A system and method for automatically determining residual magnetism of transformers in power plants

Abstract

The present invention discloses a system and method for automatically identifying residual magnetism of a power plant transformer, comprising an excitation system, a magnetic field circuit breaker FMK, an excitation coil, a generator, a first current transformer, a second current transformer, a high-voltage transformer, a main transformer, a grid-connected circuit breaker, a first circuit breaker, a 6kV working section A, a second circuit breaker, a 6kV working section B, and a generator-transformer group protection device. The excitation system is connected to the excitation coil via the magnetic field circuit breaker, the excitation coil is coupled to the generator, and the output end of the generator is divided into two paths after passing through the first current transformer, one of which is connected to the high-voltage side of the high-voltage transformer via the second current transformer, and the other is connected to the system via the main transformer and the grid-connected circuit breaker. The low-voltage side of the high-voltage transformer is divided into two paths, one of which is connected to the 6kV working section A via the first circuit breaker, and the other is connected to the 6kV working section B via the second circuit breaker. The system and method can automatically identify whether the transformer has residual magnetism that affects the startup of the unit.

Description

Technical Field

[0001] The invention belongs to the technical field of power plant electrical equipment and relates to a system and method for automatically distinguishing residual magnetism of a power plant transformer. Background Art

[0002] Transformers are important equipment in power grids. The stable operation of transformers plays a key role in ensuring continuous and reliable power supply to power systems. Due to the inherent hysteresis of ferromagnetic materials, residual magnetism remains in the iron core of the transformer. After the DC test, power transformers will produce residual magnetism. The amount of residual magnetism depends on the intensity and time of the DC current passing through the transformer winding. The longer the time, the greater the residual magnetism. Many cases have shown that when the generator-transformer group of a power plant is stepping up and has not yet been connected to the grid, if the main transformer, high-voltage transformer and other transformers (attached Figure 1 If residual magnetism in the iron core is not eliminated, the transformer will generate a large inrush current, distorting the voltage and current waveforms at the generator output, leading to false alarms and even malfunction of the relay protection device. Currently, power plant relay protection and automatic safety devices are unable to detect this abnormal phenomenon. On-site inspections of the main equipment must be dismantled and carried out section by section, requiring extensive personnel and time-consuming inspections and tests to accurately determine the cause before the generator set can be restored to grid operation. This often results in significant power losses, which is extremely detrimental to the safe and economic operation of the power plant. Summary of the Invention

[0003] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a system and method for automatically distinguishing residual magnetism of transformers in power plants, which can automatically identify whether the transformer has residual magnetism that affects the startup of the unit.

[0004] To achieve the above-mentioned object, the power plant transformer residual magnetism automatic discrimination system of the present invention comprises an excitation system, a magnetic field circuit breaker, an excitation coil, a generator, a first current transformer, a second current transformer, a high-voltage transformer, a main transformer, a grid-connected circuit breaker, a first circuit breaker, a 6kV working section A, a second circuit breaker, a 6kV working section B, and a generator-transformer group protection device;

[0005] The excitation system is connected to the excitation coil through the magnetic field circuit breaker, and the excitation coil is coupled to the generator. The output end of the generator is divided into two paths after passing through the first current transformer, one of which is connected to the high-voltage side of the high-voltage transformer through the second current transformer, and the other is connected to the system through the main transformer and the grid-connected circuit breaker. The low-voltage side of the high-voltage transformer is divided into two paths, one of which is connected to the 6kV working section A through the first circuit breaker, and the other is connected to the 6kV working section B through the second circuit breaker.

[0006] The generator-transformer group protection device is connected to the grid-connected circuit breaker, the magnetic field circuit breaker, the first circuit breaker, the second circuit breaker, the first current transformer and the second current transformer.

[0007] It also includes a DCS system; the output end of the generator-transformer group protection device is connected to the DCS system.

[0008] The generator-transformer group protection device is connected to the DCS system via a secondary cable.

[0009] The method for automatically determining residual magnetism of a power plant transformer according to the present invention comprises the following steps:

[0010] When the grid-connected circuit breaker is not closed, the magnetic field circuit breaker is closed, the generator stator current is greater than the generator stator current no-current set value, and the generator stator current second harmonic content is greater than the generator stator current second harmonic content set value, the generator-transformer group protection device will send a main transformer residual magnetism alarm signal to the DCS system after a delay to prompt the operating personnel to perform main transformer residual magnetism processing;

[0011] When the grid-connected circuit breaker is not closed, the magnetic field circuit breaker is closed, the high-voltage side current of the high-voltage transformer is greater than the no-current set value of the high-voltage side current of the high-voltage transformer, and the second harmonic content of the high-voltage side current of the high-voltage transformer is greater than the second harmonic content set value of the high-voltage side current of the high-voltage transformer, the transformer group protection device will send a high-voltage transformer residual magnetism alarm signal after a delay, which will then be sent to the DCS system through the secondary cable to prompt the operating personnel to perform high-voltage transformer residual magnetism processing.

[0012] When the no-current set value of the generator stator current is less than the minimum load current of the generator, the no-current set value is set to 5% of the rated current of the generator.

[0013] The second harmonic content of the generator stator current is set to 15%, and the delay time is greater than or equal to the generator excitation time.

[0014] The no-current setting value of the high-voltage side current of the high-voltage transformer is less than the minimum load current of the high-voltage transformer, and the no-current setting value of the high-voltage side current of the high-voltage transformer is 5% of the rated current of the high-voltage side of the high-voltage transformer.

[0015] The set value of the second harmonic content of the high-voltage side current of the high-voltage transformer is 15%, and the delay time is greater than or equal to the generator excitation time.

[0016] The present invention has the following beneficial effects:

[0017] During operation, the system and method for automatically determining residual magnetism in power plant transformers, described in this invention, determines the presence of residual magnetism in the main transformer and high-voltage transformer based on the currents of the main transformer, high-voltage transformer, and generator, as well as the status signals of the grid-connected circuit breaker and field circuit breaker. This automatically identifies abnormal conditions in the power plant's key equipment, saving significant manpower and eliminating obstacles to rapid generator grid restoration. The system and method are widely applicable to power generation companies. In actual operation, only the determination logic and alarm output circuitry need to be added to the generator-transformer group, without changing the inherent safety and reliability of the device, resulting in negligible cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a system diagram of the present invention;

[0019] Figure 2 This is the logic diagram for automatically distinguishing the residual magnetism of the main transformer in the power plant;

[0020] Figure 3 This is the automatic discrimination logic diagram for the residual magnetism of the high-voltage transformer in a power plant. DETAILED DESCRIPTION

[0021] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only embodiments of a part of the present invention, not all embodiments, and are not intended to limit the scope of the present invention. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts disclosed in the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work should fall within the scope of protection of the present invention.

[0022] The accompanying drawings illustrate schematic diagrams of the structures of the disclosed embodiments of the present invention. These figures are not drawn to scale; for the purpose of clarity, some details are exaggerated and some details may be omitted. The shapes of the various regions and layers shown in the figures, as well as their relative sizes and positional relationships, are merely exemplary and may deviate in practice due to manufacturing tolerances or technical limitations. Those skilled in the art may design regions / layers with different shapes, sizes, and relative positions as needed.

[0023] refer to Figure 1 The power plant transformer residual magnetism automatic identification system of the present invention includes an excitation system, a magnetic field circuit breaker FMK, an excitation coil, a generator, a first current transformer TA1, a second current transformer TA2, a high-voltage transformer, a main transformer, a grid-connected circuit breaker QF1, a first circuit breaker QF2, a 6kV working section A, a second circuit breaker QF3, a 6kV working section B, a generator-transformer group protection device, a DCS system, and a secondary cable.

[0024] The excitation system is connected to the excitation coil through the magnetic field circuit breaker FMK, and the excitation coil is coupled to the generator. The output end of the generator is divided into two paths after passing through the first current transformer TA1. One path is connected to the high-voltage side of the high-voltage transformer through the second current transformer TA2, and the other path is connected to the system through the main transformer and the grid-connected circuit breaker QF1. The low-voltage side of the high-voltage transformer is divided into two paths, one of which is connected to the 6kV working section A through the first circuit breaker QF2, and the other is connected to the 6kV working section B through the second circuit breaker QF3.

[0025] The generator-transformer group protection device is connected to the grid-connected circuit breaker QF1, the magnetic field circuit breaker FMK, the first circuit breaker QF2, the second circuit breaker QF3, the first current transformer TA1 and the second current transformer TA2. The generator-transformer group protection device is connected to the DCS system via a secondary cable.

[0026] The method for automatically determining residual magnetism of a transformer in a power plant according to the present invention comprises the following steps:

[0027] refer to Figure 2 The generator-transformer group protection device collects the opening and closing position signals of the grid-connected circuit breaker QF1, the magnetic field circuit breaker FMK, the first circuit breaker QF2, and the second circuit breaker QF3 in real time; the current on the low-voltage side of the main transformer is collected through the first current transformer TA1, and the current on the high-voltage side of the high-voltage transformer is detected through the second current transformer TA2. Based on the current on the high-voltage side of the high-voltage transformer and the current on the low-voltage side of the main transformer, the secondary current harmonic content of the current on the low-voltage side of the main transformer and the current on the high-voltage side of the high-voltage transformer are calculated;

[0028] refer to Figure 3 When the grid-connected circuit breaker QF1 is not closed, the magnetic field circuit breaker FMK is closed, the generator stator current is greater than the generator stator current no-current set value, and the generator stator current second harmonic content is greater than the generator stator current second harmonic content set value, the generator-transformer group protection device will send a main transformer residual magnetism alarm signal to the DCS system after a delay to prompt the operating personnel to perform main transformer residual magnetism processing;

[0029] When the no-current set value of the generator stator current is less than the minimum load current of the generator, the no-current set value is taken as 5% of the rated current of the generator; the second harmonic content set value of the generator stator current is taken as 15%, and the delay time is greater than or equal to the generator excitation time, which is 10s.

[0030] When the grid-connected circuit breaker QF1 is not closed, the magnetic field circuit breaker FMK is closed, the high-voltage side current of the high-voltage transformer is greater than the no-current set value of the high-voltage side current of the high-voltage transformer, and the second harmonic content of the high-voltage side current of the high-voltage transformer is greater than the second harmonic content set value of the high-voltage side current of the high-voltage transformer, the transformer group protection device will send a high-voltage transformer residual magnetism alarm signal after a delay, and then send it to the DCS system through the secondary cable, prompting the operating personnel to perform high-voltage transformer residual magnetism processing.

[0031] The no-current set value of the high-voltage side current of the high-voltage transformer is less than the minimum load current of the high-voltage transformer. The no-current set value of the high-voltage side current of the high-voltage transformer is 5% of the rated current of the high-voltage side of the high-voltage transformer; the second harmonic content set value of the high-voltage side current of the high-voltage transformer is 15%, and the delay time is greater than or equal to the generator excitation time, which is 10s.

[0032] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural change made to the above embodiment based on the technical essence of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for automatically determining residual magnetism of transformers in power plants, characterized in that: Based on the power plant transformer residual magnetism automatic discrimination system, the power plant transformer residual magnetism automatic discrimination system includes an excitation system, a magnetic field circuit breaker (FMK), an excitation coil, a generator, a first current transformer (TA1), a second current transformer (TA2), a high-voltage transformer, a main transformer, a grid-connected circuit breaker (QF1), a first circuit breaker (QF2), a 6kV working section A, a second circuit breaker (QF3), a 6kV working section B, and a generator-transformer group protection device; The excitation system is connected to the excitation coil via a magnetic field circuit breaker (FMK), and the excitation coil is coupled to the generator. The output end of the generator is divided into two paths after passing through the first current transformer (TA1), one of which is connected to the high-voltage side of the high-voltage transformer via the second current transformer (TA2), and the other is connected to the system via the main transformer and the grid-connected circuit breaker (QF1). The low-voltage side of the high-voltage transformer is divided into two paths, one of which is connected to the 6kV working section A via the first circuit breaker (QF2), and the other is connected to the 6kV working section B via the second circuit breaker (QF3); The generator-transformer group protection device is connected to the grid-connected circuit breaker (QF1), the magnetic field circuit breaker (FMK), the first circuit breaker (QF2), the second circuit breaker (QF3), the first current transformer (TA1) and the second current transformer (TA2); Also includes DCS system; The output end of the generator-transformer group protection device is connected to the DCS system; The generator-transformer group protection device is connected to the DCS system via a secondary cable; The following steps are involved: When the grid-connected circuit breaker (QF1) is not closed, the magnetic field circuit breaker (FMK) is closed, the generator stator current is greater than the generator stator current no-current set value, and the generator stator current second harmonic content is greater than the generator stator current second harmonic content set value, the generator-transformer group protection device will send a main transformer residual magnetism alarm signal to the DCS system after a delay to prompt the operating personnel to perform main transformer residual magnetism processing; When the grid-connected circuit breaker (QF1) is not closed, the magnetic field circuit breaker (FMK) is closed, the high-voltage side current of the high-voltage transformer is greater than the high-voltage side current no-current set value, and the second harmonic content of the high-voltage side current of the high-voltage transformer is greater than the second harmonic content set value of the high-voltage side current of the high-voltage transformer, the transformer group protection device will send a high-voltage transformer residual magnetism alarm signal after a delay, and then send it to the DCS system through the secondary cable, prompting the operating personnel to perform high-voltage transformer residual magnetism processing; When the no-current set value of the generator stator current is less than the minimum load current of the generator, the no-current set value is taken as 5% of the rated current of the generator; The second harmonic content of the generator stator current is set to 15%, and the delay time is greater than or equal to the generator excitation time; The no-current setting value of the high-voltage side current of the high-voltage transformer is less than the minimum load current of the high-voltage transformer. The no-current setting value of the high-voltage side current of the high-voltage transformer is 5% of the rated current of the high-voltage side of the high-voltage transformer. The set value of the second harmonic content of the high-voltage side current of the high-voltage transformer is 15%, and the delay time is greater than or equal to the generator excitation time.

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