SU1686587A2 - Device for current protection of neutral circuit without time delay in a network with twin reactor and insulated neutral against double ground short circuits downstream different branches - Google Patents

Abstract

The invention relates to electrical engineering, in particular, to relay protection of electrical power systems. The purpose of the invention is to increase the reliability of the device by providing protection during double earth faults before and after the dual reactor. Filters of zero-sequence currents are introduced into the device to install on the outgoing lines another branch of the twinned reactor, current relays of the indicated lines connected to them, elements NOT by the number of branches of the dual reactor, elements AND by the number of outgoing lines. The device detects and shuts down one short-circuit when double-circuited to earth behind different branches of one dual reactor, as well as double-circuited to earth before and after the reactor. 8 il.

Description

The invention relates to electrical engineering, in particular to the relay protection of electric power systems, and is an improvement of the invention according to the author. St. No. 1201951.

The aim of the invention is to increase reliability by ensuring the protection operation during double earth faults before and after the dual reactor.

FIG. 1 is a schematic diagram and current circuits of a dual reactor earth-fault protection device for a dual reactor with current measuring elements made at maximum current relays; in fig. 2 is a block diagram of a device for protection against double faults to earth behind different branches, as well as before and after a dual reactor operating

on the connection of one branch of the dual reactor, on logical elements; in fig. 3 is a block diagram of a device for protection against double earth faults before and after a double reactor acting on the connection of another branch on logical elements; in fig. 4 is a circuit diagram of the device for protection of a dual reactor against double earth faults with the implementation of logic operations on the contacts of electromechanical relays; in fig. 5 - current distribution in case of double circuit to earth before and after one branch of a twinned reactor; in FIG. 6 - the same, but behind two branches of one dual reactor; in fig. 7 is the same, but behind the branches of the two twin reactors in FIG. 8 is a replacement scheme for determining

short-circuit current through one of the windings of a single reactor with a double circuit to earth before and after the reactor.

The device (Fig 1-3) contains a dual reactor 1, filters 2-3 zero-sequence currents at the output of each branch, to which current relays 4 and 5 are connected, filters 6-11 zero-sequence currents and current relays 12-17 connected to them outgoing lines 18-23, connected to both branches, elements 24 and 25 with three input signals, are connected to the output of each element at output body 26 and 27 of protection against double earth faults behind different branches of a single dual reactor operating to disconnect one ground fault Their lines 21 and 22, connected to one of the branches, And 28-31 elements with two input signals, successively to the outputs of each And elements connected by the element HE 32-35 and the element 36-39 of the delay of protection against double earth faults to and after the double reactor on the outgoing lines 21 and 22 and 19 and 20, connected to both branches. Intermediate relays or time relays can be used to create delays for triggering elements 36-39. For single reactors 1, filters 2 and 3 are preferably installed before the reactor leads.

There are lines connected to each branch of dual reactor 1, for example lines 18 and 23 to electric motors with a voltage of 6-10 kV, with electric motor protection, which, when double-ground to earth, if one short circuit is on the connection to line 18 or to connection to line 23, acts without a time delay for disconnecting line 18 and consists of a filter 6 zero-sequence currents, a current relay 12 connected to it and an output element 40 of this protection, or acts without a time delay for disconnecting lines 23 and consists of a filter 11, the zero-sequence currents, the connected switch 17 and current output 41 body.

The device does not perform on lines 18 and 23 with line protection acting on dual ground faults without time delay. FIG. 4 relay 4 current acts on relay 42 intermediate, and relay 5 current - on relay 43 intermediate. For performing logical operations AND, the make contacts of relays 42 and 43 are used.

Negative operations are NOT performed on relays 42 and 43 with break contacts.

The number of outgoing lines attached to each branch of the dual reactor 1. may be arbitrary, for example, equal to three (Fig. 1-4).

Current relays 13–16, connected to filters 7–10 of zero sequence currents, are triggered by zero sequence currents and detect one or two damaged lines at the same time when a double earth fault occurs, if one or both of them are on lines 19-22, where filters are installed 7-10 zero sequence currents. Elements 2 and 4 and respectively 3 and 5

5 are intended to define the branch of the dual reactor 1 with one short circuit when double circuited to earth behind different branches or when double shorting to earth with one short circuit to double reactor 1 and with another short circuit after double reactor 1.

Elements 24 and 25 are designed to detect and disconnect without time delay one closure at double closing on the ground behind different branches of the same twin reactor 1.

Elements 28-31 are designed to detect and disconnect one circuit behind double reactor 1 with a double short circuit to earth before and after reactor 1.

Elements NOT 32-35, connected in series by elements AND 28-31. detect a double earth fault to

5 and after reactor 1. but do not react to a double circuit to earth behind different branches of the same twin reactor 1 or behind the branches of two reactors.

The delay elements 36-39 are intended to eliminate the non-selective operation of the double ground fault protection device before and after the double reactor 1 when the double ground circuit follows the different branches of Double Actor 5.

The principle of the device is to selectively disconnect without time delay one of the places of the double ground fault on the departing lines.

0 21 and 22, for example cable, behind different branches of dual reactor 1 until the transition to phase-to-phase short circuits, for example, three-phase, as well as in selective shutdown without time lag or with a small delay of one of the double ground points behind the filters 7 -10 zero sequence currents installed on outgoing lines 19-22, such as cable, when the other circuit is located before filter 2 or 3 and the short circuit current flows through one of the phases of the three-phase dual reactor 1. The faster the damage is shut off, the less the thermal effect of the earth's double-circuit current on the reactor and the probability of its damage. For a current-limiting reactor, the double-earth fault mode is not allowed when the short-circuit current flows through the reactor winding of one phase, i.e. double circuit to earth before and after the reactor.

The basis of the GOST requirements in terms of the resistance of reactors during short circuits for the design mode is the three-phase short circuit mode.

For single reactors, the permissible effective value of the periodic component of the short-circuit current is.

and

and

V3 (Xp + Xc) + U / lc

where U is the reactor voltage class, kV;

Хр - nominal inductive resistance of a single reactor, Ohm;

Ic is the established conditional short-circuit current in the network without a reactor in the place where the reactor is to be installed, at a rated voltage of the network corresponding to the class of reactor voltage, to A.

The current value lc is set depending on the rated current of the reactor and the type of installation.

-, &. t

where Xc is the inductive impedance of the system.

When a double circuit to earth (Fig. 8) at points K1, K2, the established short circuit current 1k flowing through the winding of the reactor of phase B. is found from the expression

, „(1.1).

U

5i

XP + 2 XC V3Xp + 2U / V

Consider the relationship of currents and

1 (e) c.dop.

Depending on the type of reactor, this ratio is in the range of 1.3-1.6, i.e. with a double circuit to earth, the value of the short circuit current through one of the reactor windings significantly exceeds the allowable, and the maximum value

electrodynamic forces in case of double circuit to earth exceeds the corresponding values of forces in case of a three-phase short circuit by 1.69-2.56 times. The effect of these forces on the winding leads to the formation of winding short circuits in the winding, mechanical damage to the winding fastening elements and inlet busbar.

10 When the flow of the double ground to the earth, exceeding by 20-40% the normalized value of g cc, with a duration of 0.5 s or more, damages occurring in the form of cavities occur in the winding wire of the reactor.

The considered mode may also occur on the branches of the double reactor.

The operation of the device is described to the extent determined by its improvement and the introduction of additional elements into the device.

With a double circuit to earth, before and after one branch of a twinned reactor 1 or a single reactor (Fig. 5), the sequence is 25. and from tires Ш1 to tires Ш.

30 In case of damage to reactor 1 and, for example, outgoing line 19 (Fig. 1.3-5), current 4 and 13 relays, current relay 5 does not operate, and a pulse is given to shut down without time lag or with a small delay of one circuit ground on line 19,

Thus, with one closure to element 2 or 3, installed on the output branch of the twinned reactor 1, and another

40 of the earth fault after elements 7 and 8 or 9 and 10 of the outgoing lines 19 and 20 or 21 and 22 (figs. 1-5) the device covers the zone located to element 2 or 3 and after elements 7 and 8 and 9 and 10 The damage probability in the reactor 1 is small compared with the damage to the lines.

The device has a dead zone between elements 2 and 7 and 8, as well as between elements 3, 9 and 10, with one short circuit to

50 ground to element 2 or 3 and another short circuit to earth after the double reactor 1 between elements 2, 7 and 8 or between elements 3, 9 and 10. The accuracy of damage to the tires of stations and substations is entirely small compared to the damage to lines, and the dead zone is practically implausible. The elimination of damage in it is done by protecting the tires.

With a double circuit to earth, for different branches of one twin reactor 1 (Fig. 6), the zero sequence component in the phase short circuit currents is absent from the H neutral to the average output and is contained in the sections from the average output to the points K1 and K2. If, for example, the outgoing lines 19 and 22 (Figs. 1-4 and 6) are damaged, the relays 4, 5.13 and 16 of the device current are triggered and a pulse is given to disconnect without time delay of one ground fault on line 22 by double-circuit protection. on the earth for different branches of mi.

The operation of the device from the double ground fault before and after the twin reactor 1 is not required when the double earth fault follows different branches and does not occur due to the relay 5 (element NO) triggered. To perform a delay operation, if it is required, an intermediate relay or a time relay with a short response time of less than 0.5 s, such as 0.1-0.2 s, can be used.

The need to use the delay is determined by the development of specific circuits of the device when considering the mode of the dual ground fault behind different branches, based on the selectivity of the operation of the AND and NOT elements. for example, in FIG. 4, the response time of the relay 38 must exceed the response time of the relay 43,

With a double circuit to earth behind the branches of two twinned reactors (Fig. 7), a section from neutral H to busbars W flows around a two-phase short circuit current, and the phase currents contain components of direct and reverse sequences, and in stations from busbars W to buses Sh1 and from buses Ш1 to points К1 and К2 - a component of zero sequence. In order not to work in this mode, the scheme of the device from the double ground to the ground and after the reactor (Fig. 1-4). The number of interconnecting contacts of elements to be connected in series should NOT be equal to the number of branches without one all reactors, for example for FIG. 7 The break contacts of the three elements are connected in series.

two twin reactors.

The use of the proposed device prevents the occurrence of emergency situations with double ground loops before and after single and double

current-limiting reactors and expands the functionality of the protection, which increases the reliability of operation and provides a positive effect.

The invention may find application.

power plants and substations with current-limiting reactors for high-voltage networks with insulated neutral.

Claims (1)

Invention Formula A device for current protection of zero-sequence without time delay in a network with a dual reactor and an isolated neutral from double earth faults behind different branches by author. St. No. 1201951, characterized in that. in order to increase reliability by ensuring the protection operation during double ground faults before and after dual reactor, filters of zero-sequence currents are introduced to install on the outgoing lines another branch of the dual reactor, current relays of the indicated lines connected to them, elements NOT by the number of branches of the dual reactor, the elements And by the number of outgoing lines, the inputs of each element AND are connected to the current relay of the branch of the double reactor and the corresponding line leaving the specified branch, the output of each element AND is connected to the disconnecting circuit of the corresponding outgoing line through the element is NOT, the control input of which is connected to the current relay of the adjacent branches of the dual reactor. 12 a F 7th 13 i eight 15 V f 16 17 gui // f Di 18 nineteen 20 On off 27 28 D6t T On off 23 N fshg, 1 22 hu LT thirty $ -, Наоткл.19 135 7G At 20 i-i Out IB Fig.z + KL, W, tf 38 r {} i yes naotkl.19 +20 fox- "03 33 // a about 1 "l. W + w fWa amnfA W R "/ L // No / tf f iJ W l about "L 25 72 ; -H 2 de wo 27 j5 -one + I l 27 HaomMtt 31 27 -22 -CH "3 vOt .p Fig.Ch. AND V No it d / zttf -A FI.5 22 I g Sh fi I & nineteen Ш2. ti tf WITH H2 f 22 FI.6 nineteen figs in