Patent EA-002377-B1 (EA)
Title: Immersed transformer self-protected by a device including a circuit breaker and fuses
Inventor: WILD JACQUES
IPC: H01F27/40
Filed: 1999-08-13
Abstract: 1. A three-phase electrical transformer (1) comprising: a tank (4) containing a liquid or gas dielectric (5), a three-phase primary circuit and a three-phase secondary circuit, both comprising windings (2, 3) immersed in the dielectric, each phase of the primary circuit entering the tank (4) via an insulating bushing (7), a protection device comprising : at least two fuses (11) immersed in the dielectric (5), the fuses being connected in series each on a phase of the primary circuit of the transformer (1) between the insulating bushing (7) and the primary circuit windings (2) and having a sufficient breaking capacity to perform breaking of the corresponding phase in case of a three-phase short-circuit of the primary circuit, a multipole circuit breaker (15) comprising, for each phase equipped with one of the fuses (11), a pole immersed in the dielectric (5) and connected in series on said phase between the corresponding fuse (11) and the windings (2), each pole comprising contact means (19, 20) able to take with respect to one another a contact position in which they ensure current flow and a separation position, the circuit breaker (15) comprising in addition an opening mechanism (22) common to all the poles, designed to move the contact means (19, 20) from their contact position to their separation position, a first tripping means (28) associated to the opening mechanism (22) of the circuit breaker (15) and comprising a overload trip device (28), the fuses (11), circuit breaker (15) and the first tripping means (28) being associated in such a way that under conditions corresponding to a short-circuit at the terminals of the secondary circuit, the contact means (19, 20) of the circuit breaker (15) separate and interrupt the current without-the fuses (11) starting to melt, and that there exists a threshold value of the current intensity flowing in each fuse, this threshold being lower than the breaking capacity of the corresponding pole of the circuit breaker (15) and above which threshold melting of the fuse (11) has taken place before a separation order of the contact means (19, 20) given by the overload trip device (28) has been able to cause separation of the contact means (19, 20). 2. A single-phase electrical transformer (1) comprising: a tank (4) containing a liquid or gas dielectric (5), a primary circuit and a secondary circuit, both comprising one or more windings (2, 3) immersed in the dielectric (5), the phase of the primary circuit entering the tank (4) via an insulating bushing (7), a protection device comprising: at least one fuse (11) immersed in the dielectric (5), connected in series on the phase of the primary circuit of the transformer (1) between the insulating bushing (7) and the winding or windings of the primary circuit (2)-and having-a -sufficient breaking capacity to perform breaking of the corresponding phase in case of a short-circuit of the primary circuit, a circuit breaker (15) comprising a pole immersed in the dielectric (5), connected in series between the fuse (11) and the windings of the primary circuit (2), and comprising contact means (19, 20) able to take with respect to one another a contact position in which they ensure current flow and a separation position, the circuit breaker (15) comprising in addition an opening mechanism (22) designed to move the contact means (19, 20) from their contact position to their separation position, a first tripping means (28) associated to the opening mechanism (22) of the circuit breaker (15) and comprising an overload trip device (28), the fuse (11), circuit breaker (15) and the tripping means (28) being associated in such a way that under conditions corresponding to a short-circuit at the terminals of the secondary circuit, the contact means (19, 20) of the circuit breaker (15) separate and interrupt the current without the fuse (11) starting to melt, and that there exists a threshold value of the current intensity flowing in the fuse (11), this threshold being lower than the breaking capacity of the corresponding pole of the circuit breaker (15) and above which threshold melting of the fuse (11) has taken place before a separation order of the contact means (19, 20) given by the overload trip device (28) has been able to cause separation of the contact means. 3. The transformer according to either one of the claims 1 and 2, characterized in that the overload trip device (28) comprises at least one measuring means (27) for measuring the intensity of the current flowing in a phase of the primary circuit of the transformer (I). 4. The transformer according to claim 3, characterized in that the measuring means (27) measures the current flowing at a point situated line-side from the fuse or fuses (11), in particular outside the tank (4), line-side from the bushing (7). 5. The transformer according to any one of the foregoing claims, characterized in that the fuse or fuses (11) have an elongate shape with two conducting ends (10, 13) designed for their line-side connection on the bushing (7) side and load-side connection on the circuit breaker (15) side, situated on each side of a middle part (12) whose external surface is insulated, and that for each phase equipped with a fuse (11), .the conducting parts situated between the 'insulating bushing (7) and the insulated external surface of the middle part (12) of the fuse are enveloped in a solid insulator. 6. The transformer according to any one of the foregoing claims, characterized in that the fuse or fuses 11 have an elongate shape with two conducting ends (10, 13) designed for their line-side connection on the bushing (7) side and load-side connection on the circuit breaker (15) side, situated on each side of a middle part (12) whose external surface is formed by an insulator, and that for each phase equipped with a fuse (11), the fuse (11) constitutes a monoblock sub-assembly with the bushing (7), and that the external surface of this sub-assembly, in its part internal to the tank (4), comprising the bushing (7), the line-side conducting end (10) and the middle, part (12) of the fuse (11), is formed by one or more solid insulators forming a solid insulation without interruption. 7. The transformer according to any one of the foregoing claims, characterized in that comprises a second trip device (30) commanding opening of the circuit breaker when at least one parameter representative of the state of said dielectric exceeds a set threshold. 8. The transformer according to any one of the foregoing claims, characterized in that comprises measuring means (27) for measuring the intensity of the current flowing in a phase of the secondary circuit of the transformer. 9. The transformer according to any one of the foregoing claims, characterized in that the fuse or fuses (11), circuit breaker (15) and a first tripping means (28) are associated in such a way that if the fuse or one of the fuses melts, the first ripping means (28) give a separation order of the contact-means. 10.The transformer according to any one of the foregoing claims, characterized in that the fuse or fuses (11) are limiting. 11. The transformer according to any one of the foregoing claims, characterized in that each pole of the circuit breaker comprises a vacuum cartridge (17) immersed in the dielectric (5). 12.The transformer according to any one of the foregoing claims, characterized in that the circuit breaker (15) comprises a closing mechanism (22) designed to move the contact means (19, 20) from their separated position to their contact position, comprising an operating means (23) accessible from outside the tank (4), the opening mechanism (22) being designed to cause opening of the circuit breaker pole or poles whatever the state of the closing mechanism (22).