Medium or low voltage transformer with step changing and its operating method

FIELD: electricity.

SUBSTANCE: invention is related to electrical engineering and can be used in distributing mains in order to decrease voltage fluctuations. The transformer contains a stepping switch on the basis of one or several mechanical switches. At switching current is directed through semiconductor switches in order to ensure uninterrupted operation.

EFFECT: simplification of design.

11 cl, 2 dwg

 

The invention relates to a transformer for medium and low voltage with step switch.

Distribution network is subject to voltage fluctuations, particularly due to the impedances of the network components and variable loads. It is desirable that these fluctuations were as small as possible. For this purpose transformers between high and medium voltages are manual switches. This switch compensates arise in the case of changes in the load voltage fluctuations, changing the transformation ratio. For this purpose, at least one of the windings of the transformer is equipped with a number of branches that can electrically be connected through voter. In addition, there is a switch that provides seamless switching between the two positions of the voter also under load. Inter-turn short circuit is prevented due to the fact that the current is forced to flow for a short time through the resistors.

It is possible that in the future energy supply in comparison with today's situation will be less centralized. This means that electricity will be produced closer to the consumer than it is today to a large number of plants of smaller capacity. Such systems are, for example, photovoltaic installation, vitros the business of installing and operating biomass power plants or block-type thermal power plants of smaller capacity. Due to implemented, rather, the combined production of electricity and heat power plants of smaller capacity, at least in principle highly preferred. If the generated electricity cannot be sampled, the required filing of the network low voltage network medium voltage, to ensure no loss transmission over long distances. For this purpose it is necessary to provide in the distribution transformer variable transformation ratio.

The objective of the invention is to provide a transformer for medium and low voltage with step switch, which would have a particularly simple design. Another object of the invention is to create a method of operation of such transformers.

This problem is solved by means of the transformer medium and low voltage characteristics of claim 1 of the formula. Preferred variants and modifications are given in the dependent clauses. Also object of the invention is solved by a method with the characteristics of claim 10 of the formula.

The proposed transformer medium and low voltage has a manual switch. When one of the windings of the transformer, mainly the secondary winding on the low voltage side has two end branches and at least one additional branch. In addition to t the th, provided at least one switching device for electrical connection of at least one of the arms with the output wire of the transformer. Finally, there is at least one semiconductor switching device, electrically connected to the output wire and one of the branches.

Preferably the first end of the branches are directly connected to the first output wire of the transformer and is no longer changed to manual switch, or used in a special way. The second end of the branch at the other end of the winding, in contrast, is used together with an additional or extra branches to step switching, and branches in a more comprehensive manner is connected to the second output wire of the transformer.

The switching device preferably includes mechanical switches, preferably having a particularly low resistance in the carrying direction, especially preferably provides independent activation and deactivation of individual branches. When this switching device suitable alternately connects a separate branch with the second output wire of the transformer.

The proposed transformer medium and low voltage is site is preferably simple and does not require maintenance due to the semiconductor switches design and offers a step switch without interrupting the load from medium voltage to low.

It is advisable, but not necessary, if the stepping switch includes a control device that spontaneously manages the switching of the load. For this control unit contains the appropriate tools that allow you to detect when to change. For example, we can talk about the means to determine the voltage and/or current at the input or output side. They allow you to determine whether you need the switch, if, for example, during high load on the output side, is detected by a corresponding slight decrease in the output voltage. Alternatively, the control load switching may also be out of step switch. In this case, step switch contains suitable means providing control from the outside. It can be indirect, such as digital, remote control, in which step the switch is converted by the control device in the actual management of the switch. Also we can talk about direct analog control from the outside, which can be carried out, if necessary, even without the internal control device, for example, by directly applying current from the outside to the Executive bodies is well switching element.

Particularly preferably, if a switching device is connected only with additional branches, i.e. not with apical branches. It is advisable, if you have a few extra branches, i.e. at least two. It is advisable also, if the semiconductor switching device connected to one of the terminal branches. This construction provides a particularly preferred operation.

As soon as the switch will be required, turns on the semiconductor switching device. This inclusion occurs preferably by passing an alternating voltage through zero, and it is advisable take into account the delay of switching of the semiconductor switches semiconductor switching devices, i.e, for example, delayed ignition of the thyristors. This prevents the surge voltage.

When the semiconductor switching device is turned on, there is inter-turn short circuit, as between one of the additional branches through the switching element and the semiconductor switching device occurs directly connected to the terminal branch. As a result, in this circuit will be current. To slow down the occurrence of this current predominantly in series with the semiconductor is omputational the device inductance. Alternatively, or in addition to, the current limit may be a resistor.

Due to the relative positioning of the semiconductor switching devices on the end of the branch and the switching element in one of the branches of the current in the short circuit between the coils is opposite to the load current. Consequently achieved the point in time at which the current in the short circuit between the coils takes the same value as the load current, and thereby, through the switching element is almost no current flows. In other words, at this point in time the load current is commutated with a semiconductor switching device.

This time is used to turn off the connection through the switching element. Because during the time that through the switching element, no current flows or flows very little current also drops accordingly little voltage can be switched off without arc, which is particularly gentle to the switching element. Alternatively, can be carried out also in the interruption of the switching element before the zero crossing, in particular in the point in time at which the semiconductor switching device is already securely conductive. In atomlike by opening the switching element will have an arc, which, however, in the process of switching power goes out very quickly, usually in the range of microseconds, since the current through the switching element disappears.

Preferably, if the transformer medium and low voltage includes means for determining values representing the voltage and/or current through the switching element, because then you can determine the time for opening the switching element. This time in the above-described method of operation occurs, for example, when the current becomes zero. Another possibility of disconnection of the switching element, is that the current or voltage, in particular its maximum value within each period, below a certain threshold, which is slightly greater than zero. Another alternative is to set the time for opening the switching element, using the time control depending on time of the semiconductor switching devices, for example through 2 MS after turning it on.

After disconnection of the switching element through the semiconductor switching device flows in the load current, and turn-to-turn short circuit is eliminated.

Then, the switching element is closed to create a connection with each the m of the additional winding branches. Also in this case, preferably, if for circuit connection, you select the suitable point in time. You can choose, for example, the point in time at which the voltage across the switching element corresponds to the voltage across the semiconductor switching device. It should be assumed that because the semiconductor switches through the semiconductor switching device always drops a small voltage. With the closure of the switching element, it is preferable to consider the time circuits, which required him to create an electrical contact. The circuit at this point in time allows to avoid power surges. An alternative method consists in the closure of the switching element when the voltage due to the frequency passes through zero.

After switching the item again will create an electrical connection of a semiconductor switching device can be turned off, or depending on the semiconductor switch can be eliminated the ignition.

In one embodiment of the invention, the semiconductor switch is provided thyristor circuit. It is preferable that it is made samootkryvayuschiesya and provides, therefore, a simple control. Thyristor to the contour consists preferably of two anti-parallel connected thyristor elements, each consists of a thyristor or parallel and/or series circuits of the thyristors. Together with thyristors can also be used with other electrical elements.

Alternatively, the thyristors as semiconductor switches can also be used off semiconductor switches, in particular GTO (Gate Turn-Off Thyristor - the GTO). It provides active off-line through a semiconductor switch that, in turn, reduces the time Magwitch short circuit through the closed switching element and a conducting semiconductor switch.

In one preferred embodiment, the invention provides a means for determining the current in the area of the switching element, or a semiconductor switch.

Preferred, but in any case not limiting the invention, examples of its implementation are explained in more detail using the drawings. While the signs depicted schematically, and the relevant characteristics denoted by the same reference position. In the drawings represent:

- figure 1: the first transformer with a solid secondary winding with step switch;

- figure 2: a diagram of the process step of switching from the first transformer.

The drawings depicted in the ways of execution transformers medium and low voltage. In actual practice, they are suitable three-phase. However, for better clarity of the drawings shows only a single phase execution. For the same reason, the stepping switches are examples only three possible installation of the transformation ratio, whereas in reality speed switches can often set more than three coefficients of transformation. The invention can also be used with more than three coefficients of transformation. The voltage on the primary windings should be, for example, 10 kV, while on the side of the secondary winding is given a voltage of 400 C.

1 shows a transformer with 1 stage gearing. In addition to the primary winding (not shown) it contains a solid secondary winding. It consists of four sections 17A-17d. The first section 17A covers about 70% of the length of the secondary winding, while the second, third and fourth sections 17b-17d cover about 10% of its length. The diagram in figure 1 presents not exactly to scale. The relative share of the secondary winding arise installed the coefficients of transformation, and it is clear that it is also possible an entirely different division of the secondary winding. Section 17A-17d are formed first 2, second 3 and third 4 branches, the first branch 2 is 70%, vtoro is an offshoot of 3-80%, and the third branch of 4-90% of the length of the secondary winding. With the beginning of the secondary winding is connected to the first output wire 11 of the transformer 1. His second output wire 12 is connected with 2-4 branches in a more comprehensive manner for the implementation of the manual switch.

For step switch provides a manual step switch 20, the average output of which is connected with the second output wire 12. The switch 20 can create a connection between its intermediate output and the first 13, second 14 and third 15 connection. The first connection 13 connects the branch 2 and one of the conclusions of the switch 20. A second connection 14 connects the branch 3 with the other output of the switch 20, and a third connection 15 - branch 4 with his final conclusion. When the switch 20 is made appropriate so that the separation of the findings and create connections between them can occur independently of each other, i.e. several mechanical switching elements together form the switch 20.

Further, between the end of the branch 52 of the secondary winding and the second output wire 12 has a fourth connection 18, which leads through the thyristor circuit 5 consisting of two anti-parallel connected thyristors. Scheme of the two thyristors is an example only. Depending on the expected load one and the thyristors may represent, respectively, the serial and/or parallel circuit of several of the thyristor elements, such as IGBT (integrated gate bipolar transistor insulated gate), GTO, etc. in series with the thyristor circuit 5 includes an inductance 53, which serves to delay the current in the turn-to-turn short circuit.

In each of compounds 13-15 and in the middle of the output switch 20 is provided for measuring point 7-10. In addition, a control unit 6. He can determine the voltage at the measuring points 7-10 and use the obtained values to control the thyristor circuit 5 and the switch 20.

The process speed switching through device 1 is explained with help of figure 2. At the first stage 21 should proceed from the fact that the mechanical switch 20 generates an electrical connection between the second output wire 12 and the first connection 13. The first current path leads 26, therefore, from the first output wire 11 through the first section 17 of the secondary winding and the first connection 13 to the second output wire 12. It uses about 70% of the secondary winding. The thyristors are not lit.

At the second stage 22 is switching. In this case, the mechanical switch 20 is switched between its findings so that instead of the first branch 2 with the second output wire 12 connects the second branch 3. During the switching thyristor circuit 5 passes current. This is going on the t uninterrupted, moreover, the exact switch shown below. During switching the second current path 27 leads, therefore, from the first output wire 11 through all sections 17A-17d of the secondary winding. Next it goes through a fourth connection 18 and, thereby, through the thyristor circuit 5 to the second output wire 12. This uses all of the secondary winding. As soon as the switch 20 is switched, the thyristor ignition circuit 5 is completed.

After switching occurs, is used on the third stage 23. This uses about 80% of the secondary winding, and a third current path 28 leads from the first output wire 11 through the first 17A and second 17b section of the secondary winding and a second connection 14 to the second output wire 12.

In the fourth stage 24 is again switching. In this case, the mechanical switch 20 is switched between its findings so that instead of the second branch 3 with the second output wire 12 connects the third branch 4. During the switching thyristor circuit 5 passes current. During switching the fourth current path 29 leads, therefore, from the first output wire 11 through the secondary winding. Next it goes through a fourth connection 16 and thus through the thyristor circuit 5 to the second output wire 12. As soon as the switch 20 is switched off, the ignition thyristor the th circuit 5 is completed.

After switching occurs, is used on the fifth stage 25. It uses 90% of the secondary winding, and a current path leads from the first output wire 11 through the first 17A, the second 17b 17c and the third section of the secondary winding and a third connection 15 to the second output wire 12.

Further, the switching is carried out in a similar way. When the switch 20 should not switch between the neighboring branches 2-4, and switching can occur between any of the branches, i.e, for example, directly from the first branch 2 to the third branch 4, or Vice versa.

The method by which switching is carried out, more accurately explained by example. It should be assumed that the control unit 6 determines that the switching between the two branches is necessary. Based on this, the control unit provides the ignition of the thyristors in the thyristor circuit 5. The ignition timing is selected in the same way that there is no surge. The ideal way to do this, select the point on the length of time lies before passing voltage through zero, and this period of time corresponds to the delay of ignition of the thyristors. Thus, the thyristors when passing voltage through zero can, in principle, to miss Magnuson the th current.

When the thyristors are in a conducting state due to the connection through the switch 20 and the thyristors occurs inter-turn short circuit, which involves one section of the secondary winding. In this circuit, a short circuit can flow very high current. Working speed is limited in this example, the inductance 53.

Due to the relative positioning of the thyristors at the end of the branch 52 and the switch 20 in one of the secondary branches 2-4 current in the short circuit between the coils is opposite to the load current. Consequently achieved the point in time at which the current in the short circuit between the coils takes the same value as the load current, and thereby, through the switch 20 is no longer the current flows.

This time is used to turn off the connection through the switch. This opening of the switch can be carried out more preferably shortly before the expected zero crossing, in particular in the point in time at which the thyristors are already in a highly conducting state. In this case, when the opening operation of the switching element will have an arc, which, however, in the process of switching power goes out very quickly, usually in the range of microseconds, since the current through the switching element disappears. If the arc once the of asle, when the increase of the voltage through the switching element bigger it does not occur again. For smooth switching appropriate, if disconnection of the connection control switch 20 is such that it opens only when the thyristors are already in a conducting state.

As a consequence, the thyristors pass the load current, as by opening switch 20 inter-turn short circuit is eliminated. The new circuit connection switch 20 is preferably in the natural passing voltage through zero to achieve a smooth transition line. Because after closure of the switch 20 again occurs inter-turn short circuit, it is advisable to complete the ignition of the thyristors in a timely manner before passing through zero in order to avoid the firing of the thyristors simultaneously with the opening operation of the switch 20.

1. The transformer (1, 50) for transformation between medium and low voltage with step switch, which
one of the windings of the transformer has two end branches, and at least two secondary branches;
- provided at least one switching device (20, 35, 36) for dial-up electrical connection of one of the secondary branches with the output wire of the transformer and at least one the semiconductor switching device is lower than the 5.37), electrically connected to the output wire directly to one of the terminal branches.

2. The transformer according to claim 1, in which means are provided for determining values representing the voltage and/or current through the switching element.

3. The transformer according to claim 1 or 2, in which means are provided for determining values representing the voltage across the semiconductor switching device.

4. The transformer according to claim 1 or 2, in which the switching device (20, 35, 36) includes mechanical switches(20, 35, 36).

5. The transformer according to claim 1 or 2, in which the semiconductor switching device (5, 37) comprises two anti-parallel connected semiconductor element, in particular two thyristor.

6. The transformer according to claim 1 or 2, in which the semiconductor switching device (5, 37) contains turn off semiconductor elements, particularly transistors, such as GTO or IGT.

7. The transformer according to claim 1 or 2, in which in series with the semiconductor switching device (5, 37) includes inductance or resistor.

8. The method of operation of the transformer (1, 50) for transformation between medium and low voltage with step switch according to any one of claims 1 to 7, containing a semiconductor switching device for temporary p is lowering the current in the switching process of the switching device moreover, in the process of switching the switching device to determine the first point in time at which the current through the switching device becomes zero, and a switching device to this point in time is opened.

9. The method of claim 8, wherein the semiconductor switching device include shortly before the zero crossing.

10. The method according to claim 8 or 9, in which, after disconnection of the switching device determines the second point in time at which the voltage between the target branch switching device and the output wire of the transformer corresponds to the voltage across the semiconductor switching device and a switching device for this second time closes.

11. The method according to claim 10, in which the duration of the circuit of the switching element, take into account when determining the second point in time.



 

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