HIGH-VOLTAGE THYRISTOR CONVERTER

Abstract: The invention relates to a high-voltage thyristor converter in which the controlled light beam (3) of an irradiator (2) is directed towards a plurality of thyristor modules (ET) by means of a plurality of half mirrors (6a, 6b, 6c) arranged in sequential manner in the light beam (3).

Description: The invention relates to a high-voltage thyristor converter having a plurality of thyristor modules, the thyristors of which are controlled by means of light sensitive elements, electric components and reflecting mirrors individually associated with the thyristor modules from a light beam irradiator emitting a light beam in response to a external operation command. Fig. 1 is a connection diagram of a high-voltage thyristor converter to which the present invention is to be applied, wherein an alternating current supplied from AC buses R, S and T is converted into a direct current via bridge-connected valves U - Z or a direct current from DC buses P and N is converted into an alternating current. Each of the valves U - Z constituting the high-­ voltage converter is assembled as illustrated in Fig. 3 by superposing a desired number of thyristor modules SM on one another by the use of insulator pillars B, each thyristor module SM comprising, as illustrated in Fig. 2, a plurality of thyristor elements Sl - Sn and accessory components such as an anode reactor AL, resistors and capacitors. In transferring a gate signal to individual thyristor elements constituting a thyristor module SM, there are known a mode which transfers to a high-voltage section an electric signal converted by means of a pulse transformer at a ground potential, and a mode which converts an operation command into a light signal by a transducer at a ground potential and then transfers the light signal to a high-voltage section via a light guide LG such as an optical cable as illustrated in the example of Fig. 3. Fig. 4 shows the principle of a gate signal transfer system employing optical cables, wherein a transducer 1 for converting a thyristor-valve operation command into a light signal is equipped internally with light emitting elements EL. There are also shown a light guide LG composed normally of an optical cable and serving to transfer the output signal of the light emitting element EL to a thyristor module SM at a high voltage level; a joint JT disposed between the thyristor module SM and the light guide LG and so formed as to be detachable by the use of a coupler; and a light sensitive element LE for converting an input into an electric signal which serves as a trigger signal to drive a thyristor ET. Meanwhile, due to the service life of electric circuit components constituting the thyristor module SM, it is necessary to replace each thyristor module with a new one after the lapse of a predetermined term. In such replacement where a joint JT needs to be attached to or detached from the thyristor module SM for connection of the cable to transfer electric or light signal, it has been unavoidable that some damage is caused to the light guide LG. Particularly the optical cable for transfer of light signal has a relatively low flexibility and is therefore prone to be broken during the work of replacement. Furthermore, in an UHV-class thyristor valve employed in a 500 kV DC transmission system, the withstand voltage charac­ teristic of the optical cable is inferior to that of an epoxy cast product or the like, so that some proper improve­ ment has been required in this aspect as well. From DE-A-25 14 528 it is known to have separate light paths one beside the other, and in each light path a mirror is placed for reflecting the light beam into the corresponding thyristor level. It is an object of the present invention to provide a novel thyristor converter in which only one light beam irradiator is necessary and which avoids the necessity of costly light guide devices which are subject to be destroyed or at least mis-aligned upon changes at the thyristor modules, or the necessity of a plurality of parallel light paths. The object of the invention is solved by a high­ voltage thyristor converter which is characterized by a plurality of half mirrors disposed sequen­ tially on the travel path of the light beam signal emitted from said irradiator for reflecting the light beam signal from said irradiators towards each of said thyristor modules. The invention will now be described in connection with the accompanying drawings in which: Fig. 1 is an electrical connection wiring diagram of a high-voltage thyristor converter to which the present invention can be applied; Fig. 2 is a circuit diagram of a thyristor module employed in the converter of Fig. 1; Fig. 3 is a side view schematically showing a conventional high-voltage thyristor converter; Fig. 4 is a block diagram of means for transfer of firing signals in the converter of Fig. 3; Fig. 5 is a block diagram illustrating the principle of firing signal transfer in a high-voltage thyristor converter embodying the invention; and Fig. 6 is a side view schematically showing the high-voltage thyristor converter based on the principle of Fig. 5. Detailed Description of the Preferred Embodiments: Hereinafter an exemplary embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 5 illustrates the principle of the invention, wherein a transducer 1 converts a thyristor valve operation command into an electric signal which is capable of controlling a pulsed laser beam signal 3 outputted from a laser beam irradiator 2. It is desired that the laser beam irradiator 2 be of a small output type in a dimensionally compact structure so as to be handled with facility. A preferred example is a helium-neon laser or a semiconductor laser whose output is in a visible light region of short wavelengths. (The output of a helium-neon laser has a wavelength of 6328 angstroms and an intensity on the order of 1 to 10 watts.) A light sensitive element 4 is incorporated in a thyristor module SM disposed in a high-voltage section. A photodiode or the like may be employed to serve as the light sensitive element 4. And a converter circuit 5 is provided for converting the electric output of the light sensitive element 4 into a trigger signal to drive an electrically triggered thyristor ET. Both the laser beam irradiator 2 and the trans­ ducer 1 are placed at a ground potential and are operated while being kept out of contact with the high-voltage section where the thyristor module SM and so forth are located. Since the helium-neon laser or semiconductor laser is a device that emits an output within a visible light region of short wavelengths, it is capable of responding to a high-frequency input signal of several kilohertz as well and is therefore suited for transfer of a thyristor control signal. Although the entire thyristors used in the embodiments are of an electrically triggered type, employment of optically triggered thyristors developed lately for practical application can omit the light sensitive elements 4 and the converter circuits 5 incor­ porated in the thyristor modules. The embodiment of Fig. 5 is equipped with a single laser beam irradiator 2 which is so disposed as to form a travel path of a laser beam signal 3 intersecting the optical axes of light sensitive elements 4 in a plurality of thyristor modules SM. Half mirrors 6a, 6b and 6c are disposed at individual intersections of the beam signal path and the optical axes of the light sensitive elements 4. The half mirrors 6a, 6b and 6c have such properties as to partially reflect the energy of the laser beam signals 3 emitted from the irradiators 2 while permitting transmission of the remaining energy therethrough. The laser beam signals reflected respectively at the half mirrors 6a, 6b and 6c are introduced via the individual paths 3a, 3b and 3c to the light sensitive elements 4 in the associated thyristor modules SM. The ratio of the reflected light to the incident light is expressed as (1 - γ) in which γ represents the light transmissivity of the half mirrors 6a, 6b and 6c. When n pieces of half mirrors are employed in total, the ratio αi of the reflected light and the ratio βi of the transmitted light to the initial output light of the i-th mirror are given by the following equations: αi = γ i - 1 . (1 -γ ) βi = γ i Therefore, by the use of half mirrors whose transmissivity γ is approximately 1, it becomes possible to retain within a relatively narrow range the amount of the light reflected from each half mirror. For example, when the mirrors have a transmissivity of 0.9, the ratio between the reflected light α1 from the first mirror and the reflected light α8 from the eighth mirror is Thus, there exists an advantage that selection of a proper transmissivity can eliminate the necessity of rendering the light sensitive elements 4 individually different for the thyristor modules SM respectively. If the transmissi­ vities of the half mirrors are so established as to become gradually lower as the mirrors recede from a laser beam source, the amounts of the laser beams reflected from the half mirrors are rendered substantially equal to one another, whereby the same advantageous effect as the foregoing is also achievable. Fig. 6 shows an exemplary aerial insulation type high-voltage thyristor converter based on the principle of Fig. 5. In this example, a laser beam irradiator 2 is disposed in the vicinity of a leg area of the high-voltage thyristor converter. A control signal for a laser beam 3 outputted from a transducer 1 in response to an operation command is transferred via a cable 7 to the laser beam irradiator 2. The laser beam 3 from the irradiator 2 is reflected at half mirrors 6 which are located respectively in thyristor modules SM and are adjustable with respect to the angles of attachment thereof, so as to be distributed to the individual thyristor modules. The laser beams thus distributed are then converted into electric signals by light sensitive elements 4 provided substantially horizontally in the thyristor modules SM, thereby controlling the thyristors in the modules. In such arrangement where the entire laser beam irradiators 2 are located in the vicinities of the floor, maintenance and inspection are facilitated for the laser beam irradiators. Furthermore, due to the structure that distributes the laser beam obtained from a single irradiator, the total number of irradiators to be installed is minimiz­ able to eventually reduce the production cost as well as to enhance the operational reliability. In addition, directional adjustment of the half mirrors 6 enables fine correction of any deviation of the beam travel path induced during assembly or replacement, whereby the positional error of the module caused in the assembling step is absorbable.

Claims: 1. A high-voltage thyristor converter having a plurality of thyristor modules (SM), the thyristors (ET) of which are controlled by means of light sensitive elements (4), electric components and reflecting mirrors (6a, 6b, 6c; 6) individually associated with the thyristor modules from a light beam irradiator (2) emitting a light beam (3) in response to a external operation command, characterized by a plurality of half mirrors (6a, 6b, 6c; 6) disposed sequentially on the travel path of the light beam signal (3) emitted from said irradiator (2) for reflecting the light beam (3) signal from said irradiator towards each of said thyristor modules (ET). 2. The thyristor converter as defined in claim 1, characterized in that said half mirrors (6a, 6b, 6c; 6) have different transmissivities which become sequentially lower in accordance with increase of the distance from said light beam irradiator (2). 3. The thyristor converter as defined in claim 1 or 2, characterized in that said mirrors (6a, 6b, 6c; 6) are directionnaly adjustable. 4. The thyristor converter as defined in any of the preceeding claims, characterised in that the light beam irradiators (2) are laser beam irradiators.

Inventors: YOSHIOKA, AKIYOSHI C/O MITSUBISHI DENKI K. K., YOSHIZUMI, TOSCHIAKI C/O MITSUBISHI DENKI K. K.
Applicants: MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1984
Main classification: H02M1
IPC codes: H02M1