A three-phase adaptive reclosing method for photovoltaic grid-connected tie lines

Abstract

This invention discloses a three-phase adaptive reclosing method for photovoltaic grid-connected tie lines, comprising: acquiring a tie line with three phases disconnected by a circuit breaker; connecting the tie line to a fast grounding switch and continuously for a preset connection time; briefly applying photovoltaic power to the tie line and then injecting a three-phase fundamental frequency AC signal, continuously for a preset connection time; acquiring the voltage and current values ​​generated on the disconnected line, and determining whether the voltage and current values ​​are less than preset voltage and current setting values, respectively. This method can quickly and reliably determine various faults occurring on the tie line, unaffected by the location of the fault or the magnitude of the transition resistance. Furthermore, when it is determined that there is no fault on the tie line, the tie line can quickly and successfully reclose; when it is determined that there is a fault on the tie line, the tie line can be reliably blocked, successfully preventing the tie line from reclosing to the fault.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of power system relay technology, and particularly relates to a three-phase adaptive reclosing method for a photovoltaic grid-connected tie line. BACKGROUND

[0002] In recent years, photovoltaic power as a representative of new energy has been widely applied through centralized grid connection. Large-capacity photovoltaic power is mainly connected to the grid through high-voltage overhead lines. More than 80% of the faults occurring in high-voltage overhead lines are transient faults. When a transient fault occurs in a transmission line and is disconnected by a circuit breaker, normal power supply can be restored through primary reclosing. Therefore, in order to improve power supply reliability, reclosing devices are widely used in transmission lines.

[0003] Large photovoltaic power stations are mostly connected to the grid through single-circuit 220 kV overhead transmission lines. When a single-phase reclosing transmission line fails and the circuit breaker is tripped in a single phase, if the reclosing is reclosed on a permanent fault, the circuit breakers on both sides will be tripped again in three phases. When a three-phase reclosing transmission line fails, the circuit breaker will be tripped in three phases. After the circuit breaker is tripped in three phases, the transmission line is disconnected from the system, and the electromagnetic energy stored in each energy storage element on the line will continue to decay. When there is no shunt reactor on the line, the electromagnetic energy decays rapidly, making it difficult to identify the nature of the fault. Therefore, studying a three-phase adaptive reclosing method suitable for photovoltaic grid-connected tie lines without shunt reactors is helpful for the safe and stable operation of photovoltaic grid-connected power generation systems. SUMMARY

[0004] The present application provides a three-phase adaptive reclosing method for a photovoltaic grid-connected tie line, which is used to solve the technical problem that the reclosing control cannot be performed on a photovoltaic grid-connected tie line without a shunt reactor.

[0005] The present application provides a three-phase adaptive reclosing method for a photovoltaic grid-connected tie line, which includes: obtaining a tie line tripped in three phases by a circuit breaker; connecting the tie line to a fast grounding switch and maintaining a preset connection time; injecting a three-phase fundamental frequency alternating current signal into the tie line after a photovoltaic power source is temporarily added to the tie line for a preset injection time; obtaining a voltage value and a current value generated on a power-off line, and determining whether the voltage value and the current value are less than a preset voltage setting value and a preset current setting value, respectively; if the voltage value is not less than the preset voltage setting value or the current value is not less than the preset current setting value, it is determined that there is a fault on the tie line, and the reclosing is locked out.

[0006] Further, the injection of the three-phase fundamental frequency alternating current signal into the tie line after the photovoltaic power source is temporarily added to the tie line includes: temporarily adding the photovoltaic power source to the tie line based on a lead line, and injecting the three-phase fundamental frequency alternating current signal.

[0007] Further, the preset connection time is 0.1s.

[0008] Further, the preset input duration is 0.1s.

[0009] Further, the expression for calculating the preset voltage setting value is: , wherein, is a reliability coefficient, , is a phase voltage amplitude of a three-phase fundamental frequency alternating current signal.

[0010] Further, the expression for calculating the preset current setting value is: , wherein, is a phase voltage amplitude of a three-phase fundamental frequency alternating current signal, is a tie line impedance, is a transition resistance.

[0011] Further, after judging whether the voltage value and the current value are less than preset voltage setting values and preset current setting values respectively, the method further comprises: if the voltage value and the current value are less than preset voltage setting values and preset current setting values respectively, determining that there is no fault on the tie line, and after cutting off the three-phase fundamental frequency alternating current signal line, the line is reclosed.

[0012] The three-phase adaptive reclosing method of the photovoltaic grid-connected tie line can quickly and reliably determine various faults on the tie line, and is not affected by the fault location and the transition resistance. In addition, when it is determined that there is no fault on the tie line, the tie line can be quickly and successfully reclosed; when it is determined that there is a fault on the tie line, the tie line can be reliably locked, thereby successfully avoiding reclosing the tie line on the fault. BRIEF DESCRIPTION OF DRAWINGS

[0013] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0014] Figure 1 is a flow chart of a three-phase adaptive reclosing method of a photovoltaic grid-connected tie line provided by an embodiment of the present application;

[0015] Figure 2 is a flow chart of another three-phase adaptive reclosing method of a photovoltaic grid-connected tie line provided by an embodiment of the present application;

[0016] Figure 3 is a schematic diagram of a photovoltaic power injection scheme provided by an embodiment of the present application;

[0017] Figure 4 is a simulation result diagram of voltage generated on the tie line when a single-phase ground fault occurs at the midpoint of the tie line of the photovoltaic grid-connected power generation system provided by an embodiment of the present application;

[0018] Figure 5 is a simulation result diagram of current generated on the tie line when a two-phase short-circuit fault occurs at the midpoint of the tie line of the photovoltaic grid-connected power generation system provided by an embodiment of the present application;

[0019] Figure 6 is a simulation result diagram of current generated on the tie line when a two-phase ground short-circuit fault occurs at the midpoint of the tie line of the photovoltaic grid-connected power generation system provided by an embodiment of the present application;

[0020] Figure 7 is a simulation result diagram of current generated on the tie line when a three-phase short-circuit fault occurs at the midpoint of the tie line of the photovoltaic grid-connected power generation system provided by an embodiment of the present application. DETAILED DESCRIPTION

[0021] To make the objectives, technical solutions, and superiorities of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described below in connection with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some, but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of the present application.

[0022] Please refer to Figure 1 , which shows a flowchart of a three-phase adaptive reclosing method of a photovoltaic grid-connected tie line.

[0023] As shown in Figure 1 , the three-phase adaptive reclosing method of the photovoltaic grid-connected tie line specifically includes the following steps:

[0024] Step S101, a tie line with three-phase disconnection of a circuit breaker is acquired.

[0025] Step S102, the tie line is connected to a fast grounding switch, and the connection lasts for a preset connection duration.

[0026] In this embodiment, the preset connection duration is set to 0.1s.

[0027] Step S103, a three-phase fundamental frequency alternating current signal is injected after a photovoltaic power supply is temporarily added to the tie line, and the injection lasts for a preset injection duration.

[0028] In this embodiment, the photovoltaic power supply is temporarily added to the tie line based on a lead line, and the three-phase fundamental frequency alternating current signal is injected, and the injection duration is 0.1s.

[0029] Step S104, the voltage value and the current value generated on the power-off line are obtained, and it is determined whether the voltage value and the current value are respectively less than a preset voltage setting value and a preset current setting value.

[0030] In the embodiment, if the voltage value and the current value are both less than the preset voltage setting value and the preset current setting value, it is determined that there is no fault on the tie line, and the line is reclosed after the three-phase base frequency alternating current signal line is cut off.

[0031] Specifically, the expression for calculating the preset voltage setting value is: , wherein, is a reliability coefficient, , is the phase voltage amplitude of the three-phase base frequency alternating current signal.

[0032] The expression for calculating the preset current setting value is: , wherein, is the phase voltage amplitude of the three-phase base frequency alternating current signal, is the impedance of the tie line, is the transition resistance.

[0033] Step S105, if the voltage value is not less than the preset voltage setting value or the current value is not less than the preset current setting value, it is determined that there is a fault on the tie line, and the reclosing is locked out.

[0034] The method of the embodiment, after the tie line with three-phase disconnection of breakers on both sides is connected to the fast grounding switch and the residual voltage of the line is discharged, the photovoltaic power system power is added to the tie line with three-phase disconnection of breakers on both sides through a lead line for a short time, the three-phase base frequency alternating current signal is injected, and whether there is a fault on the line is determined based on the voltage and the current generated on the power-off line. The various faults occurring on the tie line can be quickly and reliably determined, and are not affected by the fault position and the size of the transition resistance.

[0035] Please refer to Figure 2 which shows a flowchart of another photovoltaic grid-connected tie line three-phase adaptive reclosing method of the application.

[0036] The photovoltaic power system power is added to the tie line with three-phase disconnection of breakers on both sides for a short time, the three-phase base frequency alternating current signal is injected, and whether there is a fault on the line is determined based on the voltage and the current generated on the power-off line. The implementation is specifically as follows:

[0037] Step 1, the tie line with three-phase disconnection of breakers on both sides is first connected to the fast grounding switch, the residual voltage of the line is discharged, and the connection time is set to 0.1 s.

[0038] Step 2: Briefly connect the photovoltaic power supply to the interconnection line and inject a three-phase baseband AC signal for 0.1 seconds.

[0039] Step 3: Based on the voltage and current generated on the power outage line in Step 2, if the amplitude of the three-phase voltage and current does not exceed the set value, it is determined that there is no fault on the tie line.

[0040] (1)

[0041] In the formula, For reliability coefficient, , This represents the phase voltage amplitude of the three-phase fundamental frequency AC signal. In this embodiment... kV.

[0042] (2)

[0043] In the formula, This represents the phase voltage amplitude of the three-phase fundamental frequency AC signal. For the tie line impedance, This is the transition resistor. In this embodiment, A.

[0044] Step 4: If the generated voltage exceeds the setting value shown in Equation (1) or the current exceeds the setting value shown in Equation (2), it is determined that there is a fault on the tie line and the reclosing is blocked; if the generated voltage and current are both less than the setting values ​​shown in Equation (1) and Equation (2), it is determined that there is no fault on the tie line, and the line is reclosed after the injected signal line is disconnected.

[0045] Based on PSCAD / EMTDC, such as Figure 3 The photovoltaic grid-connected system model is shown. The system voltage level is 220 kV, and the frequency is 50 Hz. The rated capacity of the power station is 150 MW, and the external system three-sequence equivalent impedance is Ω. The parameters of each component in the power station are as follows: the inverter power supply has a rated capacity of 1.5 MW and a rated voltage of 0.69 kV. The tie line is 40 km long, with positive-sequence and zero-sequence impedances of Ω / km and Ω / km, respectively, and positive-sequence and zero-sequence capacitances of 0.0086μF / km and 0.0061μF / km, respectively. The tie line fault occurrence time is set to 0.9 s, the circuit breaker tripping time is set to 0.94 s, and a fast grounding switch is connected at 1 s with a connection duration of 0.1 s. At 1.1 s, a signal is injected from the photovoltaic power supply with an injection duration of 0.1 s, and the injected signal is a 0.9 kV three-phase fundamental frequency AC voltage.

[0046] To verify the effectiveness of the three-phase adaptive reclosing method of this invention, a large number of fault simulations and analyses were conducted, such as... Figures 3-7As shown, specifically, simulations and fault nature identification were performed for single-phase grounding, two-phase short circuit, two-phase short circuit to ground, and three-phase short circuit faults in the photovoltaic grid-connected tie line under different fault locations and different transition resistances. The simulation results are shown in Tables 1-4.

[0047] , As can be seen from Table 1, when a single-phase ground fault occurs in the tie line, the voltage of the non-faulty phase exceeds the set value under different fault locations and different transition resistances. Therefore, the three-phase adaptive reclosing method of the present invention can accurately identify the fault on the line and thus block the reclosing.

[0048] ,

[0049] ,

[0050] ,

[0051] As can be seen from Table 2-4, when a two-phase short circuit, a two-phase short circuit to ground, or a three-phase short circuit occurs on the tie line, the short circuit current on the line exceeds the set value under different fault locations and different transition resistances. Therefore, the three-phase adaptive reclosing method of the present invention can accurately identify the fault on the line and thus lock out the reclosing.

[0052] In summary, this invention proposes a three-phase adaptive reclosing method for photovoltaic grid-connected tie lines. This method can quickly and reliably determine various faults occurring on the tie lines, unaffected by the location of the fault or the magnitude of the transition resistance. Furthermore, when no fault is determined on the tie line, the tie line can quickly and successfully reclose; when a fault is determined on the tie line, the tie line can be reliably blocked, successfully preventing the tie line from reclosing at the fault.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A three-phase adaptive reclosing method for photovoltaic grid-connected interconnection lines, characterized in that, include: Obtain the disconnected tie line of the three phases of the circuit breaker; Connect the connecting line to the fast grounding switch and maintain the connection for a preset duration; After the photovoltaic power is briefly applied to the interconnect line, a three-phase base frequency AC signal is injected and the preset activation time is continuously applied. Obtain the voltage and current values ​​generated on the power outage line, and determine whether the voltage and current values ​​are less than the preset voltage setting value and the preset current setting value, respectively; If the voltage value is not less than the preset voltage setting value or the current value is not less than the preset current setting value, then a fault is determined to exist on the connection line, and reclosing is blocked.

2. The three-phase adaptive reclosing method for a photovoltaic grid-connected interconnection line according to claim 1, characterized in that, The step of briefly applying photovoltaic power to the interconnect line and then injecting a three-phase fundamental frequency AC signal includes: A photovoltaic power source is briefly applied to the interconnect line via a lead wire, and a three-phase baseband AC signal is injected.

3. The three-phase adaptive reclosing method for a photovoltaic grid-connected interconnection line according to claim 1, characterized in that, in, The preset access duration is 0.1s.

4. The three-phase adaptive reclosing method for a photovoltaic grid-connected interconnection line according to claim 1, characterized in that, in, The preset input time is 0.1s.

5. The three-phase adaptive reclosing method for a photovoltaic grid-connected interconnection line according to claim 1, characterized in that, in, The expression for calculating the preset voltage setting value is: YOU op =K rel ·E, In the formula, K rel K is the reliability coefficient. rel =1.2~1.3, where E is the phase voltage amplitude of the three-phase fundamental frequency AC signal.

6. The three-phase adaptive reclosing method for a photovoltaic grid-connected interconnection line according to claim 1, characterized in that, in, The expression for calculating the preset current setting value is: In the formula, E is the phase voltage amplitude of the three-phase fundamental frequency AC signal, and Z... L R is the tie line impedance, and R is the transition resistance.

7. A three-phase adaptive reclosing method for a photovoltaic grid-connected interconnection line according to claim 1, characterized in that, After determining whether the voltage value and the current value are less than preset voltage setting values ​​and preset current setting values, respectively, the method further includes: If both the voltage and current values ​​are less than the preset voltage and current settings, it is determined that there is no fault on the tie line, and the line reconnects after the three-phase baseband AC signal line is disconnected.

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