RU2368990C1 - Electronic device for fast blocking of transformer differential protection - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention is related to electric engineering, to relay protection of power transformer and may be used for fast blocking of differential protection in case of start-up current rushes, when there is access to measurement of voltage that generates short-circuit current and rush current. For this purpose specified voltage is memorised in memory circuit in dynamic mode, and is used to create typical copies of rush and short-circuit currents on simple elements - models, which are further together with current realisation of mode in the form of voltage on loading resistance of current measurement transformer are exposed to correlation processing and comparison.

EFFECT: improved efficiency.

1 dwg

Description

The invention relates to electrical engineering, namely to the differential protection of a transformer, when it is required to make a quick decision on the occurrence of an inrush magnetization current when it is turned on at idle or on a short circuit. It is believed that in the place of installation of protection there is access through voltage transformers to voltage, under the influence of which these modes occur.

Widely known and widely used differential relays with saturable transformers type RNT [1]. Due to saturation of the intermediate transformer and the presence of short-circuited windings, the relay is detuned even from a surge transformed through a measuring current transformer when half-waves appear that are inverse to the direct component of the switching current. However, the speed and degree of the indicated tuning of the relay needs to be improved, especially for high-power high-voltage transformers.

Known electronic differential protection with a relay containing a transreactor, a converter in the form of a rectifier bridge, a resonant circuit tuned to the frequency of the network, and output relay elements [2].

The quality factor of the resonance circuit of this analogue and, therefore, its selectivity is limited by the necessary speed.

A known prototype of the proposed device [3], containing a resonant circuit, tuned already to the second harmonic of the protected network, therefore, the protection speed is improved, however, all the disadvantages associated with the inertia of the applied resonant circuits are preserved.

Both in the analogue and in the prototype, when using resonant circuits, the transformation of the investigated implementation of the inrush current or short-circuit current is used. in the form of the well-known overlay integral, the Duhamel integral, in which the integral is taken from the product of the indicated realization and free vibrations of the filter in the form of a harmonic pattern. In this case, the establishment of these free oscillations always requires time, which reduces the speed of relay protection with resonant filters.

In the inventive device for calculating the overlay integral, instead of slowly establishing model oscillations, an oscillation is taken, formed in advance even before the moment of the throw or short-circuit on specially offered simple models, which speeds up protection and was not previously known. Moreover, the samples used are much closer to real ones.

The drawing shows a block diagram of one phase of the proposed high-speed device for blocking differential protection during throws. Here 1 is the power system, 2 is the circuit breaker, 3 is the substation busbars with power transformer 4, circuit breaker 5 and current measuring transformer 6 with active load resistance 7. Voltage measuring transformer - 9 is connected to the busbars 3 through a fuse. The input terminals of the interlock device are terminals - 10, 11. Active resistors - 12, 15, 17, 18, 19, 20, 22. Diode - 21. Multiplication units - 23, 28. Integrators - 24, 29. Rectifiers 25, 30. Comparison scheme - 26. The reacting organ is 27.

The scheme operates as follows. A substation with busbars 3 is powered from system 1 via a switch 2. A switch 5 leaves the busbars 3, to which a shielded transformer 4 is connected via a measuring transformer 6. A voltage proportional to the current of the transformer 4 is removed from the resistance 7, and from the phase of the voltage transformer, voltage proportional to the voltage on the tires. This voltage in dynamic mode is stored on the inductive-capacitive oscillatory circuit 14, 13 and significant time is saved due to the resistors 12, 15. It is important that this voltage is already available until the short-circuit time. or throw and this ensures speed. It is saved after short-circuit and after turning on the transformer 4 at idle. To simulate inductive currents and the surge voltage of the circuit is shifted to a delay by the inertial chain: resistor 15 - capacity 16. Further information on the form of current short-circuit it is detected on the divider 17-18, and the shape of the surge is constructed in the form of a half-wave with a constant component, when the half-wave of the current passes through the diode 21, and the smaller reverse half-wave through the resistor 20 approximately simulates the reverse transformed half-wave, which provides the necessary calculated bias coefficient. With a nominal voltage on the busbars 3, the expected short-circuit current forms are formed on the resistors 18 and 22. and inrush current, and by calculating the resistance values, the effective values of these current samples are set equal. Next, the mutual correlation function between the samples and the current implementation is calculated by multiplying them on blocks 23, 28, integrating them on blocks 24, 29 and averaging on rectification blocks 25, 30. At block 25, the highest voltage is generated at short circuit and in load mode. During a surge, the voltage at the output of block 30, on the contrary, exceeds the voltage at block 25. The comparison circuit 26 fixes this situation and, through the reacting organ 27, allows or prohibits the action of the protection.

Testing of the proposed device showed that, with the appropriate choice of the shape of the sample of the inrush current with negative half-wave, the blocking starts at the moment the transformer is switched on at idle and continues even with the subsequent significant loss of the DC component of the current, which closes into the magnetization circuit of the measuring transformer. The throw detection time is of the order of one to two periods, and the tripping current can be less than the rated current with the corresponding elimination of the unbalance current of the differential protection arms.

Literature

1. L.I. Kakuevitsky and T.V. Smirnova. Directory of protection relays and automation. Edited by M.E.Heifitz. Ed. 3rd, overwork. and add. M .: Energy, 1972.

2. A.S. USSR No. 439876, class Н02Н 3/28, 08/15/74. Bull. Number 30.

3. A.S. USSR No. 1101946, class Н02Н 1/045, 07/07/84. Bull. Number 25.

Claims (1)

An electronic device for quickly locking the transformer diffuser during magnetizing current surges, containing electronic multiplication, integration, rectification, comparison and decision circuits connected in each phase to the active load resistance of the current transformer and through a voltage measuring transformer with a memory circuit to a phase-shifting active-capacitive circuit , characterized in that the output of the phase-shifting circuit through its ballast resistance is connected to the first resistor and ground, and the same output is black h another ballast is connected to the second resistor, shunted by the diode and then sequentially to the load resistance and ground, while the voltage on the first resistor is connected to the input of the multiplication unit, and the voltage from the second resistor is connected to the input of another multiplication unit, the second inputs of which are to load resistance of the current transformer, and each output of the multiplication unit is connected to its integrator with rectifiers at the output and then to its input of the comparison circuit with the reacting organ.

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