Predictive maintenance made easy
For those organisations where failure of critical power/plant results in significant downtime costs, continuous predictive maintenance can no longer be regarded as a luxury option, but should be seen as a necessity for critical risk management.
For example, in a steel or aluminium manufacturing plant, the typical cost of production downtime may be as high as £100,000 per day, whilst in a building such as a data centre this could be as high as several million.
Of course, many buildings have a maintenance department to deal with problems like these, but often, because of time and resource constraints, the maintenance team becomes reactive, fire fighting problems as they occur, with no predictive maintenance systems, little preventive maintenance, and often with no maintenance strategy at all.
The more enlightened maintenance departments are using the latest condition monitoring and predictive maintenance systems, including bearing vibration monitoring, acoustic emissions monitoring and thermography to protect plant and machines.
Risk assessments should be carried out regularly to see what effect breakdowns would have on critical, bottleneck machines and equipment. The severity and likelihood of breakdowns on particular machines are assessed and given a corresponding risk value.
Of course, companies can protect their plant without using condition monitoring or predictive maintenance systems, for example, by holding more stock of a particular component such as a gearbox, bearing, coupling or shaft, and running to failure. However, as well as the obvious increase in stock holding costs, the company also runs the risk of the stock deteriorating or becoming obsolete over time, and the costs associated with an unplanned outage.
A power critical business is one which, in the event of a major power failure, will incur significant downtime costs, or a compromise in safety. Examples include computer data centres, large scale manufacturing or chemical processing plants, or establishments serving the financial services sector, telecommunications, defence or Government.
When it comes to electrical failure and power outages, the most common cause is bad connections. These cannot be detected via metering or load measurements, or through measurement of power quality. However, the thermal increase can be detected using thermally sensitive devices.
Thus, if it is mission critical and within the enclosure, thermal inspection should be considered. Over the last decade, the accepted preventative method of reducing the risk of key electrical switchgear failure has been periodic thermal imaging, but it is not ideal.
Thermal imaging, also known as thermography or thermographic scanning, is a non-contact technique used in an ever-widening range of areas, including predictive maintenance, condition monitoring, problem diagnostics and research and development. All objects above absolute zero emit infra-red energy and we exploit this using long wave IR imaging systems to identify faults which if left unchecked would often result in costly repercussions.
Thermal imaging photography finds many uses. Power line maintenance technicians locate overheating joints and parts, a tell-tale sign of their failure, to eliminate potential hazards. And where thermal insulation becomes faulty, building construction technicians can see heat leaks to improve the efficiencies of cooling or heating air conditioning.
Traditionally, thermal imaging has been carried out using expensive thermal imaging cameras, which are easily damaged. Though the appearance and operation of a modern thermographic camera is often similar to a camcorder, thermographic cameras are much more expensive than their visible-spectrum counterparts, and higher-end models are often export-restricted. Their resolution is considerably lower than of optical cameras, mostly 160×120 or 320×240 pixels, up to 640×512 for the most expensive models. Images can be hard to interpret accurately even with experience and accurate temperature measurements are very hard to make. Most cameras have +/-2% or poorer accuracy (not as accurate as contact measurement methods) and only surface areas may be measured.
Using this method, inspection is carried out externally to the switchgear enclosure; and, as no infra-red device can penetrate solid objects, only components or terminations immediately adjacent to the external panel can be inspected. These components cause the panel surface to heat via radiation and only this image is seen by the infra-red camera. This method requires the operator to rely on a correction factor to correlate the results. Thermal windows improve the situation, but still require direct line of sight to the target, anything hidden by internal structures or other components cannot be accurately inspected. They can also add significant cost.
Like thermal imaging, the ExerTherm from QHi uses non-contact infrared to measure the temperature of the target, but that’s where the similarity ends.
ExerTherm uses patented, small, plastic bodied, non-contact infra-red (IR) sensors, which require no external power. This enables them to provide lifetime warranty and lifetime calibration, avoiding the need to remove sensors for re-calibration at regular intervals (necessary for any ISO organisation). The sensors, being non-contact devices, are not affected by high vibration levels, which contributes to them having an MTBF of in excess of 1000 years. The sensors are placed inside the enclosure to thermally monitor any component directly in any location within the panel. ExerTherm is a system specifically designed to provide continuous thermal monitoring of mission critical electrical equipment within enclosures, and to detect and identify the exact location of the problem at an early stage of development via on-going trend analysis and alarms.
While traditional thermal imaging inspections are periodic, generally on just one or two days per year, Exertherm is a continuous monitoring system, meaning that it is more effective at detecting faults before failure.
The Exertherm system also has two alarm levels (warning and alarm), which trigger in the event the temperature of any monitored component exceeds pre-set, user-definable limits. These can be integrated into a BMS or other host system, send SMS messages, or simply provide a remote warning.
ExerTherm can also be used to thermally monitor other critical plant. An increase in heat is a common symptom of malfunction across diverse cross section of plant, including bearings, motors, gearboxes and pumps. Thus, virtually all key plant can be continuously thermally monitored on the same system, using non-contact IR, contact thermocouples, or air temperature sensors.
To monitor small cable terminations, ExerTherm utilises patented cable sensors which simply strap onto the cable, adjacent to the termination to be monitored.
Exertherm IR sensors can be placed inside electrical enclosures to monitor key problem areas such as circuit breakers (ACB, MCB, MCCB) and critical busbar connections. Cable sensors are utilised to monitor critical cable terminations. IR sensors utilise Delta T (rise above ambient) measurement for electrical monitoring, but are also available in a wide variety of temperature ranges and stainless steel housings (including an optional air purge kit for use in harsh environments) for monitoring mechanical assets in industrial environments.
Each sensor connects back to an 8 channel data acquisition card, which conditions and linearises the input signal, and converts it to the desired output protocol. Within each panel the data cards are interconnected, providing a single RS485 cable connection to the host system outstation.
As well as being designed into new installations, ExerTherm can also be retro-fitted or subsequently expanded, by just adding to the existing system. Systems can be from as low as 16 sensing points or up to several thousand.
Although ExerTherm can also be installed as a stand alone system where required, it can also very easily interface with existing BMS and SCADA systems. This facilitates the thermal monitoring of all critical equipment ,not just in one building, but for any location via WAN or Intranet/Wireless systems.
Over the life of the switchgear, ExerTherm will provide a considerable saving against the total cost of periodic thermal imaging inspections. In addition, shutdowns for conventional intrusive maintenance can often be extended, providing further significant savings. Generally, payback is achieved within one to three years.
With the advent of Internet-based monitoring, the level of remote monitoring will increase as an increasing number of buildings are designed with LAN infrastructure built in. The advent of Internet access from mobile phones using WAP technology and the third-generation technologies mean that a building’s operations could be monitored from anywhere and at any time. Contractors will be able to stay in touch with their customers’ building services system no matter where they are.