A method for judging slow-fusing of excitation PT

Abstract

The present invention relates to the field of excitation motor monitoring, specifically a method for determining an excitation PT slow-fuse, comprising: collecting three-phase voltages of two groups of voltage transformers PT1 and PT2 input to an excitation regulator, calibrating the collected three-phase voltages to ensure the consistency of the three-phase voltages of PT1 and PT2 under normal circumstances, and then calculating the slow-fuse determination characteristic values ​​K1 and K2 of the three-phase voltages of PT1 and PT2 respectively according to the effective values ​​and phase quantities of the three-phase voltages of PT1 and PT2, and determining that PT1 is slow-fuse when K1 exceeds a threshold value and K2 and the current of the generator meet certain conditions, and determining that PT2 is slow-fuse when K2 exceeds a threshold value and K1 and the current of the generator meet certain conditions. The technical solution has a relatively high sensitivity for PT slow-fuse determination, and can be used for an excitation regulator to perform PT self-test and channel switching, and can also be used for an excitation PT slow-fuse online monitoring device.

Description

Technical Field

[0001] The invention relates to the field of excitation motor monitoring, and in particular to a method for determining an excitation PT slow-fuse. Background Art

[0002] The excitation PT is an important part of the excitation power supply. It usually converts the AC voltage in the system into the required DC voltage to supply the excitation system of the generator, and is used to provide a stable DC excitation current to stimulate the generator to generate an electromagnetic field. This ensures that the generator always maintains a stable output voltage and frequency during operation.

[0003] PT slow fusing (abbreviated as "slow fusing") is a common fault in power systems and power grids. When PT slow fusing occurs, the PT cannot transmit the primary voltage normally, and the secondary voltage of the faulty phase slowly decreases, while the excitation system mistakenly judges that the machine-end voltage has dropped. In order to maintain the constant machine-end voltage, the AVR continues to increase magnetization, which may lead to serious consequences such as false operation of relay protection equipment, false alarm or misadjustment of the excitation regulator.

[0004] In the early stage of slow melting of the excitation PT, the voltage of the fault phase does not drop much, perhaps only about 1V to 3V, which does not reach the PT line break alarm threshold of the excitation regulator. Therefore, the excitation equipment cannot sensitively respond to the PT slow melting fault. When the PT fuse of the generator AVR operation channel slowly melts, the excitation system is difficult to identify the PT slow melting condition, which will cause the secondary voltage at the generator end to slowly drop, and the voltage sampling channel cannot be switched in time, so that the excitation regulator will mistake it for a fault state, and will continue to increase the excitation current or even reach a strong excitation state, which may cause the generator set to overexcite, endanger the safety of the unit, and may cause protection actions such as generator overexcitation and excitation overcurrent, resulting in serious consequences such as tripping. Summary of the invention

[0005] The object of the present invention is to provide a method for identifying a slow-fusing excitation PT to solve the problems raised in the above-mentioned background technology.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions: a method for determining a slow-fuse excitation PT, comprising the following steps:

[0007] Step S100. Collect the three-phase voltages in the generator excitation regulators PT1 and PT2 and the three-phase current in the generator, and calculate the maximum value of the three-phase current and the negative sequence current of the generator;

[0008] Step S200. Calibrate the three-phase voltage collected from the engine excitation regulators PT1 and PT2 according to the voltage calibration method;

[0009] Step S300. Calculate the slow-fuse characteristic values ​​K1 and K2 corresponding to PT1 and PT2 respectively according to the calibrated three-phase voltages of PT1 and PT2;

[0010] Step S400. When the slow-fusing characteristic values ​​K1 and K2 and the generator current meet the triggering conditions, it is determined that PT1 or PT2 has a slow-fusing;

[0011] Step S500: When a slow blow occurs in PT1 or PT2, the PT switching program is started and an alarm signal is issued.

[0012] Furthermore, in step S100, after collecting the three-phase voltages and three-phase currents of generators PT1 and PT2, the maximum value I of the three-phase current is calculated according to the formula I=P / (U·√3), where P is the rated capacity of the generator, U is the rated voltage of the generator, and the negative sequence current is obtained by simulation calculation using power system simulation software.

[0013] Generator excitation PT1 and PT2 refer to two key components in the excitation system, which are used to control and monitor the excitation state of the generator. Excitation PT1 is a transformer, usually installed in the generator excitation system, used to monitor the output voltage of the generator and step down the output voltage of the generator to a low voltage signal suitable for measurement. Excitation PT2 is also a transformer, usually used to provide an excitation voltage stabilization system or automatic adjustment device with a reference voltage signal for comparison and control.

[0014] Further, in step S200, the voltage calibration method for calibrating the three-phase voltages of PT1 and PT2 is as follows:

[0015]

[0016]

[0017] Where: They are the three-phase voltage phasors after PT1 calibration, They are the three-phase voltage phasors before PT1 calibration, They are the three-phase voltage phasors after PT2 calibration, They are the three-phase voltage phasors before PT2 calibration, They are the PT2 three-phase voltage calibration coefficient phasors respectively. The calibration coefficient phasors satisfy the requirement that when PT1 and PT2 are fault-free, the corresponding phase voltage phasors of PT1 and PT2 after calibration are the same, that is, (φ is A, B, C).

[0018] By calibrating the generator PT1 and PT2, the calibrated three-phase voltage value is made more accurate, the difference between the two groups of PTs used for comparison is reduced, and it is beneficial to improve the detection sensitivity.

[0019] Furthermore, step S300 includes:

[0020] Step S301. The method for calculating the slow-melting characteristic value K1 corresponding to PT1 is as follows:

[0021] The phase corresponding to the minimum value of the three-phase voltage effective value after PT1 calibration is the φ phase (φ can be A, B, C), and its voltage phasor is The previous phase voltage phasor is The voltage phasor of the next phase is PT1 slow-blow characteristic value K 1 The calculation formula is as follows:

[0022]

[0023] Where: max is the maximum value function, e is the base of natural logarithm, j is the symbol of imaginary number;

[0024] Step S302. The method for calculating the slow-melting characteristic value K2 corresponding to PT1 is as follows:

[0025] The phase corresponding to the minimum value of the three-phase voltage effective value after PT2 calibration is the φ phase (φ can be A, B, C), and its voltage phasor is The voltage phasor of the previous phase is The next phase voltage phasor is PT2 slow-blow characteristic value K 2 The calculation formula is as follows:

[0026]

[0027] Where:

[0028] Since the three-phase voltages satisfy a 120-degree relationship, if the phase difference modulus between any non-fault phase after rotating 120 degrees and the fault phase is greater than a fixed value, it is considered abnormal. By calculating the characteristic values ​​K1 and K2 of PT1 and PT2 respectively, the phase difference between the slow-melting fault phase and the other two normal phases rotated to the fault phase is directly compared, which can better highlight the difference and improve the sensitivity of detecting PT slow-melting faults.

[0029] Further, in step S400, when the slow-fusing characteristic values ​​K1 and K2 and the generator current meet the triggering conditions, it is determined that PT1 or PT2 has a slow-fusing, and the triggering conditions are as follows:

[0030] The conditions for determining that PT1 is slow-fusing are:

[0031]

[0032] The conditions for determining whether PT2 is slow-fusing are:

[0033]

[0034] Where: K set is the slow-blow discrimination threshold, ranging from 1% to 2.5%, I max is the maximum value of the three-phase current of the generator, I e is the rated current of the generator, which is calculated based on the generator capacity and rated voltage. 2 is the generator negative sequence current, I 2set is the negative sequence current setting threshold, take 0.03×I e ~0.2×I e ;

[0035] As a preference, K set Take 1.5%, I 2set Take 0.03×I e .

[0036] Furthermore, in step S500, when it is determined that there is a slow fuse in PT1 or PT2, the PT switching program is started to switch the working PT, and an alarm is issued after a fixed time delay.

[0037] This technical solution has a relatively high sensitivity for PT slow-fuse discrimination, and can be used for PT self-test and channel switching in an excitation regulator, and can also be used for an excitation PT slow-fuse online monitoring device.

[0038] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0039] 1. The present invention can calibrate the three-phase voltages of two groups of generator PTs. After calibration, the difference between the two groups of PTs used for comparison is reduced, which is beneficial to improving the detection sensitivity. Compared with the prior art, it avoids the problem that the difference in collected data in the uncalibrated state leads to an increase in the comparison threshold and a reduction in the sensitivity of the criterion.

[0040] 2. The present invention can directly compare the phase difference between the slow-melting fault phase and the other two normal phases rotating to the fault phase through the characteristic value of the generator excitation PT, which can better highlight the difference, better highlight the difference between the fault phase and the non-fault phase voltage, improve the sensitivity of detecting PT slow-melting faults, solve the problem that the previous excitation system was difficult to detect PT slow-melting, and improve the reliability of detection.

[0041] 3. The present invention has established an evaluation system for the slow-fusing characteristics, and when the PT slow-fusing state is found, timely protective operation is performed and an alarm notification is issued, which can prevent the excitation PT from fusing and overloading to damage the excitation power supply and other related equipment, protect the excitation system, and ensure the stability and reliability of its operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0043] Figure 1 It is a flow chart of a method for determining a slow-fuse excitation PT according to the present invention. DETAILED DESCRIPTION

[0044] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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.

[0045] See also Figure 1 The present invention provides a technical solution: a method for determining a slow-fuse excitation PT, comprising the following steps:

[0046] Step S100. Collect the three-phase voltages in the generator excitation regulators PT1 and PT2 and the three-phase current of the generator, and calculate the maximum value of the three-phase current and the negative sequence current of the generator;

[0047] In step S100, after collecting the three-phase voltages and three-phase currents of generators PT1 and PT2, the maximum value I of the three-phase current is calculated according to the formula I=P / (U·√3), where P is the rated capacity of the generator, U is the rated voltage of the generator, and the negative sequence current is obtained by simulation calculation using power system simulation software.

[0048] Step S200. Calibrate the three-phase voltage collected from the engine excitation regulators PT1 and PT2 according to the voltage calibration method;

[0049] In step S200, the specific method for calibrating the three-phase voltages of PT1 and PT2 is as follows:

[0050]

[0051]

[0052] Where: They are the three-phase voltage phasors after PT1 calibration, They are the three-phase voltage phasors before PT1 calibration, They are the three-phase voltage phasors after PT2 calibration, They are the three-phase voltage phasors before PT2 calibration, They are the PT2 three-phase voltage calibration coefficient phasors respectively. The calibration coefficient phasors satisfy the requirement that when PT1 and PT2 are fault-free, the corresponding phase voltage phasors of PT1 and PT2 after calibration are the same, that is, (φ is A, B, C).

[0053] By calibrating the generator PT1 and PT2, the calibrated three-phase voltage value is made more accurate, the difference between the two groups of PTs used for comparison is reduced, and it is beneficial to improve the detection sensitivity.

[0054] Step S300. Calculate the slow-fuse characteristic values ​​K1 and K2 corresponding to PT1 and PT2 respectively according to the calibrated three-phase voltages of PT1 and PT2;

[0055] Step S300 includes:

[0056] Step S301. The method for calculating the slow-melting characteristic value K1 corresponding to PT1 is as follows:

[0057] The phase corresponding to the minimum value of the three-phase voltage effective value after PT1 calibration is the φ phase (φ can be A, B, C), and its voltage phasor is The previous phase voltage phasor is The voltage phasor of the next phase is PT1 slow-blow characteristic value K 1 The calculation formula is as follows:

[0058]

[0059] Where: max is the maximum value function, e is the base of natural logarithm, j is the symbol of imaginary number;

[0060] Step S302. The method for calculating the slow-melting characteristic value K2 corresponding to PT1 is as follows:

[0061] The phase corresponding to the minimum value of the three-phase voltage effective value after PT2 calibration is the φ phase (φ can be A, B, C), and its voltage phasor is The voltage phasor of the previous phase is The next phase voltage phasor is PT2 slow-blow characteristic value K 2 The calculation formula is as follows:

[0062]

[0063] Where:

[0064] Since the three-phase voltages satisfy a 120-degree relationship, if the phase difference modulus between any non-fault phase after rotating 120 degrees and the fault phase is greater than a fixed value, it is considered abnormal. By calculating the characteristic values ​​K1 and K2 of PT1 and PT2 respectively, the phase difference between the slow-melting fault phase and the other two normal phases rotated to the fault phase is directly compared, which can better highlight the difference and improve the sensitivity of detecting PT slow-melting faults.

[0065] Step S400. When the slow-fusing characteristic values ​​K1 and K2 and the generator current meet the triggering conditions, it is determined that PT1 or PT2 has a slow-fusing;

[0066] In step S400, when the slow-fusing characteristic values ​​K1 and K2 and the generator current meet the following conditions, it is determined that PT1 or PT2 has a slow-fusing condition:

[0067] The conditions for determining that PT1 is slow-fusing are:

[0068]

[0069] The conditions for determining whether PT2 is slow-fusing are:

[0070]

[0071] Where: K set is the slow-blow discrimination threshold, ranging from 1% to 2.5%, I max is the maximum value of the three-phase current of the generator, I e is the rated current of the generator, which is calculated based on the generator capacity and rated voltage. 2 is the generator negative sequence current, I 2set is the negative sequence current setting threshold, take 0.03×I e ~0.2×I e ;

[0072] As a preference, K set Take 1.5%, I 2set Take 0.03×I e .

[0073] Step S500: When a slow blow occurs in PT1 or PT2, the PT switching program is started and an alarm signal is issued.

[0074] In step S500, when it is determined that there is a slow fuse in PT1 or PT2, the PT switching program is started to switch the working PT, or an alarm is issued after a fixed time delay.

[0075] Example: Collect the three-phase voltage of generator excitation PT1 and PT2, the three-phase current of the generator, and record the three-phase voltage of PT1 as The three-phase voltage of PT2 is recorded as The maximum phase current calculated based on the three-phase current of the generator is recorded as I max , the negative sequence current is recorded as I 2 .

[0076] Calibrate the three-phase voltages of PT1 and PT2 to ensure the consistency of the voltage output of the two groups of PTs under normal conditions. The calibration method is shown in the following formula. The PT1 voltage remains unchanged before and after calibration, and the PT2 voltage is calibrated by the coefficient. The three-phase voltage of PT1 after calibration is recorded as The three-phase voltage after PT2 calibration is recorded as

[0077]

[0078] The three-phase voltage after PT1 calibration is recorded as The three-phase voltage after PT2 calibration is recorded as

[0079] The calibration coefficient of PT2 should satisfy the requirement that when PT1 and PT2 are fault-free, the corresponding phase voltages of PT1 and PT2 after calibration are the same. The calculation method of PT2 calibration coefficient is as follows:

[0080]

[0081] in: They are the three-phase voltage phase quantities of PT1 and PT2 under normal fault-free conditions.

[0082] According to the calibrated PT1 and PT2 three-phase voltages, the slow-fuse characteristic values ​​K corresponding to PT1 and PT2 are calculated respectively. 1 and K 2 , and judge whether slow melting occurs according to the slow melting characteristic value and the current value. In this embodiment, the voltage phase sequence follows the order of ABCA, such as the previous phase of phase B is phase A, and the next phase is phase C; the previous phase of phase A is phase C, and the next phase is phase B;

[0083] When the slow-fusing characteristic values ​​K1 and K2 and the generator current meet the triggering conditions, it is determined that PT1 or PT2 has a slow-fusing phenomenon and can be delayed to alarm or start PT switching.

[0084] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0085] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for determining a slow-fuse excitation PT, characterized in that: The method comprises the following steps: Step S100. Collect the three-phase voltages in the excitation regulators PT1 and PT2 and the three-phase currents in the generator, and calculate the maximum three-phase current and negative sequence current of the generator; Step S200. Calibrate the three-phase voltages in the excitation regulators PT1 and PT2 according to the voltage calibration method; Step S300. Calculate the slow-fuse characteristic values ​​K1 and K2 corresponding to PT1 and PT2 respectively according to the calibrated three-phase voltages of PT1 and PT2; Step S400. When the slow-fusing characteristic values ​​K1 and K2 and the generator current meet the triggering conditions, it is determined that PT1 or PT2 has a slow-fusing condition; Step S500. When a slow fuse occurs in PT1 or PT2, the PT switching program is started and an alarm signal is issued; The PT represents a voltage transformer, and PT1 and PT2 represent two excitation regulators of the voltage transformer respectively; Step S301. The method for calculating the slow-melting characteristic value K1 corresponding to PT1 is as follows: The phase corresponding to the minimum value of the three-phase voltage effective value after PT1 calibration is φ phase, φ is A or B or C, and its voltage phasor is The previous phase voltage phasor is The voltage phasor of the next phase is The calculation formula of PT1 slow-blow characteristic value K1 is as follows: Where: max is the maximum value function, e is the base of natural logarithm, j is the symbol of imaginary number; Step S302. The method for calculating the slow-melting characteristic value K2 corresponding to PT1 is as follows: The phase corresponding to the minimum value of the three-phase voltage effective value after PT2 calibration is φ phase, φ is A or B or C, and its voltage phasor is The voltage phasor of the previous phase is The next phase voltage phasor is The calculation formula of PT2 slow-blow characteristic value K2 is as follows: Where:

2. A method for determining a slow-fuse excitation PT according to claim 1, characterized in that: In step S100, after collecting the three-phase voltage and three-phase current of the generator PT1 and PT2, according to the formula The maximum three-phase current I is calculated, where P is the rated capacity of the generator, U is the rated voltage of the generator, and the negative sequence current is obtained by simulation calculation using power system simulation software.

3. A method for determining a slow-fuse excitation PT according to claim 2, characterized in that: In step S200, the voltage calibration method for calibrating the three-phase voltages of PT1 and PT2 is as follows: Where: They are the three-phase voltage phasors after PT1 calibration, They are the three-phase voltage phasors before PT1 calibration, They are the three-phase voltage phasors after PT2 calibration, They are the three-phase voltage phasors before PT2 calibration, They are the PT2 three-phase voltage calibration coefficient phasors respectively. The calibration coefficient phasors satisfy the requirement that when PT1 and PT2 are fault-free, the corresponding phase voltage phasors of PT1 and PT2 after calibration are the same, that is, φ is A or B or C.

4. A method for determining a slow-fuse excitation PT according to claim 3, characterized in that: In step S400, when the slow-fusing characteristic values ​​K1 and K2 and the generator current meet the triggering conditions, it is determined that PT1 or PT2 has a slow-fusing condition, and the triggering conditions are as follows: The conditions for determining that PT1 is slow-fusing are: The conditions for determining whether PT2 is slow to blow are: Where: K set is the slow-blow discrimination threshold, ranging from 1% to 2.5%, I max is the maximum value of the three-phase current of the generator, I e is the rated current of the generator, which is calculated based on the generator capacity and rated voltage. I2 is the negative sequence current of the generator. 2set is the negative sequence current setting threshold, take 0.03×I e ~0.2×I e .

5. A method for determining a slow-fuse excitation PT according to claim 4, characterized in that: K set Take 1.5%, I 2set Take 0.03×I e .

6. A method for determining a slow-fuse excitation PT according to claim 4, characterized in that: In step S500, when it is determined that there is a slow fuse in PT1 or PT2, the PT switching program is started to switch the working PT, and an alarm is issued after a fixed time delay.

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