Item:

• A hydro-electric generator, under test

Problem:

• During pre-delivery balancing and testing, a balance-weight retaining nut fell into the air gap, damaging both the rotor and stator
• It was uncertain as to whether this occurred whilst the generator was insured

Objective:

• To determine the probability that the damage occurred during the period of insurance cover, and thus establish the insurer’s liability

Approach:

• Review of witness statements, damage reports and electrical test results
• Construction of an event tree, with probabilities assigned to all branches

Conclusions:

• Demonstrated, without doubt, that the nut which caused the damage had not come loose, as suggested by the plant owner, but had been inadvertently left in the machine during balancing trials
• Probability of damage occurring during the period of insurance cover was demonstrated to be less than 2%

Benefits:

• Insurer’s liability limited to no more than 2% of the total loss