ON-LOAD TAP-CHANGER AND METHOD FOR OPERATING AN ON-LOAD TAP-CHANGER

Description

[0001] The invention relates to an on-load tap changer for uninterrupted switching between winding taps of a tapped transformer under load.

[0002] The on-load tap changer consists of a mechanical tap selector for powerless pre-selection of the respective winding tap to which switching is to take place, and a load transfer switch with semiconductor switching elements as switching means for the actual uninterrupted switching from the previous to the pre-selected, new winding tap under load.

[0003] On-load tap-changers of this type are commonly referred to as hybrid tap-changers because, in addition to the power electronic switching devices, they also feature mechanical contacts. EP 2319058 B1 describes such a hybrid tap-changer. It has two load branches, each connecting a winding tap via a mechanical switch and a series circuit of two oppositely connected IGBTs to a common load terminal. A diode is provided in parallel with each IGBT. A varistor is provided in parallel with each individual IGBT. During steady-state operation, each of the load branches is bridged with a mechanical permanent main contact. The IGBTs on both sides are controlled by a common IGBT driver.

[0004] The mechanical tap selector and, if applicable, other mechanical switching elements provided in the diverter switch are actuated by means of a motor drive, whereas the power electronic switching means are operated via a separate actuating means which must be supplied with power.

[0005] From the document WO 2020 / 030445 A1 an on-load tap-changer according to the preamble of claim 1 is known.

[0006] The object of the present invention is to provide an improved concept for the power supply of the power electronic switching means of an on-load tap-changer.

[0007] This object is achieved by the respective subject matter of the independent claims. Further embodiments are the subject matter of the dependent claims.

[0008] The improved concept is based on the idea of ​​supplementing the fixed contacts of the on-load tap-changer, each of which can be connected to a winding tap of the transformer's control winding, with an additional connection contact that can be contacted by an auxiliary contact of the on-load tap-changer.

[0009] According to a first aspect of the improved concept, an on-load tap-changer is specified for uninterrupted switching between winding taps of a tapped transformer. The on-load tap-changer comprises a first fixed contact, which is connectable to a first winding tap of the tapped transformer, and a second fixed contact, which is connectable to a second winding tap of the tapped transformer. The total number of fixed contacts depends on the number of winding taps. A first selector arm of the on-load tap-changer can contact each of the fixed contacts, and a second selector arm can also contact each of the fixed contacts. To carry out a switchover from a first fixed contact to a second fixed contact, the on-load tap-changer has a load diverter switch.Furthermore, the on-load tap-changer comprises an additional connection contact, which is arranged analogously to the fixed contacts, and an auxiliary contact, which can contact either the connection contact or one of the fixed contacts.

[0010] The connection contact is designed in such a way that it can be contacted by the auxiliary contact.

[0011] Each fixed contact is configured to be contacted by the first and / or second selector arm. Preferably, each fixed contact has a first contact surface that can be contacted by the first selector arm and a second contact surface that can be contacted by the second selector arm. Furthermore, the first or second contact surface can be contacted by the auxiliary contact.

[0012] According to the invention, the connecting contact is bridged with the second fixed contact. Thus, the connecting contact does not need to be electrically connected to an additional winding tap.

[0013] Furthermore, according to the invention, the auxiliary contact is mechanically coupled to the first selector arm.

[0014] In concrete terms, this means that the auxiliary contact and the first selector contact are located on adjacent contacts when switched on, i.e., when they are not moved. Consequently, the auxiliary contact and the first selector arm are never located on the same fixed contact or on the connecting contact at the same time.

[0015] According to at least one embodiment, the load changeover switch for switching has a plurality of semiconductor switching elements which can be actuated by means of a control unit.

[0016] The semiconductor switching elements are preferably designed as IGBT switching elements and / or as thyristors and / or as JFET switching elements and / or as MOSFET switching elements and / or as integrated gate commutated thyristors (IGCTs). Particularly preferably, the semiconductor switching elements are each designed as an IGBT with diodes in a bridge circuit.

[0017] According to at least one embodiment, the control unit is designed as a microcontroller.

[0018] According to at least one further embodiment, the control unit and thus also the semiconductor switching elements are supplied with power, while the auxiliary contact contacts the connection contact or one of the fixed contacts and the first selector arm also contacts one of the fixed contacts.

[0019] Due to the mechanical coupling of the first selector arm and the auxiliary contact, the first selector arm and the auxiliary contact cannot be on the same fixed contact or on the connecting contact at any time during the switching process. This, in turn, means that at any time during the switching process in which the first selector arm contacts a fixed contact, a voltage equal to a step voltage is present between the first selector arm and the auxiliary contact, which supplies power to the control unit. Thus, the control unit and thus also the semiconductor switching elements are operated independently using the applied step voltage. An additional external power supply, for example, from a motor controller, is therefore not required.

[0020] According to at least one further embodiment, the control unit has an energy storage device that is charged when the control unit is supplied with power.

[0021] The energy storage device is charged via the voltage difference that exists between the first selector arm and the auxiliary contact due to the mechanical coupling and the contacting of different fixed contacts or the connecting contact and the first fixed contact.

[0022] During the actuation of the first selector arm and the auxiliary contact, no step voltage is present. Consequently, the control unit is not supplied with power during this time. For this reason, an energy storage device can be provided as a safety measure to ensure that the power electronics are supplied with power at all times during the switching process.

[0023] The energy storage device is preferably made of ceramic capacitors and therefore has high temperature resistance. A switching power supply with an extremely wide input voltage range, which still functions even at low step voltages, is preferably used to charge the energy storage device.

[0024] According to a second aspect of the improved concept, a method for operating an on-load tap-changer designed according to the first aspect of the improved concept is specified.

[0025] With regard to the method, reference is made to the preceding explanations, preferred features and / or advantages in an analogous manner as has already been explained with regard to the first aspect of the improved concept or one of the associated advantageous embodiments.

[0026] The method comprises the following steps for switching from a first fixed contact to a second fixed contact: Actuating at least one of the semiconductor switching elements of the load changeover switch, switching a second selector arm from the first fixed contact to the second fixed contact, Actuating at least one of the semiconductor switching elements of the load changeover switch, switching a first selector arm from the first fixed contact to the second fixed contact, wherein at the same time as the switching of the first selector arm to the second fixed contact, an auxiliary contact is switched from a connection contact to the first fixed contact.

[0027] According to a preferred embodiment, switching from the second fixed contact to a third fixed contact, which is designed according to the second fixed contact and is connected to a third winding tap of the tapped transformer, comprises the following steps: Actuating at least one of the semiconductor switching elements of the load changeover switch, switching the second selector arm from the second fixed contact to the third fixed contact, Actuating at least one of the semiconductor switching elements of the load changeover switch, switching the first selector arm from the second fixed contact to the third fixed contact, wherein at the same time as the first selector arm is switched to the third fixed contact, the auxiliary contact is switched from the first fixed contact to the second fixed contact.

[0028] Further embodiments and implementations of the method arise directly from the various embodiments of the tap changer, and vice versa. In particular, one or more of the components and / or arrangements described with regard to the tap changer can be implemented accordingly to carry out the method.

[0029] The invention will now be explained in detail using exemplary embodiments with reference to the drawings. Components that are identical, functionally identical, or have an identical effect may be provided with identical reference numerals. Identical components or components with identical functions may only be explained with reference to the figure in which they first appear. The explanation is not necessarily repeated in subsequent figures.

[0030] It shows Figure 1 shows a schematic representation of an exemplary embodiment of an on-load tap-changer according to the improved concept; Figures 2a to 2g show an exemplary switching sequence of the on-load tap-changer from Figure 1 . The figures merely illustrate embodiments of the invention, without, however, limiting the invention to the illustrated embodiments.

[0031] Figure 1shows a schematic representation of an exemplary embodiment of an on-load tap-changer 10 for a tapped transformer 1 according to the improved concept. The tapped transformer 1 has a main winding 2 and a control winding 3 with different winding taps NJ, N J+1, ..., NN, which are switched on or off by the on-load tap-changer 10.

[0032] According to the improved concept, the on-load tap-changer 10 comprises at least a first fixed contact 12, which can be connected to a first winding tap NJ, a second fixed contact 13, which can be connected to a second winding tap N J+1 , and a third fixed contact 14, which can be connected to a third winding tap N J+2 of the control winding 3 of the tapped transformer 1. The total number of fixed contacts depends on the number of winding taps. In addition to the fixed contacts, the on-load tap-changer 10 has a further connection contact 11, which is bridged to the second fixed contact 13. The connection contact 11 is not directly connected to any of the winding taps NJ , N J+1 , ..., NN.

[0033] For powerless pre-selecting of the fixed contacts 12, 13, the on-load tap-changer 10 comprises a selector 30 with a first selector arm 31 and a second selector arm 32, which can be operated independently of each other and can contact each of the fixed contacts. In addition to the selector arms 31, 32, the on-load tap-changer 10 has an auxiliary contact 33, which is mechanically coupled to the first selector arm 31.

[0034] The on-load tap changer 10 further comprises a load transfer switch 20 for performing the actual load switching between the preselected fixed contacts 12, 13. The load transfer switch 20 has a total of three current branches: a main branch 24 with a mechanical switching element 25, which can connect both the first selector arm 31 and the second selector arm 32 to a load terminal 15; a first auxiliary branch 26 with a first semiconductor switching element 22, which is arranged parallel to the main branch 24 and can connect the first selector arm 31 to the load terminal 15; and a second auxiliary branch 27 with a second semiconductor switching element 23, which can connect the second selector arm 32 to the load terminal 15. A varistor 28 is arranged parallel to each of the first and second auxiliary branches 26, 27. The semiconductor switching elements 22 and 23 are actuated by a control unit 21.

[0035] The described specific circuit arrangement of the diverter switch 20 was chosen as an example. In principle, the improved concept can be implemented in any on-load tap-changer that has a diverter switch with semiconductor switching elements as switching means for uninterrupted switching.

[0036] In the presentation in Figure 1The on-load tap-changer 10 is in a stationary position. The first and second selector arms 31, 32 are both located on the first fixed contact 12. The auxiliary contact 33 is connected to the additional connection contact 11, which is bridged to the second fixed contact 13. As a result, a step voltage is applied between the selector arm 31 and the auxiliary contact 33, and the control unit 21 is supplied with power. The load current IL flows from the contacted fixed contact 12 via the first selector arm 31, the main branch 24, and the closed mechanical switching element 25 to the load shunt 15. The two semiconductor switching elements 22 and 23 are switched off.

[0037] In the Figures 2a to 2g is an example switching sequence of the on-load tap-changer from Figure 1 shown.

[0038] During a switching process from the first fixed contact 12 to the second fixed contact 13, in a first step ( Figure 2a) the first semiconductor switching element 22 is switched on by means of the control unit 21.

[0039] In the next step ( Figure 2b ), the second selector arm 32, which is de-energized, is moved from the first fixed contact 12 to the second fixed contact 13.

[0040] The mechanical switching element 25 is then opened (see Figure 2c ). The load current IL now flows via the first auxiliary branch 26 and the activated first semiconductor switching element 22.

[0041] In the next step ( Figure 2d ), the first semiconductor switching element 22 is preferably switched off at the zero crossing of the current. The temporal course of the current can be detected by the control unit 21, for example, using a current sensor (not shown) arranged in the current branch of the downstream line 15. When the first semiconductor switching element 22 is switched off, the load current IL is transferred to the varistor 28 arranged in parallel thereto.

[0042] In the next step, shown in Figure 2e , the second semiconductor switching element 23 is switched on after a specified period, for example, 5 µs. The load current IL is thus switched to the second fixed contact 13 and flows from the second selector arm 32 via the second auxiliary branch 27 and the activated second semiconductor switching element 23 to the load shunt 15.

[0043] The first selector arm 31, which is now de-energized, is then switched to the second fixed contact 13 and at the same time the auxiliary contact 33 is switched from the connecting contact 11 to the first fixed contact 12 ( Figure 2f ).

[0044] In the next step ( Figure 2g) the mechanical switching element 25 is closed again and then the second semiconductor switching element 23 is switched off by the control unit 21. The on-load tap-changer 10 has now reached the second stationary position. With the closure of the mechanical switching element 25, the load current IL is transferred back to the main branch 24. The first and second selector arms 31, 32 are both located on the second fixed contact 13 and the auxiliary contact 33 is on the first fixed contact 12. The load current IL now flows from the second fixed contact 13 via the first selector arm 31 and the main branch 24 with the closed mechanical switching element 25 to the load shunt 15. The load switching to the second fixed contact 13 is thus completed.

[0045] A switchover from the second fixed contact 13 to the third fixed contact 14 is carried out analogously to steps 2a - 2g, with the only difference that the auxiliary contact 33 is not on the connection contact 11 at the beginning of the switchover, but on a fixed contact, namely the first fixed contact 12.

[0046] A switchover in the opposite direction, for example from the second fixed contact 13 to the first fixed contact 12, takes place in exactly the reverse order, that is, according to the Figures 2g to 2a . REFERENCE SYMBOL

[0047] 1 Tap transformer 2 Main winding 3 Regulating winding 10 On-load tap changer 11 Connection contact 12 First fixed contact 13 Second fixed contact 14 Third fixed contact 15 Load derivation 20 Load diverter switch 21 Control unit 22 First semiconductor switching element 23 Second semiconductor switching element 24 Main branch 25 Mechanical switching element 26 First auxiliary branch 27 Second auxiliary branch 28 Varistor 30 Selector 31 First selector arm 32 Second selector arm 33 Auxiliary contact (NJ , N J+1 , ..., NN )Winding taps

Claims

1. On-load tap-changer (10) for uninterrupted advanced retard switch between winding taps (NJ, NJ+1, ..., NN) of a tapped transformer (1), comprising a first fixed contact (12) which can be connected to a first winding tap NJof the tapped transformer (1), a second fixed contact (13) which can be connected to a second winding tap NJ+1of the tapped transformer (1), a first selector arm (31) which can contact each of the fixed contacts (12, 13), a second selector arm (32) which can contact each of the fixed contacts (12, 13), a diverter switch (20) for bushing an advanced retardter switch operation from a first fixed contact (12) to a second fixed contact (13) of the on-load tap-changer (10), characterized in that the on-load tap-changer (10) further comprises a connection contact (11) which is arranged in addition to the fixed contacts (12, 13) and which is bridged with the second fixed contact, and an auxiliary contact (33) mechanically coupled to the first selector arm, which can optionally contact the connection contact (11) or one of the fixed contacts (12, 13).

2. The on-load tap-changer (10) according to claim 1, wherein the diverter switch (20) for the advanced retard switch operation has a plurality of semiconductor switching elements (22) which can be actuated by means of a control unit (21).

3. On-load tap-changer (10) according to claim 2 wherein the control unit (21) is supplied with current while the auxiliary contact (33) contacts the connection contact (11) or one of the fixed contacts (12, 13) and the first selector arm (31) contacts one of the fixed contacts (12, 13).

4. The on-load tap-changer (10) according to claim 3, wherein the control unit (21) has an energy accumulator which is charged when the control unit (21) is supplied with power.

5. Method for actuating an on-load tap-changer (10) which is designed according to one of the preceding claims 2 to 4, wherein an advanced retard switch from a first fixed contact (12) to a second fixed contact (13) comprises the following steps: Actuating at least one of the semiconductor switching elements (22) of the diverter switch (20), advanced retard switch of a second selector arm (32) from the first fixed contact (12) to the second fixed contact (13), actuating at least one of the semiconductor switching elements (22) of the diverter switch (20), switching a first selector arm (31) from the first fixed contact (12) to the second fixed contact (13), an auxiliary contact (33) being switched over from a connection contact (11) to the first fixed contact (12) at the same time as the first selector arm (31) is switched over to the second fixed contact (13).

6. The method according to claim 5, wherein an advanced retard switch from the second fixed contact (13) to a third fixed contact (14) comprises the following steps: Actuating at least one of the semiconductor switching elements (22) of the diverter switch (20), advanced retard switch of the second selector arm (32) from the second fixed contact (13) to the third fixed contact (14), actuating at least one of the semiconductor switching elements (22) of the diverter switch (20), switching the first selector arm (31) from the second fixed contact (13) to the third fixed contact (14), the auxiliary contact (33) being switched from the first fixed contact (12) to the second fixed contact (13) at the same time as the first selector arm (31) is switched to the third fixed contact (14).