SOLAR INVERTERS
SOLAR INVERTERS
The Golmud PV plant uses 5756 DC combiner boxes. The fault ratio of DC combiner boxes is about 18 %, and the fault ratio caused by fuse blown is around 21 %. DC combiner boxes have the following major defects: fuse blown( due to poor fuse quality or extremely small rated current of fuses), abnormal communication
Inverter Failure Rate in 2015
( including the damage of the communications collection module in the combiner box), wiring terminals overheated( caused by loose terminals and high resistance), circuit breaker faults( such as heating and tripping), branch faults( such as grounding faults and overcurrent), and DC arcing.
Type |
Product Name |
Number of Installed Inverters |
Number of Faults |
Failure Rate(%) |
|
Brand A |
70 |
2 |
2.86 |
|
Brand B |
58 |
2 |
3.45 |
|
Brand C |
84 |
10 |
11.90 |
|
Brand D |
38 |
7 |
18.42 |
Centralized type |
Brand E
Brand F
Brand G
|
118
10
60
|
32
3
19
|
27.12
30
31.67
|
|
Brand H |
58 |
22 |
37.93 |
|
Brand I |
20 |
10 |
50 |
|
Brand J |
58 |
32 |
55.17 |
|
Brand K |
128 |
185 |
144.53 |
String Type |
5372 |
9 |
0.16 % |
Shi Tianze said that the Golmud 590 MW PV plant contains 702 central inverters and 5372 string inverters. The comparison analysis shows that the inverter faults locate in fan damage, fuse blown, module overtemperature, and circuit breaker tripping.
Among the central inverters of 11 brands, the highest fault ratio reaches 144.53 %, while the lowest is 2.86 %. The fault ratio of string inverters, however, is only 0.16 %. Judging from the energy yield and availability, which solution is more competitive is obvious. Because there is no DC combiner box in the string inverter solution, each PV string directly connects to the inverter on the DC side. The fuse-free design in addition to short and few DC power cables ensures proactive security protection and suppresses arcing effectively. On the AC side, short-circuit currents are from the power grid and are very high( 10 – 20 kVA). Once an exception occurs, the circuit breaker in the AC combiner box trips immediately to minimize the harm.
Xu Hailiang, vice president of TÜV SÜD Greater China pointed out that TÜV SÜD evaluates the overall quality of PV plant devices based on the device status indicators such as the fault ratio of key devices, fault duration, and availability. TÜV SÜD evaluated the annual failure rate, availability, and array yield of inverters for Golmud 220 MW PV plant before long.
Xu Hailiang Said That,“ For fairness and impartiality, we chose five different PV plants each with several mainstream inverters, and we got the comparison results of the three indicators. The annual failure rates of string inverters are all below 0.4 %, and the lowest one is 0.189 %. The availability of all the string inverters is above 99.99 %.” The data answers why string inverters are widely used in large-scale ground-mounted PV plants for recent years.
www. EQMagPro. com EQ December 2016 65