JPS5936914A - Transformer with exciting rush current preventing device - Google Patents

Abstract

PURPOSE:To completely eliminate any exciting rush current, by installing an autotransformer with a special on-load tap changer on the primary side of a transformer for supplying a power necessary for a load. CONSTITUTION:A second transformer 4 with an on-load tap changer is installed on the primary side of a first transformer 2 whose capacity, voltage and impedance are variable with load. The transformer 4 has a core with a magnetic flux density which is not larger than 1/2.8 of the saturated magnetic flux density in a normal operative state, and a winding with the number of taps allowing the secondary voltage to be variable from 1/3 or less to 3/3 of the primary voltage. Any exciting rush current due to the transformer 4 is completely eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an excitation rush current prevention device, and particularly to an excitation rush current prevention device suitable for exciting a transformer connected to a load that generates an excitation rush current.

Conventionally, a two-stage long sword method is well known as a method for preventing excitation rush current. This means that a series resistor is inserted in the first stage, and a series resistor is inserted in the second stage.
There is a method of short-circuiting this resistance in stages, but this method requires an extra closing circuit breaker in addition to a large resistor, and this method cannot completely eliminate the excitation rush current. There were some drawbacks. Another option is to lower the magnetic flux density of the transformer itself under normal usage conditions, but if the transformer is connected to the load side of the transformer, this load will also be excited at the same time, so It is impossible to eliminate the rush.

FIG. 1 is a configuration diagram in the case where no measures against excitation rush current are taken. In this case, even if the transformer 2 does not generate an excitation rush, if there is a possibility that the load 3 will cause an excitation rush in a transformer or the like, an excitation rush will occur when the circuit breaker 1 is closed. FIG. 2 shows a method in which the closing circuit breaker 1 is constructed in two stages as a countermeasure against excitation rush current, in which a series resistor 6 is inserted in the first stage, and this resistor is short-circuited with another circuit breaker in the second stage. In this case, there is a drawback that an extra resistor and circuit breaker are required, and even with this method, the rush current cannot be completely removed.

An object of the present invention is to provide a device that completely eliminates excitation rush current by installing an autotransformer with a special on-load tap changer on the primary side of the transformer that supplies the power necessary for the load.

In order to satisfy the conditions of completely eliminating the excitation rush current, the present invention: (1) The voltage on the load side is gradually increased to a predetermined voltage.

(2) The magnetic flux density of the transformer that receives the system voltage is lowered during normal use, and the structure is such that no excitation rush current occurs.

method was adopted.

FIG. 3 shows an embodiment of the invention. The magnetic flux density in normal use is 1/2.8 or less of the saturation magnetic flux density, and the tap transformer 4 with single-turn connection, the on-load tap changer 5, and the specified capacity, voltage, impedance, etc. according to the load are installed. It consists of a transformer 2 with characteristics. The operating method for this device is to set the tap changer 5 to the lowest tap of the tap transformer 4, turn on the circuit breaker, and after turning on the tap changer, increase the voltage to the primary side voltage V1 of the tap transformer 4 at a predetermined speed. let

If the device is structured and operated in this manner, the theoretical maximum magnetic flux density BM in the iron core of the tap transformer 4 immediately after the circuit breaker is closed will be By = When the magnetic flux density under normal use is set as B. 2.8B,,l, but the saturation magnetic flux density is Ba
Since the transformer 4 is designed so that BIIl<Bs/2.8, the relationship BM<B11 always holds true, and the magnetic flux density in the iron core is below the saturation magnetic flux density, that is, the excitation by the transformer 4 No rush current occurs. Furthermore, when the circuit breaker is closed, the voltage applied to the transformer 2 and the load 3 is the negative side voltage v
Since it is less than 1/3 of I, transformer 2 and load 3
It can be seen that no excitation rush current occurs. In the present invention, the tap transformers 4 are connected in series, but since they are autotransformers, the impedance during steady operation is
Copper loss remains unchanged and has almost no effect on characteristics.

According to the present invention, by installing an autotransformer with an on-load tap changer in front of the transformer and the load that can eliminate the possibility of generating an excitation rush current, it is possible to completely prevent an excitation rush current from occurring. Voltage fluctuations of other devices connected to the same system are eliminated.

[Brief explanation of the drawing]

Fig. 1 shows a conventional wiring diagram without measures to prevent excitation rush current, Fig. 2 shows a conventional connection diagram with a measure to prevent excitation rush current using a resistor, and Fig. 3 shows a measure to prevent excitation rush current according to the present invention. It is a wiring diagram. 1... Circuit breaker, 2... General purpose transformer, 3... Load, 4... Tap transformer (single turn), 5... Tag changer on load.

Claims (1)

[Claims] 1. On the primary side of the first transformer whose capacity, voltage, and impedance are variable according to the load, (1) the magnetic flux density of the iron core under normal use is 1/2 of the saturation magnetic flux density. .8 or less, (2) The secondary side voltage is 3/3 from 1/3 or less of the primary side voltage.
(3) It is an autotransformer, and (4) It has the same capacity as the first transformer connected to the secondary side as a continuous container. A second transformer with an on-load tap changer was fully installed, and the first
A transformer with an excitation rush current prevention device, characterized in that the primary side of the transformer is always connected to the secondary 0111 of the second transformer.