Control circuit for actively intervening alternating current into direct current

Abstract

The invention relates to the technical field of electric power, and provides a control circuit for actively intervening alternating current to be connected in series with direct current, which comprises a direct current grounding monitoring unit, an alternating current voltage monitoring unit and an active grounding intervention unit. When it is detected that alternating current is connected into a direct current system in series, the active grounding intervention unit intervenes, alternating current fault current is formed by adding a manual grounding point in the direct current system, and the mechanism enables a current transformer to sense and trigger a relay, so that a switch is closed, the grounding point is kept, and an alarm is given out. And meanwhile, the formation of the fault current also triggers the alternating-current circuit breaker to trip and cut off the alternating-current power supply, so that the problem that the device can only give out a direct-current grounding alarm and cannot actively eliminate the fault when the alternating current is connected into the direct-current system in series is solved.

Description

Technical Field

[0001] The invention relates to the field of electric power technology, and in particular to a control circuit for actively intervening alternating current into direct current. Background Art

[0002] In power plants and substations, the reliability and stability of DC systems are crucial because, as a control, signal and protection power source, the DC system is directly related to the safe operation of the entire power system. However, due to the complexity of the DC system topology and the widespread distribution of cables, as well as the sharing, crossing or parallel laying of AC and DC cables, the risk of AC power entering the DC system cannot be ignored.

[0003] The reasons why AC current is connected to the DC system include overheating of the terminals and overheating and short circuit of the DC-controlled AC contactor, which leads to unexpected electrical connection between the AC circuit and the DC circuit. Due to damaged cable insulation, AC current is connected to the DC system through the damaged part. Human operational errors are also an important reason for AC current to be connected to the DC system.

[0004] The harm of AC entering the DC system is that AC forms an AC channel through the distributed capacitance of the DC system, which interferes with the normal operation of the DC system and causes equipment malfunction or failure to operate. After AC enters the DC system, it causes a grounding fault in the DC system, further affecting the stable operation of the power system.

[0005] At present, DC insulation monitoring devices can usually monitor the grounding resistance of DC systems and detect grounding signals. However, when AC is connected to the DC system, the device can only issue a DC grounding alarm, but cannot actively eliminate the fault. When an AC fault occurs, manual intervention is required to eliminate the fault, which undoubtedly increases the time and complexity of fault handling. Summary of the invention

[0006] The purpose of the present invention is to provide an active intervention AC power injection control circuit to solve the problem that when AC power is injected into a DC system, the device can only issue a DC grounding alarm but cannot actively eliminate the fault.

[0007] The present invention provides an active intervention AC power injection control circuit, comprising: the circuit comprises a DC grounding monitoring unit, an AC voltage monitoring unit and an active grounding intervention unit;

[0008] The driving signal of the DC grounding monitoring unit is connected to the active grounding intervention unit;

[0009] The AC voltage monitoring unit is connected to the active grounding intervention unit. The AC voltage monitoring unit monitors whether AC power is connected to the DC system through a capacitor C. When the AC voltage reaches the set value of the voltage relay V of the AC monitoring unit, the action signal of the AC voltage monitoring unit closes the switch KV of the active grounding intervention unit.

[0010] When the DC system is grounded and an AC voltage is detected, the active grounding intervention unit closes the switch K1 or K2. The closure of KV adds an artificial grounding point in the DC system, so that the AC power forms a loop to generate a fault AC current. When the current transformer CT senses the AC current, the current relay I is actuated to close the switch KI to maintain the artificial grounding point. At the same time as the current relay I is actuated, the alarm switch is closed to send out an alarm signal.

[0011] Furthermore, the present invention provides an active intervention AC power injection DC control circuit, wherein the AC voltage monitoring unit includes: a first capacitor and a first voltage relay coil.

[0012] The first end of the first capacitor C is connected to the positive bus of the DC system, the second end of the first capacitor C is connected to the first end of the first voltage relay coil, and the second end of the first voltage relay coil is connected to the ground.

[0013] Furthermore, the present invention provides an active intervention AC power injection DC control circuit, wherein the active grounding intervention unit includes: a first switch K1, a second switch K2, a third switch KV, a fourth switch KI, a first through-core current transformer CT, and a first current relay I.

[0014] Furthermore, the present invention provides an active intervention AC power injection control circuit, the active grounding intervention unit comprising: a first end of the first switch K1 is connected to a positive bus of a DC system, a second end of the first switch K1 is connected to a second end of a second switch K2, a first end of a third switch KV, and a first end of a fourth switch KI, a first end of the second switch K2 is connected to a negative bus of a DC system, a second end of the second switch K2 is connected to a second end of the first switch K1, a first end of the third switch KV, and a first end of the fourth switch KI, a first end of the third switch KV is connected to a second end of the first switch K1, a first end of the second switch K2, and a first end of the fourth switch KI, The second end of the switch K2 is connected to the first end of the fourth switch KI, the second end of the third switch KV is connected to the second end of the fourth switch KI and the ground, the first end of the fourth switch KI is connected to the second end of the first switch K1, the second end of the second switch K2, and the second end of the third switch KV, the second end of the fourth switch KI is connected to the second end of the third switch KV and the ground, the middle hole of the first through-core current transformer CT passes through the second end of the third switch KV and the second end of the fourth switch KI and then is connected to the ground, and the first end of the first through-core current transformer CT is connected to the coil of the first current relay I.

[0015] Furthermore, the present invention provides an active intervention control circuit for AC power injection into a DC system. AC power injected into a DC system causes the DC system to be grounded, automatically increasing the grounding point of the same-pole busbar to form an AC fault current, tripping the AC or DC circuit breaker in the injection interval to cut off the AC power.

[0016] Furthermore, the present invention provides an active intervention AC power injection DC control circuit, which also includes a communication unit for connecting to a remote host computer and sending an alarm signal to the remote host computer through the communication unit.

[0017] Beneficial effects of the present invention: The present invention provides an active intervention in the injection of AC into DC control circuits that can actively eliminate faults, cut off AC power by forming an AC fault current and triggering the circuit breaker to trip, effectively eliminate faults and reduce processing time and complexity. Secondly, the present invention improves the reliability and stability of the power system by real-time monitoring and timely handling of potential problems. In addition, the present invention can also reduce the risk of malfunction of voltage-type intermediate relays in the DC system due to the injection of AC power, and promptly notify operation and maintenance personnel through the intelligent alarm function. At the same time, the present invention enhances system protection to prevent AC from causing further damage to the DC system, and is adaptable to DC systems of various power plants and substations. Finally, the control circuit structure of the present invention is simple and easy to implement and maintain. In summary, the present invention is an important innovation in the field of power technology that can significantly improve system reliability and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0019] Figure 1 A schematic diagram of the structure of an active intervention AC power injection DC control circuit provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described in conjunction with the specific embodiments of the present invention and the corresponding drawings. 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 are within the scope of protection of the present invention. The technical solutions provided by the embodiments of the present invention are described in detail below in conjunction with the drawings.

[0021] See also Figure 1 , The present invention provides an active intervention AC power series connection DC control circuit, The present invention provides an active intervention AC power series connection DC control circuit, comprising: The circuit comprises a DC grounding monitoring unit, an AC voltage monitoring unit and an active grounding intervention unit;

[0022] The driving signal of the DC grounding monitoring unit is connected to the active grounding intervention unit. The DC grounding monitoring unit is used to monitor whether the DC system is grounded. When the positive pole of the DC system is grounded, the driving signal of the DC grounding monitoring unit closes the active grounding intervention unit switch K1. When the negative pole of the DC system is grounded, the driving signal of the DC grounding monitoring unit closes the active grounding intervention unit switch K2.

[0023] The AC voltage monitoring unit is connected to the active grounding intervention unit. The AC voltage monitoring unit monitors whether AC power is connected to the DC system through a capacitor C. When the AC voltage reaches the set value of the voltage relay V of the AC monitoring unit, the action signal of the AC voltage monitoring unit closes the switch KV of the active grounding intervention unit.

[0024] When the DC system is grounded and an AC voltage is detected, the active grounding intervention unit closes the switch K1 or K2. The closure of KV adds an artificial grounding point in the DC system, so that the AC power forms a loop to generate a fault AC current. When the current transformer CT senses the AC current, the current relay I is actuated to close the switch KI to maintain the artificial grounding point. At the same time as the current relay I is actuated, the alarm switch is closed to send out an alarm signal.

[0025] The specific implementation of the present invention mainly includes the following steps: First, the DC system is continuously monitored by a DC grounding monitoring unit and an AC voltage monitoring unit. When the AC voltage monitoring unit detects that the AC voltage reaches a set threshold, the active grounding intervention unit is triggered. According to the grounding polarity of the DC system, an artificial grounding point KV is added to the DC system by closing the corresponding switch K1 or K2, thereby forming an AC loop. After the AC forms a loop, a fault AC current will be generated, which is sensed by the current transformer CT, thereby triggering the current relay I to operate. After the current relay I operates, the switch KI will be closed, the artificial grounding point will be maintained, and an alarm signal will be triggered at the same time. The formation of the fault AC current will eventually cause the AC circuit breaker QF to trip, thereby cutting off the AC power supply. In this process, the control circuit will also send an alarm signal to the remote host computer through the communication unit. In this way, the present invention can not only detect the situation of AC entering the DC system in a timely manner, but also actively intervene to eliminate faults and ensure the safe operation of the power system.

[0026] Specifically, the present invention provides an active intervention AC power injection DC control circuit, wherein the AC voltage monitoring unit includes: a first capacitor and a first voltage relay coil.

[0027] The first end of the first capacitor C is connected to the positive bus of the DC system, the second end of the first capacitor C is connected to the first end of the first voltage relay coil, and the second end of the first voltage relay coil is connected to the ground.

[0028] Specifically, the present invention provides an active intervention AC power injection DC control circuit, wherein the active grounding intervention unit includes: a first switch K1, a second switch K2, a third switch KV, a fourth switch KI, a first through-core current transformer CT, and a first current relay I.

[0029] Specifically, the present invention provides an active intervention AC power injection control circuit, the active grounding intervention unit comprising: a first end of the first switch K1 is connected to a positive bus of a DC system, a second end of the first switch K1 is connected to a second end of a second switch K2, a first end of a third switch KV, and a first end of a fourth switch KI, a first end of the second switch K2 is connected to a negative bus of a DC system, a second end of the second switch K2 is connected to a second end of the first switch K1, a first end of the third switch KV, and a first end of the fourth switch KI, a first end of the third switch KV is connected to a second end of the first switch K1, a first end of the second switch KV, and a first end of the fourth switch KI. The second end of the switch K2 is connected to the first end of the fourth switch KI, the second end of the third switch KV is connected to the second end of the fourth switch KI and the ground, the first end of the fourth switch KI is connected to the second end of the first switch K1, the second end of the second switch K2, and the second end of the third switch KV, the second end of the fourth switch KI is connected to the second end of the third switch KV and the ground, the middle hole of the first through-core current transformer CT passes through the second end of the third switch KV and the second end of the fourth switch KI and then is connected to the ground, and the first end of the first through-core current transformer CT is connected to the coil of the first current relay I.

[0030] Specifically, the present invention provides an active intervention control circuit for AC power injection into a DC system. AC power injected into a DC system causes the DC system to be grounded, automatically increases the grounding point of the same-pole busbar, forms an AC fault current, trips the AC or DC circuit breaker in the injection interval, and cuts off the AC power.

[0031] Specifically, the present invention provides an active intervention AC power injection DC control circuit, which also includes a communication unit for connecting to a remote host computer and sending an alarm signal to the remote host computer through the communication unit.

[0032] The present invention provides a specific technical solution for actively intervening alternating current in series with a direct current control circuit, including: a low-voltage alternating current system is usually a directly grounded system, and a direct current system is an ungrounded system. When single-phase alternating current is connected to a direct current system, the direct current system will be directly grounded, which will cause false operation or refusal of protection on the one hand, and on the other hand, the alternating current will also pass through the long cable distributed capacitance of the direct current system, so that the voltage-type intermediate relay coil in the direct current system will be charged with voltage. If the operating power of the relay is lower than 5W specified by the countermeasure, it is easy to malfunction; even if the operating voltage meets the requirement of not less than 55%Un specified by the "countermeasure", due to the periodic zero crossing of the alternating current, the voltage of the direct current relay will change periodically and cross the zero point, thereby causing a frequency jitter of 50Hz or 100Hz, which is easy to malfunction the outlet trip.

[0033] The technical solution of the present invention is to directly connect the DC load at point d or connect the single-phase AC power supply AC through a relay. Figure 1, so that the DC system is superimposed with AC (0-220V). At this time, the DC grounding monitoring device detects that the positive (or negative) grounding resistance is less than the set value, thereby issuing a DC grounding alarm, and at the same time closing the relay output contact K1 (or K2). The AC passes through QF, DC load, DC circuit breaker DK, capacitor C, and AC voltage relay V to form a loop. When the voltage of relay V reaches the action value, the contact KV closes, and the AC passes through QF, DC load, DK, DC bus, K1 (or K2), contact KV, and through the through-core CT to form a loop. When the secondary current flowing through the through-core CT reaches the action value of the current relay I, relay I operates, contact KI closes, and the AC passes through QF, DC load, DK, positive (or negative), K1 (or K2), and KI to form an AC short-circuit loop. QF trips under the action of the short-circuit current and cuts off the AC from the DC system. After QF trips, the voltage relay V loses power and KV returns. During the period when short-circuit current flows through KI, the DC load switch DK will also trip due to the short-circuit current and can also cut off the AC power. When the AC circuit breaker QF is disconnected and the through-hole CT cannot detect the AC current, the current relay I loses power, the contact KI is disconnected, the grounding signal of the DC grounding device disappears, and K1 (or K2) is disconnected, thereby restoring the stable operation of the DC system.

[0034] The present invention uses an active intervention AC power injection into DC control circuit to effectively solve the problem that when AC power is injected into a DC system, the device can only issue a DC grounding alarm but cannot actively eliminate the fault.

[0035] The working principle and operation flow of the active intervention AC power injection DC control circuit provided by the present invention are as follows:

[0036] First, the DC system is continuously monitored through the DC grounding monitoring unit and the AC voltage monitoring unit. When the DC system is grounded or AC power is connected in series, the DC grounding monitoring unit and the AC voltage monitoring unit will send out signals in time.

[0037] When the AC voltage monitoring unit detects that the AC voltage reaches the set threshold, the active grounding intervention unit is triggered. The AC voltage monitoring unit adds an artificial grounding point KV in the DC system by closing the corresponding switch K1 or K2 according to the grounding polarity of the DC system, thereby forming an AC circuit.

[0038] When the alternating current forms a loop, a fault alternating current will be generated, which will be sensed by the current transformer CT, thereby triggering the action of the current relay I. After the current relay I is actuated, the switch KI is closed, the artificial grounding point is maintained, and an alarm signal is triggered at the same time.

[0039] The formation of fault AC current will eventually cause the AC circuit breaker QF to trip, thereby cutting off the AC power supply and preventing it from further affecting the DC system. During this process, the control circuit will also send an alarm signal to the remote host computer through the communication unit to promptly notify the operation and maintenance personnel for processing.

[0040] The active intervention AC power injection control circuit provided by the present invention can not only detect the situation of AC power injection into a DC system in a timely manner, but also actively intervene to eliminate faults and ensure the safe operation of the power system.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. An active intervention AC power injection DC control circuit, characterized in that: include: The circuit includes a DC grounding monitoring unit, an AC voltage monitoring unit, and an active grounding intervention unit; The driving signal of the DC grounding monitoring unit is connected to the active grounding intervention unit; The AC voltage monitoring unit is connected to the active grounding intervention unit. The AC voltage monitoring unit monitors whether AC power is connected to the DC system through a capacitor C. When the AC voltage reaches the set value of the voltage relay V of the AC monitoring unit, the action signal of the AC voltage monitoring unit closes the switch KV of the active grounding intervention unit. When the DC system is grounded and an AC voltage is detected, the active grounding intervention unit closes the switch K1 or K2. The closure of KV adds an artificial grounding point in the DC system, so that the AC power forms a loop to generate a fault AC current. When the current transformer CT senses the AC current, the current relay I is actuated to close the switch KI to maintain the artificial grounding point. At the same time as the current relay I is actuated, the alarm switch is closed to send out an alarm signal.

2. The active intervention AC power injection DC control circuit according to claim 1, characterized in that: The AC voltage monitoring unit includes: a first capacitor and a first voltage relay coil; The first end of the first capacitor C is connected to the positive bus of the DC system, the second end of the first capacitor C is connected to the first end of the first voltage relay coil, and the second end of the first voltage relay coil is connected to the ground.

3. The active intervention AC power injection DC control circuit according to claim 1, characterized in that: The active grounding intervention unit includes: a first switch K1, a second switch K2, a third switch KV, a fourth switch KI, a first through-core current transformer CT, and a first current relay I.

4. The active intervention AC power injection DC control circuit according to claim 1, characterized in that: The active grounding intervention unit includes: a first end of the first switch K1 is connected to the positive bus of the DC system, a second end of the first switch K1 is connected to the second end of the second switch K2, the first end of the third switch KV, and the first end of the fourth switch KI, a first end of the second switch K2 is connected to the negative bus of the DC system, a second end of the second switch K2 is connected to the second end of the first switch K1, the first end of the third switch KV, and the first end of the fourth switch KI, a first end of the third switch KV is connected to the second end of the first switch K1, the second end of the second switch K2, and the first end of the fourth switch KI, a second end of the third switch KV is connected to the second end of the fourth switch KI and the earth, a first end of the fourth switch KI is connected to the second end of the first switch K1, the second end of the second switch K2, and the second end of the third switch KV, a second end of the fourth switch KI is connected to the second end of the third switch KV and the earth, a middle hole of the first through-core current transformer CT passes through the second end of the third switch KV and the second end of the fourth switch KI and then connects to the earth through a cable, and a first end of the first through-core current transformer CT is connected to the coil of the first current relay I.

5. The active intervention AC power injection DC control circuit according to claim 1, characterized in that: When AC is injected into a DC system, it causes the DC system to be grounded, automatically increasing the grounding point of the busbar with the same polarity, forming an AC fault current, tripping the AC or DC circuit breaker in the interval where it is injected, and cutting off the AC power.

6. The active intervention AC power injection DC control circuit according to claim 1, characterized in that: It also includes a communication unit, which is used to connect to a remote host computer and send an alarm signal to the remote host computer through the communication unit.

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