Apparatus for testing the shaft/bearing insulation of a turbo-machine

摘要

Apparatus provided for testing the shaft/bearing insulation characteristic of a rotary machine, e.g., a turbo-machine, wherein the shaft is normally earthed by means of an earthing brush on the shaft and connected to ground. A first circuit arrangement is provided for breaking the shaft-earthing connection, a second circuit arrangement is provided for applying an increasing test voltage between the shaft bearing which is grounded and the earthing brush while the shaft-earthing connection remains broken, this being in the form of a progressively charged capacitor connected between the shaft bearing and earthing brush, and a third circuit arrangement is provided for measuring the change in voltage across the capacitor resulting from a breakdown in the insulation between the shaft and its bearing during the testing operation. The testing operation is performed periodically and a test cycle is terminated as soon as the test voltage reaches a predetermined maximum value, or there is a breakdown in the insulation between the shaft and its bearing whichever occurs first.