SU1042122A1 - Alternating-current-mainns discriminating-protection device with current-limiting controllers - Google Patents

Abstract

DEVICE FOR SELECTIVE. AC NETWORK PROTECTION WITH CURRENT; LIMITING AUTOMATIC SYSTEMS / Contains current derivative sensors in each connection of the protected network, sequentially connected to the converter, to the input of which is connected to one element of the comparison, to another input The organ of setting the response parameter is connected, and the output of the comparison element through the threshold organ is connected to disconnecting circuits of current-limiting automata, characterized in that, in order to improve speed, The rectifiers, the second adder, the subtraction elements, the gain control element through the channel of the through current derivative are entered, the output of the first adder through the rectifier is connected to the first input of the subtractor, the output of which is connected to the reference element, the outputs of the converters are rectified by rectifiers - jiy connections are connected to the inputs of the second adder, the output of which is connected to the first input of the second subtraction element, to the second input of which the output of the first rectifier is connected l and vyhbd subtracting the second element through the element controlling transmission channel coefficient produ water through current is connected to the second input of the first member nor the subtraction.

Description

The invention relates to relay protection and can be used in AC networks of autonomous power systems. There are known devices for selective protection of sections of AC and DC networks, which are based on the differential principle. Their main feature is absolute selectivity - it follows from the principle of continuity of the energy current. A disadvantage of the known protection devices that do not allow to use. them in power systems With current-limiting automata, is their low speed. According to the principle of operation, the known differential protection devices can be divided into the following groups of devices that react to the current value of the currents in the connections of the protected area, devices that react to the instantaneous value of these currents ; devices that respond to the instantaneous value of the first derivative of these currents over time. The first group of devices has its own response time in the range, not 0.02OD, the second group of devices; in the range of 0.002-0.02 CJB depending on the type of reacting body and on the ratio of the short circuit current. Regarding the operation setpoint) The closest to the invention according to the technical essence is the differential protection device, which reacts to the instantaneous value of the first current derivative within the protected area. . In this device, the derived current sensors installed in the connections of the protected area through the input converters connected to an adder, the output of which is connected to one of the inputs of the comparison element. To another input of which the trigger parameter setting body is connected and the output of the comparison element is connected through the threshold organ. with current-limiting automatic disconnection circuits. The intrinsic response time of this protection, when operating by direct assignment in a DC network, is several tens of microseconds and is due mainly to transients in the input protection parameters. In principle, such protection is also operable in the AC 2 network. However, its performance is much lower due to the fact that it is already determined by transients in the primary network, which are characterized by much longer time constants and mean; at a constant current., due to a larger number of factors influencing their course. Such speed is completely unsatisfactory for networks with current-limiting automatic switches. The purpose of the invention is to increase speed. The goal is achieved by the fact that the device for selective protection of the AC network with current-limiting automata, containing current-derivative sensors in each connection of the protected network, connected in series with converters connected to the adder, is connected to the output the input of the comparison element, to another input of which the parameter setting body / trigger is connected, and the output of the comparison element is connected via a threshold element to the open-circuit current-limiting automatons, additional rectifiers, a second summatr, subtraction elements, an element for controlling the transmission coefficient through an output through current channel are added, while the output of the first adder is connected via a rectifier to the first input of the subtraction element, the output of which is connected to the comparison element, outputs converters are rectified by the number of connections connected to the inputs of the second adder, the output of which is connected to the first input of the second subtraction element, to the second input of which the output of the first is connected rectifier, and the output of the second subtraction element through the element: adjusting the transmission coefficient through the channel of the through current derivative. connected to the second input of the first | subtraction element. . : In FIG. 1, this functional circuit diagram of a device for selective protection of an AC network with current-limiting automata; figure 2 is a graph of the performance of protection depending on the multiplicity of the input signal. The device (figure 1) contains Datch: IK 1-3. derivative of current in each connection of the network, converters 4-6, sukalatoEad 7 and 8, rectifiers 9 and 10, elements of subtraction 11 and 12, organ for setting the response parameter 13, element of comparison 14, threshold element 15, element for controlling transmission coefficient over the channel the through current derivative 16. the inputs of the rectifier unit 10 connect 6 parallel with the inputs of the adder 7 to the input converters 4-6, and its outputs - to the sumimator 9 When the protection device is turned on in the tia output of the adder 8, an electrical signal Sg proportional toThe amplitude of the sum of the modules of the first derivative currents in all connections of the protected area. The geometric interpretation of the expression is the project of the polygon composed by the vectors of the total current derivatives of the protected network section on an arbitrary time axis. In the general case, if the current presence of an internal circuit and a through current on the protected section, the polygon is closed by the vector of the derivative of the internal short circuit current. To determine the projection of the through TOKaScKgl J .- / on the same time axis, one needs to subtract the projection of the derivative of the internal short circuit current from the projection of the polygon of the derivatives of the total current

di.

WITH){

eat. KZ

(2)

dt

l

Gg1

A signal proportional to the first derivative of the through current is generated when the protection device turns on the output of the subtracting element 12. For this, the signal from the output

adder 8 is fed to the first input of subtraction element 12, and to its second input is fed a rectified rectifier. 9 a signal from the output of adder 7i SCKB signal proportional to the first derivative of through current

through the protected area, is used to reduce the signal level of the netshlans 5 entrance of the threshold organ by subtracting the first signal "la - of the second.

The signal unbalance occurs at the output of the adder 7 (and, respectively

rectifier 9) when a large multiplicity of current flows through the protected section of the through current. Subtraction is the element of subtraction 11; To the direct input of which the output of the rectifier 9 is connected, and to the inverting output of the element regulating the transmission coefficient through the channel of the through current 16, the input of which is connected to the output of the subtraction element 12. When the protection device is activated, an electrical signal is generated at the output of the subtraction element 11 ".

-ftS (.W

v dt

-

 CK6 dt

s1

where / 5 is the transmission coefficient as the through current.

The second term HZ expression allows in the considered mode to reduce the value of the third term, provided that the expression (the whole is negative or equal to zero, and false protection does not occur. Its level is determined by the factor / s, the minimum acceptable value by the condition of the absence of a false alarm, protection can be determined: from (3) with (4),,

 -.

I 24K -k K (5y :)

; . / max NSv dr-t / cf / - ..

Pwin: A Pi (

Hard currency

/ tmh

In the arc-close mode on the Protected area with a large residual voltage simultaneously with the internal short-circuit current. This section can also flow through - the suction current to the load, the load exceeding the internal closure current: Can. In this case, in the expression (3) there are all three terms, but the protection only works if the first term exceeds the absolute. the sum of the other two. This condition is satisfied if the coefficient determined for the mode in question from (3) does not exceed some maximum value

. (6)

R.

moix

SCR The optimal value of the coefficient of nodes is determined by the modes of operation of the protected network section. In the mode of limiting through currents through the protected area, the first term is an expression (3 I is equal to zero only if there are no errors in the sensors and input converters. For real devices, there are always errors with respect to the nominal transmission coefficient, denoted by ± dK, the error of the operation of forming a controlled parameter, i.e., the appearance of an unbalance signal at the output of the block 11 when a large through-current flows through the protected area. through pi (r + 1) -l1 sensors, having maximum error values of different signs, the unbalance signal is equal .-, (.- (V - axj-) Thus, expressions (5) and (b J determine the range of permissible under normal / Noah conditions, the protection of the transmission coefficient values of the current-carrying channel (the threshold organ of the protection device, consisting of blocks 13–15, works similarly to the corresponding prototype body. Therefore, the full operating mode of the selective protection device on current-limiting automata can be represented as П J . j / rr-dfhScKB th; (M | .g - command to turn off; signal level on. shutdown; current number; the number of connections of the protected area / conversion factor of the G-th sensor, the total current in the r-TOY branch of the protected area; conversion factor of the input transform bodies; the preset value is the CP protection response parameter (response threshold). The sensors of the current derivative produce a signal that characterizes the rate of change of the currents that flow through the connections of the installed site, i.e. signal of their first derivatives with respect to time: J (cos u ,,) (- f-, dt Krm at Т „/ where r is the current number (of the protected area, sensor of the input converter) ;. the initial value of the aperiodic component of the current The short time of the primary circuit; the time constant of the primary network is determined at the point of the short circuit. The intrinsic response time of the protection is determined by substituting in (8) the values of the derivatives and resolving the resulting equation with respect to time. The solution obtained for these constant time values and angle difference otr q (worst initial conditions), presented graphically in Fig. 2. The abscissance axis of the graph shows the relative values of the derivative, the internal short circuit current on a logarithmic scale (the base value is taken as the trigger parameter} on the 4 axis of ordinate is indicated by the time. Choice is optimal the value of the transmission coefficient over the channel of the derivative of the through current under the conditions; .. ((7) makes it possible to ensure that the triggered value of the response parameter is no more than 0.5. When the multiplicity of the input signal is relative to the nominal value of the order of 10 (the same as for the prototype), the intrinsic response time of the protection -fccj is obtained in accordance with the curve (Fig.2G equal to 0.125 ms, i.e. decreases by more than than the order. Such speed allows to ensure the implementation of selentive protection of sections of the AC network on the basis of current-limiting circuit breakers. A specific circuit implementation of the device of selective protection on fine-limiting automata as well as and its structure is determined by the purpose of the invention and is reduced to ensuring a minimum delay when electric signals pass through the circuits of the device. For this purpose, air current-current transformers or transfactory carbon-iron sensors are used as current-derived sensors. on the basis of conventional resistive dividers matched with the characteristic impedance of the communication lines; Glidators and rectifiers of the logical unit of the protection device shown in FIG. The most general form is made according to known circuits. On the basis of operational amplifiers (in the latest version of devices, K140UD8AK type amplifiers are used. Rectifiers are performed on operational amplifiers c. the purpose of reducing the forward voltage drop across these elements, i.e. reduction of the additive measurement error (especially at low extremes of currents in the connections of the protected area). The threshold element of the protection device, consisting of blocks 13-15, is made on the basis of a single comparator. In power engineering and in relay protection, the task of speeding up, eliminating accidents, the operation of power system operation modes and their consequences has always been and remains highly relevant. Accelerating the short-circuit trip in the system reduces the degree of damage to the main equipment, reduces the danger of fire, reduces undersupply of energy to consumers, improves its quality, increases the stability of parallel operation in the system.

Elimination of emergency modes with the help of switching devices that provide the limitation of the shock current, a short ferment, offers even more tangible advantages, since in addition to what IT provides

i the minimum possible time off is almost eliminating the thermal effects of short circuit current on equipment, and its dynamic effect is significantly reduced, causing the most serious damage. 15 On the basis of the aforementioned devices, non-selective and limited - and selective protection systems for the simplest sections of the network are performed. For example, there are circuit solutions that provide for the use of such devices as bus connecting switches, which, when

emergency mode, the power system is divided into separate sections, thereby reducing the short-circuit point and making it easier to turn off.

Some circuit solutions provide protection with current-limiting automata of the radial part; distribution network, the shutdown of which in the event of a closure occurs in the same way non-selectively, and then the logical device produces cascading auto-reclose of intact sections. All solutions similar to those described are half-measures, associated with significant post-accident disruption of the operating mode of the power grid. ,

The proposed device for selective protection on current-limiting machines x) ensures the creation of protection that has a specific absolute selectivity: and is suitable for any parts of the electrical network. .

Claims (1)

DEVICE FOR SELECTIVE. „PROTECT AC VOLTAGE WITH ΤΟΚΟ-. BY LIMITING AUTOMATICS, containing sensors of the derivative of the current in each connection of the protected network, connected in series with converters connected to the adder, the output of the latter is functionally connected to one input of the comparison element, the input of the setting parameter is connected to the other input, and the output of the comparison element through a threshold organ it is connected to disconnecting circuits of current-limiting automats, characterized in that, in order to improve performance, rectifiers are additionally introduced, the second the adder, subtraction elements, an element for regulating the transmission coefficient along the channel of the derivative of the through current, while the output of the first adder through the rectifier is connected to the first input of the subtraction element, the output of which is connected to the comparison element, the outputs of the converters through rectifiers are connected to the inputs of the second adder by the number of connections, the output which is connected to the first input of the second element of I-subtraction, the second input of which is connected to the output of the first rectifiers of the phone, and the output of the second element of subtraction through e ement regulation channel produ water through current gain connected to a second input of the first subtraction of element. -Ch-nz ЧЗ— * 0 in Sdhik. ’Gshgpt .1 This performance is completely unsatisfactory for networks with current-limiting circuit breakers. The purpose of the invention is improving performance. This goal is achieved by the fact that in the device for selective protection of the current, these alternating current with current-limiting machines, containing the derivatives of the current in each connection of the protected network, connected in series with the converters connected to the adder, the output of the latter is functionally connected to one input of the comparison element ., to another input of which the sub-keys are the parameter setting body. · triggering, and the output of the comparison element through the threshold element is connected to disconnect circuits of current-limiting ohms, additionally introduced rectifiers, a second adder, subtraction elements, an element for regulating the transmission coefficient along the channel of the derivative of the through current, while the output of the first adder through the rectifier is connected to the first input of ele-. subtraction, the output of which is connected to the comparison element, the outputs of the converters through rectifiers 30, by the number of connections, are connected to the inputs of the second adder, the output of which is • connected to the first input of the second subtraction element, the output of the first rectifier is connected to the second input of which the output of the second subtraction element is through the transmission coefficient control element over the through-current derivative channel. connected to the second input of the first subtraction element.