JPS6295924A - Tap changing transformer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a tap-changing transformer, and more particularly to a tap-changing transformer equipped with means suitable for preventing a floating state when changing the polarity of a tap winding.

[Background of the invention]

With the practical application of ultra-high voltage, transformers are 500/230 K
V, 400/115 KV are increasingly being used for interconnection between ultra-high pressures (i'). In such a tap-changing transformer, in order to protect the tap winding from the transition voltage to the tap winding due to the intrusion of lightning surge from the high-voltage line terminal or the medium-voltage line terminal, for example, Japanese Patent Publication No. 60-9410, To the tap winding, as described in
It has been proposed to connect surge suppressing elements made of zinc oxide (hereinafter abbreviated as ZnO) elements in parallel. However, when switching the polarity of the tap winding, the tap winding becomes a floating state and the ground potential of the tap winding moves to a potential determined by the capacitance between the windings and between the ground. No particular consideration was given to the possibility that excessive voltage would be generated in the tap changer, causing dielectric breakdown of the tap changer. This will be further explained below using FIGS. 3 and 4.

In FIG. 3, which is an example of a tap-changing autotransformer, the tap winding 6 is provided on the side of the secondary terminal 2. 1 in the diagram
3 is a primary terminal, 3 is a neutral point terminal, 4 is a series winding, 5 is a shunt winding, 8 is a polarity switch, and 9 is a tap terminal. This example is a method for switching the secondary voltage, but it can also be used to switch the negative voltage.

Similarly, a tap winding is provided on the secondary terminal 2 side.

In this type of autotransformer, as shown in FIG. 4, a tap winding 6, a shunt winding 5, and a series winding 4 are wound concentrically around an iron core 2o in this order from the inner diameter side.

In FIG. 3, when the polarity switch 8 is switched with the tap switch 7 connected to the tap terminal 91, the tap winding 6 is in a floating state during the switching operation. The ground potential Vt of the tap winding 6 in this floating state is expressed by the following equation (1).

However, VT is the tap winding potential to ground in a floating state,
v2 is the shunt winding (secondary line) terminal potential, VR is the maximum tap-to-tap potential of the tap winding, Cw is the capacitance between the shunt winding and the tap winding, and GE is the capacitance between the tap winding and ground. It is capacitance.

Here, since the capacitances CE and Cw are almost the same, if Cp=Cw, there will be an excessive potential difference between the terminals 81 and 82 and between 81 and 83 of the polarity switch 8. This causes dielectric breakdown in the polarity switch 8.

In order to prevent the tap winding from floating, it is conceivable to connect the tap winding and the transformer main winding to which it is provided with a resistor element having a certain resistance value. in this case,
The problem is which part of the tap winding 6 should the resistive element be connected to, and the problem is to minimize the voltage applied to the float prevention resistive element of the tap winding 6 and reduce the current flowing through the resistive element during normal operation. Required to minimize and improve long-term reliability. Conventionally, a normal linear resistor has been used as a float prevention resistance element, but this cannot satisfy the above conditions and has the disadvantage that a considerable amount of current flows even under normal operating conditions, resulting in a large temperature rise. , there were problems with long-term reliability.

[Purpose of the invention]

The purpose of the tap change transformer of the present invention is to prevent a floating state when changing the polarity of the tap winding and to improve insulation reliability.

[Summary of the invention]

In the present invention, a main winding for drawing out line side and neutral point side terminals and a tap winding for drawing out a plurality of tap terminals switched by a tap changer are wound around the iron core, and the main winding and the tap winding When configuring a tap switching transformer by connecting the
Connect one end of a float prevention resistance element whose main component is Zn○ to the tap terminal part of the wire, and connect the other end to the line side terminal drawn out through a tap changer that switches the tap terminal of the main winding or tap winding. It is characterized by the following.

In the float prevention resistor element described above, when the tap winding floats, the potential of the tap winding is determined by the value of the charging current flowing through the circuit consisting of the resistor and the capacitance between the winding and ground, and the value of the resistor. Therefore, the value of the resistance element is determined so that this potential is less than the dielectric strength of the polarity changer of the tap changer. However, since the charging current value that determines the value of the resistance element is determined by the capacitance between the windings and the ground, the calculation accuracy of the capacitance becomes a problem. Conversely, a characteristic is desired in which the voltage across the resistance element does not change much even if the charging current value changes slightly.

Furthermore, in normal operation, a voltage of 1/2 of the maximum tap-to-tap voltage of the tap winding is applied to the resistance element, so it is desirable that the resistance element has characteristics such that as little current as possible flows when a low voltage is applied during normal operation. It will be done.

Therefore, for this anti-float resistance element, an element is used in which the main component is Zn○, mixed with various oxides, and fired. This element has high nonlinear characteristics, and I=(
V/C)'' (■: constant current■=voltage, C: capacitance), it has high nonlinearity as shown in curve 10 in Figure 5 where α=15 to 50. Therefore, at the voltage under normal operating conditions, only a very small resistance leakage current (approximately several tens of microns) flows, and the tap winding becomes a float state, the potential to ground shifts, and the float prevention resistor When a charging current (of the order of several mA) flows through the element, the change in charging current.

The terminal voltage of the anti-float resistance element has an extremely good characteristic of being a nearly constant voltage.

[Embodiments of the invention]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an explanation will be given using a single-phase wiring diagram of an autotransformer shown in FIG. 1, which is an embodiment of the present invention. - Next terminal 1 is connected to the connection point between series winding 4 and shunt winding 5 drawn out from other terminals, so that tap winding 6, which uses shunt s5 as the main winding, can switch polarity. Both ends of the tap winding 6 are connected to each other via a polarity switch 8, so the number of turns of the tap winding 6 is only 1/2 of the number of turns required for the tap switching voltage width. 3 is a neutral point terminal. The secondary terminal 2 is connected to a tap terminal 9 through a tap changer 7 consisting of a switching switch and a tap selector (not shown). The above-mentioned element, that is, the float prevention resistance element 101 mainly composed of ZnO having high non-linear characteristics, has one terminal wound with a tap winding of 1 sI.
6, and is connected to the central tap terminal 95, and the other terminal is connected to the shunt winding end 51.

With this configuration, when the polarity switch 8 is switched with the tap switch 7 connected to the tap terminal 91, the float prevention resistive element 101 is connected to the circuit shown in FIGS. 6(a) and 6(b). A charging current determined by flows, and a voltage determined by the VI characteristic shown by curve 10 in FIG. 5 becomes the potential difference between the shunt winding end 51 and the tap winding 6. By selecting the characteristics of the float prevention resistance element 101 so that this potential difference is less than or equal to the dielectric strength of the polarity changer 8 of the tap changer used, it is possible to prevent dielectric breakdown of the polarity changer 8. This has the effect of improving insulation reliability including the tap changer.

In the autotransformer shown in FIG. 2 showing another embodiment of the present invention, the difference from FIG. 1 is that the float prevention resistor element 101 is
This is because the other terminal is connected to the secondary terminal 2. In this way, in addition to the same effect as shown in Fig. 1, if the tap is switched in normal operation, for example, if the tap changer 7 is connected to a tap terminal other than the tap terminal 91°92.98, the float prevention resistor Since the normal operating voltage applied to the element 101 is 172 or less of the maximum tap-to-tap voltage of the tap winding 6, the current flowing through the float prevention resistance element 101 is further reduced, and long-term reliability is also improved. effective.

〔Effect of the invention〕

According to the invention, the polarity of the tap winding is switched.

This prevents the tap winding from floating and keeps the potential below the dielectric strength of the polarity switch.

It improves the insulation reliability of tap-changing transformers, and further improves the long-term reliability of tap-changing transformers by suppressing the current flowing through the anti-float resistance element to an extremely small resistance leakage current during normal operation. It has the effect of causing

[Brief explanation of drawings]

1 and 2 are connection diagrams showing different tap-change transformers of the present invention, FIG. 3 is a connection diagram of a normal tap-change transformer, and FIG. 4 is a winding arrangement diagram of FIG. FIG. 5 is a voltage and current characteristic diagram of a nonlinear element used in the tap-changing transformer of the present invention, and FIGS. 6(a) and (b) are diagrams explaining the principle of the present invention. 1...-secondary terminal, 2...secondary terminal, 3...neutral point terminal. 4...Series winding, 5...Shunt winding, 6...Tap winding, 7...Tap changer, 8...Polarity changer, 9
...Tap terminal, 20...Iron core, 101...Float prevention resistance element.

Claims (1)

[Claims] 1. A main winding that draws out line side and neutral point side terminals, and a tap winding that draws out a plurality of tap terminals that are switched by a tap changer are wound around the iron core, and the main winding and the tap winding are connected to each other. In a device that is connected via a polarity switch, one end of a float prevention resistance element whose main component is zinc oxide is connected to the tap terminal of approximately 1/2 of the switching voltage of the tap winding, and the other end is connected to the main component. A tap-changing transformer characterized in that it is connected to a line-side terminal drawn out through a tap changer that switches the end of a winding or a tap of a tap winding.