JPH0779058B2 - Load tap changer - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load tap changer for a static induction device such as a transformer.

[0002]

2. Description of the Related Art Conventionally, an apparatus of this kind is shown in FIG.
Those shown in are known. 1, 2,
Is a tap provided on the tap winding 3 of the transformer, and can be selectively switched by the movable contacts 4 and 5 of the tap selector. 101 is a changeover switch, and fixed contacts 102, 1 connected to the movable contacts 4, 5 respectively.
03 and movable contact 10 connected via current limiting resistor 105
4 and. Reference numeral 106 denotes auxiliary switches 107 and 10 connected to the movable contact 4.5.
8 is a bidirectional switching element connected between the common terminal 109 and the external terminal 110, and is formed by a thyristor connected in antiparallel. Reference numerals 111 and 112 are main switches for energization, which are respectively connected by the movable contacts 4 and 5, and are connected to the external terminal 110 via the current transformers 113 and 114, respectively. Then, the current limiting resistor 10
5 is connected to the external terminal 110 via the resistor switch 115 and the current transformer 116. Reference numerals 117 and 118 denote AND circuits. The AND circuit 117 outputs an output only when both the current transformers 113 and 116 generate an output, and the AND circuit 118 causes the current transformers 116 and 114 to generate an output. The output is sent only when Reference numeral 119 denotes a gate circuit, which receives the output signals of the AND circuits 117 and 118 and causes the switching element 106 to fire the gate.

The operation will be described below. In the illustrated state, the current is tap 1-movable contact 4-main switch 1
11-flows through the circuit of the external terminal 110. And
When switching from tap 1 to tap 2, first, the movable contact 5 is turned on, and the movable contact 104 of the changeover switch 101 is switched from the fixed contact 102 to the fixed contact 103. next,
When the resistance switch 115 is closed, the tap 2-movable contact 5-fixed contact 103-movable contact 104-current limiting resistor 10
The inter-tap bridging current flows through 5-resistor switch 115-external terminal 110-main switch 111-movable contact 4-tap 1. Therefore, the current transformers 113 and 116 both output the output, and the AND circuit 117 outputs the output, and the switching element 106 is gate-fired.

Next, when the main switch 111 is opened, the current flowing from the tap 1 through the main switch 111 and the external terminal 110 and the bridging current between the taps are almost arcless, and the auxiliary switch 107 and the switching element 106.
Commuted to a circuit consisting of. This commutation causes current transformer 11
Since the output of 3 and the output of the AND circuit 117 become zero, the output of the gate signal from the gate circuit 119 is stopped, and the current commutated to the switching element 106 is cut off at the next current zero point.

As a result, the current is tapped 2-moving contact 5
-Fixed contact 103-Movable contact 104-Current limiting resistance 105-
The resistor switch 115-flows through the electric path of the external terminal 110. Next, the auxiliary switch 107 in the currentless state is opened, then the auxiliary switch 108 and the main switch 112 are closed, and finally, the resistance switch 11
Open circuit 5. This completes the 1-tap switching operation.

[0006]

However, in the device constructed as described above, the AND circuit detects that a current has flowed in both the main switch and the resistor switch, and sends out a gate signal. Since the switching element is designed to ignite the gate, a control power supply is required, and when this control power supply is insulated on the drive side of the gate, it becomes extremely difficult to insulate the gate for three phases. There is a problem in that the size and weight are extremely large to drive, and when insulation is performed on the power supply side, high-voltage insulation is required, and the size increases and if the control power supply is lost for some reason. It has the problem of becoming inoperable. The present invention has been made in view of the above points, and an object of the present invention is to provide a gate drive that can be driven without using a control power supply.

[0007]

In order to achieve the above object, the present invention is configured so that a bidirectional switching element is directly gate-driven through a current transformer by a current flowing through a main switch.

[0008]

Embodiments of the present invention will be described below with reference to FIGS. It should be noted that in the figure, 1 to 5 are the same as the conventional ones, and therefore the description thereof is omitted. In FIG. 1, reference numeral 6 denotes a first changeover switch, which is composed of fixed contacts 6a and 6b and a movable contact 6c which are respectively connected to the pair of movable contacts 4 and 5. The movable contact 6c is connected to the external terminal 9 via the current limiting resistance 7 and the resistance switch 8 connected in series. Reference numeral 10 denotes a second changeover switch, which is fixed contacts 10a and 10b connected to the movable contacts 4 and 5, respectively.
And the movable contact 10c. 11 is the second
Of the changeover switch 10 and the external terminal 9
It is a bidirectional switching element inserted between and and is formed by connecting thyristors Th _{1 and} Th ₂ in antiparallel. Reference numerals 12 and 13 are a pair of main switches, one end of which is connected to the pair of movable contacts 4 and 5 through a pair of current transformers 14 and 15 and the other end of which is connected to the external terminal 9. 16 is connected from the secondary side of the current transformers 14 and 15 and is connected to the switching element 11 by the current transformers 14 and 15.
It is a gate circuit that outputs the next current as a gate signal.

The gate circuit 16 will be further described with reference to FIG. 2. The current transformers 14 and 15 are formed by a pair of current transformers 14a, 14b and 15a, 15b, respectively. The output terminals are connected to each other, the secondary output terminals of the current transformers 14b and 15b are also connected to each other, and the secondary output terminals of the current transformers 14a and 15a are switched via the resistor R _S1 for limiting the gate current. Between the gate and cathode of the thyristor Th ₁ of the element 11, and also the current transformer 14b
And 15b are connected between the gate and the cathode of the thyristor Th ₂ via the resistor R _S2 for limiting the gate current, and the thyristor Th ₁ is connected to the thyristor Th ₁ by a positive half-wave of the alternating current, and the negative output of the alternating current, for example, a negative half. The thyristor Th ₂ is designed to ignite the gate in a half wave. The resistors R _S1 and R _S2 are
Even if there are variations in the gate voltage-current characteristics of the thyristor Th _1, Th _2, the gate current is made to limit so as to be a predetermined value. In addition, the current transformers 14a and 15
a and 14b, it is between secondary output terminal in common connection 15b, and the voltage suppressing circuit DC 1 which is formed by connecting a nonlinear element comprising a diode or the like into a plurality _{antiparallel,} DC ₂ was inserted respectively, current transformer 2 of vessels 14a, 14b, 15a, 15b
When the next current is about to exceed the predetermined value, it is shunted to suppress the increase of the gate current. Incidentally, D _1, D ₂ which is inserted in parallel between the gate and cathode of the thyristor Th _1, Th ₂ is a diode for reverse voltage blocking,
C _1, C ₂ and R _1, R ₂ are capacitors and resistors for preventing malfunction.

In the suppression circuits DC _{1 and} DC ₂ , for example, as shown in FIG. 3A, a diode string in which a plurality of diodes are connected in series is connected in anti-parallel, or in FIG.
As shown in (B), it is configured by connecting a plurality of single-phase bridge circuits in which the DC output terminals are short-circuited in series, and an overcurrent (for example, a rated load current of the rated load current) is applied to the primary side of the current transformers 14 and 15. Two
Even if 0 times flows, the voltage between terminals is low (for example, several V).
To prevent magnetic saturation of the current transformer, and to prevent gate breakdown by selecting the above resistors R _S1 and R _S2 so that the gate input power does not exceed the allowable value by this clamp voltage source. It is like this.

Next, the operation will be described with reference to FIG. now,
In the changeover switch 6, the movable contact 6c is changeably connected to the fixed contact 6b, in the changeover switch 10, the movable contact 10c is changeably connected to the fixed contact 10a, the main switch 12 is closed, and the resistance switch 8 and the main switch 13 are opened. Current is 1-4
It flows through the circuit of -12-9. At this time, since the current flows through the primary side of the current transformer 14, the secondary current outputs a gate signal to the switching element 11 via the gate circuit 16 and becomes conductive. Since the voltage drop is set to be extremely smaller than the ON voltage of the switching element 11, the switching element 11
Is waiting in a state where it can conduct electricity (Fig. 4).
(A)).

In this state, when the tap 1 is switched to the tap 2, the resistance switch 8 is first closed to make it 2-5-6.
An inter-tap bridging current flows through b-6c-7-8-12-4-1 (FIG. 4 (B)). Then the main switch 12
When the circuit is opened, an arc voltage is applied between the terminals of the switching element 11 by the arc generated when the contacts are opened,
The switching element 11 is instantly turned on, the arc of the main switch 12 is extinguished, and the current is 1-4-1.
0a-10c-11-9, the secondary current of the current transformer 14 becomes zero by this commutation, the gate signal stops (Fig. 4 (C)), and the current is cut off at the AC zero point. Is
The current flowing through the switching element 11 is 2-5
-6b-6c-7-8-9 flowing through the circuit (Fig. 4
(D)).

Next, the movable contact 10c of the changeover switch 10
Separates from the fixed contact 10a (FIG. 4 (E)) and closes the main switch 13. Due to this closed circuit, the secondary current of the current transformer 15 is output to the gate of the switching element 11 via the gate circuit 16. As a result, similarly to the above, the switching element 11 stands by in a conductive state, and the contact voltage drop of the switch 13 is caused by the resistance switch 8 and the current limiting resistance 7.
Since it is much smaller than the voltage drop of
The commutation flows to the circuit 3-9 (FIG. 4 (F). In the above operation, the movable contact 10c of the changeover switch 10 separates from the fixed contact 10a without arcing.

Next, the movable contact 10 of the changeover switch 10
c is switch-connected to the fixed contact 10b, and the resistance switch 8 is opened. As a result, the main switch 13 and the switching element 11 are in parallel, but since the ON voltage of the switching element 11 is much larger than the contact voltage drop of the main switch 13 as described above, no current flows through the switching element 11 (see FIG. G)).

Next, the movable contact 6c of the changeover switch 6 is switched and connected to the fixed contact 6a. (FIG. 4 (H)). On this occasion,
The movable contact 6c is switched and connected without arc. This completes the 1-tap switching operation. When switching from tap 2 to tap 1, the operation reverse to the above may be performed.

In the tap switching operation, even if the current increases or the secondary current of the current transformers 14 and 15 increases due to the flow of overcurrent, the gate circuit 16 is provided with the suppression circuits DC _{1 and} DC _2. Since the current can be shunted, the increase in the gate current can be suppressed, and the switching element 11 can be properly ignited without causing the gate breakdown.

Moreover, since the secondary voltage of the current transformers 14 and 15 is clamped to a low voltage (for example, several V), magnetic saturation of the current transformers can be prevented. Further, since the switching element 11 is gate-driven before the opening of the main switch 12 and stands by in a conductive state, when the arc voltage generated by the opening of the main switch 12 is applied between the anode and the cathode. The current can be instantaneously turned on to cause a commutation of the current. The commutation also instantaneously extinguishes the arc, the secondary current of the current transformer 14 becomes zero, and the gate signal can be stopped. That is, the arc connection time can be made minute. In other words, it is possible to automatically stop the gate signal by following the variation in the opening timing of the main switch. Further, since the switching element 11 is gate-driven and stands by in a conductive state, even if an excessive impulse surge voltage is applied, the switching element 11 is instantly conductive to protect the switching element from overvoltage breakdown.

Although the switching element is formed by connecting unidirectional thyristors in antiparallel in the above embodiment, it goes without saying that a bidirectional thyristor such as a triac can be used. In this case, the current transformer and the gate circuit can be configured by one, and the configuration can be further simplified.

[0019]

According to the present invention, the main switch and the current transformer are inserted in series in the movable contactor, and the bidirectional switching element is connected in parallel to the series circuit of the main switch and the AC device. The gate of the switching element, 2 of the current transformer above
Since the next current is sent to drive the gate directly, the gate can be driven without using a special control power supply, and high insulation should be provided even for those operating in the high voltage charging part. Instead, it can be made compact and lightweight.

Further, since the switching element is gate-driven and stands by in a conductive state before the opening of the main switch, if the main switch is opened, the switching element can be instantly turned on and commutated to a current. The gate drive is on standby until all the current in the main switch commutates to the switching elements, and when the current in the main switch becomes zero, the gate current automatically becomes zero, so even if the contact opening of the main switch varies. Even if the above occurs, the timing of stopping the gate signal can be made to automatically follow the above variations, and no special electronic control circuit for timing adjustment is required, eliminating the risk of surge voltage breakdown due to these. You can Moreover, since the current commutated to the switching element is interrupted at the AC zero point, it can be interrupted without generating surge voltage and noise, and the switching element can be energized for a maximum of half a cycle. No cooling fin is required, and an inexpensive element having a small current capacity and high versatility can be applied.

Further, the arc connection time of the main switch is such that the switching element is instantly turned on by opening the electrode,
Since the current of the main switch is commutated, the arc energy becomes instantaneously extremely small, and the wear of the contact can be further reduced as compared with the conventional case, and the contact life can be remarkably increased.

Furthermore, the gate circuit connected to the secondary output terminal of the current transformer is provided with a voltage suppressing circuit connected in antiparallel with a plurality of non-linear elements so that an excessive current flows on the primary side of the current transformer. Since the secondary voltage is clamped to a low voltage even when flowing, magnetic saturation of the current transformer core can be prevented and the core can be downsized. Moreover, when the gate current tries to exceed the predetermined value, it is shunted to the suppression circuit, so that it is possible to prevent the switching element from being destroyed due to an excessive gate current, and to accurately target a wide range of currents. It is possible to provide a device having further improved reliability such as being able to respond.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing a specific example of the gate circuit of FIG.

FIG. 3 is a circuit diagram showing an embodiment of the suppression circuit of FIG.

FIG. 4 is an explanatory diagram of the tap switching operation of FIG.

FIG. 5 is a block diagram showing a conventional example.

[Explanation of symbols]

1, 2 taps 3 tap windings 4, 5 movable contact 6 first changeover switch 7 current limiting resistance 8 resistance switch 9 external terminal 10 second changeover switch 11 switching element 12, 13 main switch 14, 15 current transformer 16 Gate circuit DC _1, DC ₂ voltage suppression circuit

Claims (2)

[Claims] 1. A pair of main switches connected via a pair of current transformers between a pair of movable contacts for selecting a plurality of taps and an external output terminal, and fixed to the pair of movable contacts. A first changeover switch connected to the external output terminal via a current limiting resistance and a resistance switch in which the movable contacts are connected in series, and fixed contacts are connected to the pair of movable contacts. A second contact switch whose movable contact is connected to the external output terminal via a bidirectional switching element and from the secondary side of the pair of current transformers to connect the switching element to the current transformer. A load tap switching device comprising: a gate circuit configured to send a secondary current as a gate signal. 2. The load tap switching device according to claim 1, wherein the gate circuit has a plurality of non-linear elements connected in parallel at its input end and a resistor connected in series at its output end.