A Hybrid Conditions-Dependent Outage Model of a Transformer in Reliability Evaluation

Constant failure rate model used in the conventional reliability assessment of power systems cannot reflect the impacts of the various operating conditions such as transformer loading, ambient temperature, weather on component reliability. A hybrid conditions-dependent outage model (CDOM) of a transformer is proposed in this paper to include those impacts. The CDOM is the combination of three failure models: the aging failures due to the loss of mechanical strength of conductor insulation; the random failures considering weather conditions, and the outages caused by the direct trips of the overload protections. The component reliability using the proposed model has been tested under different operating conditions. The model is also applied in power system operational reliability assessment. The reliability indices using CDOM are compared with that using the condition-independent outage model. The reliability indices using the CDOMs of transformers can provide useful information for operators to understand possible system and component failure risk in real-time operation and to make important alleviation decisions.