CN110611317B - A ground fault current compensation system and method for self-generated power supply phase power supply - Google Patents

Abstract

The present invention discloses a ground fault current compensation system and method for self-generated power supply phase power, including a phase power supply generator, a phase power supply phase compensator, a switching switch, a controller and a transformer, and the output end of the phase compensator of the power supply is connected to the neutral point of the system through the switching switch. The system can passively generate power supply phase power and harmonic phase power of the distribution network, and put the reverse power supply phase power and harmonic phase power into the system according to the fault logic. It realizes the complete compensation of reactive current, harmonic current and active current of ground fault in the distribution network, overcomes the disadvantage of incomplete compensation by using the power electronic device inverter injection method after taking power from the bus system, and solves the problem that the metallic grounding compensation effect of the active inverter method is poor and the traditional arc suppression coil cannot achieve full compensation. The present invention is efficient and accurate, can fully compensate for the overvoltage and overcurrent generated by the ground fault, ensures the safety of the power grid and equipment, and completely avoids the risk of electric shock.

Description

A ground fault current compensation system and method for self-generated power supply phase power supply

Technical Field

The present invention relates to the technical field of power distribution network, and in particular to a ground fault current compensation system and method for a self-generated power supply phase power supply.

Background Art

Single-phase grounding faults in distribution networks at home and abroad account for more than 80%, which seriously affects the safe operation of power grids and equipment. Safely handling grounding faults plays an important role in social and economic development. When the capacitive current of the system is greater than 10A, the arc suppression coil grounding method is adopted. The arc suppression coil can reduce the fault current to a certain extent, and the system can operate with the fault for 2 hours, but the arc suppression coil cannot achieve full compensation. There is still a residual current of less than 10A at the fault point. The existence of residual current can cause electric shock and fire accidents, and seriously threaten the safe and stable operation of power grids and equipment. When the capacitive current of the system is large, a small resistance grounding method is often used. 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. However, the power supply reliability of this grounding method is difficult to guarantee, and there is a risk of relay protection failure when high-resistance grounding is used.

At present, in order to completely eliminate the hazards of single-phase grounding faults and ensure power supply reliability, many methods for completely compensating the current at the single-phase grounding fault point have been proposed at home and abroad.

Swedish Neutral published "Application of Full Compensation Technology of Ground Fault Neutral" which disclosed a method of injecting current into the neutral point of the system through an active compensator to compensate the current of the ground fault point. However, the residual current of the ground fault in this method cannot be directly obtained, and the residual current value is calculated by using the system's ground distribution parameters, which has a large deviation; at the same time, the compensator uses power electronic devices to control the current phase and amplitude, and its current phase and amplitude accuracy cannot be guaranteed at the same time, and the compensation current has a large harmonic content, complex control, and poor stability; therefore, the compensation effect of the GFN (ground fault neutralizer) manufactured by Swedish Neutral in Sweden deviates greatly from the ideal value. The results of the simulation test of the device in a certain place in Zhejiang show (Field Test Research on Fault Line Selection Based on Neutral Full Compensation Technology "Zhejiang Electric Power" 2018 Issue 04) that for metallic ground faults, the ground residual current after compensation by the GFN device is still above 5A, which is far from the ideal value, that is, zero current, and is only equivalent to the compensation effect of the arc suppression coil.

Domestically, patent CN102074950A discloses a distribution network ground fault arc extinguishing and protection method, which is similar to the arc extinguishing method of Swedish Neutral. The fault phase voltage is suppressed to zero by injecting current into the neutral point of the distribution network system. This method has the problem of how to control the fault voltage to 0 when the metallic grounding is performed and the fault phase voltage is 0. This method is only effective for high-resistance grounding faults, and to control the fault phase voltage, it is necessary to accurately control the amplitude and phase of the injected current, which is difficult to achieve.

Patent application number 201710550400.3 discloses a method for actively reducing voltage and safely handling ground faults in non-effectively grounded systems. This method sets a tap joint on the transformer system side winding, and reduces the fault phase voltage by short-circuiting the fault phase winding tap to the ground or short-circuiting through impedance, so as to achieve the purpose of limiting the current at the ground fault point. In essence, this method is to create another grounding point on the system bus side when a single-phase grounding occurs in the power grid line, and shunt the original single-phase grounding current. Obviously, this method has a poor compensation effect for metallic single-phase grounding faults, or even ineffective, and malfunction of the device will cause phase-to-phase short circuit.

Patents with application numbers 201710544978.8 and 201710544976.9 disclose methods for reducing voltage and extinguishing arcs in phases of ground faults in non-effectively grounded systems. Both methods involve applying an external power supply between the bus and ground, or between the line and ground, or between the neutral point and ground, or between the tap of the winding on the neutral point non-effectively grounded system side and the ground when a single-phase ground fault occurs, in order to reduce the fault voltage. The only difference between the two methods is that one of the external power supplies is a voltage source and the other is a current source, and there is no essential difference. There are also problems with the phase voltage accuracy of the control system of the voltage source and the current source, and the problem that the relative voltage to the ground is zero and cannot be controlled when a metallic short circuit occurs. In the implementation of the two methods, if the external power supply is directly applied between the bus or line and the ground, the system line voltage will be changed, causing the system load (such as a distribution transformer) to be unable to operate normally.

In summary, there is no method in the prior art that is simple to control, accurate, and efficient to fully compensate for single-phase grounding fault current, and a technology that can take into account both the power supply reliability and safety of the distribution system.

Summary of the invention

In view of this, the purpose of the present invention is to provide a ground fault current compensation system and method for self-generated power supply phase power supply, which converts the line power supply on the bus into a reverse phase power supply through a line-phase converter, and connects the neutral point of the switching switch to the fault phase to suppress the overvoltage of the fault phase, so as to achieve the purpose of full compensation, and effectively solves the problems of complex current control and difficulty in complete compensation of metallic grounding in single-phase grounding faults in distribution systems. At the same time, a transformer is also provided in the system to adjust the voltage after the line power supply is converted into a phase power supply, so as to achieve the purpose of full compensation of current and voltage in the event of a ground fault. After full compensation, no arc occurs in the present invention, which avoids the risk of electric shock and improves the reliability and safety of power supply.

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

The present invention provides a ground fault current compensation system for a self-generated power supply phase power supply, comprising a phase power supply generator, a phase power supply phase compensator, a switching switch, a controller and a transformer, wherein the transformer is a compensation capacitor group (reactor group) or a series capacitor group (series reactor group) or a voltage regulator. After the phase power supply generator is connected to the bus, the output end is connected to the input end of the power supply compensator, and the output end of the phase power supply phase compensator is connected to the system neutral point through the switching switch. The output end of the phase power supply phase compensator will obtain a voltage with the opposite phase and the same amplitude as the power supply voltage of the power grid system, and this voltage can completely compensate for the current at the ground fault point.

Furthermore, the lead-out points of the primary winding of the phase power supply generator are connected to the busbar of the power grid system; the lead-out points of the secondary winding of the phase power supply generator are respectively connected to the corresponding phase connection points of the primary winding of the phase power supply phase compensator.

The secondary winding of the phase power supply phase compensator is respectively provided with a phase A compensation connection point, a phase B compensation connection point, a phase C compensation connection point and a neutral point lead-out point n; the neutral point lead-out point n of the phase power supply phase compensator should be grounded.

Furthermore, the switching switch is provided with an A-phase switch connection point, a B-phase switch connection point, a C-phase switch connection point and a common connection point.

Further, the A-phase compensation connection point, B-phase compensation connection point, and C-phase compensation connection point of the secondary winding of the phase power supply phase compensator are respectively connected to the A-phase switch connection point, B-phase switch connection point, and C-phase switch connection point of the switching switch.

Furthermore, the system line voltage is converted into phase voltage by the phase power supply generator to generate the power supply phase power. The connection form of the phase power supply generator can be Dy, Zy, Yd or Yy, etc., but when the neutral point of the secondary winding of the phase power supply generator is led out, it must not be grounded. According to the transformer principle, there is a phase difference between the power supply phase power generated by the phase power supply generator and the phase voltage of the power supply of the power grid system. and

in is the phase difference between the line voltage of the phase power supply generator and the corresponding line voltage of the power grid system, and n is an integer in the range of [0,11].

Furthermore, the rated voltage of the phase power supply generator has no principle conflict or influence on the implementation of the present invention, but considering the existing mature technology and the more convenient implementation of the present technology, the recommended rated line voltage of the secondary winding of the phase power supply generator is 0.4kV or above and within the rated voltage of the power grid system. However, the voltage ratio between the primary winding and the secondary winding of the phase power supply generator is k.

The phase compensator of the phase power supply compensates the phase voltage phase difference generated by the phase power supply generator; its connection form can be Dyn, Zyn or Yyn, and its y neutral point lead must be grounded. There is a phase difference between its output line voltage and input line voltage

The rated voltage of the primary winding of the phase power supply phase compensator is the rated voltage of the secondary winding generated by the phase power supply, the rated line voltage of the secondary winding of the phase power supply phase compensator is the rated voltage of the power grid system, and the voltage ratio of the primary winding to the secondary winding is 1/k.

Furthermore, in order to more conveniently implement the present technology, Table 1 shows the connection groups that can be used by the partial phase power supply generator and the connection groups that should be used by the corresponding phase power supply phase compensator.

Table 1 Connection groups that can be used for partial phase power supply generators and phase power supply phase compensators

Furthermore, the switching switch is a fast switching switch such as a mechanical switch or a power electronic switch.

Furthermore, when the phase power supply generator and the phase power supply phase compensator output the compensation current, a voltage drop is generated in the internal impedance of the phase power supply generator and the phase power supply phase compensator, so that the voltage amplitude obtained at the output end (i.e., the neutral point) of the phase power supply phase compensator will be lower than the voltage amplitude of the power supply of the power grid system. Therefore, the technical solution sets a transformer, and the voltage drop generated when the phase power supply phase compensator outputs the compensation current is appropriately adjusted through the transformer, so that the voltage amplitude obtained at the output end (i.e., the neutral point) of the phase compensator is equal to the phase voltage amplitude of the system power supply.

Furthermore, the present technology provides three different implementation methods for voltage transformation, which can be selected arbitrarily in the specific implementation. The voltage transformation device is a compensation capacitor group (reactor group), a series capacitor group (series reactor group) or a voltage regulator.

Furthermore, when the transformer is a compensation capacitor group (reactor group),

The compensation capacitor group is a group of triangle-connected capacitors connected to the three-phase output end of the secondary winding of the phase compensator of the phase power supply. The compensation capacitor group is triangle-connected, and its lead-out ends are respectively connected to the A-phase compensation connection point, B-phase compensation connection point, and C-phase compensation connection point of the secondary side of the phase power supply phase compensator.

The capacitor capacity of each phase of the parallel voltage regulating capacitor bank can be calculated as follows:

C is a series regulating capacitor, ω is the angular frequency of the power grid system, and Z _L is the equivalent leakage reactance of the phase power supply generator and the phase power supply phase regulator.

Furthermore, when the transformer device is a series capacitor group (series reactor group):

The series regulating capacitor is connected in series between the common connection point of the switching switch and the neutral point of the power grid system. The common connection point of the switching switch is connected to one end of the primary winding of the series capacitor group, and the other end of the primary winding of the series capacitor group is grounded. One end of the secondary winding of the series capacitor group is connected to the neutral point of the system, and the other end of the secondary side is grounded.

Its capacitance can be calculated as follows:

Wherein, C is the series regulating capacitor, ω is the grid system angular frequency, and Z _L is the equivalent leakage reactance of the phase power supply generator and the phase power supply phase regulator.

Furthermore, when the transformer is a voltage regulator, the common connection point of the switching switch is connected to one end of the primary winding of the voltage regulator, the other end of the primary winding of the voltage regulator is grounded, one end of the secondary winding of the voltage regulator is connected to the neutral point of the system, and the other end of the secondary winding is grounded. The voltage regulator is connected in series between the common connection point of the switching switch and the neutral point of the power grid system, and the voltage regulator is used to compensate the voltage at the neutral point of the input system so that the neutral point voltage is equal to the phase voltage amplitude of the system power supply. The transformer can be any combination of a compensation capacitor group, a series capacitor group and a voltage regulator. The transformer can be any combination of a compensation capacitor group, a series capacitor group and a voltage regulator.

Furthermore, the controller mainly includes a fault judgment module and a switch control module.

The fault judgment module judges whether the system has single-phase grounding and the grounding phase according to the system zero-sequence voltage, three-phase voltage, line zero-sequence current, etc. The switch control module controls the corresponding switch of the switching switch to close according to the grounding phase determined by the fault occurrence judgment module.

Further, a ground fault current compensation method of a self-generated power supply of the present invention is specifically performed according to the following steps: S1: determining whether a single-phase grounding occurs in the system and determining the grounding phase through a controller;

S2: A ground fault occurs in a phase, and the controller controls the switching switch to close the phase switch corresponding to the fault;

S3: voltage compensation through a transformer;

S4: When the closing time of the switching switch reaches the set time, the controller controls the switching switch to open;

S5: The controller continues to determine whether a single-phase grounding fault exists;

S6: If the ground fault still exists, jump to step 2. If the single-phase ground fault does not exist, the single-phase ground fault compensation process ends.

Furthermore, the disconnection time of the switching switch set in step S4 is set according to the line working condition, such as the disconnection time is set according to the situation that the line has many tree-barrier grounding faults or other situations that are likely to cause many grounding faults.

The present invention innovatively proposes to convert the unchanged line voltage before and after single-phase grounding in the system into the phase power supply of the system power supply through the phase power supply generator; the phase power supply phase compensator is used to compensate for the active power and reactive power formed by the ground impedance when the system is single-phase grounded. The purpose of complete compensation is achieved by suppressing the voltage and current at the single-phase grounding fault point to zero. Under a single-phase grounding fault, the system can be energized and there is no risk of electric shock and arcing at the single-phase grounding fault point; and the method provided by the present invention only controls the opening and closing of the switch, which greatly simplifies the control method of the single-phase grounding fault full compensation technology.

The beneficial effects of the present invention are:

(1) The technical solution proposed by the present invention obtains a power supply with a phase opposite to the system power supply voltage and an equal amplitude from the system through passive components, which can completely compensate for the current at the single-phase grounding fault point, eliminate the grounding arc, ensure the power supply reliability of the power grid system, and avoid the risk of electric shock. The power grid system can be continuously powered and the power supply safety is improved.

The compensation system proposed in the present invention can use passive components to obtain components with a voltage phase opposite to that of the power supply phase of the system fault phase. No phase adjustment is required, only the voltage amplitude needs to be adjusted and the corresponding switch needs to be switched. Compared with the existing active full compensation technology based on power electronic inverter technology, even if the system voltage fluctuates, there is no need to adjust the voltage and phase. Its compensation accuracy is higher, the control method is simpler, and it has incomparable technical advantages.

(2) The technical solution provided by the present invention uses transformers, voltage regulators, capacitors, switches and other components that are extremely mature in the prior art and can operate stably for a long time, and their stability is significantly better than that of easily damaged power electronic devices; compared with power electronic inverters that are complex to maintain, the components used in this technical solution are common and mature components of the power system that are easy to maintain or even maintenance-free; the components used in this technical solution are mature in technology and low in cost; therefore, compared with the existing power electronic active full compensation technology, the hardware cost, R&D cost and maintenance cost in the implementation of this technical solution are relatively low, and it has high stability and low maintenance cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of a ground fault current compensation system of a self-generated power supply according to the present invention;

FIG2 is a schematic diagram of a compensation voltage structure of a series capacitor bank of a ground fault current compensation system of a self-generated power supply according to the present invention;

3 is a schematic diagram of the compensation voltage structure of a compensation capacitor group of a ground fault current compensation system of a self-generated power supply according to the present invention;

FIG4 is a schematic diagram of a voltage regulator compensation voltage structure of a ground fault current compensation system of a self-generated power supply according to the present invention;

FIG5 is a schematic diagram of the phase power supply generation and conversion process of the present invention;

FIG6 is a flow chart of a method for compensating ground fault current of a self-generated power supply according to the present invention;

Among them: phase power supply generator 1, phase power supply phase compensator 2, switching switch 3, controller 4, transformer 5, compensation capacitor group (compensation reactor) 51, series capacitor group (series reactor group) 52, voltage regulator 53 and line phase converter 6.

DETAILED DESCRIPTION

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application.

As shown in FIG1 , a ground fault current compensation system and method of a self-generated power supply phase power supply of the present invention is shown in FIG1 :

In this embodiment, referring to FIG. 2-4 , a typical embodiment is given; it includes a phase power supply generator 1 , a phase power supply phase compensator 2 , a switching switch 3 , a controller 4 , and a transformer 5 .

The phase power supply generator 1 is a Dy11-connected transformer connected to the bus to convert the bus line voltage into a phase voltage; the phase power supply phase compensator 2 is a Dyn7-connected transformer connected to the phase power supply generator 1 to compensate for the phase; the switching switch 3 is connected to the phase power supply phase compensator 2 and is controlled by a controller 4.

In this embodiment, the controller 4 is used to control the switching of the switching switch 3 and determine the fault phase;

In this embodiment, one end of the transformer 5 is connected to the switching switch 3, and the other end is connected to the neutral point of the busbar.

In this embodiment, the bus power supply line voltages are respectively U _AB , U _BC , and U _CA , and the bus power supply phase voltages are respectively U _A , U _B , and U _C ; the line voltages output by the phase power supply generator 1 are respectively U _ab1 , U _bc1 , and U _ca1 , and the phase voltages are respectively U _a1 , U _b1 , and U _c1 . According to the transformer principle, for the transformer of the Dy11 connection group, the secondary side line voltage leads the primary side voltage by 30°, that is, after the bus line voltage is transmitted by the phase power supply generator 1 , the bus line voltages U _AB , U _BC , and U _CA are converted into phase voltages U _a1 , U _b1 , and U _c1 , and the phase angles of U _ab1 , U _bc1 , and U _ca1 lead the angles of U _AB , U _BC , and U _CA by 30°, respectively, as shown in Formula 1:

The voltage ratio between the primary winding and the secondary winding of the phase power supply generator 1 is k; therefore, there is formula 2:

The line voltage output by the phase compensator 2 of the phase power supply is U _ab2 , U _bc2 , and U _ca2 , and the phase voltages are U _a2 , U _b2 , and U _c2 , respectively. According to the transformer principle, for the transformer of the Dyn7 connection group, the secondary line voltage lags behind the primary line voltage by 210°, that is, the phase angles of U _ab2 , U _bc2 , and U _ca2 lag behind U _ab1 , U _bc1 , and U _ca1 by 210°, respectively, which can be expressed as Formula 3:

The voltage ratio between the primary winding and the secondary winding of the phase compensator 2 of the phase power supply is 1/k, so as shown in formula 4:

According to equation 1 and equation 3, we can get equation 5:

According to equation 2 and equation 4, we can get equation 6:

Furthermore, from Formula 7, we can know that:

In this embodiment, the bus line voltages U _AB , U _BC , and U _CA are in opposite phases to U _ab2 , U _bc2 , and U _ca2 after being transmitted by the phase power supply generator 1 and the phase power supply phase compensator 2. Therefore, the system bus side phase power supply voltages U _A , U _B , and U _C are in opposite phases to U _a2 , U _b2 , and U _c2 after being transmitted by the phase power supply generator 1 and the phase power supply phase compensator 2, and have equal amplitudes. If a single-phase grounding of phase A occurs in the system, the A-phase switch of the switching switch 3 is closed, and U _a2 is the neutral point voltage U ₀ after the transformer 5. U ₀ is in opposite phase to U _A , and has equal amplitudes, and the active and reactive power that needs to be compensated is naturally output. Therefore, the grounding phase voltage is zero, the system grounding phase voltage is zero, and the grounding point current is also zero, so as to achieve the purpose of fully compensating the grounding current and ensuring the reliability and safety of power supply.

In this embodiment, see FIG5 for a schematic diagram of voltage phase changes during the phase power supply generation and conversion process of the present invention. After the bus line voltage is transmitted by the phase power supply generator 1, the bus line voltage U _AB , U _BC , U _CA is converted into phase voltages U _a1 , U _b1 , U _c1 , and the phase angles of U _ab1 , U _bc1 , and U _ca1 are respectively 30° ahead of U _AB , U _BC , and U _CA. After further passing through the phase power supply phase compensator 2, U _a2 , U _b2 , and U _c2 are opposite in phase to the phase power supply voltages U _A , U _B , and U _C on the bus side of the system.

The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should be included in the scope of the claims of the present invention. The techniques, shapes, and structural parts not described in detail in the present invention are all known technologies.

Claims (10)

1. The utility model provides a ground fault current compensation system of self-generating power supply, its characterized in that includes line phase transformer (6), on-off switch (3), controller (4), the neutral point of access system through on-off switch (3) after line phase transformer (6) are connected with the generating line, the input of controller (4) is connected with the voltage transformer of generating line, the output of controller (4) is connected with the input of on-off switch (3), changes the line voltage source on the generating line into the phase voltage source that the amplitude is the same, the phase is reverse through line phase transformer (6), combines on-off switch (3) access system's neutral point, inserts the phase voltage source corresponding with the trouble, suppresses the overvoltage of trouble phase, reaches full compensation's purpose.

2. A ground fault current compensation system for a self-generated electrical phase source as set forth in claim 1 wherein: the ground fault current compensation system of the self-generated power supply also comprises a voltage transformation device (5).

3. A ground fault current compensation system for a self-generated electrical phase source as set forth in claim 1 wherein: the line-phase converter (6) comprises a phase power supply generator (1) and a phase power supply phase compensator (2), wherein the input end of the phase power supply generator (1) is connected with a bus of a power grid system, the output end of the phase power supply generator (1) is connected with the input end of the phase power supply phase compensator (2), and the output end of the phase power supply phase compensator (2) is connected with the input end of a switching switch (3).

4. A ground fault current compensation system for a self-generating electrical phase source as defined in claim 3 wherein: the phase power supply generator (1) is connected in a Dy or Zy or Yd or Yy mode, and the phase power supply phase compensator (2) is connected in a Dyn or Zyn or Yyn mode.

5. A ground fault current compensation system for a self-generated electrical phase source as claimed in claim 2 wherein: the transformation device (5) is a compensation capacitor bank or a reactor bank (51), and the compensation capacitor bank or the reactor bank (51) is connected with the phase compensator (2) of the phase power supply in a triangle or star shape.

6. A ground fault current compensation system for a self-generated electrical phase source as claimed in claim 2 wherein: the voltage transformation device (5) is a series capacitor bank or a series reactor bank (52), and the series capacitor bank or the series reactor bank (52) is connected in series between the switching switch (3) and the neutral point of the system.

7. A ground fault current compensation system for a self-generated electrical phase source as claimed in claim 2 wherein: the voltage transformation device (5) is a voltage regulator (53), and the voltage regulator (53) is connected in series between the switching switch (3) and a system neutral point.

8. A ground fault current compensation system for a self-generated electrical phase source as set forth in claim 1 wherein: the switching switch (3) can be a mechanical switch or a power electronic fast switching switch.

9. A compensation method of a ground fault current compensation system based on a self-generated electrical phase source as claimed in any one of claims 1-8, characterized by comprising the steps of:

S1, judging whether a single-phase grounding occurs in a system or not and judging a grounding phase through a controller;

S2, a certain phase has a ground fault, and the controller controls the on-off switch (3) to close a phase switch corresponding to the fault;

S3, voltage compensation is carried out through a voltage transformation device (5);

S4, when the closing time of the switching switch reaches the set time, the controller controls the switching switch to be opened;

S5, the controller continuously judges whether single-phase earth faults exist or not;

S6, if the grounding fault still exists, jumping to the step 2, and if the single-phase grounding is not present, ending the single-phase grounding compensation process.

10. The method for compensating for ground fault current of a self-generated electrical phase source as set forth in claim 9, wherein: and the time for switching off the switching switch set in the step S4 is set according to the working condition of the line.