CN117996691A - Heavy gas protection method and device for on-load tap-changer - Google Patents
Heavy gas protection method and device for on-load tap-changer Download PDFInfo
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Abstract
The invention provides a heavy gas protection method and device for an on-load tap-changer, and belongs to the field of transformer protection. The method comprises the following steps: acquiring a current oil flow velocity instantaneous value of a detection point in a conservator connecting pipe connected with an on-load tap changer to be detected; if the current oil flow speed instantaneous value is greater than a preset flow speed protection action threshold value, a tripping signal is sent to the protection relay, so that the protection relay opens the circuit breaker; if the current oil flow speed instantaneous value is not greater than the preset flow speed protection action threshold value, acquiring a load current value; calculating a flow protection action threshold value based on the load current value; calculating a current accumulated flow value based on the current oil flow instantaneous value; and if the current accumulated flow value is larger than the flow protection action threshold value, sending a tripping signal to the protection relay to enable the protection relay to open the circuit breaker. The invention can improve the reliability of the protection device and avoid misoperation, so as to solve the problems of low reliability and misoperation of mechanical gas protection in the prior art.
Description
Technical Field
The invention relates to the technical field of transformer protection, in particular to a heavy gas protection method and device for an on-load tap-changer.
Background
An on-load tap-changer (OLTC) plays an important role in regulating reactive power and stabilizing grid voltage in a power system, and is a key component of an on-load voltage regulating transformer. According to the difference of arc extinction principle, on-load tap-changer is divided into vacuum arc extinction on-load tap-changer and insulating oil arc extinction on-load tap-changer. Currently, most of large-capacity transformers use on-load tap changers with arc extinction by insulating oil.
In the voltage regulation process, the OLTC needs to be frequently switched, so that the insulation performance of the insulating oil is fast reduced, and therefore, a switching oil chamber of the OLTC is independent and is not communicated with a transformer oil tank. When the OLTC is switched, the switching of the transformer tap is completed in the oil chamber, the transfer of current is realized, and the arc is reliably extinguished in the insulating oil. When the load fluctuates, frequent switching is needed to realize voltage regulation, and the OLTC runs rapidly under high voltage and high current, so that faults such as poor contact, insufficient action and the like are easy to occur. When the fault occurs, continuous heating or continuous electric arc can be generated, so that the insulating oil is vaporized and decomposed, gas expands and rises, and the insulating oil is enabled to surge towards the conservator. Meanwhile, the quality of the insulating oil is reduced, and the normal operation of the on-load tap-changer is directly influenced.
Statistics show that the transformer faults caused by OLTC abnormality account for more than 20% of the total faults, and the main fault type is mechanical faults. For converter transformers of high-voltage direct-current transmission systems, OLTC is more frequent in voltage regulation operation and has higher requirements for operation reliability. Currently, the non-electric quantity protection of transformer OLTC is mainly provided with a pressure release valve, an explosion-proof membrane and gas protection. The pressure release valve and the explosion-proof membrane are pressure sensitive protection, and the setting values of the pressure release valve and the explosion-proof membrane are not uniform at home and abroad. With the increase of the capacity of the transformer, when the transformer is in heavy-load operation, the switching current under the condition of normal switching of the OLTC is larger, the fluctuation range of the pressure in the oil chamber is large, and the pressure release valve is at risk of misoperation. The gas relay can solve the problems caused by pressure sensing type protection, but the current gas relay still continues the basic principle and the mechanical structure of the Buchholz relay for century, and the protection fixed value is an empirical value summarized in long-term operation. The on-load tap-changer can separate out a large amount of oil sludge due to oxide falling and insulating oil degradation in the long-term use process, and once the oil sludge is attached to mechanical components such as a gas protection baffle, a floater or a spring, the accuracy and the flexibility of the action of an electric appliance are seriously affected, and a heavy gas detection mechanism consisting of the mechanical baffle and the spring can only measure a single index of the oil flow velocity, and the running state is screened only by the single index of the flow velocity, so that the gas protection can be possibly caused to make an erroneous judgment. The on-load tap-changer can generate remarkable and continuous oil flow surge under the normal operation switching condition, the oil flow surge conditions under different load currents are different, particularly when the high-capacity transformer is operated repeatedly, the current is larger under the normal operation switching condition of the on-load tap-changer, the caused oil flow velocity is larger than the gas protection experience value which is suitable for the on-load tap-changer of the smaller-capacity transformer, and the protection misoperation is caused. The existing mechanical gas protection is more and more difficult to meet the requirement of the protection reliability of the on-load tap-changer for the high-capacity transformer. According to engineering practical operation experience and related report records, a plurality of cases of gas protection misoperation of the on-load tap changer for the large-capacity transformer are presented. Therefore, there is a need for new, accurate and reliable OLTC non-electrical protection methods that quickly cut out OLTC when a fault occurs during its operation.
Disclosure of Invention
The embodiment of the invention provides a heavy gas protection method and device for an on-load tap-changer, which are used for solving the problems of low reliability and misoperation of mechanical gas protection in the prior art.
In a first aspect, an embodiment of the present invention provides a heavy gas protection method for an on-load tap changer, including:
Acquiring a current oil flow velocity instantaneous value of a detection point in a conservator connecting pipe connected with an on-load tap changer to be detected;
Judging whether the current oil flow speed instantaneous value is larger than a preset flow speed protection action threshold value or not;
if the voltage is larger than the preset voltage, a tripping signal is sent to the protection relay, so that the protection relay opens the circuit breaker;
If not, acquiring a current value of the on-load tap-changer to be detected;
calculating a flow protection action threshold value based on the current value; calculating a current accumulated flow value based on the current oil flow instantaneous value;
And if the current accumulated flow value is larger than the flow protection action threshold value, sending a tripping signal to the protection relay to enable the protection relay to open the circuit breaker.
In one possible implementation, calculating the flow protection action threshold based on the current value includes:
Acquiring operation parameters of an on-load tap-changer to be tested; the operation parameters comprise a contact moving speed and a transition resistance value;
calculating the cut-off current of a transition contact of the on-load tap-changer to be tested according to the transition resistance value and the current value;
calculating a contact arc energy value of the on-load tap-changer to be tested according to the cut-off current of the transition contact, the contact moving speed and the current value;
and calculating a flow protection action threshold value according to the contact arc energy value.
In one possible implementation, the transition resistance values include a first transition resistance value and a second transition resistance value;
the transition contact comprises a first transition contact and a second transition contact;
the transition resistance value, the current value, and the off-current satisfy the following relationship:
Wherein, I 2,I3 cuts off the current of the first transition contact K 1 and the second transition contact K 2 respectively; r 1 is a first transition resistance value; r 2 is a second transition resistance value; u i is the stage voltage; i is a current value;
The contact arc energy values include an a-phase contact arc energy value, a B-phase contact arc energy value, and a C-phase contact arc energy value;
the switching-off current, the contact moving speed, the current value and the contact arc energy value of the on-load tap-changer to be tested of the transition contact meet the following relations:
Wherein E is the electric field strength in the arc column; b is the contact moving speed; w AK、WBK、WCK is the arc energy of the contacts of the phase A, the phase B and the phase C respectively;
The contact arc energy value and the flow protection action threshold value satisfy the following relationship:
sth＝k·(WAK+WBK+WCK)/S
Wherein, s th is a flow protection action threshold value; k is a proportionality coefficient; s is the cross section area of the connecting pipe of the conservator.
In one possible implementation, the calculation formula of the current accumulated flow value is:
Si＝Si-1+vi(t)·Δt
wherein, S i is the initial accumulated flow value corresponding to the i-th current oil flow velocity instantaneous value, and S i-1 is 0 when i is 1; v i (t) is the i-th instant value of the current oil flow rate; Δt is a preset sampling time interval.
In one possible implementation manner, before determining whether the current oil flow velocity instantaneous value is greater than the preset flow velocity protection action threshold value, the method further includes:
Judging whether the current oil flow velocity instantaneous value is larger than a starting threshold value of the protective relay or not; wherein, the starting threshold value is smaller than a preset flow rate protection action threshold value;
if the current oil flow velocity instantaneous value is smaller than the starting threshold value, returning to the step of acquiring the current oil flow velocity instantaneous value of a detection point in the conservator connecting pipe connected with the on-load tap-changer to be detected;
and if the current oil flow velocity instantaneous value is not smaller than the starting threshold value, sending a starting signal to the protective relay to start the protective relay.
In one possible implementation, the calculation formula of the start threshold is:
vst＝vnor.max
V st is a starting threshold value, v nor.max is a maximum value of oil flow velocity in the oil pillow connecting pipe in a normal switching process of the on-load tap-changer when the transformer is in maximum load operation.
In one possible implementation, if the current accumulated flow value is not greater than the flow protection action threshold value, the method further includes:
Acquiring a current oil flow velocity instantaneous value of a next moment of a detection point in a conservator connecting pipe connected with an on-load tap-changer to be detected; and returning to the step of judging whether the current oil flow velocity instantaneous value is larger than a preset flow velocity protection action threshold value.
In one possible implementation, the calculation formula of the preset flow rate protection action threshold value is:
vth＝Krel1vnor.max
Wherein v th is a preset flow rate protection action threshold value; k rel1 is a reliability coefficient, and the reliability coefficient is larger than 1; v nor.max is the maximum value of the oil flow velocity in the oil pillow connecting pipe in the normal switching process of the on-load tap-changer to be tested when the transformer is in maximum load operation.
In a second aspect, an embodiment of the present invention provides a heavy gas protection device for an on-load tap-changer, including:
the measuring and collecting module is used for obtaining the current oil flow velocity instantaneous value of a detection point in the oil conservator connecting pipe connected with the on-load tap-changer to be measured;
the instantaneous trip signal judging module is used for judging whether the instantaneous value of the current oil flow speed is larger than a preset flow speed protection action threshold value or not;
The instantaneous trip signal judging module is also used for sending a trip signal to the protection relay if the instantaneous trip signal is larger than the instantaneous trip signal judging module, so that the protection relay opens the circuit breaker;
the measuring and collecting module is also used for acquiring the current value of the on-load tap-changer to be measured if the current value is not larger than the current value;
The calculating module is used for calculating a flow protection action threshold value based on the current value; calculating a current accumulated flow value based on the current oil flow instantaneous value;
and the instantaneous trip signal judging module is also used for sending a trip signal to the protection relay to enable the protection relay to open the circuit breaker if the current accumulated flow value is larger than the flow protection action threshold value.
In one possible implementation manner, the measurement acquisition module is further used for acquiring an operation parameter of the on-load tap-changer to be measured; the operation parameters comprise a contact moving speed and a transition resistance value;
The computing module is specifically used for:
calculating the cut-off current of a transition contact of the on-load tap-changer to be tested according to the transition resistance value and the current value;
calculating a contact arc energy value of the on-load tap-changer to be tested according to the cut-off current of the transition contact, the contact moving speed and the current value;
and calculating a flow protection action threshold value according to the contact arc energy value.
Compared with the traditional method that oil flow velocity value is adopted to judge whether the on-load tap-changer has faults or not, the embodiment of the invention considers that the on-load tap-changer generates a plurality of electric arcs to trigger flow velocity disturbance in the normal switching process, but the reliable arc extinction can be realized in the normal switching process, the electric arc energy is smaller, and the volume of gas generated by the decomposition of insulating oil is small; the flow velocity signal is longer in time delay, the rising speed is slower, and the flow velocity signal quickly falls back after reaching the peak value. Therefore, the fault and normal switching state can be effectively distinguished according to the current accumulated flow value, and misoperation is avoided. Specifically, the embodiment of the invention obtains the current oil flow velocity instantaneous value of the detection point in the oil conservator connecting pipe connected with the on-load tap-changer to be detected; if the current oil flow speed instantaneous value is greater than a preset flow speed protection action threshold value, a tripping signal is sent to the protection relay, so that the protection relay opens the circuit breaker; if the current oil flow speed instantaneous value is not greater than the preset flow speed protection action threshold value, acquiring a load current value; calculating a flow protection action threshold value based on the load current value; calculating a current accumulated flow value based on the current oil flow instantaneous value; and if the current accumulated flow value is larger than the flow protection action threshold value, sending a tripping signal to the protection relay to enable the protection relay to open the circuit breaker. The embodiment of the invention can improve the reliability of the protection device by judging the instantaneous value and the current accumulated flow value of the oil flow rate, can avoid misoperation, and solves the problems of low reliability and misoperation of mechanical gas protection in the prior art.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the embodiments or the description of the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is an application scenario diagram of a heavy gas protection method for an on-load tap-changer provided by an embodiment of the present invention;
FIG. 2 is a flowchart of an implementation of a heavy gas protection method for an on-load tap changer according to an embodiment of the present invention;
FIG. 3 is a block diagram of an implementation flow of a heavy gas protection method for an on-load tap changer according to an embodiment of the present invention;
fig. 4 is a graph showing a trend of oil flow velocity change in a conservator connecting pipe under normal conditions of an on-load tap changer according to an embodiment of the present invention;
fig. 5 is a graph of the trend of the oil flow velocity in the conservator connecting pipe under the fault of the on-load tap changer according to the embodiment of the invention;
FIG. 6 is a diagram showing oil mass characteristics of an on-load tap changer under normal conditions according to an embodiment of the present invention;
FIG. 7 is a diagram of oil mass characteristics under an on-load tap changer fault provided by an embodiment of the invention;
Fig. 8 is a schematic structural diagram of a heavy gas protection device for an on-load tap changer according to an embodiment of the invention.
Detailed Description
In the following description, for purposes of explanation and not limitation, specific details are set forth such as the particular system architecture, techniques, etc., in order to provide a thorough understanding of the embodiments of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail.
For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the following description will be made by way of specific embodiments with reference to the accompanying drawings.
Fig. 1 is an application scenario diagram of a heavy gas protection method for an on-load tap changer provided by an embodiment of the present invention.
As shown in fig. 1:
In this embodiment, fig. 1 includes: the on-load tap-changer 1 to be tested, the conservator connecting pipe 2 connected with the on-load tap-changer 1 to be tested, the heavy gas protection device 3 of the on-load tap-changer, the protection relay 4 and the conservator 5 provided by the embodiment of the invention. The heavy gas protection device 3 of the on-load tap-changer is arranged on the outer wall of the oil conservator connecting pipe 2, and can detect the instantaneous value and the current value of the oil flow velocity in the oil conservator connecting pipe 2 when the on-load tap-changer 1 to be detected is in the working state; and judges whether the on-load tap-changer 1 to be tested has a fault or not based on the detected oil flow velocity instantaneous value and current value. When the on-load tap-changer 1 to be tested is judged to have faults, the device 3 sends a tripping signal to the protective relay 4, and after the protective relay 4 receives the tripping signal, the device sends a disconnection signal to the circuit breaker to control the circuit breaker to be disconnected, so that the transformer is disconnected from the power grid, and the fault expansion of the on-load tap-changer 1 to be tested is prevented, and other lines or equipment in the power grid are influenced.
The aim of the embodiment of the invention is that: the heavy gas protection method of the transformer on-load tap changer, which is adaptive to the switching current, can accurately judge the OLTC fault and normal switching of the oil immersed transformer, and avoid the malfunction of a protection action element during the fault due to improper setting value or during normal switching.
Fig. 2 is a flowchart of an implementation of the heavy gas protection method of the on-load tap changer according to the embodiment of the present invention, as shown in fig. 2:
Step 210: and acquiring the current oil flow velocity instantaneous value of a detection point in the oil conservator connecting pipe connected with the on-load tap changer to be detected.
In this embodiment, the heavy gas protection device of the on-load tap-changer may be pre-installed on a detection point in the conservator connecting pipe connected with the on-load tap-changer to be detected. When the on-load tap-changer to be tested starts to operate, in each preset acquisition period, acquiring the current oil flow velocity instantaneous value of the detection point in real time through a measurement acquisition module in the device; the measurement acquisition module may include an ultrasonic flow rate sensor, a digital flowmeter, etc., which is not limited herein.
In some embodiments, after obtaining the current oil flow velocity instantaneous value of the detection point in the conservator connecting tube connected with the on-load tap changer to be detected, before judging whether the current oil flow velocity instantaneous value is greater than the preset flow velocity protection action threshold value, the method further includes:
Judging whether the current oil flow velocity instantaneous value is larger than a starting threshold value of the protective relay or not; wherein, the starting threshold value is smaller than a preset flow velocity protection action threshold value.
And if the current oil flow velocity instantaneous value is smaller than the starting threshold value, returning to the step of acquiring the current oil flow velocity instantaneous value of the detection point in the conservator connecting pipe connected with the on-load tap-changer to be detected.
And if the current oil flow velocity instantaneous value is not smaller than the starting threshold value, sending a starting signal to the protective relay to start the protective relay.
In this embodiment, before judging whether the on-load tap-changer to be tested fails, it is necessary to judge whether the protection relay is turned on; thus, it is possible to determine whether the protection relay is activated based on the current oil flow rate instantaneous value. Specifically, judging whether the instantaneous value of the current oil flow velocity is larger than the starting threshold value of the protective relay or not; if the current oil flow rate instantaneous value is smaller than the starting threshold value, the protector is not started at the moment, and the acquired current oil flow rate instantaneous value is invalid, so that a new current oil flow rate instantaneous value needs to be acquired again. If the current oil flow speed instantaneous value is not smaller than the starting threshold value, the current oil flow speed instantaneous value is indicated to reach the standard of the protection relay, so that a starting signal is required to be sent to the protection relay to start the protection relay.
In this embodiment, in order to ensure the reliability of the method, the start threshold is set to be smaller than the preset flow rate protection action threshold. The starting threshold value can be set according to the maximum value of the oil flow velocity in the oil conservator connecting pipe in the normal switching process of the on-load tap-changer to be detected; the start threshold may be less than the maximum oil flow rate, such as v st＝0.9vnor.max、vst＝0.95vnor.max、vst＝0.95vnor.max, etc. The start threshold may also be equal to the maximum oil flow rate, where the start threshold is set optimally, i.e., v st＝vnor.max. V st is a starting threshold value, v nor.max is a maximum value of oil flow velocity in the oil pillow connecting pipe in a normal switching process of the on-load tap-changer when the transformer is in maximum load operation.
Step 220: and judging whether the current oil flow speed instantaneous value is larger than a preset flow speed protection action threshold value.
In this embodiment, after the on-load tap-changer to be tested fails, the oil flow velocity value in the oil conservator connecting pipe is continuously increased, so that the state of the on-load tap-changer to be tested can be primarily determined by determining whether the current oil flow velocity instantaneous value is greater than a preset flow velocity protection action threshold value
Step 230: if the voltage is larger than the preset voltage, a tripping signal is sent to the protection relay, so that the protection relay opens the circuit breaker.
In this embodiment, if the current oil flow velocity instantaneous value is greater than the preset flow velocity protection action threshold value, it is indicated that the on-load tap-changer to be tested has a fault, and at this time, the transformer where the on-load tap-changer to be tested is located needs to be timely removed from the power grid, so as to avoid the expansion of the fault of the on-load tap-changer to be tested and influence other circuits or devices in the power grid. Therefore, if the instantaneous value of the current oil flow rate is larger than the preset flow rate protection action threshold value, a tripping signal is sent to the protection relay, the protection relay acts instantaneously after receiving the tripping signal, and meanwhile, the circuit breaker is opened.
In this embodiment, the calculation formula of the preset flow rate protection action threshold value may be:
vth＝Krel1vnor.max
Wherein v th is a preset flow rate protection action threshold value; k rel1 is a reliability coefficient, and the reliability coefficient is larger than 1; v nor.max is the maximum value of the oil flow velocity in the oil pillow connecting pipe in the normal switching process of the on-load tap-changer to be tested when the transformer is in maximum load operation. Wherein, the value of K rel1 can be 1.4, 1.5, 1.6, etc., and is not limited herein.
Step 240: and if the current value is not greater than the current value, acquiring the current value of the on-load tap-changer to be detected.
In this embodiment, if the current oil flow velocity instantaneous value is not greater than the preset flow velocity protection action threshold value, this cannot indicate that the on-load tap-changer to be tested has no fault, and therefore, further judgment needs to be performed on the on-load tap-changer to be tested.
Step 250: calculating a flow protection action threshold value based on the current value; a current cumulative flow value is calculated based on the current instantaneous oil flow value.
In this embodiment, it is considered that when an arc is generated inside the OLTC, the insulating oil is decomposed to generate a large amount of gas and wrap the arc, and the high-temperature and high-pressure gas is continuously expanded under the internal arc to generate a great pressure while pushing the insulating oil to flow toward the outlet. Under the action of continuous electric arc, the oil flow rate in the oil conservator connecting pipe is continuously increased after short delay, and the rising speed is higher. The flow rate of the insulating oil during this time is substantially equivalent to the volume of the generated gas, which is proportional to the arc energy.
In the normal switching process of the OLTC, flow velocity disturbance caused by a plurality of electric arcs can be generated, but the electric arcs can be reliably extinguished in the normal switching process, the single electric arc burning time is not more than 10ms, the electric arc energy is small, and the volume of gas generated by the decomposition of insulating oil is small; the flow velocity signal is longer in time delay, the rising speed is slower, and the flow velocity signal quickly falls back after reaching the peak value. When the OLTC fails, a larger arc current is generated and the generated gas is not automatically extinguished, so that the generated gas has a large volume, the flow rate is caused to rise rapidly and tends to a stable value, and the generated gas is obviously larger than the data in normal switching.
Therefore, based on the characteristic that the time delay of the flow velocity signal is different under normal switching and fault and the gas volume is in direct proportion to the electric arc energy, the embodiment of the invention reflects the characteristic through the flow protection action threshold value and the current accumulated flow value. The method and the device can effectively distinguish faults and normal switching states, avoid misoperation and improve the protection reliability.
In a specific embodiment, the flow protection action threshold value may be calculated by:
Acquiring operation parameters of an on-load tap-changer to be tested; the operation parameters comprise a contact moving speed and a transition resistance value.
And calculating the cut-off current of the transition contact of the on-load tap-changer to be tested according to the transition resistance value and the current value.
And calculating the contact arc energy value of the on-load tap-changer to be measured according to the cut-off current of the transition contact, the contact moving speed and the current value.
And calculating a flow protection action threshold value according to the contact arc energy value.
In this embodiment, the heavy gas protection device of the on-load tap-changer may include a speed sensor and a dc resistance tester. When the on-load tap-changer to be tested starts to work, the moving speed of the contact of the on-load tap-changer to be tested can be obtained through a speed sensor; and obtaining the transition resistance value of the on-load tap-changer to be tested through a direct current resistance tester. The transition resistance values include a first transition resistance value and a second transition resistance value.
After the transition resistance value and the current value are obtained, the cut-off current of the transition contact of the on-load tap-changer to be measured can be calculated according to the following formula, wherein the transition contact comprises a first transition contact and a second transition contact:
Wherein, I 2,I3 cuts off the current of the first transition contact K 1 and the second transition contact K 2 respectively; r 1 is a first transition resistance value; r 2 is a second transition resistance value; u i is the stage voltage; i is a current value.
In the switching process of the on-load tap-changer to be tested, three contacts can generate three-phase amplitude; phase a, phase B and phase C, respectively. Each corresponding to one of the contact arc energy values. Correspondingly, the contact arc energy value of the on-load tap-changer to be measured can be calculated according to the following formula:
Wherein E is the electric field strength in the arc column; b is the contact moving speed; w AK、WBK、WCK is the arc energy of the contacts of the A phase, the B phase and the C phase respectively.
Considering that when an arc is generated inside the on-load tap-changer to be measured, the flow rate during the period is basically equivalent to the volume of generated gas, and the volume of the gas is proportional to the energy of the arc, the change of the volume of the gas at the moment can be represented by the flow rate. Accordingly, the flow index value, that is, the flow protection action threshold value may be calculated by:
sth＝k·(WAK+WBK+WCK)/S
Wherein, s th is a flow protection action threshold value; k is a proportionality coefficient; s is the cross section area of the connecting pipe of the conservator.
In a specific embodiment, the calculation formula of the current accumulated flow value may be:
Si＝Si-1+vi(t)·Δt
wherein, S i is the initial accumulated flow value corresponding to the i-th current oil flow velocity instantaneous value, and S i-1 is 0 when i is 1; v i (t) is the i-th instant value of the current oil flow rate; Δt is a preset sampling time interval.
Step 260: and if the current accumulated flow value is larger than the flow protection action threshold value, sending a tripping signal to the protection relay to enable the protection relay to open the circuit breaker.
In this embodiment, under normal conditions, the flow protection action threshold value is far greater than the current accumulated flow value; when serious faults occur, the protection can rapidly act under the condition that the flow rate in the on-load tap-changer oil tank rapidly rises in a short time, serious consequences caused by the faults are prevented, and the defect of the protection based on flow signals on the speed is overcome to a certain extent. However, when the on-load tap-changer to be tested fails, the condition that the current accumulated flow value is larger than the flow protection action threshold value can be generated, the on-load tap-changer to be tested is described to fail, and the transformer where the on-load tap-changer to be tested is located needs to be cut off from the power grid in time at the moment, so that the expansion of the failure of the on-load tap-changer to be tested is avoided, and other lines or equipment in the power grid are influenced. Therefore, if the current accumulated flow value is larger than the flow protection action threshold value, a tripping signal is sent to the protection relay, the protection relay acts instantly after receiving the tripping signal, and meanwhile, the circuit breaker is opened.
In some embodiments, if the current accumulated flow value is not greater than the flow protection action threshold value, the method may further include:
Acquiring a current oil flow velocity instantaneous value of a next moment of a detection point in a conservator connecting pipe connected with an on-load tap-changer to be detected; and returning to the step of judging whether the current oil flow velocity instantaneous value is larger than a preset flow velocity protection action threshold value.
In this embodiment, if the current oil flow speed instantaneous value and the current accumulated flow value of the on-load tap-changer to be detected are both within the normal standard through detection in the current detection period, it is indicated that the on-load tap-changer to be detected has no fault in the current detection period. Therefore, the current instantaneous value of the oil flow rate at the next moment can be obtained, and the step 220 is returned, and in the new detection period, the on-load tap changer to be detected is detected based on the preset flow rate protection action threshold value, the recalculated flow protection action threshold value in the current period and the current accumulated flow value.
In summary, the method provided by the embodiment of the invention can be applied to improving the protection effect of the OLTC of the oil immersed transformer in the voltage regulation process. The on-load voltage regulating transformer is provided with the OLTC, so that the on-load voltage regulating transformer not only can stabilize the load center voltage, but also is an important device for connecting a power grid, adjusting load flow and improving reactive power distribution, and the safe operation of the on-load voltage regulating transformer has great significance to the stability of the system. But OLTC can be switched rapidly under high voltage and heavy current in the voltage regulation process, is frequently used, is easy to fail, and can directly influence the normal operation of a power transformer. The invention provides a novel OLTC protection method based on a digital flow rate sensor, which can be used for rapidly identifying and reliably cutting off faults in the operation process of the OLTC.
FIG. 3 is a block diagram of an implementation flow of a heavy gas protection method for an on-load tap changer according to an embodiment of the present invention; as shown in fig. 3:
in this embodiment, taking a CMD iii type on-load break-up switch as an example, the feasibility of the method provided by the embodiment of the present invention is described:
Specifically, an ultrasonic flow rate sensor is installed on the outer wall of a conservator connecting pipe connected with an on-load tap-changer to be tested, when the on-load tap-changer to be tested starts to work, the operation parameters including the contact moving speed and the transition resistance value are obtained, and the current accumulated flow value S i-1 at the moment is initialized to 0, namely i=1 and S i-1 =0 at the moment. And then collecting the current oil flow velocity instantaneous value v i (t) in the oil pillow connecting pipe in the operation process of the on-load tap-changer to be detected in real time. Comparing the collected instantaneous value v i (t) of the current oil flow speed with the starting threshold value v st of the protective relay;
if v i(t)＜vst, then a new current oil flow instantaneous v i (t) will be re-acquired;
If v i(t)＞vst, the current oil flow speed instantaneous value v i (t) reaches the starting speed of the protection relay, and the protection relay is started, then v i (t) is continuously compared with the preset flow speed protection action threshold value v th.
If v i(t)＞vth indicates that the on-load tap-changer to be tested has a fault, then the protection relay is required to start protection action;
If v i(t)＜vth, further acquiring a current value I of the on-load tap-changer to be detected, and calculating a flow protection action threshold value s th based on the current value I; meanwhile, a current accumulated flow value S i is calculated according to v i (t);
If S i＞sth shows that the on-load tap-changer to be tested has a fault, then the protection relay is required to start the protection action;
If S i＜sth indicates that the on-load tap-changer to be tested has not failed in the current detection period, the current instantaneous value v i (t) of the oil flow at the next moment needs to be collected again, and whether v i (t) is greater than v st is judged again.
Fig. 4 is a graph showing a trend of oil flow velocity change in a conservator connecting pipe under normal conditions of an on-load tap changer according to an embodiment of the present invention; fig. 5 is a graph of the trend of the oil flow velocity in the oil conservator connecting pipe under the fault of the on-load tap changer according to the embodiment of the invention, as shown in fig. 4 and 5:
It can be seen that during normal switching, the oil flow rate is oscillated from an initial value of less than 0.05m/s to a maximum value of 0.23m/s, and the oscillation is restored to about 0.05 m/s; in case of failure, the oil speed continuously rises within 5s, and the flow speed is maximally 1.25m/s. Therefore, if v i(t)＞vth indicates that the on-load tap-changer to be tested has a fault, then the protection relay is required to start the protection action at the moment, so that the circuit breaker is disconnected, and then the transformer charging network corresponding to the on-load tap-changer to be tested is cut off.
FIG. 6 is a diagram showing oil mass characteristics of an on-load tap changer under normal conditions according to an embodiment of the present invention; fig. 7 is a characteristic diagram of oil quantity under fault of the on-load tap changer according to the embodiment of the invention, as shown in fig. 6 and fig. 7:
The oil flow rate of the on-load tap-changer is slowly increased under normal and fault conditions, but the oil flow rate rises to less than 0.45m in 8s during normal switching, and the flow rate in 5s reaches 4.5m during fault conditions, so that the values are greatly different. Therefore, if S i＞sth indicates that the on-load tap-changer to be tested has a fault, then the protection relay is required to start the protection operation.
Therefore, under two conditions, the difference of the oil pressure and the flow characteristics is obvious, and by means of the identification method, the normal switching and the fault state of the on-load tap-changer can be effectively distinguished by means of the combination of the oil flow speed and the flow characteristics, so that the reliability of pressure protection action is improved.
For a portion of the disclosure where embodiments of the present invention are not described in detail, reference may be made to the other related embodiments described above.
It should be understood that the sequence number of each step in the foregoing embodiment does not mean that the execution sequence of each process should be determined by the function and the internal logic, and should not limit the implementation process of the embodiment of the present invention.
The following are device embodiments of the invention, for details not described in detail therein, reference may be made to the corresponding method embodiments described above.
Fig. 8 is a schematic structural diagram of a heavy gas protection device for an on-load tap changer according to an embodiment of the present invention, and for convenience of explanation, only the parts related to the embodiment of the present invention are shown, and the details are as follows:
as shown in fig. 8, the heavy gas protection device 8 for an on-load tap changer includes:
the measurement acquisition module 81 is used for acquiring a current oil flow velocity instantaneous value of a detection point in a conservator connecting pipe connected with the on-load tap-changer to be detected;
An instantaneous trip signal judgment module 82 for judging whether the instantaneous value of the current oil flow rate is greater than a preset flow rate protection action threshold value;
The instantaneous trip signal judging module 82 is further configured to send a trip signal to the protection relay if the instantaneous trip signal is greater than the instantaneous trip signal, so that the protection relay opens the circuit breaker;
the measurement acquisition module 81 is further configured to acquire a current value of the on-load tap-changer to be measured if the current value is not greater than the current value;
a calculating module 83, configured to calculate a flow protection action threshold value based on the current value; calculating a current accumulated flow value based on the current oil flow instantaneous value;
the instantaneous trip signal judgment module 82 is further configured to send a trip signal to the protection relay to cause the protection relay to open the circuit breaker if the current accumulated flow value is greater than the flow protection action threshold value.
In one possible implementation, the measurement acquisition module 81 is further configured to acquire an operation parameter of the on-load tap-changer to be measured; the operation parameters comprise a contact moving speed and a transition resistance value;
The calculation module 83 is specifically configured to:
calculating the cut-off current of a transition contact of the on-load tap-changer to be tested according to the transition resistance value and the current value;
calculating a contact arc energy value of the on-load tap-changer to be tested according to the cut-off current of the transition contact, the contact moving speed and the current value;
and calculating a flow protection action threshold value according to the contact arc energy value.
In one possible implementation, the transition resistance values include a first transition resistance value and a second transition resistance value;
the transition contact comprises a first transition contact and a second transition contact;
the transition resistance value, the current value, and the off-current satisfy the following relationship:
Wherein, I 2,I3 cuts off the current of the first transition contact K 1 and the second transition contact K 2 respectively; r 1 is a first transition resistance value; r 2 is a second transition resistance value; u i is the stage voltage; i is a current value;
The contact arc energy values include an a-phase contact arc energy value, a B-phase contact arc energy value, and a C-phase contact arc energy value;
the switching-off current, the contact moving speed, the current value and the contact arc energy value of the on-load tap-changer to be tested of the transition contact meet the following relations:
Wherein E is the electric field strength in the arc column; b is the contact moving speed; w AK、WBK、WCK is the arc energy of the contacts of the phase A, the phase B and the phase C respectively;
The contact arc energy value and the flow protection action threshold value satisfy the following relationship:
sth＝k·(WAK+WBK+WCK)/S
Wherein, s th is a flow protection action threshold value; k is a proportionality coefficient; s is the cross section area of the connecting pipe of the conservator.
In one possible implementation, the calculation formula of the current accumulated flow value is:
Si＝Si-1+vi(t)·Δt
wherein, S i is the initial accumulated flow value corresponding to the i-th current oil flow velocity instantaneous value, and S i-1 is 0 when i is 1; v i (t) is the i-th instant value of the current oil flow rate; Δt is a preset sampling time interval.
In one possible implementation, the heavy gas protection device of the on-load tap-changer further includes a start judgment module 84; the start-up determination module 84 is specifically configured to:
Before judging whether the current oil flow velocity instantaneous value is larger than the preset flow velocity protection action threshold value, the method further comprises the following steps:
Judging whether the current oil flow velocity instantaneous value is larger than a starting threshold value of the protective relay or not; wherein, the starting threshold value is smaller than a preset flow rate protection action threshold value;
if the current oil flow velocity instantaneous value is smaller than the starting threshold value, returning to the step of acquiring the current oil flow velocity instantaneous value of a detection point in the conservator connecting pipe connected with the on-load tap-changer to be detected;
and if the current oil flow velocity instantaneous value is not smaller than the starting threshold value, sending a starting signal to the protective relay to start the protective relay.
In one possible implementation, the calculation formula of the start threshold is:
vst＝vnor.max
V st is a starting threshold value, v nor.max is a maximum value of oil flow velocity in the oil pillow connecting pipe in a normal switching process of the on-load tap-changer when the transformer is in maximum load operation.
In one possible implementation, the measurement acquisition module 81 is further configured to:
If the current accumulated flow value is not greater than the flow protection action threshold value, the method further comprises:
Acquiring a current oil flow velocity instantaneous value of a next moment of a detection point in a conservator connecting pipe connected with an on-load tap-changer to be detected; and returning to the step of judging whether the current oil flow velocity instantaneous value is larger than a preset flow velocity protection action threshold value.
In one possible implementation, the calculation formula of the preset flow rate protection action threshold value is:
vth＝Krel1vnor.max
Wherein v th is a preset flow rate protection action threshold value; k rel1 is a reliability coefficient, and the reliability coefficient is larger than 1; v nor.max is the maximum value of the oil flow velocity in the oil pillow connecting pipe in the normal switching process of the on-load tap-changer to be tested when the transformer is in maximum load operation.
In the foregoing embodiments, the descriptions of the embodiments are emphasized, and in part, not described or illustrated in any particular embodiment, reference is made to the related descriptions of other embodiments.
Those of ordinary skill in the art will appreciate that the templates, elements, and algorithm steps described in connection with the embodiments disclosed herein can be implemented as electronic hardware, or combinations of computer software and electronic hardware. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the solution. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
The modules/units, if implemented in the form of software functional units and sold or used as separate products, may be stored in a computer readable storage medium. Based on such understanding, the present invention may implement all or part of the procedures in the methods of the above embodiments, or may be implemented by a computer program for instructing related hardware, where the computer program may be stored in a computer readable storage medium, and the computer program may implement the steps of the heavy gas protection method embodiments of the on-load tap changer when executed by a processor. Wherein the computer program comprises computer program code which may be in source code form, object code form, executable file or some intermediate form etc. The computer readable medium may include: any entity or device capable of carrying the computer program code, a recording medium, a USB flash disk, a removable hard disk, a magnetic disk, an optical disk, a computer memory, a read-only memory, a random access memory, an electrical carrier wave signal, a telecommunication signal, a software distribution medium, and so forth.
The above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention, and are intended to be included in the scope of the present invention.
Claims (10)
1. The heavy gas protection method for the on-load tap-changer is characterized by comprising the following steps of:
Acquiring a current oil flow velocity instantaneous value of a detection point in a conservator connecting pipe connected with an on-load tap changer to be detected;
Judging whether the current oil flow velocity instantaneous value is larger than a preset flow velocity protection action threshold value or not;
if the voltage is larger than the preset voltage, a tripping signal is sent to the protection relay, so that the protection relay opens the circuit breaker;
if not, acquiring the current value of the on-load tap-changer to be tested;
calculating a flow protection action threshold value based on the current value; calculating a current accumulated flow value based on the current oil flow instantaneous value;
And if the current accumulated flow value is larger than the flow protection action threshold value, sending a tripping signal to the protection relay to enable the protection relay to disconnect a breaker.
2. The heavy gas protection method of claim 1, wherein calculating a flow protection action threshold based on the current value comprises:
Acquiring the operation parameters of the on-load tap-changer to be tested; wherein the operation parameters comprise a contact moving speed and a transition resistance value;
Calculating the cut-off current of the transition contact of the on-load tap-changer to be tested according to the transition resistance value and the current value;
Calculating a contact arc energy value of the on-load tap-changer to be tested according to the cut-off current of the transition contact, the contact moving speed and the current value;
And calculating a flow protection action threshold value according to the contact arc energy value.
3. The heavy gas protection method of an on-load tap changer of claim 2, wherein the transition resistance values comprise a first transition resistance value and a second transition resistance value;
the transition contact comprises a first transition contact and a second transition contact;
The transition resistance value, the current value, and the off-current satisfy the following relationship:
Wherein I 2,I3 cuts off current of the first transition contact K 1 and the second transition contact K 2, respectively; r 1 is the first transition resistance value; r 2 is the second transition resistance value; u i is the stage voltage; i is the current value;
the contact arc energy values include an a-phase contact arc energy value, a B-phase contact arc energy value, and a C-phase contact arc energy value;
The switching-off current of the transition contact, the contact moving speed, the current value and the contact arc energy value of the on-load tap-changer to be tested meet the following relations:
wherein E is the electric field strength in the arc column; b is the contact moving speed; w AK、WBK、WCK is the arc energy of the contacts of the phase A, the phase B and the phase C respectively;
The contact arc energy value and the flow protection action threshold value satisfy the following relationship:
sth＝k·(WAK+WBK+WCK)/S
S th is the flow protection action threshold value; k is a proportionality coefficient; s is the cross section area of the connecting pipe of the conservator.
4. The heavy gas protection method of an on-load tap changer according to claim 1, wherein the calculation formula of the current accumulated flow value is:
Si＝Si-1+vi(t)·Δt
wherein, S i is the initial accumulated flow value corresponding to the i-th current oil flow velocity instantaneous value, and S i-1 is 0 when i is 1; v i (t) is the i-th instant value of the current oil flow rate; Δt is a preset sampling time interval.
5. The heavy gas protection method of an on-load tap changer according to claim 1, further comprising, before said determining whether said current oil flow instantaneous value is greater than a preset flow protection action threshold:
Judging whether the current oil flow velocity instantaneous value is larger than a starting threshold value of the protective relay or not; wherein the starting threshold is smaller than the preset flow rate protection action threshold;
if the current oil flow velocity instantaneous value is smaller than the starting threshold value, returning to the step of acquiring the current oil flow velocity instantaneous value of a detection point in the oil conservator connecting pipe connected with the on-load tap-changer to be detected;
and if the current oil flow velocity instantaneous value is not smaller than the starting threshold value, sending a starting signal to the protection relay to start the protection relay.
6. The heavy gas protection method of an on-load tap changer according to claim 5, wherein the starting threshold is calculated by the following formula:
vst＝vnor.max
V st is a starting threshold value, v nor.max is a maximum value of oil flow velocity in the oil pillow connecting pipe in a normal switching process of the on-load tap-changer when the transformer is in maximum load operation.
7. The method of claim 1, wherein if the current accumulated flow value is not greater than the flow protection action threshold value, further comprising:
Acquiring a current oil flow velocity instantaneous value of a next moment of a detection point in a conservator connecting pipe connected with an on-load tap-changer to be detected; and returning to the step of judging whether the current oil flow speed instantaneous value is larger than a preset flow speed protection action threshold value.
8. The heavy gas protection method of an on-load tap changer according to claim 1, wherein the calculation formula of the preset flow rate protection action threshold value is:
vth＝Krel1vnor.max
Wherein v th is the preset flow rate protection action threshold value; k rel1 is a reliability coefficient, which is greater than 1; v nor.max is the maximum value of the oil flow velocity in the oil pillow connecting pipe in the normal switching process of the on-load tap-changer to be tested when the transformer is in maximum load operation.
9. The utility model provides a heavy gas protection device of on-load tap changer which characterized in that includes:
the measuring and collecting module is used for obtaining the current oil flow velocity instantaneous value of a detection point in the oil conservator connecting pipe connected with the on-load tap-changer to be measured;
The instantaneous trip signal judging module is used for judging whether the instantaneous value of the current oil flow speed is larger than a preset flow speed protection action threshold value or not;
The instantaneous trip signal judging module is further used for sending a trip signal to the protection relay if the instantaneous trip signal is larger than the instantaneous trip signal judging module, so that the protection relay opens the circuit breaker;
the measuring and collecting module is also used for acquiring the current value of the on-load tap-changer to be measured if the current value is not larger than the current value;
The calculating module is used for calculating a flow protection action threshold value based on the current value; calculating a current accumulated flow value based on the current oil flow instantaneous value;
And the instantaneous trip signal judging module is also used for sending a trip signal to the protection relay to enable the protection relay to open the circuit breaker if the current accumulated flow value is larger than the flow protection action threshold value.
10. The heavy gas protection device of an on-load tap changer of claim 9, comprising:
the measurement acquisition module is also used for acquiring the operation parameters of the on-load tap-changer to be measured; wherein the operation parameters comprise a contact moving speed and a transition resistance value;
the computing module is specifically configured to:
Calculating the cut-off current of the transition contact of the on-load tap-changer to be tested according to the transition resistance value and the current value;
Calculating a contact arc energy value of the on-load tap-changer to be tested according to the cut-off current of the transition contact, the contact moving speed and the current value;
And calculating a flow protection action threshold value according to the contact arc energy value.
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