Method of determining an operational setting of an on-load tap changer

Abstract

An operational setting of an on-load tap changer used to switch between various winding taps of a tapped transformer is determined by first placing the on-load tap changer in operation with the tapped transformer and then moving the changer in a first rotational direction through a regulating range of its stationary operational settings on different winding taps of the tapped transformer toward an end abutment of the tapped transformer. The position is registered on reaching the end abutment of the regulating range of the on-load tap changer, and then the movement is reversed to return to the first stationary operational setting that is then configured as a predefined operational setting with the help of the parameterization that is stored in a nonvolatile memory of the control device.

Claims

1. A method of determining a predefined operational setting of an on-load tap changer actuatable by a motor drive for switching between different winding taps of a tapped transformer, the method comprising the steps of: placing the on-load tap changer in operation with the tapped transformer; thereafter activating the motor drive by a parameterized control device in a first rotational direction so that the on-load tap changer begins to run through its stationary operational settings on different winding taps of the tapped transformer toward a first winding tap of the tapped transformer; detecting reaching of an end abutment of the regulating range of the on-load tap changer by the parameterized control device; activating the motor drive by the parameterized control device in a second opposite rotational direction so that the on load tap changer subsequently runs through the regulating range until reaching the first stationary operational setting; and subsequently configuring the first stationary operating setting as a predefined operational setting with the help of the parameterization that is stored in a nonvolatile memory of the control device.

2. The method defined in claim 1, further comprising the steps of: detecting reaching of the end abutment of the on-load tap changer by the control device by the substeps of: monitoring a current intensity of the motor drive after activation thereof in a first rotational direction subject to nonvolatile storage, comparing this current intensity subject to nonvolatile storage at defined intervals in time with a maximum value parameterized as current limit value in the control device, and if a previously defined target value is exceeded by the instantaneously determined current intensity, generating an electrical signal by the control device so that the control device indicates the mechanical end abutment of the on-load tap changer.

3. The method defined in claim 1, wherein reaching of the end abutment of the on-load tap changer is detected by the control device by the substeps of: detecting the rotational speed of the drive shaft of the motor drive by a sensor at regular intervals in time and, on reaching the determined value of 0 of the rotational speed, generating an electrical signal by the control device so that the control device indicates the mechanical end abutment of the on-load tap changer.

4. The method defined in claim 1, further comprising the steps of: detecting reaching of the end abutment of the on-load tap changer by the control device in that during transit of the regulating range of the on-load tap changer in a first rotational direction a reporting contact is connected on each attainment of a next stationary operational setting, storing the trigger instant in a nonvolatile memory of the control device, comparing the time between two trigger instants with a maximum permissible limit value, and if the maximum permissible limit value is exceeded, generating an electrical signal so that the control device indicates the mechanical end abutment of the on-load tap changer.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) A method according to the invention shall be explained in more detail in the following by way of example on the basis of a single FIGURE that is a schematic flow chart of the method according to the invention.

SPECIFIC DESCRIPTION OF THE INVENTION

(2) Placing an on-load tap changer together with a tapped transformer into operation forms the starting point of the method according to the invention. When placed in operation, the on-load tap changer is connected by its connecting contacts with the regulating winding of the tapped transformer, the motor drive is mounted and the on-load tap changer and the motor drive are connected with a software-supported electronic parameterized control device that for its part can in turn be connected with an output device. The parameterized control device is to be parameterized when placing in operation takes place, in particular in that case an initial direction of movement of the drive shaft of the motor drive is to be defined, in addition a number of permissible stationary operational settings of the on-load tap changer is to be indicated, and finally it is to be defined where the start of the regulating range, i.e. the first permissible stationary operational setting, and the end of the regulating range, thus the last permissible operational setting, of the on-load tap changer lie. These parameters are to be stored in nonvolatile form in the parameterized control device. As already explained, on-load tap changers usually have a selector for power-free selection of the respective winding tap of the tapped transformer that is to be switched to and a load changeover switch for the actual changeover from the previous to the new, preselected winding tap. Depending on the switch type on which the on-load tap changer is based, in the case of a regulating winding with, for example, five winding taps five stationary operational settings are permissible in accordance with the resistance fast switching principle and nine stationary operational settings in accordance with the reactor switching principle, since here middle settings are acceptable as stationary operational settings.

(3) Subsequently, a motor drive is activated by the then parameterized parameterized control device in a first rotational direction, so that the on-load tap changer begins to run through its stationary operational settings, thus the different winding taps of the tapped transformer, in the direction of the first winding tap. By first winding tap there is meant here the main winding of the tapped transformer at the next positioned winding tap of the regulating winding, thus the start of the regulating range of a tapped transformer. The motor drive is, for example, a step motor known from the prior art.

(4) In a next following method step reaching of the end setting is recognized by the parameterized control device. By end setting there is to be understood in the context of the present invention the mechanical end abutment of the on-load tap changer against which the moved part of the on-load tap changer travels when it has reached the start or the end of its regulating range. This can take place, for example, through the parameterized control device recognizing the mechanical end abutment of the regulating range of the on-load tap changer in that the current intensity of the motor drive after activation thereof in a first rotational direction is subject to nonvolatile storage and is compared at defined intervals in time with a maximum value parameterized in the parameterized control device as current limit value. If in that case the instantaneously determined current value exceeds the defined target value then an electrical signal is generated that indicates to the parameterized control device the mechanical end abutment of the on-load tap changer. Alternatively, it is also possible for the mechanical end abutment of the regulating range of the on-load tap changer to be detected by way of the parameterized control device in that the rotational speed of the drive shaft of the motor drive is detected by a sensor at regular intervals in time. If the ascertained value of the rotational speed is equal to 0, then an electrical signal is generated that indicates the mechanical end abutment of the on-load tap changer to the parameterized control device. According to yet a further form of embodiment of the invention in the case of transiting of the regulating range of the on-load tap changer in a first rotational direction a reporting contact is connected on each attainment of the next stationary operational setting, wherein the trigger instant, i.e. the connection of the reporting contact, is subject to nonvolatile storage by the parameterized control device, wherein the time between two trigger instants is compared with a maximum permissible limit value, wherein in the case of exceeding the maximum permissible limit value an electrical signal is generated that indicates the mechanical end abutment of the on-load tap changer to the parameterized control device. This can be carried out, for example, in that at least one cam disk is brought into rotational engagement with the drive shaft of the motor drive, which cam disk for its part actuates at least one microswitch per revolution of the cam disk. Depending on the respective translation ratio the revolution of the cam disk can take place synchronously with switching of the load changeover switch from a first to an adjacent, second stationary operational setting. The microswitch is thus triggered once per revolution of the cam disk and accordingly per switching, thus permissible stationary operational setting of the on-load tap changer, and thereby reports a successfully concluded changeover process.

(5) In a following method step the motor drive is activated by the parameterized control device in a second rotational direction so that the selector of the on-load tap changer subsequently runs through the regulating range in the opposite switching direction until reaching the first or predefined stationary operational setting. The motor drive stops on reaching the first stationary operational setting.

(6) Finally, configuration of the first stationary operational setting as predefined operational setting is carried out with the help of the parameterization that is stored in nonvolatile manner, of the parameterized control device. The method according to the invention thus independently defines, after the on-load changer has been placed in operation, a first or predefined stationary operational setting as a reference variable for all subsequent switching processes. Since this defined operational setting is subject to software-assisted nonvolatile storage it is thus clear at any later point in time how many switchings in which switching direction of the on-load tap changer have been executed and ultimately in which stationary operational setting the on-load tap changer is instantaneously disposed. In other words, according to the essence of the invention the mechanical abutment of the regulating range of the on-load tap changer is thus used in order to subsequently undertake normalization to a defined stationary operational setting of the on-load tap changer.