Obvius A89DC-08 - Manual (Page 13)

Alarm configuration
The A89DC-08 provides features to detect alarm conditions related to Solar PV applications. For example, in a PV array,
the system may have 10 pv panels wired in series per string, and 8 strings that run back to a combiner box. The A89DC-08
can be installed at the combiner box to monitor the current levels on all 8 strings at the same time. If a panel in one of the
strings fails, the A89DC-08 can detect the reduction in current from the failed string and set an alarm flag to indicate the
problem.
To configure the A89DC-08 to detect this fault condition, several options must be configured. These options include the
following:
● Deviation threshold.
● Minimum current threshold.
● Minimum deviation time for alarm.
The first item to do is calculate what level you need to detect. If you have 10 panels in series and one fails, there should be a
10% reduction in power production. The deviation threshold should be set less than but close to 10%. A good starting
point will be 7%, and then adjust the set point after the system has some working data to review.
The second item is the minimum current threshold. In a solar PV system, the total current produced varies throughout the
day. At sunrise and sunset, the amount of power produced is minimal. The minimum level at which the A89DC-08 can
detect current is 0.5A, so the differences between channels will be below the ability of the A89DC-08 to detect. To prevent
this, the minimum current threshold option sets the point at which current levels must reach in order to enable the alarm
feature. If the minimum current threshold is set to 4 amps, the alarm feature will become operational when the average
current per channel level exceeds 4 amps. A good value to set for this option is the maximum current expected, less 10%.
This will allow the average to exceed the minimum current threshold even if one channel fails completely.
The third feature that you must set is the minimum deviation time for alarm. This feature allows you to select the period of
time which the alarm must be in effect before it is reported. This will help suppress transient alarms when brief problems
occur such as shadows from a truck or plane are present on one or more panels in a single string.
Page 13 A89DC-08 – DC Current Monitor