RU2213406C2 - Disconnecting switch of internal automatic protective gear for oil-immersed power transformer - Google Patents

Abstract

FIELD: power transformer protective gear. SUBSTANCE: disconnecting switch is component part of automatic protective gear of power transformer immersed in tank filled with liquid dielectric. It functions to disconnect transformer primary winding from supply mains in case of emergency drop of cooling liquid level. Disconnecting switch has first-degree lever rotating about pin that divides it into two arms, short and long ones. Long arm carries bowl with hole on one of its ends. Its other end mounts facility in the form of stop that ensures automatic filling of bowl with liquid dielectric through hole in the course of filling the tank and prevents escape of this cooling liquid from bowl as soon as tank is filled up. In this way cooling liquid level in transformer tank is permanently under control and in case of abnormal situations protective gear is automatically thrown in operation. EFFECT: enhanced reliability of protective gear operation throughout entire running period of transformer. 6 cl, 4 dwg

Description

 The invention relates to electric power or distribution transformers, in particular to oil transformers with automatic protection.

 An oil transformer is a transformer whose windings and magnetic circuit are immersed in a liquid dielectric, for example, in mineral oil, which is poured into a hermetically sealed tank to cool them. It is called a transformer with automatic protection if it is equipped with devices that automatically, without using external energy sources, disconnect its primary windings from the mains in case of internal malfunctions that can lead to a tank explosion. An example of such malfunctions is a too large increase in the pressure of the liquid dielectric or a significant decrease in the level of the liquid dielectric due to its leakage from the tank. A detailed description of automatic protection devices for multiphase transformers is given in European patent application EP-A-0653765 in the name of the Applicant or in other published documents, such as EP 0093076 or USP 4.223.364.

 Typically, an automatic protection device consists of a switch and a drive, which itself is driven by a disconnector equipped with a sensor that responds to changes in such parameters of the liquid dielectric that can lead to an emergency inside the tank, for example temperature, pressure or the level of the liquid dielectric in the tank.

 The invention can be used in a device of automatic protection of this type, in which there is a disconnector that responds at least to a level change, in order to avoid dangerous situations associated with the loss of liquid cooling dielectric as a result of, for example, its leakage from the tank, allowing protective shutdown in the case when this level reaches the minimum acceptable value.

 Such a disconnector may be of a float type with a float of a material whose density is less than the density of a liquid dielectric (e.g., polystyrene), which accurately monitors the level of the liquid. However, it is impossible to guarantee long-term operation of the float type device. Considering that the service life of the transformer of the type in question is usually thirty years, or even more, it must be borne in mind that the float, especially if it is porous, is inevitably saturated with oil, since it is in an environment where the pressure constantly increases and drops.

 Under these conditions, it gradually loses buoyancy, which can lead to a false triggering of the protective device, which is always very unpleasant, since after that you need to manually dismantle the upper part of the transformer in order to bring it back into working condition.

 One could replace the traditional float with a hollow hermetically sealed vessel containing air. However, the use of such a vessel requires a very fine adjustment of the sensitivity of the protective device, and besides, it would simply be very difficult to manufacture, because, despite the low weight, it would have to withstand the vacuum equally well during the entire operation time (filling of the transformer occurs in a vacuum), as well as an increase in pressure (during operation of the transformer, overpressure can reach 0.2 mbar), as well as temperatures that often exceed 100 degrees Celsius.

 The objective of the invention is to offer manufacturers of electric power or distribution transformers with automatic protection a simple and economical device that monitors the level of cooling liquid dielectric in the tank and is able to provide, in case of abnormal situations associated with this level, effective and reliable operation of the automatic protection device throughout the entire period functioning of the transformer.

 The problem is solved in that in the disconnector of the device for internal automatic protection of an electric power or distribution transformer immersed in a tank filled with a cooling liquid dielectric, disconnecting the primary winding from the supply network in the event of an emergency decrease in the level of the cooling liquid dielectric, the disconnector being part of the device, comprising a switch, which is actuated by a drive, which is actuated by a disconnector consisting of a lever of the kind rotating around an axis that divides it into one short arm representing resistance and one long arm representing the applied leverage, according to the invention, a vessel with an inlet is installed at the end of the long arm, and it comprises means for automatically filling the vessel with cooling liquid dielectric through the hole in the process of filling the tank, while the tool is provided at the end of the short arm to transfer force to the drive, and the shutdown occurs when the force p the set shutdown threshold is increased, the relative sizes of the lever arms and the dimensions of the vessel are such that when the tank is filled with a cooling liquid dielectric, the vessel is completely immersed in this cooling liquid dielectric, and the force with which it acts on the drive is less than the set shutdown threshold, and if the surface of the cooling liquid dielectric drops to a level that is considered abnormally low, the vessel that remains filled with the cooling liquid dielectric reaches a degree of ascent, at which I eat its weight force transmitted to the drive exceeds the specified trip threshold.

 The invention also relates to an electric power or distribution transformer equipped with an automatic protection device comprising such a disconnector.

 From the foregoing, it is clear that the concept of a lever type disconnector, which reacts to changes in the level of a cooling liquid dielectric in a tank not as a float, but as a vessel of a certain mass, mounted on the end of a long lever arm (a lever called a “force lever”), is the cornerstone of the idea of the invention. and experiencing the action of buoyant Archimedean force from this fluid. This vessel, initially empty, is then automatically filled with the same cooling liquid dielectric as the transformer tank during filling of the latter. Once filled, this vessel always remains full, and its weight is balanced by the strength of Archimedes until the moment when, as a result of an emergency lowering of the liquid level in the tank, it emerges from the liquid so that its apparent weight, equal to the difference in the forces acting on it, is increased by the transfer the ratio of the lever and attached to the switch, triggers a protective device.

 The main advantage of the disconnector, in accordance with the invention, is that it can easily satisfy conflicting requirements for lever floats designed to be installed in narrow places where they should occupy as little space as possible (in this case, under the cover, in the upper, very cluttered part of the transformer). In fact, you must either use a massive float, but then it will be too voluminous to maintain buoyancy, or use a small float, but in this case you need to mount it on a longer lever in order to maintain the desired moment value, and such a lever will take up more space. It should be emphasized that this problem is especially acute for automatic transformer protection devices with primary circuit disconnection, since it is necessary that the breaking force with which the lever end acts on the drive is relatively large (of the order of a kilogram) in order to avoid too high sensitivity devices that may cause unjustified and untimely outages.

The invention is illustrated by the following description with reference to the drawings given in the appendix, on which:
- figure 1 schematically represents a section of the tank of the oil transformer and the device, in accordance with the invention, before filling the tank with a liquid cooling dielectric;
- FIG. 2 represents the same tank and the same device while filling the tank;
- FIG. 3 represents the same tank and the same device at the end of filling the tank;
- FIG. 4 represents the same tank and the same device after leakage of the cooling liquid dielectric caused a dangerous decrease in the level of the cooling liquid dielectric in the tank. All the drawings depict, and for clarity with magnification, only those elements that are needed to better understand the essence of the invention. In particular, they do not represent electrical components, which can be of any type known to the skilled person. Similarly, the components of the automatic protection device, the full description of which can, if necessary, be found, for example, in the already mentioned document EP 0653765, the contents of which are incorporated herein by reference, are not presented in details here, except for the disconnector.

 In all the drawings, each element appears under the same number.

 Figure 1 schematically shows only some of the traditional elements of the equipment of an electric power or distribution transformer with automatic protection, namely tank 1, the active zone 19 of the transformer, shown by dashed lines (in which you can distinguish three parts corresponding to the location of the phase windings of a three-phase transformer), and device 5 for disconnecting from the mains (circuit breaker), which should be triggered in case of malfunctions that could cause the explosion of the transformer, such as emergency lowered th level of the cooling liquid dielectric. The tank 1 is hermetically closed by a lid 3, in which there is a filler neck 4, which allows the tank 1 to be completely filled in a vacuum with a cooling liquid dielectric, such as mineral oil, for the first time, when the transformer is turned on. This filler neck is usually also hermetically sealed with a cap 18. In FIG. 1 tank 1 is shown before it is initially filled with oil.

Inside the tank 1 is installed, in accordance with the invention, an automatic protection device with a lever disconnector containing the following elements:
- lever of the first kind 6;
- the horizontal axis of rotation 7, located so that divides this lever 6 into two unequal shoulders, length d for shorter 8, to which "resistance" is attached, length D for long, to which "acting force" is applied;
- a vessel 10 at the end of the long arm 9 with an open hole 20, the weight of which through the gear ratio D / d of the lever causes the appearance of an upward force F at the end of the short arm 8. In this case, the hole 20 is formed simply as a result of the absence of the upper lid of the vessel;
- a pusher 11 at the end of the short arm 8, transmitting the force F to the actuator 2, which counteracts it with a force Fd equal to the selected cut-off threshold, after which the circuit breaker 5 of the network supplying the transformer primary windings is tripped.

 The combination of the disconnecting lever 6, the actuator 2 and the switch 5 and is an internal automatic protection device to which the invention relates.

 As for the lever 6, which is actually the subject of the invention, its parameters and the location of its constituent elements are determined in accordance with the criteria that have already been discussed, and which will again be explained below.

 All elements of the self-defense device are made of durable materials (metal or plastic) that can withstand, without collapsing, the effects of a cooling liquid dielectric on them throughout the entire duration of the transformer. In addition, the disconnecting lever 6 with the vessel 10 at the end is made of a material whose density is less than the density of the cooling liquid dielectric, so that during normal operation of the transformer it naturally occupies a stable upward position, as can be seen from FIG. 3.

 During the installation of a new transformer, when there is no cooling liquid dielectric in the tank 1, the lever 6 is tilted towards its long arm 9, and the pusher 11 acts on the actuator 2 with an idle pressure Fo equal to the weight of an empty vessel 10 times the gear ratio of the lever, and less than the set trip threshold Fd, above which the isolation drive 2 must trip.

 The device also contains a stop 12, the purpose of which will be explained below.

 In FIG. 2 shows a transformer tank during its filling with a cooling liquid dielectric 13. The cooling liquid dielectric enters the tank 1 from the tank 14 through a hose 15 connected to the filler neck 4 of the cover 3. As can be seen from FIG. 2, as soon as the surface of the cooling liquid dielectric 13 reaches the vessel 10 at the end of the long shoulder 9 of the lever 6, it, being empty, will gradually rise under the action of the Archimedes force, remaining afloat until it touches the stop 12 in the upper position.

 In Fig. 3 we see the tank 1 of the transformer when a nominal amount of cooling liquid dielectric is poured into it, which "completely" or "almost completely" fills its volume. In any case, its surface 16 is at maximum height, so that the vessel 10 is completely immersed in a cooling liquid dielectric. As already noted, the upper edge of the vessel 10 rested against the stop 12, which did not allow the vessel to rise above, and when the level 16 of the cooling liquid dielectric reaches the edge of the hole 20, the vessel 10 is automatically filled with a cooling liquid dielectric. As soon as the vessel 10 is filled, it is completely immersed in the same cooling liquid dielectric that fills it, and in this position it is desirable that the plunger 11 is somewhat removed from the drive 2, or, in any case, that it acts on it with force less than the set shutdown threshold Fd.

 In FIG. 4 shows a transformer tank having received a hole 17, as a result of which a cooling liquid dielectric flows out of it. This causes a gradual decrease in the level of the surface 16 of the cooling liquid dielectric 13 in the tank and, consequently, a corresponding decrease in the Archimedean force acting on the vessel 10, as soon as it is slightly supported by the resistance force Fd with which the drive acts on the plunger 11 at the end of the short arm of the lever, begins to protrude from the cooling liquid dielectric.

 Since the vessel remains filled with the cooling liquid dielectric 13, at a certain degree of its protrusion above the surface of the cooling liquid dielectric, an equilibrium state arises between the buoyant Archimedean force and the bulk density of the vessel 10. Outside this equilibrium, the force F with which the pusher 11 acts on the actuator 2 begins to increase . When it reaches and exceeds the selected value of the set trip threshold Fd, the protective device trips. This can happen either immediately or after a time delay caused by the short movement of the trigger lever (not shown in the drawing) of the actuator 2. The position of the axis of rotation 7, the dimensions of the arms of the lever 6 (determining its gear ratio) and the capacity of the vessel 10 are calculated as follows so that the force F can reach a value significantly higher than the set cut-off threshold Fd, and so that it exceeds the set cut-off threshold Fd when the level 16 of the surface of the cooling liquid dielectric is lower so that there is a danger of explosion of the transformer. Of course, this level is determined by the type of transformer.

 As an abstract example, one can choose a lever 6 made of polypropylene with a density of 0.9, a total length of 330 mm, divided into two arms, long 9 (the place of application of the acting force) of length D = 300 mm and short 8 (the place of application of the resistance force) of length d = 30 mm (with gear ratio D / d = 10). The vessel 10 has a weight of 20 g and a usable volume of 100 cubic centimeters, in which 90 g of a cooling liquid dielectric (mineral oil) is placed.

 In this case, the pusher 11 acts on the actuator 2 with a force Fo equal to 200 g, in the case when the vessel is empty and it does not come in contact with the cooling liquid dielectric in the tank. However, the lever 6 is adjusted so that the transformer is switched off only when the force with which the pusher 11 acts on the drive exceeds the set trip threshold Fd equal to 800 g.

 When the transformer is filled with a cooling liquid dielectric, the vessel 10 is completely immersed in it. The force acting on the side of the pusher 11 on the actuator 2 is zero if the design does not provide for constant contact between them, and, in any case, less than 200 g due to the difference of the Archimedean forces pushing the long arm 9 of the lever 6, which, moreover, , lower density than the cooling liquid dielectric in which it is immersed.

 But when the oil level drops, as shown in figure 4, where the filled vessel 10 partially protrudes from it, to 200 g acting on the drive from the pusher 11 in the case when the vessel is empty, a force of 90 * is added 10 = 900 g, the source of which is the weight of the cooling liquid dielectric 13 contained in the vessel 10. Therefore, the force F is 200 + 900 = 1100 g, which is significantly more than the set cut-off threshold Fd Fd = 800 g: the transformer is switched off. The weakening of this force due to the fact that part of the long arm of the lever still remains immersed in a cooling liquid dielectric, is a second-order value compared to other forces acting at this moment.

 As you can see, this device for tracking the level of a cooling liquid dielectric, which is extremely simple in concept, in manufacture and in operation, has very high reliability. Its virtues do not diminish over time. Another advantage, compared to a device with a classic float, is that before or during filling the transformer, the float device provokes the circuit breaker to trip. Therefore, after filling it must be brought into working condition, provided that it is provided for by the design, except for the case when the float is blocked in the upper position in the time of filling the tank, which further complicates the design of the disconnecting device.

 It goes without saying that the invention is not limited to the example described in the appendix with the help of the drawings, but can relate to many variations and equivalents to the extent that this corresponds to the definition of the invention given in the following claims.

 For example, the stop 12 may be part of the inner side of the cover 3. In this case, so that the cooling liquid dielectric 13 can freely pass into the vessel 10 when it abuts against the cover 3, in its upper edge, preferably from the side of the lever, one or more cuts have been made. The holes drilled in the side walls of the vessel near its upper edge could also perform the same function.

 Similarly, the automatic filling of the vessel 10 may not necessarily be through the top. In fact, you can make a hole in its bottom through which the cooling liquid dielectric penetrates while the transformer tank is filling, while the non-return valve blocking the hole prevents its return to the surrounding liquid dielectric.

 In general, means for automatically filling the named vessel with a cooling liquid dielectric through the inlet during filling of the tank should be such as to prevent the exit of this cooling liquid dielectric from the vessel through the same hole.

Claims (6)

 1. Disconnector of the device for internal automatic protection of an electric power or distribution transformer (19) immersed in a tank (1) filled with a cooling liquid dielectric, disconnecting the primary winding from the supply network in the event of an emergency decrease in the level of the cooling liquid dielectric and containing a switch (5), on which the actuator (2) acts, which is driven by the specified disconnector, consisting of a lever (6) of the first kind, rotating around an axis (7), which divides it into one a short arm (8), representing resistance, and one long shoulder (9), representing the applied force of the specified lever, characterized in that a vessel (10) with an inlet (20) is installed at the end of the long shoulder of the specified lever, there is a means for automatically filling the vessel with a cooling liquid dielectric through the hole (20) in the process of filling the tank, and means (11) at the end of the short arm (8) of the specified lever for transmitting force to the drive (2), and disconnection occurs when the force exceeds the set th threshold of shutdown, and the relative dimensions of the indicated arms (8, 9) of the specified lever and the dimensions of the vessel (10) are such that when the tank is filled with a cooling liquid dielectric (13), the vessel is completely immersed in this cooling liquid dielectric, and the force with which it acts on the drive, less than the set cut-off threshold, while if the surface (16) of the cooling liquid dielectric falls to a level that is considered abnormally low, the vessel that remains filled with the cooling liquid dielectric (13) reaches such a degree of ascent, at which, under the influence of its weight, the force transmitted to the drive exceeds the set cut-off threshold.  2. The disconnector according to claim 1, characterized in that the vessel (10) at the end of the long arm (9) of said lever is open in its upper part (20).  3. The disconnector according to any one of p. 1 or 2, characterized in that the means for automatically filling the vessel (10) with a cooling liquid dielectric penetrating through the hole (20) during filling of the tank is a stop (12) interacting with the edge of the vessel.  4. The disconnector according to any one of p. 1 or 2, characterized in that the means for automatically filling the vessel (10) with a cooling liquid dielectric penetrating through the hole (20) during filling of the tank, is a cutout made in the edge of the vessel .  5. The disconnector according to claim 1, characterized in that the vessel (10) has an inlet opening in its bottom, and the means for automatically filling the vessel with a cooling liquid dielectric penetrating through the opening is a check valve interacting with the latter.  6. An electric power or distribution transformer immersed in the tank and containing an internal automatic protection device that disconnects it from the electrical network in the event of a decrease in the level (16) of the cooling liquid dielectric in the tank (1) in which it is contained, and containing a disconnector that responds to level changes and consisting of a lever (6) of the first kind, rotating around an axis (7), which divides it into one short shoulder (8), representing resistance, and one long shoulder (9), representing the applied force of the specified a lever, characterized in that a vessel (10) with an inlet (20) is installed in the disconnector at the end of the long arm of the specified lever and there is a means for automatically filling the vessel with a cooling liquid dielectric through the aforementioned hole (20) in the process of filling the tank, and means ( 11) at the end of the short arm (8) of the specified lever for transmitting force to the actuator (2), moreover, the shutdown occurs when the force exceeds the set threshold of shutdown, the relative dimensions of the specified shoulders (8.9) of the specified lever and size The vessels (10) are such that when the tank is filled with a cooling liquid dielectric (13), the vessel is completely immersed in this cooling liquid dielectric, and the force with which it acts on the drive is less than the set cut-off threshold, while if the surface (16) of the cooling liquid dielectric drops to a level that is considered abnormally low, the vessel that remains filled with the cooling liquid dielectric (13) reaches a degree of ascent at which the force transmitted to the drive exceeds the established force Threshold shutdown threshold.

Images