Preventing downtime
September 1st 2006

Ken West, regional marketing manager Industrial Tools, Fluke (UK) explains the the use of thermal imagers in predictive maintenance.

New on the market are cost effective thermal imagers specifically aimed at maintenance engineers for troubleshooting in a wide range of applications. The new ranges of thermal imagers will quickly provide a return on investment by preventing downtime, by avoiding catastrophic equipment failures and by reducing overall maintenance costs when used as part of a comprehensive predictive maintenance programme. Thermal imagers are designed to be very easy-to-use, however in order to maximise their potential, training can open up a wide range of areas in which this technology can be put to good use to predict potential problems

Unusually high temperatures may highlight potential electrical problems but they will probably not determine the cause of a failing component. Inspection procedures should recognise this and identify the next stages in troubleshooting a particular problem e.g. the use of power quality tools, clamp meters and digital multimeters (DMMs).

Thermal images are also an easy way to identify apparent temperature differences in three-phase electrical circuits, compared to their normal operating conditions. By inspecting the thermal gradients of all three phases side-by-side, electricians can quickly spot performance anomalies on individual legs due to unbalance or overloading. Even a small voltage unbalance can cause connections to deteriorate, reducing the amount of voltage supplied. A severe unbalance can blow a fuse, reducing operations down to a single phase. Overloading or unbalance should then be investigated using other types of measuring instruments such as a clamp meter or power quality analyser.

3. Motors and control panels

A thermal imager is also good for spot checks to see if motors and associated panels and controls are operating too hot.

A motor's heat signature will tell a lot about its quality and condition. If a motor is overheating, the windings will rapidly deteriorate. When a motor bearing fails, the motor heats up and lubrication begins to break down. Eventually the temperature sensor cuts out and stops the motor.

Worst case, the shaft binds up, the rotor locks up and the motor fails completely.

There are three primary causes for abnormal thermal patterns in supply panels:

Most are the result of a high-resistance contact surface, either a connection or a switch contact.

Load imbalances, whether normal or out of specification, appear equally warm throughout the phase or part of the circuit that is undersized/overloaded. Harmonic imbalances create a similar pattern.

Failed components typically look cooler than similar, normally functioning ones.

A blown fuse can result in a 'singlephase' condition and, possibly, costly damage to the motor.

4. Transformers A thermal imager can be used to look at external connections, cooling tubes and cooling fans and pumps as well as the surfaces of critical transformers. Overheating in a connection indicates it is loose or dirty, and unbalanced or overloaded phases can be identified. On oil-cooled transformers, if one or more tubes are comparatively cool, oil flow is being restricted and the root cause of the problem needs to be determined. A fan or pump that is not functioning at all will be cold.

Inspection routing and reporting The latest thermal imagers allow an inspection route to be downloaded from a PC, with clear step-by-step, on-camera instructions prompting the user through the series of locations to be scanned. They will allow the images from the previous inspection to be downloaded, so that previous and current images can be compared side-by-side at the point of capture. This will help to determine whether a hot spot is unusual or not, and also help to verify that repairs have been successful.

The new, captured data can then be uploaded and stored on a computer and compared with other measurements over time, with the software enabling detailed automated reporting.

Predictive maintenance Predictive maintenance is a means of improving productivity, product quality and overall effectiveness of manufacturing and production plants. It is a condition-driven preventative maintenance programme.

Instead of relying on industrial or in-plant average-life statistics (i.e. mean-time-tofailure) to schedule maintenance activities, predictive maintenance uses direct monitoring of the operating condition, efficiency, heat distribution and other indicators to determine the actual meantime- to-failure or loss of efficiency that would be detrimental to plant operations for all critical systems in the plant or facility.

Thermal imaging is one of the costeffective tools, alongside vibration monitoring, tribology and other nondestructive testing methods, that together can provide a comprehensive predictive maintenance management programme.

The benefits of such a programme include elimination of unscheduled downtime caused by equipment or system failures, increased maintenance manpower utilisation, increased production capacity, and reduction of maintenance costs.

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