This time of year many plants are starting up their chillers. Common testing for electric motors includes vibration analysis for mechanical components and insulation resistance (Meg-Ohm) testing for winding insulation.
July 6, 2010
by Steve Gahbauer
Plumbing for a chiller system at a manufacturing facility.
This time of year many plants are starting up their chillers. Common testing for electric motors includes vibration analysis for mechanical components and insulation resistance (Meg-Ohm) testing for winding insulation. However, vibration analysis may miss critical findings due to insulation resistance and the location of bearings and mechanical components.
High-voltage tests are frowned upon by a number of hermetic chiller manufacturers, while improper information arising from the interpretation of results and understanding test standards create additional challenges.
Modern technologies that combine electrical signature analysis (ESA) and motor circuit analysis (MCA) using the methodology presented in IEEE Std 1415-2006 verifies the condition of a chiller motor.
ESA uses the voltage and current information to evaluate the power supply, dynamic condition of the motor’s electrical and mechanical components, and the general condition of the driven equipment. The technology detects broken rotor bars and bearing issues with a high degree of accuracy and also trends conditions for time to failure estimation (TTFE) as part of a predictive maintenance program.
Moisture and acids in refrigerants and lubricating oils, and coil movement during start-up wear away the inter-turn and ground wall insulation systems within the machines.
The MCA method avoids the issue of high voltage testing, both for winding shorts and insulation-to-ground fault aggravation, through the use of a series of low voltage techniques that can not only detect faults but also trend degradation and contaminant impact on motor windings.
Perform testing while the equipment is de-energized, which allows the evaluation to be done before start-up with each cooling season. While the IEEE Std 43-2000 calls for 5 Meg-Ohms in machines under 1,000 volts and 100 Meg-Ohms in machines over 1,000 volts, hermetic machines typically have much lower readings before start-up.
Source: Motor Diagnostics and Motor Health News, with permission.