KR101517656B1 - Method and device for detecting failure of a vacuum interrupter of an on load tap changer - Google Patents

Abstract

1. A method for detecting a failure of a vacuum circuit breaker in an on-load tap-changer, the tap-changer comprising an oil-filled housing, a hydrogen sensor arranged in the housing, a diverter switch (3) comprising movable contacts (MC, RC) And at least one vacuum circuit breaker (MVI, RVI) arranged to block the current passing through the movable contact of the switch (3). The method of detecting a breakdown in a vacuum circuit breaker comprises repeatedly measuring the hydrogen content of the oil, transferring the measurement data of the hydrogen content to the computing unit, and determining the breakdown voltage of the vacuum breaker (MVI, RTI ID = 0.0 > RVI) < / RTI > is detected.

Description

TECHNICAL FIELD [0001] The present invention relates to a method and device for detecting a failure of a vacuum circuit breaker of an on-load tap-changer,

The present invention relates to a method and a device for detecting a failure of a vacuum circuit breaker in an on-load tap-changer wherein the tap-changer comprises an oil-filled housing, a diverter switch (3) comprising movable contacts ) And at least one vacuum interrupter (MVI, RVI) arranged to interrupt the current through the movable contact of the divertor switch.

A tap switch is a device used with transformers for regulation of voltage levels. This is achieved by having a tap changer for changing the number of windings of the transformer.

On-load tap-changers OLTC typically include a tap selector switch and a diverter switch that operate as a unit that affects the transfer current from one voltage tap to the next.

The divertor switch generates and blocks the currents at full load, while the tap selector pre-selects the tap to which the divertor switch will deliver the load current. The tap selector operates to interrupt the load. If the power output from the transformer is to be changed from one voltage level to another voltage level, this means that, first, the diverter switch is still fed from the existing voltage level and the selector is switched to the tap point of the transformer winding corresponding to the new voltage level .

Thus, the connection of the selector occurs without a current load. When the selector is connected to the tap for the new voltage level, then a switching action occurs so that the output current is taken from the new tap point of the transformer with the aid of the divertor switch. When the transformer has a plurality of tap points, the switching typically occurs only between two tap points that are close to each other in terms of voltage. If adjustment to a more distant position is desired, this happens step by step. Diverter switches of the type referred to herein are typically used in power control or distribution transformers. The OLTC may also be advantageously used to control other types of electrical devices, such as power transmission or distribution products, such as reactors, industrial transformers, phase shifters, capacitors, and the like.

The operation of the divertor switch involves the commutation of one circuit to another and the consequent occurrence of an electric arc. The diverter switch, with all the subsystems, is placed in the tank and immersed in oil. The on-load tap-changer includes a tank with oil, diverter switches and subsystems.

The oil in the tank acts as an electrical insulator and coolant to remove heat generated in the OLTC. The oil will also quench the arcs that occurred during switching. Arcing during operation of the OLTC will contaminate the insulating oil and wear the switch contacts.

In order to overcome arcing in oil, it has been previously known to use vacuum switches or vacuum breakers for switching operations in which an arc occurs. Thereafter, electrical contact wear and arcs will only occur in the vacuum switch. For an appropriate procedure from an electrical point of view, this kind of divertor switch is provided with at least one main branch and one resistor branch each having a vacuum breaker.

Diverter switches of this type are previously known, for example, from US 5,786,552 (D0). Thus, the divertor switches described in the document have one main branch and one resistor branch in a normal situation, connected in parallel and connected to the output line. Each branch is provided with a vacuum switch and a contact connected in series with it. It is important that they operate in a finite sequence when divertor switching occurs and in this case for the OLTC the main branch operates before the resistor branch but for some load breakers it is ensured that the main branch does not run before the resistor branch . In this manner, the vacuum switch of the main branch may be dimensioned only for blocking the load current, and the vacuum switch of the resistor branch may be dimmed for the generated circulating current. In the case of the inverse sequence, the vacuum switch of the main branch will be forced to block the sum of these currents, and thus will be dimmed for it.

US 3,206,569 (D1) describes a tap changer 8 provided with vacuum switches. The tap changer is connected to the main transformer 1 (5). The tap changer is separate from the transformer and is provided to the same container and liquid as the transformer (FIG. 2) or to a separate container and separate liquid (FIG. 3). The hood 39 provided for collecting the gas is arranged on the tap changer and the hood 39 is adapted to deliver the gas to the gas sensor 40. The gas sensor 40 is of a type that senses hydrogen and hydrocarbon gases. If the vacuum switch fails (see column 5, lines 11-25), the contacts 9, 10 are opened and an arc is generated which creates gas bubbles. The gas is detected by a sensor providing an alarm. In this way, the alarm indicates that the vacuum switch is malfunctioning.

In the event of a vacuum breaker failure, the auxiliary contact system in the OLTC can interrupt the current with a limited number of operations, possibly between 10 and 500 operations, depending on the OLTC type and load.

If the auxiliary contact system, i.e. the movable contact of the divertor switch, has to interrupt the current more than a limited number of times, the wear of the auxiliary contacts by the arcs will make the contacts no longer accessible and unable to draw current. If the auxiliary main contacts are inaccessible, two things can happen:

1. The main circuit is cut off and the load is transferred through the resistor circuit. Due to the continuous full load on the transition resistors, the resistors will eventually melt and as a result will be damaged by increased arcs inside the OLTC. This arc will hopefully be detected and should bring an immediate emergency shut-down of the OLTC-transformer system. A long-term repair or replacement of the divertor switch will result, and the transformer will be off-line for the repair time.

2. Continuous arcing occurs over auxiliary contacts that can cause a short circuit between the two phases, which will cause a catastrophic failure, such as an explosion or fire. If you are lucky, the continuous arc is quenched and returns to point (1).

Therefore, it is important to monitor the operation of the vacuum breakers to prevent such possible failures. Currently there is no simple and reliable way to detect whether the vacuum breaker of the tap changer has failed and the severity of the malfunction.

The ABB provides a monitoring and computing system, referred to as TEC (Transformer Electronic Control), which monitors transformers and tap converters, such as the OLTC. The system with TEC is equipped with sensors and measurement units and is configured to measure and monitor the condition and performance of the tap changer or transformer. It also includes a computing unit that computes process data from measurements. For example, the TEC system measures and monitors the bottom and top oil temperature of the transformer tank and calculates the hot spot temperatures of the transformer windings. Other monitored data include, but are not limited to, voltages and currents passing through high and low voltage bushings, atmospheric temperature, aging due to cumulative use time, thermal aging, relative aging with temperature, peak load, The water content of the oil, the hydrogen content of the oil, expressed in ppm, the state of the cooling equipment, the tap changer position, the status of the sensors, e.g. faults. The TEC is also adapted to display reference values such as reference values for the top and bottom temperatures.

The hydrogen sensor is arranged in the transformer oil and provides measurements of the hydrogen of the transformer, indicating communicable arcing or sparks in the transformer portion of the OLTC when communicatively connected to the TEC. The TEC is described in more detail in the "Intelligent Monitoring System, Type TEC User's Manual," published on the Web at http://www.abb.com/electricalcomponents.

The event is also registered by the TEC computing system when the automatic control unit of the tap changer provides a switching command to the motor drive mechanism of the tap changer to subsequently bring the tap change in the tap changer.

It is an object of the present invention to provide a method for detecting a failure of vacuum breakers of an on-load tap-changer (OLTC).

This object is achieved by a method as claimed in claim 1.

The present invention can be used to improve the functionality of TEC systems from ABB and similar monitoring and control systems for tap converters from other suppliers.

The method includes repeatedly measuring the hydrogen content of the oil in the housing of the tap changer, and determining if there is a failure in the vacuum breaker based on measurements of the hydrogen content of the oil. The method is provided to monitor the hydrogen content, making it possible to monitor the change.

In addition, the determining step may include utilizing the switching history of the tap changer, for example, how much tap changer has been switched or how often it is switched to determine a failure. The measurement of the hydrogen content is compared to the predicted content based on the switching history and the method shows a failure only if the measured content deviates from the predicted content by a certain amount, i. E. The difference is greater than the threshold value.

Although the hydrogen sensor and TEC system combination as described above may be used, the sensor should be placed in tap-changer oil instead of (or in addition to the sensor of) the transformer oil and since the performance of the transformer is no longer being measured, Different analyzes should be performed. Also, the use of a tap changer is monitored by monitoring the number of operations, which is used to analyze changes in hydrogen content and hydrogen content in the oil.

Another object of the present invention is to provide a device for detecting a failure of vacuum breakers of a tap changer.

This object is achieved by the device according to claim 10.

The device comprises an oil filled housing of a tap changer arranged with a sensor 10 for repeatedly measuring the hydrogen content in the oil, the computing unit analyzing the measurements of the hydrogen content of the oil, and the vacuum breakers MVI, RTI ID = 0.0 > RVI). ≪ / RTI >

An object of the present invention is solved by implementing that in the event of a vacuum breaker failure, the current is no longer blocked by the vacuum breaker, but is blocked by the auxiliary contact system. The auxiliary contacts have to interrupt the current and thus generate arcs in the oil. These arcs are combined with the known fact that arcs of insulating oil increase the amount of hydrogen in the insulating oil. Using the hydrogen sensor, it is possible to detect that the vacuum breaker could not shut off the current by detecting the absolute hydrogen amount of the oil or the hydrogen change rate of the oil, thereby allowing detection of the breaker breakdown.

In another embodiment of the present invention,

Storing a measure of the hydrogen content of the oil, and

- determining whether a fault exists in the vacuum circuit breaker (MVI, RVI), based on at least one stored measurement of the hydrogen content of the oil and the hydrogen content of the oil.

Determining if a fault exists in the vacuum circuit breaker can be accomplished by comparing the measured level of hydrogen in the oil to a fixed maximum allowed hydrogen level and / or by using stored previous measurements of the oil's oil to increase the hydrogen in the oil over time Quot ;. < / RTI >

In another embodiment of the present invention,

- if the failure is determined in the vacuum circuit breaker, performing an action.

The action may be to send a warning to the tap changer or the control system of the transformer. Warnings can also be sent to the plant wide control system. The action may also be to allow only a limited number of critical operations without overloading the divertor switch. The action may also be to completely stop the diverter switch from moving. The selected action may depend on the hydrogen level in the oil or the rate of increase in the hydrogen level in the oil.

When a severe vacuum breaker failure is detected, the OLTC must either stop the operation immediately, or only perform a limited number of critical operations without overloading if they are considered critical to the operation of the system in which it is serviced. The limited number of operations of the divertor switch may be less than 200, or even less than 20, until the OLTC is checked by the maintainer.

When the OLTC stops operating, the transformer can still be used, while the voltage level is no longer controllable, but this is a desirable condition for the case where the error is not detected and the OLTC suffers a catastrophic failure.

In another embodiment of the present invention, the step of determining whether a failure exists in the vacuum circuit breaker comprises the steps of:

- receiving operation data of the tap changer,

Calculating a predicted change in hydrogen content based on the mathematical model of the tap changer and the operating data of the tap changer, and

Determining whether a failure of the vacuum circuit breaker exists based on at least two of the predicted changes in the calculated hydrogen content and the hydrogen content measurements.

Performing the steps repeatedly means that they are performed almost continuously or in discrete time steps in seconds or in discrete time steps in several minutes. The operation of the tap changer is the timing of switching operations of the diverter switch and load current at the switching motion time. The model may be a physical model that allows for planning hydrogen emissions based on the number of switches and the load current, or the model may be based on measurements and / or look-up based on historical data, on which average hydrogen emissions are calculated based on the number of switches and load current Model.

The hydrogen level of the tap-changer oil will change naturally depending on how the tap-changer operates, how often the taps are performed and what load currents should be blocked. This model-based determination of vacuum breaker failure will be much less likely to generate errors in determining failures than a system that simply compares the measured hydrogen level of the oil to the absolute hydrogen level. Making a faulty determination of a vacuum breaker failure can cause an unnecessary shutdown of the transformer-tap converter system. This unnecessary shutdown will result in the potential power loss of all access systems, such as very expensive industrial equipment or housings for equipment.

In another embodiment of the present invention, the determination of whether a failure of the vacuum circuit breaker is present,

Is true.

는 오일에서의 현재 측정된 수소 함유량을 기술하는 파라미터이며, 이것은 단일 측정치이거나 또는 다수의 측정치들의 일부 중앙값 (mean) 또는 평균값 (average) 일 수 있다.

Is a parameter describing the presently measured hydrogen content in the oil, which may be a single measurement or some of the mean or mean of a plurality of measurements.

은 오일에서의 이전에 측정된 수소 함유량을 설명하는 파라미터이며, 이것은 단일 측정치이거나 또는 다수의 이전 측정치들의 일부 중앙값 또는 평균값일 수 있다.

Is a parameter describing the previously measured hydrogen content in the oil, which may be a single measurement or some median or average value of a number of previous measurements.

는 탭 전환기의 동작에 기초한 오일의 수소 함유량의 예상되는 변화이다. 탭 전환기의 동작은 스위칭 움직임들의 시간에서의 디버터 스위치 및 부하 전류의 스위칭 움직임들의 타이밍이다.

Is an expected change in the hydrogen content of the oil based on the operation of the tap changer. The operation of the tap changer is the timing of switching operations of the diverter switch and load current at the time of the switching movements.

eps is a safety parameter to ensure that failure of the vacuum circuit breaker is not determined if the measured increment of hydrogen is not greater than eps. The eps may be from a few ppm to a few hundred ppm of hydrogen in the oil, depending on the type of tap changer, the load, the oil life, and the risk of false alarms.

Hydrogen detection and monitoring in the tap changer has the additional advantage that it can also be used to detect:

- Rectified sparks - will produce much less hydrogen in the oil than full arc.

- partial discharges - will produce a hydrogen signal that is different from the hydrogen signal for the arc as a constant low rate of hydrogen in the oil

- Severe overheating with associated arcs - will produce a hydrogen signal different from the hydrogen signal for the tap-change arc.

In another embodiment of the present invention, the computing unit is configured to send an alert to the control system when a failure of the vacuum breakers (MVI, RVI) is detected.

In another embodiment, the computing means is an integral part of the control system and can be provided by a computer program product to upgrade an existing control program.

In another embodiment of the present invention, the computing unit is configured to send a signal to the control system to stop or limit the movement of the diverter switch when a failure of the vacuum breakers (MVI, RVI) is detected.

In another embodiment of the present invention, a computing unit is configured to receive operational data of the tap changer, the computing unit being operative to calculate an expected change in hydrogen content and to calculate an expected change in hydrogen content of the hydrogen content in the oil And compare the analyzed measurements to determine the failure in vacuum interrupters (MVI, RVI).

The drawings form a part of this specification, and include illustrative embodiments of the invention, which may be embodied in various forms.
Fig. 1 schematically shows an on-load tap-changer in a transformer having an embodiment of the invention.
Figures 2A-2E schematically illustrate the switching of an on-load tap-changer without vacuum breakers.
Figures 3A-3H schematically illustrate the switching of the on-load tap-changer with vacuum breakers.
Figure 4 illustrates one situation in which arcing is present in the auxiliary switches in the on-load tap-changer with vacuum circuit breakers.
5 is a schematic diagram of an on-load tap-changer.
Figures 6 to 8 are schematic diagrams of the evolution of different hydrogen or hydrogen content in oil and warning or alarm levels over time in the tap changer.
Figure 9 shows an embodiment of the present invention which provides an alternative to the on-load tap-tap diverter device of Figure 1;

Detailed descriptions of preferred embodiments are provided herein. However, it will be understood that the invention may be embodied in various forms. Accordingly, it is to be understood that the specific details disclosed herein are not to be construed as limiting, but rather, as a basis for the claims, as well as those of skill in the art to which the invention pertains in virtually any appropriate and appropriate manner, It should be understood as a representative basis.

Fig. 1 schematically shows an on-load tap-changer 2 in a transformer 8 having an embodiment of the invention. The tap selector (1) is mounted below the diverter switch (3). The motions of the OLTC, here, get energy from the motor drive mechanism 9 mounted on the wall of the transformer 8. Movements from the motor 9 are transmitted by the shafts 6 ', 6 "and the bevel gear 7. The oil reservoir 5 ensures that there is sufficient oil in the OLTC at all temperatures.

The hydrogen sensor device 10 is immersed in the oil of the tap changer and the position in the figure only shows that it can be arranged anywhere in the housing.

The hydrogen sensor device 10 sends a signal to the drive control unit 11 which controls the motions of the motor 9 driving the diverter switch 3.

Alternatively, the hydrogen sensor device 10 sends a signal to the computing unit, and the computing unit also receives signals indicative of manipulation of the diverter switch, such as drive command signals for the motor 9, , For example, a drive command signal received from the motor 9. The transformer 8 and the OLTC 2 are both oil-filled but have different housings, and the oil of the OLTC and the oil of the transformer never come into contact. It is also possible to arrange the OLTC outside the transformer tank.

Figure 1 shows a first embodiment in which the sensor 10 is communicatively connected to a drive control unit 11 comprising means for determining a fault based on hydrogen measurements. The control unit 11 may be included in the control system of the electricity transmission substation.

Figure 9 shows an alternative embodiment in which the sensor 10 is communicatively connected to a computing unit 12 that includes means for determining faults based on hydrogen content. The computing unit 12 is also communicatively coupled to the motor drive mechanism in Figure 9 and receives signals from the motor drive mechanism when the tap changer is operated. These signals may be command signals that the motor drive mechanism 9 receives from the drive control unit 11 via a drive control connection that operatively connects the drive control unit 11 to the motor 9. [ The embodiments of Figures 1 and 9 include arranging the sensor 10 in the oil of the tap changer, which transfers the measurements to the computing units 11, 12. The communication may be provided by electrical signaling of analog signals from the sensor and the analog signals may be provided to the I / O < RTI ID = 0.0 > I / O < / RTI & Module which converts the electrical analog signals of the measurements from the sensor and converts the signals into digital data which is subsequently transmitted by Ethernet to, for example, the computer control system of the substation . Alternatively, the sensor 10 includes digital processing and communication means and samples the measurements into data that is communicated to a computing unit of the substation control system, e.g., via a digital data bus. Thus, the hydrogen sensor device 10 sends a signal to the computing means 11, 12 adapted to determine if the vacuum circuit breaker is malfunctioning, based on the hydrogen content, preferably its history or hydrogen content variation. The computing means is also suitably adapted to utilize the operational data of the tap changer and to utilize the data to improve the analysis to better determine if the vacuum breaker has failed. In this way, the effect of switching the tap changer can be accounted for in evaluating the hydrogen content, so that the expected level of hydrogen content based on normal hydrogen content variation and also the hydrogen content increase resulting from switching can only be achieved with a fixed hydrogen content alarm level Can be used instead.

The computing means can be provided by a computer program that enhances the performance of the control system when installed in the control computer of the substation for electricity transmission, by adding the vacuum breaker malfunction determination function according to the present invention. Thus, the computer program will use signals from a properly installed hydrogen sensor in the OLTC oil filled containment chamber to enable it to determine if the vacuum circuit breaker is malfunctioning. The computer program will also provide a means for using signals representative of the operation of the OLTC to further enhance the determination. Signals indicative of the operation can be provided from the drive signals of the motor drive mechanism 9 already present in the control system, or actions are taken to provide corresponding signals in systems that have not used the signals so far . Signals are suitably received from the motor drive mechanism 9 when the motor drive mechanism 9 is operated or from the drive control unit 11 which provides these command signals to the motor 9. [

2A-2E schematically illustrate the switching sequence of the on-load tap-changer from position 6 to position 5 on the transformer winding.

The dominant electrical flows are indicated by gray arrows.

The sequence is specified as a symmetric flag cycle. This means that the main switching contact of the divertor switch is broken before the transition resistors are connected across the regulating step. This ensures maximum reliability when the switch is operating with overloads.

At rated load, breakage occurs at a first current of zero after disconnecting the contacts, which means an average arcing time of approximately 4-6 ms. The total time for the complete sequence is approximately 50 milliseconds. The tap switching operation time of the motor drive mechanism is approximately 5 s / step.

2a: selector contact V connects tap selector 6 and tap selector contact H on tap 5. Fig. The main contact x carries the load current.

2b: the main contact x is open. The load current passes through the resistor Ry and the resistor contact y.

2C: The resistor contact u is closed. The load current is shared between Ry and Ru. The circulating current is limited by the resistance added to Ru plus Ry.

2D: The resistor contact y is open. The load current passes through Ru and contact u.

2e: the main contact v is closed, the resistor Ru is bypassed, and the load current passes through the main contact v. The on-load tap-changer is in its current position (5).

Arcs arise in any of the movements in which the contacts are open.

Figures 3A-3H schematically illustrate the switching of the on-load tap-changer with vacuum breakers. By using the auxiliary contact system MC, RC in combination with the vacuum circuit breakers MVI, RVI, only two vacuum circuit breakers per phase are required.

Figure 3A shows the current path from x to the starting point (which may also be in the next phase) during normal operation. The main electrical path is indicated by gray arrows.

When replacing the load from x to v, the steps of the operational sequence are:

Figure 3b - opens the main vacuum circuit breaker (MVI), so that current flows through the transition resistor (TR).

3C, 3D - After that, the main contact MC is rotated to connect to v.

3e - after that, the main vacuum circuit breaker is closed, which means that the new taps are connected and cause an associated cycling current driven by the voltage potential difference.

Figure 3f - The transition resistor is disconnected when opening the resistor vacuum breakers (RVI). The load current passes through the normal path from the current v to the starting point.

Figure 3g - After that, the resistor contacts RC are rotated and in place.

3h. Finally, the sequence is completed and the next service position is reached when the resistor vacuum breaker is closed.

Fig. 4 is the same position as in Fig. 3C but has a difference that the main vacuum breaker MVI is not opened or the current in the main auxiliary contact MC is not blocked. When the main contact MC is rotated to connect with v, the current is blocked by the movement in the main auxiliary contact MC. The appearing arc is quenched by the oil, but some damage will occur when the auxiliary contacts are not designed to take on repeated arcs. If this occurs more than 10-500 times, there is a risk that, depending on the load current, the auxiliary contacts will fail and the OLTC will experience a catastrophic failure. If the current is blocked by auxiliary contacts and is quenched by oil, the hydrogen concentration will increase rapidly in the oil, and detecting this will be a sure way of indicating this error condition.

Figure 5 is a schematic diagram of an on-load tap-changer for use with embodiments of the present invention. The illustrated tap changer 12 is formed of two main parts, a diverter switch 24 and a tap selector 26, which are interconnected by connections 30. The diverter switch 24 may include a common upper housing 28.

6 shows a schematic diagram of a possible evolution of hydrogen content / concentration 46 in oil over time in the tap changer. The hydrogen detector measures the hydrogen content / concentration 46 in the oil, and the analysis of the measurements is made by comparing the measured data with different warning or alarm levels, for example warning level 40, first alarm level 41, 2 alarm level (42).

Each level may be associated with different actions. For example, if the hydrogen concentration is above the warning level 40 (43), the control system alerts the monitoring system for the transformer or the power plant wide control system to inform the operators that something is not OK in the tap diverter " If the hydrogen concentration is above the first alarm level 41 (44), the control system alerts operators to the monitoring system for the transformer or the plant wide control system, and will only perform the most essential tap conversions . If the hydrogen concentration is higher than the second alarm level (45), the control system alerts the monitoring system for the transformer or the plant wide control system, alerts the operators and stops all tap conversions.

Figure 7 shows a schematic diagram of a possible evolution of hydrogen content / concentration (46) in oil over time in the tap changer. The hydrogen detector measures the in-oil hydrogen concentration 46 and the analysis of the measurements performed by the computing means compares the measured hydrogen concentration data series with different warning or alarm levels for increased hydrogen concentration.

At reference numeral 52, the rate of increase of the measured hydrogen concentration is greater than the possible warning increase (50). At 53, the rate of increase of the measured hydrogen concentration is greater than the possible alarm increase (51). The analysis of the data series 46 may include smoothing or filtering of the measured values.

Figure 8 shows a schematic diagram of the possible evolution of hydrogen content / concentration 46 in oil over time in a tap changer, where each tap transition is associated with an up-tic of hydrogen concentration. This is to illustrate that the analysis system should also include the frequency of tab switching or the time between tabs. Multiple tap conversions 51 may produce a greater hydrogen increase rate than in case 50 using fewer taps. However, an increase 50 of the curve when using fewer taps may indicate a problem. The system should be able to disconnect both cases 50 and 51 and be suitably adapted to do so and provide warning / alarm for case 50 but not for case 51. [ The relative sizes of the curves and alarm levels in Figures 6-8 are for illustration purposes only.

It is known that arcs in insulating oil produce hydrogen in the oil. This effect is sometimes used to monitor the operation of the transformer. This is not used to monitor OLTCs without vacuum breakers, since arcs in the oil occur in normal operation.

With the introduction of the OLTCs with vacuum interrupters, the normal arcs in the oil have been removed and during normal operation all the arcs are generated in the vacuum interrupters. If an arc in the oil appears on the OLTC with vacuum breakers, this is an indication that something is seriously wrong.

As can be seen in Figure 2, in the case of a typical OLTC with arc quenching in oil operating according to the flag cycle principle, there are two interrupts with arcs occurring for all tap operations. One arc occurs when the main contact is broken (i.e., between FIGS. 2A and 2B), and one arc occurs when breaking the transition contacts (i.e., between FIGS. 2C and 2D).

The arc at the main contacts has the same current as the load current, but the current at the transition contacts is constituted by the half of the load current and the circulating current. The cycling current depends on the step voltage and the resistance of the transition resistor, and thus is load independent.

Each of these arcs typically lasts for a period of at most half, and the average will be half the period of 5 ms for 50 Hz. The energy in these arcs determines the amount of gas generated. Gas generation can be assumed to be linear with energy dissipation of the arcs.

The primary goal for OLTCs that arc quenched in vacuum interrupters is to prevent arcs in the oil. Arcing in oil provides several disadvantages, such as higher corrosion of contact materials in breakdown contacts and oil breakdown due to high temperatures in arcs. Oil decay creates materials that, in the presence of moisture, reduce the dielectric withstand of the oil and increase the wear of the mechanism.

The diverter switch disconnects current from one tap, which is done before connecting to the other tap. To avoid creating interruptions in the circuit, the load current passes through the transition contacts for the time it takes for the main contacts to safely disconnect the current from the tab 1 until the tab 2 is connected.

If there is a failure of the load in the OLTC, for example due to a faulty vacuum circuit breaker, there is a risk that the tap 2 will be connected before it is disconnected. Due to the electrical characteristics of the transformer, a single short circuit in the regulation stage causes enormous currents to destroy the OLTC and the transformer windings / windings. There will also be a serious risk of greater damage from fire, explosion, and so forth.

By designing the rectification of the currents to be carried out by the vacuum circuit breakers, they become critical components. If they fail to block, the serious defects described above may occur.

By designing the auxiliary contacts to block the load current or the circulating current in the event of a failure of the vacuum circuit breaker, a greater safety margin is obtained against these serious failures.

Since the auxiliary contacts are mainly made to conduct current, the materials are selected for low resistance and are not selected for good arc resistance. The goal is that they must be able to achieve a half cycle of operation and at the same time be able to block the rated load current with the function retained as both a current conductor and a broken contact at the maximum.

Thus, some management devices must provide alarms before they are so much destroyed by the arcs that the contacts do not meet their capabilities. The purpose is to provide an alarm to prevent the transformer from operating. There is no need to operate the transformer, as several operations are possible. A number of detection methods are possible, such as pressure detection, detection of oil flow (from the tube to the oil reservoir), light detection, radio emission detection, and the like.

The present invention addresses the possibility of using hydrogen concentration changes in insulating oil as a parameter for the detection of arcs in oil.

It is based on the fact that the arcs in the vacuum circuit breaker do not produce any gas in the oil. However, OLTCs with vacuum breakers for high currents generally have bypass contacts that bypass the vacuum circuit breaker circuit when the OLTC is in position, thereby preventing the vacuum circuit breakers from continuing to conduct current And protects them from short circuit currents.

The bypass contact will generate commutation sparks when current is rectified from the bypass path to the vacuum circuit breaker circuit due to small inductances in the circuit. These sparks will generate a small amount of hydrogen. Although the oil is only a few percent of the energy of the actual arc, there is energy to be released, and gas generation is associated with it.

These OLTCs without bypass contacts still have auxiliary contacts. They do not rectify any current, but are potentially short disconnected during switching, providing them with a voltage that causes small capacitive discharge spikes. The energy at these is less than the energy from the rectifying sparks at the bypass contacts, but will produce a small amount of hydrogen in the oil after a large amount of operation at the voltage.

Thus, the invention can be used in different types of OLTCs, e.g., OLTCs with bypass contacts and OLTCs without bypass contacts. The analysis performed by the computing means must be correspondingly adapted, but its main features may be the same.

The compositions of these gases cause about 75% hydrogen (H ₂ ) and about 20% acetylene (C ₂ H ₂ ). For small capacitive discharge sparks, the composition will be close to 100% hydrogen. Acetylene is readily soluble in oils due to its similarity to hydrocarbons in oil, but hydrogen is not readily soluble.

By analyzing the hydrogen content in the oil, cheaper and more reliable measurement devices are available compared to when hydrocarbons need to be analyzed. Continuous measurements of hydrogen in transformer oils are also a well-proven method that has been used for quite some time.

Therefore, measuring hydrogen in transformer oil is not new. The results should be interpreted in a way that provides a reliable method of management. The interpretation should operate at a low operating frequency, at low current, for at least many different applications when using different breathing systems.

There are two possible ways to interpret hydrogen measurements:

1. How to provide an alarm at a specific hydrogen concentration in oil

2. A method for evaluating the rate of hydrogen generation associated with the number of operations per unit of time and the load current at the time of switching.

Interpretation 1. Since there will be a certain amount of hydrogen that will disappear over time to the surrounding atmosphere, small occurrences will soon find equilibrium between generation and extinction, resulting in low and fairly constant concentrations. The alarm level can be set high enough to operate over the full range of load currents because the hydrogen generation for the arcs in the oil is so much higher. Arcs in the oil will provide a rapid rise in the concentration that will cause the alarm level to pass even at low load currents. Such a device does not require any intelligence, and is therefore a simple and inexpensive way.

Interpretation 2. This method requires some intelligence and availability of information about when the operations occur and the load on the transformer. However, it offers the advantage of being more sensitive and responsive, especially in applications with low currents and / or low operating frequency. This method is preferably used in conjunction with an ABB TEC or similar transformer control and protection system that already has access to the necessary data. Of course, it can be manufactured as a separate unit.

The interpretation is made up of a special program of the control system. The interpretation is made such that the change in hydrogen concentration is related to the spark energy emitted per time unit. The load current and the number of operations per unit time are available. Thus, the arc energy may be easily calculated, and the hydrogen concentration is related to it.

When the load is changed and / or the operating frequency is changed, the method has to be adapted to automatically calculate the expected values within a certain tolerance width. This width can be very large because the difference between the hydrogen evolution in normal service and the arcs in the oil is so different. Therefore, the calculation need not be very accurate.

Claims (14)

CLAIMS What is claimed is: 1. A method for detecting a failure of a vacuum circuit breaker in an on-load tap changer,
The on-load tap switching device includes:
- an oil filled housing;
A hydrogen sensor arranged inside the oil filled housing,
- diverter switch (3) comprising movable contacts (MC, RC), and
- at least one vacuum circuit breaker (MVI, RVI) arranged to interrupt the current through the movable contact of said diverter switch (3)
The method for detecting a failure of the vacuum circuit breaker comprises the steps of:
Measuring the hydrogen content of the oil,
- transferring the measurement data of the hydrogen content to the computing unit, and
- determining whether a fault is present in said vacuum circuit breaker (MVI, RVI) based on a measure of the hydrogen content of said oil,
Wherein the step of determining whether a failure exists in the vacuum circuit breaker comprises:
- receiving operational data of the on-load tap-changer,
Calculating an expected change in hydrogen content based on the mathematical model of the on-load tap-changer and the operating data of the on-load tap-changer, and
- determining whether a failure of said vacuum circuit breaker is present based on at least two of said hydrogen content measurements and an expected change in said calculated hydrogen content . The method according to claim 1,
A method of detecting a failure of the vacuum circuit breaker,
Storing a measure of the hydrogen content of the oil, and
- determining whether a fault exists in the vacuum circuit breaker (MVI, RVI) based on at least one stored measurement of the hydrogen content of the oil and the hydrogen content of the oil. / RTI > The method according to claim 1,
A method of detecting a failure of the vacuum circuit breaker,
- executing an action if a fault is determined in said vacuum circuit breaker. The method of claim 3,
The action includes:
- generating a warning. The method of claim 3,
The action includes:
- allowing only a limited number of critical operations that do not have an overload of said divertor switch. The method of claim 3,
The action includes:
- stopping said divertor switch from moving. The method according to claim 1,
The operation data comprising: A current of the contacts, and a load current. The method according to claim 1,
Wherein the step of determining whether a failure of the vacuum circuit breaker is present comprises:

Is true,

- parameters describing the currently measured hydrogen content,

- parameters describing previously measured hydrogen content,

An expected change in hydrogen content based on operating data, and
eps - a safety parameter that ensures that failure of the vacuum circuit breaker is not determined if the measured hydrogen increase is not greater than eps. An on-load tap-changer having means for detecting a failure of the vacuum circuit breaker in the on-load tap-changer,
Wherein the on-load tap switch comprises:
- an oil filled housing, a diverter switch (3) comprising movable contacts (MC, RC), vacuum breakers arranged in series to interrupt the current before the movable contacts (MC, RC) (MVI, RVI)
The on-load tap switching device includes:
Characterized in that the oil filled housing comprises a sensor (10) arranged to repeatedly measure the hydrogen content of the oil and communicatively connected to the computing means of the on-load tap-changer and to transmit the measuring signals of the hydrogen content to the computing means Respectively,
- the computing unit is configured to analyze the measurements of the hydrogen content of the oil and to determine if a fault exists in the vacuum breakers (MVI, RVI)
Wherein the computing unit is configured to receive operational data of the on-load tap-changer and the computing unit is configured to calculate an expected change in the hydrogen content and to calculate an expected change in the hydrogen content based on the analyzed measurements of the hydrogen content of the oil Is configured to determine a fault in the vacuum circuit breakers (MVI, RVI). 10. The method of claim 9,
Wherein said on-load tap-changer comprises a control system (11) for controlling the movement of said divertor switch, and said computing unit is operable, when a failure of said vacuum breakers (MVI, RVI) is detected, To-load tap-changer. 10. The method of claim 9,
Wherein the computing unit is configured to send a signal to the control system to stop or limit the movement of the diverter switch when a failure of the vacuum breakers (MVI, RVI) is detected. A computer program product for detecting a malfunction of a tap selector, comprising:
The computer program product is configured to perform the determining of the method of detecting a failure of the vacuum circuit breaker of any one of claims 1 to 8 when it is run on a computer. delete delete

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