RU2353015C2 - Multiple three-phase electric circuits protection system from remote short circuit currents - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to protection systems for electrical circuits with long lines from the remote short circuits in case powerful electric motors are available in the circuits. Multiple three-phase electric circuit protection systems includes protection device, e.g. switch, with current sensors and semi-conducting release. There is a comparison unit in the release to compare current flowing through the unit with current setting by short circuit current I_sd. The unit is designed so that low setting level I_sd can be set up within (1.5÷3) from the unit operating current I_r. Long mainline electric line is connected to the draining terminals of protection unit. Feeder lines with different types of loads are connected to the above mainline electric line along the whole length. The feeder lines are also connected to electric motor. Short circuit current value at the end of mainline line I_sc is equal or lower than the value of start-up current in motor I_sm coupled with the beginning of middle parts of mainline, but it is higher or equal to the current setting value I_sd-(I_sm≥I_sh≥I_sd). In addition, protection unit release includes the control unit of current sum of squares for all three phases {Si²(t)} and comparison of maximum current sum of squares value relation {S_maxi²(t)} to its minimum value {S_mini²(t)} in the first period of current occurrence exceeding the setting I_sd,. It also includes logic unit, which automatically increases current setting value I_sd to I_sd1 value equal to 1.1÷1.5 of startup current value I_sm -I_sd↑{I_sd1=(1.1÷1.5)I_sm} under condition that the above relation expressed by the coefficient K_s={S_maxi²(t)}/{S_mini²(t)} is equal or more than 1.4 (K_s≥1.4).

EFFECT: improving protection reliability of long lines from remote short circuits and ensuring uninterrupted power supply during electric motor start-up not affecting fire safety class and protection system cost.

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Description

The invention relates to protection systems for circuit breakers of three-phase branched electrical circuits against short-circuit currents, in particular, electric circuits with long lines and sufficiently powerful electric motors connected to these lines, the starting current of which may be greater than the short-circuit current (SC) at the end of a long line.

Known are systems for protecting branched electric circuits with long lines, in particular, systems for protecting electric circuits of Oblenergo (agricultural facilities) [1] based on circuit breakers in which a long main overhead line is connected to the outlet terminals of the input switch of the complete transformer point (KTP), in different parts of which feeder lines are connected along its length, the loads of which are electric motors of sufficient power (grits, pumps, etc.).

Due to the fact that overhead lines are mainly made by steel wires (with a large resistivity) and have a large length, the short-circuit current values at the end of such a line are relatively small. As a result, in these protection systems, the value of the short-circuit current at the end of a long line (I _short ) often turns out to be close to the value of the working current of the protective device (I _r ).

Therefore, for reliable protection of the circuits from remote short-circuit currents, the values of the corresponding current settings of the releases (I _sd ) are chosen sufficiently small, equal to (1.5 ÷ 3) I _r . However, if a feeder with a sufficiently powerful electric motor is connected at the beginning of the main line, the value of its starting current (I _pd ) at the beginning of the starting process is greater than the value of the current setting of the release (I _sd ).

If the branched electric circuit has a power backup system, then at the time of switching in the circuit there are even greater currents than I _PD , the simultaneous self-starting currents of all electric motors I _sz .

Thus, in the considered protection systems of branched electrical circuits with long lines, in order to ensure the reliability of protecting such circuits from remote short-circuit currents, it is necessary to implement the following technical solutions:

1. Increase the cross section of the wires of the long line in order to increase the short-circuit current at the end of this line.

2. Increase the response time of the protection device (selective switch) to the maximum possible value (0.4 ÷ 0.5) s so that the value of the starting current or the self-starting current during this time can be sufficiently reduced. In this way, a certain “detuning” of protection against starting currents and self-starting currents of electric motors is performed.

The indicated technical solutions used in the protection systems of branched electric circuits with long lines are not optimal from both an economic and a technical point of view.

Indeed, an increase in the cross-section of wires increases the cost of the line, and with an increase in the time delay during shutdown, the thermal stability of the line decreases, especially when a short circuit occurs at the beginning of the line, which reduces the fire safety index of the protected electrical circuits.

The basis of the invention is the task of constructing such a system for protecting branched three-phase electric circuits against remote short circuit currents, in which by analyzing the instantaneous current values in all phases of the circuit, namely the sum of the squares of the above instantaneous current values in three poles, it is fast (within one period of current change) recognition of the occurrence of inrush currents or self-starting currents of electric motors in the circuit, resulting in increased reliability of protection of long circuits from shock ennyh RS and it is possible to start the normal electric motors, and also reduces fire hazards and the cost of the protected circuits.

This problem is solved in a system for protecting branched three-phase electric circuits from remote short-circuit currents, comprising a protection device with current sensors and a semiconductor release, which has a device for comparing the current flowing through the device with the value of the current setpoint for short-circuit current I _sd and _configured to of the lower level setpoints within I _sd (1,5 ÷ 3) from the working machine current I _r, connected to the outlet terminals of the protection unit length of the main electric line to co Ora throughout its length connected feeder lines with different types of loads including a motor, wherein the magnitude of the short circuit at the end of the trunk line I _ks is equal to or less than the starting motor current I _PD connected to the mains current at its beginning or in the middle, but greater than or equal to the setting current I _sd - (I _pd ≥I _kz ≥I _sd ), due to the fact that the trip unit of the protection device additionally contains a node for monitoring the sum of the squares of currents of all three phases {Si ² (t)} and comparing the ratio of maximum the values of the indicated sum of squares of currents {S _max i ² (t)} to its minimum value {S _min i ² (t)} in the first period of occurrence of the current of a higher setpoint I _sd , as well as a logical node, which, provided that the indicated relation, expressed by the coefficient K _s = {S _max i ² (t)} / {S _min i ² (t)}, equal to or greater than 1.4 (K _s ≥1.4), automatically increases the value of the set current I _sd to the value I _sd1 , equal to (1.1 ÷ 1.5) of the inrush current I _{pd of the} electric motor - I _sd ↑ {I _sd1 = (1.1 ÷ 1.5) I _pd }.

It is due to the fact that the trip unit of the protection device additionally contains a node for monitoring the sum of squares of currents of all three phases {Si ² (t)} and comparing the ratio of the maximum value of the indicated sum of squares of currents {S _max i ² (t)} to its minimum value {S _min i ² (t)} in the first period of occurrence of a current of a higher setpoint I _sd , as well as a logical node, which provided that the indicated ratio, expressed by the coefficient K _s = {S _max i ² (t)} / {S _min i ² (t)}, equal to or greater than 1.4 (K _s ≥1.4), automatically increases the setting current I _sd to the value I _sd1 equal to (1.1 ÷ 1, 5) the inrush current value I _{PD of the} electric motor - I _sd ↑ {I _sd1 = (1.1 ÷ 1.5) I _PD }, it ensures both the reliability of protecting the long line from remote faults and the possibility of the normal starting of the electric motors.

In the event that both inrush currents and self-starting currents can occur in the protected circuit, the trip unit of the protection device additionally contains a memory unit that controls the presence or absence in the previous 20–40 ms of the instant of occurrence of the current in the circuit equal to the set value I _{sd of the} current “History” I _p , as well as a logical node, which if the value of the coefficient K _s = {S _max i ² (t)} / {S _min i ² (t)} is equal to or greater than 1.4 (K _s ≥ 1,4), and the value of the current "history" I _p is zero, automatically increases the value of the current setting I _sd to the value I _sd2 , equal to (1.1 ÷ 1.5) the self-starting current I _{sz of} all motors connected to the circuit - I _sd ↑ {I _sd2 = (1.5 ÷ 1.5) I _sz }.

Indeed, as the analysis of the features of the dependence of the sum of squares of the values of the currents of three phases in the function of time - (S _max i ² (t)} (the main results of such an analysis will be given below) shows, it is the value of the ratio of the maximum and minimum values of the indicated dependence S _max i ² ( t) allows you to recognize cases of starting the electric motor or simultaneous self-starting of several electric motors from the occurrence of a remote short circuit and to select the current setting necessary for each of these cases (I _sd1 or I _sd2 ).

The physical essence of recognizing the occurrence of inrush currents and remote short-circuit currents is that the value of the inductance of the circuit, and therefore the value of cosφ for the above cases, are significantly different from each other. So, in the case of starting the electric motors, the value of cosφ of the circuit is in the range 0.2–0.3, and in the case of short circuit on cable and overhead lines, the values of cosφ are usually in the range (0.65–0.8), where cosφ (0.65) refers to overhead lines with steel wires.

Thus, by analyzing the value of cosφ of the circuit (or the angle of shear between the current and voltage in each phase), it is indeed possible to recognize cases of starting the motors and remote short circuit on the line. However, the implementation of such a technical solution in relation to electronic trip units of circuit breakers is difficult, and in some cases simply impossible for the following reasons:

- Firstly, these are reasons of a constructive and economic nature. Indeed, in addition to the signals from current sensors in each phase, with the given technical solution, all three phase voltages should be additionally fed to the release of the release, and the corresponding measurement and processing channels for such additional input parameters should be supplied to the releases themselves. All this leads to a significant increase in the dimensions of the releases, their cost, which is most often unacceptable for the most massive small-sized circuit breakers in plastic cases.

- Secondly, these are technical and functional reasons. It is known that due to the presence of a transient process at the first moment after the occurrence of a starting or emergency current, for several periods of current change there is an aperiodic component of the current of the electric circuit. The presence of such an aperiodic component of the current leads to a significant error in determining the value of cosφ, if such a determination is carried out quickly enough, for example, in the first period of the current change. Therefore, the considered technical solution can be used only if the protection speed is not required and therefore the value of cosφ can be determined after attenuation of the aperiodic component of the current, namely, 2-3 periods after the occurrence of an inrush current in the circuit.

In view of the above considerations, the implementation of a protection system against remote short-circuit by directly measuring the value of the angle of shift φ between voltage and current or the value of cosφ has drawbacks that do not allow the use of such a technical solution for protection systems in which small-sized switches in plastic cases are used as protection devices . Moreover, if the electronic releases of such switches have integral settings for the implementation of high-speed "integral" selective protection [2]. In the latter case, the control signal for the trip operation must be generated during the first current period (up to 20 ms).

Thus, in order to implement a protection system against remote faults based on small-sized circuit breakers, which also provide high-speed selective protection of circuits, the value of the circuit inductance should be determined based on the analysis of only currents flowing through the device (without voltage), and this analysis should be carried out quickly enough - during the first half-cycle of a current change (short-circuit current or inrush current).

Such a quick determination of the cosφ of the protected circuit using only current sensors can be made based on an analysis of the transient parameters of the currents in phases.

As you know, the current instantaneous value of the current (recorded by the current sensor) in the considered phase, taking into account the aperiodic component of the short-circuit current, is determined by the following expression:

where I _m = √2I _eff is the amplitude value of the symmetric component; I _eff is the effective value of the symmetric component of the current, φ is the phase angle by which the periodic component of the current lags the phase EMF; φ = arctan (ωL / r); ψ is the angle of the emf in phase, corresponding to the beginning of the process (short circuit or start); T is the electromagnetic time constant of the circuit T = L / r = tgφ / ω.

From expression (1), it is impossible to determine cosφ from the instantaneous values of current in one phase i, since there are two unknown quantities on the right side of the expression — the desired value of the angle φ and a random value — the moment of inrush current occurrence, which is characterized by the angle ψ.

However, if we analyze the dependence of the change in the sum of squares of the instantaneous values of the currents of all three phases in time S {i ² (t)}, then such an analysis, as will be shown below, allows us to determine the value of cosφ. It should be noted that the dependence S {i ² (t)} can conditionally be called the "power" characteristic of the circuit, because it characterizes the electrodynamic forces that the protection apparatus has to overcome when current flows through it. The indicated forces are proportional to the square of the instantaneous value of current i ² in each phase; therefore, the dependence of the sum of squares of currents in time for all phases of the circuit S {i ² (t)} is the power characteristic of the circuit.

The "power" characteristic of the circuit S {i ² (t)} in general form can be represented as:

where i _l (t), i _c (t) and i _p (t) are the known functions of the current in time in the left, middle and right phases of the circuit. The expression for S {i ² (t)} can be written as follows:

Given that I _eff = I _m / √2, the expression for S {i ² (t)} takes the form:

As follows from expression (4), the instantaneous value of the sum of the squares of the currents of all three phases no longer depends on a random variable - the initial phase of the inrush current or short-circuit current. The magnitude of the "power" characteristics of the circuit at a given current value I _eff depends only on the electromagnetic constant circuit T (or on the value of cosφ).

The considered feature of the "power" characteristic of the circuit S {i ² (t)} is the basis for constructing a system for protecting branched electrical circuits from remote short-circuit currents with detuning from starting currents and self-starting currents of powerful electric motors by analyzing the nature of the "power" circuit characteristic.

The invention is presented in figures 1-8.

Figure 1 shows a schematic diagram of a system for protecting a branched circuit from currents of remote short circuits in the presence of powerful electric motors in it.

Figure 2 shows the dependence of the "power" characteristics of the circuit as a function of time S {i ² (t)} for different values of cosφ.

Figure 3 shows the dependence of the coefficient Ks = S _max {i ² (t)} / S _min {i ² (t)} as a function of cosφ.

Figure 4 shows the circuit protection system and the nature of the change in the "power" characteristics of the circuit S {i ² (t)} when a fault occurs at the end of the trunk line.

Figure 5 shows the protection system and the nature of the change in the "power" characteristics of the circuit S {i ² (t)} when starting a powerful engine at the beginning of the trunk line.

Figure 6 shows the algorithm for the implementation of the switch-off function from the starting current by the microprocessor release by automatically increasing the setpoint I _sd to the value I _sd1 based on the analysis of the coefficient value Ks = S _max {i ² (t)} / S _min {i ² ( t)}.

Figure 7 shows the protection system and the nature of the change in the "power" characteristics of the circuit S {i ² (t)} during self-start of several electric motors after switching the circuit to backup power.

Figure 8 shows the algorithm for the implementation of the switch-off function from the self-starting currents by the microprocessor release of the switch from self-starting currents by automatically increasing the setpoint I _sd to the value I _sd2 based on the analysis of the coefficient value Ks = S _max {i ² (t)} / S _min {i ² ( t)} and taking into account the background current I _p .

Before considering the operation of the claimed protection system, we point out the features of the "power" function of the circuit, which are the basis for the principle of "detuning" from the starting currents when implementing protection against remote faults.

The inventive protection system (Fig. 1) includes a main current source 1 (power transformer), a disconnector 2, with which power is supplied from a transformer 1 to a distribution busbar 3, the exhaust busbars 4 and 5. A main switch is connected to the busbar 5 6 (BA1) with a microprocessor release 7. A long overhead (or cable) line 8 is connected to the outlet clamps of the switch 6, to which, along the entire length of it, up to the end of the long line 9, outlet feeder lines 10, 11 and 14 are connected The feeder line 11 includes a feeder switch 12 (BA2) and an electric motor connected to its outlet terminals 13. The feeder line 14 includes a feeder switch 15 (VAZ) and an electric motor 16 connected to its outlet terminals.

In addition to the main source 1, the protection system has a backup current source 17 and a disconnector 18 for connecting a backup source to the distribution bus 3.

Figure 2 shows the dependence of the "power" function of the circuit S {i ² (t)} for different values of cosφ. It can be seen from the above dependences that the maximum value of the “power” function S _max {i ² (t)) and its minimum value S _min {i ² (t) are quite significantly different for different values of the cosφ of the circuit. This means that by their values, and best of all by their ratio, it is possible to determine the cosφ value of the circuit quite accurately and quickly.

Figure 3 shows the dependence of the coefficient Ks, which determines the ratio of the maximum value of the force function to its minimum value Ks = S _max {i ² (t)} / S _min {i ² (t)}, on the value of cosφ. If we assume that when starting the electric motor, the value cosφ = 0.7, and with a remote short circuit on the line, cosφ = 0.3, then the value of Ks for a circuit with cosφ = 0.5 can be taken as a criterion for recognizing the starting of a motor or a remote short circuit ( if Ks≥1,4, then the motor starts, if Ks≤1,4, then there is a remote short circuit).

Taking into account the selected recognition criterion for a remote short-circuit or inrush current, we consider the operation of the protection system under different modes of its operation.

The protection system operates as follows.

Suppose that in the protection system powered by the main current source 1 (Fig. 4), the circuit breaker 6 was turned on and voltage from the current source was applied to line 8. Moreover, all feeder lines 10 and 11 to line 8 remain unconnected (their feeder switches are turned off).

The position of the switching equipment corresponding to the above state of the protection system is shown on the left side of FIG. Suppose that at the moment of turning on the switch 6 (or some time after its inclusion) a short circuit occurred at the end of a long line 8 (point 9). The magnitude of the remote circuit current (I _sc) equal to the current I _sd at the rate of the release 7 of the main switch 6. Since for remote faults on the line cosφ value equal to 0.7, the behavior of the "power" chains characteristic S {i ² ( t)} will have the character shown in Fig. 4, and the value of the coefficient Ks characterizing the ratio of the maximum value of the “power” function S _max {i ² (t)} to the minimum value S _min {i ² (t) will be 1 , 2. Since the value of the coefficient Ks turns out to be less than 1.4, there is no automatic increase in the set current value from the value I _sd to I _sd1 , which means that under the action of the release 7, switch 6 will disconnect the circuit. The switching position of the devices of the protection system after the occurrence of a remote short circuit (and its shutdown) is shown in the right part of figure 4.

Suppose that in the protection system (Fig. 5), the switch 6 is turned on and voltage is supplied to line 8 from the current source. Moreover, all feeder lines 10 and 11 remain unconnected to line 8, their feeder switches are in the “off” position.

The position of the switching equipment corresponding to the above state of the protection system is shown on the left side of FIG. Let the feeder switch 12 turn on now and start the process of starting the electric motor 13. At that, the value of the starting current I _PD at the initial moment is greater than the setting current I _{sd of the} release 7 of the switch 6.

Since when starting the electric motor the value of cosφ of the circuit is 0.3, the nature of the change in the “power” characteristic of the circuit S {i ² (t)} will have the character shown in Fig. 5, and the value of the coefficient Ks characterizing the ratio of the maximum value of “power »Of the function S _max i ² (t) to the minimum value of S _min i ² (t) will be equal to 2.7. Since the value of the coefficient Ks turns out to be greater than 1.4, the setpoint current automatically increases from the value of I _sd to the value of I _sd1 . Due to the fact that the value of the current setting I _{sd1 is} greater than the value of the starting current I _PD , the switch 6 will not turn off, the start of the electric motor 13 will be successful and uninterrupted power supply of all feeders will be ensured.

The switching position of the main and feeder circuit breakers of the protection system in the process of starting the motor and after starting it is shown in the right part of figure 5.

In the above cases, the protection system when a short circuit occurs at the end of the line (point 9) or when the electric motor 13 is connected at the beginning of the line, all feeder lines 10 remain unconnected to line 8. This means that no history current I _p passed through switch 6 , i.e. current due to the loads of the remaining feeders 10.

When the history current I _p flows through the switch 6, the values of the coefficient Ks will differ from those that were indicated above for the case without taking into account the history current (Ks = 1.2 and 2.7). In this case, there may be cases where the difference in the value of Ks when starting the electric motor and remote short circuit will not be so significant, which means that the selection of these cases will be less reliable.

For a proper analysis and subsequent “detuning” of inrush currents (or self-starting currents), it is necessary to isolate from the chaotic picture of the total total current in the circuit only the above currents caused by the starting of the motors.

Therefore, to ensure the reliability of the protection system, the value of the coefficient Ks must be determined only for cases of three-phase disturbing currents and taking into account the magnitude of the background current I _p . For this, when determining the value of the coefficient Ks under the values of currents in phases i (t), one should not accept the absolute values of currents in phases, but their excess Δi (t) over currents of history i _p (t). With this in mind, the value of the square of the excess current in the phase Δi ² (t) when determining the coefficient Ks is determined as the difference between the current values of the current recorded in the second - i ₂ ² (t) and in the first - i ₁ ² (t) periods of current change - Δi ² (t) = i ₂ ² (t) -i ₁ ² (t). Moreover, the current value in the first period i ₁ ² (t) in this case is the current of the history i _p (t). When analyzing the values of Ks to exclude cases of the occurrence of two-phase or single-phase overcurrent currents, the three-phase and symmetry of the circuit are checked (powerful electric motors are always three-phase). For such a check, for example, the following restrictive condition can be established: the effective values of the overcurrent current in each of the three phases for the first half-time ΔIf must be at least 0.8 of the average value of the sum of the indicated currents in all three poles (ΔI _f ≥0.8∑ΔI _f ).

Other known methods for identifying a three-phase current in a circuit can be used.

The implementation of the indicated algorithm for determining the effective current value and instantaneous values of the excess current i ² (t) in comparison with the background current i _p (t), as well as with the identification of a three-phase current in the circuit, is not difficult when microprocessor based components are used in releases.

In view of the foregoing, Fig. 6 shows the corresponding algorithm for the implementation by the microprocessor release of the circuit breaker of the function of protecting the circuits from remote faults by "detuning" from the starting currents of the electric motors, based on the analysis of the values of the coefficient Ks.

The microprocessor trip operation algorithm provides for the following operations and their sequence:

1. Moving, with the crowding out of previous values, memorizing the currents of "history" (i _p ; i _pc and i _pp ) for the previous period (item 1).

2. Sliding, with the displacement of the previous values, the determination of the effective values of the phase current (4) in each of the poles of the switch (pos.2).

3. Determination of excess current Δi and squares S (Δi ² ) in the three poles of the switch (item 3).

4. Determination of the current value of the coefficient Ks (item 4).

5. Checking the boundary condition for the presence of a three-phase current in the circuit — determining the effective value of the excess current ΔI _f in each phase and comparing them with the average current value of all three phases (item 5).

6. Comparison of the current value of Ks with its boundary value (Ks = 1.4) and under the condition Ks> 1.4, the generation of a control signal to the summing unit (item 6).

7. The operation of summing the signal from nodes 5 and 6 and generating a control signal according to the logic circuit “And” and “And” to increase the current setting (pos. 7)

8. Formation of the increased current setting I _sd1 (pos. 8);

9. Comparison of the current value in the circuit I _f with the value of the current setpoint I _sd1 and, if it exceeds the setpoint value, generating a control signal to the control signal generating unit to the release actuator (pos. 9).

10. Development (if necessary) of a control signal for actuator actuation.

The occurrence of self-starting currents is possible when the circuit power is transferred from the main source 1 (Fig. 1) to the backup 17 and the disconnector 18 is turned on. Since the main busbar is switched on again with voltage with a certain time delay, the self-starting mode of electric motors D ₁ and D ₂ occurs.

Given the specified initial conditions, the state of the protection system after turning on the backup power will be as shown in Fig. 7 on the left.

Since during self-starting of electric motors the value of cosφ of the circuit is 0.3, the nature of the change in the “power” characteristics of the circuit S {i ² (t)} will have the character shown in Fig. 7, and the value of the coefficient Ks characterizing the ratio of the maximum value of “power »Characteristics S _max i ² (t) to the minimum value of S _min i ² (t), will be equal to 2.7. Since the value of the coefficient Ks turns out to be more than 1.4, and the background current I _p during self-start is zero, an automatic increase in the set current from I _sd to I _{sd2 occurs} . Due to the fact that the value of the current setting I _{sd2 is} greater than the value of the self-starting current I _sz , the switch 6 will not turn off, the motor 13 will start up successfully and uninterrupted power supply to all feeders will be ensured.

The switching position of the main B ₁ and feeder switches B ₂ and B ₃ of the protection system in the process of starting the electric motor and after it is started is shown in the right part of Fig. 7.

The algorithm for the implementation by the microprocessor release of the circuit breaker of the function of protecting the circuits from remote faults by means of "detuning" from the self-starting currents of electric motors based on the analysis of Ks values is shown in Fig. 8:

1. Moving, with the crowding out of previous values, the determination of instantaneous current values in phases (i _l ; i _s and i _p ) ( _{item 1} ).

2. Sliding, with the displacement of the previous values, the determination of the effective values of the phase current (I _f ) in each of the poles of the switch (pos.2).

3. Determination of the sum of squares of current S (i ² ) in the three poles of the switch (item 3).

4. Determination of the current value of the coefficient Ks (item 4).

5. Checking the boundary conditions: the presence in the current circuit of the history of I _p (5) and the development of a control signal at I _p = 0.

6. Comparison of the current value of Ks with its boundary value (1.4) and under the condition K _s ≥1.4, the generation of a control signal to the summing unit (item 6);

7. The operation of summing the signal from nodes 5 and 6 and generating a control signal according to the logic circuit “AND” and “AND” to increase the current setting (pos. 7).

8. Formation of the increased current setting I _sd2 , (pos. 8).

9. Comparison of the current value in the circuit I _f with the value of the current setting I _sd2 and, if it exceeds the set value, generating a control signal to the control signal generating unit to the release actuator (pos. 9).

10. Development (if necessary) of a control signal for actuator actuation.

Thus, the analysis of the instantaneous values of the currents flowing through the circuit breaker, namely the sum of the squares of the currents of all three phases S {i ² (t)}, allows you to protect electrical circuits from remote short-circuit, while maintaining the ability to start the motors normally even in those cases when their starting currents I _PD or self-starting currents I _{sz are} greater than the current of the remote fault.

In comparison with the closest analogue, the long-line protection system, in which, for protection against remote short-circuiting, they are limited only to choosing the minimum setting for the trip of the circuit breaker and thereby reduce the likelihood of uninterrupted power supply in the event of the start of powerful electric motors, the claimed system provides both reliable protection against remote short-circuit and uninterrupted power supply in the event of the launch of powerful electric motors.

Information sources

1. Budzko I.A. and others. "Electricity supply in agriculture." - M .: Agropromizdat, 1990, p.190-196.

2. RF patent №2259623, Н02Н 7/00, Н01Н 73/00, application 04/27/2004, publ. 08/27/2005 (bull. No. 24).

Claims (1)

A system for protecting branched three-phase electrical circuits against remote short-circuit currents, comprising a protection device with current sensors and a semiconductor release having a device for comparing the current flowing through the device with the value of the short-circuit current setting I _sd and configured to set the lower level of settings I _sd within 1.5-3 working device current I _r, connected to the outlet terminals of the protection apparatus of the electrical length of the main line, to which over its entire length is connected us feeder lines with different types of loads, including electric motors, the value of short-circuit current at the end of the main line I _sc is equal to or less than the starting current of the motor I _PD connected to the main line at the beginning or in the middle, but most or equal to the setpoint current I _sd - (I _pd ≥I _kOe ≥I _sd), characterized in that the trip unit protection apparatus further comprises a sum of squares of the control part of all three phase currents {Si ² (t)} and comparing the ratio of the maximum value of said sum to adratov currents {S _max i ² (t)} to its minimum value {S _min i ² (t)} in the first period of occurrence of a current greater setpoint I _sd, and logic that, provided that said ratio, expressed as the coefficient K _s = {S _max i ² (t)} / {S _min i ² (t)}, equal to or greater than 1.4 (K _s ≥1.4), automatically increases the value of the set current I _sd to the value L _sd1 equal to 1.1 ÷ 1.5 inrush current values I of the motor _{nq - I sd ↑ {I sd1 =} ( 1, l ÷ 1,5) I _nq}

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