RU2521616C1 - Relay protection of csr power winding - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: single-system differential current protection of a reactor power winding includes two insaturable current sensors connected between two outputs of the power winding neutral point and a point of their connection to the earthing network, at that a current relay (a measuring element of the protection) is activated by the current difference of the above sensors upon separation of the main component of the first harmonic by filters, which passes through each current sensor and applies when the preset value is exceeded for a shutdown of the reactor switch without time delay.

EFFECT: increase in the response speed and sensitivity of the relay protection.

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Description

The invention relates to the field of electrical engineering and electric power industry, in particular to relay protection, and can be used for high-speed protection of a network winding controlled by magnetization of shunt reactors installed in high voltage electric networks. The technical result consists in increasing speed, sensitivity and simplifying the protection of the controlled reactor from internal short circuits in the primary winding connected to the network.

In accordance with the requirements of the Electrical Installation Rules (PUE), transformers and reactors for high voltage networks with a capacity of more than 6.3 MVA must have high-speed (differential current) protection against internal short circuits in the windings - interphase, coil and single-phase to ground (magnetic circuit).

For triple winding controlled shunt reactors (CSR), the primary network winding (CO) is protected by a set of differential current protections (longitudinal and transverse) with their redundancy with maximum current protections (MTZ) on the supply side and on the side of the compensation winding (KO) of low voltage [1]. In combination with gas protection, this fully complies with the requirements of the PUE and the usual set of protection for uncontrolled shunt reactors (SHR) of overhead lines (VL) of extra-high voltage (IH) 330-750 kV and higher.

Double winding controlled by magnetization reactors with a voltage of 35 ... 220 kV of relatively low power (10 ... 50 MVA) do not have similar electrical protections with absolute selectivity (without time delay), since the built-in current transformers (CTs) do not have corresponding measuring sensors in the CO branches from the neutral side. This is due to the fact that the sections of the primary CO winding and the secondary winding of the op-amp of these reactors are located coaxially on the rods of the magnetic circuit and have electromagnetic coupling, which in turn leads to the appearance of a constant component of the rectified bias current in the CO branches in transient modes of power gain or discharge [1 ]. Therefore, even if electromagnetic CTs were installed in these branches of the CO, they could not function properly due to the saturation of the CO current components with constant components.

Some solutions to this problem are given in [1], in particular, the installation of built-in electromagnetic CTs with special circuits for connecting the CO branches or the transition to unsaturated magnetoelectric and optoelectronic built-in CTs. However, to date, double-winding CSRs with a capacity of 10, 25, 32 MVA have been produced and are being produced by the plant without CT in the CO phases from the neutral side, which leads to the absence of differential protection against interphase and coil short circuits. and directly contradicts the PUE.

Closest to the proposed one is the solution described in [1] to use a remote unsaturated current sensor with its connection to the half-neutrals of the network winding displayed on the reactor tank lid. This allows you to apply the well-known single-system transverse current differential protection, which is used in powerful generators with parallel branches in the stator winding and connected between the neutrals of the two "stars" of the stator winding.

However, such protection must be rebuilt (or braking or blocking algorithms should be applied) from external single-phase short circuits. from the supply side, as well as from the asymmetry of the mains voltage and switching switching modes or reclosure. This leads, on the one hand, to an increase in the current setpoint and to a decrease in sensitivity, on the other hand, to an actual increase in the response time up to the time of operation of the backup transformer substation on the supply side (when the protection is tuned in time) and, on the third, to a significant complication of the algorithms protection with an increase in the likelihood of its malfunction, and therefore to a decrease in reliability.

The aim of the invention is to increase the speed and sensitivity of protection while simplifying its algorithm and increasing reliability. This goal is achieved by the fact that the relay protection device of the network winding controlled by the magnetization of the shunt reactor from short circuits, using transverse differential current protection and a current sensor at the neutral terminals of the winding, differs in that in order to increase speed and sensitivity it contains two unsaturated current sensors connected between the two terminals of the neutral of the network winding and their connection to the ground loop, while the current relay - measuring protective device - is switched on p the variability of the currents of these sensors after the filters highlight the main component of the first harmonic flowing through each current sensor.

If the specified difference in currents exceeds the specified setting, the current protection relay acts to trip the reactor switch without delay. The current response parameter (current setting) is determined by the imbalance of current sensors with identical parameters and design, as well as high measurement accuracy and a large permissible multiplicity of the measured current. The structural imbalance of the phase branches of the CO reactor also does not exceed 1%. Inrush current surges and pass-through currents for such CSRs - no more than 3 times the nominal values in the СО phases - they are practically absent in the neutral neutral terminals, therefore the setting of the current protection relay can be minimal (less than 0.1 pu or 5 ... 7% of the nominal values of current СО), which provides a sufficiently high sensitivity to the most probable winding circuit faults.

Figure 1. Composition and connection diagram of the protection device:

1 - the electromagnetic part of the CSR,

2 - network winding of the reactor,

3 - external current sensors,

4 - relay protection terminal with software or hardware filtering of input signals.

The principle of operation and advantages of the inventive device are illustrated in figure 1, where in the oil-filled tank of the electromagnetic part 1 of the reactor is located connected to the "star with a grounded neutral" network winding 2, to the terminals of which are connected unsaturated (for example, Hall sensors) current sensors 3, the secondary output signals of which are supplied to the relay protection terminal 4, where after filtering and separating the first harmonic, the difference of these currents is compared in the measuring body (current relay) with the setpoint. If the obtained current difference in half-neutrals of the network winding exceeds the setpoint, a signal is sent to shut down the reactor without delay.

With short-circuit short circuits external to the reactor, including single-phase ones, on the supply side, the difference in currents in half-neutrals is zero (or these currents simply do not exist with short-circuit shorts without ground), so protection is not required or time delay (blocking) is required. The same applies to switching modes or to modes associated with short-term or long-term asymmetry of the mains voltage, since in these modes (and any other ones not related to the internal asymmetry of the CO winding itself) the currents in the sensors will be equal, and their difference in the protection relay will be zero.

This ensures the absence of a time delay (speed) and increased sensitivity (there is no need to detach from the zero sequence currents, including for reasons of asymmetry of the supply voltage). The lack of sophisticated braking or locking algorithms simplifies protection and increases its reliability compared to the prototype.

The presence of two relatively inexpensive current sensors instead of one practically does not complicate and does not increase the cost of the device, providing a fundamentally different connection of protection, which solves all of the prototype problems listed above - the need for detuning from external short-circuit, switching on and automatic reclosure, asymmetries of the mains voltage, etc. P. due to the introduction of time delay and complication of algorithms (braking or blocking by symmetrical components). Thus, the task is achieved to increase the speed, sensitivity and reliability of the protection device WITH CSR.

It should be noted that the proposed protection is valid for all types of internal short circuits in the CO winding, except for symmetrical short-circuit If the prototype with the connection of one current sensor between the neutrals, it was necessary to rebuild or block at short circuit to the ground from the supply side, which led to the inoperability of the protection and with internal short circuit on the magnetic circuit, then the proposed solution is equally successful and with higher sensitivity acts with coil short circuits, with internal single-phase short circuits to a tank or magnetic circuit, as well as for interphase unbalanced short circuits with the closure of a different number of turns of different phases.

Figure 2. The calculated oscillograms of currents in the network winding of the reactor and in current sensors.

On the oscillograms of external (a) and internal (b) short circuits From top to bottom, the same phenomena of currents of the three phases of CO, the current in the grounding branch of CO and two current sensors in the semi-neutrals of CO are shown.

The scale of the currents is indicated in the upper left corner of each phenomenon - all 0.5 kA on the left; 1 and 5 kA - on the right, where the supply currents from the system are much greater.

The values of the neutral sensor currents in the two lower oscillograms are equal to the left (their difference in the relay is zero) and are substantially not equal to the right with an internal short circuit

The indicated modes and the corresponding characteristics of the proposed CO protection were modeled and tested in the specialized NRAST program, which has been successfully used for many years for research on controlled reactors and transformers. Figure 2 shows the calculated waveforms of the currents of the phases of the CO, the currents in the half-neutrals of the CO of the reactor (through current sensors) and the total current in the common grounding circuit of the CO in the external (a) and internal (b) single-phase earth faults (to the magnetic circuit). They illustrate the described principle of the protection - with external short-circuit or external asymmetry, the currents in the sensors are equal, and their difference in the relay is zero or an insignificant unbalance current. With internal coil short circuit or short to the magnetic circuit the periodic component of the short-circuit current It is present mainly in the half-neutral connected with the damaged CO branch, the current difference in the relay is maximum and causes its operation.

The number of CSRs for networks with an insulated neutral voltage of 6 ... 35 kV is still insignificant - out of 80 manufactured by magnetization-controlled reactors 35 ... 500 kV, only 3 reactors 25 MVA, 35 kV are in operation. The neutral of their network winding is not grounded, so the problem of detuning from external single-phase short circuits and there is no network asymmetry, and instead of two current sensors, one can be used.

In principle, the claimed protection device can be used for three-winding CSR of higher voltage and power. In this case, instead of the three-system phase-by-phase transverse differential protection of the CO, a simpler and more sensitive one will be used, since a typical phase-phase differential protection must be detached from phase inrush currents during switching and external short-circuit protection. taking into account the large errors of the built-in electromagnetic current transformers (practically the transverse protection setting of the network winding of the reactors is 0.2 ... 0.3 pu, i.e. 2-3 times more than in the claimed device).

Thus, the present invention is aimed at improving the performance and sensitivity of the relay protection of the network winding controlled by magnetization of shunt reactors, and its technical result is achieved by changing the number of primary current sensors, the circuit diagram of their inclusion and the method of connecting a measuring protective device to them.

Literature

1. A.G. Dolgopolov. Magnetization-controlled shunt reactors: Composition and design features of relay protection. - Vestnik MPEI, No. 5, 2012

Claims (1)

Relay protection device of the network winding of the shunt reactor controlled by magnetization against short circuits using transverse differential current protection and a current sensor at the neutral terminals of the winding, characterized in that, in order to increase speed and sensitivity, it contains two unsaturated current sensors connected between two neutral terminals network windings and their connection to the ground loop, while the current relay - measuring protection device - is turned on by the difference in currents of the indicated dates Ikov after separation filters main component of the first harmonic of the current flowing through each sensor, and operates above a given setpoint reactor shutdown switch without time delay.

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