WO2005022573A1

WO2005022573A1 - Method for monitoring insulating oil

Info

Publication number: WO2005022573A1
Application number: PCT/EP2004/005175
Authority: WO
Inventors: Rainer Frotscher; Konrad Roider
Original assignee: Maschinenfabrik Reinhausen Gmbh
Priority date: 2003-07-30
Filing date: 2004-05-14
Publication date: 2005-03-10
Also published as: DE10334688B3; EP1649475B1; ATE424031T1; PT1649475E; ES2321516T3; DE502004009048D1; EP1649475A1

Abstract

The invention relates to a method for monitoring the contamination of insulating oil in load tap changers, whereby only the latest transformer load current is measured, and the transfer of rust to be expected is determined by means of calculation while taking the parameters specific to the load tap changer into account. This eliminates the need for sensors and other components inside the load tap changer.

Description

Process for monitoring insulating oil

The invention relates to a method for monitoring the contamination of insulating oil in on-load tap-changers.

Most of the on-load tap-changers currently commercially available for uninterrupted switching under load between different winding taps of a tap-changer, often also referred to as "tap-changer" for short, still work with mechanical switch contacts in insulating oil. A typical on-load tap-changer of this type with a separate oil container in which the So-called diverter switch is arranged, is described in the company publication "tap changer type M and MS" of the applicant, printing imprint VK03 / 93de-0793/2000.

Every time the diverter switch contacts of such an oil-filled on-load tap-changer are actuated, brief arcs occur in the insulating oil, which over time lead to its decomposition and soot formation.

Oil filter systems are known for cleaning the insulating oil, for example from the company publication of the applicant "Oil filter system OF100", pressure imprint IN173 / 01 de-1099/1000, which have a filter insert which cleans the insulating oil and can also dry it at the same time.

Nevertheless, it is necessary to change the insulating oil in the on-load tap-changer at certain intervals, especially since by no means all of these on-load tap-changers are equipped with an oil filter system, which can be supplied as special equipment.

So far, no satisfactory method has been known for reliably determining when the insulating oil actually needs to be changed. As a rule, the manufacturers make do by prescribing a change after reaching fixed switching numbers; For safety reasons and product liability reasons, reserves are of course provided so that the insulating oil is often not yet used up when it is changed according to such a rigid scheme. This causes unnecessary costs for the operator.

Furthermore, such insulating oil change intervals are also after certain periods, e.g. B. after 8 years. With such a rigid timing, the number of switching operations actually completed during this period is of course not taken into account; this is also unsatisfactory for the operator. Numerous oil sensors are known for other oils, in particular oils in internal combustion engines, which are arranged there in the oil pan and are intended to determine the oil condition. These are based on a wide variety of physical principles, but they are not all readily applicable to on-load tap-changers. In internal combustion engines, criteria such as viscosity, lubricity and cooling ability are important for evaluating the quality of the oil, while the dielectric or insulating properties, which are particularly important for on-load tap-changers, are not important.

In addition, the arrangement of an oil sensor, however designed, in the on-load tap-changer is on the one hand unsuitable for a retrofit solution, and on the other hand, because of the required electrical connection lines from the sensor inside the oil tank to the outside, it is undesirable for reasons of dielectric strength and is also only difficult to implement.

The object of the invention is therefore to provide a method for monitoring the insulating oil, d. H. the determination of its current state, to be specified in an on-load tap-changer that does not require an additional sensor or other components inside the oil container, but nevertheless provides information that depends on the actual situation and whether, and if so when, the insulating oil must be changed.

Another object of the invention is to replace the previously rigid oil change intervals with condition-dependent maintenance, but at least to significantly extend these maintenance intervals by overlaying them with a condition-dependent component.

According to the invention, these objects are achieved by a method having the method steps of the first claim. The subclaims relate to particularly advantageous developments of the method according to the invention.

The general inventive idea is to use the arc energy released during a power shift under oil to determine the oil soot of the insulating oil and to derive the information about the required oil change from the progressive degree of the oil contamination determined in this way.

For the first time, the method according to the invention therefore uses only a measured electrical variable for determining the soot content; it therefore does not require any additional sensors or other components inside the on-load tap-changer.

As explained, the method according to the invention is based on the arc energy E, which is released under oil during a load switching. The oil decomposes and produces soot. Switch and resistance contacts of the on-load tap-changer with their different switching currents contribute their respective - different - share. The individual switching currents are measured using the measured current transformer load current determined. This load current is the only variable input variable that has to be measured.

In the method according to the invention, the arc energy E generally results for each

Operation of the on-load tap-changer as follows:

E = ∑JU _L b- AnzSek [Ws]

It is

∑J = USKMJWKI d. that is, the amounts of the switching currents for both the

Switch contact and the resistance contact or the resistance contacts determined.

This happens for the switch contact according to the relationship

J ^J s ^κ ParSec

and for the resistance contact about the relationship

2 - R _ü

ParSek means the number of parallel sectors of the diverter switch, ie the parallel connection of individual switch contacts, U _s is the respective nominal step voltage and S _res is the resulting current division. R _ü denotes the size of the contact resistance. The quantities mentioned are all tap-changer-specific and are not stored volatile as on-load tap-changer parameters, ie they are defined before the start of the process.

The calculation of the individual switching currents with the aid of the measured current transformer load current itself is already known from DE 100 03 918 C1. However, there it is a procedural step for a method for the volume determination of the contact erosion or its monitoring. This publication does not deal with any kind of monitoring of the condition of insulating oil. However, it has surprisingly been found that the calculation of the individual switching currents can also be used according to the invention for monitoring the soot content.

The arc energy E occurring in the respective load switching is then determined in the invention in accordance with the above relationship: E = ∑JU _Lb -tLb-AnzSek [Ws] The AnzSek factor designates the number of diverter switch sectors or switching segments. U _Lb denotes the mean arc voltage and t _Lb the mean arc time. These factors are also switch-dependent and belong to the on-load tap-changer parameters that have not been saved in advance.

The respectively determined arc energies are summed up with each load switching and result in the accumulated arc energy GE, which is compared with a previously set and also non-volatile stored value GE _max ; depending on the comparison, warning or shutdown functions can be generated. Experience has shown that a practical limit value can be set with GE _max = 50,000 KWs.

Since only small amounts of soot are produced or calculated at very low load currents, the limit value GE _{max would} in such a case occur during the entire lifetime of the on-load tap-changer and the like. U. never be reached. Therefore, after a first development of the method according to the invention, an additional check is carried out to determine whether a maximum number of load shifts has been reached. If this is the case, a warning or the like is generated, irrespective of the level of the total arc energy GE.

For the same reason, after a second development of the method according to the invention, an additional check is carried out to determine whether a specific time interval from commissioning, ie H. a maximum permissible operating time that can be allowed to the on-load tap-changer without intermediate maintenance has been reached. If this is the case, a warning or the like is generated - again regardless of the amount of the arc energy GE added up to that point.

The two described developments of the method according to the invention can also be combined.

These further developments take into account the fact that not only the increasing soot entry leads to a decrease in the breakdown voltage of the insulating oil, but also an increasing moisture content, resulting aging and cracking products or the like can render the insulating oil unusable over time. However, these factors are not directly dependent on the arc energy, so that in many cases it may make sense to replace the insulating oil, even if this alone would not be necessary after comparing the cumulative arc energy GE with the predetermined limit value GE _max .

The invention will be explained in more detail below by way of example. Figure 1 shows the flow chart of a first method according to the invention

Figure 2 shows the flow chart of a second method according to the invention

FIG. 3 shows the flow chart of a third method according to the invention

FIG. 4 shows the flow chart of a fourth method according to the invention.

First, the method shown in Figure 1 will be explained in more detail. At the beginning, there is an input and non-volatile storage of specific constant on-load tap-changer parameters or characteristic data. These are the maximum permissible limit value of the arc energy GE _max , the number of parallel sectors of the diverter switch ParSek, the nominal step voltages U _s in each operating position of the step switch (or, alternatively, the mean step voltage). Furthermore, these are the average arc voltage U _Lb and the average arc time tu. For a step switch of the applicant of the type “M” mentioned at the beginning, for example, a value U | _b = 25 V and a value tu = 6 x 10 ^"3 s result. Finally, the switch type-dependent number of diverter switch sectors AnzSek, the resulting current division S _res and the size of the contact resistance R _{ü must also be} entered.

The variable n denotes an index that is increased by 1 each time the on-load tap-changer is actuated.

In the method according to the invention, the load current J _{L is first} measured each time the on-load tap-changer is actuated. In the next step of the method, the switching currents J _S κ and J _{wκ of} the disconnecting contacts, more precisely the switching and resistance contacts, are determined. Such a determination has already been explained in detail with the aid of on-load tap-changer-specific parameters. Again, these switching currents are added together and result in ∑J. The arc energy E _n occurring in the respective load switching is then calculated and finally the cumulative arc energy GE _{n is} determined therefrom. The value of the accumulated arc energy GE _n is in each case temporarily stored and, upon the next actuation, together with the then again calculated arc energy E _{π +} ι, the new total value GE _{π +} ι is then accumulated.

In each cycle, this cumulative arc energy GE _n is then compared with a previously set limit value GE _max . A two-stage comparison is shown as an example in FIG. Is a certain percentage of the limit value GE _max reached, e.g. B. 90%, a warning can be generated, which indicates an upcoming oil change. The operator can then take appropriate precautions and still have enough time to carry out such an oil change e.g. B. to be carried out as part of a maintenance. Once 100% of the limit value has been reached, a second, more conspicuous warning message can be generated; alternatively, the transformer could also be switched off. Numerous other comparison modes are of course conceivable within the scope of the invention; the only important thing is that the arc energy GE _n accumulated in the course of the load circuits is compared with a corresponding limit value. FIG. 2 shows a second method according to the invention, in which a check is also carried out to determine whether a certain total number of operations has been reached, ie the index n has reached a certain maximum value n _max .

Finally, FIG. 3 shows a further method in which, in addition to the method shown in FIG. 1, a check is also carried out to determine whether a certain absolute operating time t of the on-load tap changer has reached a limit value t _max .

It has already been explained above that with the process sequences shown in FIGS. 2 and 3 it is possible to take into account, in addition to the soot of the oil as the most important criterion for its aging, also other phenomena which, regardless of the accumulated arc energy GE, increase can make an oil change appear sensible at certain times. In Figures 2 and 3, these additional process steps are added to the end of the process shown in Figure 1; it is also possible within the scope of the invention to insert these method steps at a different point in the overall method. The only important thing is that the results of the additional comparisons with the permissible number of switching operations n _max or the permissible operating time t _{max can} also lead to warnings or the like, regardless of the comparison of the cumulative arc energy GE _π with its maximum value GE _max .

Finally, FIG. 4 shows a method in which both the additional number of switching operations n and the operating time t are compared with corresponding limit values n _max and t _max . This can also be inserted at various points in the process sequence according to FIG. 1.

Claims

claims

1. Procedure for monitoring the contamination of insulating oil in on-load tap-changers with the following features:

- Entry and non-volatile storage of the characteristic on-load tap-changer parameters and a limit value of the permissible arc energy GE _max

- Increasing an index n with each switchover, d. H. Actuation of the on-load tap-changer

- Measurement of the transformer load current J [_ during the switchover

- Determining the switching _current J _{sκ of} the switching contact that switches off and the switching _current J _w ″ of the at least one switching contact that switches off

- Sum of the amounts of the determined switching currents J _S κ and J _W κ to the total switching current

ΣJ

- Determination of the arc energy E _π using the relationship E = ∑JU _Lb -t _Lb -AnzSek [Ws] where U _{Lb is} the average arc voltage, tu, the average arc time and AnzSek the number of diverter switch sectors or switching segments and not these factors volatile stored on-load tap-changer parameters

- Determination of the cumulative total arc energy GE _n = GE _π-1 + E _n as the sum of the determined arc energies of all previous switchovers (1 ... n)

- Comparison of the accumulated arc energy GE _n with the limit value of the arc energy GE _max and generation of messages when this limit value is exceeded or a predetermined percentage of this limit value.

2. The method of claim 1, wherein the switching current J _S κ for the switch contact according to the relationship

^{Jsκ "} ParSec

and the switching current J _κ for the resistance contact according to the relationship R "

U _S + J _L

I _ ^S res w ^κ ~ 2 - R _ü

ParSek determines the number of parallel sectors of the on-load tap-changer, i.e. the parallel connection of individual switch contacts, U _s the respective nominal step voltage, S _res the resulting current division and R _ü the size of the transition resistance and these values refer to the non-volatile specific ones On-load tap-changer parameters belong.

3. The method according to claim 1 or 2, wherein additionally the current index n is compared with a predetermined limit value nm _ax and a message is generated when this limit value n _{max is} reached.

4. The method of claim 1 or 2 or 3, wherein in addition the operating time t of the on-load tap-changer in each case compared with a predetermined limit value t _max and a message is generated when this limit value t _{max is} reached.