Status: INVALID , NT_870 but reading values

Status: INVALID , NT_870 but reading values

Hi all
I have one substation with SIPROTEC4 and thiese SIPROTECS are connected to AK-1703 and I am reading values from AK-1703 with AK-driver. All the variables are ok without currents, they have status : INVALID,COT0,COT1,NT_870 but i can read the values and they are changing all the time(and this is not for all devices, most of them are ok ), so the are not like usual INVALID status 0 or last valid value.
What coud be the reason for this?
Best regards!
Angel Markov

This is a migrated post! Originally posted on 01.04.2014 by user geleto021. Please be aware that information can be outdated.