JPS6118847B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention provides a separate method for when insulation breakdown occurs in the connection lead wire of the main secondary winding that connects the system protection relay, resulting in a short circuit between the main secondary winding terminals. This invention relates to a parent-child instrument transformer that prevents malfunctions of system protection equipment due to residual voltage in the sub-secondary winding.

FIG. 1 is a diagram illustrating the structure and operation of a conventional parent-child instrument transformer. In the figure, 1 is the primary winding on the high voltage side, 2 is the main secondary winding on the low voltage side (hereinafter referred to as the parent winding), and 3 is the sub secondary winding on the low voltage side (hereinafter referred to as the child winding). , these windings are commonly wound around the same iron core 4.

A system protection relay (hereinafter referred to as protection Ry) 5 is connected to the parent winding 2, which operates when a system abnormality occurs. Further, the parent winding 2 and the child winding 3 are connected via a voltage differential relay (hereinafter referred to as differential Ry) 6 that operates when the difference in voltage between the two windings exceeds a certain value. ing. Further, the operation time is coordinated between the protection Ry5 and the differential Ry6. 7 is parent winding 2
This is the lead wire of the cable etc. that connects the and protection Ry5.

In the configuration shown in FIG. 1, the F-
If insulation breaks down between F′ and a short circuit occurs, protection Ry5
Then, the input on the differential Ry6 protection Ry5 side becomes zero, while the voltage from the child winding 3 remains slightly, so the differential
Ry6 works. Protection Ry5 for more than this operating time
By slowing down the operation time, the protection Ry5 will not malfunction in the event of a failure unrelated to the system, such as a lead wire, and power supply will not be interrupted.

As is clear from the above, in a parent-child type voltage transformer that can be used for such purposes, there must be a residual voltage in the child winding 3 sufficient to operate the differential Ry 6 when the parent winding 2 is short-circuited.

This residual voltage is generated as follows. In other words, an overcurrent flows through the parent winding 2 due to a short circuit between the lead wires F and F'. This overcurrent is limited by the leakage impedance of the primary winding 1 and the parent winding 2, and at this time, the magnetic flux remaining in the iron core is limited by the overcurrent and the leakage impedance of the parent winding 2 (lead wire impedance up to point F-F'). (including) is equivalent to the voltage generated by the product. Since this magnetic flux passes through the child winding 3, a voltage corresponding to the magnetic flux is generated as a residual voltage. It is necessary that this residual voltage is sufficient to operate the differential Ry6, but in conventional parent-child type instrument transformers, it is necessary to
45%, it was difficult to operate the conventional differential Ry6 at high speed, and the disadvantage was that a more expensive high-sensitivity differential Ry had to be developed and used.

The present invention was made to eliminate this drawback, and an object of the present invention is to provide a parent-child type voltage transformer that can use an inexpensive differential Ry.

An embodiment of the present invention will be described below with reference to FIG. As is clear from FIG. 2, the parent-child type voltage transformer of the present invention has an iron core 14 having three legs, and a primary winding 11, a parent winding 12, and a child winding 13 each provided on a separate leg. , protects the parent winding 12 with Ry
It is the same as the conventional method that the child winding 13 is connected to the differential Ry and the child winding 13 is connected to the differential Ry. The equivalent load on the parent winding 12 due to Ry is Zz, and the equivalent load on the child winding 13 is
Let's say Za.

In such a parent-child instrument transformer, when a voltage (V ₁ ) is applied to the primary winding 11, a magnetic flux (φ) is generated in the leg of the primary winding 11. During normal use, this φ is shunted to the other two legs, and a magnetic flux of φ/2 passes through the iron core legs of the parent winding 12 and child winding 13, respectively, and the same voltage (Vz =
V ₃ ) will occur.

Next, when the insulation breaks down between the lead wires F and F' of the main winding 12 and a short circuit occurs, an overcurrent flows through this main winding circuit, and this current cancels the magnetic flux of the iron core legs.
It becomes almost zero. This canceled magnetic flux of φ/2 moves to the core leg of the child winding 13, and the total magnetic flux of the child winding core becomes φ.Therefore, the child winding voltage at this time is equal to the normal voltage. Almost twice as much residual voltage will be generated.

That is, due to a short circuit between the parent winding terminals, the residual voltage in the child winding increases compared to the normal state, so a large voltage is applied to the differential Ry, and the low-cost, low-sensitivity differential Ry can be sufficiently driven.

In addition, in the configuration shown in FIG. 2 as described above, under normal conditions, the respective voltages Vz and V3 appear on the balance of magnetic flux cancellation due to the current flowing through the burden Zz and _Z3 of the parent and child windings 12 and ₁₃ . Therefore, under normal conditions, Vz≒
It may be necessary to add an additional impedance corresponding to and matching the load Zz, _Z3 so that _V3 . To eliminate this inconvenience, the configuration of FIG. 3 is obtained.

FIG. 3 shows another embodiment of the present invention, in which windings 8 and 8' are further wound around the core legs of the primary winding 11 and the parent winding 12 in addition to the structure of the embodiment shown in FIG. The wires 8 and 8' are connected to function as a coupled winding. In this way, for example, the main winding 1
When the magnetic flux in the iron core 14 is about to be canceled by the burden current of 2, current flows through the coupling windings 8 and 8', creating magnetic flux. That is, the coupled winding functions to always maintain the core magnetic flux φ of the primary winding 11 and the magnetic flux of the parent winding 12 at φ/2. In other words, Vz remains almost constant even if the load changes. On the other hand, since the magnetic flux of the parent winding core is always maintained at φ/2, the magnetic flux of the child winding core is maintained at φ/2, and Vz≈V ₃ during normal operation. Note that this relationship holds that the coupled windings 8 and 8' are connected to the child winding 1.
The effect is the same whether it is applied to the third side or both the parent and child windings 12 and 13.

Next, in the configuration shown in Fig. 3, if a short circuit occurs between F and F' of the lead wire of the main winding 12, the magnetic flux of the main winding core is almost canceled by this short circuit current, but there is a method to compensate for this. A current flows through the coupling windings 8, 8' and acts to cancel the magnetic flux of the primary winding 11. After all, according to the general transformer theory, there is a leakage impedance in the primary winding core that includes the primary leakage impedance, the coupling winding 8' seen from the coupling winding 8, the parent winding 12, and the lead wire up to the short circuit point. A magnetic flux corresponding to the divided voltage is generated. All of this magnetic flux flows into the child winding side iron core and induces a residual voltage in the child winding 13. On the other hand, under normal conditions, the child winding 13 is designed such that a steady voltage is generated at 2/1 of the magnetic flux of the primary winding core.
Since the number of turns is, for example, twice the terminal voltage will be induced in the child winding according to the present invention when the child winding 13 is temporarily installed on the primary winding side iron core. As shown in FIG. 1, the conventional parent-child type instrument transformer is almost equivalent to temporarily installing a sub-winding on the primary winding side iron core, so in the case of the present invention, the sub-winding 13 is installed more than the conventional case. It is possible to obtain more than twice the residual voltage. The residual voltage is 50 to 70% of the normal voltage of the child winding 13, and 80 to 130% if the leakage impedance of the coupled winding is considered. If a residual voltage of this magnitude is obtained, even an inexpensive low-sensitivity differential Ry can be sufficiently driven.

In the configuration shown in FIG. 3, if it is desired to obtain a larger residual voltage in the child winding, this can be achieved by inserting an appropriate impedance into the coupled winding circuit.

FIG. 4 shows still another embodiment of the present invention, and FIG.
In the embodiment shown in FIG. 3, a three-legged iron core is used in the iron core configuration, but even if two iron cores 14a and 14b are combined as shown in the figure, the effect is exactly the same.

Although the above explanation deals with the case where the parent winding circuit is short-circuited, in practice, there may also be a short-circuit in the child winding circuit. In this case as well, it is obvious that the differential Ry is driven in exactly the same way as in the case of the parent winding.

As described above, according to the present invention, when the lead wire of the parent (child) winding is short-circuited, the residual voltage in the child (parent) winding can be approximately the same as or higher than the normal voltage. , there is an advantage that the inexpensive and economical voltage differential relay that has been widely used in the past can be used as is.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of a conventional parent-child instrument transformer.
FIG. 2 is a schematic diagram of the parent-child instrument transformer of the present invention;
FIGS. 3 and 4 are schematic diagrams of parent-child voltage transformers showing other embodiments of the present invention, respectively. 5... System protection relay, 6... Voltage differential relay, 8, 8'... Combined winding, 11... Primary winding,
12... Main secondary winding, 13... Sub-secondary winding, 1
4, 14a, 14b...iron core.

Claims (1)

[Claims] 1. A primary winding, a main secondary winding, and a sub-secondary winding are wound around an iron core, a system protection relay is connected to the main secondary winding, and a main secondary winding and a sub-secondary winding are connected to the main secondary winding. In a parent-child type instrument transformer in which the secondary winding is connected via a voltage differential relay, the primary winding is connected to one leg of the iron core with three legs.
A parent-child instrument transformer characterized in that one leg is provided with a main secondary winding, and the remaining leg is provided with a sub-secondary winding. 2. Claim 1, characterized in that separate windings are wound around the leg around which the primary winding is wound and the leg around which the main secondary winding is wound, and these windings are connected to form a coupling circuit. Parent-child instrument transformer as described in Section 1. 3. The parent-child instrument transformer according to claim 2, characterized in that an impedance is connected to the coupling circuit.