Earthing Truck [PDF]

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User manual



2005



MV vacuum circuit breaker



Evolis Merlin Gerin 24 kV



Earthing truck



Earthing truck (cmalt) operation 0



cmalt.tif



Function



DE31050b



The earthing truck has the function of connecting the busbars in one half-switchboard to earth. Naturally, the earthing operation must be carried out when de-energised so as not to create a short-circuit.



Interlocking In order to de-energise a half-busbar in complete safety, it is necessary to use a key centre. This centre enables the operator to ensure that all of the circuit breakers are racked out in the half-switchboard to be connected to earth. The operation is carried out in the following manner (in order to earth busbar A, cf. figure 1): b rack out all of the circuit breakers on the half-switchboard, including that of the bus-sectioning cubicle (circuit breakers in cubicles 1 - 2 - 3), b lock these circuit breakers in the “racked out” position and remove the keys which are released (keys D1, D2 and C), b place these three keys in the corresponding key centre and remove the key that is released (STA). This then locks the circuit breaker keys in place, b unlock the earthing truck using the released key, which only enables the truck to be racked in the half-switchboard which has just been de-energised.



DE31050d



Figure 1: single line diagram example



AD type feeder cubicle



AD type incomer cubicle Busbar A



D1



CL-GL type bussectioning cubicle



D2



1



C



2



STA



STB



AD type feeder cubicle



D5



3 Earthing truck cmalt



1



AD type incomer cubicle Busbar B



D6



4



5



Key centre



C



D2 D1 STA



C



D6 D5 STB



Schneider Electric 07897591EN REV.A0



Earthing truck (cmalt) operation 0



Mechanism to disable racking of the earthing base in the energised half-switchboard Cubicles in a switchboard equipped with an earthing base include a mechanism to avoid incorrect operation. This fool-proof system is different according to whether the cubicle is part of the half-busbar A or B in the switchboard (cf. figure 1). The earthing truck cannot be racked into a cubicle unless the key latch opposite the fool-proof system is lowered using the right key. The fool-proof system is mounted with one screw on the higher hole in cubicles belonging to the half-switchboard on the left hand side (cf. figure 2, safety no. 1), and with one screw on the lower hole in cubicles belonging to the half-switchboard on the right hand side (cf. figure 2, safety no. 2). Two screws are mounted on the bussectioning cubicle to make it impossible to rack in the earthing truck (cf. figure 2, safety no. 3).



DE31050e



Safety device no. 1: Insertion impossible in the right hand half-switchboard



x3



fig.2cmalt_en.eps



Figure 2: locking mechanism, front view



Earthing base



Cradle



Earthing base



Cradle



STA



STB



Safety device no. 2: Insertion impossible in the left hand halfswitchboard



STA



STB



Safety device no. 3: Bus-sectioning cubicle, impossible to insert the earthing truck



Earthing base



Cradle



STA



STB



Schneider Electric 07897591EN REV.A0



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Earthing truck (cmalt) operation 0



synoptique.tif



Operation Once the truck is unlocked, the sequence of operations is as follows: b insert the earthing truck in one of the cubicles of the de-energised half-switchboard, b rack-in the device with the door open, b manually charge the spring using the handle, b close the contacts of the earthing truck (press on the closing button). When the earthing base is closed, a padlockable runner enables access to the opening button to be disabled, and thus enables the earthing truck to be locked in the closed position. Moreover, an interlock disables the possibility of racking the earthing truck out when it is closed (as for a circuit breaker). The earthing of busbars can therefore be made secure using padlocks (three padlocks at most).



ouvert.tif



fermé.tif



When the earthing truck is open, this same runner also enables padlocked disabling of access to the closing button. In this position, racking out is possible.



Closed



Open



These features should enable an earthing truck to be correctly installed and used on conventional switchboards having only one bus-sectioning cubicle but with an unlimited number of feeder and incomer cubicles. In the case of large switchboards with several bus-sectioning cubicles (i.e. switchboards in which it is not possible to talk in terms of half-switchboards) a specific study is required to adapt the interlocks to the configuration in question.



Electrical characteristics An earthing truck exists for each cubicle width.



Un insulation voltage making capacity



3



kV U impulse power frequency kA kÂ



cmalt phase distance 230mm 24 125 50 25 65



cmalt phase distance 250mm 24 125 50 31.5 82



Schneider Electric 07897591EN REV.A0



Schneider Electric Industries SAS Address: Department MV F - 38050 Grenoble cedex 9 Tel : +33 (0)4 76 57 60 60 Fax : +33 (0)1 47 51 80 20



As standards, specifications and designs change from time to time, please ask for confirmation of the information given in this publication.



http:/www.schneiderelectric.com RCS: Nanterre B 954 503 439



Design: Technical documentation department Medium Voltage, Varces (38), France



07897591EN - REV. A0



This document has been printed on ecological paper.



04/2005



07897531EN © - Schneider Electric - All rights reserved.



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