Application - ABB RELION REX640 Technical Manual

Section 10
Power quality measurement functions
10.1.6
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Figure 830: The 10-minute interval with time synchronization and free running 3
seconds
The 10-minute mean value is shown in the monitored data until the next 10-minute
mean value has been cumulated. Another 10-minute calculation might be started when
time synchronization is used to change the protection relay's internal clock. The first
calculation continues for 10 minutes and is then seen in the monitored data with a time
stamp. An event is sent every time a 10-minute value calculation is ready in the
monitored data.
See the Time synchronization chapter in this document.
When the protection relay is powered on, the shown value is zero until the first 10-
minute mean value has been cumulated. During this time, the 10-minute output
quality is marked questionable in the IEC 61850 data.
When the settings Reference Cur Sel or Demand current are changed, older data is not
cleared. Although older data is calculated based on different setting values, those can
still be used as they are used to calculate mean values. The influence might be seen in
mean values. These are considered as minor adjustments to the reference current,
similar to varying fundamental current.
Changing setting Sliding interval has influence on the seen mean values. Sliding
values change slowly towards the input value during the time interval. When mean
values have not been calculated for a full interval, quality is marked questionable in
the IEC 61850 data. Questionable quality is also indicated for a full interval if the
protection relay is reset.

Application

Typically, the measured short-time 3-second mean values are used with a suitable
logic to give alarms. If a more stabilized value is needed, a 1-minute or 5-minute mean
value should be selected.
One example of using short-time mean values is to compare the level of THD or TDD
and some harmonics, for example, 5
limit can be combined with MAX3R and MAPGAPC can be used to test if the settable
th th
and 7 . The values to be compared to the same
1MRS759142 C
REX640
Technical Manual