SU1737615A1 - Device for compensation of emf of faulty phase under single- phase short-circuits in network with ungrounded neutral - Google Patents

Abstract

Use: Prevent the flow of current through the point of closure caused by a voltage drop due to a large load current. The essence of the invention: when a fault occurs in the network, the block 13 for recognizing the faulty phase issues a signal to the block 4 of switching elements for closing the corresponding pair of switching elements 5-10. If the circuit has the character of a metallic, the symmetric thyristor discharge 12 is locked and the voltage drop from the load current cannot cause any additional currents in the location of the circuit. 2 Il. VI with V4 Os (I Figure 1

Description

The invention relates to electric power industry and can be used in three-phase distribution networks with a voltage of 6-35 kV to completely suppress other processes during single-phase earth faults (APS) and prevent the development of this type of damage in more severe accidents, such as phase-to-phase short circuits.

A device is known for compensating the total current of a single-phase circuit capable of completely suppressing arc processes at the APS site. In addition to a plunger DGR connected to a neutral network with an auto-tuning device for compensating capacitive currents connected to the network via a network voltage sensor, the active component is in the form of a single-phase dependent inverter connected in succession with the DGR. The inverter is powered by direct current from the controlled rectifier, to the control input of which is connected the output of the automatic compensation of the compensation of the active component, also connected to the network via a network voltage sensor. The output of the network voltage sensor, in addition, is fed to the inputs of the network mode recognition unit and the damaged phase recognition unit, the outputs of which are connected to the additional inputs of auto-regulators for compensation of capacitive and active components of OZNZ currents.

The drawback of the device is the low speed of the plunger DGR, which is manifested in the resumption of arc breakdowns at the HSS for some time in the event that a detuning of compensation occurred in the HSS mode. In addition, the device is quite cumbersome.

In devices with automatic shunting of the damaged phase, the extinguishing of the arc process in the site of an AOR occurs at the moment of the imposition of a shunt. Such devices contain three earthing single-phase switches connected to the mains phases, a network voltage sensor, a damaged phase recognition unit and a network operating mode recognition unit, as well as a switch control unit connected via its damaged phase detection unit. with single-phase switches.

The drawbacks of these devices are high speed requirements, since the delay in imposing a shunt over the first period of the network frequency drastically reduces the probability of self-removal of the HSS. At the same time, the reduction of the time spent on recognition of the damaged phase inevitably reduces the reliability of the specified recognition. The incorrect recognition of the damaged phase leads to a short circuit with the flow of short-circuit currents. through the grounding switch and OZNZ place,

which contributes to the further development of the accident and, in addition, can lead to a disconnection of electricity consumers and to the failure of the device.

Similar defects have compensation devices for the electromotive force of the damaged phase using a single-phase (compensating) transformer connected between the mains neutral and the ground. In addition to the specified transformer, such devices also include a network voltage sensor connected to the network, the output of which is connected to the input of the damaged phase recognition unit that controls the switching elements, which, depending on the damaged phase, are connected to the primary (low-voltage) winding of the transformer current phase of a three-phase low-voltage source of emf (for example, a transformer) phased with emf

5 network power sources,

A disadvantage inherent only in the devices under consideration and also resulting from low-resistivity is the flow through the point of current closure,

0 caused by imperfect transformers. To eliminate this (last) disadvantage, it is proposed to add to the EMF of a low-voltage source additional automatically-adjustable EMF, compensating for the voltage drops on the internal resistances of the transformers, which complicates the design and reduces its reliability.

Lack of class

The device (high speed requirements, including the speed of the damaged phase recognition unit) is eliminated by combining the compensation of the electromotive force of the damaged phase with a single-phase compensating transformer with auto-compensation of capacitive currents using an arc-suppressing reactor.

Closest to the proposed

0 is a device containing a connecting step-down transformer connected to the network, between the neutral terminal of which and the earth is connected to the DGR, provided with an additional winding. WITH

5, by said additional winding DGR, a block of switching elements consisting of three parallel-connected branches, each of which is formed by two series-connected switching elements (triacs), is connected.

The connection points of these branches form the output poles of the switching unit, and the three connection points of the switching elements in the branches x connect the terminals of the three phases of the secondary winding of the connecting transformer. The output poles of the switching elements block are connected to the secondary winding of the GDR (via a mating transformer, the presence of which is not necessary with the corresponding transformation ratio of the connecting transformer or GHF).

The prototype device also contains a network voltage sensor connected to the network (for example, a three-phase measuring voltage transformer), the output of which is connected to the input of the damaged phase recognition unit and to the first input of the compensation autotuning unit, the second input of which is connected to the output of the damaged phase recognition unit . The output of the faulty phase recognition unit is also fed to the control input of the switching elements block so that when any phase is recognized as damages in 03 NC mode, a pair of switching elements in the specified block connects the secondary winding of the connecting transformer to the auxiliary winding DGR , the voltage at which is in phase with the EMF of the damaged phase.

The presence of additional winding on the DGR in the device-prototype gives the DGR additional functions of the compensating transformer of the considered analogues. Therefore, the connection of the corresponding phase of the secondary winding of the connecting transformer to the DGR additional winding leads to the fact that the EMF transformed into the main winding of the DGR substantially compensates the EMF of the damaged phase, which, in turn, leads to a significant decrease in the voltage of the damaged phase and to suppression arc process in the place OZNZ. The output of the compensation self-tuning unit is connected to the input of the DGR actuator (for example, a plunger drive, in the case of a plunger type DGR). The thus formed closed-loop capacitive current auto-tuning system OZNZ supports the resonant tuning of the network zero-sequence contour (KNPS).

For the prototype device, the requirements for the speed of recognition of the damaged phase are significantly reduced, since the resonant tuning of the CNPC leads to the fact that after the first arc sample

at the site of the open hearth, the free oscillations excited by this breakdown in the end of the circuit for a sufficiently long time (up to 10–20 periods) compensate for the damaged phase of the damaged phase, resulting in a slow increase in the voltage on the damaged phase (and as a result, a high percentage of self-removal of the aperiodix). The time allowed for recognition of a damaged phase allows for this operation to be performed with sufficient reliability. After completing the operation of recognizing the faulty phase and activating the corresponding switching elements in

5 further, the EMF of the damaged phase is compensated by the EMF transformed from the additional winding of the GDR.

The main drawback of the prototype device is the low resistance of the junction connecting transformer - switching element unit - compensating transformer based on DGR - OZNZ place - grounding circuit (low resistance). This leads to the flow of a current in the indicated low-resistance circuit caused by a drop in the voltage of the outflow load on the damaged phase of the line from the installation site of the connecting transformer to the OZNZ,

0 When metal OZNZ this current can be many times higher than the current 03 FROM. The occurrence of such additional currents drastically reduces the efficiency of the device, increases the likelihood of heat development, phase-to-phase faults near the site of an AHCC, and electric shock. Attempts to eliminate this disadvantage by introducing additional automatically controlled compensating voltages aimed at compensating for the drop in voltage from the load current, just as is done in these devices to compensate for the non-ideality of the compensating transformer, encounter the following difficulties.

Firstly, it is important to obtain information about the voltage drop on the indicated section of the line, since the distance to the APS site is unknown, and

This voltage supply, in general, is difficult to distinguish from the voltage drop at the APS site, since the phase-to-earth resistance at the APS site and capacitive to networks are also usually unknown.

5 Secondly, it is the difficulty of implementing regulated EMF sources for such purposes. In addition, low impedance determines the criticality of the device of the prototype to the accuracy of compensation of the EMF of the damaged phase by the voltage applied to the neutral,

since even insignificant differences, caused, for example, by the inaccuracy of the installation of the transformation ratios or the imperfection of the compensating transformer (on the basis of the DGR) and the connecting transformer, lead to very significant currents through the fault point in the AHSS modes.

The aim of the invention is to increase the efficiency in the operation of the device and to improve the safety conditions for metal single-phase closures by preventing current flowing through the OPZS place due to a voltage drop (on the conductors of the damaged phase of the line section from the installation site to the single-phase closure) caused by current load.

This Znl is achieved by the fact that in a device containing a connecting step-down transformer connected to the network, between the neutral terminal of which and the ground is connected an arc-suppressing reactor equipped with an additional winding, a switching element unit connected by three inputs to the corresponding phases of the secondary winding of the connecting transformer, and the first output associated with the first output of the additional winding of the arc-suppressing reactor, the voltage sensor of the network, the output of which is connected to the input of the unit neither the damaged phase nor the first input of the compensation autotune unit, the output of which is connected to the input of the reactor executive, and the output of the damaged phase recognition unit is connected to the second input of the compensation autotune unit and the control input of the switching elements block between the second input of the switching elements block and the second output In addition, a symmetric thyristor arrester is connected to the coil of the arc-suppressing reactor.

When an additional coil of the GDR and a thyristor discharge is connected in series in the OZNZ network, a voltage common to the EMF of the damaged phase and equal in amplitude to the EMF of the damaged phase multiplied by the transformation ratio from the additional coil of the GDW to its main winding is applied. The thyristor switching voltage is calculated based on the maximum possible difference between the voltage of the connecting transformer and the OZNZ place (where the electromotive voltage of the damaged phase enters, the voltage drop on the network conductors from the load current, the voltage resistance of the primary winding of the connecting transformer) and the voltage between the output poles of the switching unit

elements (which includes the EMF of the damaged phase and the voltage drop in the connecting transformer), taking into account the transformation coefficient Kt between the coils of the GDH.

0 If a low-impedance (metal) OZNZ appeared in the network, then the voltage across the discharge equal to the specified voltage difference (taking into account the CT coefficient of the DGR transformation) will not exceed the voltage of the unlocking discharge. In this case, the network will only act as compensation for the capacitive current of the SHPZ, in the place of the closure iy there will be an active component

0 higher harmonics (which is not dangerous with a metal OZNZ due to the small resistance of the circuit and, consequently, a small amount of power allocated to it), and the voltage drop on the line

5 from the load current as well as the non-ideality of the transformers due to the locked state of the arrester will not be able to cause additional current through the OZNZ place. If an intermittent0 arc arrester occurs in the network, then as the free oscillations in the CPCC, due to arc breakdown, attenuate, the voltage on the thyristor voltage (which

5 with a locked discharger, approximately in proportion to the proportionality coefficient Kt to the voltage on the damaged phase). Since in the overwhelming majority of cases, the voltage of the breakdown gap is much greater than the voltage unlocked for the thyristor arrester (which, being reduced to the high side, i.e. being divided by the transformation coefficient Kt between windings

5 GHD, is usually the value of 300-500 V), the specified bit is triggered, connecting the secondary phase of the connecting transformer to the additional GD winding, resulting in a neutral neutral voltage bias voltage of approximately the phase.

As a result, the voltage on the damaged phase and the voltage on the thyristor arrester are reduced to almost zero, the arrester thyristors are locked and the process is repeated. Thus, the triacs of the thyristor arrester will lead to the maintenance of a voltage on the damaged phase that does not go beyond the limits of the voltage of its tripping, as a result of which the arc process in the OZNZ place will be suppressed. This in turn will lead to the exclusion of the possibility of further damage development. Minor current values through the place of a blind OZNZ, as well as the elimination of the arc process in the mode of intermittent arc OZNZ significantly improve the electrical safety conditions. In addition, the lack of triggering of the device in the presence of the OZNZ network indicates that there is a deaf OZZZ network. Thus, information appears on the nature of the PBLN in the network, which expands the functionality of the device.

Figure 1 shows an example of a functional concept of the proposed device; FIG. 2 is a circuit for replacing the network zero-sequence circuit (with the proposed device) at the APSN in phase C.

In Fig. 1, the following notation is adopted: a three-phase network 1 with an ungrounded neutral, with a phase EMF of the power source equal to ЕА (Т), Ee (t) and Ec (t), with capacitances between the phases of the network and ground equal to Сд, Sv and Ss. and with load resistors of the damaged line, equal to ZHA, ZHB and ZHG, through which phase load currents flow, equal to lHA (t), nv (t) and lHc (t); a connecting transformer 2 with an arc-suppressing reactor (DGR) 3 connected between the neutral of the connecting transformer and the ground and provided with an additional winding with a transformation ratio between the main and additional windings equal to KT; block 4 switching elements; switching elements 5-10, included in its composition; symmetric thyristor discharge 11c with a tripping voltage ± UoJ 12 voltage network sensor (DNS); a faulty phase recognition unit 13 controlling the switching elements 5-10 of the switching elements 4 of the switching elements; block 14 of the autotuning compensation (AN K), the output of which is connected to the input of the executive body 15 (PSI) of the extinguishing reactor 3.

In Fig. 2, the following symbols are accepted: the source of the 16 emf of phase C of the connecting transformer 2 (Ecn (t)), reduced to the main winding of the DGR 3; E cnW - KTEcn (t); 17 and 18 are the scattering inductance Llpn K Lpn and resistance R4i K iRn of the connecting transformer 2; 19 - equivalent to thyristor 11

(TR) with the operation voltage, reduced to the main winding of the DGR 3; 20 and 21 are the inductance Lp2 K t1p2 5 scattered and the active resistance R p2 K iRp2 of the additional winding DGR 3; 22 - inductance U of the magnetization circuit GGR 3; 23 and 24 - inductance Lpi and resistance Rpi respectively

0 main winding DGR 3; 25 - total capacitance C Cd + St + Cc between the phases of the network and the ground; 26 - EMF Ec (t) of the power source of the damaged phase of the network 1; 27 - source of EMF Enp (t), equal to the voltage drop

5 (-Enp (t) in Fig. 1) on the conductor of the damaged phase C (in the line section from the installation site of the device to the OZNZ location) from the current lHc (t) of the ZHC load (see fig, 1).

The device works as follows.

In normal network operation, the indicated mode is detected by the faulty phase recognition unit 13, for example, by a low amplitude value em of the voltage 5 (e) of the neutral displacement supplied to the RPF block 13 by the network voltage sensor 12. The signal about the damaged phase from the output of block 13 of the RPF to the input of block 4 of the switching elements in the normal mode is not received, as a result of which the switching elements 5-10 are open. The automatic compensation adjustment unit 14, by changing the inductance of the DGR 3, maintains the resonant state of the circuit of the zero-sequence network (CNPC).

When an OZNZ occurs (for example, in phase C in Fig. 1) the block 13 recognizes the damaged phase, determining the indicated mode, for example, by increasing the amplitude

0 volts of the voltage e (t) of the displacement of the neutral above a certain threshold (on the order of 0.15Et. Where Et is the amplitude of the phase EMF of the network) and recognizing the faulty phase, gives a signal to the block 4 of switching elements on

5 closure of the corresponding pair of switching elements 5-10. So, when OZNZ in phase A closes 1 elements 5 and 10, when OZNZ in phase B closes elements 8 and 9, and when OZNZ in phase C closes elements 6 and

0 7. In addition, information about the damaged phase is transmitted to the compensation auto-tuning unit 14 and it continues to maintain the CNPC resonance setting.

The processes occurring in the network after

5, the closures of the corresponding switching elements of the block 4 are conveniently considered using the replacement circuit of CNPC, shown in FIG. 2. At the same time, for definiteness, we assume that the OZNZ occurred in phase C, i.e. closed switching elements 6 and 7 (figure 1) and, therefore:

E cKt) -KTEc (t). (1)

If OZNZ in the network has the character of a metallic, i.e. Us (t) 0, then the equality e (t) - Ec (t) + Enp (t) holds.

As can be seen from the circuit shown in Fig. 2, with the smallness of the parameters Lpi and Rpi, the voltage U p (t) on the element 19 (TP). depicting a thyristor gamut 11, in the mode of a metal OZNZ approximately equal to the drop -Enpft) voltage on the conductors of the line from the load current, which is not enough to unlock the said discharge and therefore the latter is locked. The voltage drop -Enp (t) on the line from the load current when the discharge switch is closed cannot cause any additional

currents in place OZNZ. In terms of resonance1

setting of the KNPS {«and C yyyy-) through the meSU LQ

One hundred percent of the damage is only the active component of the current OZNZ (capacitive compensated by reactor 3, which corresponds to the inductance LO in figure 2) and higher harmonics. Owing to their relatively small size and low resistance of the SHA at the specified place, no significant power (and voltage) can be allocated. Therefore, OZNZ can not develop into a phase-to-phase circuit and, moreover, long-term operation of the network in this mode can not lead to fires or electrical injury.

If an intermittent arc OZNZ (at the moment of time to) occurs in the network, then the first arc breakdown initiates an oscillatory transient process with a frequency o) with () equal to the frequency from the network (since KNPS was previously tuned to resonance in normal mode network operation unit 14 auto-adjustment compensation). After the arc goes out (at the moment of time to + A, where A is a small value), the voltage e (t) of the neutral displacement is equal to

e (to + A) Ec (to + A) + + Enp (to + A) Ec (to + A). (2) Further, as the decaying transition process proceeds, it partially compensates the phase emf Ec (t). Therefore, the voltage

Ua (t) Ec (t) + Enp (t) - e (t) -Ec (t) - e (t) on the damaged phase slowly increases (as e (t) decays. After the damaged phase is detected by the block 13 and closed corresponding switching elements 5-10 (in this case, elements 6 and 7), the voltage Up (t) (on the element 19 of the replacement circuit, which represents the word 11), as follows from figure 2, will be described by the expression

U p (t) E cn (t) -e (t),

Taking into account (1) this expression takes the following form:

Up (t) - Ec (t) - e (t) U3 (t) - Enp (t). When the voltage U p (t) exceeds the limits of the interval (-Ctr Uo, Ctr Do) element 19

0 is unlocked (which corresponds to unlocking one of the thyristors of the arrester 11). As a result, the source 16 will be connected in parallel (if we ignore the small parameters t pn, R p, L P2, R P2, Upi,

5 Rpi) of capacitance 25 C. As a result, it will appear that e (t) E cn (t) Ec (t), and the voltage Uz (t) at the damaged phase does not exceed the amplitude of the voltage drop -Enp (t) on the line from load current. After reloading capacity 25

0 C (at time ti) the current through element 19 stops, i.e. surge 11 is forbidden, and the transition process in voltage e (t) will start with the following initial conditions: e (ta) - Ercn (ti) - Ec (ti).

5 Since this situation is almost completely identical to the situation (2), the process is then repeated.

As a result, a sequence of pulses lp (t) flows through discharger 11 (or 19) (or

0 p (t)), and the voltage Ua (t) of the damaged phase does not exceed the limits -U0-Emnp, U0 + Emnp, where Emnp is the amplitude of the voltage drop -Enp (t) on the line from the load current. The specified sequence of current pulses lp (t)

5 provides compensation for energy losses in the CNPC due to the active conductivity of the network insulation and losses in steel and copper in the DGR 3, as a result of which the CNPC maintains oscillations with amplitude and phase close to

0 amplitude and phase of the EMF EC (t) of the damaged phase. Due to the relatively small value of Uo (on the order of 0.1 Em), the high-frequency transients occurring at the moment of unlocking the thyristors of the surge voltage generator 11 are not significant and cannot create overvoltages of any kind that are dangerous to the insulation. In most cases, the arc gap voltage is higher than Uo + Emnp. and arc

0, the process at the OZNZ location is terminated. In the case of a very significant weakening of the dielectric strength of the insulation (to a value below Uo + Emnp), the overvoltages that occur under these conditions are all the more

5 are minor and do not pose any danger to the insulation of the network and high-voltage equipment. The voltage drop -Enp (t) on the network conductors from the installation site of the device to the OZNZ, due to the load current, does not create

at the same time any additional current in the place of OZNZ. The conditions for suppressing arc OZNZ and the nonideality of the connecting transformer 2 and the transformer based on DGR 3 do not worsen, since with a locked 11, the current in the auxiliary winding circuit of the DGR 3 does not flow vt voltage drop on equivalent elements 17,18,20,21 is missing. It is also significant that when a misalignment of capacitive current compensation occurs in the intermittent arc OZNZ mode, the voltage on the damaged phase, however, does not go beyond the limits of -Uo-Emnp, U0 + Emnp (in this case, only 11). Therefore, the speed requirements of the auto-tuning of the capacitive component in the AHSS modes are not rigid and are determined mainly by the thermal mode of the generator 11 and the additional winding DGR 3. Recognizing the fact that the normal operation of the network has been restored to normal operation can be performed by the damaged phase recognition unit 13 by testing disconnection of switching elements 5-10 after some time (10-30 s) after the occurrence of an APS. The present invention eliminates one of the main drawbacks of all transformer EMF devices of the damaged phase — the current flowing through the metal OZNZ current caused by the voltage drop (from the load current) on the conductors of the damaged phase of the line section between the installation site and the OZNZ place. As a result, this is quite simple to implement, the technical solution approaches in efficiency to compensating for the total current of an APS. In cases when an additional winding of sufficient power is provided for the DGR, this solution is more preferable than automatic shunting of the damaged phase (even if in the latter case, measures are taken to prevent a portion of the load current from flowing through the shunt, ground circuits and OZNZ) due to the fact that switching operations are performed on

low voltage. Its use significantly increases the probability of self-abolishment of the AHSP, sharply reduces the likelihood of further development of the accident, the occurrence of phase-to-phase short circuits, fires, as well as the risk of electrical injury. Therefore, it can be allowed long-term operation of the network equipped with the proposed device, if there is

In this case, the AHSP, which allows to postpone switching, disconnection and repair work for a time convenient for electricity consumers and thereby reduce the damage from interruptions in electricity supply. In the final

As a result, the use of the proposed device leads to increased reliability and security of power supply.

Claims (1)

Invention Formula A device for compensating the EMF of a damaged phase in single-phase closures in networks with an ungrounded neutral, containing a connecting step-down transformer connected to the network. between the neutral terminal of which and the earth, an arc-suppressing reactor, equipped with an additional winding, is connected, a block of switching elements connected by three inputs to the corresponding phases of the secondary the winding of the connecting transformer, and the first output connected with the first output of the auxiliary winding of the arcing reactor, the network voltage sensor, the output of which is connected to the input the damaged phase recognition unit and to the first input of the compensation autotuning unit, the output of which is connected to the input of the reactor actuator, and the output of the recognition unit damaged phase is connected to the second input of the compensation autotuning unit and the control input of the switching elements block, characterized in that, in order to increase efficiency and safety when deaf single-phase earth faults occur in the network, between the second output of the switching elements block and the second output of the auxiliary winding arc A symmetrical thyristor arrester is connected to the reactor.