JPH0779059B2 - 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 resistor current transformer 116. Reference numerals 117 and 118 denote AND circuits, and the AND circuit 117 is used for the current transformers 113 and 11 described above.
6 outputs an output only when both are producing an output, and the AND circuit 118 sends an output only when both the current transformers 116 and 114 are producing an output. 11
Reference numeral 9 denotes a gate circuit, which receives the output signals of the AND circuits 117 and 118 to cause the switching element 106 to fire the gate.

Next, the operation will be described. In the illustrated state, the current flows through the circuit of the tap 1-4-11-110. Then, when switching from tap 1 to tap 2, first, the movable contact 5 is turned on, and the changeover switch 1
From the fixed contact 102 to the fixed contact 1
Switch to 03. Next, when the resistor switch 115 is closed, 2-5-103-105-115-110-111
The inter-tap bridging current flows through 4-1. 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 gated through the gate circuit 119.

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.
Commute 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 2-5-103-10.
4-105-115-110. Next, the auxiliary switch 107 in the currentless state is opened, and then the auxiliary switch 108 and the main switch 1
12 is closed, and finally the resistance switch 115 is opened. This completes the 1-tap switching operation.

[0006]

However, in the device configured as described above, the AND circuit detects that a current has flowed in both the main switch and the resistance switch, and the gate circuit detects the current. A control power supply is required because it sends a signal and causes the switching element to ignite the gate. If this control power supply is insulated on the drive side of the gate, the insulation becomes extremely difficult and the three-phase There is a problem in that the size and weight are extremely large when driving the minute gate, and when the control power supply is insulated on the power supply side, high withstand voltage insulation is required and the size is increased. There is a problem that if the control power supply is lost for some reason, it becomes 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 connection terminal 10 via the current limiting resistor 7, the resistor current transformer 8 and the resistor switch 9 which are connected in series. Reference numeral 11 denotes a second changeover switch, which is composed of fixed contacts 11a and 11b respectively connected to both ends of the current limiting resistor 7 and a movable contact 11c. Reference numeral 12 denotes the movable contact 1 of the second changeover switch 11.
A bidirectional switching element inserted between 1c and the external connection terminals 10 are formed by connecting the thyristor Th _1, Th ₂ in inverse parallel. One end of each of the movable terminals 13 and 14 is connected to the pair of movable contacts 4 and 5 through the pair of main current transformers 15 and 16, and the other end thereof is connected to the external connection terminal 10.
A pair of main switches connected to. Reference numeral 17 denotes a third changeover switch, which includes a fixed contact 17a connected from the secondary side of the main current transformers 15 and 16 and a fixed contact 17b connected from the secondary side of the resistance current transformer 8. Movable contact 17c interlocking with movable contact 11c of the second changeover switch 11
Is formed by. 18 is the third changeover switch 1
The secondary currents of the main current transformers 15 and 16 and the resistor current transformer 8 are connected to the movable contact 17c of No. 7 and selectively output as the gate signal to the switching element 12 by the third changeover switch 17. This is the gate circuit.
Reference numerals 19 and 20 denote voltage suppression circuits composed of non-linear elements inserted between the secondary output terminals of the main current transformers 15 and 16 and between the secondary output terminals of the resistor current transformer 8, respectively. When the secondary currents of 15, 16 and 8 are about to exceed a predetermined value, they are shunted to suppress the increase of the gate current. As shown in FIG. 3, for example, the voltage suppressing circuits 19 and 20 may be configured by connecting a diode string in which a plurality of diodes are connected in series in anti-parallel (FIG. 3 (A)) or by short-circuiting a DC output terminal. It is configured by connecting a plurality of phase bridge circuits in series (FIG. 3 (B)), and
An overcurrent (for example, a rated load current of 20
Even if a double current flows, the terminal voltage is selected to be clamped at a low voltage (for example, several V) to prevent magnetic saturation of the current transformer.

The gate circuit 18 will be further described with reference to FIG. 2. The main current transformers 15 and 16, the resistor current transformer 8, the voltage suppression circuits 19 and 20, and the third changeover switch 17 are the switching element 12 Thyristor Th ₁ , T
One set of current transformers 15a and 15b corresponding to h ₂
And 16a, 16b, current transformers 8a and 8b for resistance, voltage suppression circuits 19a and 19b, 20a and 20b, and third changeover switches 171 and 172. The secondary output terminals of the current transformers 15a and 16a are connected to each other, and the secondary output terminals of the current transformers 15b and 16b are also connected to each other, so that the current transformers 15a and 16a and 15b and 16b are connected to each other. Voltage suppression circuits 19a, 19 between commonly connected secondary output terminals
b, respectively, the voltage suppressor circuits 20a and 20b are respectively inserted between the secondary output terminals of the current transformers 8a and 8b, and one ends of the voltage suppressor circuits 19a and 20a, 19b and 20b are commonly connected. Then, the above thyristor Th
₁ and Th ₂ , respectively, and the other ends of the voltage suppression circuits 19a and 20a are connected to the fixed contacts 171a and 171b of the changeover switch 171, and the voltage suppression circuit 19b and
The other end of 20b is connected to the fixed contact 172 of the changeover switch 172.
a and 172b, and the movable contact 171c of the changeover switch 171 is connected to the switching element 1 via a resistor R _S1 for suppressing the gate current provided at the input end of the gate circuit 18.
To the gate of the thyristor Th ₁ of 2 and also the changeover switch 1
Similarly to the above, the movable contact 172c of 72 is connected to the gate of the thyristor Th ₂ via the resistor R _S2, and the secondary currents of the current transformers 15 and 16 and the resistor current transformer 8 are switched to the changeover switch 17. The switching element 12 is selectively sent out to the switching element 12 via the secondary current and the switching element 12 is directly gate-driven by the secondary current. And the resistance R
_The values of _S1 and R _S2 are selected by the clamp voltage sources of the voltage suppressing circuits 19 and 20 so that the gate input power of the thyristors Th ₁ and Th ₂ does not exceed the permissible value, and gate destruction is prevented. ing. Also, thyristor T
D _{1 and} D ₂ inserted in parallel between the gate and cathode of h ₁ and Th ₂ are reverse voltage blocking diodes, and C 1
_1, C ₂ and R _1, R ₂ are capacitors and resistors for preventing malfunction.

The switching element 12 may be formed of a bidirectional thyristor such as a triac. In this case, as understood from the above description, the current transformer 15,
The 16-resistor current transformer 8, the third changeover switch 17, and the voltage suppression circuits 19 and 20 can be configured as a single unit.

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 6a, and in the changeover switch 11, the movable contact 11c is changeably connected to the fixed contact 11a. 1
7a, the main switch 13 is closed, the resistance switch 9 is closed, the main switch 14 is open, and the main current flows through the circuit 1-4-15-13-10 (FIG. 4). (A)). At this time, since the main current flows through the primary side of the main current transformer 15, the secondary current is sent as a gate signal to the switching element 12 through the gate circuit 18 and becomes conductive, but the main switch 13 Since the contact voltage drop of is much smaller than the ON voltage of the switching element 12, it means that the switching element 12 is on standby in a conductive state. Also, 1-4-6a-6c
The circuit of -7-8-9-10 is also closed, but the voltage drop of the current limiting resistor 7 is set to be extremely large compared to the contact voltage drop of the main switch 13, so the main current is closed as described above. It doesn't flow in the circuit.

When switching from tap 1 to tap 2 in this state, first the main switch 13 is opened. At this time, the switching element 1 is generated by the arc generated when the contacts are opened.
An arc voltage is applied between the two terminals, the switching element 12 instantly turns on, and the main current is 1-4-6a-6.
Commutated to the circuit of c-11a-11c-12-10. Due to this commutation, the arc generated by opening the main switch 13 is extinguished instantaneously. Due to this disappearance, the secondary current of the main current transformer 15 also becomes zero, the gate signal stops (FIG. 4 (B)), and the main current is cut off at the zero point of the current.
The main current is 1-4-6a-6c-7-8-9-10.
Flows to the circuit of (Fig. 4 (C)). At this time, the voltage due to the main current and the resistance value of the current limiting resistor 7 is applied between the terminals of the switching element 12, but the secondary currents of the main current transformers 15 and 16 are zero. Therefore, the gate signal is stopped and the switching element 12 does not turn on.

Next, the movable contact 11c of the changeover switch 11
Is separated from the fixed contact 11a, and the movable contact 17c of the changeover switch 17 that interlocks with the changeover switch 11 has the fixed contact 1a.
When the movable contact 11c of the change-over switch 11 is switched and connected to the fixed contact 11b when separated from 7a (FIG. 4 (D)),
The movable contact 17c of the changeover switch 17 is also the fixed contact 17
It is switch-connected to b and closes the main switch 14. Due to the closed circuit of the main switch 14, 2-5-16-14-9-
The inter-tap bridging current flows through the circuit of 8-7-6c-6a-4-1, and the movable contact 17c of the changeover switch 17 is switched and connected to the fixed contact 17b. Due to the current, the switching element 12 receives the gate signal via the gate circuit 18 and stands by in a conductive state (FIG. 4 (E)). At this time, the movable contact 11c of the change-over switch 11 is switch-connected to the fixed contact 11b, but the contact voltage drop of the resistance switch 9 is extremely small compared to the on-voltage of the switching element 12, so the switching element 12 is turned on. Do not work.

Next, the resistance switch 9 is opened. Due to this opening, an arc is generated between the contacts, this arc voltage is applied between the terminals of the switching element 12, the switching element 12 instantaneously turns on, and the arc generated by the opening of the resistance switch 9 is instantaneously turned on. Disappear. Due to the disappearance of this arc, the secondary current of the current transformer 8 becomes zero, the gate signal stops, and the inter-tap bridging current becomes 2-5-16-14-12-11c-11b-7-6c.
-6a-4-1 once flows into the circuit (FIG. 4 (F)), and is cut off at the current zero point. Due to this interruption, the main current is 2
It flows through the circuit of -5-16-14-10 and is switched from tap 1 to tap 2 (FIG. 4 (G)). At this time, the voltage between the taps is applied between the terminals of the switching element 12, but since the secondary current of the current transformer 8 is zero and the gate signal is stopped, the switching element 12 does not turn on. .

Next, the movable contact 6c of the changeover switch 6 is connected to the fixed contact 6a by switching. (FIG. 4 (H)). Since this switching operation is performed without current, no arc is generated.

Next, the movable contact 11c of the changeover switch 11
Is switched and connected to the fixed contact 11a. This changeover switch 1
The movable contact 1 of the changeover switch 17 is interlocked with the changeover operation of 1.
7c is also switched and connected to the fixed contact 17a. Then, the resistor switch 9 is closed. By this closed circuit, 6b-6c-
The circuit 7-8-9 is also closed and inserted in parallel between the movable contact 5 and the external connection terminal 10, but the contact voltage drop of the main switch 14 is caused by the changeover switch 6 and the current limiting resistor 7. , Which is much smaller than the voltage drop of the resistor switch 9, the main current flows through the circuit of 2-5-16-14-10, and the gate signal is switched via the gate circuit 18 by the secondary current of the current transformer 16. The signal is sent to the element 12, and the switching element 12 stands by in a conductive state (see FIG. 4).
(E)). This completes the switching operation for one tap. When switching from tap 2 to tap 1, the operation reverse to the above may be performed.

In the tap switching operation, even if an overcurrent flows through the circuit and the secondary current of the current transformers 15, 16 and 8 increases, the current is output between the secondary output terminals of the current transformers 15, 16 and 8. Since the voltage suppression circuits 19 and 20 are inserted to divert the current, the increase of the gate current is suppressed,
The gate of the switching element 12 can be accurately fired without damaging the gate.

Moreover, since the secondary voltage of the current transformers 15, 16 and 8 is clamped to a low voltage (for example, several V), magnetic saturation of the current transformer can be prevented.

Further, the switching element 12 is gate-driven and waits in a conductive state before the main switches 13 and 14 and the resistance switch 9 are opened, so that the switching element 12 is connected between the anode and the cathode of the switching element 12. When an arc voltage generated by opening the main switches 13 and 14 and the resistance switch 9 is applied, the switching element 12 instantly turns on to allow a current to flow. Moreover, due to this commutation, the arc disappears instantaneously and the secondary currents of the current transformers 15, 16 and 8 become zero, and the gate signal can be stopped. That is, the duration of the arc generated when the switches are opened can be made minute, and the wear of the contacts can be significantly reduced.
In other words, the gate signal is automatically stopped by following the variation in the opening timing of the main switch and the resistance switch, which is automatically performed.

Further, since the switching element 12 is gate-driven and stands by in a conductive state, the switching element 12 is instantly turned on to protect the switching element from overvoltage breakdown even if an excessive impulse surge voltage is applied. You can

Furthermore, in spite of the construction in which the main switch and the resistance switch generate an arc twice when the switch is opened, the switching element is operated by the interlocking second and third changeover switches to open each of the above switches. Since they are inserted in parallel in front of each other, it is possible to configure so-called one arm. Moreover, since the switching element is designed to allow the main current and the inter-tap bridging current to individually pass during tap switching, the responsibility of the thyristor that constitutes the switching element is to divide the main current and the inter-tap bridging current. Both the voltage and the current can be reduced to a maximum of 1/2 compared to those that can be passed at the same time. Therefore, the capacitance can be reduced to a maximum of 1/4, and the thyristor element can have a small capacitance, which is versatile. It will be possible to construct a high price.

In the above embodiment, the switching element 1
Although 2 has been described as being configured by connecting unidirectional thyristors in antiparallel, it is not limited to this, and may be configured by a bidirectional thyristor such as a triac. In this case, the main current transformer connected in series with the main switch, the current transformer for resistance connected in series with the current limiting resistor, and the gate circuit can also be unified, so it is further simplified. It becomes possible to configure.

[0023]

According to the present invention, the main switch and the main current transformer are inserted in series in the movable contactor, and the bidirectional switching element is inserted in parallel in the series circuit of the main switch and the main AC. Since the switching element is directly gate-driven by the secondary current of the current transformer, it can be gate-driven without using a control power source and is operated in the high voltage charging part. Can be made compact and lightweight without high insulation.

Since the switching element is gate-driven and stands by in a conductive state before the opening of the main switch, when the main switch is opened, the switching element is instantly turned on and commutated to the main current. The gate drive is maintained until all the main current flowing in the main switch is commutated to the switching element, and if the main current of the main switch becomes zero due to commutation, the secondary current of the main current transformer is also Since the gate signal becomes zero and the gate signal stops, even if there is a variation in the contact opening of the main switch, the timing for stopping the gate signal can be made to automatically follow the above variation, which is a special case for timing adjustment. There is no need to provide an electronic control circuit, and there is no risk of surge voltage breakdown due to these.

Moreover, since the main current commutated to the switching element is cut off at the AC zero point, the main current can be cut off without generating surge voltage or noise.
Since the switching element may be energized for a maximum half cycle, a cooling fin for heat dissipation is not required, and an inexpensive and versatile element having a small current capacity can be applied.

Further, as for the arc duration of the main switch, the switching element is instantly turned on by the opening,
Since the main current of the main switch is designed to be commutated, the arc energy becomes instantaneously extremely small, and the contact wear can be further reduced compared to the past, and the contact life can be extended. Can be planned.

Furthermore, a current transformer for resistance is interposed between the current limiting resistance and the resistance switch, fixed contacts are connected to both ends of the current limiting resistance, and a movable contact is connected to the switching element. The secondary output end of the current transformer connected in series with the main switch via the changeover switch of
The third changeover switch, in which the fixed contact is connected to the next output terminal and the movable contact is connected to the gate circuit, is the second switch.
When the resistance switch is opened, the switching element is connected in parallel to the resistance switch, and the current flowing through the resistance switch is instantly commutated to the switching element. It is possible to cut off at least, and even if the switching element has one arm, it is possible to reduce the blocking duty of the switching element to the same level as that of the two arms, and it is possible to configure the switching element with a smaller and cheaper one. .

Moreover, the second and third changeover switches can be changed over without current, and the second changeover switch has two energization times when the taps are changed, but the energization time is maximum. Since it is a half cycle, it is possible to reduce the capacity in an extremely short time, and the third changeover switch also has a small capacity of several volts and several A. The switch can be configured with an extremely simple switch, and can be configured at a lower cost than a configuration in which a switching element is provided in parallel with a main switch and a resistor switch.

Furthermore, a plurality of non-linear elements are inserted in the voltage suppressing circuit connected to the secondary output terminal of the current transformer so that even if an excessive current flows in the primary side of the current transformer, the secondary voltage Is clamped to a low voltage, magnetic saturation of the current transformer core can be prevented, and the core size can be reduced.

Moreover, since the current is divided when the gate current exceeds a predetermined value, the current transformation ratio can be increased, so that the switching element can be accurately gate-driven even if the main current is small. Therefore, it is possible to prevent destruction of the switching element due to an excessive gate current, and it is possible to appropriately respond to a wide range of currents.

[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 voltage 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 current transformer for resistance 9 resistance switch 10 external connection terminal 11 second changeover switch 12 switching element 13, 14 Main switch 15,16 Current transformer 17 Third changeover switch 18 Gate circuit 19,20 Voltage suppression circuit

Claims (2)

[Claims] 1. A pair of movable contacts for selecting a plurality of taps, and between the pair of movable contacts and an external connection terminal,
A pair of main switches respectively connected via a pair of main current transformers, and fixed contacts are respectively connected to the pair of movable contactors, and the movable contacts are connected in series to a current limiting resistance and a current transformer for resistance. A first changeover switch connected to the external connection terminal via a resistor and a switch for resistance, and fixed contacts connected to both ends of the current limiting resistor, respectively, and a movable contact via the bidirectional switching element. Fixed contacts are respectively connected to the second changeover switch connected to the external connection terminal, the secondary side of the pair of main current transformers and the secondary side of the resistance current transformer, and the movable contact is the first contact. A third changeover switch which is interlocked with the movable contact of the second changeover switch and is connected from the movable contact of the third changeover switch so as to send the secondary current of the current transformer as a gate signal to the switching element. The gate Load tap changing device that features that it has and a road. 2. A voltage suppressing circuit having a plurality of non-linear elements connected in parallel is inserted between the secondary output terminals of the main current transformer and the resistor current transformer, and the gate circuit has a resistor connected in series at the output end. The tap switching device under load according to claim 1, characterized in that the tap switching device under load is constructed by inserting the device into a tap.