Controllable distribution transformer

Abstract

The utility model discloses a controllable distribution transformer. The controllable distribution transformer comprises a power supply winding and a control winding, wherein the power supply winding and the control winding are positioned on a low-voltage side; the power supply winding and the control winding are both wound on an iron core of the distribution transformer, a winding on one side of the additional mutual inductor is connected with the power supply winding in series, a winding on the other side of the additional mutual inductor is connected with the control winding in parallel, and the first loop switch and the second loop switch are arranged at the two ends of the winding on one side respectively. The first loop switch, the second loop switch, the side winding and the control switch unit are connected in series, and the control switch unit is connected with the control winding; the power compensation control system controls the first loop switch, the second loop switch and a control switch in the control switch unit according to the voltage at the two ends of the power supply winding so as to control the number of turns connected to the winding and control the voltage value and phase change on the winding, and then series compensation of the voltage at the two ends of the power supply winding is achieved. According to the utility model, the working current of the switch can be greatly reduced, and the reliability is improved.

Description

Technical Field

[0001] The utility model relates to the technical field of electrical equipment, and more particularly to a controllable distribution transformer. Background Art

[0002] The impacts of distributed photovoltaics on the power grid and users mainly include: the impact on the local voltage stability of the distribution network, the impact on the frequency stability of the power grid, the contribution to the short-circuit current in faults, the impact on power quality, and the changes in the requirements for power factor and reactive power configuration.

[0003] Most early 10kV distribution lines used single radial distribution power supply, resulting in low system security. In the construction and renovation of urban distribution networks, consideration is gradually being given to establishing ring-type power supply and open-loop operation. In various distribution network structures, static and dynamic voltage fluctuations can impact line protection and system operational safety. Under steady-state operation, voltage theoretically decreases gradually along the transmission line's power flow direction. However, after the integration of distributed photovoltaic systems, fluctuations in transmission power and the characteristics of distributed loads can cause voltages at various nodes on the transmission lines to be either too high or too low, resulting in voltage deviations exceeding technical indicators for safe operation.

[0004] Figure 1 This article describes the impact of distributed photovoltaic integration on local voltages in distribution networks. Large-scale distributed photovoltaic integration can lead to static voltage offsets at local nodes in the distribution network. Distribution networks, especially low-voltage networks, are particularly sensitive to voltage variations. To mitigate these effects, controllable transformers are required when selecting medium- and low-voltage transformers.

[0005] Therefore, a controllable distribution transformer is needed. Summary of the Invention

[0006] The utility model provides a controllable distribution transformer to solve the problem.

[0007] In order to solve the above problems, according to one aspect of the present invention, a controllable distribution transformer is provided, wherein the distribution transformer comprises: a high-voltage winding, a distribution transformer core, a power supply winding, a control winding, an additional mutual inductor, a control switch unit, a first circuit switch, a second circuit switch and a power compensation control system;

[0008] Among them, the power supply winding and the control winding are both located on the low-voltage side; the power supply winding and the control winding are both wound on the iron core of the distribution transformer, one side winding of the additional mutual inductor is connected in series with the power supply winding, and the other side winding of the additional mutual inductor is connected in parallel with the control winding, the first loop switch and the second loop switch are respectively arranged at the two ends of one side winding, the first loop switch, the second loop switch, one side winding and the control switch unit are connected in series, and the control switch unit is connected to the control winding; the power compensation control system controls the control switches of the first loop switch, the second loop switch and the control switch unit according to the voltage at both ends of the power supply winding, so as to control the number of turns connected to the winding to control the voltage value and phase change on the winding, thereby realizing series compensation of the voltage at both ends of the power supply winding.

[0009] Preferably, the control switch unit includes: at least two control switches, the number of control switches is the same as the number of segments of the control winding, and a control switch is provided at the non-grounded side of the control winding and at the connection between any two segmented windings of the control winding.

[0010] Preferably, if the voltage U2 across the power supply winding is greater than a preset voltage upper limit, the voltage U2 across the power supply winding is reduced to perform reverse phase compensation, including: controlling the first circuit switch to be disconnected, the second circuit switch and the control switch K to be closed. M Closed, this is reverse compensation, and adjust the control switch K in turn M to K1, until the compensation result satisfies that the voltage U2 across the power supply winding is less than the preset voltage upper limit; wherein M is the number of control switches.

[0011] Preferably, if the voltage U2 across the power supply winding is less than the preset voltage lower limit, the voltage U2 across the power supply winding is increased to perform in-phase compensation, including: controlling the second loop switch to be disconnected, the first loop switch and the control switch K M Closed, this is positive compensation, and adjust the control switch K in turn M to K1, until the compensation result satisfies that the voltage U2 across the power supply winding is greater than the preset lower limit value; wherein M is the number of control switches.

[0012] Preferably, when adjusting the control switch K M When it reaches K1, it is necessary to close the lower switch first and then open the higher switch; control switch K M The levels down to K1 decrease in sequence.

[0013] Preferably, the power compensation control system is further used for:

[0014] If it is detected that the voltage across the power supply winding is lower than a preset voltage threshold, all switches are controlled to be disconnected.

[0015] The utility model provides a controllable distribution transformer, comprising: a power supply winding and a control winding both located on a low-voltage side; the power supply winding and the control winding both wound on an iron core of the distribution transformer; a winding on one side of an additional transformer connected in series with the power supply winding, and a winding on the other side of the additional transformer connected in parallel with the control winding; a first loop switch and a second loop switch respectively arranged at both ends of one winding; the first loop switch, the second loop switch, one winding, and a control switch unit connected in series; and the control switch unit connected to the control winding; a power compensation control system controls the first loop switch, the second loop switch, and the control switch unit in operation according to the voltage across the power supply winding, so as to control the number of turns connected to the winding, the voltage value on the winding, and the phase change, thereby achieving series compensation of the voltage across the power supply winding; compared with a traditional on-load tap-changing distribution transformer, the controllable distribution transformer of the utility model reduces the operating voltage of the switch, greatly reducing insulation cost and equipment size; and, by appropriately increasing the voltage of the additional winding and increasing the transformation ratio of the auxiliary transformer, greatly reducing the operating current of the switch and improving reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] By referring to the following drawings, a more complete understanding of exemplary embodiments of the present invention can be obtained:

[0017] Figure 1 The impact of distributed system access on local voltage of distribution network;

[0018] Figure 2 Schematic diagram of the structure of a controllable distribution transformer 200 according to an embodiment of the present utility model;

[0019] Figure 3 This is an example diagram of a controllable distribution transformer in a distributed photovoltaic access area according to an embodiment of the present invention;

[0020] Figure 4 Schematic diagram of reverse compensation according to an embodiment of the present utility model;

[0021] Figure 5 2 is a schematic diagram of the in-phase compensation principle according to an embodiment of the present utility model. DETAILED DESCRIPTION

[0022] Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to provide a detailed and complete disclosure of the present invention and to fully convey the scope of the present invention to those skilled in the art. The terms used in the exemplary embodiments shown in the accompanying drawings are not intended to limit the present invention. In the accompanying drawings, identical units / elements are denoted by the same reference numerals.

[0023] Unless otherwise specified, the terms used herein (including technical terms) have the meanings commonly understood by those skilled in the art. In addition, it is understood that terms defined in commonly used dictionaries should be understood to have the same meanings as those in the context of the relevant fields, and should not be understood as idealized or overly formal meanings.

[0024] In order to solve the impact of distributed photovoltaic access on the local voltage of the distribution network, the utility model proposes a controllable distribution transformer, which sets the tap changer on the low-voltage side. At the same time, considering the large current on the low-voltage side, additional mutual inductor technology is adopted to effectively reduce the switching current of the tap changer, which has higher reliability and economy.

[0025] Figure 2 FIG is a schematic structural diagram of a controllable distribution transformer 200 according to an embodiment of the present invention. Figure 2 As shown, the controllable distribution transformer provided by the embodiment of the present invention, compared with traditional on-load tap-changing distribution transformers, reduces the operating voltage of the switch, significantly reducing insulation costs and equipment size. Furthermore, by appropriately increasing the additional winding voltage and increasing the auxiliary transformer ratio, the operating current of the switch can be significantly reduced, thereby improving reliability. The controllable distribution transformer 200 provided by the embodiment of the present invention includes: a high-voltage winding 201, a distribution transformer core 202, a power supply winding 203, a control winding 204, an additional transformer 205, a control switch unit 206, a first circuit switch 207, a second circuit switch 208, and a power compensation control system 209.

[0026] Among them, the power supply winding and the control winding are both located on the low-voltage side; the power supply winding and the control winding are both wound on the iron core of the distribution transformer, one side winding of the additional mutual inductor is connected in series with the power supply winding, and the other side winding of the additional mutual inductor is connected in parallel with the control winding, the first loop switch and the second loop switch are respectively arranged at the two ends of one side winding, the first loop switch, the second loop switch, one side winding and the control switch unit are connected in series, and the control switch unit is connected to the control winding; the power compensation control system controls the control switches of the first loop switch, the second loop switch and the control switch unit according to the voltage at both ends of the power supply winding, so as to control the number of turns connected to the winding to control the voltage value and phase change on the winding, thereby realizing series compensation of the voltage at both ends of the power supply winding.

[0027] Preferably, the control switch unit includes: at least two control switches, the number of control switches is the same as the number of segments of the control winding, and a control switch is provided at the non-grounded side of the control winding and at the connection between any two segmented windings of the control winding.

[0028] Preferably, if the voltage U2 across the power supply winding is greater than the preset voltage upper limit, the voltage across the power supply winding is reduced to perform reverse phase compensation, including: controlling the first loop switch to be disconnected, the second loop switch and the control switch K to be closed. M Closed, this is reverse compensation, and adjust the control switch K in turn M to K1, until the compensation result satisfies that the voltage U2 across the power supply winding is less than the preset voltage upper limit; wherein M is the number of control switches.

[0029] Preferably, if the voltage across the power supply winding is less than the preset voltage lower limit, the voltage across the power supply winding is increased to perform in-phase compensation, including: controlling the second loop switch to be disconnected, the first loop switch and the control switch K to be closed. M Closed, this is positive compensation, and adjust the control switch K in turn M to K1, until the compensation result satisfies that the voltage U2 across the power supply winding is greater than the preset lower limit value; wherein M is the number of control switches.

[0030] Preferably, when adjusting the control switch K M When it reaches K1, it is necessary to close the lower switch first and then open the higher switch; control switch K M The levels down to K1 decrease in sequence.

[0031] Combine Figure 3 As shown in the figure, the controllable distribution transformer of the present invention is described by taking five control switches as an example. Among them, AN is the high-voltage winding of the distribution transformer, an is the power supply winding, T is the core of the distribution transformer, T1 is the additional mutual inductor, K6 and K7 are the first circuit switch and the second circuit switch respectively, U1 is the high voltage, U2 is the power supply voltage, U3 is the control winding voltage, and U 2E is the induced potential of the power supply winding, Zan is the power load of the distribution network. N3 is the control winding, which is wound on the core of the distribution transformer. f1 The winding is connected in parallel with the control winding, N f2 The winding is connected in series with the power supply winding, and the N f2 The voltage value and phase on the winding are adjusted to achieve series compensation for U2. The control unit includes: control switches K1-K5.

[0032] The working principle of the controllable distribution transformer is as follows: first, the U2 voltage is input into the power compensation control system, and the power compensation control system determines the control switch action according to the real-time value of U2.

[0033] Among them, if the voltage U2 across the power supply winding is greater than the preset voltage upper limit, it is necessary to reduce the U2 voltage value, that is, reverse compensation. The specific control switch strategy is: first control switch K6 to be disconnected, and K7 and K5 to be closed. At this time, it is reverse compensation. Adjust K5 to K1 in sequence until the compensation result satisfies that U2 is less than the preset voltage upper limit. When adjusting K5 to K1, it is necessary to close the next level switch first, and then disconnect the previous level switch. For example, from K5 to K4, close K4 first, and then disconnect K5, so as to ensure that the circuit is not disconnected. The reverse compensation principle diagram is as follows Figure 4 As shown. At this time, U2=U 2E -U5, by adjusting the size of U3, the amount of reverse compensation voltage can be adjusted.

[0034] Among them, if the voltage U2 across the power supply winding is less than the preset voltage lower limit, it is necessary to increase the U2 voltage value, that is, in-phase compensation. The specific control switch strategy is: first control switch K7 to be disconnected, and K6 and K5 to be closed. At this time, it is forward compensation. Adjust K5 to K1 in sequence until the compensation result satisfies that U2 is greater than the preset voltage lower limit. When adjusting K5 to K1, it is necessary to close the next level switch first, and then disconnect the previous level switch. For example, from K5 to K4, close K4 first, and then disconnect K5, so as to ensure that the circuit is not disconnected. The schematic diagram of in-phase compensation is as follows Figure 5 As shown. At this time, U2=U 2E +U5, the size of U5 is approximately proportional to U3. By adjusting the size of U3, the in-phase compensation value of U2 can be adjusted.

[0035] In the present invention, the fineness of the control switch adjustment needs to be considered according to the design requirements. Assuming that the upper and lower limits of the preset supply voltage are ±10% of the rated voltage U, each level of adjustment voltage of K1-K5 can be controlled within 5%, and the number of switches is determined by the upper and lower limits of the voltage that may appear in the system.

[0036] Specifically, the principle for designing the number of switches is as follows: assuming that the number of switches to be designed is n, and the voltage percentage to be adjusted is ±a, in general, considering that the system's voltage deviation requirement for the 220V user side is -7% to +10%, and the adjustment fineness of a single switch is set to λ, then the number of switches is calculated according to For example, if the voltage upper limit may reach ±30% of the rated voltage, a 20% adjustment is required, and in this case, 5 switches can be designed. If the voltage upper limit may reach ±20% of the rated voltage, a 10% adjustment is required, and in this case, 3 switches can be designed.

[0037] If you encounter a special situation, such as a higher voltage stability requirement, for example, requiring its deviation to be less than ±3%, the adjustment fineness of a single switch should be adjusted to 2%. The adjustment fineness of the control switch in the utility model can be adjusted according to actual conditions.

[0038] Assume that the number of turns of the primary winding of the additional transformer is N f1 , powered by the control winding, the number of turns of the control winding connected to the circuit is N3, then the control winding voltage is:

[0039] U3=e zr ×N3(1)

[0040] where e zr The turn potential of the main iron core is: e zr =U1 / N pr

[0041] Then the additional transformer turn potential is e fz =U B / N f1 The number of turns of the secondary winding is N f2 , which is connected in series with the power supply winding of the distribution transformer, so the compensation amount of the distribution transformer power supply voltage is: u b =e fr N f2 .

[0042] e zr Substituting into the above formula, we can get:

[0043]

[0044] Among them, u b is the compensation voltage of the secondary winding of the additional transformer; N pr is the number of turns of the high-voltage winding of the distribution transformer; N3 is the number of turns of the control winding; N f1 N is the number of turns of the additional transformer primary winding; f2 is the number of turns of the secondary winding of the additional transformer; U1 is the voltage on the high voltage side.

[0045] When the number of turns of the additional transformer winding is determined, the value of N3 can be calculated according to formula (2), and then the number of turns of each segment winding of N3 can be evenly distributed according to the number of switches.

[0046] Preferably, the power compensation control system is further used for:

[0047] If it is detected that the voltage across the power supply winding is lower than a preset voltage threshold, all switches are controlled to be disconnected.

[0048] The distribution transformer of this utility model also has a short-circuit protection function. If the power compensation control system detects that the voltage is less than the preset voltage threshold of 100V, it can determine that the power supply winding is short-circuited. At this time, all switches are controlled to open. At this time, the power supply winding is equivalent to carrying a large load T1, which can greatly reduce the short-circuit current and thus protect the distribution transformer.

[0049] In the present invention, the power compensation control system obtains the voltage across the power supply winding. The power compensation control system controls the first loop switch, the second loop switch and the control switch in the control switch unit according to the voltage across the power supply winding, so as to control the number of turns connected to the winding to control the voltage value and phase change on the winding, thereby realizing series compensation of the voltage across the power supply winding.

[0050] The present invention has been described with reference to a few embodiments. However, it is known to those skilled in the art that other embodiments than the ones disclosed above are equally within the scope of the present invention as defined by the appended patent claims.

[0051] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a / the [means, component, etc.]" are to be interpreted openly as referring to at least one instance of the means, component, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not necessarily need to be performed in the exact order disclosed, unless explicitly stated otherwise.

[0052] In the description of the present invention, terms such as "up", "down", "left", "right", "inside", and "outside" indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings. This is merely for the convenience of description and does not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the present invention.

[0053] In the description of this utility model, unless otherwise specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to direct connections, indirect connections through an intermediate medium, or internal communication between two components. Those skilled in the art will understand the specific meanings of these terms in this utility model based on the specific circumstances.

[0054] 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 it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A controllable distribution transformer, characterized in that: The distribution transformer comprises: a high-voltage winding, a distribution transformer core, a power supply winding, a control winding, an additional mutual inductor, a control switch unit, a first circuit switch, a second circuit switch and a power compensation control system; Among them, the power supply winding and the control winding are both located on the low-voltage side; the power supply winding and the control winding are both wound on the iron core of the distribution transformer, one side winding of the additional mutual inductor is connected in series with the power supply winding, and the other side winding of the additional mutual inductor is connected in parallel with the control winding, the first loop switch and the second loop switch are respectively arranged at the two ends of one side winding, the first loop switch, the second loop switch, one side winding and the control switch unit are connected in series, and the control switch unit is connected to the control winding; the power compensation control system controls the control switches of the first loop switch, the second loop switch and the control switch unit according to the voltage at both ends of the power supply winding, so as to control the number of turns connected to the winding to control the voltage value and phase change on the winding, thereby realizing series compensation of the voltage at both ends of the power supply winding.

2. The distribution transformer according to claim 1, characterized in that The control switch unit includes at least two control switches. The number of the control switches is the same as the number of segments of the control winding. A control switch is provided at the high-voltage end of the control winding and at the connection between any two segmented windings of the control winding.

3. The distribution transformer according to claim 1, characterized in that If the voltage U2 across the power supply winding is greater than the preset voltage upper limit, the voltage U2 across the power supply winding is reduced to perform reverse phase compensation, including: controlling the first circuit switch to be disconnected, the second circuit switch and the control switch K M Closed, this is reverse compensation, and adjust the control switch K in turn M To K1, until the compensation result satisfies that the voltage U2 at both ends of the power supply winding is less than the preset voltage upper limit; wherein, K is set in sequence from the ground side to the high voltage side of the control winding. M to K1, M is the number of control switches.

4. The distribution transformer according to claim 1, characterized in that If the voltage U2 across the power supply winding is less than the preset voltage lower limit, the voltage U2 across the power supply winding is increased to perform in-phase compensation, including: controlling the second circuit switch to be disconnected, the first circuit switch and the control switch K M Closed, this is positive compensation, and adjust the control switch K in turn M To K1, until the compensation result satisfies the voltage U2 at both ends of the power supply winding is greater than the preset lower limit value; wherein, K is set in sequence from the ground side to the high voltage side of the control winding. M to K1, M is the number of control switches.

5. The distribution transformer according to claim 3 or 4, characterized in that: Adjust the control switch K M When it reaches K1, it is necessary to close the lower switch first and then open the higher switch; control switch K M The levels down to K1 decrease in sequence.

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