The most common fault found with modern transformerless inverters is earth leakage.
Transformerless inverters take DC power from the turbine, boost it to the required voltage and directly inject it into the grid. It is essential that the DC side is isolated from earth because usually the neutral side of the grid is earthed. The inverter has circuits which work a bit like an RCD or ELCB to detect earth leakage, and also initially to measure “RISO” (Resistance of Isolation).
These circuits will detect leakage via other inverters connected to the same DC supply. For this reason, if you use two or more inverters on the same DC from a turbine, you need to isolate the grid via a transformer on the second and subsequent inverters. So for example, if you have a 15kw turbine on a single phase supply, you would need 3 x 5kw inverters and 2 x isolation transformers. You would disable RISO detection on the two inverters that are isolated
Sometimes, the inverter will fail to start because of a RISO error. The inverter may report a different fault (e.g. IGBT saturation) but the root cause is often RISO. RISO seldom arises in a solar PV environment because the DC side is isolated from the frames. However, water ingress into turbine windings, poor quality underground cables, or exposed connections can all cause tiny earth leakage which will cause failure.
Please read Aurora RISO earth leakage information for further information on how to resolve this problem when it arises.