JPH05226174A - Instrument transformer - Google Patents

Abstract

PURPOSE:To make an alteration of the rating of a fuse or an impedance unnecessary every alteration of the rating of the main body of an instrument transformer, by connecting the primary winding of an auxiliary transformer fitted with taps in series with the secondary winding of the main body of the instrument transformer, and by connecting respectively the fuse and the impedance in parallel with the secondary winding of the auxiliary transformer fitted with taps. CONSTITUTION:In an instrument transformer, a primary winding 7 of an auxiliary transformer 6 fitted with taps is connected in series with a secondary winding 2 of the main body 3 of the instrument transformer. Further, a fuse 4 and an impedance 5 are connected respectively in parallel with a secondary winding 8 fitted with taps of this auxiliary transformer 6. By altering the taps of the secondary winding 8 of the auxiliary transformer 6 while keeping the ratings of the fuse 4 and the impedance 5 constant, such an instrument transformer deals with the alterations of the respective ratings of the main body 3. Thereby, the prevention of a malfunction in the case of a natural disconnection of the fuse and the suppression of a short circuit current when the secondary side of the instrument transformer is short-circuited are made possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of a transformer for measuring instruments.

[0002]

2. Description of the Related Art FIG. 2 shows a standard circuit diagram of a conventional instrument transformer. The instrument transformer has a primary winding 1
A transformer main body 3 composed of a secondary winding 2 and a secondary winding 2, and a fuse 4 connected in series to the secondary winding 2 of the main transformer body 3 for protection during a secondary short circuit. Was becoming.

By providing the fuse 4 in this way, it is possible to prevent the secondary winding 2 from being burned by the secondary short-circuit current.

However, in such a standard instrument transformer, if the fuse 4 is naturally blown, it is not a system accident or a secondary short-circuit accident, but it causes a malfunction such as tripping the system. is there.

In order to avoid this, when the fuse 4 is set to a large current rating so that the fuse 4 does not spontaneously blow,
The secondary winding 2 of the instrument transformer main body 3 must also take measures such as thickening the electric wire in accordance with the fuse 4, and the instrument transformer main body 3 itself becomes unnecessarily large and expensive. There is a problem that becomes.

FIG. 3 shows an example of an instrument transformer proposed to avoid such a problem.
This instrument transformer has a structure in which an impedance 5 is connected in parallel to a fuse 4 which is connected in series to the secondary winding 2. The impedance 5 is a fuse 4
Is larger than the impedance of the secondary load and smaller than the impedance of the secondary load.

With this structure, it is possible to prevent the secondary voltage from becoming zero when the fuse 4 spontaneously blows, and to suppress the secondary short-circuit current.

[0008]

However, in the conventional instrument transformer shown in FIG. 3, the rating of the fuse 4 and the impedance value of the impedance 5 must be changed for each rating of the instrument transformer main body 3. However, there is a problem that design and manufacturing become complicated.

Further, the rating of the fuse 4 is determined by the rating of the instrument transformer main body 3, and the risk of spontaneous disconnection is not improved.

An object of the present invention is to provide an instrument transformer in which the fuse rating and the impedance need not be changed for each rating of the instrument transformer main body.

[0011]

The structure of the present invention which achieves the above-mentioned object will be described. A transformer for a meter of the present invention is a primary transformer of an auxiliary transformer with a tap on the secondary winding of the transformer main body. The windings are connected in series, and the fuse and the impedance are respectively connected in parallel to the tapped secondary winding of the tapped auxiliary transformer.

[0012]

[Operation] In this way, the primary winding of the tapped auxiliary transformer is connected in series to the secondary winding of the instrument transformer main body, and the fuse and impedance are connected to the tapped secondary winding of the tapped auxiliary transformer. When they are connected in parallel, if the rating of the instrument transformer body is changed, this is dealt with by changing the tap of the tapped secondary winding that connects the fuse and the impedance in parallel.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of a transformer for a meter according to the present invention. The parts corresponding to those in FIG. 3 described above are designated by the same reference numerals.

In the instrument transformer of this embodiment, the primary winding 7 of the tapped auxiliary transformer 6 is connected in series to the secondary winding 2 of the instrument transformer main body 3. A secondary winding 8 with a tap of the auxiliary transformer 6 with a tap has a fuse 4 and an impedance 5
Are connected in parallel.

In such an instrument transformer, the ratings of the fuse 4 and the impedance 5 are constant, and for each rating of the instrument transformer main body 3, the tapped secondary winding of the tapped auxiliary transformer 6 is used. This is dealt with by changing the tap.

The winding ratio of the tapped auxiliary transformer 6 is N: 1.
(N is an arbitrary number, for example, 0.1, ..., 1, 2 ...) The impedance of the fuse 4 is Z _{f and} the impedance value of the impedance 5 is Z {Z >>
Z _f and N ² · Z are approximately (5 to 10) Z _VT } The internal impedance of the transformer main body 3 for an instrument is the impedance of the burden connected to the Z _VT secondary winding 2 to the Z _B secondary winding 2 The secondary voltage of V is set to V ₂ .

In the case of an instrument transformer, it is generally designed so that Z _VT <(Z _B / 50), depending on the error accuracy.

The normal case, the case of the secondary short circuit, and the case of the natural disconnection of the fuse 4 will be examined.
The internal impedance of the tapped auxiliary transformer 6 is
Exclude from consideration.

(1) Normal case The error of the instrument transformer main body 3 is

[Equation 1] Therefore, by providing the auxiliary circuit composed of the auxiliary transformer with tap 6, the fuse 4 and the impedance 5, the error is usually hardly affected.

The current I ₂ flowing in the secondary side of the tapped auxiliary transformer 6 is I ₂ = (V ₂ / Z _B ) · N. The fuse 4 should be rated above this value.

(2) In the case of secondary short circuit The current I ₂ ′ flowing in the secondary side of the tapped auxiliary transformer 6 is I ₂ ′ = (V ₂ / Z _VT ) N> 50I ₂ and the tapped auxiliary The fuse 4 provided in the auxiliary circuit including the transformer 6 is blown. At this time, since a current flows through the impedance 5 connected in parallel to the fuse 4, the secondary short-circuit current Is of the transformer main body 3 for an instrument is Is = V ₂ / (Z _VT + N ² · Z) = V ₂ / (6-11) Z
_It becomes _VT and the secondary short circuit current can be suppressed to about 1/5 to 1/10,
It is possible to prevent the secondary winding 2 of the transformer main body 3 from burning.

On the other hand, the secondary voltage of the transformer main body 3 is
It depends on the ratio of the internal impedances of the primary winding 1 and secondary winding 2 of the instrument transformer main body 3, but it is about 50% of the normal state.
It drops below.

(3) In the case of natural disconnection At this time, the secondary voltage V ₂ ^〃 of the instrument transformer main body 3 is

[Equation 2] , And about 90% or more of the voltage at the time of soundness remains, obviously 2
It can be distinguished from the next short circuit.

[0024]

As described above, in the transformer for a meter according to the present invention, the primary winding of the auxiliary transformer with a tap is connected in series to the secondary winding of the transformer main body for an instrument, and the auxiliary with the tap is connected. Since the fuse and the impedance are respectively connected in parallel to the tapped secondary winding of the transformer, it is possible to prevent malfunction of the fuse during natural disconnection and to suppress short-circuit current during secondary short-circuit.

In particular, according to the present invention, optimum fuse ratings and impedance values are selected and made constant, and various ratings of the instrument transformer main body are provided with taps 2 for connecting fuses and impedances in parallel. This can be dealt with by changing the tap of the next winding. Therefore, according to the transformer for an instrument of the present invention, it is possible to standardize the parts used.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of an instrument transformer according to the present invention.

FIG. 2 is a standard circuit diagram of a conventional instrument transformer.

FIG. 3 is a circuit diagram of another example of a conventional instrument transformer.

[Explanation of symbols]

1 ... Primary winding, 2 ... Secondary winding, 3 ... Instrument transformer main body,
4 ... Fuse, 5 ... Impedance, 6 ... Auxiliary transformer with tap, 7 ... Primary winding, 8 ... Secondary winding with tap.

Claims (1)

[Claims] 1. A primary winding of a tapped auxiliary transformer is connected in series to a secondary winding of an instrument transformer body, and a fuse and an impedance are respectively provided in the tapped secondary winding of the tapped auxiliary transformer. An instrument transformer characterized by being connected in parallel.