The phase reference does not work if the current channel is not available.For example, when the circuit breaker is opened and no current flows.Although the phase angle difference between the different phases is firm,the whole system appears to be rotating when the measurement functionsare observed.4.2.2 Relationships between setting parameter Base Current, CTrated primary current and minimum pickup of a protection IEDNote that for all line protection applications the parameter Base Current (i.e. IBase settingin the IED) used by the relevant protection function, shall always be set equal to the largestrated CT primary current among all CTs involved in the protection scheme. The rated CTprimary current value is set as parameter CTPrim under the IED TRM settings.For all other protection applications (e.g. transformer protection) it is typically desirableto set IBase parameter equal to the rated current of the protected object. However this isonly recommended to do if the rated current of the protected object is within the range of40% to 120% of the selected CT rated primary current. If for any reason (e.g. highmaximum short circuit current) the rated current of the protected object is less than 40%of the rated CT primary current, it is strongly recommended to set the parameter IBase inthe IED to be equal to the largest rated CT primary current among all CTs involved in theprotection scheme and installed on the same voltage level. This will effectively make theprotection scheme less sensitive; however, such measures are necessary in order to avoidpossible problems with loss of the measurement accuracy in the IED.Regardless of the applied relationship between the IBase parameter and the rated CTprimary current, the corresponding minimum pickup of the function on the CT secondaryside must always be verified. It is strongly recommended that the minimum pickup of anyinstantaneous protection function (e.g. differential, restricted earth fault, distance,instantaneous overcurrent, etc.) shall under no circumstances be less than 4% of the usedIED CT input rating. This corresponds to 40mA secondary for main CTs with 1A ratingand to 200mA secondary for main CTs with 5A rating. This shall be individually verifiedfor all current inputs involved in the protection scheme.4.2.3 Setting of current channelsThe direction of a current depends on the connection of the CT. Unless indicatedotherwise, the main CTs are supposed to be Wye (star) connected. The IED can beconnected with its grounding point towards the object or away from the object. Thisinformation must be set in the IED via the parameter CT_WyePoint, which can be changedbetween FromObject and ToObject. Internally in the IED algorithms and IED functions,the convention of the directionality is defined as follows:Section 4 1MRK 506 334-UUS AAnalog inputs90Application manual
