CN215601032U - Three-phase power system convenient to eliminate interphase short-circuit fault - Google Patents

Abstract

The utility model discloses a three-phase power system convenient for eliminating interphase short-circuit faults, which comprises a circuit, wherein a plurality of controlled switches are arranged on the circuit, the controlled switches can detect current signals and trip when the current signals reach preset conditions, and the lower port of a first controlled switch close to a power supply is connected with the ground through a grounding switch and a current-limiting resistor. The system can effectively remove the interphase short-circuit fault, and is simpler in structure and convenient to implement.

Description

Three-phase power system convenient to eliminate interphase short-circuit fault

Technical Field

The utility model relates to the field of power system protection, in particular to a three-phase power system convenient for eliminating interphase short-circuit faults.

Background

At present, when an interphase short circuit occurs in a certain line of a three-phase power system, the following elimination method is generally adopted: 1. the reclosing mode is adopted: the first breaker on the line is cut off firstly and then closed, if the first breaker is a transient phase-to-phase short circuit and is eliminated after the first breaker is closed, normal power supply is continued. And if the interphase short-circuit fault still exists after the first breaker is closed, the first breaker is cut off to wait for maintenance. 2. Adopting a time step difference matching method: the method can isolate a fault area, but for a fault with a fault point close to the power supply, a power supply system has long short-circuit current tolerance time and large impact on a power grid. 3. The first breaker is tripped firstly when overcurrent occurs, then the load switches are tripped out without current at the last (other load switches are in a closing state), then the first breaker is superposed, if the fault occurs below the last load switch, the fault can be eliminated, otherwise, the fault current still exists after the first breaker is superposed, at the moment, the first breaker is tripped out again when overcurrent occurs, then the last load switch is tripped out without current, then the first breaker is reclosed again, and if the interphase short circuit occurs between the last load switch and the last load switch, the fault can be eliminated. And by parity of reasoning, the load switch is switched off under no current sequentially upwards until the fault is eliminated. However, during this operation, the power supply system is repeatedly subjected to a large short-circuit current surge, and if the number of times is excessive, damage may be caused to the line, and in addition, the time for removing the line fault is also long. The utility model patent application 2020114536325 and the utility model patent application 2020114536310 provide two methods for processing an inter-phase short circuit, and when the inter-phase short circuit occurs, the purpose of cutting off a fault point is achieved by artificially constructing a detection loop comprising a fault phase and an inter-phase short circuit fault point and triggering tripping operation by utilizing pulse number or time length information of switch detection current on the detection loop. This method needs a signal generating switch to connect the system bus or neutral point to the ground, and also needs a switch to connect the jumped-off outgoing line to the ground, which is complicated in structure.

SUMMERY OF THE UTILITY MODEL

The utility model aims to provide a three-phase power system convenient for eliminating interphase short-circuit faults, which can effectively eliminate the interphase short-circuit faults, and is simpler in structure and convenient to implement.

In order to achieve the purpose, the utility model adopts the following technical scheme:

a three-phase power system convenient for eliminating interphase short-circuit faults comprises a circuit, wherein a plurality of controlled switches are arranged on the circuit, the controlled switches can detect current signals and trip when the current signals reach preset conditions, and the lower port of a first controlled switch close to a power supply is connected with the ground through a grounding switch and a current-limiting resistor; when an inter-phase short-circuit fault occurs on a line, the first controlled switch can cut off at least one fault phase and make another fault phase conductive, the grounding switch can ground the cut fault phase, a detection loop comprising a fault phase conductor from the first controlled switch to an inter-phase short-circuit fault point, the grounding switch, the current limiting resistor and the ground can be formed by utilizing a fault phase single-phase ground-to-ground voltage, a current signal is generated, the controlled switch detects the current signal and trips according to a preset condition, and the preset condition enables the controlled switch close to a power supply to trip later than the controlled switch far away from the power supply.

Preferably, a parallel switch is provided, said parallel switch being capable of switching back on the phase in which said first controlled switch is switched off.

Preferably, the parallel switch can be switched on and off circularly or continuously.

Preferably, the grounding switch can be switched on and off circularly or continuously.

Preferably, the current limiting resistor is an adjustable resistor.

Preferably, the grounding switch is a thyristor or a mechanical fast on-off switch.

Preferably, the parallel switch is a thyristor or a mechanical fast on-off switch.

In the scheme, a detection loop comprising an interphase short-circuit fault point, a fault phase conductor and the ground can be artificially constructed by utilizing the characteristic that the neutral point is grounded (namely the neutral point is grounded through a small resistor or grounded through an arc suppression coil) or other outgoing lines have capacitance effect to the ground when the neutral point is suspended, the detection loop generates a current signal by utilizing the single-phase voltage to the ground of the fault phase conductor and can regulate and control the current signal through the on-off operation of a switch, and thus, after the controlled switch is switched off according to the preset information such as the current pulse number or the current duration, the fault can be eliminated. In the construction process of the detection loop, no device is used for connecting a system bus or a neutral point to the ground independently, and current signals are directly generated in a pair mode by utilizing the capacitance effect of other outgoing lines to the ground when the neutral point of the system is grounded or suspended, so that the system structure is simplified, and the cost is reduced.

Drawings

FIG. 1 is a schematic diagram of a related structure of a low-resistance grounded three-phase power system according to the present invention;

fig. 2 is a related structure schematic diagram of the arc suppression coil grounding three-phase power system.

Fig. 3 is a related structure schematic diagram of a three-phase power system with a suspended neutral point.

Detailed Description

The utility model will be further illustrated by the following specific embodiments in conjunction with the accompanying drawings:

in a three-phase power system in which a neutral point is not suspended, the neutral point is generally grounded through a small resistance or an arc suppression coil, and when a phase conductor is grounded, as shown in fig. 1 and 2, a circuit can be formed with the grounded neutral point to generate a current. A three-phase system with a floating neutral point is shown in fig. 3, and there is a capacitance between the wires on the line and the ground, so that when one phase of the wires is grounded, a current can be generated. In the three-phase power system shown in fig. 1, 2 and 3, the three-phase power system includes a power supply, a bus 3, a plurality of outgoing lines 1 and a load, wherein a plurality of controlled switches are distributed on the outgoing lines 1, including a first controlled switch 2 close to the power supply and other controlled switches 4 under the first controlled switch 2, and the controlled switches 4 can detect a current signal and trip when the detected current signal meets a preset condition (a circuit breaker can be cut off according to the current condition, so the circuit breaker can be used as a controlled switch). According to the preset conditions, the three-phase power system is also provided with a protection device, when the phase-to-phase short circuit occurs on the outgoing line, the protection device can be detected by the protection device and send a control signal, for example, the first controlled switch 2 is enabled to cut off the current, and the protection device is the prior art, such as optical fiber differential protection, 5G differential protection and the like.

In one embodiment, the neutral point is grounded through a small resistor or an arc suppression coil, when two-phase interphase short circuit fault occurs on the outgoing line, the first controlled switch 2 trips off one fault phase to cut off fault current, and keeps the other fault phase conducted (the third phase is a non-fault phase, and may or may not trip off), a grounding switch 9 and a current limiting resistor 8 are arranged between the lower port of the first controlled switch 2 and the ground, and after the first controlled switch 2 trips off one fault phase, the grounding switch 9 connects the tripped fault phase with the ground at the lower port of the first controlled switch 2, so that a detection loop including a system neutral point, an interphase short circuit fault point, a fault phase conductor between the interphase short circuit fault point and the first controlled switch 2, the grounding switch 9 and the current limiting resistor 8 is constructed, and a current signal is generated. If the grounding switch 9 is switched on and off in a circulating way, a current pulse can be generated, and the grounding switch 9 is switched on continuously to generate continuous current. The current limiting resistor 8 can make the detection loop current in a desired range, for example, if the current limiting resistor is set to be a resistor of not less than 100 ohms, the current value can be controlled below 60 amperes. In a preferred embodiment, the current limiting resistor 8 is an adjustable resistor, and the current value is more controllable through the adjustment of the resistance value. The first controlled switch 2 and the controlled switch 4 each have a function of detecting a current signal and cutting off a current according to a preset condition, for example, the first controlled switch 2 and the controlled switch 4 may detect the number of current pulses, and the last controlled switch 4 on the outgoing line is set to detect one current pulse, that is, trip, and the last controlled switch (last but one) is set to detect two current pulse numbers and then trip, and the last controlled switch is set to detect three pulse numbers and then trip, and so on, so that the nearest controlled switch upstream (upstream near the power supply side) of the interphase short-circuit fault point can be cut off, thereby accurately removing a fault. Similarly, the controlled switch may be made to detect the current duration, and the current duration detected by the last controlled switch is the shortest (e.g., 0 ms), and then the current duration triggered to trip by the upward controlled switch is sequentially extended (e.g., sequentially increased by 100 ms), so that the controlled switch functions when the continuous current is generated in the detection loop and the upstream controlled switch closest to the fault point trips. Of course, the function of the controlled switch for detecting the current pulse or the current duration does not conflict with the current of the power system in normal operation, and the controlled switch enters the detection role only after the inter-phase short circuit fault occurs. It is of course also conceivable to set other conditions than the current pulse or the current duration, the principle of which is still to trip the controlled switch 4 closer to the first controlled switch 2 later than the controlled switch 4 further away from said first controlled switch 2, so that the fault can be removed accurately. The phase of the first controlled switch 2 which is kept on is cut off according to the current pulse number or the current duration, and the current pulse number is set to be the largest or the current duration is set to be the longest, so that when the fault point is positioned between the first controlled switch 2 and the next-most-adjacent controlled switch 4, the phase of the first controlled switch 2 which is kept on is tripped, thereby cutting off the fault. In this embodiment the first controlled switch 2 switches off one faulted phase and keeps the other faulted phase conducting from the beginning, while in another embodiment the first controlled switch 2 can also switch off both faulted phases simultaneously and then switch on one faulted phase again by means of the switch 6 in parallel with the first controlled switch, which also achieves the above-mentioned effect. Or in the third embodiment, the controlled switch 2 is firstly cut off the two fault phases, then the grounding switch 9 connects the cut fault phase with the ground, and the parallel switch 6 is circularly switched on and off to generate current pulse, or the parallel switch 6 is continuously switched on to generate continuous current, so that the controlled switch can be tripped to cut off the fault, and in the embodiment, the current limiting resistor can be connected between the grounding switch and the ground in series, or can be connected at the parallel switch 6 in series instead. In another embodiment, the phase switch of the first controlled switch 2 that is kept conductive can be cycled on and off for single phase control to generate current pulses, or continuously conductive to generate continuous current, in which case the parallel switch 6 is not needed.

In an embodiment of a neutral point suspension system, when a three-phase-to-phase short circuit fault occurs, a first controlled switch 2 trips off two fault phases and maintains the other fault phase conductive, so that a fault current can be cut off, then one of the tripped two fault phases is connected with the ground from the lower port of the first controlled switch 2 through a grounding switch 9 and a current limiting resistor 8, so that a detection loop comprising a system single phase-to-ground voltage, two fault phase conductors, a phase-to-phase short circuit fault point, a grounding switch, a current limiting resistor and the ground is constructed, and a current signal is generated to the ground single-phase voltage by using the fault phase conductor. The controlled switch 4 trips according to a preset pulse number or current duration to remove the fault by cyclically switching on and off the grounding switch 9 to generate current pulses or continuously switching on the grounding switch 9 to generate continuous current. Similarly, the three-phase fault phase can be cut off simultaneously, the parallel switch 6 is used to connect the one-phase fault phase with the power supply, then the parallel switch 6 is switched on and off cyclically to generate current pulse, or the parallel switch 6 is switched on continuously to generate continuous current, or the one-phase switch which maintains the first controlled switch 2 on is switched on cyclically to generate current pulse, or the first controlled switch is switched on continuously to generate continuous current.

In the above embodiment, it is preferable that the current limiting resistor 8 is an adjustable resistor, so that the resistance value of the adjustable resistor is adjusted to make the current value of the generated current signal within a desired range.

For details of the number of current pulses or duration of current flow in sequence with the tripping of the controlled switch, reference may be made to patent application 2020114536325 and patent application 2020114536310.

In the above embodiment, in a scenario where the arc suppression coil or the small resistor is installed, the ground switch 9 and the current limiting resistor 8 may be directly connected to the ground as described above, or may be connected to a lead wire, and the lead wire may be connected to the ground of the arc suppression coil or the small resistor.

In the above embodiment, the grounding switch 9 and the parallel switch 6 may be thyristors, so as to be switched on and off instantly. Also can select for use quick on-off switch of mechanical type, utility model patent CN209880524U, CN209859894U all disclose the switch of an asymmetric current source, rotate through machinery and realize quick break-make, can regard as the quick on-off switch of mechanical type of this embodiment.

The above embodiments are merely illustrative of the concept and implementation of the present invention, and are not restrictive, and technical solutions that are not substantially changed under the concept of the present invention are still within the scope of protection.

Claims (7)

1. A three-phase power system convenient for eliminating interphase short-circuit faults comprises a circuit and is characterized in that a plurality of controlled switches are arranged on the circuit, the controlled switches can detect current signals and trip when the current signals reach preset conditions, and the lower port of a first controlled switch close to a power supply is connected with the ground through a grounding switch and a current-limiting resistor; when an inter-phase short-circuit fault occurs on a line, the first controlled switch can cut off at least one fault phase and make another fault phase conductive, the grounding switch can ground the cut fault phase, a detection loop comprising a fault phase conductor from the first controlled switch to an inter-phase short-circuit fault point, the grounding switch, the current limiting resistor and the ground can be formed by utilizing a fault phase single-phase ground-to-ground voltage, a current signal is generated, the controlled switch detects the current signal and trips according to a preset condition, and the preset condition enables the controlled switch close to a power supply to trip later than the controlled switch far away from the power supply.

2. A three-phase power system facilitating the clearing of a phase-to-phase short circuit fault as recited in claim 1 further including a shunt switch capable of re-conducting the phase for which the first controlled switch is switched off.

3. The three-phase power system facilitating the clearing of a phase-to-phase short circuit fault of claim 2 wherein the shunt switch is capable of cycling or continuously conducting.

4. The three-phase power system facilitating the clearing of a phase-to-phase short circuit fault of claim 1 wherein the grounding switch is capable of being cycled on and off or continuously conducting.

5. The three-phase power system facilitating the clearing of a phase-to-phase short circuit fault of claim 1 wherein the current limiting resistor is an adjustable resistor.

6. The three-phase power system facilitating the clearing of a phase-to-phase short circuit fault of claim 1 wherein the grounding switch is a thyristor or a mechanical fast on-off switch.

7. The three-phase power system facilitating the clearing of a phase-to-phase short circuit fault of claim 2 wherein the parallel switch is a thyristor or a mechanical fast on-off switch.

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