JPS5937844B2 - transformer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transformer capable of suppressing potential oscillations occurring inside transformer windings.

When an AC voltage at or near the commercial frequency is applied to a transformer, a uniform voltage is induced between each turn of the winding, so the potential at each point inside the winding can be easily calculated. can.

However, the potential inside the winding for impulse voltages with steep wavefronts, etc. is strongly influenced by stray capacitance, and is completely different from the potential distribution for AC voltage. A high voltage may be applied locally between the Therefore, especially for the internal insulation of the winding, the insulation must be designed with sufficient consideration given to the potential distribution characteristics of the impulse voltage. An example of the potential distribution of the disc winding is the first
The result will be as shown in the figure. The vertical axis represents the ground potential, and the horizontal axis represents the number of turns. Curve a represents the initial distribution, curve b represents the final distribution, and curve c represents the highest potential envelope. Focusing on one point P in the winding, the potential at the moment the rectangular wave voltage is applied is VPI, and this shifts to the final potential VP2, but since it is an LC circuit, the potential at point P is the same as the point VP2. Go too far V
When it reaches P3, drops again, and returns to near the VPI point, the potential oscillation is repeated. During this process, each part of the winding is locally subjected to high stress, which may cause damage or breakdown of the winding insulation. The present invention has been made in consideration of the above points, and its purpose is to alleviate the local excessive stress caused by the highest potential and prevent damage to the winding insulation without overinsulating. It is an object of the present invention to provide a transformer that can prevent such problems, is inexpensive, and can improve reliability.

Hereinafter, the present invention will be described with reference to an embodiment shown in the drawings.

When the windings 4, 5, and 6 of the transformer are connected in a Δ type as shown in Figure 2, the vicinity of the point corresponding to the P point showing the highest potential in the potential distribution characteristics of each winding as shown in Figure 1 above. A non-linear resistor element 7 (hereinafter abbreviated as element) consisting of a non-linear resistor whose main component is a metal oxide is placed at the winding position of point Q, which will be described later. 4, 5, 6
and the ground. The element T is connected to any intermediate point of the winding excluding the end of the winding, that is, to a position corresponding to the middle between the beginning and the end of the winding, excluding the ends of the winding. Next, the operation of the present invention will be explained.

For example, for the winding 4 shown in FIG. 2, the transformer winding end 1
When an impulse voltage is applied to
For example, if the highest potential distribution characteristic of the potential distribution characteristic of the winding 4 is curve B, as shown in FIG. 3, the potential at point Q of the winding should be 3. Winding Q
Due to the limiting voltage of the element 7 connected near the point, the potential at point Q does not rise to 3, but is suppressed to the potential.

Therefore, by connecting the element 7, the highest potential curve of the winding 4 becomes a curve A with a lower potential than the curve B of the winding 4 alone. That is, V applied to the transformer winding end 1.

By connecting the element 7, only the potential VB, which should be increased to 3 inside the winding, is suppressed to a potential lower than VB, and is applied to the winding 4. Therefore, the potential vibration of the winding 4 can be reduced and suppressed, and the effect can be exerted without impairing the performance of the winding insulation. Further, similar effects can be mentioned regarding the windings 5 and 6. It goes without saying that the present invention can also be applied to cases where the transformer windings are connected in other ways, such as Y-type connection or V-type connection.

Furthermore, by connecting elements between the windings of each phase, the same effect as the present invention can be obtained against surges that occur in the event of an accident such as a line phase short circuit. As explained above, according to the present invention, a non-linear resistor element is connected between any winding midpoint of the transformer winding other than the winding end and the ground, or between the windings. Accordingly, it is possible to provide a transformer that can suppress potential oscillations inside the windings, improve reliability without impairing the winding insulation performance.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the potential distribution characteristics of the disk winding of a conventional transformer, Fig. 2 is a circuit diagram showing the main parts of the transformer of the present invention, and Fig. 3 is a diagram showing the circular diagram of the transformer of the present invention. FIG. 3 is a diagram showing potential distribution characteristics of a plate winding. 1, 2, 3... Transformer winding end, 4, 5, 6... Transformer winding, 7... Non-linear resistor element mainly composed of metal oxide.

Claims (1)

[Scope of Claims] 1. A transformer is characterized in that a non-linear resistor element mainly composed of a metal oxide is connected between an intermediate point of the transformer winding except for the end of the winding and the ground. transformer. 2. The transformer according to claim 1, wherein the non-linear resistor element has a limiting voltage lower than the limiting voltage of a lightning arrester provided externally. 3. The transformer according to claim 1, wherein a nonlinear resistor element is connected between the windings of the transformer.