Three-phase voltage transformer with automatic load shedding function in case of single-phase line disconnection

Abstract

The present invention discloses a three-phase voltage transformer with a function of automatically cutting off the load when a single-phase line is broken. The device is composed of a single-phase line break accident identification module, a three-phase voltage transformer with Yynd11 group wiring, a control and communication module, and a power supply module, wherein the single-phase line break accident identification module, the control and communication module, and the power supply module are installed in a three-phase voltage transformer device with Yynd11 group wiring. The device of the present invention is connected to the line, or the busbar to which the line is connected. When a single-phase line break accident occurs, the device of the present invention before the line break point cannot sense the accident state, so the load before the line break point will maintain normal operation, and the device of the present invention after the line break point will sense the accident state, so it will automatically cut off the load of the branch where it is located. The device of the present invention is safe, reliable, and fast. The neutral point of the high-voltage side winding of the three-phase voltage transformer with Yynd11 group wiring is not grounded, so it can also effectively avoid the situation where the voltage transformer participates in ferromagnetic resonance accidents.

Description

Technical Field

[0001] The present invention relates to the field of intelligent three-phase voltage transformers, and in particular to an intelligent three-phase voltage transformer with a function of automatically shedding load when a single-phase line is broken. Background Art

[0002] In power grid operations, nearly 70% of ferroresonance incidents are caused by single-phase disconnections on heavily loaded lines. This is primarily due to the fact that the voltage at the line break, where a single-phase disconnection occurs, is 1.5 times higher than the phase voltage, and the current is high, making it difficult to extinguish the persistent arc. The resulting overvoltage can saturate the core of the ferromagnetic transformer, leading to a resonance incident. However, 66kV transformers and 66kV line protection systems lack single-phase disconnection protection. Given the large number of T-connected power lines currently in the power grid, there is an urgent need to develop a protection device with automatic load shedding in the event of a single-phase disconnection. This would remove the load downstream of the disconnection point, thereby ensuring that the voltage at the line break does not exceed the rated phase voltage and preventing arc overvoltage at the break from inducing ferroresonance in the power grid. On the other hand, a single-phase line break can cause voltage anomalies in the load downstream of the breakpoint. A common situation is that the voltage of two phases is halved, leaving one phase normal. The phase sequence is no longer 120 degrees apart, but rather the two phases with halved voltages are identical and 180 degrees apart from the normal phase. This can cause the motor to stall or even burn out, necessitating the rapid removal of rotating loads behind the single-phase line breakpoint. Furthermore, conventional three-phase voltage transformers utilize a Ynynd0 wiring scheme, meaning the high-voltage side utilizes a star wiring scheme, with the neutral point of the winding drawn out and grounded. Because the high-voltage side has a path to ground, when a conventional transformer enters a ferromagnetic saturation state due to an accident, its high-voltage winding easily resonates with the distributed capacitance of the power grid to ground, potentially triggering a ferromagnetic resonance event in the power grid. Therefore, conventional voltage transformers also require technical improvements and the introduction of intelligent features. This requires the development of an intelligent three-phase voltage transformer with the ability to automatically remove loads when a single-phase line break occurs. Summary of the Invention

[0003] The purpose of the present invention is to solve the problems existing in the prior art and to provide an intelligent three-phase voltage transformer with high reliability, high safety and the ability to automatically cut off the fault phase load.

[0004] In order to achieve the above-mentioned object, the present invention provides an intelligent three-phase voltage transformer with a function of automatically shedding load when a single-phase line is broken, which comprises: a three-phase voltage transformer with Yynd11 group wiring, wherein the three-phase voltage transformer comprises a high-voltage side winding connected to the line and a star-connected winding and a delta-connected winding on the low-voltage secondary side, wherein the star-connected winding and the delta-connected winding are simultaneously connected to the input end of a single-phase line break accident identification module, and the three-phase voltage transformer collects the voltage signal of the line in real time; a single-phase line break accident identification module, wherein the output end of the single-phase line break accident identification module is connected to the input end of a control and communication module, and the single-phase line break accident identification module collects the secondary side star-connected winding and the delta-connected winding. and sends a single-phase disconnection indication of the fault phase to the control and communication module when it is determined that the output voltage meets the fault criterion; a control and communication module, wherein the output end of the control and communication module is connected to a preset circuit breaker, and after receiving the single-phase disconnection indication, the control and communication module sends a trip signal to the circuit breaker to cut off the line of the fault phase; a power supply module, wherein the input end of the power supply module is connected to the low-voltage secondary side angle-connected winding of the three-phase voltage transformer, the output end of the power supply module is connected to the power supply end of the single-phase disconnection accident identification module and the control and communication module, and the power supply module provides an AC voltage from the secondary side angle-connected winding and outputs a DC voltage to the single-phase disconnection accident identification module and the control and communication module.

[0005] In a preferred embodiment, the fault criterion of the single-phase disconnection accident identification module is:

[0006] When the single-phase disconnection accident identification module detects that the voltage amplitude of a phase of the star-connected winding is only half of the normal value and the voltage amplitudes of the other two phases are normal, the phase with the voltage amplitude halved is the star-connected fault phase; when the single-phase disconnection accident identification module simultaneously detects that the output voltage amplitudes of two phases of the delta-connected winding are half of the normal value and the voltage amplitude of the other phase is normal, the phase preceding the normal phase of the delta-connected winding is the delta-connected fault phase;

[0007] When the phase difference between the star-connected fault phase and the delta-connected fault phase is the same, the single-phase line break accident identification module sends a single-phase line break indication of the fault phase to the control and communication module; when the phase difference between the star-connected fault phase and the delta-connected fault phase is different, the single-phase line break accident identification module sends an abnormal alarm signal to the control and communication module.

[0008] In a preferred embodiment, the high-voltage side winding of the three-phase voltage transformer with Yynd11 group connection is a star connection method, and the neutral point is not grounded; the low-voltage secondary side star connection winding of the three-phase voltage transformer with Yynd11 group connection is a star connection method, and the neutral point is grounded; the low-voltage secondary side delta connection winding of the three-phase voltage transformer with Yynd11 group connection is a closed-loop delta connection method.

[0009] The beneficial effects of the present invention are as follows: the present invention is connected to a line, or a busbar to which the line is connected. When a single-phase line break accident occurs, the device of the present invention before the line break point cannot sense the accident state, so the load before the line break point will maintain normal operation, and the device of the present invention after the line break point will sense the accident state, so it will automatically cut off the load of the branch where it is located; the device of the present invention is safe, reliable and fast. The neutral point of the high-voltage side winding of the three-phase voltage transformer with Yynd11 group wiring is not grounded, so it can also effectively avoid the situation where the voltage transformer is involved in ferromagnetic resonance accidents. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is the overall structural diagram of the device of the present invention;

[0011] Figure 2 This is the wiring diagram of the primary and secondary windings of the Yynd11 voltage transformer of the present invention;

[0012] Figure 3 The voltage phasor diagram of the star-connected secondary winding of the voltage transformer when phase A of the line is disconnected according to the present invention;

[0013] Figure 4 The voltage phasor diagram of the delta-connected secondary winding of the voltage transformer when phase A of the line is disconnected according to the present invention;

[0014] Figure 5 This is a schematic diagram of automatic load shedding after a line breakage according to the present invention. DETAILED DESCRIPTION Specific embodiment:

[0016] like Figure 1As shown, the device of the present invention consists of a single-phase disconnection accident identification module, a three-phase voltage transformer with Yynd11 group wiring, a control and communication module, and a power supply module. The single-phase disconnection accident identification module, control and communication module, and power supply module are installed in the three-phase voltage transformer device with Yynd11 group wiring. The single-phase disconnection fault identification module collects the output voltages of the secondary star-connected and delta-connected windings of a three-phase voltage transformer with Yynd11 group wiring. If it detects that the voltage amplitude of one phase of the secondary star-connected winding is only half of its normal value and the voltage amplitudes of the other two phases are normal, the phase with the halved voltage amplitude is the secondary star-connected fault phase. If it detects that the voltage amplitude of two phases of the delta-connected winding is only half of its normal value and the voltage amplitude of the other phase is normal, the phase preceding the normal delta-connected winding phase is the secondary delta-connected fault phase. If the phase difference between the secondary star-connected fault phase and the secondary delta-connected fault phase is the same, the single-phase disconnection fault identification module issues a single-phase disconnection indication to the control and communication module. If the phase difference between the secondary star-connected fault phase and the secondary delta-connected fault phase is different, the single-phase disconnection fault identification module issues an abnormality alarm signal to the control and communication module. A normal value refers to a deviation of the measured voltage value from the rated value within ±10%. The single-phase disconnection fault identification module draws power from the power supply module.

[0017] like Figure 1 As shown, the low-voltage side delta-connected winding of the three-phase voltage transformer with Yynd11 connection only provides power to the power module and is not connected to external equipment. The power module is used to convert AC into DC and supply power to the single-phase line break accident identification module and the control and communication module. It has low power consumption, high efficiency and stability, and has little effect on the voltage output of the low-voltage side star-connected winding of the three-phase voltage transformer with Yynd11 connection.

[0018] like Figure 1 As shown, the control and communication module is connected to the single-phase line break accident identification module and is also connected to the power supply module. The control and communication module exchanges information with the single-phase line break accident identification module. The control and communication module obtains power from the power supply module. When receiving the single-phase line break indication sent by the single-phase line break accident identification module, the control and communication module sends a tripping signal to the pre-set circuit breaker to achieve the purpose of automatically cutting off the load after the single-phase line break break point.

[0019] like Figure 2As shown, the three-phase voltage transformer with Yynd11 group connection has three windings. There is one group of high-voltage side windings, which adopts star connection and the neutral point is not grounded. The high-voltage side winding is connected to the fuse, the fuse is connected to the disconnector, and the disconnector is connected to the line; there are two groups of low-voltage side windings, one of which adopts star connection, that is, star-connected winding, with the neutral point grounded. The star-connected winding is connected to the single-phase line break accident identification module, and is also connected to external measurement and control devices, meters, protection and safety automatic devices and other equipment. The other group adopts closed-loop delta connection, that is, delta-connected winding, and is connected to the single-phase line break accident identification module, and is also connected to the power module.

[0020] like Figure 3 、 4 As shown, when a single-phase disconnection accident occurs in phase A of the line, for example, phase A, the output voltage of the secondary star-connected winding of the three-phase voltage transformer with the Yynd11 connection group will reflect that the voltages of phases B and C are normal, the voltage amplitude of phase A is halved and the direction is opposite to that during normal operation, and the phase A with the voltage amplitude halved is the fault phase. The output voltage of the delta-connected winding of the three-phase voltage transformer with the Yynd11 connection group reflects that the voltage of phase B is normal, the voltage amplitude of phases A and C is halved and the direction is opposite to that of phase B, and the previous phase of phase B is phase A. Based on this, it can be determined that a single-phase disconnection accident has occurred in the phase A line. Due to the use of the dual-source redundant authentication method, the single-phase disconnection accident identification module works reliably and quickly. As Figure 5 As shown, since the device of the present invention is connected to the line or the busbar to which the line is connected, when a single-phase line break occurs, the device of the present invention before the line break point cannot sense the accident state, so the load before the line break point maintains normal operation; the device of the present invention after the line break point will sense the accident state, and will automatically cut off the load after the line break point.

[0021] The present invention is significantly different from a conventional three-phase voltage transformer. The conventional three-phase voltage transformer adopts a Ynynd0 wiring method, that is, the neutral point of the high-voltage side star-connected winding is drawn out and grounded. Since there is a path to the ground, the high-voltage side winding of the conventional transformer is easily involved in the ferromagnetic resonance accident of the power grid. The output voltage of the secondary star-connected winding of the conventional transformer is mainly used for measurement and control devices, meters, protection and safety automatic devices, etc. The winding of the low-voltage side delta-connected winding is open, and one end of the open end is grounded, and the other end of the open end is used for line insulation monitoring. In contrast, the present invention adopts a Yynd11 group wiring method, which is the most sensitive to power grid accidents. Since the neutral point of the high-voltage side winding is not grounded, the high-voltage side winding of the transformer is not easily involved in the ferromagnetic resonance of the power grid. The delta-connected winding on the low-voltage side adopts a closed-loop connection method, providing a zero-sequence path. Therefore, the vector characteristics of the three-phase voltage of the delta-connected winding can reflect many power grid accidents and can be mutually verified with the voltage vector characteristics of the secondary star-connected winding, with high reliability. In use, the high-voltage side winding is connected to one end of a fuse, the other end of the fuse is connected to one end of an isolating switch, and the other end of the isolating switch is connected to a line or busbar. The device offers high reliability in accident detection, automatically disconnecting loads after a single-phase line break, avoiding arc overvoltage at the line break. It also addresses the issue of conventional voltage transformers being susceptible to ferromagnetic resonance accidents.

[0022] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A three-phase voltage transformer with the function of automatically cutting off the load when a single-phase line is broken, characterized in that: It includes: Yynd11 group-connected three-phase voltage transformer, the three-phase voltage transformer includes a high-voltage side winding connected to the line and a star-connected winding and a delta-connected winding on the low-voltage secondary side. The star-connected winding and the delta-connected winding are simultaneously connected to the input end of the single-phase line break accident identification module. The three-phase voltage transformer collects the voltage signal of the line in real time; the single-phase line break accident identification module, the output end of the single-phase line break accident identification module is connected to the input end of the control and communication module, the single-phase line break accident identification module collects the output voltage of the secondary side star-connected winding and the delta-connected winding, and sends a fault signal to the control module when it determines that the output voltage meets the fault criterion. The control and communication module sends a single-phase line break indication of the fault phase; the control and communication module, the output end of the control and communication module is connected to a preset circuit breaker, and after receiving the single-phase line break indication, the control and communication module sends a trip signal to the circuit breaker to cut off the line of the fault phase; the power supply module, the input end of the power supply module is connected to the low-voltage secondary side angle-connected winding of the three-phase voltage transformer, the output end of the power supply module is connected to the power supply end of the single-phase line break accident identification module and the control and communication module, and the power supply module provides AC voltage from the secondary side angle-connected winding and outputs DC voltage to the single-phase line break accident identification module and the control and communication module; The high-voltage side winding of the three-phase voltage transformer with Yynd11 group connection is a star connection method, and the neutral point is not grounded; the low-voltage secondary side star connection winding of the three-phase voltage transformer with Yynd11 group connection is a star connection method, and the neutral point is grounded; the low-voltage secondary side delta connection winding of the three-phase voltage transformer with Yynd11 group connection is a closed-loop delta connection method.

2. The three-phase voltage transformer with the function of automatically shedding load when a single-phase line is broken according to claim 1, characterized in that: The fault criterion of the single-phase disconnection accident identification module is: When the single-phase disconnection accident identification module detects that the voltage amplitude of a phase of the star-connected winding is only half of the normal value and the voltage amplitudes of the other two phases are normal, the phase with the voltage amplitude halved is the star-connected fault phase; when the single-phase disconnection accident identification module simultaneously detects that the output voltage amplitudes of two phases of the delta-connected winding are half of the normal value and the voltage amplitude of the other phase is normal, the phase preceding the normal phase of the delta-connected winding is the delta-connected fault phase; When the phase difference between the star-connected fault phase and the delta-connected fault phase is the same, the single-phase line break accident identification module sends a single-phase line break indication of the fault phase to the control and communication module; when the phase difference between the star-connected fault phase and the delta-connected fault phase is different, the single-phase line break accident identification module sends an abnormal alarm signal to the control and communication module.

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