Selection of Predictive Maintenance Techniques - Continued

DOE-STD-1052-93

Radio Frequency Monitoring - a technique used to detect, internal

arcing of an electrical generator - Generator arcing is caused by

component failures such as stator winding insulation failure,

conductor fatigue failure, or voltage breakdown because of reduced

clearances between components that are at different voltages. The

arcs cause short-duration current pulses containing measurable radio

frequency signal components.

In-leakage Detection - a technique using helium detectors to locate

pathways for the ingress of contaminants into steam, condensate,

and feedwater systems - This technique has proven to be effective

in detecting air in-leakage into condensers, valves, and flanges.

Insulation Resistance (Meggering) - a technique used to measure

leakage currents in electrical insulation - This technique is used in

monitoring degradation of electrical insulation of motors,

generators, and cables.

Polarization Index - a technique used to measure the mechanical

integrity of insulation - This technique is used to monitor

degradation of electrical systems by measuring the ratio between

one-minute and 10-minute readings for insulation resistances.

Electric Circuit Monitoring - a technique used to determine the

condition of a circuit and aid in fault location - This technique

performs basic measurements such as inductance, capacitance, and

resistance, and measures distance through time domain

reflectometry. Electric circuit monitoring is effective in determining

the condition of electrical connections, contacts, terminations,

moisture damage, and damaged insulation and its location.

Plant Performance Monitoring - in addition to the predictive

maintenance techniques already described, various other methods

may be used as a predictive approach to monitoring plant

performance, including the following:

1) Eddy current testing is commonly used to monitor heat

exchanger tube wall thickness.

2) Temperature differential is used as a means of monitoring heat

exchanger performance.