SU758353A1 - Device for protecting from earthing in the mains with insulated or compencated neutral wire - Google Patents

Description

The invention relates to energy, in particular to the technique of relay protection of the power system, and can be used as a group protection against earth faults in networks with isolated or compensated neutrals. '

Devices are known that detect a damaged line in the single-phase circuit mode by comparing the phases of the current of several connections {ί].

The device is complicated according to the scheme, since it contains a zero-sequence current transformer (TYPE) on each line, rectifier bridges, filters of the first half-cycle of the transient current, twice the number of signal elements with memory compared with the number of lines.

ten

15

20

The closest to the proposed is a device containing on each line a reed switch installed in the resulting magnetic current pble of its three phases, an executive body with “memorizing the input signal. The use instead of the combination "TYPE - the threshold element" of one reed switch greatly simplifies and reduces the cost of the protection scheme (.2]. 39

Such a device, when used in networks with isolated or earthed neutrals through arc suppressing reactors, does not satisfy the sensitivity requirements because of the need to avoid the amplitude of transient currents of intact lines. Such a detuning is necessary, since otherwise, due to the high speed of the reed switches (0.52 ms), the device can falsely operate in transition modes. 'The own capacitive current of intact lines in the transient process is ten times the magnitude of the steady-state current. Therefore, the setting of the protection device operation should be ten times more. Than the setting when applied without detuning, and the sensitivity is ten times less.

; / The aim of the invention is to increase the sensitivity of the device.

This "is achieved by the fact that in a known device containing for each line a reed switch installed in the resulting magnetic field of the currents of its three phases, and an executive unit with memory, the reed switches are polarized and additionally

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four

each line is entered a logical element, ment And, the output of which is connected to the ’

the input of the said executive body, the first input — to the polarized reed switch of the corresponding lines / the second input — to the output of the additionally introduced logical element “exclusive OR”, and the inputs of the last to the mentioned polarized reed switches of all lines.

Since the phases of the currents on the damaged and other connections are opposite, for the first perio “‘ ^^ yes ^ per ^ ^ KOCnOO tfedoyo memeyoy 'half-period, when only the reed switch of the damaged line is activated. Availability

"Only a single signal at the inputs of the element" exclusive OR "causes by ......" the phenomenon of a permissive impulse on its

output At the inputs of the element And the damaged line are the same, the signals from the reed switch and the element "exclusive OR", the executive body is triggered 'and. fixes the fault.

In another half period of the first period ............ Oda and further the number of triggered

reed switches of serviceable lines is not equal to 1, at the output of the element "exclusive OR".

'there is no permissive impulse, the inclusion of elements And and the executive bodies of the other lines is blocked.

..... For the operation of the proposed device, one first transition period is sufficient. For everyone

“^ • * YY ^^ '0in'okg>' atn'0 exhibit the same maximum sensitivity of the reed switches, determined by

"types" of reed switches and constructive

..... features of their attachment. '

In the drawing, given the 'block diagram of the proposed device.

Tires; substations ‘connected lines 1,2,3, in the resulting magnetic field of the currents of their three phases are installed identically polarized reed switches 4, 5, 6. The reed switches are connected to the first input of logic elements I 7,8, 9

'and with the inputs of the logic element 10 "exclusive OR", the output of the latter is connected to the second input of the element I. The output of each element And is connected

executive’s memorizing 11, 12, 13 respectively. The longitudinal axes of the reed switches are oriented to the same

. possible sensitivity. In the norm mode of the current. Zero sequence in the lines is missing, the reed switches are open, the device is in standby mode. ’, ......., ·. ·..

When single-phase ^ / amycane appears on line 1, the discharge current of capacitances on lines 2, 3 is directed to the substation buses, and on line 1 to the place of damage. If the polarity of the first half-wave of the transition current corresponds to ’^ ^^ NSH ^ IZhveti'yklycheniya reed switch 4, the latter is closed, on the other lines the polarity of the current-wave half is opposite, the reed switches 5, 6 are open. Only one signal arrives at the input of element 10, an enabling pulse is generated at the output. The coincidence of the signals from the reed switch 4 and the element 10 at the inputs of the element And 7 provides

³ actuating actuator 11. On the remaining elements And there is no signal from reed switches 5, 6. In the next half-period of polarity half-waves

_N currents accessions changed. The reed switch 4 is opened, the contacts are reed switches, 5, 6 are closed and give a pulse to the inputs of the elements AND 8, 9 and 10. Since the number of signals at the inputs of the element 10 exceeds 1, the enabling pulse

15 at the exit of the element is missing, the bodies 12, 13 do not work.

.. Since there is no need to tune out the amplitude of the transient current, the sensitivity of the proposed protection in networks with low earth-fault currents can be increased tenfold. Additional sensitivity increase is provided by the fact that

25 not to build on their own loans. ” bone current lines in steady state. In addition, polarized

^ erkons are constructive in several. times more sensitive than usual. Blocking the protection according to the stated principle of NS · includes false triggering regardless of the amplitude of the transient process currents, i.e. increases the reliability of the protection.

³⁵ , 'g.

Claims (1)

Claim A device for protection against earth fault in a network with an isolated or compensated neutral, containing 4θ a reed for each line, installed in the resulting magnetic field of the currents of its three phases, and the executive body with memory, about In addition, in order to increase sensitivity, the reed switches are polarized and, in addition, an I AND is added to each line, the output of which is connected to the input of the said executive 50 Authority vhod'- first reed switch corresponding to the polarized line _D py _{Goi input YOU} _ _to move further inputted logical element "XOR" and the latter to the inputs of said polarized reed contact all lines.