Voltage transformer compensation device

Abstract

The utility model discloses a voltage transformer compensation device which comprises a standby knife switch, a standby capacitor and a working capacitor, and the standby knife switch and the working capacitor are connected in series and then are connected with the positive electrode of a power supply; one contactor and one corresponding divider resistor are connected in series to form a branch; and after the plurality of branches are connected in parallel, one end is connected between the standby capacitor and the working capacitor, and the other end is connected with the negative electrode of the power supply.

Description

Technical Field

[0001] The utility model relates to the field of charging pile circuits, and particularly relates to a voltage transformer compensation device. Background Art

[0002] Capacitor Voltage Transformer (CVT) is the most widely used mutual inductance device in the current power grid. It has almost completely replaced the traditional electromagnetic voltage transformer in occasions of 35kV and above. The original text of the technical guidelines of China Southern Power Grid states: "For the voltage transformers of 10kV - 35kV indoor distribution devices, dry-type insulated electromagnetic voltage transformers shall be adopted. For the voltage transformers of outdoor distribution devices of 35kV and above, capacitor voltage transformers shall be adopted. When the capacity and accuracy level do not meet the requirements, electromagnetic voltage transformers can also be selected. Anti-resonance measures shall be taken for electromagnetic voltage transformers." Due to the capacitive voltage division structure of CTV, it has the advantages of good insulation performance, strong voltage withstand ability, and no ferroresonance, so it is widely used. However, CTV also has the disadvantages of insufficient capacity and accuracy in some occasions. Insufficient capacity is only a cost issue, while insufficient accuracy is a technical defect.

[0003] The power system is a high-voltage system. Measuring instruments cannot directly measure the voltage. It is necessary to convert the high voltage of the primary system into the low voltage of the secondary system through a voltage transformer before it can be used for voltage and power measurement, reactive power regulation devices such as metering devices for gateway meters, static var compensation devices, relay protection devices for step-up substations, local and dispatching agency measurement systems, etc. Existing voltage transformers are divided into electromagnetic types (such as Figure 1 and Figure 2 ) and capacitive types (such as Figure 3 and Figure 4 ). The accuracy of electromagnetic voltage transformers is very high and stable, and the measurement accuracy for power frequency and harmonics is the same. From the equivalent circuit diagram, the voltage loaded on the load only differs from the power supply voltage by the internal resistance of the transformer, and this internal resistance is very small, so the accuracy of electromagnetic voltage transformers is guaranteed; the accuracy of capacitive voltage transformers is also very high, but unstable, and the accuracy for power frequency and harmonics is different. From the equivalent circuit diagram, the voltage loaded on the load differs from the power supply voltage not only by the internal resistance of the transformer, but also the power supply voltage (C2 voltage) will change with the change of the load reactance, which is determined by the capacitive voltage division structure. Therefore, capacitive voltage transformers can guarantee the measurement accuracy of power frequency voltage, but cannot guarantee the measurement accuracy of harmonic voltage.

[0004] As can be seen from the equivalent circuit, capacitive voltage transformers cannot guarantee the measurement accuracy of harmonic voltages. The reason is that there are two components with different characteristics, capacitance and reactance, in the equivalent circuit, and their interaction affects the supply voltage (C2 voltage). Electromagnetic voltage transformers can guarantee the measurement accuracy of harmonic voltages because their equivalent circuits only have reactance and no capacitance. Therefore, this circuit structure can be borrowed to compensate for the reactance in the equivalent circuit of the capacitive voltage transformer to avoid the interaction between reactance and capacitance affecting the supply voltage (C2 voltage), and the problem will be solved. As is well known, the reactance value is proportional to the frequency (XL = ωL); the capacitive reactance value is inversely proportional to the frequency (XC = 1 / ωC). In the equivalent circuit of the capacitive voltage transformer, when the frequency is low, the capacitor voltage division circuit shows a high impedance, and the influence of the load-side reactance value is relatively large, directly affecting the voltage value of C2 in the capacitor voltage division circuit. Thus, the measurement accuracy of harmonic voltages cannot be guaranteed. Therefore, it is necessary to compensate for the reactance in the equivalent circuit to reduce the influence of the reactance value. As mentioned above, the reactance value is proportional to the frequency (XL = ωL); the capacitive reactance value is inversely proportional to the frequency (XC = 1 / ωC). In the equivalent circuit of the capacitive voltage transformer, when the frequency is high, the capacitor voltage division circuit shows a low impedance, the voltage value of C2 in the voltage division circuit is very stable, and the influence of the load-side reactance value is small, only slightly affecting the voltage value of C2 in the capacitor voltage division circuit. At this time, the CTV can guarantee the measurement accuracy of harmonic voltages.

[0005] To sum up, without a compensation device, for lower-order harmonics, the CTV cannot guarantee the measurement accuracy of harmonic voltages; for higher-order harmonics, the CTV can guarantee the measurement accuracy of harmonic voltages. With a compensation device, for lower-order harmonics, the measurement accuracy of harmonic voltages by the CTV is improved; for higher-order harmonics, the measurement accuracy of harmonic voltages by the CTV remains basically unchanged because connecting a small-capacity reactance or capacitor in parallel to C2 has little influence. In a sense, the compensation device is for lower-order harmonics. When the compensation device operates properly, the CTV can guarantee the measurement accuracy of overall harmonics.

[0006] However, the existing compensation devices are divided into two forms, general compensation devices (such as Figure 5 ) and transformer-controlled compensation devices (such as Figure 6 ). Each branch of the general compensation device consists of a capacitor + a controller. The controller is controlled by a monitoring device, and triggering the controller according to a predetermined strategy can control the switching of the capacitor; the transformer-controlled compensation device, abbreviated as the voltage-controlled compensation device, consists of a transformer + a capacitor. The transformer has an adjustable turns ratio, and the tap is controlled by a monitoring device. Adjusting the transformer tap according to a predetermined strategy can control the voltage across the capacitor, thereby controlling the switching of the capacitor capacity. Generally, a spare capacity is reserved.

[0007] However, for general compensation devices: they have a large number of circuits and still cannot be continuously adjusted; they need to find the zero-crossing point for switching, which consumes resources and has a slow adjustment speed. For voltage-controlled compensation devices: the combination of a transformer and a capacitor belongs to the nature of a reactor and a capacitor, and is prone to resonance in a harmonic environment. The reason for the above is that traditional compensation devices are designed for power frequency and large-capacity working environments, and actually do not meet the needs of voltage transformer compensation.

[0008] Therefore, it is necessary to develop a new voltage transformer compensation device to cover the above problems. Utility Model Content

[0009] To overcome the deficiencies of the prior art, the purpose of the present utility model is to provide an improved voltage transformer compensation device, which controls the capacitor voltage by using the method of resistor voltage division, so as to achieve the purpose of controlling the capacitor capacity.

[0010] The present utility model is realized through the following technical solutions: a voltage transformer compensation device includes a spare knife switch, a spare capacitor and a working capacitor. The spare knife switch and the working capacitor are connected in series and then connected to the positive pole of the power supply; a contactor and a corresponding voltage-dividing resistor are connected in series to form a branch; multiple branches are connected in parallel, one end of which is connected between the spare capacitor and the working capacitor, and the other end is connected to the negative pole of the power supply.

[0011] Further, in the circuit wiring, the voltage transformer compensation device is connected to any winding on the load side.

[0012] Further, the voltage transformer compensation device is connected to the lightest load winding.

[0013] Compared with the prior art, the beneficial effects that the present utility model can achieve are:

[0014] The voltage transformer compensation device of the present utility model controls the capacitor voltage by using the method of resistor voltage division, thereby controlling the capacitor capacity. The resistors are grouped unevenly and then combined to obtain a relatively smooth capacitor capacity curve. The parallel structure of the device realizes the functional integration and interaction. Description of the Drawings

[0015] Figure 1 Shown is the first existing electromagnetic PT wiring diagram (single-phase);

[0016] Figure 2 Shown is the second existing electromagnetic PT wiring diagram (single-phase);

[0017] Figure 3 Shown is the first existing capacitive PT wiring diagram (single-phase);

[0018] Figure 4 Shown is the second existing wiring diagram of capacitive PT (single-phase);

[0019] Figure 5 It is a schematic diagram of the structure of an existing general compensation device;

[0020] Figure 6 It is a schematic diagram of the structure of an existing transformer control compensation device;

[0021] Figure 7 It is a schematic diagram of the voltage transformer compensation device of the present invention;

[0022] Figure 8 It is a schematic diagram of the CTV with compensation wiring of the voltage transformer compensation device of the present invention;

[0023] Figure 9 It is an equivalent circuit diagram of the CTV with compensation of the voltage transformer compensation device of the present invention. Specific embodiments

[0024] Next, in combination with the accompanying drawings and specific embodiments, the present invention will be further described. It should be noted that, on the premise of no conflict, any combination of the following-described embodiments or technical features can form a new embodiment.

[0025] As Figure 7 shown, an embodiment of the present invention discloses a voltage transformer compensation device, including a spare knife switch, a spare capacitor, and a working capacitor. The spare knife switch and the working capacitor are connected in series and then connected to the positive pole of the power supply; a contactor and a corresponding voltage-dividing resistor are connected in series to form a branch; multiple branches are connected in parallel, one end of which is connected between the spare capacitor and the working capacitor, and the other end is connected to the negative pole of the power supply. In this way, the resistance control compensation device controls the switching of the resistance through the contactor, changes the voltage-dividing ratio of the resistance and the capacitor, and can control the switching capacity of the capacitor. Thus, the voltage of the capacitor is controlled by the method of resistance voltage division, thereby controlling the size of the capacitor capacity; the resistors are grouped unevenly and then combined to obtain a relatively smooth capacitor capacity curve; the parallel structure of the device realizes the functional integration and interaction.

[0026] As Figure 8 and Figure 9 shown, in the circuit wiring, the voltage transformer compensation device is connected to any winding on the load side. According to the equivalent circuit of the transformer, when the compensation device is connected to any winding on the load side, the overall reactance can be compensated. Preferably, in this embodiment, the voltage transformer compensation device is connected to the lightest load winding.

[0027] Specifically, the voltage control strategy of the present invention:

[0028] The principle of resistor grouping is as follows: When the resistors are divided into several groups, multiple equivalent resistors can be generated through parallel connection, thereby adjusting the voltage of the capacitor within a certain range. The minimum number of groups is two. When the number of groups = 2, there are 3 combinations. When the number of groups = 3, there are 7 combinations, and so on. Moreover, the values of the grouped resistors can be different, and the value of R / XC can be 1, 2, or 3. The more combinations there are, the more accurate the switching capacity will be.

[0029] For example, when the number of groups = 3, the input capacitor capacity is as shown in the following table:

[0030]

[0031]

[0032] It can be seen from the table that the minimum input capacitor capacity is 10.00% of the rated capacity, and the maximum is 77.07%. Of course, as the number of combinations increases, the maximum value of the input capacitor capacity will continue to increase.

[0033] In summary, the main features of the voltage transformer compensation device of this utility model are as follows:

[0034] 1. Safety: In general compensation schemes, when the capacitor is put into operation, it is necessary to accurately capture the zero-crossing of the voltage. Due to the fact that the voltage of the capacitor cannot change suddenly, the capacitor must be put into operation at the zero-crossing of the external voltage. Otherwise, a sudden voltage will be generated, which will affect the equipment in the circuit. For a set of compensation equipment with relatively frequent switching, constantly searching for the zero-crossing is resource-consuming, and it cannot be guaranteed 100% due to algorithm and equipment performance reasons. In the scheme of this utility model, there is also a zero-crossing problem when the capacitor is first put into operation, but it doesn't exist afterwards, so this problem can basically be ignored.

[0035] 2. Quickness: In general compensation schemes, the compensation capacity of the capacitor is proportional to the number of capacitors put into operation. Its compensation rate curve is a straight line with a fixed slope, and the compensation speed is average. In the scheme of this utility model, the compensation capacity of the capacitor is proportional to the square of the voltage value of the capacitor. Its compensation rate curve is a quadratic power function curve with a large slope, and the compensation speed is very fast.

[0036] 3. Reliability: In general compensation schemes, the standby capacity and the working capacity of the capacitor are of exactly the same type, and the cost is relatively high. In the scheme of this utility model, since the equipment capacity and its control link are independent, the standby capacity of the capacitor is easier to set, and the cost is lower.

[0037] In addition, the scheme of this utility model inherits the advantages of transformer control compensation and at the same time adapts to the harmonic working environment.

[0038] The above embodiments are only the preferred embodiments of the present utility model, and the scope of protection of the present utility model cannot be limited thereby. Any non-substantial changes and substitutions made by those skilled in the art based on the present utility model fall within the scope of protection required by the present utility model.

Claims

1. A voltage transformer compensation device, comprising a spare knife switch, a spare capacitor and a working capacitor, characterized in that: The spare knife switch and the working capacitor are connected in series and then connected to the positive pole of the power supply; A contactor and a corresponding voltage-dividing resistor are connected in series to form a branch; Multiple branches are connected in parallel, one end of which is connected between the spare capacitor and the working capacitor, and the other end is connected to the negative pole of the power supply.

2. The voltage transformer compensation device according to claim 1, characterized in that, In the circuit wiring, the voltage transformer compensation device is connected to any winding on the load side.

3. The voltage transformer compensation device according to claim 2, characterized in that, The voltage transformer compensation device is connected to the lightest load winding.

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