Title of Invention

METHOD OF MONITORING THE FUNCTIONAL CAPABILITY OF A TAP SELECTOR

Abstract

A method of monitoring the functional capability of a tap selector actuable by electrically- I operated drIVe means to carry out changeover between loads comprises the steps of measuring effective current and voltage values at an electric motor of the drive means,determining the motor torque in dependence on the motor actual power as calculated from the measured values, and detecting the tap selector setting. Torque and setting values can then be correlated and compared with stored target values. Alternatively, a torque course can be formed, normalised with respect to time to exclude differences dependent on rotational direction of the drive, and subdivided into time ranges corresponding with different stages in the load changeover sequence. Values of the time ranges can then be compared with stored target values. If the result of the target and actual value comparison shows that a preset threshold has been exceeded, an appropriate warning or drive shutdown signal can be issued.

Full Text

The present invention relates to a method of monitoring the functional capability of a tap selector, especially a tap selector which serves for uninterrupted switching over between taps of a tapped transformer. It is known from German (Federal Republic) Patent Specification 42 14 431 that the motorized drive associated with a tap selector can provide specific data. These are data about the tap setting, the respective actual setting of the tap selector during a load changeover process, the reaching of the upper and lower end settings, the selected mode of operation, the tripping of a motor circuit breaker, etc. These data are not sufficient, however, to monitor the tap selector for operating capability. Also known is a microprocessor-controlled voltage regulator of type TCS (see company brochure of Maschinenfabrik Reinhausen GmbH: Mikroprozessorgesteuerter Spannungsregler TCS, imprint VK34/96 de - 0896/1000), which realises certain monitoring functions, for example monitoring the circuit reactive current between two transformers connected in parallel, realizing excess-current blocking of the tap selector, monitoring for under-voltage, monitoring for over-voltage with safety switching off, and comparison of target and actual values of the regulated voltage. In this case, too, no data is detected which allow a direct monitoring of the operational state of the tap selector. Only current and voltage are present as input magnitudes and these cannot provide suitable statements about the operational state without additional data and special methods for data processing. Moreover, it is known from Japanese Patent Application JP-60-176213 A to detect and store the torque of a drive shaft, which leads from the motorized drive to the tap selector switching system, in order to compare this actual torque course with a characteristic target torque course specific to type. A similar method is later described in German (Democratic Republic) Patent DD 246 409; according to that, the torque course over time is to be measured during a load changeover and the result compared with the typical torque course over time for the respective tap selector. If an impermissible deviation of the actual course from the target course occurs, switching-off shall take place. Due to the difficulty of detecting torque, however, this method has not been carried into practice in the past. Finally, it has been proposed to ascertain torque not directly by mechanical measuring means, but indirectly by detection of the actual power of the drive motor producing the torque. This, too, has evidently not been realised in the past. It is the object of the invention to provide a method of monitoring the functional capability of a tap selector, especially a method by which, proceeding from readily ascertainable electrical measurement magnitudes, reliable monitoring of the tap selector may be possible and, on occurrence of detected faulty functions, appropriate reactions may be carried out. According to a first aspect of the invention there is provided a method of monitoring the functional capability of a tap selector actable by electrically-operated drive to carry out changeover between loads, comprising the steps of measuring the effective values of voltage and current at an electric motor of the drive during actuation of the tap selector, calculating the motor actual power from the measured values, determining the motor torque from the calculated actual power, detecting the actual setting of the tap selector during actuation thereof, associating values indicative of determined torques with values indicative of detected tap selector settings at which those torque values have arisen so as to form actual value pairs, comparing the formed actual value pairs with stored target value pairs specific to the respective tap selector, and generating warning or drive shutdown signals in the event of the differences between compared value pairs exceeding predetermined thresholds. According to a second aspect of the invention there is provided a method of monitoring a tap selector, characterised by the following method steps: -during the load changeover, i.e. the actuation of the tap selector, the effective values of voltage and current at the drive motor of an associated motorized drive are measured, -the actual power is calculated from these values and from that in turn the torque is determined, a detection of the position of the respective actual setting of the tap selector is carried out at the same time, the values, which have been determined over time, for the torque are stored, subsequently a synchronisation is effected by a synchronising pulse which is produced on the reaching of a characteristic state in the load changeover at a specific time instant, for example on triggering offered storage means, subsequently the normalized course of the torque is broken down into typical time ranges which correspond with determined parts of the changeover sequence specific to the tap selector, the torque values in these time ranges are respectively compared with previously stored characteristic target values, and in the event of deviations, which exceed specific predetermined thresholds, of the compared value pairs from one another, signals are generated which stop the motorised drive and thus the tap selector or indicate maintenance. A method exemplifying the invention may permit, in simple manner, monitoring of the tap selector during the entire time of the load changeover, i.e. the actuation of the coupled motorised drive. It is possible, on the basis of the ascertained torque courses, to associate respective specific parts of these torque courses with the corresponding time periods of the load changeover sequence. Thus, conclusions are possible about the function of individual subassemblies, such as preselector or reverse, fine selector and load changeover switch, of the tap selector, which subassemblies are actuated in succession in a specific sequence, typical to the tap selector, in every load changeover. Examples of the method of the invention will now be more particularity described with reference to the accompanying drawings, in which: Fig. 1 is a diagram illustrating steps in a method exemplifying the invention; Figs. 2a) and b) are diagrams showing two typical detected torque courses in opposite rotational directions of a motorised drive of a tap selector monitored by a method exemplifying the invention; and Fig. 3 is a diagram illustrating additional steps in a modified method exemplifying the invention. Referring now to the drawings there is shown in Fig. 1 the steps involved in monitoring the functional capability of a tap selector with an electrically-powered motorised drive by which the tap selector is actuable to perform load changeover. Initially, the effective values of the current and the voltage at the drive are ascertained at each load changeover and the actual power is calculated therefrom in known manner and from that, in turn, the corresponding torque. At the same time a position determination is carried out in the motorised drive, i.e. it is ascertained which region of the switching sequence has just been run through in the load changeover process. From that it can be determined in which actual position the individual subassemblies, such as preselector, selector and load changeover switch, are disposed within the switching sequence. This position detection can be carried out in particularly advantageous manner by means of a resolver, which allows a continuous detection. Subsequently, in accordance with a first method exemplifying the invention, value pairs are formed on the one hand from the determined positions during the load changeover process, which positions can be stepped, for example raftered, almost as finely as desired, and on the other hand from torque values ascertained at these positions. These ascertained value pairs are compared with previously stored value pairs, the target values and limit values, specific to the tap selector. Specific status reports are issued according to the result of this comparison. If the comparison yields an agreement of the respectively corresponding actual value pairs with the target value pairs, an "OK" report is produced. This can, however, be suppressed. If the comparison shows deviations within certain preset limits and/or only in a similarly preset number of value pairs, a report is produced which indicates that maintenance is due, without interrupting the normal operation of the tap selector. If, however, the deviations exceed the preset limits, an error report is produced which stops the drive. In accordance with a second method exemplifying the invention, the same initial method steps, i.e. ascertaining the effective values of current and voltage and carrying out a position determination at the same time, are performed. Subsequently, in this method an association of the determined torques is carried out over time, which corresponds with the rotational angle covered during the load changeover. In that case an actual value of the torque is produced at uniform short time intervals, for example every 20 milliseconds, and stored in a ring buffer. Synchronisation by means of a synchronising pulse is then carried out. Such a synchronising pulse is generated from the start of a particular characteristic function rundown during the load changeover sequence, at a time instant tsyn (Figs. 2a) and b)). The triggering of a force storage device, which initiates the abrupt actuation of the load changeover switch, can be used with for the generation of this synchronising pulse. There thus takes place a measurement value recording according to the known principle of a transient recorder. The advantages of this procedure are explained in the following by reference to Figs. 2a) and b). Fig. 2a) shows a measured torque course during the time t of the load changeover or over the path s which the tap selector covers during a load changeover in one rotational sense of the drive shaft of the motorised drive. Fig. 2b) shows another measured torque course in opposite rotational sense of the drive shaft, i.e. opposite switching direction. It can be seen that due to mechanical tolerances in the gear train, to initial breakaway torques and to other influences and in dependence on the rotational direction, different times after the starting of the motorised drive at a time instant to result until attainment of a first characteristic point of the torque course at a time instant to. The corresponding courses are thus not comparable without further measures and firstly have to be normalized in terms of time. This is effected by the already mentioned synchronisation. Subsequently, in this method the torque course synchronised in such a manner is broken down into characteristic parts, so-called windows. In that case each window corresponds to a characteristic stage of the elapsing load changeover sequence. Such windows can comprise, for example, the time period of the actuation of the preselector, the fine selector or even the load changeover switch. Each window is bounded by two characteristic time instants which fix the beginning and end of the window in terms of time, thus to - ti, ti . Each torque value in these windows is compared with a previously stored target value. Through this selective comparison not only a deviation of the actual values from the target values of the torque, and thus a fault, can be detected, but also an occurring fault can be assigned to the specific subassembly which causes it. Apart from the described fault detection, a trend analysis of the mechanical components is possible at the same time. In addition, it is obviously also possible with both methods exemplifying the invention to preset a maximum value for the torque, on the exceeding of which value a stopping of the motorised drive is immediately effected independently of other criteria. In a modification, account can be taken of magnitudes relating to other parameters of the tap selector, as illustrated in Fig. 3. In that case, in addition to the described detection of actual motor power and thus torque on the one hand and the position detection of the tap selector on the other hand, measured temperatures of the insulating medium in the load changeover switch, the transformer oil in which usually also the selector of the tap selector is disposed, and the ambient air are taken into consideration. Moreover, the burning of contacts of the load changeover switch can be ascertained and utilized, by way of a burning model, in the determination of the operational state. WE CLAIM:- 1. A method of monitoring the functional capability of a tap selector actuable by electrically-operated drive means to carry out changeover between loads, comprising the steps of measuring the effective values of voltage and current at an electric motor of the drive means during actuation of the tap selector, calculating the motor actual power from the measured values, determining the motor torque from the calculated actual power, detecting the actual setting of the tap selector during actuation thereof, associating values indicative of determined torques with values indicative of detected tap selector settings at which those torque values have arisen so as to form actual value pairs, comparing the formed actual value pairs with stored target value pairs specific to the respective tap selector, and generating warning or drive shutdown signals in the event of the differences between compared value pairs exceeding predetermined thresholds. 2. A method according to claim 1, comprising the step of correcting the stored target value pairs in dependence on measured ambient temperature. 3. A method of monitoring the functional capability of a tap selector actuable by electrically-operated drive means to carry out changeover between loads, comprising the steps of measuring the effective values of voltage and current at an electric motor of the drive means during actuation of the tap selector, calculating the motor actual power from the measured values, determining the motor torque from the calculated actual power, detecting the actual setting of the tap selector during actuation thereof, storing values indicative of the determined torque to provide a torque course over time, normalising the torque course with respect to time by means of a synchronising pulse produced on reaching a given characteristic state in the load changeover sequence at a specific time instant, resolving the normalised torque course into time ranges corresponding with predetermined stages of the load changeover sequence, the sequence stages being specific to the respective tap selector, comparing actual torque values of the time ranges with stored target values, and generating warning or drive shutdown signals in the event of the differences between compared torque values exceeding predetermined thresholds. 4. A method according to claim 3, wherein the given characteristic state in the load changeover sequence is the triggering offeree storage means in tap switching means of the tap selector. 5. A method according to any one of the preceding claims, wherein the step of detecting the actual setting of the tap selector is carried out continuously by means of a resolver. 6. A method according to any one of the preceding claims, wherein the step of comparing is carried out with consideration of measured magnitudes relating to parameters of the tap selector operation. 7. A method according to claim 6, wherein the parameters comprise at least one of oil temperature of load changeover switching means of the tap selector, oil temperature of a transformer associated with the tap selector, ambient air temperature and degree of burning of mechanical contacts of the switching means. 8. A method according to any one of the preceding claims and substantially as hereinbefore described with reference to Fig. 1 or Fig. 3 of the accompanying drawings.

Documents:

2246-mas-1998-abstract.pdf

2246-mas-1998-claims filed.pdf

2246-mas-1998-claims granted.pdf

2246-mas-1998-correspondnece-others.pdf

2246-mas-1998-correspondnece-po.pdf

2246-mas-1998-description(complete)filed.pdf

2246-mas-1998-description(complete)granted.pdf

2246-mas-1998-drawings.pdf

2246-mas-1998-form 1.pdf

2246-mas-1998-form 26.pdf

2246-mas-1998-form 3.pdf

2246-mas-1998-form 4.pdf

2246-mas-1998-form 5.pdf