Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F29/00—Variable transformers or inductances not covered by group H01F21/00
  • H01F29/02—Variable transformers or inductances not covered by group H01F21/00 with tappings on coil or winding; with provision for rearrangement or interconnection of windings
  • H01F29/04—Variable transformers or inductances not covered by group H01F21/00 with tappings on coil or winding; with provision for rearrangement or interconnection of windings having provision for tap-changing without interrupting the load current

Definitions

• the invention relates to a medium-low voltage transformer with tap-change.
• Transformers use high-voltage and medium-voltage tap changers.
• the tap changer compensates for the voltage fluctuations that occur during load changes by changing the transmission ratio.
• at least one of the windings of the transformer is provided with a series of taps, which can be electrically connected by a selector mechanism.
• a diverter switch is provided, which makes the switching between two selector positions without interruption even under load.
• Winding short circuit is avoided by briefly forcing current flow through resistors.
• Object of the present invention is to provide a medium-low-voltage transformer with tap-change, which is particularly simple. Another object of the invention is to provide an operating method for such a transformer.
• the medium-low voltage transformer according to the invention has a tap changer.
• one of the windings of the transformer preferably the low-voltage-side secondary winding, has two end taps and at least one further tap.
• at least one switching device is provided for the switchable electrical connection of at least one of the taps with an output line of the transformer.
• at least one semiconductor switching device is provided, which is electrically connected to the output line and to one of the taps.
• a first of the end taps is directly connected to a first output line of the transformer and is not further changed or used in a special way for the tap changer.
• the second end tap at the other end of the winding is used together with the one or more taps for the tap changer and the taps are for this purpose connected in a more complex manner with the second output line of the transformer.
• the switching device preferably comprises mechanical switches, which advantageously have a particularly low on-resistance, and particularly preferably allows independent connection and disconnection of individual taps.
• the switching device expediently alternately connects one of the taps to the second output line of the transformer.
• the medium-low voltage transformer according to the invention advantageously has a simple and low maintenance by the semiconductor switch construction and allows a tap changer circuit without load interruption in the middle to low voltage range.
• the tap changer contains a control device that automatically performs a control of the load switching.
• the control device expediently means that allow detection when a switch should occur.
• these may be means for determining voltage and / or current on the input or output side. This determines whether a changeover is necessary, for example by detecting the corresponding slight decrease in the output voltage when the load on the output side is higher.
• the control of the load switching can be made from outside the tap changer.
• the tap changer expedient means on which allow external control. This can be an indirect, for example, digital remote control, which is implemented in the tap changer by a control device in the actual control of the switch. It may also be a direct, analog control from the outside, which if necessary. Even without an internal control device can be done, for example, by directly applying an actuator of the switching element from the outside with electricity.
• the switching device is connected only to the further taps, that is to say it is not connected in negative terms to the end taps. It is useful if there are several more taps, so at least two. It is also expedient if the semiconductor switching device is connected to one of the end taps. This structure allows a particularly advantageous operation. In this case, as soon as a switch appears necessary, the semiconductor switching device is turned on. This switching is preferably carried out at the zero crossing of the AC voltage, wherein expediently a switch-on delay of the semiconductor switch or switches of the semiconductor switching device is taken into account, that is, for example, an ignition delay of thyristors. As a result, a voltage jump is avoided.
• an inductance is preferably provided in series with the semiconductor switching device.
• a resistance element may also be provided to limit the current.
• the current in the short-circuit winding circuit is opposite to the load current. As a result, therefore, a point in time is reached at which the current in the winding short circuit assumes the same amount as the load current and thus virtually no current flows via the switching element. In other words, the load current at this time is completely commutated to the semiconductor switching device.
• This time is used to turn off the connection through the switching element. Since in the time in which no or very little current flows through the switching element, and accordingly less voltage drops over it, the shutdown without an arc is possible and therefore particularly gentle for the switching element. Alternatively, the opening of the switching element
• Switching element can be made before the zero crossing, in particular at a time at which the semiconductor switching device safely already passes. In this case will When the switching element is opened, an arc occurs which, however, disappears very rapidly during the current commutation, typically in the range of microseconds, since the current across the switching element disappears. Once the arc extinguished, it does not emerge when the voltage across the switching element increases.
• the medium-low voltage transformer comprises means for determining a value representing the voltage across the switching element and / or the current through the switching element, since then the time for opening the switching element can be determined directly. This time in the operating method described above, for example, given when the current is just zero. Another possibility is to effect the opening of the switching element when the current or the voltage, in particular the maximum amounts thereof within each period, falls below a certain threshold, which is slightly greater than zero. Another alternative is to set the time for the opening of the switching element on the basis of a time control function of the turn-on time of the semiconductor switching device, for example, 2 ms after switching on the semiconductor switching device.
• the semiconductor switching device After opening by the switching element, the semiconductor switching device carries the load current and the short-circuiting of the winding is canceled.
• the switching element is closed again to make a connection with another of the other taps of the winding.
• a suitable time for closing the connection is selected.
• a time can be selected at which the voltage across the switching element corresponds exactly to the voltage across the semiconductor switching device. It is assumed that due to the semiconductor switch due to the semiconductor switching device always drops a low voltage.
• closing the Switching element it is advantageous to take into account the closing time, which requires the switching element for making the electrical contact. Closing at said time makes it possible to avoid voltage jumps.
• An alternative method is to cause the closing of the switching element when the voltage just shows a zero crossing due to the line frequency.
• the semiconductor switching device can be turned off or depending on the semiconductor switch used the ignition can be canceled.
• a thyristor circuit is provided as semiconductor switch. It is advantageous that this issabumbled and thus allows easy control.
• the thyristor circuit preferably consists of two anti-parallel connected thyristor elements, wherein each of the thyristor elements consists of a thyristor or a parallel and / or series connection of thyristors. Other electrical components can be used together with the thyristors.
• turn-off semiconductor switches can also be used as semiconductor switches, in particular transistors, GTOs (Gate Turn-off Thyristor) or IGCTs (Integrated Gate Commutated Transistor).
• GTOs Gate Turn-off Thyristor
• IGCTs Integrated Gate Commutated Transistor
• means for determining the current in the region of the switching element or semiconductor switch are provided.
• FIG. 1 shows a first transformer with continuous secondary winding with tap changer
• FIG. 2 shows a flowchart for the tap-changer with the first transformer
• the invention is equally applicable with more than three gear ratios.
• the voltage on the side of the primary windings should be exemplified 10 kV, while on the side of the secondary winding, a voltage 400 V is output.
• FIG. 1 shows a transformer 1 with a stage circuit.
• the transformer 1 has, in addition to a primary winding which is not significant in this exemplary embodiment, a continuous secondary winding.
• the continuous secondary winding consists of a first to fourth part 17a ... d.
• the first part 17a comprises approximately 70% of the winding length of the secondary winding
• the second, third and fourth parts 17b ... d each comprise approximately 10% of the winding length.
• the representation in Fig.l is not exactly to scale. From the relative proportions of the secondary winding arise the adjustable ratios and it is clear that even very different divisions of the secondary winding are possible.
• D are defined by a first, second and third tap 2, 3, 4, the first tap 2 being at 70% of the winding length of the seconds. därwicklung is located, the second tap 3 at 80% of the winding length of the secondary winding and the third tap 4 at 90% of the secondary winding.
• a first output line 11 of the transformer 1 is connected to the beginning of the secondary winding.
• Transformer 1 is connected in a more complex manner with the taps 2, 3, 4, in order to realize the tap changer.
• a mechanical switch 20 is provided whose center connection is connected to the second output line 12 according to FIG.
• the switch 20 can establish a connection between its center connection and a first, second or third connection 13, 14, 15.
• the first connection 13 connects the tap 2 and one of the connections of the mechanical switch 20.
• the second connection 14 connects the second tap 3 to a further connection of the switch and the third connection 15 connects the third tap 4 to a last connection of the mechanical switch 20
• the switch 20 is expediently designed so that the separation and production of the connection between the terminals can be done independently of one another, that is to say a plurality of mechanical switching elements together form the switch 20.
• the structure of two thyristors is exemplary in this case.
• one of the thyristors can represent one series connection and / or parallel connection of a plurality of actual thyristor elements. Also here, other elements such as IGBTs, GTOs o.a. be used.
• an inductance 53 is provided, which is the
• Delay of the current in the case of a winding short circuit is used.
• a measuring point 7 ... 10 is provided at each of the connections 13, 14, 15, 18 and in the region of the central connection of the switch 20, a measuring point 7 ... 10 is provided.
• a controller 6 is present at each of the connections 13, 14, 15, 18 and in the region of the central connection of the switch 20, a measuring point 7 ... 10 is provided.
• the controller 6 can determine the voltage at the measuring points 7... 10 and control the thyristor circuit 5 and the switch 20 on the basis of the determined values.
• a switchover is performed.
• the mechanical switch 20 switches between its terminals so that instead of the first tap 2, the second tap 3 is connected to the second output line 12.
• the thyristor circuit 5 takes over the power. This happens without interruption, the exact circuit is shown below, for example.
• the second current path 27 thus leads during the switching from the first output line 11 over all parts 17a ... d of the secondary winding. It also leads via the fourth connection 18 and thus the thyristor circuit 5 to the second output line 12. Thus, the entire secondary winding is used.
• the state used in the third step 23 results.
• about 80% of the secondary winding is used and the third current path 28 leads from the first output line 11 via the first and second Part 17a, b of the secondary winding and the second connection 14 to the second output line 12th
• a changeover is performed again.
• the mechanical switch 20 switches between its terminals so that instead of the second tap 3, the third tap 4 is connected to the second output line 12.
• the thyristor circuit 5 takes over the power.
• the fourth current path 29 thus leads during the switching from the first output line 11 over the entire secondary winding. Further, it leads via the fourth connection 16 and thus the thyristor circuit 5 to the second output line 12. As soon as the mechanical switch 20 has switched, the ignition of the thyristor circuit 5 is terminated.
• the state used in the fifth step 25 is obtained.
• 90% of the secondary winding is used and the current path leads from the first output line 11 via the first, second and third part
• the mechanical switch 20 does not have to switch between adjoining taps 2, 3, 4, but the switching can take place between any of the taps, that is, for example, directly from the first tapping 2 to the third tapping 4 or vice versa.
• the controller 6 determines that a switch between two of the taps appears necessary. As a result, the controller ensures that the thyristors in the thyristor circuit 5 are ignited.
• the time of ignition is selected such that no voltage jump occurs.
• a time is used that would be one Period of time before a zero crossing of the mains voltage is, wherein the time period corresponds to the ignition delay of the thyristors. This ensures that the thyristors can take over the load current in principle at the zero crossing of the voltage.
• the opening of the switch is preferably already made shortly before the expected zero crossing, in particular at a time at which the thyristors are already reliably conducting.
• an arc will occur, but in the course of Stromkommutierung very fast, typically in the range of microseconds, extinguished because the current disappears via the switching element yes. Once the arc extinguished, it no longer arises when the voltage across the switching element increases.
• the switch 20 for opening the connection is activated such that it only opens when the thyristors are already conducting.
• the thyristors carry the load current, and the opening of the switch 20 causes the shorting of the winding canceled.
• Closing of the new connection of the switch 20 preferably takes place in a natural zero crossing of the mains voltage, in turn to achieve a smooth transition of the line. Since after the closing of the switch 20 again a indentation short-circuit exists, it is expedient to stop the ignition of the thyristors in time before the zero crossing in order to prevent simultaneous conduction of the thyristors with the switch 20.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Control Of Electrical Variables (AREA)
• Driving Mechanisms And Operating Circuits Of Arc-Extinguishing High-Tension Switches (AREA)
• Protection Of Transformers (AREA)
• Electronic Switches (AREA)
• Ac-Ac Conversion (AREA)
• Power Conversion In General (AREA)

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• 2008
  • 2008-12-22 DE DE102008064487A patent/DE102008064487A1/de not_active Withdrawn
• 2009
  • 2009-12-15 RU RU2011130542/07A patent/RU2516462C2/ru not_active IP Right Cessation
  • 2009-12-15 ES ES09797014.9T patent/ES2530433T5/es active Active
  • 2009-12-15 EP EP09797014.9A patent/EP2361435B2/de active Active
  • 2009-12-15 CN CN200980144210.5A patent/CN102209998B/zh active Active
  • 2009-12-15 PL PL09797014T patent/PL2361435T5/pl unknown
  • 2009-12-15 WO PCT/EP2009/067207 patent/WO2010072623A1/de active Application Filing
  • 2009-12-15 UA UAA201107828A patent/UA103786C2/ru unknown
  • 2009-12-15 BR BRPI0924890-0A patent/BRPI0924890A2/pt not_active Application Discontinuation

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