JPS5814710Y2 - Overcurrent prevention device for high-speed shutdown of DC generators - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an overcurrent prevention device for high-speed interruption of a DC generator.

Such devices are mainly devices for removing metals by electrolysis (
used in molding, grinding).

In order to effectively remove metal, the gap between the workpiece and the counter electrode is made as small as possible, and the electrolyte is pumped through this gap.

In this case, it is usually unavoidable to reduce the gap between the workpiece and the counterelectrode below a certain value, which allows extremely high currents to be applied in extreme cases, e.g. when the workpiece and the counterelectrode come into contact. This will cause a short circuit.

This is caused, for example, by vibrations of the processing equipment, the pressure of pumping the electrolyte through the processing gap, as well as unevenness and the collection of conductive particles on the workpiece or counterelectrode.

It is necessary to interrupt the main rectifier carrying the direct current as soon as possible to avoid damage to the workpiece and counterelectrode due to arcing caused by high field strengths or excessive heating caused by high currents. It is.

It should be noted that the pulse-controlled inverter is an already known circuit device for protecting controllable semiconductor elements (German Patent Application Publication No. 1).
According to Japanese Patent Publication No. 488,948), a device is provided for forced commutation of Cyrisk.

The commutation capacitor of this device for forced commutation is discharged via a controllable semiconductor valve.

The commutating capacitor is charged via an oscillating circuit connected in parallel to the semiconductor valve, and this oscillating circuit has a commutating reactor and a diode connected in series with it. It is charged to the arc-extinguishing voltage when connected for operation.

This device configuration is particularly characterized by the fact that the voltage level at the extinguishing capacitor is not sufficient in any case to ensure reliable extinguishing of the main thyristor, and furthermore there is a risk of re-ignition of the main thyristor. There are drawbacks.

In the case of a device for blocking the discharge section of a rectifier in the event of a fault (German Patent Specification No. 944 619), a controllable arc-extinguishing rectifier element and an extinguisher are installed in parallel with the main discharge section of a gated rectifier. A series connection with an arc capacitor is provided.

The arc-extinguishing capacitor is charged via a resistor with the voltage of the DC distribution current.

There is therefore a risk that, due to the time required to charge the arc-extinguishing capacitor, a second arc-extinguishing that follows the first arc-extinguishing will soon be impossible.

Furthermore, in the known method of shutting off the inverter (German Patent No. 885,882), the arc extinguishing capacitor is charged with an auxiliary DC current source, but in order to reliably extinguish the inverter, the load current must be attenuated. This decay time of the load current is relatively large in the presence of inductance in the load circuit, and thus ensures reliable dissipation. Either arcing is not done, or the arc-extinguishing capacitor must be made significantly larger.

No auxiliary means are provided to maintain the extinguishing voltage.

The fundamental problem according to the invention is therefore to provide a device for rapidly and precisely interrupting the respective current-carrying main rectifiers and for preventing the resulting contact between the workpiece and the counter-electrode. The objective is to provide a device that avoids damage.

This problem is solved by the present invention as follows.

That is, in the secondary circuit of the transformer, a controllable main rectifying element, an output terminal of a DC generator, and a current limiter are provided in series with the secondary winding of the transformer, and furthermore, the controllable main rectifying element, the output terminal of the DC generator, and the current limiter are provided. In parallel to the main rectifying element, a diode or a low-resistance resistor, an energy accumulator chargeable by means of an auxiliary voltage source to a higher voltage than the operating voltage at the output terminal of the direct current generator, and a controllable switching element. A series circuit is provided in which the connection point between the diode or the resistor and the energy accumulator is connected to the choke and the controllable switching element is connected to the main rectifier. It is connected to the main rectifying element through a number of parallel diodes corresponding to the number of elements, and the voltage detected between one of the output terminals of the DC generator and the main rectifying element is a predetermined voltage. When the value is exceeded, the controllable switching element is controlled to conduct, and as a discharge path for the energy storage device, a main rectifying element, a diode or a low-resistance resistor and a controllable switching element are provided in parallel with the main rectifying element. a first discharge path including a switching element and a diode in parallel with the main rectifier; and a second discharge path including a diode and a controllable switching element in parallel with the choke and the transformer secondary winding. are formed so that the respective current-conducting main rectifier elements are arc-extinguished.

Next, the present invention will be described in detail with reference to embodiments shown in the drawings.

A primary coil 4 of a transformer 5 is connected to a three-phase AC power supply network 1 via a fuse 2 and a main switch 3.

The secondary coils 6 of the transformer 5 are connected to each other via an interphase reactor 7.

Each of the secondary coils 6 is connected to the anode of a respective thyristor 8 whose cathodes are interconnected.

Furthermore, each one of the secondary coils 6 of the transformer 5 is connected with a diode 9, whose cathodes form an OR element whose cathodes are interconnected.

The common connection point of the diode 9 is connected to the anode of the arc-extinguishing thyristor 10, and its cathode is connected to the arc-extinguishing capacitor 1.
1 to the anode of a diode 12.

The cathode of the diode 12 is connected to a common connection point of the cathodes of the thyristor 8.

A series connection of a DC generator 13, a switch 14, and a current limiting resistor 15 are connected in parallel to the arc-extinguishing capacitor 11.

DC generator 13 charges arc-extinguishing capacitor 11 to a relatively high voltage compared to the operating voltage applied to terminals 16 and 17 when switch 14 is closed.

A smoothing choke coil 18 connected to the interphase reactor 7 of the transformer 5 is connected to the anode of the diode 12.

Furthermore, a measuring resistor 19 is provided between the output terminal 16 and the common connection point of the anodes of the thyristor 8.

Furthermore, a basic load resistor 20 is connected in parallel to the output terminals 16 and 17.
is provided.

The operation of the circuit arrangement is as follows.

When the primary coil 4 of the transformer 5 is connected to the three-phase AC power supply network 1, a voltage is induced in the secondary coil 6 of the transformer 5.

Six thyristors 8 are used for rectification and voltage or current control.

These thyristors are operated in phase control via a control device, which is not shown.

A voltage drop occurs across the measuring resistor 19 located between the output terminal 16 and the cathode of the thyristor 8, depending on the current flowing therethrough.

When this voltage exceeds a certain value, it triggers a circuit arrangement, not shown, which fires the extinguishing thyristor 10.

When the arc-extinguishing thyristor becomes conductive, the arc-extinguishing capacitor 1
1 discharges.

In this case, a short-term current flows through the diode 12 and the respective conductive thyristor 8, one of the diodes 9 and the extinguishing thyristor.

Furthermore, a part of the discharge current flows via the smoothing choke coil 18 , the interphase reactor 7 and one of the secondary coils 6 , one of the diodes 9 and the arc-extinguishing thyristor 10 .

Even after current no longer flows through the diode 12 and one of the thyristors 8 due to this discharge, the cathode potential of the thyristor 8 remains positive compared to its anode potential for longer than the turn-off time defined for the thyristor.

As a result, the thyristor 8, which is conducting in each case, is completely extinguished.

In short, the arc extinguishing capacitor 11 is charged by the DC generator 13 to a higher voltage than the operating voltage applied between the terminals 16, 17 of the DC supply.

When the thyristor 10 is ignited, a current pulse initially flows through the main rectifying element 8 and the diode 9.

The smooth choke 18 initially has a high electrical resistance to the current, but that resistance quickly decreases.

As a result, the thyristor 8 is not only not damaged, but also the positive potential applied to the cathode of the main rectifying element 8 is removed from the choke 1.
It is also maintained when the current circuit via 8 is closed.

That is, the potential of the cathode of the thyristor 8 is positive compared to the potential of its anode for a time interval sufficient to extinguish the thyristor 8.

This time is the so-called turn-off time of the thyristor 8.

Restarting the circuit arrangement is only possible after a short delay, during which the arc-extinguishing capacitor 11 should be charged to a sufficient voltage again by closing the switch 14.

The above-mentioned device is simple in construction and inexpensive to produce, and it also provides a quick and reliable interruption of the current-carrying thyristor if the current between the workpiece and a counter electrode placed opposite the workpiece is too large. It has the advantage of being able to perform

Instead of a transformer operating in a circuit with a phase-to-phase reactor connection, as shown in the exemplary embodiments, the transformer can also have other connection types, for example a bridge connection, a star connection or a star connection.

The OR element 9 and the arc-extinguishing thyristor 10 can also be replaced with arc-extinguishing thyristors of a number corresponding to the number of main rectifying elements.

Finally, if the commutation for the thyristor 8 is made to flow through a load resistor, the device can be constructed without the diode 12.

In this case, if it is applied to the thyristor 8, the cut-off time can be made faster.

[Brief explanation of the drawing]

The figure is a circuit diagram of an embodiment of the device according to the invention. 1... Three-phase AC power network, 2... Fuse, 3... Main switch, 4... Primary coil of transformer, 5... ...Trance, 6...
- Secondary coil of transformer, 7... Interphase reactor, 8... Thyristor, 10... Arc-extinguishing thyristor, 11... Arc-extinguishing capacitor, 13.
...DC generator, 15... Current limiting resistor, 18... Smooth choke coil, 19...
...Measurement resistance, 20...Load resistance.

Claims (1)

[Scope of utility model registration request] In the secondary circuit of the transformer 5, a controllable main rectifying element 8, an output terminal 16, 17 of a direct current generator, and a choke 18 are provided in series with the transformer secondary winding 6, and furthermore, the In parallel to the controllable main rectifying element 8, an energy supply is provided which can be charged by a diode 12 or a resistor of low resistance and by an auxiliary voltage source 13 to a higher voltage than the operating voltage at the output terminal 16.17 of the DC generator. A series circuit is provided from an accumulator 11 and a controllable switching element 10, the connection point between the diode 12 or a low-resistance resistor and the energy accumulator 11 being connected to the choke 18. The controllable switching element is connected to the main rectifying element 8 via a number of parallel diodes 9 corresponding to the number of main rectifying elements 8, and is also connected to the output terminal of the DC generator. When the voltage detected between one of the main rectifying elements and the main rectifying element exceeds a predetermined value, the controllable switching element 10 is controlled to be conductive, and the main rectifying element 8 and the main rectifying element are connected as a discharge path to the energy accumulator 11. A first discharge path including a diode 12 or a low-resistance and controllable switching element 10 provided in parallel with the rectifying element, a parallel diode 9 connected to the main rectifying element, and the choke 18 A second discharge path including a diode 9 and a controllable switching element 10 is formed in parallel with the transformer secondary winding 6, so that the main rectifying element 8 conducting the current is extinguished. Overcurrent prevention device for high-speed shutdown of DC generators.