JP2590614B2 - Instrument transformer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wound instrument transformer having a plurality of secondary windings.

[0002]

2. Description of the Related Art In an instrument transformer, a secondary voltage becomes zero when an accident occurs in a primary side system, so that a relay connected to a secondary side is operated to issue a command to a circuit breaker. I try to give. However, if a short circuit accident occurs on the secondary side of the instrument transformer, the secondary voltage becomes zero and the relay malfunctions even though the primary side is not a system failure. To prevent this, conventionally, as shown in FIG. 4, an instrumentation transformer PT having one primary winding 1 and two secondary windings 2 and 3 is used. A voltage balancing relay is connected to the secondary side, and when one secondary winding is short-circuited, a malfunction of the relay is prevented by utilizing a residual voltage generated in the other secondary winding.

In the instrument transformer shown in FIG. 4, when a short-circuit fault occurs on the primary side system, the voltages of both the two secondary windings 2 and 3 become zero. Issue a shutdown command. One of the secondary windings, for example, the secondary winding 2
Is short-circuited, a residual voltage is generated in the sound secondary winding 3, so that there is a difference between the induced voltages of the secondary windings 2 and 3. When the voltage balancing relay detects this difference voltage, it is determined that there is no system fault, and the relay is locked to prevent a malfunction of the circuit breaker.

As described above, when two secondary windings 2 and 3 are provided in an instrument transformer to prevent a malfunction of a relay by using a difference voltage between the two secondary windings, one unit is provided. The larger the residual voltage induced in the healthy secondary winding when the secondary winding is short-circuited, the higher the settling voltage of the voltage balancing relay can be set, so that malfunction of the relay is prevented. Is advantageous.

[0005]

FIG. 5 shows an equivalent circuit of a conventional instrument transformer. In FIG. 5, Z1 is a primary impedance, Z0 is an excitation impedance, and Z2a is 2
The impedance of the secondary winding 2, Z2b, is the impedance of the secondary winding 3. Here, when the secondary winding 2 is short-circuited,
The ratio of the residual voltage generated in the secondary winding 3 to the normal voltage is Z
2a / (Z1 + Z2a), and only a residual voltage of about 50 to 20% of the normal voltage was obtained. Therefore, when a conventional instrument transformer is used, the setting voltage of the voltage balancing relay must be set low, and the relay may malfunction.

An object of the present invention is to provide an instrument transformer capable of increasing the residual voltage induced in another secondary winding when a short circuit fault occurs in one secondary winding. It is in.

[0007]

According to the present invention, in order to achieve the above object, an adjusting impedance comprising a resistor or a resistor connected in series to a resistor is connected in series to at least one secondary winding. I do. Then, a voltage generated in at least a part of the adjustment impedance is applied to another secondary winding via the auxiliary transformer.

It is needless to say that the magnitude of the adjustment impedance must be kept within a range where the error of the instrument transformer does not exceed the standard value.

[0009]

Generally, in a transformer for an instrument, the secondary short-circuit current flowing at the time of secondary short-circuit is much larger than the secondary burden current (for example, 100 times the secondary burden current). When the adjustment impedance is connected in series to the secondary winding, a large short-circuit current flows in the adjustment impedance when the secondary winding to which the adjustment impedance is connected is short-circuited, and a large voltage is generated in the adjustment impedance. Therefore, when this voltage is applied to the healthy secondary winding via the auxiliary transformer, the residual voltage of the healthy secondary winding can be increased. The magnitude of the residual voltage can be arbitrarily set by appropriately adjusting the magnitude of the adjustment impedance and the turns ratio of the auxiliary transformer.

[0010]

FIG. 1 shows an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a primary winding, and reference numerals 2 and 3 denote first and second secondary windings, respectively. In this embodiment, an adjustment impedance 8 made of a resistor is connected in series to the first secondary winding 2, and an auxiliary transformer 9 is connected to both ends of the adjustment impedance 8.
Are connected in parallel. The secondary winding of the auxiliary transformer 9 is connected in series to the second secondary winding 3.

Here, the turns ratio of the auxiliary transformer is n, and the impedance of the adjustment impedance 8 is Zk. Normally, the secondary load current I2a flows through the secondary winding 2,
When the secondary winding 2 is short-circuited, it is approximately 100 times as large as the secondary load current.
The next short-circuit current I2s flows. Therefore, in a normal state, the terminal voltage V8 across the adjustment impedance 8 is V8 = I2a
When the secondary winding 2 is short-circuited, the voltage across the adjustment impedance 8 becomes V8 '= I2s ×
Zk, and a voltage approximately 100 times the normal voltage appears at both ends of the adjustment impedance 8. When this terminal voltage V8 'is applied to the auxiliary transformer 9 as shown in the figure, the secondary voltage V9 of the auxiliary transformer becomes V9 = nV8' = nI2sZk.
Since this voltage is applied to the secondary winding 3, the residual voltage of the secondary winding 3 becomes sufficiently higher than before. The magnitude of the residual voltage of the secondary winding 3 can be arbitrarily set by adjusting the turns ratio n of the auxiliary transformer 9 and the magnitude of the adjustment impedance.

The magnitude of the adjustment impedance 8 is set to an appropriate value in consideration of the turns ratio of the auxiliary transformer and a desired value of the residual voltage within a range where the error of the instrument transformer can be kept within a standard range. Set.

In the example shown in FIG. 1, the adjustment impedance 8 is connected in series only to one of the secondary windings 2. However, as shown in FIG. Can be connected. In the example of FIG.
An adjustment impedance 10 composed of a resistor is connected in series to the next winding 3, one winding of the auxiliary transformer 9 is connected to both ends of the adjustment impedance 8, and the other winding of the auxiliary transformer 9 is connected to both ends of the adjustment impedance 9, respectively. They are connected in parallel.

In this embodiment, a voltage generated at both ends of the adjustment impedance 8 when the first secondary winding 2 is short-circuited is applied to the second secondary winding 3 via the auxiliary transformer 9. When the second secondary winding 3 is short-circuited, a voltage generated at both ends of the adjustment impedance 10 is applied to the first secondary winding 2 via the auxiliary transformer 9. Therefore, even if one of the secondary windings is short-circuited, the residual voltage of the other secondary winding can be increased.

In the above embodiment, the adjustment impedance is made up of a resistor, but as shown in FIG.
And the reactor 8 </ b> B connected in series can be used as the adjustment impedance 8. In this case, the voltage at both ends of the adjustment impedance may be applied to another secondary winding via the auxiliary transformer 9, but a part of the voltage of the adjustment impedance may be applied to the other secondary winding via the auxiliary transformer.
It may be applied to the next winding. In the example of FIG. 3, the voltage across the reactor 8B is applied to the second secondary winding 3 via the auxiliary transformer 9.

As described above, when an impedance in which a resistor and a reactor are connected in series is used as the adjustment impedance connected in series to the secondary winding 2, the value of the voltage applied to the secondary winding 3 and the phase angle are determined. Since the adjustment can be made arbitrarily, the error of the secondary winding 3 can be adjusted.

[0017]

As described above, according to the present invention, the adjusting impedance is connected in series to at least one of the plurality of secondary windings provided in the instrument transformer. Since the voltage generated in at least a part of the adjustment impedance is applied to another secondary winding via the auxiliary transformer, if the secondary winding to which the adjustment impedance is connected is short-circuited, , The residual voltage of the sound secondary winding can be increased. Therefore, by increasing the differential voltage of the secondary winding when the secondary side is short-circuited, it is possible to clearly distinguish between a short-circuit accident on the primary side and a short-circuit accident on the secondary side. Can be prevented.

Further, since a voltage generated in the adjustment impedance connected to at least one secondary winding is applied to another secondary winding via the auxiliary transformer, the secondary winding is connected by the auxiliary transformer. Can be insulated. Therefore, the residual voltage characteristics of the secondary windings can be improved without impairing the insulation performance of each secondary winding.

[Brief description of the drawings]

FIG. 1 is a connection diagram showing an embodiment of the present invention.

FIG. 2 is a connection diagram showing another embodiment of the present invention.

FIG. 3 is a connection diagram showing still another embodiment of the present invention.

FIG. 4 is a configuration diagram of a conventional instrument transformer.

FIG. 5 is an equivalent circuit diagram of the instrument transformer of FIG. 4;

Claims (1)

(57) [Claims] 1. An instrument transformer having a plurality of secondary windings, wherein an adjusting impedance comprising a resistor or a resistor connected in series to a resistor is connected in series to at least one secondary winding, A transformer for an instrument, wherein a voltage generated in at least a part of the adjustment impedance is applied to another secondary winding via an auxiliary transformer.