JPH0263281B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a control transformer that supplies control power to a control device, a relay, etc. [Technical Background of the Invention] Generally, certain types of power control devices, relays, etc. (hereinafter simply referred to as relays) operate normally even in the event of a one-wire disconnection accident or a two-phase short circuit accident on the three-phase power supply side. required to do so. For this reason, in the past, as shown in Figure 1, for example, 3-phase 6600V was received with a 3-phase V-connection transformer, lowered to an appropriate secondary voltage, and converted to DC using a 3-phase Gretz connection, resulting in control power. was being supplied to the relay. According to this, three-phase
When a single wire disconnection or two-phase short circuit occurs on a 6600V distribution line, the voltage equivalent to single-phase full-wave rectification, that is, 2/3 of the normal value, is supplied to the relay without loss of DC output voltage. be able to. On the other hand, the lower limit of the voltage at which an operating relay can no longer maintain its operating state due to a drop in the applied voltage and returns to its original state (hereinafter referred to as the "return voltage") can be determined by using a circuit attached to the relay. It is said to be about 30% of the time. Therefore, under the above circuit conditions, the voltage is maintained at 2/3 of the normal voltage, so the relay does not malfunction. [Problems with Background Art] However, in the above-mentioned conventional system, a rectifier and a capacitor and a resistor for protecting the rectifier from surges must be attached, making the device complicated, large-sized, and expensive. Moreover, the number of parts increases,
There were drawbacks such as decreased reliability as a system. [Object of the invention] The present invention provides a control transformer that eliminates the need for accessories such as capacitors and resistors, and that can secure the minimum voltage necessary for normal operation of the relay even in the event of a disconnection of at least one wire on the three-phase power supply side. The purpose is to provide [Summary of the Invention] For this reason, the present invention provides gaps on the legs on both sides of the iron core, inserts a pair of coils into each leg to form a three-phase V connection, and adjusts the ratio of the number of turns of the two secondary coils. It is characterized in that it is configured with a ratio of 1:0.37 to 1:1, and a single-phase control power source is taken out between both terminals. [Embodiment of the Invention] Fig. 2 shows a conceptual diagram of a control transformer (hereinafter referred to as Tr) according to an embodiment of the present invention.
Although not shown, there is a secondary coil inside and a secondary coil outside.
This is a coil wound so that the next coil is arranged coaxially. The number of turns of the two primary coils is the same, but for the secondary coil, one is set to 1 and the other is set to 0.5. These primary coils and secondary coils are connected to a three-phase V connection, and a load is connected between u and w. 2 is a three-phase, three-leg iron core, with legs 2U and 2W on both sides into which the coil 1 is inserted.
A gap 3 is provided between the upper and lower yokes. No gap is provided on the center leg 2V.
Although the legs 2U and 2W into which the coil 1 is inserted are not shown, they are tightened together with other core parts by tightening clamps. According to the above configuration, since the legs 2U and 2W are provided with the gaps 3, the magnetic resistance becomes large. Therefore, more excitation current flows in order to induce magnetic flux corresponding to the voltage applied to the secondary coil. That is, the excitation impedances Zou and Zow of the U phase and W phase become small. By appropriately selecting the size of gap 3, the values of Zou and Zow can be set to the required values. Since there is no gap in the leg 2V, the magnetic resistance is small and the excitation impedance Zov is large. Now, when a single-phase voltage is applied between UV, a magnetic flux proportional to the voltage is generated in leg 2U, but that magnetic flux is divided into legs 2V and 2W. Let α be the ratio of the magnetic flux of the leg 2W to the magnetic flux passing through the leg 2V. When there is no gap in the legs, the magnetic flux passes in inverse proportion to the magnetic path length, so the value of α is approximately 0.4. If the same gap length is provided for all three phases of the legs, the magnetic resistance is determined mostly by the gap length, so it becomes almost equal and α=0.5. Using a three-phase iron core with a leg cross-sectional area of 5cm x 5cm and a window size of 3.5cm x 10cm, a 1.05mm gap is provided on the legs on both sides, and a single-phase connection is made between the UVs with no gap in the center. The value of α when voltage was applied was 0.11. Furthermore, when a three-phase voltage is applied to the Tr of this embodiment, when any phase of the three-phase voltage is open,
The vector diagram of the induced voltage of the primary and secondary coils and the voltage between uw when any two-phase short circuit occurs is shown in Table 1 below. However, although the formulas in Table 1 are general, the numerical values are for the case where the rated voltage of the secondary coil is 115.4 (V) and the ratio of the number of turns is 1:0.5. Also,
As shown in the vector diagram in Table 1, in order to obtain the desired voltage across uw where the U and W phase secondary coils constituting the V connection are equivalently connected in series, 1
The polarity of the primary coil and the secondary coil must be the same for both the U and W phases.

【table】

〔Effect of the invention〕

As described above, according to the present invention, the ratio of the number of turns of the two secondary coils can be set to 1:0.37 to 1:1 using only one transformer, without requiring additional circuits such as resistors and capacitors. By doing so, it is possible to secure the voltage necessary to prevent malfunction of the relay in the event of a disconnection accident in at least one of the distribution lines. Therefore, it is possible to obtain a control transformer that has a simpler structure than the conventional case, and is small, lightweight, economical, and highly reliable.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a conventional control power supply device;
The figure is a conceptual diagram of a control transformer showing one embodiment of the invention, and FIG. 3 is an explanatory diagram of an iron core according to another embodiment of the invention. 1...Coil, 2...Iron core, 3...Gap.

Claims (1)

[Claims] 1. Provide a gap on any two legs of the 3-phase, 3-leg iron core, and wind the primary and secondary coils around each leg with the gap, and make a 3-phase V connection. is the ratio of the number of turns, and if there is no need to consider two-phase short circuits, it is 1:
0.37 to 1:1, or 1:0.37 to 1:0.74 when two-phase short circuit needs to be considered, and a control transformer configured to extract single-phase control power from between both terminals. vessel.