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Sepam 80 Trip Circuit Supervision - can the Sepam MES120 support AC (alternating current) voltages for the logic inputs?

In some substations, the control voltage used for the Circuit Breaker Trip Coil is an AC voltage.  The question has been raised as to whether or not AC voltages can be connected directly to the logic inputs on the Sepam 80 MES120 card.

In fact, the MES120 cards are designed to support DC voltages only.  So, the Trip Circuit Supervision function on Sepam 80 will not work if the Trip Coil control voltage is an AC voltage.

The best solution would be to use another 3rd-party TCS relay to achieve this function.  The ARTECHE range of relays may have a TCS relay which supports AC voltages.

If the customer wishes to monitor the status of the 3rd-party TCS function through the Sepam, then a DC contact from the 3rd-party relay could be wired to a Logic Input on the Sepam, and an assignment made in the SFT2841 Matrix to give an Alarm or Event in case of a TCS fault.

At a small number of sites, a "recitifier circuit" consisting of diodes, resistors, and capacitors was installed to effectively convert the AC voltage of the trip circuit to a DC voltage.  The converted DC voltage was then wired to the Sepam logic inputs.  However, we do not recommend this as the components may eventually fail, which would make the TCS function unreliable.  It is best to use a TCS relay which supports AC control voltages.


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