EP1859331B1 - Method for controlling cooling on a power transformer - Google Patents

Abstract

The invention relates to a method for controlling devices for cooling an oil-filled power transformer with one or more cooling stages during which only the respective type of cooling of the transformer and the type of coolant for each existing cooling stage have to be input and by comparing with all non-volatile stored technically possible and meaningful combination possibilities, the corresponding characteristic quantities are determined for calculating the oil temperature or winding temperature.

Description

The invention relates to a method for controlling devices for cooling an oil-filled power transformer as a function of its oil or winding temperature.

Oil-filled power transformers are internationally characterized by their design and type of cooling with a 4-letter code. The first two letters refer to the type of cooling of the transformer itself; for this there is the abbreviation ON for "Oil Natural", OF for "Oil Forced", OP for "Oil Forced", but with an oil cooling system with axial pump, OD for "Oil Directed", as well as GF for "Gas Forced" (for transformers with SF ₆ cooling) as special design. The following two letters indicate the respective type of cooling medium; there are ON for "Air Natural", AF for "Air Forced", WF for "Water Forced".

By combining different types of cooling of transformers as well as different types of cooling medium therefore exist a variety of types of transformers, which can be represented by the illustrated coding.

Furthermore, an oil-filled power transformer usually has several cooling stages, which can be based on different types of cooling or types of cooling medium.

For controlling cooling devices on the power transformer, such as pumps or fans, which operate in the individual cooling stages, it is known to detect the respective temperature of the insulating oil or the winding temperature and to compare with a predetermined limit value for each cooling stage exceeding which the respective cooling device is put into operation; until the limit value of the respective stage has fallen below again.

The calculations of the explained instantaneous values of the temperature of the insulating oil or of the winding temperature are familiar to the person skilled in the art and are described in detail in the IEC 354 "Loading guide for oil-immersed power transformers", pages 25ff, in particular page 33f. Depending on the type of transformer and the respective cooling stage, this IEC defines the most varied variables and parameters as well as different calculation rules.

From the US 2002/0161558 A1 are a device and implicitly a corresponding method for controlling devices for cooling an oil-filled power transformer with at least one cooling stage depending on its oil or winding temperature known. In this case, the oil or winding temperature is determined according to the calculation rules of said IEC and compared as a basis for the actuation of the cooling stages with a respective corresponding limit. In this known device and the corresponding method must therefore first of all, separated for each cooling stage, the respective variables, the transformer type in combination with the respective Cooling method, laboriously selected from the IEC and entered into a corresponding control unit, so that a correct calculation of oil or winding temperature and subsequently a comparison can be made with a cooling level dependent limit value. Such input is cumbersome for the user. On the one hand, it is troublesome to take the individual parameters correctly from the IEC. Often, the IEC is not available to the user at the moment, often the operator is inexperienced in dealing with the extensive publication. On the other hand, errors in the selection of the respective parameters and formulas from the standards and their manual transmission can occur in a corresponding control unit.

This is where the invention starts. The object of the invention is to provide a method that decreases the user this complex activities.

This object is achieved by a method having the features of the claim. In this method, it is only necessary to identify the type and types of cooling of the respective power transformer and to specify the above-explained letter-coded characterization of the respective type of cooling of the transformer and the cooling medium in its respective cooling stages. These few necessary details about the power transformer are known to the user; They are included on the type plate and can be easily, easily and without transmission errors in a corresponding control unit.

The method according to the invention makes use of the circumstance that the calculation rules to be used for calculating the specific oil and winding temperatures, including the respective variables and parameters, are clearly defined in the cited IEC and must therefore be used by the user. Therefore, these values are already stored non-volatile in the factory, so that practically only one parameter has to be entered manually: The 4-letter coding for each existing cooling stage of the corresponding power transformer.

Only if the IEC changes, if the specified parameters and calculation rules change, a change of the non-volatile stored values would be necessary. However, since such changes to relevant criteria are only rarely expected in binding standards, at most after several years, the cost of such internal post-parameterization can be accepted.

To perform the process, for example, the offered by the Applicant electronic control unit TAPCON ^® is the 260th

Figur 1

das erfindungsgemäße Verfahren in schematischer Darstellung aller nacheinander ablaufender Verfahrensschritte

Figur 2

eine erweiterte Darstellung wichtiger Verfahrensschritte sowie der Parameterauswahl beim erfindungsgemäßen Verfahren.

The invention will be explained in more detail by way of example with reference to drawings. Show it:

FIG. 1

the method according to the invention in a schematic representation of all sequentially proceeding process steps

FIG. 2

an expanded view of important process steps and the selection of parameters in the inventive method.

First should be on hand of FIG. 1 the complete procedure will be described.

A unique non-volatile storage of all possible 4-letter codes and the associated specific variables and calculation instructions according to the explained IEC is made in the factory in the respective controller or the electronic control unit in which the process is to run.

Furthermore, the non-volatile storage of limit values θ ₁ ... Θ _n for the oil or winding temperature for each cooling stage 1... N present at the corresponding power transformer initially takes place.

After this is done, the actual process can begin. First, the input of each type of cooling of the transformer and the type of cooling medium for each existing cooling stage 1 ... n separated in 4-letter code.

Subsequently, in the computer from the non-volatilely stored value pairs of all possible 4-letter codes, the reading of the according to IEC applicable computation rules, variables and constants for the entered values for the respective calculation of oil or winding temperature θ.

The actual calculation of the current actual oil or winding temperature θ is carried out below with these values.

This calculation is made in accordance with the specific requirements of IEC 354 applicable to the particular transformer. For this calculation, the top oil temperature, the load current, the load factor - that is the quotient of the load current and the rated current - and other specific ones provided by the IEC Parameter used.

Subsequently, a comparison of the calculated oil or winding temperature θ with the limit value θ ₁ ... θ _n for each cooling stage 1 ... n separated. For this comparison, the non-volatile stored limit values θ ₁ ... θ _n are used.

By the term "separate comparison" is meant that it is first checked whether the calculated value θ exceeds the limit value θ ₁ , for the first cooling stage. If this is the case, the first cooling stage is activated. Furthermore, it is checked whether the calculated value θ is so large that, moreover, it also exceeds the limit value θ _{2 of} the second cooling stage. In such a case, the second cooling stage is activated. This comparison is continued for any further cooling stages in an analogous manner.

In addition, if the limit value θ _n for the last (highest) existing cooling stage n is exceeded, it is also advisable to initiate the triggering of a warning, possibly also the stopping of the transformer.

The most important procedural steps will be described below with reference to FIG. 2 be clarified once again. The control unit used for carrying out the method in this example has four switching contacts S1 ... S4; it is suitable for a transformer with up to four different cooling levels 1 ... 4. If fewer cooling stages are available for the respective transformer, the remaining contacts remain unused.

In the upper part of FIG. 2 It is shown how the respective type of cooling (these are the first two capital letters) and the corresponding type of cooling medium (these are the following two capital letters) results in the already discussed 4-letter coding.

Cooling level 0, d. H. Normal operation is usually always called ONAN. Cooling stages with the same type of cooling are indicated in ascending order with an index beginning with the number 1. Each cooling stage is associated with characteristic parameters, the gradient gr, the winding exponent y and the winding time constant tau, which depend on the type of transformer and the type of cooling, and thus on the respective 4-letter coding.

In the middle of FIG. 2 the matrix of all possible 4-letter encodings and the associated explained parameters are shown as stored non-volatilely.

From this matrix, the respective relevant parameters are read out, which result from the input of the transformer and cooling type specifically for the individual cooling stages. These parameters are then used to calculate the current oil or winding temperature θ.

In the lower part of FIG. 2 is the non-volatile storage of the limits θ ₁ ... θ _n for each cooling stage 1 ... n - here expressed as a percentage switching point expressed in degrees Celsius above the respective calculated winding temperature θ.

The described comparison of the calculated temperature θ with the respective limit value θ ₁ ,... Θ _n for each cooling stage 1... N is subsequently carried out using these non-volatile stored values. In the example shown here, the transformer actually has four cooling stages 1... 4, so that all contacts S1... S4 present on the control unit are occupied here.

In addition, in this example, two more switching contacts 5 and 6 are provided, the switching contact 5 when exceeding the limit θ ₄ for the last cooling stage 4 triggers a warning signal that signals that the regular cooling stages are obviously not able to (over ) heated power transformer to cool down again. One reason for this can be z. B. are in a failed pump.

Another switching contact 6 is triggered, although the limit value for this warning message is still significantly exceeded; then the entire transformer is shut down to prevent damage.

In the example shown, the cooling stages 1... 3 are designed in the ONAF design and, as explained above, are therefore supplemented by an index 1. The last cooling stage 4 in this example is of the OPAF type.

In principle, both the calculated oil temperature and the calculated winding temperature can be used as the comparison variable in the method according to the invention, which is why here consistently both types of calculated temperature are provided with the same reference symbol θ. Differences arise, however, in terms of responsiveness, since the winding temperature changes much faster than the oil temperature, which follows with a certain inertia of this.

Claims (1)

1. Method for controlling installations for cooling an oil-filled power transformer with at least one cooling stage (1...n) in dependence on the power transformer's oil or winding temperature ζ ., whereby the oil or winding temperature ζ. is calculated in compliance with the IEC specifications and compared with a respective limit value, so that information for activating the minimum number of at least one cooling stage results from the comparison,
   so that the respective cooling stage (1...n) is activated if its respective limit value ζ₁...ζ_n is exceeded
   and an alert, an error message or the triggering of a protective switch is actuated if the actual oil or winding temperature ζ also exceeds a limit value of the last cooling stage (n),
   characterised by the fact
   that the type of the respective transformer cooling system and the type of the coolant are entered separately in a 4-letter code for each existing cooling stage (1..n),
   that the respective 4-letter code that has been entered is compared with a non-volatile table stored in advance of all technically possible 4-letter codes and with the attributed specific variables and calculation specifications in compliance with IEC, that the respective calculation specifications, variables and constants for calculating the oil or winding temperature ζ. for the entered 4-letter code are determined and that each calculated oil or winding temperature ζ is compared with each non-volatile stored limit value ζ₁...ζ_n for the oil or winding temperature of each existing cooling stage (1...n).

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