Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
  • H02H1/00—Details of emergency protective circuit arrangements
  • H02H1/0007—Details of emergency protective circuit arrangements concerning the detecting means
  • H02H1/0015—Using arc detectors
  • H02H1/0023—Using arc detectors sensing non electrical parameters, e.g. by optical, pneumatic, thermal or sonic sensors

Definitions

• the invention relates to an arc relay intended for detecting an arc possibly flashing up at one or more points of a switchgear and for extinguishing it by causing a circuit-breaker supplying current to the switchgear to be opened.
• the arc relay comprises a pickup sensor for collecting light, an optical fibre connected to the pickup sensor for transmitting the collected light forwards along the fibre, a photo ⁇ sensor connected to the end of the fibre, and an elec ⁇ tronics unit connected to the photosensor for control- ing the circuit-breaker in response to the detected arc.
• switchgears used in the distribution of electricity with an arc relay which detects an arc created and extinguishes it by causing one or more of the circuit-breakers supplying current to the switch- gear to be opened.
• the duration of the arc is in this way reduced as much_ as to one tenth, so that large damages can be avoided and the degree of utilization of the switchgear can be increased.
• the arc creates a light, pressure, heat and sound effect each one of which could be used for detecting the arc.
• the object of the present invention is to avoid the above drawbacks and provide a novel type of arc relay which is more advantageous in price as its structure is simpler than that of prior devices. This is achieved by means of an arc relay of the type de ⁇ scribed in the beginning in such a manner that a transparent cladding surrounding the core of an op ⁇ tical fibre is arranged as a pickup sensor.
• the basic idea of the invention is thus to eli- minate the need of collector lenses and to use the fibre as a pickup sensor so that a plurality of sen ⁇ sors can be positioned along one and the same fibre.
• the arc relay according to the invention re ⁇ quires one optical fibre and one photosensor only for monitoring several points, e.g. the different cells of the switchgear, wherefore the price of the device is advantageous.
• Several switchgears can be monitored by means of a single fibre when the fibre is mounted to extend through the switchgears to be monitored. As one optical fibre only is needed, continuous auto-di ⁇ agnosis is easy to carry out.
• Figure 1 illustrates schematically the light measuring principle of an arc relay according to the invention monitoring the different cells of an elec ⁇ tric switchgear
• Figure 2 illustrates schematically an optical fibre acting as a pickup sensor and an electronics unit attached thereto
• Figure 3 illustrates the arc relay according to Figure 2, the arc relay being additionally provided with a testing part which checks the condition of the relay from time to time, and
• Figure 4 illustrates an example of a pickup sensor formed at the end of a fibre.
• Figure 1 shows an electric switchgear 1 the successive cells of which are indicated with the re ⁇ ferences A to E.
• An arc relay 2 is shown simplified so that it comprises an optical fibre 3 extending through the cells and an electronics unit 4 attached there ⁇ after.
• the light of an arc possibly created in each cell is collected in the fibre 3 from its side through the cladding of the fibre.
• the term cladding as used herein refers to a part surrounding the core and allowing the passage of light therethrough into the core along which light passes onwards. The structure of the fibre is described more closely below.
• Fig ⁇ ure 1 the light of an arc created in the cells B and D is indicated with the arrows V.
• the rest of the fibre may be coated so that it is opaque where ⁇ as the cladding of the part acting as a pickup sensor has to be transparent.
• This is illustrated in the cell E, in which a fibre part 3e acting as a pickup sensor is free, whereas the rest of the fibre 3 is provided with an opaque coating 5.
• the light collect- ing capacity can be improved and the directionality can be reduced by looping the fibre part acting as a pickup sensor.
• This is illustrated in connection with the cells B, C and D, in which fibre parts 3b, 3c and 3d acting as a pickup sensor are formed by successive loops.
• the pickup sensor can also be formed by a straight fibre part in the cell, as is shown by the sensor part 3a in the cell A.
• the arc relay according to the invention enables the detection of an arc created in any one of the cells by means of a single optical fibre 3 and a photosensor (not shown) connected there ⁇ af er and further coupled to the electronics unit 4.
• the arc relay it is not possible to de ⁇ tect in which cell the arc is created; on the other hand, location detection is not usually necessary.
• In ⁇ formation obtained from the photosensor is processed in the electronics unit 4, which controls a circuit- breaker through its relay output 6.
• FIG 2 shows schematically the optical fibre 3 acting as a pickup sensor and the electronics unit 4.
• the corresponding parts are indicated with the same reference numerals as in Figure 1.
• the fibre part 3f acting as a pickup sensor is positioned at the point to be monitored, and the fibre, now covered with the coating 5, extends further to the photosensor 7 and the electronics unit 4, which is positioned in a hous ⁇ ing 8.
• the sensor part 3f may be attached to another fibre with a connector 3g, whereby an advantage is achieved in that only the sensor part has to be re- placed if an arc should damage the fibre.
• a PIN diode or a phototransistor con ⁇ verts a light pulse arrived along the fibre into a current pulse which is amplified in a preamplifier 9 having adjustable amplification.
• a band pass filter 10 is connected which allows the passage of signals typical of the light of the arc.
• an adj-ustable comparator 11 is connected which controls the relay 12, if the signal to the comparator exceeds a preset level.
• the release circuit of the circuit-breaker is connected to extend through the contacts 6 of the re ⁇ lay 12.
• a wavelength filter 13 allowing the passage of blue and ultraviolet light is connected in front of the photosensor 7 for improving the selectivity of the detection.
• the wavelength filter 13 may also be fixed ⁇ ly integrated to the photosensor 7.
• the relay 12 may also be effected by means of semi-conductors.
• FIG 3 shows the respective structure when it is provided with a testing part for intermittently checking the condition of the device.
• the testing part comprises a light source 14 and a control unit 15 thereof.
• the fibre 3 has no free end as in the preceding example; instead, one end thereof is con ⁇ nected to the light source 14, which is controlled by the control unit so that it sends a short test pulse into the fibre e.g. at the intervals of 5 seconds, thus checking the condition of the device.
• the control unit 15 and the band pass filter 10 are connected through the comparators 11 to a logic unit 17, which generates its output signals F and G on' the basis of its input signals K and L.
• the output signal F gives an alarm of a fault through a buzzer 18 if the input signal K corresponds to the logical 1 and the input signal L to the logical 0.
• the output signal G con- trols the circuit-breaker through the contacts 6 of the relay 12 if the value of the input signal L only corresponds to the logical 1.
• the connection of the arc relay to the circuit-breaker is not more closely shown in the figures because it is effected in a manner known per se and does not belong to the basic idea of the invention.
• the optical fibre 3 required for the collecting of light is formed, as usually, by a core and a cladd ⁇ ing surrounding it, and a primary coating.
• the core 5 and the cladding may be made of plastic or glass. Due to the great light attenuation, however, previous fibres having a plastic core can have a length below 10 m only. The light attenuation of fibres having a glass core does not place any practical restrictions
• the fibre thus always comprises the core, the cladding and the primary coating, whereas the secondary and buffer
• Figure 4 shows still another example of a pick ⁇ up sensor formed at the end of a fibre and comprising
• a thin teflon hose 20 improving the sensitivity of. the sensor in the sideward direction is provided on that part of the looped optical fibre which acts as a pickup sen ⁇ sor.
• the teflon hose 20 can be left out as well.
• 25 fibre end need not necessarily be looped but it can be quite straight.
• the light enters the fibre from the side through the cladding.
• the entrance of the light into the fibre from the end of the fibre is prevented with a light shield.
• the protective sheath 21 made of bright plastic and surrounding the fibre loop is attached to the outer end of the arm.
• the protective sheath 21 is filled with a trans ⁇ parent resin filler 22 surrounding the loop.
• the pickup sensor may be provided with any trans- parent coating which guarantees a sufficient sensitiv ⁇ ity; the rest of the fibre may be provided with any opaque coating, as stated already in connection with Figure 1.
• the in ⁇ vention is not restricted thereto, but it can be mod ⁇ ified in various ways within the scope of the inven- tive idea defined in the attached claims. So the elec ⁇ tronics unit 4, for instance, can also be effected by means of switching transistors.
• the selectivity of the arc relay can be improved not only by wavelength filtration but also by connecting the light detection to some other phenomenon relating to the arc, such as a current change, and accept as an arc only events in which a change exceeding a certain limit occurs in both quantities.

Priority Applications (6)

Applications Claiming Priority (2)

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Cited By (26)

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Citations (5)

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• 1987
  • 1987-04-14 FI FI871627A patent/FI77952C/fi not_active IP Right Cessation
• 1988
  • 1988-04-07 DE DE3890265A patent/DE3890265C2/de not_active Ceased
  • 1988-04-07 GB GB8922316A patent/GB2225186B/en not_active Expired - Lifetime
  • 1988-04-07 CH CH462888A patent/CH676174A5/de not_active IP Right Cessation
  • 1988-04-07 WO PCT/FI1988/000052 patent/WO1988008217A1/en active Application Filing
  • 1988-12-01 NO NO885373A patent/NO173415C/no not_active IP Right Cessation
• 1989
  • 1989-10-11 DK DK504289A patent/DK165085C/da not_active IP Right Cessation
  • 1989-10-12 SE SE8903348A patent/SE462544B/sv not_active IP Right Cessation

Patent Citations (5)

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