CN110544931A - earth fault current compensation system and method for self-generating power phase power supply - Google Patents

Abstract

the invention discloses a ground fault current compensation system and method for a self-generated power supply phase power supply, which comprises a phase power supply converter, a fling-cut switch, a voltage regulator and a controller, wherein the input end of the phase power supply converter is connected with a bus, the output end of the phase power supply converter is connected with the input end of the fling-cut switch, a common connection point and a system neutral point of the fling-cut switch are connected with non-homonymous ends at two sides of the voltage regulator, and the other connection points of the voltage regulator are grounded. The controller is connected with a voltage transformer of the bus, and the output end of the controller is connected with the input ends of the fling-cut switch and the voltage regulator. The system can passively generate a power supply phase power supply and a harmonic phase power supply of the power distribution network, and the reverse phase power supply and the harmonic phase power supply are put into the system according to fault logic, so that the complete compensation of the ground fault reactive current, the harmonic current and the active current of the power distribution network is realized, and the problems that the active inversion method is poor in metallic ground compensation effect and the traditional arc suppression coil cannot realize full compensation are solved.

Description

earth fault current compensation system and method for self-generating power phase power supply

Technical Field

The invention relates to the technical field of power distribution networks, in particular to a system and a method for compensating earth fault current of a self-generated power phase power supply.

background

The single-phase earth fault of the power distribution network at home and abroad accounts for more than 80 percent, the safe operation of the power grid and equipment is seriously influenced, and the safe processing of the earth fault plays an important role in social and economic development. When the capacitance current of the system is more than 10A, an arc suppression coil grounding mode is adopted. The arc suppression coil can reduce the fault current to a certain extent, and the system can take the trouble to operate for 2 hours, but the arc suppression coil can not realize full compensation, and the fault point still has the residual current that is less than 10A, and the existence of residual current can cause the person to electrocute, the conflagration accident to and threaten the safe and stable operation of electric wire netting and equipment seriously. When the capacitance current of the system is large, a small-resistance grounding mode is mostly adopted, when a single-phase grounding fault occurs, the zero sequence current of the fault line is amplified, and the relay protection device quickly cuts off the fault line.

Currently, in order to be able to thoroughly eliminate the single-phase earth fault hazard, the reliability of power supply is guaranteed simultaneously. Various methods for completely compensating the current of the single-phase earth fault point are proposed at home and abroad.

Swidish Neutral, sweden, "application of full compensation technique for ground fault neutralizer" discloses a method for compensating the current at the ground fault point by injecting current to the system Neutral point through an active compensator. However, the residual current of the ground fault in the method can not be directly obtained, and the residual current value is calculated by adopting the distribution parameters of the system to the ground, so that the deviation is large; meanwhile, the compensator adopts a power electronic device to realize the control of current phase and amplitude, the accuracy of the current phase and the amplitude cannot be simultaneously ensured, the harmonic content of the compensation current is large, the control is complex, and the stability is poor; therefore, the compensation effect of the GFN (ground fault neutralizer) manufactured by Swedish Neutral in sweden deviates greatly from the ideal value, and the result of a simulation test performed by the device at a place in the zhejiang (Zhejiang power 2018, a fault line selection field test research based on a Neutral point full compensation technology) shows that for a metallic ground fault, the ground residual current compensated by the GFN device is still above 5A, has a large difference from the ideal value, namely zero current, and is only equivalent to the compensation effect of an arc suppression coil.

Domestically, patent CN102074950A discloses a method for extinguishing and protecting the arc of a ground fault of a power distribution network, which is similar to the arc extinguishing method of Swedish Neutral, sweden. The method only has the effect on high-resistance grounding faults, controls the fault phase voltage, needs to accurately control the amplitude and the phase of the injected current, and is difficult to realize.

the patent with application number 201710550400.3 discloses an active voltage reduction safety processing method for ground fault of non-effective grounding system, which is to set a tap joint on the side winding of the transformer system, and reduce the voltage of fault phase by short-circuiting the tap joint of the fault phase winding to ground or via impedance, so as to achieve the purpose of limiting the current of the ground fault point. Essentially, when a power grid line is subjected to single-phase grounding, another grounding point is manufactured on the side of a system bus to shunt the original single-phase grounding current, obviously, the method has poor or even ineffective compensation effect on metallic single-phase grounding faults, and the inter-phase short circuit is caused by the misoperation of the device.

the patent application numbers 201710544978.8 and 201710544976.9 disclose phase-down arc suppression methods for an ineffective grounding system ground fault, and both methods apply power between a bus and ground, or a line and ground, or a neutral point and ground, or a tap of a neutral point ineffective grounding system side winding and ground when a single-phase ground fault occurs, so as to reduce the fault voltage. The difference between the two methods is that one of the external power supplies is a voltage source, and the other external power supply is a current source, so that the two methods have no essential difference. The method also has the problems of the phase voltage precision of a control system of a voltage source and a current source and the problem of incapability of controlling the control system when the relative ground voltage is zero in the case of metallic short circuit. In both methods, when an external power source is applied directly between the bus or line and ground, the system line voltage is changed, and the system load (such as a distribution transformer) cannot operate normally.

In summary, in the prior art, there is no technology for fully compensating the single-phase earth fault current, which is simple, convenient, accurate and efficient to control, and can give consideration to both the reliability and the safety of the power supply of the power distribution system.

disclosure of Invention

In view of the above, an object of the present invention is to provide a ground fault current compensation system and method for generating a phase power source by itself, in which a line power source on a bus is changed into a reverse phase power source through a line phase converter and a voltage regulator, and a neutral point of a switching switch access system is combined to access a fault phase to suppress an overvoltage of the fault phase, so as to achieve a full compensation purpose, thereby effectively solving the problems of complex current control, difficulty in complete compensation of metallic grounding, and the like in a single-phase ground fault of a power distribution system. The invention has no arc after complete compensation, avoids the risk of personal electric shock, and improves the reliability and safety of power supply.

The invention solves the technical problems by the following technical means:

in one aspect, the present invention provides a ground fault current compensation system for a self-generated phase power supply, comprising a phase power supply converter, a switch, a voltage regulator, and a controller. The input end of the phase power supply converter is connected with the bus, the output end of the phase power supply converter is connected with the input end of the fling-cut switch, the voltage regulator is connected between the fling-cut switch and a system neutral point in series, the voltage transformer of the bus is connected with the input end of the controller, and the output end of the controller is connected with the fling-cut switch and the input end of the voltage regulator.

the power supply is converted into a three-phase power supply with the same amplitude as the power supply phase through the phase power supply converter, and then is connected to the non-homonymous ends at two sides of the voltage regulator through the common connection point of the fling-cut switch and the system neutral point, so that phase voltage with the same amplitude and the opposite phase as the power supply is obtained at the neutral point, and the purposes of completely compensating the passive earth fault current and ensuring the power supply reliability and safety of the system are achieved.

Further, the phase power supply converter is a transformer of a Yyn0 connection group three-phase three-limb iron core structure, and is used for converting line voltage of a system bus into phase voltage and generating a power supply phase power supply. According to the transformer principle, a phase power supply generated by a phase power supply converter is equal to the phase voltage phase of a power supply of a power grid system.

Further, the switching switches are respectively provided with a switch connection point and a common connection point of the A phase, the B phase and the C phase; the switching switch can be a mechanical switch, a power electronic switch and other quick switching switches. The primary side of the phase power supply transformer is connected with a three-phase bus of a power grid system, the secondary side of the phase power supply transformer is connected with connection points of an A phase, a B phase and a C phase of the fling-cut switch, and a neutral point of the secondary side of the phase power supply transformer is grounded.

further, the controller is used for detecting whether the system has a ground fault, judging a ground fault phase, controlling a switching switch of the ground phase and controlling the output of the voltage regulator.

Further, when the compensation current is output, the internal impedance of the phase power supply converter generates a voltage drop, so that the voltage amplitude obtained at the output end (i.e. the neutral point) of the phase power supply converter is lower than the voltage amplitude of the power supply of the power grid system. Therefore, the voltage regulator is arranged in the technical scheme, the voltage drop generated when the phase power supply converter outputs the compensation current is regulated through the voltage regulator, and meanwhile, the common connection point of the fling-cut switch and the system neutral point are connected to the non-homonymous ends on two sides of the voltage regulator, so that the phase voltage which is equal to the amplitude of the power supply and opposite to the phase is obtained at the neutral point.

The rated voltage of a primary winding of the phase power supply converter is not lower than the rated voltage of a power grid system, and the rated voltage of a secondary winding of the voltage regulator, namely the side connected with a neutral point of the power grid system, is not lower than the rated voltage of the power grid system.

On the other hand, the ground fault current compensation method of the self-generated power supply provided by the invention is specifically executed according to the following steps:

s1, judging whether the system is in single-phase grounding or not and judging the grounding phase through the controller;

S2, when a certain phase has a ground fault, the controller controls the fling-cut switch to close the phase switch corresponding to the fault;

S3, voltage compensation is carried out through the voltage regulator;

S4, when the on-off time of the fling-cut switch reaches the set time, the controller controls the fling-cut switch to be switched off;

s5, the controller continuously judges whether the single-phase earth fault exists;

And S6, if the ground fault still exists, jumping to the step 2, and if the single-phase ground does not exist, ending the single-phase ground compensation process.

Further, the off time of the fling-cut switch set in the step S4 is set according to the line condition, for example, the off time is set according to the condition that there are many ground faults of the line tree fault or other conditions that easily cause many ground faults.

The invention provides a phase power supply for converting line voltage which is not changed before and after a single-phase grounding in a system into a system power supply through a phase power supply converter for compensating active power and reactive power formed by impedance to ground when the system is grounded in a single phase. The purpose of complete compensation is achieved, wherein the voltage and the current of the single-phase grounding fault point are both suppressed to be zero. Under the condition of single-phase earth fault, the system can be operated in a live-line mode, and the single-phase earth fault point has no electric shock risk and arcing risk; and the method provided by the invention only controls the on-off of the switch, thereby greatly simplifying the control method of the single-phase earth fault full-compensation technology.

The invention has the beneficial effects that:

(1) according to the technical scheme provided by the invention, the power supply with the phase voltage opposite to that of the power supply of the system and the same amplitude is obtained from the system through the passive element, the single-phase earth fault point current can be completely compensated, the earth arc is eliminated, the power supply reliability of a power grid system is ensured, and the personal electric shock risk is avoided. The power grid system can continuously supply power, and the power supply safety is improved.

The compensation system provided by the invention can obtain an element with a phase opposite to a phase voltage of a power supply of a system fault phase by using a passive element, does not need phase adjustment, and only needs to adjust a voltage amplitude value and switch a corresponding switch. Compared with the existing active full compensation technology based on the power electronic inversion technology, the active full compensation technology has the advantages that even if the system voltage fluctuates, the voltage and the phase do not need to be adjusted, the compensation precision is higher, the control mode is simpler, and the active full compensation technology has incomparable technical advantages.

(2) in the technical scheme provided by the invention, the elements which can stably run for a long time such as a transformer, a voltage regulator, a capacitor, a switch and the like which are mature in the prior art are adopted, and the stability is obviously superior to that of an easily damaged power electronic device; compared with the power electronic inverter power supply with complex maintenance, the elements adopted by the technical scheme are all common and mature elements of the power system which are easy to maintain and even free from maintenance; the technical scheme adopts mature element technology and has low cost; therefore, compared with the existing power electronic active full compensation technology, the technical scheme has the advantages of low hardware cost, low research and development cost and low maintenance cost, and is high in stability and low in maintenance cost.

drawings

Fig. 1 is a schematic structural diagram of a self-generated power supply type ground fault compensation system according to the present invention;

FIG. 2 is a zero sequence circuit diagram of a double-winding transformer;

FIG. 3 is a schematic diagram of three single-phase grouped and zero-sequence excitation flux paths;

fig. 4 is a schematic diagram of a three-phase five-limb transformer core structure and a zero-sequence excitation flux path;

Fig. 5 is a schematic diagram of a three-phase three-limb transformer core structure and a zero-sequence excitation flux path;

Fig. 6 is a flowchart of a self-generated power supply type ground fault compensation method according to the present invention.

Detailed Description

the present invention will be described in detail with reference to the drawings and specific embodiments, and it is to be understood that the described embodiments are only a few embodiments of the present invention, rather than the entire embodiments, and that all other embodiments obtained by those skilled in the art based on the embodiments in the present application without inventive work fall within the scope of the present application.

as shown in fig. 1, the ground fault current compensation system for a self-generated phase power supply of the present invention includes a phase power supply converter 1, a switch 2, a voltage regulator 3, and a controller 4.

In this embodiment, the phase power supply converter 1 is a transformer of Yyn0 coupling group, and is connected to the bus to convert the bus voltage into the phase voltage.

In this embodiment, the input end of the phase power supply converter 1 is connected to a bus, the output end of the phase power supply converter is connected to the input end of the on-off switch 2, the voltage regulator 3 is connected in series between the on-off switch 2 and a system neutral point, the voltage transformer of the bus is connected to the input end of the controller 4, and the output end of the controller 4 is connected to the input ends of the on-off switch 2 and the voltage regulator 3.

The system bus line voltages are respectively the system bus side phase voltages and respectively the line voltages output by the phase power supply converter 1 are respectively phase voltages and respectively the transformers corresponding to Yyn0 connection groups, the homonymous ends of the primary and secondary side windings are on the same side, and the line voltages have no phase difference, namely:

The ratio of the voltages of the primary and secondary windings of the phase power supply converter 1 is k, and k may be any value, but k is 1 is the simplest for implementing the system, so in this embodiment, k is 1, and therefore the line voltage amplitudes have the following relationship:

The available system bus side phase voltage is the same as the phase transmitted by the phase power supply converter 1, as shown in formula 3:

In this embodiment, the bus line voltage is the same as the phase transmitted by the phase power supply converter 1, and therefore the system bus side phase voltage is the same as the phase transmitted by the phase power supply converter 1.

Furthermore, the common connection point of the fling-cut switch 2 and the system neutral point are connected to the non-homonymous ends of the two sides of the voltage regulator 3, and the other connection points of the voltage regulator 5 are grounded. The voltage ratio of the voltage regulator 5 is j, and k × j is 1, where k is the voltage ratio of the primary and secondary windings of the phase power supply converter 1, so that j is 1 in this embodiment. Therefore, when a switch of a certain phase of the switching switch 3 is closed, the voltages obtained at the system neutral point are respectively:

If the system generates A-phase single-phase grounding, the A-phase switch of the fling-cut switch 2 is closed, the voltage injected to the neutral point through the voltage regulator 3 is the same as the amplitude, and the phase is opposite. Therefore, the system grounding phase voltage is zero and the grounding point current is also zero, so that the aims of completely compensating the grounding current and ensuring the power supply reliability and safety are fulfilled.

In this embodiment, refer to fig. 2, which is a zero-sequence equivalent circuit diagram of a transformer without counting winding resistance and core loss. In the figure, I is a primary side of the transformer, II is a secondary side of the transformer, XI is reactance of a primary winding, XII is equivalent reactance converted from the secondary winding to the primary side, and Xm0 is zero-sequence excitation reactance. When the phase A of the system bus is grounded, the Yyn 6-connected transformer adopted by the invention is equivalent to the grounding short circuit of the phase A winding of the transformer. According to the transformer principle, the core excitation current is controlled by a zero sequence excitation reactance, which is closely related to the core structure of the transformer.

in this embodiment, referring to fig. 3 and fig. 4, for example, the phase power supply converter is a transformer with a three-phase five-limb type and three single-phase group-type iron core structure, and the zero-sequence excitation magnetic flux path thereof is shown in the figure. The current is zero-sequence current and is zero-sequence excitation magnetic flux. For a three-phase transformer group consisting of three single-phase transformers, the zero-sequence main magnetic flux of each phase is the same as the positive-sequence main magnetic flux, and an independent iron core magnetic circuit is arranged, so that the zero-sequence excitation reactance is equal to the positive-sequence excitation reactance. For a three-phase five-column transformer, zero-sequence magnetic flux can also form a loop in an iron core, and the magnetic resistance is very small, so that the value of zero-sequence excitation reactance is very large.

In the phase power supply converter with the two structures, when the phase A is in short circuit with the ground, the zero-sequence excitation reactance Xm0 is approximately equal to infinity, namely, the excitation current is ignored, and the excitation branch is disconnected, so that no energy is output to the compensation system from the secondary side of the phase power supply converter. Therefore, it cannot be used as a phase power supply converter.

In this embodiment, referring to fig. 5, the phase power supply converter is a transformer with a three-phase three-limb iron core structure, and a zero-sequence excitation flux path thereof is shown in the figure.

For a three-phase three-limb transformer, three-phase zero-sequence magnetic fluxes have equal magnitude and same phase, so that one-phase main magnetic flux can not form a loop through iron cores of the other two phases like a positive-sequence (or negative-sequence) main magnetic flux. They are forced to loop through the insulating medium and the housing, encountering significant magnetic reluctance. Therefore, the zero-sequence excitation reactance of the three-phase three-limb transformer is much smaller than the positive-sequence excitation reactance, when the phase A is in short circuit, the zero-sequence excitation reactance is a limited value, about Xm0 is 0.3-1.0, and the value can be adjusted according to the design. Therefore, the transformer with the three-phase three-limb iron core structure can be used as a phase power supply converter to compensate the system ground fault current.

In summary, when the phase power supply converter is a transformer in Yyn0 connection group, the iron core structure can only be three-phase three-limb type, and a five-limb type with independent magnetic circuits and a three-phase transformer group consisting of three single-phase transformers are not suitable.

Although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention as defined in the appended claims. The techniques, shapes, and configurations not described in detail in the present invention are all known techniques.

Claims (7)

1. The utility model provides a ground fault current compensation system from production power supply looks power, its characterized in that, includes looks power supply converter (1), on-off switch (2), voltage regulator (3) and controller (4), the input and the bus connection of looks power supply converter (1), the output is connected with on-off switch's (2) input, voltage regulator (3) concatenate between on-off switch (2) and system neutral point, the voltage transformer of bus is connected with the input of controller (4), the output of controller (4) is connected with on-off switch (2) and voltage regulator's (3) input.

2. A ground fault current compensation system for a self-generated phase power supply as claimed in claim 1, wherein: the phase power supply converter (1) is a Yyn0 connected transformer with a three-phase three-limb iron core structure, and is used for converting line voltage of a system bus into phase voltage and generating a power supply phase power supply.

3. a ground fault current compensation system for a self-generated phase power supply as claimed in claim 1, wherein: the switching switch (2) is a mechanical switch or a power electronic quick switching switch.

4. a ground fault current compensation system for a self-generated phase power supply as claimed in claim 1, wherein: and a common connection point and a system neutral point of the fling-cut switch (3) are connected to non-homonymous ends on two sides of the voltage regulator (3), and other connection points of the voltage regulator (3) are grounded.

5. A ground fault current compensation system for a self-generated phase power supply as claimed in claim 1, wherein: the controller (4) comprises a fault judgment module, a switch control module and a voltage regulator control module.

6. a ground fault current compensation method of a self-generated phase power supply is characterized by comprising the following steps:

S1, the controller judges whether the bus is earthed in single phase or not and judges the earthed phase;

S2, when a certain phase has a ground fault, the controller controls the fling-cut switch (2) to close the phase switch corresponding to the fault;

S3, compensating the voltage through the voltage regulator (3);

S4, when the on-off time of the fling-cut switch reaches the set time, the controller controls the fling-cut switch to be switched off;

S5, the controller continuously judges whether the single-phase earth fault exists;

And S6, if the ground fault still exists, jumping to the step 2, and if the single-phase ground does not exist, ending the single-phase ground compensation process.

7. The method of claim 6, wherein the method further comprises the steps of: the time for turning off the switching switch set in the step S4 is set according to the line condition.