A generator core loss test system and method for reducing test impulse current

Abstract

The invention discloses a generator core loss test system and method for reducing test impact current, comprising a power supply unit, a switch control unit, a current measuring unit, a voltage measuring unit, a multifunctional power measuring unit, an excitation coil unit, a measuring coil unit and an iron core unit to be tested; the excitation coil unit and the measuring coil unit are wound on the iron core unit to be tested, the power supply unit is connected to the excitation coil unit via the switch control unit, the excitation coil unit is connected to the multifunctional power measuring unit via the current measuring unit, and the measuring coil unit is connected to the multifunctional power measuring unit via the voltage measuring unit. The system and method can effectively reduce the impact current when the switch is closed while saving test costs, reducing workload and shortening test preparation time, thereby greatly improving the economy and safety of the iron loss test.

Description

Technical Field

[0001] The invention belongs to the technical field of motor stator core loss detection, and relates to a generator core loss test system and method for reducing test impact current. Background Art

[0002] As the source of electricity in the power system and its core position in each power plant, the generator plays a vital role in the entire power system and the people's life. Over the years, accidents caused by generator failures have occurred frequently, which is due to the lack of sufficient attention to the early signs of generator failure. At this stage, various power plants have also introduced various preventive tests to conduct regular inspections of generators, in order to eliminate the problem at the source in the early stage of generator failure, thereby improving the safety and stability of the power system. The stator core of the generator is assembled by stacking silicon steel sheets. During normal operation, the core will be subjected to the combined effects of mechanical force, thermal stress and electromagnetic force. Therefore, with the accumulation of time, the core will also have different faults. For example, when there are insulation defects between the silicon steel sheets, the core will generate eddy currents in the environment of strong magnetic flux, resulting in local temperature rise. Under long-term action, it will cause irreversible damage such as winding insulation damage or even core burning. Therefore, the iron loss test must be carried out after the core is stacked or the slot wedge is removed.

[0003] At present, conventional iron loss tests use a 300-meter-long wire with a cross-sectional area of ​​120 mm. 2 The unshielded cable is evenly wound around the entire core circumference. The generator stator core is used as the magnetic flux circuit, and the excitation winding and the measuring coil are used as the primary and secondary sides respectively. After the power circuit breaker is directly closed and the AC power is passed through, an alternating magnetic flux close to the saturation state is generated inside the core, thereby generating eddy current and hysteresis loss in the core, causing the core to heat up. The fault of the generator core is detected according to the temperature rise of the core, so that the iron loss test plays a preventive role. Under this test operation, the arrangement of a whole cable greatly increases the consumption of manpower and material resources and prolongs the test preparation time; secondly, in the actual test process, the closing operation is generally carried out at a voltage of 6kV. The operating condition of the generator stator core belongs to full-voltage no-load operation. Directly closing the circuit breaker makes it very easy to generate an impact current of 5-7 times the rated current at the moment of closing, which not only easily causes the relay protection device on the power line side to malfunction, but also causes the voltage of the upper line to rise and fall sharply, affecting the normal operation of other electrical equipment. In severe cases, it will damage the test equipment. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and to provide a generator core loss test system and method for reducing the test impact current. The system and method can save test costs, reduce workload and shorten test preparation time, while effectively reducing the impact current when the switch is closed, thereby greatly improving the economy and safety of the iron loss test.

[0005] To achieve the above-mentioned object, the generator core loss test system for reducing test impulse current of the present invention comprises a power supply unit, a switch control unit, a current measurement unit, a voltage measurement unit, a multifunctional power measurement unit, an excitation coil unit, a measurement coil unit and a core unit to be tested;

[0006] The excitation coil unit and the measuring coil unit are wound on the iron core unit to be tested, the power supply unit is connected to the excitation coil unit via the switch control unit, the excitation coil unit is connected to the multifunctional power measuring unit via the current measuring unit, and the measuring coil unit is connected to the multifunctional power measuring unit via the voltage measuring unit.

[0007] It also includes an infrared monitoring unit for real-time monitoring of the temperature of the core unit to be tested and the ambient temperature.

[0008] The switch control unit includes a computer, a logic loop controller, a high-voltage circuit breaker and a phase reference module, wherein the power supply unit is connected to the excitation coil unit via the phase reference module and the high-voltage circuit breaker, wherein the computer is connected to the high-voltage circuit breaker and the phase reference module via the logic loop controller.

[0009] The phase reference module comprises a synchronous transformer unit, a low-pass filter unit, a high-pass filter unit, a square wave conversion unit and a hysteresis comparison unit which are connected in sequence.

[0010] The excitation coils in the excitation coil unit are evenly arranged on the core unit to be tested.

[0011] The measuring coil unit is arranged at the center of the generator hall.

[0012] The excitation coil unit is connected to the multifunctional power measurement unit through a current measurement clamp.

[0013] The generator core loss test method for reducing test impulse current of the present invention comprises the following steps:

[0014] 1) Remove the connection line between the generator output line and the closed busbar, remove the connection line of the stator three-phase winding at the neutral point, and short-circuit and ground the secondary side of various CTs, generator output lines, closed busbar side and various temperature measuring elements of the measuring generator;

[0015] 2) The computer sends a test start instruction, the phase reference module processes the voltage signal on the power supply side, the synchronous transformer unit transforms the power supply voltage and keeps the output signal in the same phase and frequency as the power supply voltage, wherein the high-order harmonics and low-order harmonics in the signal are filtered out by the low-pass filter unit and the high-pass filter unit, the voltage signal is converted into a square wave signal by the square wave conversion unit, and finally the burrs in the square wave signal are eliminated by the hysteresis comparison unit, and then the signal is input into the logic loop controller, the square wave signal is logically processed by the logic loop controller and a closing instruction of the high-voltage circuit breaker is issued, wherein after receiving the test start instruction, the logic loop controller counts once every 40 μs and reads data once, reads the voltage signal and determines whether its phase is 0+kπ (k=0,1,2,...,n), if not, continues to read data, if yes, delays T=nt1-t2 (T≥0,n=1,3,5,...,n) and then outputs the closing instruction of the high-voltage circuit breaker, and the high-voltage circuit breaker performs a closing action after receiving the closing instruction of the high-voltage circuit breaker.

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

[0017] The generator core loss test system and method for reducing test impact current described in the present invention, during specific operation, performs logic processing on a square wave signal through a logic loop controller and issues a closing command for a high-voltage circuit breaker, wherein after receiving the test start command, the logic loop controller times once every 40 μs and reads data once, reads the voltage signal and determines whether its phase is 0+kπ (k=0,1,2,...,n), if not, continues to read data, and if so, outputs a closing command for the high-voltage circuit breaker after a delay of T=nt1-t2 (T≥0,n=1,3,5,...,n), so as to optimize the switch control unit, effectively reduce the impact current when the switch is closed while saving the test cost and shortening the test preparation time, and greatly improve the economy and safety of the iron loss test. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a structural schematic diagram of the present invention;

[0019] Figure 2 is a schematic diagram of a switch control unit;

[0020] Figure 3 is a schematic diagram of a logic loop controller;

[0021] Figure 4 It is the principle diagram of the present invention;

[0022] Figure 5 is the distribution diagram of the excitation coil;

[0023] Figure 6 It is a flow chart of the present invention.

[0024] Among them, 1 is the iron core unit to be tested, 2 is the excitation coil unit, 3 is the switch control unit, 4 is the power supply unit, 5 is the measuring coil unit, 6 is the voltage measuring unit, 7 is the current measuring unit, 8 is the multifunctional power measuring unit, 9 is the infrared monitoring unit, 10 is the current measuring clamp, 31 is the high-voltage circuit breaker, 32 is the phase reference module, 33 is the logic loop controller, 34 is the computer, 321 is the synchronous transformer unit, 322 is the low-pass filter unit, 323 is the high-pass filter unit, 324 is the square wave conversion unit, and 325 is the hysteresis comparison unit. DETAILED DESCRIPTION

[0025] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the described embodiment is only an embodiment of a part of the present invention, not all embodiments, and is not intended to limit the scope of the present invention. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concepts disclosed in the present invention. Based on the embodiments in 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.

[0026] The accompanying drawings show schematic diagrams of structures according to embodiments disclosed in the present invention. These figures are not drawn to scale, and some details are magnified and some details may be omitted for the purpose of clear expression. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships therebetween are only exemplary, and may deviate in practice due to manufacturing tolerances or technical limitations, and those skilled in the art may additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0027] refer to Figure 1 The generator core loss test system for reducing test impulse current described in the present invention includes a power supply unit 4, a switch control unit 3, a current measurement unit 7, a voltage measurement unit 6, a multifunctional power measurement unit 8, an excitation coil unit 2, a measuring coil unit 5, an infrared monitoring unit 9 and a core unit 1 to be tested.

[0028] The power supply unit 4 is connected to each electrical device via the switch control unit 3 to provide AC power for the entire iron loss test. The excitation coil unit 2 and the measuring coil unit 5 are wound around the core unit 1 to be tested.

[0029] refer to Figure 2The switch control unit 3 includes a computer 34, a logic loop controller 33, a high-voltage circuit breaker 31 and a phase reference module 32, wherein the power supply unit 4 is connected to the excitation coil unit 2 via the phase reference module 32 and the high-voltage circuit breaker 31, wherein the computer 34 is connected to the high-voltage circuit breaker 31 and the phase reference module 32 via the logic loop controller 33, and the phase reference module 32 includes a synchronous transformer unit 321, a low-pass filter unit 322, a high-pass filter unit 323, a square wave conversion unit 324 and a hysteresis comparison unit 325 connected in sequence, filtering, square wave conversion and hysteresis comparison of the line voltage signal to obtain a processed voltage signal, and then inputting the processed voltage signal into the logic loop controller 33, the logic loop controller 33 is connected to the computer 34 for receiving the switch closing information sent by the user and feeding back visual information to the user, and on the other hand, is connected to the high-voltage circuit breaker 31, performs logic processing on the feedback signal and outputs the circuit breaker closing instruction, controls the high-voltage circuit breaker 31 to close at the maximum or minimum value of the voltage amplitude to reduce the impact current.

[0030] Assume that the AC voltage when closing the circuit breaker is:

[0031]

[0032] Among them, α is the initial phase of voltage u when no-load closing, and magnetic flux φ is:

[0033] φ=-φmcos(ωt+α)+φmcosα

[0034] It can be seen from the above formula that the size of the magnetic flux when closing the circuit breaker under no-load condition is related to the initial phase angle of the power supply voltage by α, and has two components. The first is the steady-state component, which decreases with the passage of time; the second is the transient component. Due to the existence of internal resistance, the transient component gradually decays to 0 with the passage of time. Due to the existence of the transient component, a huge impact current is easily generated at the moment of closing the circuit breaker.

[0035] When the circuit breaker is closed at α=π / 2+kπ(k=0,1,2,...,n), we have:

[0036] φ=φmsinωt

[0037] At this time, the steady-state process is directly entered after closing the circuit breaker, and there is no transient process, that is, the excitation current is the no-load current under normal operating conditions.

[0038] When α=0+kπ(k=0,1,2,...,n), the circuit breaker is closed, then:

[0039] φ=-φm cosωt+φm

[0040] At this time, the magnetic flux has two components, namely -φm cosωt and φm. Since the relationship between magnetic flux and current is not linear, in the most extreme case, when the magnetic flux is 2φm, the core is deeply saturated, and the excitation current increases sharply. When the switch is closed under the condition of α=0+kπ(k=0,1,2,...,n), the impact current will reach dozens or even hundreds of times the no-load current during stable operation, which is 5-7 times the rated current. Therefore, according to the above analysis, the closer the initial phase of the voltage is to α=π / 2+kπ(k=0,1,2,...,n), the closer the impact current is to the no-load current.

[0041] The signal received by the logic loop controller 33 is a square wave signal converted from a voltage sine wave, so it is easy to determine the zero-crossing signal when the voltage signal is positive or negative, that is, the voltage phase α=0+kπ(k=0,1,2,...,n) at this moment. Since the phase difference between the voltage and the current is 90°, the voltage is at its maximum or minimum value 1 / 4 cycle after the voltage zero-crossing moment, which is also the current zero-crossing moment. Wherein, t1 is the 1 / 4 cycle duration at the actual voltage frequency.

[0042] The high-voltage circuit breaker 31 has a leading time of the closing pulse from the time when the closing command is issued to the time when the main contact is actually closed. The main reason is that the closing command needs to pass through the intermediate relay to drive the closing coil of the high-voltage circuit breaker 31, and the moving and static contacts of the high-voltage circuit breaker 31 start to move, and finally the main contact is completely closed. The leading time includes the sum of the action times of all intermediate components. Since the closing time of the high-voltage circuit breaker 31 is determined by itself, the leading time does not change with the change of frequency and voltage, that is, the constant leading time t2.

[0043] Based on the above reasons, after collecting the voltage zero-crossing signal, the logic loop controller 33 is used to delay the closing of the high-voltage circuit breaker 31, and the extension time is T=nt1-t2 (T≥0, n=1,3,5,...,n). The switch control unit 3 can achieve the closing of the high-voltage circuit breaker 31 at the maximum or minimum voltage value, effectively reducing the impact current at the moment of closing; on the other hand, considering the lead time, the switch control unit 3 can control the actual closing time of the main contacts in the high-voltage circuit breaker 31 to ensure the success rate of the test method.

[0044] The current measuring unit 7 is connected to the line through a current measuring clamp 10 . The current measuring unit 7 is connected to a multifunctional power measuring unit 8 for measuring the current and power of the excitation coil unit 2 .

[0045] The primary side of the voltage transformer in the voltage measuring unit 6 is connected to the measuring coil unit 5, and is connected to the multifunctional power measuring unit 8 through the secondary side of the voltage transformer in the voltage measuring unit 6, for recording the terminal voltage of the measuring coil.

[0046] The excitation coil unit 2 and the measuring coil unit 5 are both connected to the core unit 1 to be measured, wherein the excitation coil unit 2 has a length of 15 meters and a cross-sectional area of ​​120 mm 2 Of the 20 cables, 10 are evenly arranged inside and outside the core unit 1 to be tested, and then the segmented cables are connected in sequence according to the specified sequence numbers and evenly arranged on the core unit 1 to be tested.

[0047] The infrared monitoring unit 9 uses an infrared thermal imager to monitor the temperature of the core unit 1 to be tested and the ambient temperature in real time.

[0048] The generator core loss test method based on reducing the test impulse current of the present invention comprises the following steps:

[0049] 1) Remove the connection line between the generator output line and the closed busbar, remove the connection line of the stator three-phase winding at the neutral point, and short-circuit and ground the secondary side of various CTs, generator output lines, closed busbar side and various temperature measuring elements of the measuring generator;

[0050] The power supply unit 4 is led from the power plant and connected to the excitation coil unit 2 through the high-voltage circuit breaker 31 in the switch control unit 3 to provide AC power for the entire iron loss test;

[0051] The excitation coils in the excitation coil unit are evenly arranged on the stator core of the generator. Figure 5 As shown, the insulating rods are evenly laid in the generator hall, each insulating rod is 1 meter apart, and the length of the insulating rods is 1.5 meters. Cable No. 1 is arranged at the rightmost side in the generator hall, and cables No. 2 to No. 10 are evenly arranged on the left side of cable No. 1 in sequence; and cable No. 11 is arranged at the rightmost side outside the generator hall, and cables No. 12 to No. 20 are evenly arranged on the left side of cable No. 11 in sequence. Finally, the cables are connected in sequence, that is, the No. 1 cable terminal 2 is reliably connected to the No. 11 cable terminal 3, and the No. 11 cable terminal 4 is reliably connected to the No. 2 cable terminal 5. Figure 5 The same method is used to form an excitation coil.

[0052] The measuring coil unit is arranged at the center of the generator hall and connected to the primary side of the voltage transformer in the voltage measuring unit 6. The secondary side of the voltage transformer is connected to the multifunctional power measuring unit 8. On the other hand, the current measuring clamp 10 is connected to the circuit of the excitation coil unit 2 and connected to the multifunctional power measuring unit 8 to measure the current and power of the excitation coil unit 2.

[0053] An infrared thermal imager is used to record the initial temperature of the generator stator core and monitor the changes in the generator stator core temperature and ambient temperature in real time.

[0054] The computer 34 issues a test start instruction, the phase reference module 32 processes the voltage signal on the power supply side, the synchronous transformer unit 321 transforms the power supply voltage and keeps the output signal in the same phase and frequency as the power supply voltage, wherein the high-order harmonics and low-order harmonics in the signal are filtered out by the low-pass filter unit 322 and the high-pass filter unit 323, and the signal is converted into a square wave signal by the square wave conversion unit 324, and finally the burrs in the square wave signal are removed by the hysteresis comparison unit 325, and then the signal is input into the logic loop controller 33, and the logic loop controller 33 performs logic processing on the square wave signal and issues a closing instruction for the high-voltage circuit breaker 31, and the logic processing and the closing instruction output process of the high-voltage circuit breaker 31 are as follows. Figure 6 As shown, after receiving the user's start information, the logic loop controller 33 times once every 40μs and reads data once, reads the voltage signal and determines whether its phase is 0+kπ (k=0,1,2,...,n), if not, continues to read data, if so, performs a delay operation, and outputs a closing instruction of the high-voltage circuit breaker 31 after a delay of T=nt1-t2 (T≥0,n=1,3,5,...,n), and the high-voltage circuit breaker 31 performs a closing action after receiving the closing instruction of the high-voltage circuit breaker 31, so that the entire circuit is powered on.

[0055] During the test, the test data shall be recorded at least once every 15 minutes, including frequency, excitation coil current, power, measurement coil terminal voltage, stator core temperature and ambient temperature.

[0056] It should be noted that the above is only used to illustrate the technical solution of this patent and is not a limitation. Although the patent is described in detail with reference to the preferred embodiments, ordinary technicians in this field should understand that the technical solution of this patent can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of this patent.

Claims

1. A generator core loss test method for reducing test impulse current, characterized in that: A generator core loss test system based on reducing test impulse current, the generator core loss test system comprising a power supply unit (4), a switch control unit (3), a current measurement unit (7), a voltage measurement unit (6), a multifunctional power measurement unit (8), an excitation coil unit (2), a measurement coil unit (5) and a core unit to be tested (1); The excitation coil unit (2) and the measuring coil unit (5) are wound on the iron core unit (1) to be measured, the power supply unit (4) is connected to the excitation coil unit (2) via the switch control unit (3), the excitation coil unit (2) is connected to the multifunctional power measuring unit (8) via the current measuring unit (7), and the measuring coil unit (5) is connected to the multifunctional power measuring unit (8) via the voltage measuring unit (6); The switch control unit (3) comprises a computer (34), a logic loop controller (33), a high-voltage circuit breaker (31) and a phase reference module (32), wherein the power supply unit (4) is connected to the excitation coil unit (2) via the phase reference module (32) and the high-voltage circuit breaker (31), and wherein the computer (34) is connected to the high-voltage circuit breaker (31) and the phase reference module (32) via the logic loop controller (33); The phase reference module (32) comprises a synchronous voltage conversion unit (321), a low-pass filtering unit (322), a high-pass filtering unit (323), a square wave conversion unit (324), and a hysteresis comparison unit (325) which are connected in sequence; The following steps are involved: 1) Remove the connection line between the generator output line and the closed busbar, remove the connection line of the stator three-phase winding at the neutral point, and short-circuit and ground the secondary side of various CTs, generator output lines, closed busbar side and various temperature measuring elements of the measuring generator; 2) The computer (34) issues a test start instruction, the phase reference module (32) processes the voltage signal on the power supply side, the synchronous transformer unit (321) transforms the power supply voltage and keeps the output signal in the same phase and frequency as the power supply voltage, wherein the high-order harmonics and low-order harmonics in the signal are filtered out by the low-pass filter unit (322) and the high-pass filter unit (323), the voltage signal is converted into a square wave signal by the square wave conversion unit (324), and finally the burrs in the square wave signal are removed by the hysteresis comparison unit (325), and then the square wave signal is input into the logic loop controller (33), the logic loop controller (33) performs logic processing on the square wave signal and issues a closing instruction for the high-voltage circuit breaker (31), wherein the logic loop controller (33) receives the test start instruction, and every 40 μs Timing once, reading data once, reading voltage signal and judging whether its phase is If not, continue to read data, if yes, delay Then, a closing instruction of the high-voltage circuit breaker (31) is outputted, and the high-voltage circuit breaker (31) performs a closing action after receiving the closing instruction of the high-voltage circuit breaker (31), wherein: t 1 is the 1 / 4 cycle duration under the actual voltage frequency, t 2 is the constant lead time.

2. The generator core loss test method for reducing test impulse current according to claim 1, characterized in that: It also includes an infrared monitoring unit (9) for real-time monitoring of the temperature of the iron core unit (1) to be tested and the ambient temperature.

3. The generator core loss test method for reducing test impulse current according to claim 1, characterized in that: The excitation coils in the excitation coil unit (2) are evenly arranged on the iron core unit (1) to be tested.

4. The generator core loss test method for reducing test impulse current according to claim 1, characterized in that: The measuring coil unit (2) is arranged at the center of the generator hall.

5. The generator core loss test method for reducing test impulse current according to claim 1, characterized in that: The excitation coil unit (2) is connected to the multifunctional power measurement unit (8) via a current measurement clamp (10).

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