An online monitoring method for grounding transformer operating status based on equivalent resistance change rate

Abstract

The present invention discloses an online monitoring method for the operation state of a grounding transformer based on the equivalent resistance change rate, and belongs to the technical field of online monitoring of power distribution equipment. It includes: step a, collecting the voltage and current on the first and second sides of the grounding transformer; step b, calculating the equivalent resistance of each phase; step c, judging whether the equivalent resistance of each phase is less than 0, if so, executing d otherwise executing e; step d, the system is single-phase grounded; step e, solving the equivalent resistance change rate of each phase; step f, judging whether the grounding transformer is serious, if so, executing g otherwise executing p; step g, issuing a tripping command, and executing steps h, i, j, k, l, m; steps h, i, j, k, l, m, judging the fault phase; step n, judging whether the grounding transformer is abnormal, if so, executing o otherwise executing p; step o, issuing an alarm signal; step p, the grounding transformer operates normally. The present invention realizes the online detection of its operation state through the equivalent resistance change rate of each phase.

Description

Technical Field

[0001] The present invention belongs to the technical field of online monitoring of power distribution equipment, and more specifically relates to an online monitoring method for the operating state of a grounding transformer based on an equivalent resistance change rate. Background Art

[0002] The ZNyn11 grounding transformer has the advantages of not being easy to saturate when DC current flows through it and having a small zero-sequence impedance. It is widely used in different occasions in the power system. First, it can be used as a connection between AC power supply and DC power supply and is used in AC and DC systems; second, it can induce a three-phase voltage on the low-voltage side through a two-phase input on the high-voltage side, ensuring the stability of the output voltage when a single-phase grounding fault occurs in the system; third, it can provide a neutral point for a neutral point ungrounded system, for arc suppression coils or resistors to connect, to compensate for the capacitive current when the system is single-phase grounded, and to suppress the generation of overvoltage; in addition, its low-voltage winding can also be used as station power to provide power for the internal equipment of the substation. It can be seen that ensuring the safe and stable operation of the grounding transformer is of great significance to the power system.

[0003] Since most grounding transformers are installed inside switch cabinets, their winding structures and operating conditions are complex. Once a short-circuit fault occurs, if it cannot be removed in time, the large short-circuit current will cause heat and then cause the grounding transformer body to burn or explode, causing damage to the switch cabinet and other electrical equipment. This is also the case with actual operational faults. However, the current grounding transformer protection method mainly draws on ordinary distribution transformers, and its protection measures have low sensitivity. When the protection is activated, the fault has already expanded, and it cannot play an effective protective role in the early stage of the fault. At the same time, there is no operating status detection method and device specifically for grounding transformers in the prior art.

[0004] Therefore, it is of great significance to propose an online monitoring method for the operating status of the grounding transformer based on the equivalent resistance change rate, which can effectively ensure the safe and stable operation of the grounding transformer and prevent the expansion of accidents. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the existing defects and propose an online monitoring method for the operating status of a grounding transformer based on the equivalent resistance change rate. The method can judge the operating status of the grounding transformer in real time, send out an audible and visual alarm signal when the operation is abnormal, and trip in time when the situation is serious to prevent the accident from expanding and affecting the safety of other electrical equipment.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] An online monitoring method for the operating state of a grounding transformer based on an equivalent resistance change rate comprises the following steps:

[0008] Step a, obtaining the voltage and current values ​​of the primary and secondary sides of the grounding transformer;

[0009] Step b, calculating the equivalent resistance value of each phase of the grounding transformer;

[0010] Step c, determine whether the equivalent resistance of each phase is less than 0, if so, execute d, otherwise execute e;

[0011] Step d, system single-phase grounding fault;

[0012] Step e, calculating the rate of change of equivalent resistance of each phase;

[0013] Step f, determine whether the grounding transformer is in a serious state, if so, execute g, otherwise execute p;

[0014] Step g, issue a trip command and execute step h;

[0015] Step h, determine whether the equivalent resistance change rate of phase A is ≥17%, if so, execute step i, otherwise execute step j;

[0016] Step i, judging that it is a phase A fault;

[0017] Step j, determine whether the equivalent resistance change rate of phase B is ≥ 17%, if so, execute step k, otherwise execute step l;

[0018] Step k, judging that it is a phase B fault;

[0019] Step 1, determine whether the equivalent resistance change rate of phase C is ≥ 17%, if so, execute step m;

[0020] Step m, judging that it is a phase C fault;

[0021] Step n, determine whether the grounding transformer is in an abnormal state, if so, execute o, otherwise execute p;

[0022] Step o, sending out an alarm signal;

[0023] Step p, the grounding transformer continues to operate.

[0024] Furthermore, the equivalent resistance value of each phase is calculated in real time and compared with the equivalent resistance value during normal operation to calculate the equivalent resistance change rate; the equivalent resistance value during normal operation is the sum of the resistance value of the high-voltage winding converted to the operating temperature and the resistance value of the low-voltage winding converted to the high-voltage side.

[0025] Furthermore, the threshold of its operating state is determined by the maximum allowable temperature rise of the epoxy resin grounding transformer and the heat resistance grade of the insulating material; the heat resistance grade of the epoxy resin insulating material is B. When the operating temperature is higher than 130°C, the insulating material undergoes thermal oxidation decomposition, and the grounding transformer cannot continue to work. The equivalent resistance change rate at this temperature is 17%, which is a serious state; the maximum operating temperature rise of the epoxy resin grounding transformer is 80K. When the temperature rise is higher than 80K, the insulation will accelerate aging. The equivalent resistance change rate corresponding to this temperature is 8%, which is an abnormal state.

[0026] Furthermore, when the grounding transformer is judged to be in a serious state, a tripping command is first issued and then an analysis is performed to determine which phase has an equivalent resistance change rate ≥ 17%, thereby determining the faulty phase, saving a lot of time for fault finding and equipment maintenance.

[0027] Furthermore, it includes a signal acquisition unit, a logic calculation unit and a communication unit. The signal acquisition unit collects the voltage on the high-voltage side of the grounding transformer through the voltage transformer at the secondary bus of the main transformer, without installing a new PT. The three-phase voltage on the secondary side is collected through the PT on the secondary side of the grounding transformer, and the three-phase current is collected through the CT on the primary and secondary sides of the grounding transformer. The voltage and current signals collected by the signal acquisition unit are transmitted to the logic calculation unit, and the communication unit issues instructions after calculation and judgment by the logic calculation unit.

[0028] Furthermore, it also includes an audible and visual alarm unit, which receives instructions from the communication unit and generates audible and visual alarm signals to achieve real-time online monitoring of the operating status of the grounding transformer.

[0029] The beneficial effects of the present invention are:

[0030] The online monitoring method for the operating status of the epoxy resin grounding transformer based on the equivalent resistance change rate of the present invention has high sensitivity, is not affected by the unbalanced operation of the three-phase system, can accurately judge the operating condition of the grounding transformer in real time, and can distinguish the grounding phase, laying a foundation for studying the operating status detection technology of the grounding transformer under different operating conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present utility model. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0032] Figure 1 is a flow chart of the method of the present invention;

[0033] Figure 2 It is a structural block diagram of the present invention.

[0034] Figure 3 This is a diagram of the connection method of the grounding transformer in the power system. DETAILED DESCRIPTION

[0035] The following will be combined with 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.

[0036] The embodiment of the present invention discloses an online monitoring method for the operating state of a grounding transformer based on an equivalent resistance change rate, comprising the following steps:

[0037] Step a, obtaining the voltage and current values ​​of the primary and secondary sides of the grounding transformer;

[0038] Step b, calculating the equivalent resistance value of each phase of the grounding transformer;

[0039] Step c, determine whether the equivalent resistance of each phase is less than 0, if so, execute d, otherwise execute e;

[0040] Step d, system single-phase grounding fault;

[0041] Step e, calculating the rate of change of equivalent resistance of each phase;

[0042] Step f, determine whether the grounding transformer is in a serious state, if so, execute g, otherwise execute p;

[0043] Step g, issue a trip command and execute step h;

[0044] Step h, determine whether the equivalent resistance change rate of phase A is ≥17%, if so, execute step i, otherwise execute step j;

[0045] Step i, judging that it is a phase A fault;

[0046] Step j, determine whether the equivalent resistance change rate of phase B is ≥ 17%, if so, execute step k, otherwise execute step l;

[0047] Step k, judging that it is a phase B fault;

[0048] Step 1, determine whether the equivalent resistance change rate of phase C is ≥ 17%, if so, execute step m;

[0049] Step m, judging that it is a phase C fault;

[0050] Step n, determine whether the grounding transformer is in an abnormal state, if so, execute o, otherwise execute p;

[0051] Step o, sending out an alarm signal;

[0052] Step p, the grounding transformer continues to operate.

[0053] In this embodiment, the equivalent resistance value of each phase is calculated in real time and compared with the equivalent resistance value during normal operation to calculate the equivalent resistance change rate; the equivalent resistance value during normal operation is the sum of the resistance value of the high-voltage winding calculated to the operating temperature and the resistance value of the low-voltage winding calculated to the high-voltage side.

[0054] In this embodiment, the threshold of its operating state is determined by the maximum allowable temperature rise of the epoxy resin grounding transformer and the heat resistance grade of the insulating material; the heat resistance grade of the epoxy resin insulating material is B. When the operating temperature is higher than 130°C, the insulating material undergoes thermal oxidation decomposition, and the grounding transformer cannot continue to work. The equivalent resistance change rate at this temperature is 17%, which is a serious state; the maximum operating temperature rise of the epoxy resin grounding transformer is 80K. When the temperature rise is higher than 80K, the insulation will accelerate aging. The equivalent resistance change rate corresponding to this temperature is 8%, which is an abnormal state.

[0055] In this embodiment, when the grounding transformer is determined to be in a serious state, a tripping command is first issued and then an analysis is performed to determine which phase has an equivalent resistance change rate ≥ 17% to determine the fault phase, thereby saving a lot of time for fault finding and equipment maintenance.

[0056] The present invention includes a signal acquisition unit, a logic calculation unit and a communication unit. The signal acquisition unit collects the voltage on the high-voltage side of the grounding transformer through the voltage transformer at the secondary bus of the main transformer, and there is no need to install a new PT. The three-phase voltage on the secondary side is collected through the PT on the secondary side of the grounding transformer, and the three-phase current is collected through the CT on the primary and secondary sides of the grounding transformer. The voltage and current signals collected by the signal acquisition unit are transmitted to the logic calculation unit, and the communication unit issues an instruction after calculation and judgment by the logic calculation unit. The present invention also includes an audible and visual alarm unit, which receives the instruction issued by the communication unit, generates an audible and visual alarm signal, and realizes real-time online monitoring of the operating status of the grounding transformer.

[0057] The online monitoring method for the operating status of the epoxy resin grounding transformer based on the equivalent resistance change rate of the present invention has high sensitivity, is not affected by the unbalanced operation of the three-phase system, can accurately judge the operating condition of the grounding transformer in real time, and can distinguish the grounding phase, laying a foundation for studying the operating status detection technology of the grounding transformer under different operating conditions.

[0058] Example

[0059] like Figure 1 and Figure 2 As shown, the online monitoring method of the operating state of the epoxy resin grounding transformer based on the equivalent resistance change rate includes the following steps:

[0060] Step 1001, a signal acquisition unit acquires voltage and current at the primary and secondary sides of a grounding transformer;

[0061] like Figure 3 As shown, the grounding transformer is connected to the busbar at the output end of the low-voltage triangle connection of the main transformer. Its secondary side voltage can be measured by the voltage transformer TV1 at the busbar at the output end of the low-voltage triangle connection of the main transformer. There is no need to install a new voltage transformer. The secondary side voltage of the grounding transformer is measured by the voltage transformer TV2. The primary and secondary side currents can be measured by current transformers TA1 and TA2 respectively. The signal acquisition unit transmits the data to the logic calculation through the output end.

[0062] Step 1002, the logic calculation unit calculates the equivalent resistance of each phase of the grounding transformer;

[0063] The primary side A phase voltage u is grounded A (t), current i A (t) as an example, the effective value of voltage is:

[0064]

[0065] The effective value of current is:

[0066]

[0067] The power factor angle of each phase on the high and low voltage sides is calculated using the harmonic analysis method. The calculation process is as follows:

[0068] Voltage and current are decomposed by Fourier

[0069]

[0070] Where: f is the frequency; a u0 、a i0 are the DC components of phase A voltage and current respectively; A uk , A ik are the kth harmonic amplitudes of phase A voltage and current respectively; They are the phases of the kth harmonic of phase A voltage and current respectively.

[0071] Take the fundamental component of voltage and current, that is, k = 1, the expression is

[0072]

[0073] The voltage and current phase angles are

[0074]

[0075] The equivalent resistance is expressed as

[0076]

[0077] Where: U G ,I G is the effective value of the voltage and current on the primary side, U d ,I d is the effective value of the secondary side voltage and current, is the voltage and current phase angle on the primary side, is the voltage and current phase angle on the secondary side, and P0 is the no-load loss.

[0078] Step 1003, determine whether the equivalent resistance of each phase is less than 0;

[0079] The logic calculation unit determines whether the equivalent resistance of each phase of the grounding transformer is less than 0. If the equivalent resistance is less than 0, execute step 1004. If the equivalent resistance of each phase is not less than 0, execute step 1005.

[0080] Step 1004, system single-phase grounding fault;

[0081] The logic calculation unit determines that a single-phase grounding fault occurs in the system;

[0082] Step 1005, calculating the change rate of the equivalent resistance of each phase;

[0083] The logic calculation unit calculates the change rate of the equivalent resistance of each phase, and the expression is,

[0084]

[0085]

[0086] In the formula, θ0 is 75℃, θ is the temperature to be converted, R s It is the equivalent resistance at normal operating temperature, generally the sum of the resistance value of the high voltage winding at 75°C and the resistance value of the low voltage winding converted to the high voltage side. h is the equivalent resistance value at the actual operating temperature.

[0087] Step 1006, determining whether the grounding transformer is in a serious state;

[0088] The heat resistance grade of epoxy resin insulation material is B (130℃). When the operating temperature is higher than 130℃, the insulation material will undergo thermal oxidation decomposition and the grounding transformer will not be able to continue to work. Using the above formula, the equivalent resistance change rate at this temperature is 17%, which is a serious state.

[0089] The logic calculation unit determines whether the grounding transformer is in a serious state. If the equivalent resistance change rate of each phase is ≥17%, it is in a serious state, and step 1007 is executed; if the equivalent resistance change rate is <17%, step 1014 is executed;

[0090] Step 1007, issuing a trip command;

[0091] The logic calculation unit determines that a tripping instruction is issued, and executes step 1008;

[0092] Step 1008, determining whether the equivalent resistance change rate of phase A is ≥ 17%;

[0093] The logic calculation unit determines whether the equivalent resistance change rate of phase A is ≥17%, and if so, executes step 1009; otherwise, executes step 1010.

[0094] Step 1009, phase A fails;

[0095] The logic calculation unit determines that phase A of the grounding transformer is faulty.

[0096] Step 1010, determining whether the equivalent resistance change rate of phase B is ≥ 17%;

[0097] The logic calculation unit determines whether the equivalent resistance change rate of phase B is ≥17%, and if so, executes step 1011, otherwise executes step 1012.

[0098] Step 1011, phase B fails;

[0099] The logic calculation unit determines that phase B of the grounding transformer fails.

[0100] Step 1012, determining whether the C-phase equivalent resistance change rate is ≥ 17%;

[0101] The logic calculation unit determines whether the C-phase equivalent resistance change rate is ≥17%, and if so, executes step 1013.

[0102] Step 1013, phase C fails;

[0103] The logic calculation unit determines that phase C of the grounding transformer fails.

[0104] Step 1014, determining whether the grounding transformer is in an abnormal state;

[0105] The maximum operating temperature rise of the epoxy resin grounding transformer is 80K. When the temperature rise is higher than 80K, the insulation will age faster. Using the above formula to calculate, the equivalent resistance change rate corresponding to this temperature is 8%, which is an abnormal state.

[0106] The logic calculation unit determines whether the grounding transformer is in an abnormal state. If the change rate of the equivalent resistance of each phase is ≥8%, it is in an abnormal state, and step 1015 is executed; if the change rate of the equivalent resistance of each phase is <8%, step 1016 is executed;

[0107] Step 1015, sending an alarm signal;

[0108] The logic calculation unit determines and sends out an alarm signal.

[0109] Step 1016, the grounding transformer continues to operate.

[0110] The logic calculation unit determines that the grounding transformer can continue to operate.

[0111] The judgment result of the logic calculation unit can be transmitted through the communication unit to the trip command or sound and light alarm signal and output the fault phase, realizing real-time online monitoring of the operating status of the grounding transformer and greatly improving the safe and stable operation of the internal equipment of the substation.

[0112] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0113] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An online monitoring method for the operating status of a grounding transformer based on the equivalent resistance change rate, characterized in that: The following steps are involved: Step a, obtaining the voltage and current values ​​of the primary and secondary sides of the grounding transformer; Step b, calculating the equivalent resistance value of each phase of the grounding transformer; Step c, determine whether the equivalent resistance of each phase is less than 0, if so, execute d, otherwise execute e; Step d, system single-phase grounding fault; Step e, calculating the rate of change of equivalent resistance of each phase; Step f, determine whether the grounding transformer is in a serious state, if so, execute g, otherwise execute p; Step g, issue a trip command and execute step h; Step h, determine whether the equivalent resistance change rate of phase A is ≥17%, if so, execute step i, otherwise execute step j; Step i, judging that it is a phase A fault; Step j, determine whether the equivalent resistance change rate of phase B is ≥ 17%, if so, execute step k, otherwise execute step l; Step k, judging that it is a phase B fault; Step 1, determine whether the equivalent resistance change rate of phase C is ≥ 17%, if so, execute step m; Step m, judging that it is a phase C fault; Step n, determine whether the grounding transformer is in an abnormal state, if so, execute o, otherwise execute p; Step o, sending out an alarm signal; Step p, the grounding transformer continues to operate; Calculate the equivalent resistance value of each phase in real time, compare it with the equivalent resistance value during normal operation, and calculate the equivalent resistance change rate; the equivalent resistance value during normal operation is the sum of the resistance value of the high-voltage winding converted to the operating temperature and the resistance value of the low-voltage winding converted to the high-voltage side; In step b, the voltage of phase A on the primary side of the grounding transformer is u A (t), current is i A (t), the effective value of voltage is: The effective value of current is: The power factor angle of each phase on the high and low voltage sides is calculated using the harmonic analysis method. The calculation process is as follows: Voltage and current are decomposed by Fourier: Where: f is the frequency; a u0 、a i0 are the DC components of phase A voltage and current respectively; A uk , A ik are the kth harmonic amplitudes of phase A voltage and current respectively; They are the phases of the kth harmonics of the voltage and current of phase A respectively; Taking the fundamental component of voltage and current, that is, k = 1, the expression is: The voltage and current phase angles are: The equivalent resistance is expressed as: Where: U G ,I G is the effective value of the voltage and current on the primary side, U d ,I d is the effective value of the secondary side voltage and current, is the voltage and current phase angle on the primary side, is the voltage and current phase angle on the secondary side, and P0 is the no-load loss.

2. The method for online monitoring of the operating status of a grounding transformer based on the equivalent resistance change rate according to claim 1 is characterized in that: The threshold of its operating status is determined by the maximum allowable temperature rise of the epoxy resin grounding transformer and the heat resistance grade of the insulating material; the heat resistance grade of the epoxy resin insulating material is B. When the operating temperature is higher than 130°C, the insulating material undergoes thermal oxidation decomposition and the grounding transformer cannot continue to work. The equivalent resistance change rate at this temperature is 17%, which is a serious state; the maximum operating temperature rise of the epoxy resin grounding transformer is 80K. When the temperature rise is higher than 80K, the insulation will accelerate aging. The equivalent resistance change rate corresponding to this temperature is 8%, which is an abnormal state.

3. The method for online monitoring of the operating status of a grounding transformer based on the equivalent resistance change rate according to claim 2 is characterized in that: When the grounding transformer is judged to be in a serious state, a tripping command is first issued and then an analysis is performed to determine which phase has an equivalent resistance change rate ≥ 17% to determine the fault phase, saving a lot of time for fault finding and equipment maintenance.

4. The method for online monitoring of the operating status of a grounding transformer based on equivalent resistance change rate according to claim 1 is characterized in that: It includes a signal acquisition unit, a logic calculation unit and a communication unit. The signal acquisition unit collects the voltage on the high-voltage side of the grounding transformer through the voltage transformer at the secondary bus of the main transformer. There is no need to install a new PT. The three-phase voltage on the secondary side is collected through the PT on the secondary side of the grounding transformer, and the three-phase current is collected through the CT on the primary and secondary sides of the grounding transformer. The voltage and current signals collected by the signal acquisition unit are transmitted to the logic calculation unit, and the communication unit issues instructions after calculation and judgment by the logic calculation unit.

5. The method for online monitoring of the operating status of a grounding transformer based on the equivalent resistance change rate according to claim 4 is characterized in that: It also includes an audible and visual alarm unit, which receives instructions from the communication unit, generates audible and visual alarm signals, and realizes real-time online monitoring of the operating status of the grounding transformer.

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