Online ice melting system

Abstract

The embodiment of the invention discloses an online ice melting system, which comprises a first grounding transformer, a second grounding transformer, an active grounding device and a grounding end, the first end of the first grounding transformer is connected with the first end of the iced line, the second end of the first grounding transformer is connected with the first end of the active grounding device, the second end of the active grounding device is connected with the grounding end, the first end of the second grounding transformer is connected with the second end of the iced line, and the second end of the second grounding transformer is connected with the grounding end; the active grounding device, the first grounding transformer, the second grounding transformer, the iced line and the grounding end form a closed loop, and zero-sequence current is generated and superposed on original current of the iced line for ice melting; wherein the active grounding device is used for adjusting the zero sequence current. By adopting the technical scheme, the power failure of the line during the ice melting period can be avoided, the bottleneck that the power failure is required during the original ice melting operation is broken through, and the loss of the power failure of the line caused by ice coating and the power failure of the line caused by ice melting is effectively reduced.

Description

Technical Field

[0001] The invention relates to the technical field of line ice melting, and in particular to an online ice melting system. Background Art

[0002] Ice on the lines caused by snow and ice weather has a great impact on the safe and stable operation of power lines. Severe ice can cause the conductor bearing pressure to exceed the limit value, causing the conductor to break; at the same time, due to special forms of movement such as conductor dancing due to ice and conductor jumping due to ice shedding, line components will be damaged and insulation gaps will be broken, seriously interfering with the stable operation of the power system.

[0003] The distribution network has a smaller wire diameter than the main network, so the difference in resistance and reactance is not particularly obvious. The reactive component added by the AC short-circuit ice-melting technology can also be ignored. At the same time, DC ice-melting requires the addition of rectifiers and other equipment, and the construction cost is higher. Therefore, if the distribution network lines use the more mature DC ice-melting method, there will be major disadvantages. Summary of the invention

[0004] An embodiment of the present invention provides an online ice melting system, which can realize uninterrupted ice melting of distribution network lines according to a closed loop formed by an active grounding device, a first grounding transformer, a second grounding transformer, an ice-covered line and a grounding terminal.

[0005] In a first aspect, an embodiment of the present invention provides an online ice melting system, comprising a first grounding transformer, a second grounding transformer, an active grounding device and a grounding terminal;

[0006] The first end of the first grounding transformer is connected to the first end of the ice-covered line, the second end of the first grounding transformer is connected to the first end of the active grounding device, the second end of the active grounding device is connected to the grounding end, the first end of the second grounding transformer is connected to the second end of the ice-covered line, and the second end of the second grounding transformer is connected to the grounding end;

[0007] The active grounding device, the first grounding transformer, the second grounding transformer, the ice-covered line and the grounding end form a closed loop, and generate a zero-sequence current superimposed on the original current of the ice-covered line to melt ice; wherein the active grounding device is used to adjust the zero-sequence current.

[0008] Optionally, the active grounding device comprises a T-type 3-level converter and a step-up transformer, wherein the step-up transformer comprises a primary winding and a secondary winding;

[0009] The first end of the primary winding is connected to the positive input end of the T-type 3-level converter, and the second end of the primary winding is connected to the negative output end of the T-type 3-level converter;

[0010] The first end of the secondary winding is connected to the second end of the first grounding transformer, and the second end of the secondary winding is connected to the ground end.

[0011] Optionally, the system further includes a first switch module;

[0012] A first end of the first switch module is connected to a second end of the first grounding transformer, and a second end of the first switch module is connected to a second end of the second winding.

[0013] Optionally, the first grounding transformer is connected to the ice-covered line in a Z-type connection mode;

[0014] The first grounding transformer is a three-phase grounding transformer, and the first end of the first grounding transformer includes a first access end, a second access end and a third access end, and the first access end, the second access end and the third access end are respectively connected to the three phases of the first end of the ice-coated line.

[0015] Optionally, the second grounding transformer is connected to the ice-covered line in a Z-type connection mode;

[0016] The second grounding transformer is a three-phase grounding transformer, and the first end of the second grounding transformer includes a fourth access end, a fifth access end and a sixth access end, and the fourth access end, the fifth access end and the sixth access end are respectively connected to the three phases of the second end of the ice-coated line.

[0017] Optionally, the system further includes a second switch module and a third switch module;

[0018] A first end of the second switch module is connected to a first end of the ice coating circuit, and a second end of the second switch module is connected to a first end of the first grounding transformer;

[0019] The first end of the third switch module is connected to the second end of the ice coating circuit, and the second end of the third switch module is connected to the first end of the second grounding transformer.

[0020] Optionally, the system further includes a neutral point non-effective grounding module;

[0021] The first end of the neutral point non-effective grounding module is connected to the third end of the second switch module, and the second end of the neutral point non-effective grounding module is connected to the grounding end.

[0022] Optionally, the second switch module is a switching switch;

[0023] The switch is used to switch the first end of the ice-coating line to be connected to the neutral point non-effective grounding module or the first end of the first grounding transformer.

[0024] Optionally, the first grounding transformer is a three-phase grounding transformer, and the first end of the first grounding transformer includes a first access end, a second access end and a third access end;

[0025] The switching switch includes a first switching switch, a second switching switch and a third switching switch;

[0026] The first end of the first switch, the first end of the second switch and the first end of the third switch are respectively connected to the three phases of the first end of the ice coating circuit;

[0027] The second end of the first switch is connected to the first access end, the second end of the second switch is connected to the second access end, and the second end of the third switch is connected to the third access end.

[0028] Optionally, the first end of the neutral point non-effective grounding module includes a seventh access terminal, an eighth access terminal and a ninth access terminal;

[0029] The seventh access terminal is connected to the third terminal of the first switch, the eighth access terminal is connected to the third terminal of the second switch, and the ninth access terminal is connected to the third terminal of the third switch.

[0030] In this embodiment, after the first grounding transformer, the active grounding device, the grounding end and the second grounding transformer are connected in sequence, the first end of the first grounding transformer and the first end of the second grounding transformer are respectively connected to the two ends of the ice-covered line to form a zero-sequence current loop. The zero-sequence current in the loop is adjusted by the active grounding device. During the ice melting process, the adjusted zero-sequence current only flows in the loop and does not affect the power supply to the load end. The ice-covered line can be melted without power outage, breaking through the bottleneck of power outage required during the original ice melting operation, effectively reducing the losses caused by line power outages due to icing and line power outages due to ice melting, which is beneficial to ensuring the power supply at the load end of the distribution network and greatly improving the reliability of the power supply of the power grid.

[0031] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0033] Figure 1 is a structural schematic diagram of an online ice melting system provided by an embodiment of the present invention;

[0034] Figure 2 is a structural schematic diagram of another online ice melting system provided by an embodiment of the present invention;

[0035] Figure 3 It is a partial structural schematic diagram of an online ice melting system provided by an embodiment of the present invention;

[0036] Figure 4 is a structural schematic diagram of another online ice melting system provided by an embodiment of the present invention;

[0037] Figure 5 is a structural schematic diagram of another online ice melting system provided by an embodiment of the present invention;

[0038] Figure 6 is a structural schematic diagram of another online ice melting system provided by an embodiment of the present invention;

[0039] Figure 7 It is a partial structural schematic diagram of another online ice melting system provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0040] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0041] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0042] In the prior art, in the case of ice formation on the line, there are two main ice melting methods: AC short-circuit ice melting technology and DC short-circuit ice melting technology, which greatly alleviate the problem of ice on the power grid. However, it still requires power outages during the ice melting period. While solving the ice problem, it also reduces the effective power consumption rate to a certain extent. Unlike the ice melting of the main grid transmission line, the 35kV and below distribution network is directly connected to the user side. Due to the complex and changeable conditions of the sections through which the distribution lines pass, their lines account for a large proportion. Since the voltage level of the distribution network is not high in the power grid, the staff does not pay enough attention to the protection of its lines, which makes the distribution network itself have a low level of natural disaster prevention. The distribution network areas prone to ice are often located in mountainous areas with high altitudes and narrow and rugged mountain roads. Therefore, compared with the main grid, the distribution network needs more effective de-icing and ice melting methods.

[0043] Figure 1 is a structural diagram of an online ice melting system provided by an embodiment of the present invention. This embodiment can be applied to the case of melting ice on ice-covered lines of a distribution network, such as Figure 1 As shown, the online ice melting system 100 includes: a first grounding transformer 1, a second grounding transformer 2, an active grounding device 3 and a grounding terminal 4; the first end of the first grounding transformer is connected to the first end of the ice-covered line 5, the second end of the first grounding transformer 1 is connected to the first end of the active grounding device 3, the second end of the active grounding device 3 is connected to the grounding terminal 4, the first end of the second grounding transformer 2 is connected to the second end of the ice-covered line 5, and the second end of the second grounding transformer 2 is connected to the grounding terminal 4; the active grounding device 3, the first grounding transformer 1, the second grounding transformer 2, the ice-covered line 5 and the grounding terminal 4 form a closed loop, and generate a zero-sequence current superimposed on the original current of the ice-covered line 5 to melt ice; wherein the active grounding device 3 is used to adjust the zero-sequence current.

[0044] Specifically, the first end of the first grounding transformer 1 is connected to the first end of the ice-covered circuit 5, the original three-phase current of the ice-covered circuit is led out, and the three-phase current is integrated into the second end of the first grounding transformer 1 through the first grounding transformer 1. This process is actually to lead out the neutral point of the three-phase circuit through the first grounding transformer 1 to form a neutral point that can be grounded (i.e., the second end of the first grounding transformer 1), and the neutral point can output zero-sequence current. The first end of the active grounding device 3 is connected to the second end of the first grounding transformer 1, and is used to receive the zero-sequence current output by the neutral point, and adjust the zero-sequence current according to the actual ice-melting current required by the ice-covered circuit 5, and then connect the grounding terminal 4 through the second end of the active grounding device 3 to output the adjusted zero-sequence current to the grounding terminal 4. The grounding terminal 4 is also connected to the second end of the second grounding transformer 2, and the first end of the second grounding transformer 2 is connected to the second end of the ice-covered line 5, forming a closed loop including the ice-covered line 5, the first grounding transformer 1, the active grounding device 3, the grounding terminal 4 and the second grounding transformer 2. After the adjusted zero-sequence current is output from the grounding terminal 4 to the second grounding transformer 2, it is connected to the second end of the ice-covered line 5 through the first end of the second grounding transformer 2, and the adjusted zero-sequence current is output to the original three-phase circuit, so that the current flowing through the three-phase ice-covered line reaches the critical ice melting current, thereby achieving ice melting and line protection.

[0045] In this embodiment, after the first grounding transformer, the active grounding device, the grounding end and the second grounding transformer are connected in sequence, the first end of the first grounding transformer and the first end of the second grounding transformer are respectively connected to the two ends of the ice-covered line to form a zero-sequence current loop. The zero-sequence current in the loop is adjusted by the active grounding device. During the ice melting process, the adjusted zero-sequence current only flows in the loop and does not affect the power supply to the load end. The ice-covered line can be melted without power outage, breaking through the bottleneck of power outage required during the original ice melting operation, effectively reducing the losses caused by line power outages due to icing and line power outages due to ice melting, which is beneficial to ensuring the power supply at the load end of the distribution network and greatly improving the reliability of the power supply of the power grid.

[0046] Based on the above embodiments, Figure 2 is a structural schematic diagram of another online ice melting system provided by an embodiment of the present invention, Figure 3 is a partial structural diagram of an online ice melting system provided by an embodiment of the present invention. Figure 2 The online ice melting system shown in FIG. 1 illustrates the structure of the active grounding device. Figure 2As shown, the active grounding device 3 includes a T-type three-level converter 31 and a boost transformer 32, wherein the boost transformer 32 includes a primary winding 321 and a secondary winding 322; a first end of the primary winding 321 is connected to the positive input end of the T-type three-level converter 31, and a second end of the primary winding 321 is connected to the negative output end of the T-type three-level converter 31; a first end of the secondary winding 322 is connected to the second end of the first grounding transformer 1, and a second end of the secondary winding 322 is connected to the grounding terminal 4.

[0047] Specifically, refer to Figure 2 The active grounding device 3 includes a T-type three-level converter 31 and a step-up transformer 32. When the ice is melting, the active grounding device 3 can be equivalent to a controlled current source connected in series to the ice melting circuit. Its output is controlled by the T-type three-level converter 31, which can effectively adjust the ice melting current of the line to achieve ice melting.

[0048] Among them, the upper terminal of the T-type 3-level converter 31 is the positive input terminal, and the lower terminal of the T-type 3-level converter 31 is the negative output terminal; the upper terminal of the primary winding 321 in the boost transformer 32 is the first terminal, and the lower terminal of the primary winding 321 in the boost transformer 32 is the second terminal; the upper terminal of the secondary winding 322 in the boost transformer 32 is the first terminal, and the lower terminal of the secondary winding 322 in the boost transformer 32 is the second terminal. The first end of the primary winding 321 is connected to the positive input terminal of the T-type 3-level converter 31, and the second end of the primary winding 321 is connected to the negative output terminal of the T-type 3-level converter 31; the first end of the secondary winding 322 is connected to the second end of the first grounding transformer 1, and the second end of the secondary winding 322 is connected to the ground terminal 4.

[0049] refer to Figure 3The T-type 3-level converter 31 is composed of eight IGBTs, eight diodes and two capacitors. This structure can act as an inverter to inject AC into the distribution network. The magnitude and phase of the output current of the T-type 3-level converter 31 can be changed through the action of the bridge arm switch tube. Among them, the freewheeling diode connected in parallel with the IGBT provides a freewheeling channel for the current when the IGBT is turned off, avoiding voltage shock in the circuit and protecting the IGBT from damage; the capacitor is used for voltage support and level switching, helping to achieve a smooth transition of the output voltage between different levels, helping to reduce the harmonic content of the output voltage and improve the quality of power; the IGBT is the switching element of the T-type 3-level converter 31, responsible for controlling the conduction and shutdown of the current to achieve the conversion of electric energy. Multiple IGBTs are used to build a half-bridge inverter or a full-bridge inverter, which generates the voltage waveform required for ice melting through a specific control strategy. The AC power converted by the T-type three-level converter 31 is sent to the primary winding 321 of the step-up transformer 32. At this time, the AC power generates an alternating magnetic field, which passes through the iron core of the step-up transformer 32 and is induced on the secondary winding 322. Since the number of turns of the secondary winding is more than that of the primary winding, according to the principle of electromagnetic induction, a higher voltage will be generated on the secondary winding 322. The boosted AC power is output from the secondary winding 322 of the step-up transformer 32 to the ice-covered line 5, and the total ground capacitance current of the distribution network increases, thereby causing the current flowing through the ice-covered line 5 to reach the critical ice-melting current, so as to achieve ice-melting of the ice-covered line 5 without power outage.

[0050] For example, continue to refer to Figure 3 When the online ice melting system provided in this embodiment performs ice melting operation on the ice-covered line 5, the load current flowing through the ice-covered line 5 of the distribution network is firstly measured in real time, and the ice melting current value I required for the ice-covered line conductor of the distribution network to melt ice for 1 hour is obtained. m According to the existing load current in the ice-covered line 5 and the required ice-melting current value, the fault ice-melting current value I when a single-phase (A phase, B phase or C phase) grounding fault occurs in the ice-melting line is calculated. f Since the active grounding device 3 needs to provide three-phase (A phase, B phase and C phase) ice melting current value, the current value that the active grounding device 3 needs to output is calculated to be 3I f . 3I f As the actual output current value of the T-type 3-level converter 31, the capacitor voltage reference value and the current reference value are input to the T-type 3-level converter 31. Combined with the actual value of the capacitor voltage, the voltage and current dual-loop control strategy is used to achieve accurate control of the output current when the T-type 3-level converter 31 is connected to the boost transformer 32, and the output current is controlled to be the reference value 3I that can achieve the purpose of ice melting. f , after passing through the second grounding transformer 2, it is divided into zero-sequence currents of equal amplitude and phase and connected to the three-phase circuits A, B and C of the distribution network, so that the current flowing in each phase line is If , realizing ice melting of ice-covered line 5 without power outage.

[0051] It should be noted that by controlling the T-type three-level converter 31 to adjust the magnitude of the output current of the active grounding device 3, the total capacitive current of the distribution network to the ground can be increased, and then the current flowing through the ice-covered line 5 can reach the critical ice-melting current. If the critical ice-melting current cannot meet the specific rapid ice-melting occasion, the capacitive reactive current output by the active grounding device 3 can be dynamically adjusted according to the required ice-melting current value, so that the current flowing through the grounded phase ice-covered line reaches the critical ice-melting current. If rapid ice-melting is required, the output current can be appropriately increased to remove the ice on the conductor within the specified time. When it is observed that the ice layer of the ice-covered line is loose, melted and falls off, the ice-melting system stops running and disconnects from the grid.

[0052] It can be understood that when the T-type three-level converter 31 is controlled by the voltage-current dual-loop control strategy, the output current 3I of the T-type three-level converter 31 can be controlled. f The phase of the ice melting system is 90° ahead of the grid-connected neutral point voltage phase, presenting the ground capacitance characteristics to the outside. At this time, there is no active interaction between the ice melting system and the power grid. The DC side capacitor voltage can be basically kept stable during the ice melting process, and no large-capacity DC regulated power supply is required, which saves the cost and space of the ice melting system and is easy to integrate into a mobile ice melting system.

[0053] In this embodiment, an active grounding device is formed by connecting a T-type three-level converter and a step-up transformer. The magnitude and phase of the output current of the active grounding device can be changed through the action of the bridge arm switch tube of the T-type three-level converter, and the magnitude of the zero-sequence current can be dynamically adjusted according to actual conditions to achieve online ice melting, thereby improving the flexibility of the ice melting system.

[0054] Optional, such as Figure 3 As shown, the active grounding device 3 further includes an inductor L1.

[0055] Specifically, the first end of the inductor L1 is connected to the positive input end of the T-type three-level converter 31, and the second end of the inductor L1 is connected to the first end of the primary winding 321. The inductor L1 is arranged between the T-type three-level converter 31 and the primary winding 321 as a filter inductor, which can effectively reduce the high-frequency noise in the power supply. When the current passes through the inductor, the high-frequency component will be absorbed and converted into heat energy and dissipated, while the low-frequency component can continue to be transmitted to the primary winding 321 through the inductor L1, thereby reducing the internal resistance of the T-type three-level converter 31, reducing energy loss, and improving the conversion efficiency of the T-type three-level converter 31.

[0056] Optional, reference Figure 2The online ice melting system further includes a first switch module 6; a first end of the first switch module 6 is connected to a second end of the first grounding transformer 1, and a second end of the first switch module 6 is connected to a second end of the second winding.

[0057] Specifically, the first switch module 6 is disposed between the first grounding transformer 1 and the active grounding device 3, and can control the on and off of the ice-melting current, thereby realizing the control of the ice-melting operation. When the ice-melting is completed and the ice-covered line 5 needs to be disconnected from the active grounding device 3, the switch module can quickly cut off the loop current to ensure the safety of the loop. In addition, the first switch module 6 can also provide short-circuit protection and overload protection. When a short-circuit fault occurs in the ice-melting loop or the ice-melting current exceeds the rated value that the line can withstand, the first switch module 6 will immediately cut off the active grounding device 3 to avoid further damage and prevent the online ice-melting system from being damaged.

[0058] Based on the above embodiments, Figure 4 is a structural schematic diagram of another online ice melting system provided by an embodiment of the present invention, Figure 4 The online ice melting system shown further illustrates the structure of the first grounding transformer. Figure 4 As shown, the first grounding transformer 1 is connected to the ice-coated line 5 in a Z-type connection mode; the first grounding transformer 1 is a three-phase grounding transformer, and the first end of the first grounding transformer 1 includes a first access terminal a, a second access terminal b and a third access terminal c, and the first access terminal a, the second access terminal b and the third access terminal c are respectively connected to the three phases of the first end of the ice-coated line 5.

[0059] Specifically, a Z-type (zigzag) wiring method is adopted between the first grounding transformer 1 and the ice-covered line. The first access end a is connected to the A-phase circuit of the ice-covered line 5, the second access end b is connected to the B-phase circuit of the ice-covered line 5, and the third access end b is connected to the C-phase circuit of the ice-covered line, so that the first grounding transformer 1 is connected to the first end of the ice-covered line 5 and forms a first neutral point N at the second end of the first grounding transformer 1. This wiring method can provide better voltage regulation capability and higher short-circuit impedance, which helps to limit short-circuit current and improve system stability.

[0060] It can be understood that after the ice-covered line 5 is connected to the first grounding transformer 1, the first grounding transformer 1 adopts a zigzag connection (Z) so that the third harmonic electromotive force in each phase cancels each other out, and the phase electromotive force is close to a sine wave. The two sections of the winding in the two half windings on the same iron core column of the Z-type first grounding transformer 1 have the same number of turns and opposite polarities. Therefore, the first grounding transformer 1 has a large positive-sequence impedance and negative-sequence impedance; at the same time, the two sections of the winding on the same core column of the Z-type first grounding transformer 1 flow through equal zero-sequence currents to generate mutually canceling magnetic fluxes, which produce low impedance to the zero-sequence current, which can meet the system's requirement for small zero-sequence impedance, so that the system zero-sequence current passes normally.

[0061] It should be noted that, since the first grounding transformer 1 does not need to carry a secondary load, the secondary winding of the first grounding transformer 1 is omitted in this embodiment, which helps to reduce the cost, volume and quality of the online ice melting system. In the formed ice melting loop, when the current flows into the first neutral point N of the first grounding transformer 1, the zero-sequence three-phase current with the same frequency and amplitude flows out of the three-phase winding on the primary side of the first grounding transformer 1. Therefore, when the current output by the active grounding device 3 is 3I f When the current passes through the first grounding transformer 1, the current of each phase on the ice-covered line 5 is I f .

[0062] In this embodiment, the first grounding transformer is connected to the ice-covered line in a Z-type connection mode, which can provide better anti-interference performance and help maintain a stable output zero-sequence current, thereby improving the power quality and ice-melting stability of the online ice-melting system.

[0063] Based on the above embodiments, continue to refer to Figure 4 , Figure 4 The online ice melting system shown further illustrates the structure of the second grounding transformer. Figure 4 As shown, the second grounding transformer 2 is connected to the ice-covered line 5 in a Z-type connection mode; the second grounding transformer 2 is a three-phase grounding transformer, and the first end of the second grounding transformer 2 includes a fourth access terminal x, a fifth access terminal y and a sixth access terminal z, and the fourth access terminal x, the fifth access terminal y and the sixth access terminal z are respectively connected to the three phases of the second end of the ice-covered line 5.

[0064] Specifically, a Z-type (zigzag) wiring method is adopted between the second grounding transformer 2 and the ice-covered line. The fourth access terminal x is connected to the A-phase circuit of the ice-covered line 5, the fifth access terminal y is connected to the B-phase circuit of the ice-covered line 5, and the sixth access terminal z is connected to the C-phase circuit of the ice-covered line, so that the second grounding transformer 2 is connected to the first end of the ice-covered line 5 and forms a second neutral point M at the second end of the second grounding transformer 2. This wiring method can provide better voltage regulation capability and higher short-circuit impedance, which helps to limit short-circuit current and improve system stability.

[0065] It can be understood that after the ice-covered line 5 is connected to the second grounding transformer 2, the second grounding transformer 2 adopts a zigzag connection (Z) so that the third harmonic electromotive force in each phase cancels each other out, and the phase electromotive force is close to a sine wave. The two sections of the winding in the two half windings on the same iron core column of the Z-type second grounding transformer 2 have the same number of turns and opposite polarities. Therefore, the second grounding transformer 2 has a large positive-sequence impedance and negative-sequence impedance; at the same time, the two sections of the winding on the same core column of the Z-type second grounding transformer 2 flow through equal zero-sequence currents to generate mutually canceling magnetic fluxes, which produce low impedance to the zero-sequence current, which can meet the system's requirement for small zero-sequence impedance, so that the system zero-sequence current passes normally.

[0066] It should be noted that, since the second grounding transformer 2 does not need to carry a secondary load, the secondary winding of the second grounding transformer 2 is omitted in this embodiment, which helps to reduce the cost, volume and quality of the online ice melting system. In the formed ice melting loop, when the current flows out from the second neutral point M of the second grounding transformer 2, the zero-sequence three-phase current with the same frequency and amplitude flows into the primary three-phase winding of the second grounding transformer 2. Therefore, when the current output by each phase of the ice-covered line 5 is I f When the three-phase current passes through the second grounding transformer 2, the current flowing into the grounding terminal 4 is 3I f .

[0067] In this embodiment, the second grounding transformer is connected to the ice-covered line in a Z-type connection mode, which can provide better anti-interference performance and help maintain a stable output zero-sequence current, thereby improving the power quality and ice-melting stability of the online ice-melting system.

[0068] Based on the above embodiments, Figure 5 is a structural schematic diagram of another online ice melting system provided by an embodiment of the present invention, Figure 5 The online ice melting system shown further illustrates the switch module. Figure 5 As shown, the online ice melting system 100 also includes a second switch module 7 and a third switch module 8; the first end of the second switch module 7 is connected to the first end of the ice-coating circuit 5, and the second end of the second switch module 7 is connected to the first end of the first grounding transformer 1; the first end of the third switch module 8 is connected to the second end of the ice-coating circuit 5, and the second end of the third switch module 8 is connected to the first end of the second grounding transformer 2.

[0069] Specifically, a second switch module 7 is provided between the ice-coated line 5 and the first grounding transformer 1, and a third switch module 8 is provided between the ice-coated line 5 and the second grounding transformer 2. When melting ice, the second switch module 7 and the third switch module 8 are closed at the same time, so that the first grounding transformer 1 and the second grounding transformer 2 are connected to the ice-coated line 5, forming an ice-melting closed loop including the ice-coated line 5, the first grounding transformer 1, the active grounding device 3, the grounding terminal 4, and the second grounding transformer 2; when ice melting is completed, the second switch module 7 and the third switch module 8 are disconnected, so that the online ice-melting system is disconnected from the ice-coated line 5.

[0070] This embodiment controls the connection and disconnection of the online ice melting system and the ice-covered line through the second switch module and the third switch module, which not only improves the controllability of the online ice melting system and makes the online ice melting system easy to manage, but also improves the power supply stability of the power system. When a short circuit or other fault occurs in the online ice melting system, the online ice melting system can be isolated from the distribution line in time to avoid further damage to the distribution power system.

[0071] Optional, Figure 6 is a structural diagram of another online ice melting system provided by an embodiment of the present invention, referring to Figure 6 The online ice melting system 100 also includes a neutral point non-effective grounding module 9; a first end of the neutral point non-effective grounding module 9 is connected to the third end of the second switch module 7, and a second end of the neutral point non-effective grounding module 9 is connected to the ground terminal 4.

[0072] Specifically, a neutral point non-effective grounding module 9 is arranged between the second switch module 7 and the grounding terminal 4. On the one hand, it can limit the current during a single-phase grounding fault, thereby reducing the risk of fire caused by a short circuit. When a single-phase grounding fault occurs, the non-effective grounding system can keep the line voltage of the three-phase conductor unchanged, ensuring that the voltages of the other two phases to the ground remain stable, thereby improving the safety of the power system. On the other hand, grounding the second end of the neutral point non-effective grounding module 9 can quickly eliminate the arc when a fault occurs, thereby preventing the equipment from being damaged by continuous electrical stress.

[0073] Optionally, the second switch module 7 is a switching switch; the switching switch is used to switch the first end of the ice coating line 5 to be connected to the neutral point non-effective grounding module 9 or the first end of the first grounding transformer 1.

[0074] Specifically, when the ice-coated line 5 is connected to the neutral point non-effective grounding module 9 through the switching switch, the first grounding transformer 1 is disconnected from the ice-coated line 5; when the ice-coated line 5 is connected to the first grounding transformer 1 through the switching switch, the neutral point non-effective grounding module 9 is disconnected from the ice-coated line 5. After the ice-coated line 5 is disconnected from the first grounding transformer 1, the neutral point non-effective grounding module 9 continues to maintain the line stability and adjust the impedance value of the line. Exemplarily, the switching switch can be a single-pole double-throw switch, which is not specifically limited in this embodiment.

[0075] Optional, Figure 7 is a partial structural diagram of another online ice melting system provided by an embodiment of the present invention, referring to Figure 7 The first grounding transformer 1 is a three-phase grounding transformer, and the first end of the first grounding transformer 1 includes a first access terminal a, a second access terminal b and a third access terminal c; the switching switch includes a first switching switch 71, a second switching switch 72 and a third switching switch 73; the first end of the first switching switch 71, the first end of the second switching switch 72 and the first end of the third switching switch 73 are respectively connected to the three phases of the first end of the ice-coating line 5; the second end of the first switching switch 71 is connected to the first access terminal a, the second end of the second switching switch 72 is connected to the second access terminal b, and the second end of the third switching switch 73 is connected to the third access terminal c.

[0076] Specifically, the first switching switch 71 is arranged between the A phase circuit of the ice-covered line 5 and the first access terminal a of the first grounding transformer 1; the second switching switch 72 is arranged between the B phase circuit of the ice-covered line 5 and the second access terminal b of the first grounding transformer 1; the third switching switch 73 is arranged between the C phase circuit of the ice-covered line 5 and the third access terminal c of the first grounding transformer 1. When the ice is melted, the first grounding transformer 1 is connected to the three-phase circuit of the ice-covered line 5 through the first switching switch 71, the second switching switch 72 and the third switching switch 73.

[0077] Optional, continue to refer to Figure 7 The first end of the neutral point non-effective grounding module 9 includes a seventh access terminal d, an eighth access terminal e and a ninth access terminal f; the seventh access terminal d is connected to the third end of the first switching switch 71, the eighth access terminal e is connected to the third end of the second switching switch 72, and the ninth access terminal f is connected to the third end of the third switching switch 73.

[0078] Specifically, a Z-type (zigzag) wiring method can be used between the neutral point non-effective grounding module 9 and the ice-coated line. When the seventh access terminal d is connected to the third end of the first switching switch 71, the seventh access terminal d is connected to the A-phase circuit of the ice-coated line 5; when the eighth access terminal e is connected to the third end of the second switching switch 72, the eighth access terminal e is connected to the B-phase circuit of the ice-coated line 5; when the ninth access terminal f is connected to the third end of the third switching switch 73, the ninth access terminal f is connected to the C-phase circuit of the ice-coated line 5. This wiring method helps to keep the ice-coated line 5 stable after being disconnected from the first grounding transformer 1, thereby improving system safety.

[0079] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An online ice melting system, characterized in that: It includes a first grounding transformer, a second grounding transformer, an active grounding device and a grounding terminal; The first end of the first grounding transformer is connected to the first end of the ice-covered line, the second end of the first grounding transformer is connected to the first end of the active grounding device, the second end of the active grounding device is connected to the grounding end, the first end of the second grounding transformer is connected to the second end of the ice-covered line, and the second end of the second grounding transformer is connected to the grounding end; The active grounding device, the first grounding transformer, the second grounding transformer, the ice-covered line and the grounding end form a closed loop, and generate a zero-sequence current superimposed on the original current of the ice-covered line to melt ice; wherein the active grounding device is used to adjust the zero-sequence current.

2. The online ice melting system according to claim 1, characterized in that: The active grounding device comprises a T-type 3-level converter and a step-up transformer, wherein the step-up transformer comprises a primary winding and a secondary winding; The first end of the primary winding is connected to the positive input end of the T-type 3-level converter, and the second end of the primary winding is connected to the negative output end of the T-type 3-level converter; The first end of the secondary winding is connected to the second end of the first grounding transformer, and the second end of the secondary winding is connected to the ground end.

3. The online ice melting system according to claim 2, characterized in that: The system also includes a first switch module; A first end of the first switch module is connected to a second end of the first grounding transformer, and a second end of the first switch module is connected to a second end of the second winding.

4. The online ice melting system according to claim 1, characterized in that: The first grounding transformer is connected to the ice-covered line in a Z-type connection mode; The first grounding transformer is a three-phase grounding transformer, and the first end of the first grounding transformer includes a first access end, a second access end and a third access end, and the first access end, the second access end and the third access end are respectively connected to the three phases of the first end of the ice-coated line.

5. The online ice melting system according to claim 1, characterized in that: The second grounding transformer is connected to the ice-covered line in a Z-type connection mode; The second grounding transformer is a three-phase grounding transformer, and the first end of the second grounding transformer includes a fourth access end, a fifth access end and a sixth access end, and the fourth access end, the fifth access end and the sixth access end are respectively connected to the three phases of the second end of the ice-coated line.

6. The online ice melting system according to claim 1, characterized in that: The system further comprises a second switch module and a third switch module; A first end of the second switch module is connected to a first end of the ice coating circuit, and a second end of the second switch module is connected to a first end of the first grounding transformer; The first end of the third switch module is connected to the second end of the ice coating circuit, and the second end of the third switch module is connected to the first end of the second grounding transformer.

7. The online ice melting system for distribution network according to claim 6, characterized in that: The system also includes a neutral point non-effective grounding module; The first end of the neutral point non-effective grounding module is connected to the third end of the second switch module, and the second end of the neutral point non-effective grounding module is connected to the grounding end.

8. The online ice melting system for distribution network according to claim 7, characterized in that: The second switch module is a switching switch; The switch is used to switch the first end of the ice-coating line to be connected to the neutral point non-effective grounding module or the first end of the first grounding transformer.

9. The online ice melting system for distribution network according to claim 8, characterized in that: The first grounding transformer is a three-phase grounding transformer, and the first end of the first grounding transformer includes a first access end, a second access end and a third access end; The switching switch includes a first switching switch, a second switching switch and a third switching switch; The first end of the first switch, the first end of the second switch and the first end of the third switch are respectively connected to the three phases of the first end of the ice coating circuit; The second end of the first switch is connected to the first access end, the second end of the second switch is connected to the second access end, and the second end of the third switch is connected to the third access end.

10. The online ice melting system for distribution network according to claim 9, characterized in that: The first end of the neutral point non-effective grounding module includes a seventh access terminal, an eighth access terminal and a ninth access terminal; The seventh access terminal is connected to the third terminal of the first switch, the eighth access terminal is connected to the third terminal of the second switch, and the ninth access terminal is connected to the third terminal of the third switch.

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