RU2402130C1 - Device for protection against ground short circuit in networks with compensation of capacitance circuit - Google Patents

Abstract

FIELD: electricity. ^ SUBSTANCE: device includes control current source with frequency of 25 Hz, arc-suppression coil in-series connected to control current source and connected to neutral point of network and filters of zero-sequence currents installed in each network line. Responding elements are connected to filters of zero-sequence currents. At that, each responding element includes low-frequency filter, high-frequency filter, the inputs of which are connected to filter of zero-sequence currents, comparison element of amplitudes of harmonics, to the input of which low-frequency and high-frequency filter outputs are connected. ^ EFFECT: providing protection selectivity. ^ 2 dwg

Description

The invention relates to the field of relay protection and can be used to protect against earth faults in networks with capacitive current compensation.

A device for protecting against earth faults in networks with capacitive current compensation [Fedoseev A.M. Relay protection of electrical systems. - M: Energy. 1976, 360 pp.], Comprising a unit for generating an operational current with a frequency of 100 Hz, including an additional winding located on the core of the arc suppression reactor, which is switched on through a contactor and a rectifier to a resistor.

This device responds to stable faults, but may not work properly with intermittent arc faults.

Also known is a device for protection against earth faults in networks with compensated neutral [A.S. USSR No. 177958, IPC 2 Н02Н 3/16, BI. No. 2, 1966], containing a source of operating current with a frequency of 25 Hz, which is a coil whose inductance periodically changes, connected in series with an arcing reactor, reacting organs, which are electromagnetic parametric amplifiers tuned to a frequency of 25 Hz, connected to zero current filters sequences that are installed on each line of the network.

This device responds to stable faults, but may also not work correctly with intermittent arc faults.

A device for protection against earth faults in networks with capacitive current compensation [RF Patent No. 2268524, IPC Н02Н 3/16, BI No. 2, 2004], selected as a prototype, containing an operating current source with a frequency of 25 Hz, connected in series with an extinguishing reactor. The extinguishing reactor is connected to the neutral point of the network. An operating current source with a frequency of 25 Hz is a parametric frequency divider containing an output winding located on the combined rods of two magnetic circuits, connected in series with an arc suppression reactor, a first field winding located on an external rod of the first magnetic circuit, connected in series with a second field winding located on the outer core of the second magnetic circuit, and the field windings are connected through a diode to the AC auxiliary supply network, and TCA oscillating circuit located on the terminals of combined first and second magnetic circuits, shorted to series connected capacitor and choke line. Zero sequence current filters are installed on each line of the network. Responsive organs are electromagnetic parametric amplifiers tuned to a frequency of 25 Hz. Responsive bodies are connected to zero sequence current filters.

This device reacts to stable faults, but may not work correctly with intermittent arc faults due to an increase in the proportion of low-frequency harmonics in the current spectrum of the zero sequence of undamaged lines.

The objective of the invention is to provide selectivity of protection against earth faults in networks with compensation of capacitive current, both with stable faults and with alternating arc faults.

The solution to this problem is achieved by the fact that the device for protection against earth faults in networks with capacitive current compensation, as in the prototype, is based on the principle of applying an operational current with a frequency of 25 Hz to the network and contains a source of operating current with a frequency of 25 Hz, connected in series with an extinguishing reactor, which is connected to the neutral point of the network. The operating current source with a frequency of 25 Hz is a parametric frequency divider containing an output winding located on the combined rods of two magnetic circuits, connected in series with an arc suppression reactor, a first field winding located on an external rod of the first magnetic circuit, connected in series with a second field winding located on the external core of the second magnetic circuit, the field windings are connected through the diode to the AC auxiliary supply network, and the coil ebatelnogo circuit located on the terminals of combined first and second magnetic circuits, shorted to series connected capacitor and choke line. Zero sequence current filters are installed on each line of the network. Responsive bodies are connected to zero sequence current filters.

According to the invention, a low-pass filter, a high-pass filter, the inputs of which are connected to a zero sequence current filter, a harmonic amplitude comparison organ, to the input of which the outputs of a low-pass filter and a high-pass filter are inserted, are introduced into the reacting organ.

It is the claimed embodiment of the device that provides selectivity of protection against earth faults in networks with capacitive current compensation, both in case of stable faults and intermittent arc faults, due to the fact that with both types of faults in the frequency spectrum of the zero-sequence current of the damaged harmonic amplitude line with frequencies below 50 Hz are greater than the amplitudes of harmonics with frequencies above 50 Hz. For an undamaged line, on the contrary, the amplitudes of harmonics with frequencies below 50 Hz are less than the amplitudes of harmonics with frequencies above 50 Hz.

Figure 1 presents a schematic diagram of a network with elements of a device for protection against earth faults in networks with capacitive current compensation, and figure 2 is a diagram of a reacting body.

The device contains (Fig. 1) an operating current source with a frequency of 25 Hz 1, connected in series with an extinguishing reactor 2, which is connected to the neutral point of the network. The first reacting organ 3, the second reacting organ 4, the Nth reacting organ 5 are connected respectively to the first zero-sequence current filter 6, the second zero-sequence current filter 7 and the Nth zero-sequence current filter 8 installed on each line of the network with their own capacitors 9, 10, 11.

The first reacting organ 3 (figure 2) is made as follows. The low-pass filter 12 and the high-pass filter 13 are connected to the first filter of the zero-sequence current 6. The outputs of the low-pass filter 12 and the high-pass filter 13 are connected to the input of the harmonic amplitude comparison organ 14. The second reacting organ 4, the Nth reacting organ 5 is made similarly .

An operational direct current source with a frequency of 25 Hz 1 is a parametric frequency divider [RF Patent No. 2268524].

As filters of currents of zero sequence 6, 7, 8, cable transformers of current of zero sequence can be applied.

The low-pass filter 12 can be performed on standard integrated circuits of the type K140UD7.

The high-pass filter 13 can be performed on typical integrated circuits of the type K140UD7.

The comparison body 14 can be performed on standard integrated circuits of the type K140UD7.

The device operates as follows. In the normal mode of operation of the network due to the source of operational current with a frequency of 25 Hz 1, small currents with a frequency of 25 Hz flow, determined by the own capacities of 9, 10, 11 lines, flow through the network lines. When an earth fault occurs, for example, on the line where the first zero-sequence current filter 6 is installed, the line's own capacitance 9 is shunted and the equivalent conductivity of this line becomes much larger than the conductivity of the undamaged lines, the current in the damaged line increases.

With a stable ground fault, only harmonics with frequencies of 25 Hz and 50 Hz are present in the frequency spectrum of the zero sequence current of the damaged line. The frequency characteristics of the filters are such that they pass components with a frequency below 50 Hz and above 50 Hz, and a component with a frequency of 50 Hz is suppressed. Therefore, in the body for comparing the amplitudes of harmonics 14, components with a frequency below 50 Hz are greater than the amplitudes of harmonics with a frequency above 50 Hz. According to this condition, the organ for comparing the amplitudes of harmonics 14 generates a signal about a ground fault.

With an alternating arc fault, the harmonic components of the zero sequence currents are distributed along the lines so that in the damaged line the amplitudes of harmonics with frequencies below 50 Hz are greater than the amplitudes of harmonics with frequencies above 50 Hz. For an undamaged line, on the contrary, the amplitudes of harmonics with frequencies below 50 Hz are less than the amplitudes of harmonics with frequencies above 50 Hz. Therefore, at the output of the organ for comparing the amplitudes of the harmonics 14 of the reacting organ of the damaged line, a signal about ground fault is generated.

Thus, the proposed protection has selectivity, both with stable earth faults, and with alternating arc faults.

Claims (1)

A device for protection against earth faults in capacitive current compensation networks based on the principle of superimposing on-line operating current with a frequency of 25 Hz, containing an operating current source with a frequency of 25 Hz, which is a parametric frequency divider containing an output winding located on combined rods two magnetic cores, connected in series with the arcing reactor, the first field winding located on the outer core of the first magnetic circuit, connected in series with the second winding of the excitation coil located on the external terminal of the second magnetic circuit, the field windings are connected through the diode to the AC auxiliary supply network, and the oscillating circuit winding located on the combined rods of the first and second magnetic circuits is closed to a capacitor and a linear inductor, an arcing reactor connected in series with a source of operational current with a frequency of 25 Hz and connected to the neutral point of the network, zero sequence current filters installed on each line of the network, and reacting organs connected to the filters of currents of zero sequence, characterized in that each reacting body contains a filter of low frequency, a filter of high frequency, the inputs of which are connected to a filter of currents of zero sequence, a body for comparing harmonics of amplitudes, to the input of which outputs are connected low pass filter and high pass filter.

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