A 250Kva three phase 415vgenerator is installed in a small hotel complex and offers an alternative supply to the power company during peak tariff periods.
The generator neutral point is grounded via the power company earth, which is contrary to the requirement that the gen-set should have its own independent electrode with an earth electrode resistance not exceeding 10ohms. The Power Company earth is TN-C-S However, the installation is protected with rcds. These operate arbitrarily on change-over from mains to genny. The change over is automatic and on load but there is a small delay. I thought that perhaps this would lead to voltage transients that may cause nuisance tripping of the rcds. The site electrician grounded the frame of the gen-set to a temporary earth electrode. This seems to have solved the problem. I would appreciate your comments on the possible causes that tripped the rcds.


lyle dunn