DC system electrical connection detection device and method based on uninterruptible power supply technology

Abstract

The application relates to a DC system electrical parallel connection detection device and method based on uninterrupted power supply technology. The device comprises a DC uninterrupted power supply with an isolation transformer for realizing DC system electrical parallel connection detection, a measurement unit for realizing two-input voltage difference measurement of a DC load, and a logic controller for realizing control of the DC uninterrupted power supply with the isolation transformer and the measurement unit and DC system electrical parallel connection detection. The application can be applied to solving the DC system parallel connection problem under the condition of uninterrupted power supply.

Description

Technical Field

[0001] This invention belongs to the field of power equipment maintenance, specifically relating to a DC system electrical parallel connection detection device and method based on uninterruptible power supply technology. Background Technology

[0002] As a crucial system for powering the control circuits, relay protection devices, and their output circuits of substations, the DC system serves as the "main artery and capillaries" of large and medium-sized substations, permeating every corner of the station.

[0003] As the first line of defense for the power grid, relay protection (secondary equipment) undertakes the crucial task of rapidly clearing and isolating faults, serving as the "360-degree safety guardian" of the power system. The DC system within a substation is a vital system supplying power to relay protection devices, their control circuits, and output circuits, influencing the correctness of protection actions. Therefore, the DC system is a critical system affecting the stable operation of the power grid. In general, problems with the DC system directly impact the overall stability and security of the power grid.

[0004] The problem of parallel connection in a DC system refers to the electrical connection between two DC circuits that should operate independently. This connection can take the form of same-polarity or opposite-polarity connection. Loop problems are mainly caused by construction, load switching during operation, etc., and can lead to circulating currents that could cause fires, failure of DC circuit breaker differential coordination, shortened battery life, and protection system malfunctions. It is also one of the causes of relay protection malfunctions.

[0005] Considering the special characteristics of DC systems in substations, this invention first provides a brief introduction, such as... Figure 1 As shown. Since each DC device may affect the operation of the power system, it requires a radial power supply, meaning that parallel connections are not allowed (each DC load has only a separate power source).

[0006] based on Figure 1 The system network is used to illustrate various difficult-to-solve electrical parallel connection problems in DC systems. The first type of parallel connection problem is as follows: Figure 2 As shown. In Figure 2 In this case, the positive and negative poles of two different DC loads are connected by the same pole. Under normal circumstances, the power supply network is normal, so this problem is difficult to detect. In particular, the problem of single power supply same pole loop 2 is difficult to detect even when the load fails because it has no electrical circuit connection. It will also interfere with the power stability of normal loads (this problem also exists in dual power supply, so it will not be discussed further).

[0007] And in Figure 3 In the case of a single-power supply circuit with opposite poles, this problem is very easy to detect because an electrical short circuit can occur. Figure 4In the case of the dual power supply heteropolar loop, the problem becomes extremely dangerous, when the DC bus switch is not closed, the DC system is in normal operation, and the load has no any fault phenomenon. When the DC bus is divided into two columns and is converted into a ring operation, one of the power supply often fails, which seriously reduces the system stability. At this time, if the bus switch is closed, the power switch will directly trip, causing the damage of the whole station DC system of the substation, and causing the shutdown of all power supply protection devices.

[0008] The fault cause is often due to the capacity expansion of the substation. Due to the diversity and complexity of the DC load, the probability of parasitic loop increases linearly. How to find and eliminate the above problems without power outage is the key of the present application. SUMMARY

[0009] The purpose of the present application is to provide a DC system electrical parallel detection device and method based on uninterrupted power supply technology, which can be applied to solve the parallel problem of DC system under uninterrupted power supply condition.

[0010] To achieve the above purpose, the technical scheme of the present application is: a DC system electrical parallel detection device based on uninterrupted power supply technology, comprising a DC uninterruptible power supply with an isolation transformer, a measurement unit and a logic controller.

[0011] The DC uninterruptible power supply with an isolation transformer comprises an isolation transformer connected with the output of the station AC power supply, a unidirectional bridge full-control circuit for realizing controllable DC voltage output, and a detection circuit for monitoring the voltage of the DC load of the DC system.

[0012] The measurement unit is used to measure the voltage difference of the DC load of the DC system, comprising a first differential sampling circuit and a second differential sampling circuit. The two inputs of the first differential sampling circuit are used as the first pair of measurement nodes S1 and S2, and the two inputs of the second differential sampling circuit are used as the second pair of measurement nodes S3 and S4. For a dual power supply DC system, S1 and S3 are short-circuited.

[0013] The logic controller is used to realize the power supply access of the DC uninterruptible power supply with an isolation transformer, and realize the DC system electrical parallel detection according to the measurement result of the measurement unit.

[0014] In an embodiment of the present application, the first differential sampling circuit comprises first to fourth resistors, an operational amplifier, one end of the first resistor serving as a measurement node S1, the other end of the first resistor being connected to the inverting input terminal of the operational amplifier and connected to the first output terminal of the operational amplifier through the second resistor, one end of the third resistor serving as a measurement node S2, the other end of the third resistor being connected to the non-inverting input terminal of the operational amplifier and connected to the second output terminal of the operational amplifier through the fourth resistor, and the two output terminals of the operational amplifier being connected to the logic controller; and the second differential sampling circuit has the same connection structure as the first differential sampling circuit.

[0015] In an embodiment of the present application, the logic controller realizes the DC system electrical parallel detection according to the measurement result of the measurement unit in the following manner: according to the voltage difference of the DC load of the DC system measured by the measurement unit, if it is a fixed voltage difference, the DC system has electrical parallel, and if it is a floating voltage difference, the DC system does not have electrical parallel.

[0016] The present application also provides a DC system electrical parallel detection method based on the uninterrupted power supply technology, which comprises the following steps: connecting the DC system electrical parallel detection device based on the uninterrupted power supply technology to the DC load of the DC system which needs to be detected, cutting off the switch between the power supply and the DC load of the DC system, and supplying power to the DC load by the DC system electrical parallel detection device based on the uninterrupted power supply technology; at this time, the voltage difference between the two inputs of the DC load is measured by the measurement unit, if there is a fixed voltage difference, the DC system has electrical parallel, and if it is a floating voltage difference, the DC system does not have electrical parallel.

[0017] Compared with the prior art, the present application has the following beneficial effects: the present application can find and eliminate the electrical parallel problem of the DC system under the condition of uninterrupted power supply. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 For the DC system network.

[0019] Figure 2 For the single power supply same-pole parallel circuit.

[0020] Figure 3 For the single power supply different-pole parallel circuit.

[0021] Figure 4 For the double power supply different-pole parallel circuit

[0022] Figure 5 For the DC uninterrupted power supply with an isolation transformer.

[0023] Figure 6 For the measurement unit.

[0024] Figure 7 For the logic controller function flow.

[0025] Figure 8 The application discloses a DC system electrical parallel connection detection device based on uninterrupted power supply technology. DETAILED DESCRIPTION

[0026] The technical scheme of the application will be described below in combination with the drawings.

[0027] The DC system electrical parallel connection detection device based on uninterrupted power supply technology comprises a DC uninterrupted power supply with an isolation transformer, a measurement unit and a logic controller.

[0028] The DC uninterrupted power supply with the isolation transformer comprises an isolation transformer connected with an AC power supply output, a unidirectional bridge full-control circuit for realizing controllable DC voltage output and a detection circuit for monitoring the voltage of a DC load of the DC system.

[0029] The measurement unit is used for measuring the voltage difference of the DC load of the DC system and comprises a first differential sampling circuit and a second differential sampling circuit, two inputs of the first differential sampling circuit serving as a first pair of measurement nodes S1 and S2, and two inputs of the second differential sampling circuit serving as a second pair of measurement nodes S3 and S4.

[0030] The logic controller is used for realizing power supply access of the DC uninterrupted power supply with the isolation transformer and realizing DC system electrical parallel connection detection according to the measurement result of the measurement unit.

[0031] The application further provides a DC system electrical parallel connection detection method based on uninterrupted power supply technology, which comprises the following steps: connecting the DC system electrical parallel connection detection device based on uninterrupted power supply technology to a DC load of a DC system which needs to be subjected to electrical parallel connection detection; cutting off a switch between a power supply and the DC load of the DC system; supplying power to the DC load by the DC system electrical parallel connection detection device based on uninterrupted power supply technology; and measuring the voltage difference of two inputs of the DC load by the measurement unit.

[0032] The following is a specific embodiment of the application.

[0033] In the application, a DC system electrical parallel connection detection device based on uninterrupted power supply technology is designed, and the device is designed as shown in the following figure. Figure 5 The first block is a DC uninterrupted power supply with an isolation transformer and can be used for realizing power supply switching of equipment. Figure 6 The second block is a measurement unit and can be used for realizing voltage difference measurement. The third block is a logic controller and is used for controlling equipment functions, such asFigure 7 As shown.

[0034] In the design of Figure 5 , the station AC power supply is usually 380V and 220V, and the "floating ground" strategy is realized through the isolation transformer. The controllable rectification can be realized through the unidirectional bridge full-control circuit, and the output DC voltage can be set to 10-300V. Through the detection circuit, the voltage monitoring of the DC load can be realized, and the functions of anti-reverse connection and anti-reverse power are possessed. P1 and P2 represent the two ends of the power supply.

[0035] In the design of Figure 6 , the differential sampling circuit is used to realize the measurement of voltage difference. S1 and S2 represent a pair of measurement nodes, and S3 and S4 represent a pair of measurement nodes. For the double power supply measurement scheme, S1 and S3 nodes can be short-circuited to serve as the common end for measurement.

[0036] In the design of Figure 7 , the function flow is as follows:

[0037] The mechanism for judging whether there is electrical connection is that the DC uninterruptible power supply and the power supply of the substation DC power supply system are not electrically connected under normal circumstances, and are independent voltage sources. The voltage difference between the two should be floating. If there is a fixed voltage difference (DC power supply system voltage or zero), there is an electrical connection.

[0038] Once it is determined that there is a connection problem, it can be easily determined whether there is a same-pole connection or a different-pole connection problem through the fixed voltage difference condition, and the fault can be eliminated under the condition of uninterrupted operation of all devices, greatly reducing the maintenance cost and the impact of power failure. It is a breakthrough innovative technology that effectively improves the safety of substation DC system maintenance.

[0039] As shown in Figure 8 , taking a double power supply parallel circuit as an example, the automatic detection DC system load parallel device is connected to the suspected load, and the switch between the substation DC system and the load is cut off. The automatic detection DC system load parallel device supplies power to the load. At this time, the voltage difference between S1S2 (S3S4) is measured to determine whether there is a parallel problem between them. If the voltage is zero, there is a parallel problem between the branch where S1 is located and the branch where S2 is located. If the voltage is the DC power supply system voltage, the other circuit of the branch where S1 is located and the branch where S2 is located is parallel.

[0040] The above is the preferred embodiment of the present application. Any changes made in accordance with the technical solutions of the present application, as long as the functional effects generated do not exceed the scope of the technical solutions of the present application, belong to the protection scope of the present application.

Claims

1. An apparatus for detecting electrical parallel connection of a DC system based on uninterruptible power supply technology, characterized by, The DC uninterruptible power supply with an isolation transformer, a measurement unit, and a logic controller are included. The DC uninterruptible power supply with an isolation transformer includes an isolation transformer connected with an AC power output, a unidirectional bridge full-control circuit for realizing controllable DC voltage output, and a detection circuit for monitoring the voltage of a DC load of a DC system. The measurement unit is used to measure the voltage difference of the DC load of the DC system and includes a first differential sampling circuit and a second differential sampling circuit. The logic controller is used to realize the power supply access of the DC uninterruptible power supply with an isolation transformer and realize the electrical parallel detection of the DC system according to the measurement result of the measurement unit. The first differential sampling circuit includes a first to fourth resistor and an operational amplifier. The connection structure of the second differential sampling circuit is the same as that of the first differential sampling circuit. The logic controller realizes the electrical parallel detection of the DC system according to the measurement result of the measurement unit in the following way: according to the voltage difference of the DC load of the DC system measured by the measurement unit, if it is a fixed voltage difference, the DC system has electrical parallel, and if it is a floating voltage difference, the DC system does not have electrical parallel.

2. An electrical connection detection method for an uninterruptible power supply technology based DC system based on the device of claim 1, characterized in that, The DC system electrical parallel detection device based on uninterruptible power supply technology is connected to the DC load of the DC system which needs to be detected, the switch between the power supply and the DC load of the DC system is cut off, and the DC load is powered by the DC system electrical parallel detection device based on uninterruptible power supply technology. At this time, the voltage difference of the two inputs of the DC load is measured by the measurement unit. If there is a fixed voltage difference, the DC system has electrical parallel, and if it is a floating voltage difference, the DC system does not have electrical parallel.

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