CH246813A - Protective device for electrical apparatus containing insulating liquid, in particular for low power and high voltages. - Google Patents

Description

Protective device for electrical apparatus containing insulating liquid, in particular for low power and high voltages. If a defect occurs in an electrical apparatus with insulating liquid, e.g. E.g. due to electrical flashovers, local strong heating, short circuits in windings, three gas formations are known to occur. The same can happen so quickly under certain circumstances that there is a strong increase in pressure inside the liquid container.

These phenomena have been used to actuate electrical contacts and thereby give alarm signals, or by means of automatic circuit breakers to isolate the defective apparatus from its supply point. According to another proposal, the increase in pressure in the apparatus to be protected was used to mechanically, e.g. B. via a membrane, to trip the circuit breaker. In this latter way, the aim was to simplify the installation and to eliminate sources of error which could result from electrical tripping.

However, these solutions require that the electrical apparatus to be protected is supplied via an automatic circuit breaker whose tripping can be caused mechanically or electrically. However, in the case of apparatuses with a low power and, in particular, with high voltages, supply via a self-contained circuit breaker is hardly an option. Such an arrangement would take up too much space and would be prohibitively expensive.

For this reason, it has been proposed to use the gas or pressure that occurs in the apparatus to be protected in order to mechanically melt fuses that are connected upstream by short-circuiting the apparatus. The short-circuit current caused by this blows the fuses and the defective apparatus is disconnected from its supply point. However, this procedure has other significant disadvantages. Such short circuits are extremely undesirable in electrical systems because they entail the risk of further defects and switch trips. It can e.g. It can also happen, for example, that the electrical apparatus still contains air pockets after the insulating liquid has been poured in. After start-up and heating, these air pockets rise and cause the protective device to respond. But it is wrong to create a short circuit with all its dangers because of such a phenomenon, which is actually harmless in and of itself.

The present invention avoids these disadvantages. It allows electrical equipment to be safely protected > even at low power levels and very high voltages, for which the fuses are much too insensitive, without the need for the automatic circuit breakers that have been used up to now. The disconnection of a defective apparatus from the mains can take place without the inflowing current having to be increased in the slightest, or without even creating a short circuit. The proposed solution also has the advantage that it can also be used; if the apparatus to be protected is set up isolated and the float is at high voltage potential.

According to the invention, this goal is achieved in that, when gas formation occurs in the apparatus to be protected, air. in the same built-in float is moved and thereby, by means of a mechanical transmission element, activates a current isolator, which creates an insulating gap in the supply line and interrupts the current flowing to the apparatus.

The invention and how it works will be explained in more detail using a few exemplary embodiments.

1 shows an arrangement in which the current isolator is built on a bushing insulator of the apparatus to be protected. In this example, a linkage, which at least partially consists of insulating material, serves as the transmission element for the float movement to the isolator. Special aids for limiting the breaking capacity are not provided here Part of the electrical apparatus to be protected is indicated, which is housed in the insulating liquid-filled vessel 2. The expansion vessel 4 is arranged on the cover 3. The cover also contains a niche 5 for accommodating the float 6. By means of the The niche 5 can be vented by means of the shut-off valve 7. The surface of the cover rises towards the niche 5, so that rising gases must find their way into the latter The lower end of the pull rod 10 is articulated to the lever arm 11, which is at least partially made of insulating material execution 8; at its other end the float 6 is attached. A separator arm 12 is rotatably mounted in the bracket 14 by means of a shaft 13 on the upper bushing head. From the power supply line 15, which can end on a support insulator 16, the current flows via the separator arm 12, the pull rod 10 and the connecting cable 17 on the electrical apparatus 1. The mode of action is as follows: If a defect occurs in the apparatus to be protected, decomposition gases form, which rise immediately and enter the niche 5. As a result, the Sèhwimmer 6 and pulls the pull rod 10 down. As a result, the stop at the lower end of the separator arm 12 loses its support and is pivoted out by the tension spring 18 . It can be held in an approximately horizontal position by means of a stop.

The fact that the tie rod 10 is placed inside the bushing insulator 8 results in a very simple design that is particularly suitable for outdoor installation. However, it is easily possible to open the tie rod 10 on the bushing insulator 8 and lead it to its head. In this case, the tie rod 10 must be made of insulating material.

As has already been indicated, small electrical devices with high voltages are often set up in isolation or at least in a pot on the insulating material, e.g. B. Porcelain, installed. An example of such a design is shown in FIG. 2. The housing 2 is made of insulating material; e.g. B. Porcelain; The expansion vessel 4 is fastened liquid-tight on top of the same. When the float 6 sinks, connected with the rotation of the lever arm 11, the rod 10 is pushed upwards, which rotates the ratchet 25 about a pivot point 26. As a result, the separating arm 12 is released and the tension spring 18 causes the same to swing out. The niche 5 in the bottom of the expansion vessel 4 can be vented through the drain cock 7. The liquid level and the position of the float 6 can be checked through the sight glass 28 . The current takes its way via the separator arm 12 to the expansion vessel B 4 and from here via the connection 17 to part 1 of the apparatus. If one pole of the device is grounded, which is often the case with such devices, the current can flow via the lead 29 to the metal foot 30. This latter is conductively connected to earth 31.

It should also be pointed out in particular that a plate 35 can be attached to the transmission rod 10 . In the event of sudden heavy gas development in the vessel B 2, the insulating liquid will flow to the expansion vessel 4 at high speed. It hits plate 35 and immediately lifts rod 10. In this way, the apparatus can be separated from its feeding point in an extremely short time, even before the cracks have reached niche 5. In most cases, the signaling of gas formation or Response of the isolator may be desirable. In the case of arrangements according to FIG. 2, this is not possible without further ado, since the float is at high-voltage potential. This difficulty can be overcome by transmitting the float movement to a low voltage control switch 33 by means of an insulating rod, denoted 32 in FIG. The latter is housed in the apparatus ful3 30, which is at ground potential. From the. Control switches 33 lead connections to the drain terminals 34. Not only alarm signals can be given by the control switch 33, but e.g. B. switching processes can also be triggered.

Provision could also be made for the possibility of causing the isolator to respond at will by manual operation, for example by depressing the float from outside. In the case of the embodiment according to FIG. 2, it is also possible to act directly on the release pawl 25 by applying the insulating rod to the ring 36.

Fig. 3 shows another type of isolator which, when gas is formed in the apparatus to be protected, allows the connection of a sufficiently large insulating gap and thus separation from the supply network put on, which contains a thin electrical conductor 45 in its interior. The same has a mechanically weaker point about halfway along the length. With the help of the float movement, this cell can now be torn through or sheared through. This electrical conductor can be grasped at its lower end by means of Bine's lever 46 and subjected to tension by the compression spring 47 and torn. However, a retaining pawl 25 prevents the action of the spring 47 and thus the rattling of the conductor as long as the apparatus to be protected is in order. If a defect now occurs, the float 6 sinks, as a result of which the transmission rod 10 rotates the holding pawl 25. The tensioned spring 47 is thereby released, tears the electrical conductor at its weak point and creates the required separation distance. In order to be able to cope with any larger currents, the electrical conductor is dimensioned in such a way that it melts as soon as the current reaches a value that can no longer be reliably interrupted by the mechanically created isolating distance. The measures to prevent arcing known from the construction of high-voltage fuses can be provided. For example, the insulating tube can be made of a material which, as a result of the arcing effect, gives off gas which has a deionizing effect and blows out the arc. Also, the electrical conductor can be embedded in quartz sand or the like. It can also be spirally wound onto a support in a known manner.

As mentioned, the currents in such devices that are not protected by automatic circuit breakers are small when they are ready for operation. In the event of a defect, however, significantly larger currents may occur, <B>depending</B> on the type of defect. The switch-off process can now be made safer if a series resistor is provided. Such a solution is shown, for example, in FIG. 4, only the power isolator being shown for the sake of simplicity. In it, a series resistor 37 is fastened to the post insulator 16, at the ends of which the two contact plates 38 and 39 are attached. .In the closed state, the current goes directly through the current isolator 12 to the electrical apparatus to be supplied. When responding, the current isolator 12 first leaves its contact plate 39, while the auxiliary contact arm 12' remains on the contact plate 38 belonging to it for some time due to the compression spring 40. As a result, the ballast resistor 37 is briefly switched to the apparatus to be protected and the current is reduced to a value which can be subsequently interrupted by the auxiliary contact arm 12' without any difficulties. In the open state, the current isolator 12 comes to the position 41, while the auxiliary contact arm 12' has moved away from the current isolator 12 as a result of the compression spring 40 and no longer assumes the position 41'.

It is also possible not to suddenly connect the series resistor with its full value, but rather in at least two steps or gradually increasing from the value zero. Such a solution is indicated schematically in Figure 5 in elevation and in Figure 5a in side elevation. The ballast resistor 37 is designed therein as an extension of the post insulator 16 . The current isolator 12 is split into two parts at the upper end, on which the contact springs 42 are attached. In the closed state, the contact springs 42 are seated on the metal connecting piece 43. When the contact springs are activated, they slide along the rod-shaped ballast resistor 37 and. turn it on steplessly up to its full value. The series resistor 37 can be made of resistance metal or silicon carbide or the like. - You can also use a voltage-dependent resistor whose resistance value increases; when it is energized: Below another RTI ID="0004.0274" WI="12" HE="4" LX="1655" LY="658"> solution should be given, in which only for - to protect against inadmissible overstressing by using the current isolator provided for smaller breaking capacities. This consists in the current isolator working together with a high-performance fuse connected upstream of it. This is dimensioned so that it melts immediately as soon as the current reaches a value which the current isolator can no longer safely handle. A numerical example may provide the necessary insight. A 50 kV voltage transformer is loaded with 200 VA and draws a primary current of 0.004 A. The current isolator could e.g. B. still switch off a current of about 5 A safely: The smallest current for which high-voltage fuses can be built is about 1 A. At a load of 5 A, such a fuse will melt in about 1/1 second . If a defect occurs in an apparatus protected in this way, the current can increase to around 300 times the value without the fuse responding. In the case of a large number of defects, the current will not exceed a certain value, and the current isolator will perform the isolation safely. If, exceptionally, the current exceeds the operating range of the current isolator due to damage, the fuse will step in immediately and take over the protection.

A very compact design results if the high-voltage fuse is not placed separately on post insulators, but rather these are used as part of the current isolator.

In the case of very high voltages, the construction of fuses can be associated with certain difficulties. Very high overvoltages can also occur if they melt through. In the above embodiment, these disadvantages can be eliminated by connecting a high-impedance resistor in parallel with the fuse. If the fuse then melts, the current is not completely interrupted, but a small residual current still flows through this resistor. The residual current is dimensioned in such a way that it can be safely switched off by the current isolator.

This assembly of circuit breaker, high-voltage fuse and any current-limiting resistor rolls closer using examples. be explained, whereby only the current isolator is shown for the sake of simplicity. In FIG. 6, 12 again denotes the swing-out power isolator, which now contains the high-voltage fuse 50 in its middle part. In FIG. 7, the high-impedance resistor 51 already mentioned is connected in parallel with the high-voltage fuse 50 . For this latter combination there is another, simple' solution if the resistor is not provided separately, but arranged on the insulating tube of the high-voltage fuse 50 (52), as indicated in Fig. 8. Because of this, you achieve electrostatic shielding of the very thin melting wire of the fuse.

It may be added that, in a similar way, as shown in FIGS. 6 to 8, a power isolator of the type according to FIG. 3 can also be designed so that it can be swung out and, if necessary, equipped with a high-impedance parallel resistor.

Among the various devices to be protected that come into question, special mention should be made of those that are connected in series in a line, e.g. E.g. the current transformer. The same occupies a special position because the winding is at high voltage potential, but there is only low voltage between the incoming and outgoing lines and the line current must not be interrupted when the current transformer is disconnected. Such apparatuses could not be protected satisfactorily up to now, and severe damage could develop with eventual interruption of the entire continuous flow of energy. Such apparatus can also be protected with the present subject matter of the invention, as will be explained below. Based on the arrangement according to FIG. 1, for this case, for example, two current isolator arms are placed on one and the same insulator 12 directly next to each other - and only insulated from each other for small voltage differences - one for the supply line, the other for the return line. If a defect occurs in the current transformer, the two current isolating arms 12 next to one another must not simply open the circuit, because one does not want to interrupt the mains energy flowing through. Before the current isolating arms separate the current transformer, the two supply lines 15 must be connected to one another so that the flow of energy in the line is secured. This can e.g. This can be done, for example, by choosing a construction in which the movement of the rod 10 is passed on to the support insulator 16 by an extension and a bridging piece is pushed there between the two supply lines 15. Only when this has happened, i.e. the current transformer is short-circuited, does the stop release the current isolator arms 12. The faulty current transformer is thus separated from its cable run without interrupting the flow of current in it.

The response of the protective device described can be signaled in a known manner, or other measures that appear suitable can also be initiated in this way. Although only one pole is drawn in each of the examples, the circular direction can easily be implemented in multiple phases.

Claims (10)

PATENT CLAIM: Protective device on electrical apparatus containing insulating liquid and not fed via a circuit breaker with automatic tripping, in particular for low power and high voltages, which device responds when decomposition gases form in the apparatus to be protected, thereby characterized in that the gas formation moves a float built into the apparatus, which activates a flow separator by means of a mechanical transmission element, which in turn creates an isolating gap and interrupts the supply current to the apparatus. Subclaims 1. Protective device according to patent claim, characterized in that the current isolator has a contact arm which is rotatably mounted at one end and which is held in the locked position by a pawl in its switched-on position, with a float movement causing a release, whereupon the released current isolator jumps into the open position with the help of spring force. 2. Protective device according to patent claim, characterized in that the current isolator has an electrical conductor accommodated in an insulating tube which has a mechanically weakened point which is torn through by the movement of the float in order to produce the isolating isolating distance. 3. Protective device according to patent claims and dependent claim 2, characterized in that net. A tensioned spring is released by the movement of the float, whereupon this latter tears the electrical conductor at its mechanically weakened point and thus creates the isolating isolating gap. 4. Protective device according to patent claim and subclaims 2 and 3, characterized in that the insulating tube with the electrical conductor housed therein which can be torn apart is rotatably mounted at one end. 5. Protective device according to patent claim and dependent claim 1, characterized in that the power isolator is seated on a bushing insulator of the apparatus to be protected and the mechanical transmission organ is partially accommodated inside the bushing insulator. 6. Protective device according to patent claim and TJnterclaim 1, characterized -gekennzeich- net, that cover-el and float of the. protective, apparatus are at high-voltage potential and the power isolator is fastened to this cover. 7. Protective device according to claim and dependent claims 1 and. 6, characterized in that the float, which is at high voltage potential, is an insulating rod with a low-voltage control switch is connected, by means of which a response of the current isolator is signaled. 8. Protective device according to patent claim and dependent claim 1, characterized in that: a high-voltage fuse is provided to protect the current isolator. 9. Protective device according to patent claims and subclaims 1 to 8, characterized in that the high-voltage fuse is assembled with the power isolator. 10. Protective device according to patent claim and dependent claims 1, 8 and 9, characterized in that an ohmic resistor is connected in parallel with the high-voltage fuse; which is intended to limit the current after the fuse has melted to a residual current to be interrupted by the current isolator. 1l. Protective device according to patent claim and subclaims _ 1, characterized as such; daB, when the current isolator swings out for the time being. a current-limiting w i Idersiand switched on in at least one m stage in the circuit and only hern.'a.ch the residual current -is interrupted. 12. Protective device according to patent claim and subclaims 2 to 4, characterized in that next to the mechanically weaker point of the electrical conductor, this is dimensioned in its cross-section in its remaining length in such a way that it melts through as soon as it comes into contact with it - the current flowing into the apparatus reaches inadmissibly high values for the latter. 18. Protective device according to patent claim and independent claim 1, for an electrical apparatus which is connected in series in one pole of the electrical line, characterized in that two contact-poor s are arranged next to one another, and then the same only be released for swinging out after the electrical connection of the two lines leading to the electrical apparatus has been effected by the movement of the float Bine and the apparatus to be protected has been bypassed immediately.