JPH05166645A - Ac switchgear - Google Patents

Abstract

PURPOSE:To simplify the constitution of the title switchgear by a method wherein the ON/OFF control operation of a thyristor is performed by an output electric current, from a secondary winding at a current transformer, which is sent out and stopped so as to correspond to the shutting and opening operation of a switch. CONSTITUTION:A secondary winding at a current transformer CTa is connected in series across the following: a gate Ga for a thyristor Tha in which a terminal Ta2 is connected to an output terminal 10' and a terminal Ta1 which is connected to a movable contact 6a3 at a short-circuit switch 6a. On the other hand, a secondary winding at a current transformer CTb is connected in series across the following: a gate Gb for a thyristor Thb in which a terminal Tb2 is connected to the output terminal 10; and a terminal Tb1 which is connected to a movable contact 6b3 at a short-circuit switch 6b. The thyristors Tha, Thb are made conductive by a secondary-winding output electric current which corresponds to an electric current flowing to primary windings Ca1, Cb1 at the current transformers CTa, CTb and which corresponds to a current transformation ratio. Thereby, the constitution of the switchgear is simplified, the failure rate of the switchgear is lowered and the cost of the switchgear can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC switchgear which connects a switch having a contact and a thyristor in parallel to open and close an AC circuit with substantially no arc.

[0002]

2. Description of the Related Art Conventionally, as a device of this type, a switch having contacts in an AC circuit (hereinafter simply referred to as a switch) and a thyristor such as a unidirectional thyristor connected in a triac or antiparallel (hereinafter simply referred to as a thyristor). And are connected in parallel and inserted, the output terminal of the control circuit that operates by being supplied with a constant voltage from the control power supply is connected to the gate of this thyristor, and the signal input terminal of this control circuit is
An output terminal of a sensor such as a photodetector that detects an arc generated between contacts, a current transformer that detects an electric current, and a transformer for an instrument that detects a voltage between contacts generated by opening, or
When the sensor or auxiliary switch outputs a signal that detects the opening operation of the switch by connecting the output terminal of the auxiliary switch that opens and closes in conjunction with the opening and closing of the contact of the switch, the gate signal is output from the control circuit. To make the thyristor conductive and transfer the load current flowing through the switch to the thyristor, and then stop sending the gate signal so that the load current is cut off by the thyristor.
In some cases, the load is turned on by supplying a load current through the switch by opening the switch.

Further, a control device for sending an opening or closing command to the switch and a gate signal to the thyristor is provided, and the load is first turned on by the control command of the control device. The gate signal is sent to turn on the thyristor, and then the switch is closed to supply the load current through the switch.The load is cut off by sending the gate signal to turn on the thyristor and then turning on the switch. In some cases, the gate signal is stopped after switching the load current to the thyristor by opening the pole to interrupt the load current by the thyristor.

[0004]

However, the AC switchgear configured as described above requires a control power supply, a control circuit or a control device, an auxiliary switch, or the like, and the device is a high voltage circuit. When the switch and the thyristor are connected to a high voltage AC circuit, it is necessary to insulate the control power supply from the high voltage circuit or the control circuit or the control device from the high voltage circuit. There is a problem that it becomes complicated and causes a decrease in reliability.

Further, in the above-mentioned AC switching device in which the gate signal is sent out to make the thyristor conductive after receiving the output signal of the sensor for detecting the opening of the switch or the auxiliary switch, the thyristor is the gate signal. In response to this, first the local area near the gate is made conductive, and it takes time (turn-on time) until this conductive area is spread over the entire junction and the entire junction becomes conductive.Therefore, arcing occurs due to the opening of the switch. Then, a large arc voltage caused by the contact opening speed of the switch, the distance between contacts, the contact material, the power supply voltage, the magnitude of the load current, etc. is applied between the terminals of the thyristor, and the gate signal is sent to The current shifts to a thyristor at a steep rise (that is, a high current rise rate) and concentrates on the local area near the gate, heating this local area and turning it on. However, the load current from the switch to the thyristor increases because the delay of the gate signal from the switch opening and the turn-on time of the thyristor receiving the gate signal are required. However, there is a problem that the time until the process shifts to becomes longer, and the arc connecting time between the switch contacts becomes longer accordingly, and the switch contacts are consumed more.

[0006] Further, when the load current is transferred to the thyristor which detects the opening of the switch and sends the gate signal to make it conductive, the gate signal is stopped when the load current is cut off by the thyristor. Adjust the stop timing,
It is difficult to keep the temperature constant regardless of fluctuations in ambient temperature and aging of electronic components. Therefore, when the gate signal transmission time becomes long (for example, after opening the switch, half a cycle is exceeded). However, since the energization time of the thyristor becomes longer in proportion to this time, there is a problem that a thyristor having a large capacity and further a heat dissipation device for the thyristor are required.

When the switch is closed when the load is turned on,
There is a problem that load current may be intermittent due to chattering of the switch, and the arc generated at this time causes wear of the switch contact and noise.

On the other hand, in the above control device in which the gate signal is sent from the control device together with the command for opening or closing the switch, when the load is to be cut off, immediately after opening the switch, When the gate signal is stopped (for example, within half cycle) or when the load is turned on, the switch is closed immediately (for example, within half cycle) after sending the gate signal, and the energizing time of the thyristor However, it is necessary to keep the timing of stopping or sending the above gate signal constant regardless of fluctuations in ambient temperature, wear of the switch contact or its drive mechanism, etc. There was a problem that it was difficult.

The object of the present invention is to solve the above-mentioned problems and it is not necessary to particularly provide the above-mentioned control power source, auxiliary contact, control circuit or control device, and also when applied to a high voltage circuit. Without any special insulation treatment, and without adjusting the timing of sending or stopping the gate signal, the load current flowing to the switch after opening the switch can be swiftly and safely even if its rise is sharp. In order to provide an AC switchgear that can switch the thyristor to conductive state and switch off the load current instantaneously after switching to the thyristor with almost no arc, and can suppress the harmful effects of chattering when the switch is turned on. is there.

[0010]

In order to solve the above problems, the present invention inserts a circuit having a switch having contacts and a primary winding of a current transformer connected in series into an AC circuit, and the circuit is connected to this switch. Connect the thyristor in parallel to the series circuit of the sink,
The secondary winding of the current transformer is connected to the gate of the thyristor so that the thyristor is on / off controlled by the output current of the secondary winding of the current transformer.

When the fluctuation of the load current flowing in the AC circuit is large, the secondary winding of the current transformer and the resistor are connected in series to the gate of the thyristor, and the secondary winding of the current transformer is further connected. A bypass impedance having a non-linear voltage-current characteristic may be connected in parallel.

Further, a tap winding having a plurality of taps is provided in the AC circuit, and a switch having a contact is provided on at least one of the pair of movable contactors for selecting the taps of the tap winding. The primary winding of the current transformer is connected in series, the circuit of the switch and the current transformer connected in series, a thyristor is inserted in parallel, at least the other movable contact of the pair of movable contacts, A current limiting impedance that limits the circulating current between taps is inserted between the switch connected in series and the circuit of the current transformer, and the output terminal of the secondary winding of the current transformer is connected to the gate of the thyristor. do it,
It is characterized in that at least one movable contact of the pair of movable contacts selects a tap after opening the switch.

[0013]

[Function] When the switch is closed, all the load current flows through the switch, and the output current of the secondary winding of the current transformer in which this load current flows in the primary winding is used as the gate current for the gate of the thyristor. Have been sent to. As a result, the thyristor stands by in a state in which the entire junction of the elements can be conducted (that is, the thyristor is immediately conducted when a predetermined voltage is applied between both terminals of the thyristor). When the switch opens in this state, an arc occurs between the switch contacts,
This arc voltage is applied between both terminals of the thyristor so that the thyristor becomes conductive, the load current instantaneously transfers from the switch to the thyristor, and the arc between the contacts disappears, and at the same time, the secondary winding of the current transformer. The output current of the line, that is, the gate current becomes zero, and the thyristor cuts off the load current at the AC zero point of the transferred load current. Also, when the switch is energized and the switch is energized, the thyristor receiving the gate current through the current transformer becomes conductive and chattering occurs in the switch, causing the switch to open the next moment and arcing occurs. The current is instantaneously transferred to the thyristor, the arc is extinguished, and the thyristor is re-closed by the time it is turned off, so that the load current can be supplied without interruption.

A bypass impedance having a non-linear voltage-current characteristic is connected in parallel to the secondary winding of the current transformer, and a resistor is connected in series between the secondary winding of the current transformer and the gate of the thyristor. In this case, by setting the current transformer to a current ratio that can supply the gate current required for conduction of the thyristor when the load current is small, a large load current flows and the secondary winding of the current transformer Even if the output current becomes large, this output current flows into the bypass impedance and maintains a substantially constant voltage between the secondary winding terminals of the current transformer, so a stable gate current flows even if the load current fluctuates greatly. be able to.

During tap switching, when a pair of movable contacts bridges the taps of the tap winding, the current limiting impedance limits the circulating current between the taps and opens the switch to load current flowing in the AC switch. Shut off. At this time, an arc is generated between the contacts of the switches of the AC switch, but the load current instantly transfers to the thyristor, so the arc duration is extremely short. Further, since the arc energy between the contacts of the switch is very small, the consumption of the contacts is extremely small. Then, when the switch contact of the AC switch provided between the movable contactor and the output terminal connected to the next adjacent tap switch to be switched is closed, the load current flows through this AC switch.

[0016]

EXAMPLE An example in which the present invention is applied to a switching switch of a load tap changer will be described. FIG. 1 shows, for example, a circuit configuration for one phase of a load tap changer 1 for three phases. This load tap changer 1 is connected to a tap winding 2 of a transformer, for example, in a star connection. Output terminal 1 connected to neutral point N
Between 0 and 0, a tap selector 3, a current limiting impedance (current limiting resistance in this example) 4 and a switching switch 5 are provided.

In FIG. 1, the tap selector 3 is a fixed contactor 21, 23 --- and 22, 24 respectively connected to a plurality of taps provided on the tap winding 2 of the transformer.
Is provided with a pair of movable contacts 31 and 32 that can be switched and connected, and the pair of movable contacts 31 and 32 is interlocked with the opening / closing operation of the switching switch 5 by a tap switching command of a control device (not shown). Is formed to operate.

Next, the switching switch 5 will be described. 6a and 6b are a pair of short-circuit switches, and fixed contacts 6a connected to the pair of movable contacts 31 and 32, respectively.
₁ and 6b ₁ , fixed contacts 6a ₂ and 6b ₂ respectively connected to the output terminal 10, and these fixed contacts 6a ₁ and 6a ₂
And it is structured from the movable contact 6a _3, 6b ₃ for switching and connected to one fixed contact 6b _1, 6b _2. Reference numeral 7 denotes an auxiliary switch, which is the short-circuit switch 6a, 6
b respectively connected fixed contacts 7a to the movable contact 6a _3, 6b ₃ of, and 7b, and is configured from these fixed contacts 7a, a movable contact 7c of switch connected to one of 7b.

Reference numeral 8 denotes, for example, a rotary type changeover switch, which includes a fixed contact 8c connected to the movable contact 7c of the auxiliary switch 7 through a current limiting resistor 4 and the short-circuit switch 6 described above.
fixed contacts 8a and 8b respectively connected to a and 6b,
The movable contact 8d is connected to the output terminal 10. The movable contact 8d is connected to the short-circuit switch 6
It rotates in conjunction with a and 6b and the auxiliary switch 7, and once bridges between the fixed contacts 8a and 8c adjacent to each other, and then switches and connects to the adjacent fixed contact 8a, 8b or 8c.

CTa and CTb are current transformers, and their primary windings Ca ₁ and Cb ₁ are movable contacts 6a _{3 of the} short-circuit switch 6a.
And the fixed contact 8a of the changeover switch 8 and between the movable contact 6b ₃ of the short-circuit switch 6b and the fixed contact 8b of the changeover switch 8 respectively. The secondary winding of the current transformer CTa has a thyristor (a triac in this example) Tha whose output terminal 10 is connected to the terminal Ta _2.
Of the current transformer C connected in series between the gate Ga and the terminal Ta ₁ connected to the movable contact 6a ₃ of the short-circuit switch 6a.
The secondary winding of Tb is connected to the output terminal 10 at the terminal Tb as described above.
₂ is connected in series between the gate Gb of the thyristor Thb and the terminal Tb ₁ connected to the movable contact 6b ₃ of the short-circuit switch 6b, and the primary windings Ca ₁ and Cb _{1 of the} current transformers CTa and CTb are connected. The thyristors Tha and Thb are made conductive by the secondary winding output current corresponding to the current flowing through the thyristor and the current transformation ratio.

In other words, the short-circuit switch 6a is provided between the movable contact 31 and the output terminal 10 which form a part of the AC circuit.
A circuit in which the primary winding Ca _{1 of} the current transformer CTa and the switch Sa formed by the fixed contact 8a and the movable contact 8d of the changeover switch 8 are connected in series is inserted through the The thyristor Tha is connected in parallel to the series circuit of the primary winding Ca ₁ and the switch Sa, and the current transformer CT is connected between the gate Ga and the terminal Ta _{1 of the} thyristor Tha.
An AC switch 9a is configured by connecting the secondary windings of a in series, and similarly, the current transformer CTb is provided between the movable contact 32 and the output terminal 10 via the short-circuit switch 6b. The primary winding Cb ₁ of the changeover switch 8 and the switch Sb formed by the fixed contact 8b and the movable contact 8d of the changeover switch 8 are connected in series, and the primary winding Cb of the current transformer CTb is inserted.
The thyristor Thb is connected in parallel to the series circuit of b ₁ and the switch Sb, and the secondary winding of the current transformer CTb is connected in series between the gate Gb and the terminal Tb _{1 of the} thyristor Thb to form the AC switch 9b. It will be configured.

[0022] Then, the switches Sa and the voltage drop across and between 8c · 8d contacts 8a · 8d of Sb, said thyristor Tha and the terminal Ta ₁ · T required for conduction of Thb
voltage between a ₂ and terminals Tb ₁ and Tb ₂ (for example, 1.5
It is set to be extremely smaller than V).

Next, the operation of the load tap changer 1 configured as described above will be described with reference to FIGS. Now, Figure 1
As shown in, the movable contacts 31 and 3 of the tap selector 3
2 to the fixed contacts 21 and 22, the movable contact 6a ₃ of the short-circuit switch 6a to the fixed contact 6a ₁ , and the short-circuit switch 6b.
Movable contact 6b ₃ of the fixed contact 6b ₂ to the auxiliary switch 7
Of the changeover switch 8 is connected to the fixed contact 8a (that is, the switch Sa is closed), and the load current is the same as that of the tap winding 2 and the neutral point. Between N, the movable contact 31, the fixed contact 6a ₁ of the short-circuit switch 6a and the movable contact 6a ₃ , the primary winding Ca _{1 of} the current transformer CTa, the fixed contact 8a and the movable contact 8d.
(That is, the switch Sa) and the circuit of the output terminal 10 are flowing.

At this time, the current transformer CTa outputs a current from the secondary winding, which is used as a gate current for the thyristor Th.
Since the voltage drop between the contacts 8a and 8d of the switch Sa which has been closed to the terminal a is extremely smaller than the voltage between the terminals Ta ₁ and Ta ₂ required for conduction of the thyristor Tha, the load current is All flow through the switch Sa without flowing to Tha (before time t _{1 in} FIG. 2). For this reason, the thyristor Tha stands by in a conductive state over the entire junction of the elements. At this time, a switch Sa is provided between both terminals Ta ₁ and Ta _{2 of} the thyristor Tha, and both terminals Tb ₁ and Tb _{2 of the} thyristor Thb.
Are short-circuited via the short-circuiting switch 6b, and even if a surge voltage or the like from the transformer winding 2 enters the tap changer 1 at the time of load, this is caused by thyristors Tha and Thb.
Thyristor Tha, T without being applied between the terminals of
There is nothing that hb will destroy.

Then, when a tap switching command for switching from the fixed contacts 21 to the taps of the fixed contacts 21 is sent from a control device (not shown), first, the movable contact 6b of the short-circuit switch 6b.
₃ is fixedly connected to fixed contact 6b ₁ and then changeover switch 8
The movable contact 8d rotates to temporarily bridge between the fixed contacts 8a and 8c ((1) in FIG. 4). As a result, in addition to the above load current, the circulating current between taps causes the movable contact 3 to move.
2, fixed contact 6b ₁ and movable contact 6b of short-circuit switch 6b
₃ , fixed contact 7b and movable contact 7c of auxiliary switch 7, current limiting resistor 4, movable contact 8d of fixed contact 8c, fixed contact 8
a, the short-circuit switch 6a, the movable contactor 31, and the fixed contactor 21 flow. Next, at the moment when the movable contact 8d is separated from the fixed contact 8a (that is, the switch Sa is opened) and connected only to the fixed contact 8c, the contacts 8a, 8d
An arc is generated between them, and this arc voltage is applied between the terminals Ta ₁ and Ta ₂ of the thyristor Tha which is already in a conductive state by receiving the gate current, and this arc voltage is applied between the terminals necessary for the conduction of the thyristor Tha. Since the voltage is higher than the voltage, the thyristor Tha instantly conducts, and the load current and the tap-to-tap circulating current shift from the switch Sa to the thyristor Tha ((2) in FIG. 4, time t ₁ in FIG. 2).

When all the current flows from the switch Sa to the thyristor Tha, the current flowing through the primary winding Ca ₁ of the current transformer CTa becomes zero as the arc disappears, and the gate current of the thyristor Tha also becomes zero. The thyristor Tha cuts off the transferred current at the AC zero point (time t _{2 in} FIG. 2, (3) in FIG. 4).

When the movable contact 8d of the changeover switch 8 is further rotated to bridge the fixed contacts 8c and 8b, the fixed contact 8c.
All the current flowing in the fixed contact 8b is transferred to the fixed contact 8b, and the current of the fixed contact 8c becomes zero. In this case, at the moment the movable contact 8d and the fixed contact 8b is connected (i.e., the switch Sb is closing) by the (t ₃ time points in FIG. 2), the chattering is generated between said contact 8d · 8b, arc Accordingly also Occurs,
Once the switch Sb is energized, the thyristor Thb which has received the gate current through the current transformer CTb becomes conductive, and even if the switch Sb is closed the next moment by chattering and an arc occurs, the thyristor is instantly released. Since the arc disappears as the current shifts to Thb, the load current is not interrupted due to chattering, and the arc can be made extremely small, so that the harmful effects of chattering can be almost eliminated.

The movable contact 8d is further moved to contact the contacts 8d.
If only b is connected, the contacts 8c and 8d are opened at zero current, and no arc is generated between the contacts 8c and 8d. The load current is the fixed contact 22, the movable contact 32 and the short-circuit switch 6 connected to the switched tap.
The fixed contact 6b ₁ and the movable contact 6b ₃ of b, the primary winding Cb _{1 of} the current transformer CTb, the switch Sb and the circuit of the output terminal 10 flow and the gate current is sent from the current transformer CTb to the gate Gb of the thyristor Thb. (T _{3 in} FIG. 2)
After the time point, (4) in FIG. And the short circuit switch 6
The movable contact 6a ₃ of a is switched and connected to the fixed contact 6a ₂ to short-circuit the terminals Ta ₁ and Ta _{2 of} the non-energized side thyristor Tha to protect the thyristor Tha from abnormal voltage. Further, the movable contact 7c of the auxiliary switch 7 is switched and connected to the fixed contact 7a to prepare for the next tap switching operation ((5) in FIG. 4). With the above, one step of the tap switching operation is completed.

Then, when a tap switching command for switching from the fixed contacts 22 to the taps of 23 is sent, the movable contact 31 of the tap selector 3 is switched and connected to the fixed contact 23 and the short-circuit switch 6a. The movable contact 6a ₃ of the above is switch-connected to the fixed contact 6a ₁ , and the changeover switch 8 is rotated in the direction opposite to the case of the tap changeover operation ((6) in FIG. 4), and the same process as above is performed. This is because the tap switching operation is performed.

As described above, when the movable contact 8d is separated from the fixed contact 8a (that is, the switch Sa or the contact is opened), an arc is generated between the contacts 8d and 8a, and the current flowing in the switch Sa is applied. The operation proceeds to the thyristor Tha, which will be described (the same applies when the switch Sb is opened). At the time of transfer of the current, there is an inductance having a size proportional to the area of the loop formed by the switch Sa, the primary winding Ca _{1, the} thyristor Tha, the output terminal 10 and the conductor connecting them, and therefore the inductance of FIG. (C) t ₁
The rise time ((t ₁ b-t ₁ a) in FIG. 3) of the current that shifts to the thyristor Tha at this point becomes longer in proportion to the magnitude of the inductance. Arc generated between the contacts 8a · 8d lasts only the rise time _{(t 1 b-t 1 a} ), the current at t ₁ b point in Fig. 3 disappears at the same time end moves to the thyristor Tha.

Among the members forming the loop, a conductor connecting the fixed contact 8a of the switch Sa, the primary winding Ca ₁ and the terminal Ta _{1 of the} thyristor Tha, and the switch S
The conductor connecting the movable contact 8d of a, the terminal Ta _{2 of the} thyristor Tha, and the output terminal 10 is made to have the necessary minimum length, respectively, to reduce the area of the loop and the inductance to reduce the switch Sa. The duration (t ₁ b−t ₁ a) of the generated arc can be shortened to reduce the arc energy and the wear of the contacts 8 a and 8 d can be reduced.

In the thyristor Tha, the temperature of the joint portion rises only when the AC half cycle is applied at the maximum, so that no power loss occurs except when the taps are switched, and the thyristor Tha is joined. The temperature of the part is almost equal to the ambient temperature, and the thyristor Tha can be selected in consideration of only the surge-on current that instantaneously flows when taps are switched, and a small capacity thyristor Tha can be used, and no heat dissipation device is required. Becomes Therefore, the members forming the loop can be arranged closer to each other to make the loop smaller, and the arc duration can be further shortened.

As described above, when the area of the loop is reduced, the inductance of the loop is reduced and the thyristor T
Although the rise time (t ₁ b−t ₁ a) of the current that shifts to ha becomes short, the thyristor Tha is supplied with the gate current even before the rise of the current, and the entire junction of the element becomes conductive. Therefore, when a voltage is applied between the terminals Ta _{1 and} Ta ₂ , an electric current flows through the entire junction instantly. Therefore, as in the general method of using a thyristor, between the terminals Ta ₁ and Ta ₂ When a voltage is applied to the gate, a gate current is applied to make it conductive, and the current rises sharply at this time, and there is no possibility that this current concentrates near the gate and overheats to destroy the thyristor. Therefore, even when a steeply rising current flows through the thyristor Tha, a reactor for suppressing a current increase rate is provided in series with the thyristor Tha, or a gate current proportional to a large current increase rate is made to flow (so-called high gate drive). There is no need to provide a circuit.

Next, the arc energy that directly affects the wear of the contact of the switch is interrupted when the current is interrupted by using the AC switch 9a and when it is interrupted by the switch Sa alone, for example, a frequency of 60 Hz and an effective value. Calculated when the load current of 300 A was cut off at the peak value of the current,
Compare the contact life of the switches Sa.

The arc energy between the contacts 8a and 8d of the switch Sa is expressed by the following formula 1.

[Equation 1] However, in the above formula 1, Ea represents arc energy (J), ta represents arc duration (S), Ia represents arc current (A), and Va represents arc voltage (V).

The rate of decrease of the current flowing through the arc between the contacts 8a and 8d is given by the following mathematical formula 2.

[Equation 2] However, L is an inductance (in this example, the switch Sa,
(Inductance of loop formed by primary winding Ca _1, thyristor Tha, output terminal 10 of current transformer CTa) (H)
Indicates.

The inductance L is approximately 2 μm in the actual measurement example.
H, and assuming that the arc voltage Va is constant at 50 V, the arc duration ta (t ₂ b−t ₂ a in FIG. 3) is
From Equation 2 above, it can be obtained as Equation 3 below.

[Equation 3]

The arc energy Ea at this time is obtained from the above-mentioned formula 1, formula 2, and formula 3 by the following formula 4.

[Equation 4]

On the other hand, the arc energy Ea when interrupted only by the switch Sa can be obtained from the above expression 1 as the following expression 5 if the arc voltage Va is considered to be constant at 50 V as described above.

[Equation 5]

As described above, the arc energy Ea when the load Sa is cut off by the switch Sa alone (Equation 5)
Is about 300 times the arc energy Ea (Equation 4) when the AC power is interrupted by the AC interrupting device 9a. Since the consumption of the contacts 8a and 8d by the arc is proportional to the arc energy Ea, the electrical life of the switch Sa is substantially inversely proportional to the arc energy Ea. According to the above calculation result, for example, 5
If the switch Sa having a life of 1,000 times is used as a member of the AC switch 9a, it can be used up to 300 times, up to 1.5 million times.

In the above embodiment, the thyristor Tha
(And Thb) are triacs, and the current transformers CTa (and CTb) for sending gate currents to them have been described as having one secondary winding, respectively. However, instead of the triac, two unidirectional transformers are used. -Type thyristors are connected in antiparallel, and the current transformer CTa (and CTb) has two secondary windings, and these two secondary windings are respectively connected to the gates of the two thyristors. You can

The changeover switch 8 used in the above embodiment
Has been described as a rotary type changeover switch having three fixed contacts 8a, 8b, 8c and one movable contact 8d which is switchably connected to each of them, but instead of this,
You may comprise so that it may have a function equivalent to the said rotary type changeover switch 8 by three switches which have a pair of contacts.

As described above, by constructing the switching switch of the load tap switching device by using the AC switching device, the contacts of the switching switch are opened and closed with substantially no arc, and the consumption of the contacts is extremely small. Therefore, the following effects are produced. It is possible to significantly extend the electrical life of the tap changer under load, which is determined by the number of tap changes corresponding to the amount of contact wear, and make it longer than the life of the transformer body incorporating this tap changer under load. , It is possible to eliminate the need for power failure of the operating transformer for maintenance / inspection of the contacts of the load tap changer, while maintaining the same or longer life as the transformer itself, while causing voltage fluctuations. It becomes possible to supply better quality electric power by frequently performing tap switching by shortening the switching interval at the time of switching.
Also, for example, when insulating oil is used as the insulating medium of the switching switch, the insulating oil will be significantly less contaminated.Therefore, the switching switch conventionally housed in a chamber partitioned by an oil-tight structure from the transformer main body must be replaced. Since the oil can be released from the oil-tight chamber and housed in the same case as the transformer main body, the insulating oil can be shared, so that the structure of the case is simple and maintenance and labor can be saved. It is possible to eliminate the need for a live-line oil purifier dedicated to the switch. In addition, the contact that was conventionally composed of two types, the energizing contact for passing the load current in the steady state and the arcing contact that energizes only when the arc occurs, can now be composed of only the energizing contact. The cost of the switching switch can be reduced.

Further, the above embodiment is an example in which it is applied to the switching switch of the load tap changer 1 as shown in FIG. 1, but the invention is not limited to the load tap changer 1 shown in FIG. A pair of movable contactors that select a plurality of taps while interlocking with adjacent taps of the tap winding by a tap switching command of the control device, and one movable contactor of the pair of movable contactors. Between the output terminals, insert a circuit in which the switch with contacts and the primary winding of the current transformer are connected in series,
Connect a thyristor in parallel to the series circuit of this switch and current transformer, and connect an AC switch that connects or disconnects the load current by connecting the secondary winding of the current transformer to the gate of this thyristor. Then, a current limiting resistor that limits the circulating current between the taps is connected between the other movable contactor and the output terminal of the pair of movable contactors, and in conjunction with the pair of movable contactors by a tap switching command. A tap changer during load in which load current is conducted or cut off by the AC switch to perform tap switching, and between one movable contactor and an output terminal of a pair of movable contactors similar to the above, similar to the above The AC switch is inserted into the current limiting resistor and the AC switch is connected in series between the other movable contact of the pair of movable contacts and the output terminal. Connect the AC switch in parallel to the series circuit of Inserted by connecting the AC switch and current limiting reactor in series between each of the resistance type load tap changers, such as the load tap changers, and the pair of movable contacts similar to the above, and the output terminal. However, the above two current limiting reactors can be applied to a reactor type load tap changer or the like which is formed so as to cancel out the reactances of each other when the load current is applied other than when switching the taps.

In other words, a pair of movable contacts for selecting a plurality of taps of the tap winding, and a circulating current between the taps inserted between at least one of the pair of movable contacts and the output terminal. And a current limiting impedance for limiting the current limit, and the AC switch that is inserted between at least the other movable contact of the pair of movable contacts and the output terminal to open and close an AC circuit (that is, to conduct and block an AC load current). It is an AC switchgear equipped with.

In the tap switching operation, the switch Sa of the AC switch 9a inserted between the movable contact 31 and the output terminal 10 is opened, that is, the movable contact 8d of the changeover switch 8 is rotated to fix the fixed contact 8a. When switching from the fixed contact 8c to the fixed contact 8b via the fixed contact, the arc generated between the contacts 8a and 8d disappears instantly with the conduction of the thyristor Tha. Therefore, the opening speed between the contacts 8a and 8d is increased. By doing so, it is not necessary to provide a fast-cutting mechanism for shortening the arc connection time. Also, on the other hand,
In order to reduce the capacity of the current limiting resistor 4 that is inserted between the movable contact 32 and the output terminal 10 and limits the circulating current between taps, and to downsize the same, the movable contact 8d and the fixed contact 8c of the changeover switch 8 are used. The connection time with the current limiting resistor 4 is shortened, that is, the speed of the switching operation from the opening of the switch Sa of the AC switch 9a to the closing of the switch Sb of the AC switch 9b is increased.
It is sufficient to shorten the energization time of the contact 8a.
Since the arc generated between 8d disappears instantly, even if the changeover operation of the changeover switch 8 is performed at a high speed, the contacts 8a and 8d
There is no possibility that the contacts 8d and 8b are connected to each other before the arc generated therebetween disappears and a short circuit between taps via the arc occurs. Therefore, the range in which the changeover operation speed of the changeover switch 8 can be set is widened, and there is an advantage that the degree of freedom in designing the load tap changer 1 is increased.

FIG. 5 shows another embodiment of the present invention. This is as shown in FIG. 6 between both terminals of the secondary winding of the current transformer CTa of the AC switch 9a. Connect a bypass impedance Zb composed of an element having a non-linear voltage-current characteristic that operates as a low resistance for a large current to limit the terminal voltage to V _CP and operates as a high resistance for a small current. The resistor Rg is connected between the connection portion of the bypass impedance Zb and the terminal Ta ₁ or the gate terminal Ga of the thyristor Tha. In this case, the current ratio of the current transformer CTa is set so that a gate current sufficient to bring the thyristor Tha into conduction can be obtained even when the load current is small. The terminal voltage V _CP of the bypass impedance Zb and the resistance Rg are determined in consideration of the gate characteristics such as the required input current of the gate of the thyristor Tha or the allowable input power. The bypass impedance Zb is calculated according to the required inter-terminal voltage V _CP .
As shown in FIG. 5, a plurality of diodes connected in series and connected in anti-parallel, a Zener diode in anti-series, a varistor, or the like is used.

As described above, since the bypass impedance Zb and the resistance Rg are connected to the secondary winding terminal of the current transformer CTa, the variation range of the load current flowing through the primary winding Ca ₁ of the current transformer CTa is large. In this case, when the load current is small, the current-changing ratio of the current transformer CTa is set so that a gate current sufficient to conduct the thyristor Tha is obtained, and when the load current is large, the secondary current of the current transformer CTa is Although the output current of the winding becomes large, this output current flows into the bypass impedance Zb and the output voltage becomes substantially constant (V _CP ), preventing saturation of the iron core of the current transformer CTa and providing a stable gate current. Can be supplied. Further, since the saturation of the iron core of the current transformer CTa is prevented, that is, the magnetic flux is suppressed to a certain value or less, the iron core can be downsized, that is, the current transformer CTa can be downsized. As for the AC switch 9b, the AC switch 9 described above is also used.
The same as a.

[0051]

The on (or off) control of the thyristor is performed by the output current of the secondary winding of the current transformer which is sent (or stopped) in response to the closing (or opening) of the switch. Therefore, the thyristor is turned on (or off) without opening a control power supply and a control circuit for sending (or stopping) the output current of the secondary winding, that is, the gate current. The primary winding of the current transformer is connected in series with the switch, and the secondary winding of the current transformer is connected to the gate of the thyristor. Even when applied to a circuit, no special insulation is required between the current transformer and the switch or thyristor, the configuration is simplified, the failure rate is reduced, and the cost can be reduced.

While the AC circuit is closed, that is, the switch is closed and the load current is being supplied, the thyristor always receives the gate current and stands by in a conductive state. When the switch is opened, that is, when the switch is opened to cut off the load current, the thyristor can be turned on instantaneously and accurately, and the load current flowing through the switch can be immediately transferred to the thyristor and cut off. The arc generated between the switch contacts has an extremely short duration and its energy is very small, so it is possible to suppress the wear of the switch contacts and prolong the life of the contacts, and of course, switch to a thyristor when the switch is opened. Even if the load current rises sharply, this current is concentrated in the vicinity of the gate and does not heat the local area to destroy the thyristor. Lister and it can be safely migrate load current by conducting the entire bonding surface of the device.

Further, even if chattering occurs when the switch is closed, when the switch is closed, the thyristor connected in parallel to the switch becomes conductive, and the thyristor is conductive even if the switch is opened next moment. It is possible to suppress the arc generated by chattering, prevent the load current from being interrupted, and prevent noise from being generated.

Further, even if a large load current flows and the output current of the secondary winding of the current transformer becomes large, this output current flows into the bypass impedance and the voltage between the secondary winding terminals of the current transformer is changed. Since the voltage is kept almost constant, even if the load current fluctuates greatly, a stable gate current can be flowed to operate the thyristor accurately, and the magnetic flux in the iron core of the current transformer is suppressed below a certain value. It is possible to reduce the size of the sink.

During the tap switching operation, when the AC switch inserted between the movable contact and the output terminal cuts off the load current, the arc generated between the switch contacts of the AC switch is synchronized with the opening of the switch contacts. The switch contact wear is extremely small, so the operation sequence of the switch and the movable contact that interlock at a delicate timing set in advance does not change due to the wear of the switch contact. It is possible to maintain an accurate tap switching operation for a long period of time without any occurrence. Further, since the arc generated between the switch contacts disappears instantly with the conduction of the thyristor, it is not necessary to provide a switch early-switching mechanism for shortening the arc duration, and the tap switching mechanism is simplified. be able to.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a load tap changer to which an embodiment of the present invention is applied.

FIG. 2 is a timing chart showing the operation of the embodiment of the present invention.

FIG. 3 is a timing diagram showing the operation by enlarging the vicinity of t ₁ in FIG.

FIG. 4 is an explanatory diagram of the operation of the tap changer under load to which the embodiment of the present invention is applied.

FIG. 5 is a diagram showing another embodiment of the present invention.

6 is a diagram showing voltage-current characteristics of the bypass impedance of FIG.

[Explanation of symbols]

2 tap winding 4 current limiting impedance 9a, 9b AC switch 31, 32 movable contact Sa, Sb switch CTa, CTb current transformer Ca ₁ , Cb ₁ current transformer primary winding Tha, Thb thyristor Ga, Gb gate Zb Bypass impedance Rg Resistance

Claims (3)

[Claims] 1. A circuit in which a switch having a contact and a primary winding of an AC device are connected in series to an AC circuit, and a thyristor is connected in parallel to the series circuit of the switch and the current transformer. An AC switchgear is characterized in that the secondary winding of the current transformer is connected to the gate of the current transformer, and the thyristor is on / off controlled by the output current of the secondary winding of the current transformer. 2. A circuit in which a switch having a contact and a primary winding of a current transformer are connected in series is inserted in an AC circuit, and a thyristor is connected in parallel to the series circuit of the switch and the current transformer. The secondary winding of the current transformer is connected to the gate of the thyristor via a resistor, and the secondary winding of the current transformer is connected in parallel with a bypass impedance having a non-linear voltage-current characteristic to connect the thyristor. An alternating current switchgear is characterized in that on / off control is performed by an output current of a secondary winding of the current transformer. 3. A switch including a tap winding having a plurality of taps in an AC circuit, and at least one movable contact of a pair of movable contact selecting a tap of the tap winding has a contact. The primary winding of the current transformer is connected in series, the circuit of the switch and the current transformer connected in series, a thyristor is inserted in parallel, at least the other movable contact of the pair of movable contacts, A current limiting impedance that limits the circulating current between taps is inserted between the switch connected in series and the circuit of the current transformer, and the output terminal of the secondary winding of the current transformer is connected to the gate of the thyristor. Then, at least after the opening of the switch, at least one movable contact of the pair of movable contacts selects a tap.