SU907666A1 - Device for differential protection of electric equipment - Google Patents

Description

one

The invention relates to relay protection and can be used to protect electrical installations, in particular busbars, transformer busbars, power transformers (autotransformers), reactors, generators, synchronous compensators and large electric motors of power plants and substations.

A device for a differential phase device is known; it has electrical current, comprising current sensors, a diode conversion unit for input quantities, a comparison unit, a starting and a phase circuit, a voltage limiter, two threshold elements 1 J

However, this device does not have an exact matching of the input signal values, does not have sufficient performance in the presence of significant load currents arising from the damage site, as well as in cases of the ultimate search for: current transformer information.

Closest to the present invention is a device for differential-phase busbar protection, comprising current sensors included in each arm of protection, a comparison circuit on resistors and zener diodes, a starting element, a phase element connected to a rectifier bridge, two logic elements, the output of the second is connected to the input of the first and the input of the prohibition block 2.

However, this device cannot be used to protect the transformer, since it does not reject the inrush current and does not provide for coordination of the current of the arms of the protection when using current transformers with different transformation ratios. external short-circuits may clear the locking signal of the logic device, which can lead to non-selective protection. With internal short-circuits with high leakage currents, protection may be blocked. In addition, the considered devices have limited functionality, as they can be used to protect individual objects. The purpose of the invention is to expand I functionality by ensuring the protection of various objects of the power system, increasing the efficiency of operation. The goal is achieved by the fact that in a protection device containing current sensors included in each protection arm, the outputs are connected to a multi-shoulder diode half-bridge, whose cathodes and anodes are combined and are its output, a two-shoulder comparison unit connected to it consisting of two resistors connected in series and connected to the output of the multi-shoulder diode half-bridge and two stabalitrons connected in series to each other, a phase element whose input is connected to the output of a rectifying bridge, the start organ, the logical block I, whose two inputs are connected to the starting and phase organs, and the output to the output organ, the shaper of the input logic signal connected to the multi-arm diode half-bridge, the output of which is connected to the time delay unit and to one of the inputs of the first logical element, the second logic element, the inputs of which are connected to the output of the primary logic element and the output of the time delay unit, and the output is connected to the prohibition inhibitor unit, the response resolution unit whose input is connected It is connected with the output of the first logic element, and the output is combined with the output of the operation inhibit unit and connected to the third input of the logic unit I, an isolation transformer, resistors and a zener diode, differential current amplifier, a threshold element, a braking unit, a sum mater, a dosing unit, a unit are introduced. control of dead current pause, control unit for the duration of the input signal, the OR element, control resistors connected in parallel to the third windings of current sensors, gfcchem, transducer of the differential pressure ka is connected between the common point of the second windings of the sensors and the middle point of the comparison circuit and its linear output is connected to the inputs of the starting organ, threshold element, braking unit, first (m input of the adder and the second input of the first logic element, the third output of which is connected to the input of the operation inhibit unit The second input of the adder is connected to the output of the braking unit, the output of the same adder is connected to the main input of the dispensing unit, the first control input of which is connected to the output of the threshold element, and the second from the output element OR, whose inputs are connected to the outputs of the control unit for the duration of the input signal and the current-free pause, respectively, the input of the control unit for the duration of the input signal and the first input of the control unit for the current-free pause combined and connected to the output differential1 of the differential current converter, the second input of the control unit for current-free pause is a voltage input, the output of the dosing unit is connected to the first control input of the phase organ, the second input of which is connected to the output is formed l input logic signal, the cathode of the first Zener diode of the comparison circuit is connected to the cathodes, and the anode of the second Zener diode of the comparison circuit is connected to the anodes of the multi-shoulder diode half-bridge, parallel to each Zener diode of the comparison circuit with the same ends is connected a series circuit consisting of a Zener diode and a resistor, and the output of the circuit comparison through an isolating transformer connected to the output of the rectifying bridge. FIG. 1 shows a block diagram of the device; Fig. 2 illustrates the dependence of the actuation current on the amount of the through current; Fig. 3-6 - oscillograms of currents and voltages on protection elements and various operating modes. The protection device contains (figure 1) block 1 current sensors, the same

the secondary ends of which are connected to the multi-shoulder diode half-bridge 2, the shaper 3 of the input logic signal is connected to the multi-shoulder diode half-bridge, the shaper outputs are connected to the time delay unit, to one of the inputs of the first logic element 5 and to the second input of the phase organ 6. The comparison circuit 7 is connected through an isolating transformer 8 and a rectifying bridge 9 with the main input of the phase element 6. Logic block k 10, three inputs of which are connected to the outputs of the phase starting body 11 and the connected you by block 12 permitting and prohibiting 13 activation. The differential current converter is connected to a differential protection circuit, the linear output of which is connected to the inputs of the triggering device 11, the first logic element 5. of the threshold element 15, the adder 16, the braking unit 17 with the operational amplifier 18, and the differentiation output is connected to the inputs of the input control unit 19 signal and block 20 control pause. The first logic element 5, the output of which is combined with the input of the response resolution unit 12 and one of the inputs of the second logic element 21. The output of the latter is connected to the input of the operation prevention unit 13 The output of the operation prevention unit 13 is combined with the third input of the first logic element 5. Output the time delay block C with the second input of the second logic element 21. The metering unit 22, the inputs of which are connected to the outputs of the threshold element 15, the adder 16, the OR circuit 23, the 3 rd input - to the first control input of the phase 6. The output of the braking unit 17 is connected to the second input of the adder 16. An OR circuit 23, two inputs of which are connected to the outputs of the control units for the duration of the input signal 18 and the control of the pause 20, and the second output is the voltage input.

The differential current converter 9 may include, for example, a transformer and a resistor converting the current into a voltage, and a transformer with a rectifying bridge and a voltage comparator.

The braking unit can be made in the form of an active P – C filter using an operational amplifier 1. The filter blocks the first as well as the third and highest harmonics of the differential current.

The dosing unit 22 is made, for example, according to the scheme of transistor switches, the bases of which are control inputs, and the collectors are output.

The input signal duration control unit 19 is implemented, for example, using a standby multivibrator and an AND circuit, the output of which is the output of the block. The input of the multivibrator is connected to one of the inputs of the AND circuit and is the input of the block. The second input of the circuit And is connected to the output of the waiting multivibrator.

The device works as follows.

Currents from current transformers of shoulders of protection come to the primary windings of current sensors. The coarse matching of the input currents is carried out internally in the number of turns of the primary windings of the current sensors. Such matching is carried out by adjusting variable resistors connected in parallel to the third windings of the current sensors.

FIG. Figure 2 shows the dependence of the response current of the phase organ on the value of the through current.  At low currents of internal damage, the zener diodes are locked and the EMF of the secondary winding has a sinusoidal character.  There is a di ({x effective mode of operation, when the operation current does not depend on the size of the through current.  When the current exceeds the value, the zener diodes open and practically shunt the output 7, the protection switches to the phase mode of operation.  Therefore, the protection in question uses a combination of differential phase and differential principles and is not a pure phase differential.  Introducing additional elements into the comparison circuit allows one to obtain a characteristic region in which the protection operates as differential with braking.  This allows one to obtain sufficient sensitivity to internal short circuits, accompanied by outgoing load currents, while maintaining a sufficient degree of protection against unbalance currents caused by currents at which the protection does not go into phase mode of operation.  If during internal damage, when two arms are flowed around the current alternately, the voltage at input 7 did not exceed the stabilization voltage of the zener diodes, then when external, when both arms 7 flowed around, this voltage reaches the value at currents greater than stabilization current.  This circumstance is used in protection as an additional sign of an external short circuit.  Block 3 fixes the voltage at input 1, proportional to the sum of the modules of the connection currents at the level (1,, 8) Ist, forms a square signal that is fed to the input of the logic device and to the control input 6, increasing its blocking angle less than When operating the device under conditions of extremely distorted information from current transformers (for example, busbar protection), when the phase error may exceed 150, an additional logical part is provided.  Its principle of operation is based on the following properties of transient current transformers with a predominantly active load.  When a short circuit occurs, the current transformers enter saturation not immediately, but after some time, determined by the nature of the transient process, the parameters of the load current transformer and the previous state of the current transformer.  During this time (in a yellow transition process - less than 5 ms), the primary one is transformed into the secondary circuit almost completely and the magnetization current is close to zero.  If the induction reaches a value greater than the saturation induction, the secondary current is disrupted when after it acquires an almost zero value, and the instantaneous value of the magnetizing current is the value of the reduced primary current.  Thus, the leading edge of the magnetizing current always lags behind the leading edge of the secondary current.  It is known that the differential current consists of the algebraic sum of instantaneous values of the scientific research institute of secondary currents, but in case of external short circuits with severe transients, the differential current becomes equal to the magnetization current of one of the saturated current transformers.  With internal short breakers x, if the primary currents of the connections are close in phase to each other, the differential current is almost equal to the arithmetic sum of the instantaneous values of the secondary currents.  Consequently, with internal short-circuits, the leading edges of the rectified differential and the sum of the input currents coincide, and with external short circuits, the second one lags behind the first by no less than (1, ms), t. e.  in the differential current there will be pauses (FIG. H).  In fact, such a lag can be banned from triggering the device.  The signal fixing the leading edge of the secondary current is the voltage taken from the comparison circuit 7 using the shaper 3.  From output 3, the generated pulses are fed to the input of a time delay unit k, a delay signal for (1,) ms, and to one of the outputs of the first logic element 5, performing AND-NES operation,} because during the specified time current transformers operate practically without error on the second input of the logic element 5.  the signal taken from the linear output of the differential current converter 1 is zero, and the output - 1.  When the logical units at the inputs of the second logic element 21 coincide, after (1,) ms, at its output, at least briefly, logical O, which is blocked by the block 13 of the operation, is stored for a time longer than the maximum duration of pauses in the secondary current upon its breakdown when there is no doubling of the voltage at the input of the comparison circuit, and hence the signal from output 3.  Logic O from output 13 of the OR circuit with output 12, which also has logical O in this mode, is applied to one of inputs 10 and to third input 5, warning 1 on three of its inputs when the secondary current of one of the current transformers in subsequent periods of the transient process and you will have the dg:) che in this case 1 from the linear output of 1t.  The process is repeated in each period in the presence of a periodic component or a half-period in its absence.  At the same time, to confirm the steady state of block 13, it is sufficient to simply have a signal from output 3 for (1) ms, which significantly expands the functionality of the logic device when current transformers operate in the field of average inductions, when the pauses in the differential current can disappear Thus, during the entire transition process, at one of the inputs of block 10, which carries out operation I, there will be a logical O and triggering of the starting organ 11 and the phase organ b due to significant errors tr nsformatora current will not cause undue actuation output body 2.  With internal short-circuits, when the currents sent by the power sources coincide, the voltage at input 7 does not exceed Ist and the driver 3 does not emit starting pulses to the logical part of the circuit, the state of which does not change during the whole process.  Signal 1 is present at output 13, and if the signals from 11.6 coincide, the protection will work.  The presence of a logical device (as well as control of the blocking angle) makes it possible to reduce the blocking angle (of a different organ while maintaining a high isolation from external short circuits.  This is due to the need to ensure the protection operation during the first period with the maximum possible signal distortion, since in the second period (possibly in several subsequent periods) the signal distortion will be so great that blocks 6 and 11 may not work, t. e.  the protection has a response delay for a considerable Burden, determined by the constant time of the aperiodic component of the short circuit current.  Thus, a decrease in the blocking angle leads to an increase in the stability of the response of the protection.  With internal short circuits with a phase shift of the currents sent by the power sources, there is a time interval when current flows around both arms of the comparison circuit, t. e.  the voltage on the reference circuit rises to 2 East, and the logic device starts up.  However, in contrast to an external short circuit, a differential current appears simultaneously with the secondary.  Therefore, after the occurrence of the signal at output 3, the second output 5 is given a signal from the linear output and at output 5, at least briefly, an O, which is stored by the response resolution unit 12 for a time sufficient for the switch to trip the switch.  A possible inhibit signal in this mode from block 13 will be cleared and when the phase and starting organs are triggered, unit 10 issues a trigger pulse 2 (Fig. ) When using the present invention to protect power transformers (autotransformers), it is necessary to rebuild from the currents of the transformers to idle.  Studies by many authors show that there are no such signs of a surge of magnetizing current, which would not have occurred during internal short circuits, accompanied by errors of current transformers.  The latter can lead to delays in the operation of the protection for a time commensurate with the constant time of the aperiodic coupled short-circuit current.  However, the quantitative characteristics of the different signs of a surge of magnetizing current differ significantly from each other.  This makes it possible to combine these features in such a way that, with the most dangerous internal short-circuits, the braking signal would be significantly smaller than during inrush currents.  This combination of features is implemented in the present invention.  Job. the block of detuning from inrush current magnetization is as follows: From the linear output of the converter T of the differential current, the signal arrives at the inputs of the threshold element 15 and the braking unit 17. When operating in a transient mode of the transformer, the braking unit 17 generates a brake signal, locking the first harmonic di (K) of the potential current.  At the same time, in the aperiodic inrush current of the magnetization, aperiodic slope and higher harmonics are present in the output signal of the braking unit 17, and in the periodic mode, the highest harmonics are present.  Since the deceleration block 17 is a broadband filter, the delay time of the output signal is much less than the time corresponding to the blocking angle of the protection, which allows partial compensation of the false output signal of the filter by the input.  This is implemented by introducing an adder 16, to one input of which voltage is supplied from the output of the braking unit 17, and to the other from its input, and the signals are received with different signs.  The degree of compensation of the braking signal is determined from the condition of the selective operation of the protection at inrush magnetizing current.  The adder contains a voltage limiter that limits the braking signal to a level corresponding to the stabilizer voltage of the reference circuit.  With internal short-circuits, applying compensation and limiting the intensity of the output signal can significantly reduce the braking signal, which leads to an increase in protection performance.  However, with internal short circuits with large multiplicity with maximum aperiodic terms and their time constants, the current transformers are deeply saturated.  The latter can generate higher harmonics, and despite the compensation, the output signal of the adder 16 can have a significant value.  This can lead to significant delays in triggering protection.  In this mode, another distinctive feature of the short circuit from the magnetizing current rush is used to follow the protection speed in this mode.  Since saturation of the core is caused by a change in the magnetic flux, it cannot occur instantaneously.  Therefore, a stable sign of an inrush of magnetizing current is the presence of dead time in the derivative of the inrush of magnetizing current both after applying a voltage and during the entire process of switching on.  The differential output from the differential current converter is fed to the input of the input signal control unit 19 and the current input of the pause control unit 20, to the voltage input of which a signal is received from the voltage transformer installed at the outputs of the protected object.  The pause control unit 20 controls the duration of the current free pause from the moment when voltage is applied to the protected object until the derivative of the differential current appears (Fig. 5.6).  If the duration of the pause is more than 3 ms, the magnetizing current rush mode), the pause control unit 20 does not generate a control signal via the OR circuit 23 (FIG. 6), and the dosing unit transmits the entire brake signal from the output of the adder to the phase element 7, which is coarsened and does not give a signal to the circuit I.  If the duration of the dead time from the moment of voltage output to the onset of the derivative of the differential current is less than 3 ms, which corresponds to an internal short circuit, the pause control unit 20 generates a control signal (FIG. five).  The latter, via the OR circuit 23, is supplied to the second control input of the dosing unit 29, which limits the amount of the braking signal to a level sufficient for detuning from transient currents of unbalance of external short circuits. . This brake signal is very small, as the phase body 6 is largely rebuilt from external short circuits.  In order to ensure the speed of the device, after outputting the voltage, an input signal duration control unit 19 is input.  The latter is triggered by the output signal of the differentiation of the differential current converter and is blocked for AND ms.  Due to this, in the mode of aperiodic inrush of the magnetizing current at the output of the control unit 20 for the duration of the input signal, the voltage is constantly zero (Fig. 6).  This is due to the fact that the shape of the aperiodic surge of magnetization current is a sequence of peak-like pulses, the maximum duration of which does not exceed 13.5 ms, and between the pulses there are currentless pauses.  139 However, due to the 6th time: the constant time of the aperiodic inrush of the magnetizing current, the latter are poorly transformed by the current transformers of the protection arms and the current sensors of the protection device, while in the inrush curve of the magnetization current the negative half wavelength of the steepness appears. To restore the Sestok current, a differential current converter I differentiates the input signal.  In case of internal short circuits in the derivative of the short circuit current, there will be no dead time in ms and the control unit 13 for controlling the duration of the input signal will output a control signal through the OR circuit 23 to the second control input of the metering unit 22.  The latter limits the value of the brake signal to a level sufficient for detuning from transient unbalance currents of external short circuits.  For a detuning from periodic inrush current magnetization, the response threshold of the control unit 19, the duration of the input signal and the unit 20, the control of the dead-pause duration is set to a level of 1.61.  At very high internal short-circuit currents exceeding the maximum magnitude of the inrush current and unbalance current, which represent a significant danger to the stability of the system, the threshold element 15 is activated and outputs a signal to the first control input of the dispensing unit 22.  The latter completely removes the braking signal from the second control input of the phase element 6, which ensures the fastest protection action.  The proposed protection device is highly efficient.  With internal to close closures x and maximum distortion of the current transformer current, as well as during the current n phase shift and the presence of load currents, the protection response time does not exceed 20 ms at a sensitivity of 0.251ts.  The protection device is reliably tuned from the transient sky currents for external short circuits caused by the deep saturation of current transformers, as well as from aperiodic and periodic inrush currents of magnetization.  The device has wide functionality and can be used to protect tires, busbars of transformers, generator transformers, large electric motors, reactors and synchronous compensators, which reduces the cost of manufacturing and greatly simplifies the operation of protection of the main elements of stations and substations.  Structurally, protection can be carried out on separate cassettes, while the cassette of the detuning unit from magnetizing current surges is established to protect transformers and reactors, and the logic device to protect tires.  8, due to the lack of methods for assessing the economic effect of the relay protection devices, data on the latter is not given.  Formula of the Invention A device for differential protection of an electrical installation, comprising current sensors included in each protection arm, the outputs of which are connected to a multi-diode half-bridge, the cathodes and anodes of which are combined and are its output, a two-arm comparison unit connected to it consisting of connected in series connected to the output of the multi-shoulder diode half-bridge of two resistors and two zener diodes connected in series, a phase element whose input is connected to the output of a rectifier bridge, a triggering organ, a logical block I, whose two inputs are connected to the starting and phase organs and the output to the output organ, a driver of the input logic signal connected to the multi-braking diode half-bridge, whose inlet is connected to the time delay unit and to one of the inputs of the first a logic element, a second logic element, the inputs of which are connected to the output of the first logic element and to the output of the time delay unit, and the output is connected to the activation inhibit unit, the input of which is connected to the output the house of the first logic element, and the output is combined with the output of the prohibition block and connected to the third input of the logic element, i.e., in order to expand the functionality by providing protection of various power system objects and increasing the efficiency of operation, transformer, resistors and zener diodes, differential current converter, threshold element, braking unit, adder, dosing unit, dead time control unit, control unit the duration of the input signal, the element OR adjustment resistors connected in parallel to the third windings of current sensors, the differential current converter connected between the common point of the second sensor windings and the middle point of the comparison circuit, and its linear output is connected to the inputs of the trigger, threshold element, braking unit, first the input of the adder and the second input of the first logic element, the third input of which is connected to the output of the activation inhibit unit, the second input of the adder is connected to the output house brake unit, an output of the adder is connected to main input dosing unit, a first control input coupled to an output of the threshold element, and the second - yield

the OR element, whose inputs are connected to the outputs of the control unit for the duration of the input signal and the dead pause, respectively, and the input of the control unit for the duration of the input signal and the first input of the control unit for the pause-free pause are combined and connected to the differentiation output of the differential current converter; the voltage input, the output of the dosing unit is connected to the first control input of the phase element, the second input of which is connected to the output of the driver i A single logic signal, the cathode of the first Zener diode of the comparison circuit is connected to the cathodes, and the anode of the second Zener diode of the comparison circuit is connected to the anodes of the multi-shoulder diode half bridge, parallel to each Zener diode of the comparison circuit with the same ends is connected a series circuit consisting of a Zener diode and a resistor, and the output of the comparison circuit through an isolating transformer is connected to the input of a rectifying bridge.

Sources of information taken into account in the examination

1. USSR Author's Certificate in Application K 2619108/2-07,

cl. H 02 H 3/28, -1976.

2, USSR Copyright Certificate tf 2 b5 + 37 / 2A-07,

cl. H 2 H 3/28, 1975.

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Claims (1)

Claim Device for differential protection of electrical installations, containing current sensors included in each protection arm, the outputs of which are connected to a multi-arm diode half-bridge, the cathodes and anodes of which are combined and are its output, a two-arm comparison unit connected to it, consisting of series-connected multi-arm diode connected to the output half-bridge of two resistors and two zener diodes connected in series, phase organ, the input of which is connected to the output of the rectifier bridge, starting an, logical block I, whose two inputs are connected to the starting and phase organs and the output is to the output organ, an input logic signal shaper connected to a multi-arm diode half-bridge, the output of which is connected to the time delay block and to one of the inputs of the first logic element, the second a logic element, the inputs of which are connected to the output of the first logical element and to the output of the time delay block, and the output is connected to the blocking block, the input of which 15 907666 is connected to the output of the first logic element, and the output is combined with the output of the inhibition block and connected to the third input of the logical element And, characterized in that, in order to expand the functionality by providing protection of various objects of power systems and increasing the efficiency of operation , an isolation transformer, resistors and zener diodes, a differential current converter, a threshold element, a braking unit, an adder, a dosing unit, a non-control unit are introduced into it A new pause, the control unit for the duration of the input signal, the element OR regulating resistors connected in parallel to the third windings of the current sensors, the differential current converter connected between the common point of the second windings of the sensors and the midpoint of the comparison circuit, and its linear output connected to the inputs of the trigger element, braking unit, the first input of the adder and the second input of the first logic element, the third input of which is connected to the output of the block inhibit operation, the second input of the sums the torus is connected to the output of the braking unit, the output of the adder is connected to the main input of the dosing unit, the first control input of which is connected to the output of the threshold element, and the second to the output of the OR element, the inputs of which are connected to the outputs of the control units for the duration of the input signal and dead time, respectively, moreover, the input of the control unit for the duration of the input signal and the first input of the control unit for dead time are combined and connected to the differentiation output of the differential current converter, the second input The dead time pause control unit is a voltage input, the output of the dosing unit is connected to the first control input of the phase organ, the second input 15 of which is connected to the output of the input logic signal former, while the cathode of the first zener diode of the comparison circuit is connected to the cathodes and the anode of the second zener diode of comparison circuit 20 - to the anodes of the multi-arm diode half-bridge, in parallel with each zener diode of the comparison circuit of the same name, a serial circuit is connected consisting of 25 zener diodes and a resistor, and the output of the comparison circuit through an isolation transformer is connected to the input of the rectifier bridge.