RU2007006C1 - Device for protection of transformer connected to power line via isolating switch - Google Patents

Abstract

FIELD: electrical engineering. SUBSTANCE: device for protection of transformer connected to power line via isolating switch makes it possible to prevent additional intensive flux of hazardous current effects on power equipment and to avoid deep drop of voltage at users with fast and selective localization of emergency connections. EFFECT: increased operational reliability of power line. 6 dwg

Description

 The invention relates to electrical engineering, and in particular to accident protection circuits performing automatic switching in case of unacceptable deviations from the normal operating parameters of currents and voltages in the network and in the switchgear elements.

 Known switching circuits of substations 110.. . 220 kV on the branches of the supply lines, performed without switches on the higher voltage (VN) side of the step-down transformers (Kozhin A.N., Rubinchik V.A. Relay protection of lines with branches. M.: Energy, 1967). In cases of transformer damage or redundancy of circuit breakers on the low voltage side, a signal is issued for switching by a short circuit on the HV side of the artificial short circuit (ICZ) branch. The IKZ current is fixed by the relay protection of the supply line and is switched off by a linear switch. In a dead time, the branch is disconnected by a separator from the supply line, which can again be turned on under voltage.

 In conditions of intensive development of networks and an increase in levels of short circuit currents (SC), such circuits have a number of significant drawbacks. IKZ cause dangerous operating conditions for linear circuit breakers of the supply lines, classified according to GOST 687-78 as the mode of disconnection of unremoved faults or the "kilometric" effect. Deep voltage rises during ICZ can cause a disturbance in the stability of the motor load at neighboring substations and, as a result, long-term disturbances in technological processes at industrial enterprises. The shock effects of ICZ currents lead to a loss of mechanical (radial and axial) resistance of the turns of the windings of power transformers and autotransformers of the power substations. In areas with high soil resistivity with deaf ICZ, it is difficult to ensure the required reliability and safety of grounding devices.

 A device is known for protecting a transformer operating without a switch on the HV side (ed. St. USSR N 917248, class N 02 N 3/08, H 02 H 7/04, 1982). In the device for limiting ICZ currents, a non-linear resistor is included in the circuit of the switching device (or short-circuit), and the line protection units are made responsive to harmonic components of the ICZ current.

 The disadvantages of this device include the following. Firstly, the supply lines must be equipped with special protections, the setting of which depends on the non-linear characteristics of the resistors. However, such characteristics are not given. Known betel resistors for energy purposes do not possess nonlinearity. Secondly, it is necessary to justify the reliability of the resistors in the ICZ mode by demonstrating their resource bandwidth, depending on the duration of the ICZ, the number of such switching and changing due to the non-linearity of the current effect on them. Thus, the device cannot be practically implemented.

 A device is known that contains a betel resistor connected in series with a short circuit, and a special detecting unit that provides quick disconnection of the connection with a reduced ICZ current (ed. St. USSR N 1032515, class N 02 N 7/04, 1983).

 The disadvantages of this device include the following.

Firstly, it is necessary to develop non-standard high-speed and selective protection of the supply line, which is carried out on a wide elemental base, including current and voltage sensors on peak transformers of special manufacture, thyristors, zener diodes, polarized relays, etc. Protection has a rather complex circuit that requires special settings. Own time circuit breakers 110.. . 220 kV is 0.06. . . 0.1 s This means that the duration of the IHC when the main protection stage is turned off is estimated at 0.08. . . 0.15 s Taking into account the redundancy of the failure of the main protection or the cascade shutdown mode (for lines with two-way power supply), the duration of the CIP reaches 0.3-0.5 s. This means that the speed of protection does not determine the minimum duration of the through current through the current-limiting resistor and is not a decisive factor in ensuring the operability of the device. Selectivity protection, constructed on the principles of phase comparison of vectors of voltage and current in a narrow range of angles ^of 1-4, a number of schemes (e.g., dual feed circuits) is not provided. In such schemes, blocking the output signal to trip the circuit breakers with standard directional protection is required.

Secondly, to ensure reliable operation of the device, a reasonable choice of the number and circuit of the inclusion of resistors in the short-circuit circuit is necessary. The number of resistors and their connection diagram make up the betel resistor installation (BRU). BRU should be counted on multiple tripping over the service life of 10.. . 15 years with a through-current duration of 0.3. . . 0.5 s and close to the nominal phase U _f voltage on the installation. The lack of methods for choosing the value of current-limiting resistance and calculating the resource-bandwidth of the switchgear is a significant drawback of the device.

 In addition, the wiring diagram in the phase-short-circuit-resistor-ground device does not provide a limitation of the ICR current due to shunting of the resistor after turning on the short-circuit via the short-circuit contact control rod or through the low-voltage insulation of the short-circuit base.

 Closest to the claimed one is a device (ed. St. USSR N 1700624) for protecting a transformer connected to a power line through a separator containing a transformer protection unit, the output of which is connected to short-circuit connecting circuits connected in series with betel resistors assembled in an installation of m parallel branches along K of series-connected resistors in each branch between the HV terminals of the transformer and the ground, a detection unit, including current and voltage transformers, zero current relay of the first sequence with a closing contact included in the neutral wire of the secondary windings of the current transformer, the first active power relay, the windings of which are connected to the secondary windings of the current and voltage transformers of the first phase, which includes a short circuit with a resistor installation, and the closing contact of the active power relay is connected to the first the output of the alarm unit, the output of which is connected to the actuating element, the output of which is designed to connect to the circuit breaker tripping circuit, source of operational current.

 The disadvantages of this device are related to the difficulty of its practical implementation in an extensive network with several soldering on short-circuiting, as well as on substations with more than one transformer, for example, two-transformer substations. Currently, there is a tendency to increase the number of transformers at substations to three (Tsirel Y. A. On the feasibility of using three-transformer substations. / El. Stations, 1988, No. 6). In such networks, where several connections must be equipped with current-limiting switchgear, their resistance should be chosen of various sizes to ensure the required selectivity for switching off the ICZ. Moreover, for each installation, an individual selection of component parts is required. The detecting block of relay protection of the supply lines also requires additional detuning and interlocking of the circuits for fixing the IKZ through the switchgear at different connections, which reduces the reliability of its operation.

 The aim of the invention is to create a unified reliable device that is more efficient when used in networks of various structures at several connections, for example, at two- or three-transformer substations, on solders from double-circuit power lines (Fig. 1, 2, 3) without increasing the complexity of the calculation work and operational costs.

The unification of the device and increasing the efficiency of its use are as follows. In providing for various connections a constant resistance value R _BRU installation. At the same time, when selecting component resistors, the complexity of calculating their resource bandwidth, the electrical circuitry in the installation, and the structural and layout parameters of the switchgear is reduced. When setting up the relay protection detecting unit, the calculations of the relay settings fixing the ICZ through the switchgear are reduced.

 In the development of a switching circuit for shielded transformers of fixed transformers, fixed in phases and lines (Figs. 2 and 3), which determines the possibility of developing a reliable detection unit that provides the required sensitivity and selectivity of operation during ECZ through the switchgear on several connections.

 In the application of one switchgear for two short-circuiting on a two-transformer substation (Fig. 2) or three short-circuiting on a three-transformer substation (Fig. 3). This embodiment of the installation reduces by 30-50% the number of component resistors in the first circuit and by 50-70% in the second. At the same time, the complexity of construction and installation work is significantly reduced, the design binding of the switchgear on switchgear, their testing and commissioning are facilitated.

 The goal is achieved in a device for protecting a transformer connected to a power line through a separator containing a transformer protection unit, the output of which is connected to short-circuit circuits connected in series with betel resistors assembled into an installation of m parallel branches along K series resistors in each branch between leads of the high voltage transformer and ground, detection unit, including current and voltage transformers, zero sequence current relay with make contact, incl. is the neutral wire of the secondary windings of the current transformer, the first relay of active power, the windings of which are connected to the secondary windings of the current and voltage transformers of the first phase, and its make contact is connected to the first output of the alarm unit, the output of which is connected to the actuator, the output of which is designed to connect to the circuit breaker tripping circuits, the operating current source, in that a three-phase current relay with an opening contact is inserted into it, two active power relays with closing contacts acts, a repeater relay of three active power relays with a closing contact, while the three-phase current relay is connected in series with the current windings of three active power relays, the voltage windings of the second and third active power relays are connected to the secondary windings of the second and third phases of the voltage transformer, to the first the pole of the operating current source is connected in series with the NO contact of the zero-sequence current relay and the NO contact of the three-phase current relay, the second output via of the last through the make contact of the relay-repeater of three active power relays is connected to the input of the actuating element and connected to the first outputs of the make contacts of the first, second and third active power relays, the second conclusions of the make contacts of the second and third active power relays are connected to the second and third inputs, respectively the alarm unit and together with the second terminal of the make contact of the first active power relay to the first terminal of the relay repeater coil of the active relay the second output of which and the output of the signaling unit are connected to the second pole of the operating current source, with the first output of the resistor installation designed to be connected to ground, the second output to the movable contact of the short circuits of the two-transformer substation, the fixed contacts of which are designed to connect two parallel lines to the same phases at one substation, but to opposite phases with respect to another substation.

 In FIG. 1 shows a diagram of the proposed device using an example of a network containing two-transformer substations PS1 from the parallel parallel lines L1 and L2. . . PS3 connected via separators. The device contains BRU1, which is connected to the movable contacts of short-circuiting devices 2 and 3 and can therefore be introduced sequentially into the circuit of each of the short-circuiting devices when they are switched by the signal of protection 4 and 5 of the corresponding transformers 6 and 7. In the arrangement 8 installed on PS1 in this way, short-circuiting devices 2 and 3 connected to phases A of the corresponding lines L1 and L2; on PS2 - to phases B; on PS3 - to phases C. The power of the detection unit 9 for alternating voltage is provided from measuring transformers 10 of current and 11 voltage, for direct current from a source of operating current. The detecting unit 9 in the operating current circuit contains a detuning unit 12, a selective unit 13, an alarm unit 14, and an actuating element 15, the output of which is intended to provide a signal in the trip circuit of the circuit breaker 16 of the supply line L1 or L2 when an ICZ is detected through the switchgear at the appropriate connection.

 In FIG. Figures 2 and 3 show the circuits of fixed phase and switching lines of the ICZ through the switchgear, respectively, at two and three transformer substations; in FIG. 4 is a diagram of the secondary current circuits with a three-phase current relay 17, a current relay 18 of the zero sequence and phase current windings of the relay 19, 20, 21 active power; in FIG. 5 is a diagram of the secondary power circuits of the voltage windings of the corresponding phase active power relay; in FIG. 6 is a diagram of the operational current circuit of the detection unit 9 of the line relay protection with highlighting the characteristic functional blocks: the detuning unit 12, the selective unit 13 and the signaling unit 14.

 The device operates as follows.

 When the short circuit 2 or 3 is triggered by the protection signal of the corresponding transformer 6 or 7, the ICZ current limited by the BRU 1 and the ICZ location are fixed by the detection protection unit 9, which gives a signal to trip the switch 16 of the corresponding line L1 or L2.

 When switching ICZ through the BRU, the detection unit 9 is triggered by the closing contacts 22 of the zero-sequence current relay 18. This relay also allows not to detune the unit from the self-starting currents of powerful electric motors. If necessary, the start of the detection unit can be provided by the closing contacts of the output relays of the directional current protection of the zero sequence. Next, the signal is fed to the disconnecting contacts 23 of the relay 17, which allows you to block the start at various short circuits, except ICZ, through the switchgear. From the detuning unit, the signal enters the input of the selective unit 13.

The selective unit, according to the characteristic value of the measured power, corresponding to the value of the selected R _switchgear , contacts 24, 25, 26 of the corresponding active power relay 19, 20, 21, provides the selection of the switching signal ICZ through the switchgear and the winding of the relay-repeater 27 of the tripping of three active power relays, which, through its contacts 28, ensures the passage of the signal to the actuator, protecting the line, and then to turn off the switch 16. The selected signal also goes to the signaling unit 14 and provides the relay 29, 30, 31, Chains are constructed by which positioning ECI through BRU.

 For simpler dead-end circuits, unit 13 can be simplified by using phase current relays instead of active power relays. Moreover, in the secondary connection circuits of the measuring transformers 10 and 11 (Fig. 4 and 5), only current circuits remain (Fig. 4).

The circuit diagram of the operational current (Fig. 6) remains the same, where now contacts 24, 25, 26 mean contacts of phase current relays. Their response setpoint is selected according to condition I _c.z.1 = K _n ˙ I _K ^(s) (1) where K _n = 1.3 is the reliability coefficient;
I _K ^(s) is the phase current at the point of protection at a three-phase short circuit behind the transformer of the soldering substation having the smallest resistance X _T , taking into account voltage regulation.

 Detuning from the maximum self-starting current of electric motors can be omitted if you use the blocking contacts 22 of the relay 18, which does not work during self-starting.

The sensitivity coefficient of current relays 19, 20, 21 is defined as K _r = I _f.ikz / I _sz.1 ≥1.5, (2) where I _f.ikkz is the phase current at the protection site during ECZ through the switchgear in the maximum network operation mode.

получают R_БРУ= X_т/K_н·K_r≃ X_т/2 (5)
Необходимо отметить, что выражения (4) и (5) справедливы только для тупиковых ВЛ. Таким образом, область применения фазных токовых реле ограничена, тем более что на линиях с двухсторонним питанием отстроиться от внешних КЗ не представляется возможным.Taking X _t >> X _s and R _BRU >> X _s, where X _s is the equivalent resistance of the supply system, and solving equations (1) and (2) together with the expressions

get R _BRU = X _t / K _n · K _r ≃ X _t / 2 (5)
It should be noted that expressions (4) and (5) are valid only for dead-end VL. Thus, the scope of phase current relays is limited, especially since on lines with two-way power supply it is not possible to detach from external faults.

The setting of the three-phase relay 17 is selected equal
I _cz.17 = K _H17 ˙I _cz.1 , where K _n17 = 1.3 is the reliability coefficient.

 Relay 17 eliminates false triggering of detecting unit 9 for all types of short circuit on the line, except for ICZ, through the switchgear to the ground. The relay is used in block 12 detuning detection unit.

 Thus, the proposed device, having unified properties and a reliable detection unit, can be widely used in substations that require restrictions on ICZ due to the intensive development of networks at the present stage. (56) Tsirel, Y. A. On the feasibility of using three-transformer substations. Power stations. 1988, No. 6.

 USSR author's certificate N 1700624, cl. H 02 H 7/04, 1988.

Claims (1)

 A DEVICE FOR PROTECTING A TRANSFORMER CONNECTED TO A ELECTRIC TRANSMISSION LINE THROUGH A SEPARATOR, comprising a transformer protection unit, the output of which is connected to a short-circuit switching circuit connected in series with betel resistors assembled in an installation of m parallel voltage branches connected to higher voltage branches connected to K parallel higher voltage branches connected in series to each other transformer and ground, detecting unit, including current and voltage transformers, zero sequence current relay with make contact ohm, included in the neutral wire of the current transformer, the first active power relay, the windings of which are connected to the secondary windings of the current and voltage transformers of the first phase, and its make contact is connected to the first output of the alarm unit, the output of which is connected to the actuator, the output of which is designed to connect to the circuit breaker tripping circuit of the line, an operating current source, characterized in that, in order to increase reliability when using the device on solder two-transformer substations A total of not more than three, powered from parallel lines, additionally introduced a three-phase current relay with a normally open contact, two active power relays with a make contact, a repeater relay of three active power relays with a make contact, and a three-phase current relay is connected in series with current windings of three active power relays, voltage windings of the second and third active power relays are connected to the secondary windings of the second and third phases of the voltage transformer, to the first pole source and the operating current is connected in series with the NO contact of the zero-sequence current relay and the NC contact of the three-phase current relay, the second terminal of the latter is connected to one of the inputs of the actuating element and to the first conclusions of the NO contacts of the first, second and third active power relay, the second terminals of the make contacts of the second and third active power relays are connected to the second and third, respectively the inputs of the alarm unit and together with the second output of the make contact of the first active power relay are connected to the first output of the coil of the relay-relay of the active power relay, the second output of which and the output of the alarm unit are connected to the second pole of the operating current source, the first output of the resistor installation with ground, the other conclusion is with the movable contact of the short-circuiting switches of the two-transformer substation, the fixed contacts of which are designed to connect to one named phases of two parallel lines of one substation, but to opposite phases with respect to another substation.

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