- forecasting (calculation of forecast values) of equivalent insulation resistance in the current measurement interval r _p and in the subsequent interval

measurement;

с уставкой R₀ (например, 10 кОм), и повторные измерения с целью подтверждения полученного результата. При этом:- comparison of r _of , r _p ,

with setting R ₀ (for example, 10 kOhm), and repeated measurements in order to confirm the result. Wherein:

- in the case r _of <R ₀ ; r _p <R ₀ turn off the electrical equipment;

- in the case r _of <R ₀ ; r _p > R ₀ make a repeated comparison on the subsequent interval, and in case of a repeat of the event r _from <R ₀ , the electrical equipment is switched off;

производят повторное сравнение на последующем интервале и в случае события r_из<R₀ производят отключение электрооборудования, а при r_из>R₀; r_п<R₀;

производят третье измерение и при повторении события r_из>R₀; r_п<R₀;

или при r_из<R₀ производят отключение электрооборудования.- in the case r _of > R ₀ ; r _p <R ₀ ;

make a repeated comparison on the subsequent interval and in the event of an event r _from <R ₀ , the electrical equipment is switched off, and when r _from > R ₀ ; r _p <R ₀ ;

make the third measurement and when repeating the event r _from > R ₀ ; r _p <R ₀ ;

or when r _from <R ₀ , the electrical equipment is switched off.

Diagrams explaining the algorithm of the insulation resistance control system and protective shutdown of electrical equipment are shown in Fig.4.

может быть использован, например, математический аппарат нечеткой логики (Дьяконов В.П., Круглов В.В. MATLAB 6.5 SP1/7/7 SP1/7 SP2+Simulink 5/6. Инструменты искусственного интеллекта и биоинформатики. - М., Солон-Пресс, 2006, с.243-247).To determine the predicted values of r _p and

can be used, for example, the mathematical apparatus of fuzzy logic (Dyakonov VP, Kruglov VV MATLAB 6.5 SP1 / 7/7 SP1 / 7 SP2 + Simulink 5/6. Instruments of artificial intelligence and bioinformatics. - M., Solon -Press, 2006, p. 243-247).

The response time of the protective shutdown after violation of the insulation resistance does not exceed 2 measurement cycles.

Thus, the proposed method allows monitoring the insulation resistance and protecting the electrical network and provides increased measurement performance and reliability of protection due to:

- the use in the protective shutdown algorithm of the predicted values of the insulation resistance calculated at the current and subsequent measurement intervals;

- repeat measurements in case of mismatch between the measured and predicted values.

A device that implements the proposed method for monitoring the insulation resistance and protecting the electric network has successfully passed tests in the 0.4 kV network in the conditions of the testing laboratory of the National Scientific Center for Mining - Institute of Mining named after A.A. Skochinsky (NSCGP-IGD named after A.A. Skochinsky).

Therefore, the use in the proposed method of monitoring the electrical insulation resistance and protective shutdown of electrical equipment, in which form the measuring voltage in the form of a periodic sequence of pulses of the form

where u (t) is the measuring voltage; U ₁ , U ₂ - constant voltage, U ₁ > U ₂ , τ - time interval, T - the period of the power supply network, τ <T; measure the leakage current I ₁ in the time interval T <t≤2T and the leakage current I ₂ in the interval 3T <t≤4T by integrating the voltage drop across the reference resistance over the period of the supply network, calculate the insulation resistance by the formula

,

,

, сравнивают значения r_из, r_п,

с допустимым значением R₀ и:where r _t is the internal resistance of the source, compare the obtained value with the setpoint R ₀ , repeat the measurements and in the case of an unacceptable decrease in insulation resistance, turn off the electrical equipment, additionally operations: remember n consecutive values of insulation resistance, these values calculate the predicted values of insulation resistance in the current interval measuring r _p and the subsequent interval

, compare the values of r _from , r _p ,

with a valid value of R ₀ and:

- in the case r _of <R ₀ ; r _p <R ₀ turn off the electrical equipment;

- in the case r _of <R ₀ ; r _p > R ₀ make a repeated comparison on the subsequent interval, and in case of a repeat of the event r _from <R ₀ , the electrical equipment is switched off;

производят повторное сравнение на последующем интервале и в случае события r_из<R₀ производят отключение электрооборудования, а при r_из>R₀; r_п<R₀;

производят третье измерение и при повторении события r_из>R₀; r_п<R₀;

или при r_из<R₀ производят отключение электрооборудования, что позволяет повысить быстродействие измерения сопротивления изоляции и надежность защиты.- in the case r _of > R ₀ ; r _p <R ₀ ;

make a repeated comparison on the subsequent interval and in the event of an event r _from <R ₀ , the electrical equipment is switched off, and when r _from > R ₀ ; r _p <R ₀ ;

make the third measurement and when repeating the event r _from > R ₀ ; r _p <R ₀ ;

or when r _from <R ₀ , the electrical equipment is switched off, which allows to increase the speed of measuring the insulation resistance and the reliability of protection.

The use of the proposed technical solution in electrical systems for various purposes will improve the reliability and safety of electrical equipment.

Claims (1)

A method for controlling the electrical insulation resistance and protective shutdown of electrical equipment, in which a measuring voltage is formed in the form of a periodic sequence of pulses of the form

where u (t) is the measuring voltage; U ₁ , U ₂ - constant voltage, U ₁ > U ₂ , τ is the time interval, T is the period of the power supply network, τ <T; measure the leakage current I ₁ in the time interval T <t≤2T and the leakage current I ₂ in the interval 3T <t≤4T by integrating the voltage drop across the reference resistance over the period of the supply network, calculate the insulation resistance by the formula

where r _t is the internal resistance of the source, compare the obtained value with the setpoint R ₀ , repeat the measurements and in the case of an unacceptable decrease in insulation resistance, turn off the electrical equipment, characterized in that n last measured values of the insulation resistance are additionally stored, the predicted values of the insulation resistance are calculated from these values on the current measurement interval r _p and the subsequent interval r _p ⁺ , compare the values of r _from , r _p , r _p ⁺ with a valid value of R ₀ and:
- in the case r _of <R ₀ ; r _p <R ₀ turn off the electrical equipment;
- in the case r _of <R ₀ ; r _p > R ₀ make a repeated comparison on the subsequent interval, and in case of a repeat of the event r _from <R ₀ , the electrical equipment is switched off;
- in the case r _of > R ₀ ; r _p <R ₀ ; r _p ⁺ <R ₀ make a repeated comparison on the subsequent interval and in the event of an event r _from <R ₀ , the electrical equipment is switched off, and when r _from > R ₀ ; r _p <R ₀ ; r _p ⁺ <R ₀ make the third measurement and when repeating the event r _from > R ₀ ; r _p <R ₀ ; r _p ⁺ <R ₀ or when r _of <R ₀ produce a shutdown of electrical equipment.

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