A real time data management web-based software-platform for PV plant monitoring called Apis was tested for fault detection and diagnosis of large scale grid-connected photovoltaic systems. This method was compared with Metrum system which is also another web based monitoring system used in grid connected PV systems. The objective of testing and comparisons were to observe the Apis system performance in large scale PV systems particularly for fault detection, and to identify which of the two systems could give more information to easily identify type of fault and point out the fault location in PV plants.
The experiment were carried out in the selected two different arrays that have a capacity of 18.4kW and 17.6 kW with four string inverters each, to test three cases at Glava energy center solar park, Sweden. The first demonstrates the response of the systems when the wiring loose or cable disconnection fault occurs in the plant. The second demonstrates the output of the inverters when partial shading is gradually increased and the third demonstrates the output when the fault at components (i.e. at inverter, fuse and circuit breaker) is applied. Both systems collect data from inverters. However, in Apis system, data from individual inverters of the plant could be collected separately in both AC and DC sides while Metrum system was measuring the total output of the whole inverters in the plant.
During the string disconnection, the Apis monitoring system showed a power drop to zero from the defected strings making it possible to identify them. In the same way during the inverters’ fault the power output of the failed inverter was dropped to zero. However, the normal strings and inverters were still working properly. Meanwhile the Metrum system only displayed a reduced power output which doesn’t directly identify the problem and requires manual inspection. In the case of partial shading there was a persistent difference occurred between the defected string and normal one but it did not dropped to zero at all.
Apis system is able to differentiate and locate the faults by comparing input and output results of different inverters within the plant, unlike Metrum system which measures the total output of the plant. Nevertheless, Apis system still has less possibility to determine the type of fault further than estimation.