SU736253A1 - Device for testing differential protection system current circuits - Google Patents

Description

The invention relates to relay protection and can be used during normal operation of the differential and differential phase protection of generators and double-wound transformers with a running current of 0.2 nominal and above, to increase the operational reliability of these protections. The longitudinal differential protection of transformers has low operational reliability, which accounts for a very high percentage of wrong actions (up to 28.9%). Only 1-3% can be attributed to technical imperfections and insufficient equipment reliability, the rest are the result of personnel errors. ANESHIZ statistics for 1971–1973 revealed that 8% of the failures of the longitudinal differential protection of the transformers are due to the personnel errors of the TFIs working with current circuits. In this case, an incorrect assembly of current circuits is the cause of approximately twice as many cases of incorrect actions than breakages. A device for protection of a two-winding transformer is known, comprising two current transformers, two intermediate transformers equipped with an additional secondary winding, a phase matching element, a blocking element against the aperiodic component and a source of operating voltage. Additional windings and logic circuits OR are cross-connected to the two inputs of the phase comparison organ. This device eliminates false operation when current circuits are broken. However, it does not allow detecting other possible malfunctions of current circuits (crossing the polarities when connecting protection to current transformers, incorrect phase connection, the occurrence of short circuits). It is also known a device for checking the operability of connecting wires of longitudinal differential protections, which, by applying a direct current to an alternating current in the circuits of connecting wires, blocks the protection when the latter are damaged. The reactive organ is made in the form of a pulse expander with an intermediate RC link and connected via a full-wave chopper to an active shunt connected to the junction wire circuit 2. In addition, a device for monitoring current circuits, differential busbar protection, which is the closest to the proposed by the technical nature It contains a rectifying bridge, made by a three-phase four-wire circuit, a reacting organ, a micro-tube: a meter, a protective diode, a smoothing series resonant contact ur adjusting resistance with added resistance h. The device makes it possible to detect damage to the current circuits of the differential busbar protection. However, this device cannot be used for monitoring; chains of differential protection of generators and two-winding transformers with low operating current, as in normal operation it must be disconnected from unbalance currents exceeding the current of the protection mentioned. The aim of the invention is to expand the functionality of the device for monitoring current circuits n;), thereby increasing the sensitivity. This is achieved by the fact that the proposed device for control current differential protection circuits, containing a three-phase current converter into a single-phase and a reacting organ connected to it, additionally contains two ni:) three-phase three-phase current into a single-phase, while additional converters connected to it are supplied in the form of ferromagnetic triples of frequency with primary windings connected in a reverse zagzag, and the secondary windings of converters are connected according to the circulating current circuit, to a differential circuit th connected body reacts. The drawing shows a schematic diagram of the proposed device. It contains three transducers - ferromagnetic frequency doublers 1, 2, 3, made according to the reverse zigzag scheme. The inputs of the converters 1, 3 are included in the shoulders of the protectors, the inputs of the third circuit 2 in the differential circuit. The device works as follows. In normal operation, when the current protection circuits. Are connected correctly and in good order, and equal protection currents flow in the protection arms, the output signals of the transducers 1, 3 are equal and balance one another. No signal is received at the input of converter 2. Thus, there is no signal at the output of the device. In normal operation and the inequality of the protection arm currents, the high-current signals of the transducers 1, 3 included in the protection shoulders are different in magnitude to a lesser extent than the input signals. This is due to the fact that the mode of operation of the converters is the mode of operation in the field of deep saturation, where the magnetization curves of the steel of different transformers approach each other even if they are significantly different in the linear region. The difference in the output signals of the converters 1 and 3 is additionally compensated by the output signal of the converter 2, to the input of which a signal is received, equal to the difference in the currents of the arms, protection. Such compensation is possible, since converters 1 and 2 in normal operation, when the currents of the protection arms do not differ significantly from one another, operate in a mode similar to that with short-circuited outputs. In this case, the circuit of the reacting organ 4 is the load of only the inverter 3, and the accuracy of compensation of the difference between the output signals of the transducers 1 and 3 reacts with the load of the circuit of the reacting opra-i on. Thus, in the normal mode of protection in the device's response organ, the signal is practically absent. When one or two phases of any arm, for example, differential protection, are transformed, the transducers connected to the damaged arm and the differential circuit output signals that consist mainly of the first harmonic and are substantially out of phase, since their primary windings flow asymmetrically and different in phase currents. The output signal is mainly due to the transducer of the damaged shoulder. When the polarity of one of the current transformers in the shoulder of the latter is changed, the current symmetry of the currents is disturbed, an asymmetrical system of currents appears in the differential circuit, consisting mainly of the first harmonic. The signal at the output of the device is due to all three preo & ezovatel mi. When changing the frequency of two current transformers, the device works in the same way. When frightening the ends of the douf of the current transformer, the symmetry of the currents at the inputs of the converters 1, 3 does not break, and the output of the ferromagnetic tripling frequency 2 has a signal of sufficient magnitude. In the event of a two-phase short-circuit. to secondary: the circuits the device is capable of BI giving a signal of faults in current circuits if the damage is sufficiently far from the connection point of the differential circuit. The device must detect damage to the current circuit in the duty mode of the diffzashchit with a response current (0.2O, 3) 3c and above. In the tri-alarm differential protection mode, the device is deactivated by the signal of the starting organ of protection against overcurrents, and in case of loop closure x, the sensitive stage of current protection of the reverse sequence. During normal operation of the monitored protection circuits, there is practically no signal to the reacting body, and for the described faults, there is always a signal caused by a converter. This allows devices to be more sensitive than differential protection of two-winding transformers and generators with a low response current {0.25 c). A formula for monitoring differential protection current circuits, containing a three-phase current-to-single-phase converter and a reactive qjraH connected to it, characterized in that, in order to extend the functionality by increasing sensitivity, it additionally contains two three-phase current converters single-phase, with the additional and the above-mentioned converters being made in the form of ferromagnetic frequency trippers with primary windings connected in a reverse zigzag pattern, secondary windings inverters connected in a loop currents tion, to a differential circuit which is connected responsive FGAN. Sources of information taken into account in the examination 1. The author's certificate of the USSR No. 393793, cl. H 02 H 3/28, 1971. 2. Author's certificate of the USSR N9 34556O, cl. H 02 H 3/28, 1967. 3. Grek G. T. Petrov S. Ya. Differential protection of shea with braking. Electricity, 1970, No. 10, p. 42

Differential protection

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Claims (1)

Claims A device for monitoring current circuits of differential protection, comprising a converter of three-phase current into a single-phase and a reactive organ connected to it, characterized in that, in order to expand functionality by increasing sensitivity, it additionally contains two converters of three-phase current to single-phase, with _L additional and said converters are made in the form of ferromagnetic frequency triplers with primary windings connected in the reverse zigzag circuit, and secondary windings are pre educators are connected according to the circuit of currents, to the differential circuit of which a reacting organ is connected.