Distribution line isolation compensation method

Abstract

The invention discloses a distribution line isolation compensation method which specifically comprises the following steps: S1, an isolation compensation device is arranged between a system bus and a protection line, a protection line local isolation system is formed between the isolation compensation device and the protection line, and the isolation compensation device isolates the protection line; s2, when a single-phase earth fault occurs in the protection line, the isolation compensation equipment identifies an earth fault and a broken line; s3, when the single-phase earth fault is identified, identifying a fault phase, and performing closing operation on a single-phase switch of the identified fault phase; and S4, injecting the reverse voltage of the fault phase voltage into the neutral point of the protection line local isolation system for full compensation. According to the invention, the isolation of a protection circuit and the compensation of the protection circuit when a single-phase earth fault occurs can be realized, rapid arc extinguishing is realized, the efficiency is improved, the dangerous situation of electric shock of personnel is avoided, the system construction and maintenance cost is greatly reduced, various faults caused by mutual cooperation among multiple devices are avoided, and the safety of the system is improved. And reliable guarantee is provided for stable operation of the system.

Description

Technical Field

[0001] The invention relates to the technical field of single-phase grounding protection of distribution networks, and in particular to a distribution line isolation compensation method. Background Art

[0002] In 6-66kV power systems, single-phase grounding faults account for more than 80% of all faults, and the grounding current is mainly capacitive current. In order to prevent excessive capacitive current from causing grounding arcs to break through equipment insulation and cause power outages, arc extinguishing measures should be taken in time to promote instantaneous fault recovery and curb permanent fault deterioration; and effective handling of single-phase grounding faults plays a vital role in preventing wildfires caused by arcs and casualties caused by broken grounding.

[0003] Existing active full compensation devices for ground faults are mostly composed of power transformers, step-up transformers, vacuum contactors, active power compensators, controllers, etc. They can compensate the voltage and current at the single-phase ground fault point to close to 0, and completely eliminate the arc when a single-phase ground fault occurs. They are the optimal solution to solve single-phase ground faults.

[0004] However, in actual operation, single-phase grounding faults in distribution networks are mainly transient faults, and the arc extinguishing process changes the transition resistance as the fault is restored. Therefore, if the transient fault is restored, the arc extinguishing coil can effectively avoid the system operating in a resonant overvoltage state by exiting the full compensation in time; and for permanent faults, the arc extinguishing coil should maintain the full compensation arc extinguishing state to prevent the fault from worsening. It can be seen that the key to the scientific investment and withdrawal of the full compensation of the arc extinguishing coil is to quickly identify the grounding resistance to identify the type of grounding fault.

[0005] Since the initial fault transition resistance of broken grounding and arc-induced wildfires is often very large, reaching 50kΩ or even exceeding 100kΩ, the existing ground fault active full compensation device can only identify the ground fault transition resistance of about 10kΩ, which cannot adapt to the impact of arc suppression coil rapid compensation on fault information, and the real-time performance of transition resistance identification is also poor; therefore, it cannot meet the stable operation requirements of the system. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a distribution line isolation and compensation method, which realizes the isolation of the protection line from the original system during a single-phase grounding fault through a single device, and fully compensates for the voltage and current at the fault point by injecting a reverse voltage into the local isolation system of the isolated protection line, while improving the line break identification capability, eliminating arc discharge as soon as possible, and avoiding the occurrence of dangerous electric shock situations for personnel.

[0007] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows.

[0008] A distribution line isolation compensation method specifically comprises the following steps: S1. An isolation compensation device is installed between the system bus and the protection line, and a local isolation system of the protection line is formed between the isolation compensation device and the protection line. The isolation compensation device realizes the isolation of the protection line; S2. When a single-phase grounding fault occurs in the protection line, the isolation compensation equipment will identify the grounding fault and disconnection; S3. When a single-phase ground fault is identified, the fault phase is identified and the single-phase switch of the identified fault phase is closed; S4. Inject the reverse voltage of the fault phase voltage into the neutral point of the local isolation system of the protection line for full compensation.

[0009] Preferably: the isolation compensation device includes a mutually coupled primary winding, a load winding and a compensation winding, wherein the primary winding is respectively connected to each phase of the system bus; the load winding is respectively connected to each phase of the protection line to supply power to the distribution equipment of the protection line; the compensation winding has opposite polarity to the load winding, and the neutral point is grounded.

[0010] Preferably: the load winding and compensation winding of the isolation compensation device are both star-connected structures, and the three-phase output ends of the compensation winding are respectively connected to one end of three single-phase switches; the other ends of the three single-phase switches are short-circuited with each other and connected to the neutral point of the load winding.

[0011] Preferably, the transformation ratio of the primary winding to the load winding and the transformation ratio of the primary winding to the compensation winding are both 1:1.

[0012] Preferably: the capacity of the load winding matches the total load carried by the protection line local isolation system, the capacity of the primary winding and the load winding are equal, and the capacity of the compensation winding is not less than the capacitive current compensation capacity of the protection line local isolation system.

[0013] Preferably: in step S3, the isolation compensation device identifies the lagging phase of the highest voltage phase as the fault phase.

[0014] Due to the adoption of the above technical scheme, the technical progress achieved by the present invention is as follows.

[0015] The isolation and compensation equipment provided in the present invention can achieve isolation from the original system of the distribution line when a single-phase grounding fault occurs in the protection line, and form a local isolation system of the protection line between the isolation and compensation equipment and the protection line. The capacitance to ground of the local isolation system of the protection line is only one percent or even several hundredths of the capacitance to ground of the original system, and line selection and identification are performed according to the same displacement voltage starting threshold. Compared with the resonant grounding method with the best sensitivity in traditional technology, the recognition ability of the transition resistance is improved by 20 times or more, which greatly improves the line break identification ability; at the same time, after the single-phase switch of the fault phase corresponding to the single-phase grounding fault is closed, the reverse voltage of the fault phase voltage can be injected into the isolated local isolation system of the protection line, so that the voltage of the phase line to the ground becomes "zero" volt, thereby achieving full compensation of the voltage and current at the fault point, quickly eliminating arc discharge, and avoiding the occurrence of dangerous electric shock to personnel. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic diagram of the power distribution line system of the present invention; Figure 2 It is the voltage vector diagram of the system when a single-phase grounding fault occurs in the present invention.

[0017] Among them: P. primary winding, SL. load winding, SC. ​​compensation winding. DETAILED DESCRIPTION

[0018] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0019] A distribution line isolation compensation method is provided, wherein an isolation compensation device is arranged between the system bus and the protection line, and a local isolation system of the protection line is formed between the isolation compensation device and the protection line. The isolation compensation device realizes the isolation of the protection line from the original system, and can compensate the local isolation system of the protection line in the event of a single-phase grounding fault. The schematic diagram of the distribution line system is shown in FIG. Figure 1 As shown in the figure, the device in the dotted box is the isolation compensation device.

[0020] In the present invention, the isolation compensation device includes a mutually coupled primary winding P, a load winding LS and a compensation winding SC, and three single-phase switches K respectively arranged at the three-phase output ends of the compensation winding SC. A , K B and K C .

[0021] Among them, the primary winding P is a delta connection structure or a star connection structure, and it is connected to each phase A of the system bus. s , B s , C s Connect them separately; the system bus-to-ground capacitance is C OAS , C OBS , COCS .

[0022] The load winding LS is a star-connected structure, which is connected to the phases A, B, and C of the protection line respectively to supply power to the distribution equipment connected to the protection line; the protection line can be an overhead line with key protection such as passing through forest areas, grasslands or densely populated areas.

[0023] The compensation winding SC is a star-connected structure, with the opposite polarity to the load winding LS, and the neutral point of the compensation winding SC is grounded; the three-phase output ends of the compensation winding SC are connected to one end of the three single-phase switches respectively, that is, the A-phase output end of the compensation winding SC is connected to the single-phase switch K A The B-phase output end of the compensation winding SC is connected to the single-phase switch K B The C-phase output end of the compensation winding SC is connected to the single-phase switch K C The other ends of the three single-phase switches are short-circuited with each other and connected to the neutral point of the load winding LS.

[0024] In the present invention, in order to ensure that the compensation winding can fully compensate the load system, the transformation ratio of the primary winding P of the isolation compensation device to the load winding LS and the primary winding P to the compensation winding SC are both 1:1.

[0025] In terms of capacity setting, the capacity of the load winding LS matches the total load carried by the local isolation system of the protection line. Of course, it can also be 1.0 to 1.5 times according to the subsequent load capacity increase; the capacity of the primary winding P and the load winding LS are equal; the capacity of the compensation winding SC is not less than the capacitive current compensation capacity of the local isolation system of the protection line.

[0026] The present invention provides a method for isolation compensation of power distribution lines, which specifically comprises the following steps: S1. An isolation compensation device is installed between the system bus and the protection line, and a local isolation system of the protection line is formed between the isolation compensation device and the protection line. The isolation compensation device realizes the isolation of the protection line.

[0027] S2. When a single-phase grounding fault occurs in the protection line, the isolation compensation equipment will identify the grounding fault and line break.

[0028] The identification of single-phase grounding fault mainly uses zero-sequence voltage U 0 The limit is exceeded as the criterion, U 0 The calculation formula is: (1) Where: U 0 ——Displacement voltage of the system during ground fault; EA ——A phase (assumed to be the fault phase) power supply voltage; C 0 ——System single-phase to ground capacitance; R f ——Ground transition resistance.

[0029] It can be seen from formula (1) that when a single-phase grounding fault occurs, the displacement voltage is inversely proportional to the system capacitance to ground.

[0030] In the present invention, the isolation compensation device isolates the overhead line to be protected from the original distribution line system, and forms a local isolation system of the protection line between the isolation compensation device and the protection line. The capacitance C of the local isolation system of the protection line is OA , C OB , C OC It is only one percent or even several hundredths of the original system's ground capacitance. According to the same displacement voltage start threshold, line selection and identification are performed. Compared with the most sensitive resonant grounding method in traditional technology, the identification ability of transition resistance is improved by 20 times or more, reaching 50kΩ to 100kΩ or more.

[0031] In addition, the unbalanced voltage caused by a single-phase grounding fault can also be calculated according to the following formula: (2) Where: U 0 ——Displacement voltage of the system during ground fault; E——system power phase voltage; Δ——Capacitance reduced when the wire is broken.

[0032] It can be seen from formula (2) that the ratio of the displacement voltage of the system to the capacitance reduction caused by the phase disconnection and the system's overall capacitance to ground is approximately proportional to the system's overall capacitance to ground. Obviously, after isolation, the total capacitance to ground of the local isolation system of the protective line is significantly reduced, and the ability to identify disconnection is greatly improved.

[0033] S3. When a single-phase grounding fault is identified, the faulty phase is identified, and the single-phase switch of the identified faulty phase is closed.

[0034] According to formula (1), during the ground fault process, the transition resistance R f When changing from 0 to infinity, the displacement voltage is obtained U 0 The trajectory is EA A semicircle with a diameter in the upper half, such as Figure 2 shown.

[0035] Depend on Figure 2 It can be intuitively determined that the lagging phase of the highest voltage phase is the fault phase. Therefore, after a single-phase grounding fault occurs, the isolation compensation device closes the single-phase switch corresponding to the fault phase according to the determined fault phase.

[0036] S4. Inject the reverse voltage of the fault phase voltage into the neutral point of the local isolation system of the protection line for full compensation.

[0037] In this embodiment, it is assumed that the fault phase is phase A, and after a single-phase grounding fault, the single-phase switch K A After closing the circuit, according to the circuit principle, the relative ground voltage of the protection circuit is:

[0038]

[0039]

[0040] So, U 0 That is, the voltage injected into the neutral point of the local isolation system of the protection line is -E A At this time, the voltage of the fault phase line to ground is: (3) It can be seen from formula (2) that in the present invention, when a single-phase grounding fault occurs in the protection line, the isolation compensation device can inject a reverse voltage of the fault phase voltage into the neutral point of the isolation system of the key protection line, so that the voltage of the phase line to the ground is "zero" volts. According to the circuit principle, the fault point flows through the grounding transition resistor R g The current must be "zero" ampere, so that the voltage and current at the fault point are all compensated to "zero".

[0041] The present invention can achieve isolation and compensation of the protection line when a single-phase grounding fault occurs through a single device, and realize rapid arc extinguishing, which not only improves efficiency and avoids the occurrence of dangerous situations of electric shock to personnel, but also greatly reduces the cost of system construction and maintenance, avoids various faults caused by the cooperation between multiple devices, and provides reliable guarantee for the stable operation of the system.

Claims

1. A distribution line isolation compensation method, characterized in that: The specific steps include: S1. An isolation compensation device is installed between the system bus and the protection line, and a local isolation system of the protection line is formed between the isolation compensation device and the protection line. The isolation compensation device realizes the isolation of the protection line; S2. When a single-phase grounding fault occurs in the protection line, the isolation compensation equipment will identify the grounding fault and disconnection; S3. When a single-phase ground fault is identified, the fault phase is identified and the single-phase switch of the identified fault phase is closed; S4. Inject the reverse voltage of the fault phase voltage into the neutral point of the local isolation system of the protection line for full compensation.

2. A distribution line isolation compensation method according to claim 1, characterized in that: The isolation compensation device includes a mutually coupled primary winding (P), a load winding (LS) and a compensation winding (SC), wherein the primary winding (P) is respectively connected to each phase of the system bus; the load winding (LS) is respectively connected to each phase of the protection line to supply power to the distribution equipment of the protection line; the compensation winding (SC) has opposite polarity to the load winding (LS), and the neutral point is grounded.

3. A distribution line isolation compensation method according to claim 2, characterized in that: The load winding (LS) and the compensation winding (SC) of the isolation compensation device are both star-connected structures, and the three-phase output ends of the compensation winding (SC) are respectively connected to one end of three single-phase switches; the other ends of the three single-phase switches are short-circuited with each other and then connected to the neutral point of the load winding (LS).

4. A distribution line isolation compensation method according to claim 2, characterized in that: The transformation ratio of the primary winding (P) to the load winding (LS) and the transformation ratio of the primary winding (P) to the compensation winding (SC) are both 1:

1.

5. A distribution line isolation compensation method according to claim 2, characterized in that: The capacity of the load winding (LS) matches the total load carried by the local isolation system of the protection line, the capacity of the primary winding (P) and the load winding (LS) are equal, and the capacity of the compensation winding (SC) is not less than the capacitive current compensation capacity of the local isolation system of the protection line.

6. A distribution line isolation compensation method according to claim 1, characterized in that: In step S3, the isolation compensation device identifies the lagging phase of the highest voltage phase as the fault phase.

Images