Issue
We have MiCOM P123 protection relays and found a issue in fault record extraction over Modbus.

If accessed via Modbus RTU RS485, the relay server houses this data in 25 contiguous addresses 3700h-3718h. in this case, the data structure used is a circular list, where the most recent fault is stored in the +1 address of the last one inserted, that is, as if it were a queue. Therefore, the last fault will have a variable memory address. This forces us –in principle- to bring all the faults to be able to analyze them and locate the last one, which will finally be the one we will keep, discarding the others.

If accessed via the keypad on the front of the relay, the last fault –or most recent- is always in the same position, as if it were a battery. This will always be at the top of the stack, and you only have to access it to locate it. As you go down the pile, you find the oldest faults.

The data structure to manage the relay trips, addresses (3700h-3718h), implies an additional complexity that is to bring all the faults to be able to find the newest one.
So far the problem. Now, I am getting in touch to see if there is a more recent failure rate, such that, for example, starting from the base address 3700h + index, I can retrieve the last shot in a single question..

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Product Line
MiCOM P12x, P12y

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Environment
Normal.

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Solution
Latest non-acknowledged fault record can be retrieved from Address 3E00h. Each new record have to be either retrieved or manually acknowledged to keep the register abreast with latest record.

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*Warning:  Installation, maintenance, up-gradation, down-gradation of MiCOM device should only be performed by qualified, competent personnel that have appropriate training and experience. Failure to follow the instructions / warnings in the Installation / Operation Guide can result in unwanted disruption to the power system, permanent damage to the device, severe injury or death.*

Released for: Schneider Electric Singapore