Power line protection device in the external power supply network of a through traction substation

Abstract

FIELD: electrical engineering.SUBSTANCE: invention relates to relay protection of power transmission lines extending from through traction substations. A protection device is created that blocks the resistance relay in the event of damage on an adjacent line. To solve the problem of line protection, blocking of the resistance relay and starting of emergency overcurrent protection are used. The device uses combined relays for voltage, phase current and its emergency components, which distinguish the loss mode of voltage circuits from the modes of three-phase damage and swings.EFFECT: ensuring selectivity of the protection action of a line adjacent to a through traction substation in shutdown modes of an adjacent line.1 cl, 2 dwg

Description

[0001] This invention relates to the electric power industry, specifically to relay protection and automation (RPA) of power transmission lines (PTL) in the external power supply network of a traction substation. It solves the problem of non-selective operation of distance protection (DPP) of power lines at a through traction substation during the shutdown of an adjacent line.

[0002] At through-passage substations of the external power supply network for AC traction loads, the measuring voltage transformers for the monitored line are connected to the buses of the adjacent line (Fig. 1). Without additional measures, this connection causes non-selective disconnection of the monitored line from the distance protection when the adjacent line is disconnected, for example, due to a fault on it. In this case, the voltage at the input of the distance protection resistance relay will be practically zero, and the current-swing blocking triggers will be in the tripped state, responding to the fault on the adjacent line, which will lead to non-selective disconnection. At such facilities, additional information about the state of the adjacent line for the protection of the monitored line is absent, and therefore, only the mode parameters of the monitored line can serve as information parameters for blocking protection during external short circuits and unblocking it during internal short circuits.

[0003] The closest approach to the claimed technical solution is the method described in [1], where, to eliminate the non-selective action of the remote protection system in the event of loss of voltage circuits, it is proposed to use a special emergency overcurrent protection (EOP), the coverage area of ​​which should cover the length of the monitored line and ensure its protection for the entire period of absence of voltage circuits in the protection. This method was selected as the prototype of the invention. Its disadvantage is that the EOP is activated only after the activation of the voltage circuit fault blocking module (VCF) of the protection, which, due to the specifics of the operation of the automation at through traction load substations, is disabled and acts only on the signal. Furthermore, the VCF may also fail to operate at low load currents and when an adjacent line is disconnected.

[0004] The purpose of the invention is to ensure selectivity of line protection during the shutdown of an adjacent line at a through traction substation. This objective is achieved by using a special protection device instead of blocking the line during voltage circuit faults in the remote control. This device, when the voltage circuits fail, immediately blocks the operation of the distance protection resistance relay based on the phase currents and voltages and the additional fault current, and unblocks the emergency overcurrent protection module, which will protect the line for the duration of the voltage circuit failure in the remote control.

[0005] The device's operating algorithm is illustrated by the block diagram shown in Fig. 2. The device is installed on one of the lines of a pass-through substation and is activated upon loss of voltage in the protection circuits of the monitored line. The device's block diagram (Fig. 2) contains the following modules and elements:

[0006] - minimum voltage control module in protection (module 1), consisting of phase minimum voltage relays (blocks 2, 3, 4) and a logical element “AND” D1 for recording the loss of voltage at the inputs of the resistance relay;

[0007] - module for the presence of at least two phase currents, the values ​​of which are lower than the minimum current of a three-phase or interphase short circuit (SC) (module 5), calculated in the minimum mode at the end of the line, which includes three phase current relays (blocks 6,7,8) and a “two out of three” majority circuit assembled on the “AND” logical elements D2, D3, D4 and the “OR” element D5;

[0008] - module for monitoring changes in emergency phase current components (module 9), the values ​​of which do not exceed the maximum value of the switched load current, and which includes three emergency phase current relays (blocks 10,11,12), the outputs of which are combined on the logical element “AND” D6;

[0009] - module for generating output signals of the device (module 13), which, by means of the logical element “AND” D7, upon the operation of modules 1, 5 and 9 of the device, generates a blocking signal to the protection resistance relay and to other measuring elements (signal 14) that respond to the network voltage, and a signal for starting the AMTZ (signal 15), which, by means of the logical element “OR” (D8), can also be influenced by the BNN module (element 16) [1].

[0010] The protection device operates as follows.

[0011] Figure 1 shows the structural diagram of a pass-through traction substation with a variant of connecting the voltage measuring transformer (VMT) circuits to the buses of an adjacent line: for the protection set (PS) of the first line (L1), the VMT1 transformer is connected to the buses of line L2, and VMT2 for the K32 set, respectively, to the buses of line L1. When a fault occurs, for example, on line L1, the protections of the K31 set trip the circuit breaker B1 of line L1 and the sectional switch SV, thereby reducing the voltage on VMT2 for the K32 set to practically zero. This situation leads to non-selective operation of the resistance relay of the K32 set and, as a result, to the disconnection of line L2. Possible blocking of the K32 set protections from the VMT is impossible due to the effect of the VMT only on the signal.

[0012] To prevent such situations, the proposed device has module 1 with three voltage relays, which is triggered when the voltage drops in all phases at once in accordance with the expression:

[0013]

[0014] where ν=A, B, C - values ​​of phase voltages at the input of the protection device; U уст.мин - the response value (setting) of the voltage relay, which can be selected based on the imbalances in the voltage circuits according to the expression

[0015]

[0016] A voltage drop in all phases can also be observed in the event of a close three-phase fault. In this case, the protection must be enabled and generate the appropriate response to the line circuit breakers. Therefore, the device includes the following features to identify symmetrical short circuits and differentiate them from loss-of-voltage circuit modes:

[0017] - a combined phase current relay that operates when there are currents in two or three phases of the line, the value of which is lower than the minimum short-circuit current in accordance with the expression:

[0018]

[0019] where ν=A, B, C - values ​​of phase currents at the input of the protection device;

[0020] I КЗ мин - estimated current of a three-phase (interphase) short circuit in minimum mode at the end of the line;

[0021] - change of emergency components of phase currents that do not exceed the maximum value of the switched load current:

[0022]

[0023] where ν=A, B, C emergency components of phase currents, calculated using the methods of method [2];

[0024] I нагр мак - the maximum value of the load current that may occur at the moment of switching the line or when turning on the traction load.

[0025] When the voltage circuits are lost, for example, due to disconnection of an adjacent line in the short-circuit mode in accordance with expression (1), module 1 is activated. In this case, all three voltage relays will operate; their output signals are fed to the logical element "AND" D1 of module 1 (Fig. 2), from the output of which the logical "1" signal is fed to the first input of the "AND" element D7 of module 13. At the same time, in the absence of a three-phase short circuit in the line in the network, from the outputs of modules 5 and 9, formed according to the expressions in accordance with formulas (2) and (3), to the other two inputs of the "AND" element D7 of module 13 due to the operation of combined current relays 6, 7, 8 and relays 10, 11, 12 of the emergency components and the receipt of logical "1" signals at the other inputs of the "AND" element D7, blocking of the protection resistance relay (signal 14) will occur, which will prevent non-selective disconnection of the protected line. Signal 14 of the blocking resistance relay through the “OR” element D8 of module 9 (Fig. 2) is simultaneously sent to the start of the AMTZ.In accordance with the regulatory documentation [1], the AMTS is also activated by a signal from the BNN (block 16), which can be triggered when the integrity of the secondary voltage circuits is compromised.

[0026] In the near three-phase short circuit mode, the voltage relays (blocks 2, 3, 4) may be triggered due to a drop in voltage at the device inputs, and as a result, a logical "1" signal will appear at the output of module 1. However, in this mode, the combined phase current relays (blocks 6, 7, 8) of module 5 will not be triggered, since the phase short circuit current values ν=A, B, C, as a rule, during a short circuit on lines with a voltage of 110-220 kV, the calculated minimum fault currents I will exceed КЗ мин,That is, the output of element D5 of module 5 will be a logical "0" signal. A similar picture will be observed for module 9, where blocks 10, 11, and 12 will not operate due to a significant increase in current during a three-phase short circuit. Thus, the inputs of logic element "AND" D7 of module 13, which generates the device's output signals, receive logical "0" levels, preventing the protection resistance relay from blocking.

[0027] In the swing or asynchronous mode, a decrease in network voltage is observed near the swing center, which can cause the voltage relay (blocks 2, 3, 4) to operate, as in the symmetrical short-circuit mode. At the same time, the phase currents reach their maximum absolute value, which will also lead to the operation of the combined phase current relays (blocks 6, 7, 8) of module 5. However, in this mode, blocks 10, 11, 12, which respond to emergency current components, will not operate. ν=A, B, C of module 9. In the swing mode, at the output of the emergency component filter, only a minor amount of imbalance is observed, caused by a deviation in the network frequency, which does not exceed 3% of the nominal current in the permissible range of operating frequencies of 45÷55 Hz [2].

[0028] Table 1 shows a summary of the operating results of the proposed protection device for a walk-through traction substation, where the logical unit “1” indicates the operation of the module, the logical zero “0” indicates its non-operation, and the designation “1 / 0” means a different state of the module depending on the current value in the mode under consideration.

[0029]

[0030] Thus, according to the principle of its operation, the proposed protection device for a pass-through traction substation allows preventing non-selective disconnection of the controlled line in the event of loss of voltage circuits.

[0031] Sources of information

[0032] 1. Order of the Ministry of Energy of the Russian Federation dated 13.02.2019 No. 101 ''On approval of requirements for equipping power transmission lines and equipment of electric power facilities of 110 kV and higher with relay protection and automation devices and complexes, as well as the operating principles of relay protection and automation devices and complexes''.

[0033] 2. Patent 2035815 Russian Federation, IPC N 02 N 3 / 38. Method for isolating the emergency component of short-circuit current / Yu. Ya. Lyamets, V. A. Efremov, V. A. Ilyin. Published 20.05.1995.

Claims

A power transmission line protection device in the external power supply network of a through traction substation, characterized in that in order to disconnect the line from the protection upon loss of voltage circuits, an emergency overcurrent protection is started, distinguished in that in order to ensure selectivity of the protection action in the adjacent line disconnection mode, a module of three phase minimum voltage relays, combined on a logical element according to the "AND" circuit, the output signal of which is fed to the first input of the logical element "AND" of the output signal generation module, a module of a combined relay of three phase currents, the outputs of which are fed to a majority element, and its output acts on the second input of the logical element "AND" of the output signal generation module, and a module of emergency components of three phase currents, combined according to the logical circuit "AND", the output signal of which is connected to the third input of the logical element "AND" of the output signal generation module, are introduced into the protection,the output signal of which blocks the protection resistance relay and, together with the external blocking signal in case of voltage circuit faults, starts the emergency overcurrent protection relay.

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