In a recent ME Plant & Maintenance article, Wireless Vibration Monitoring –improves reliability and enhances safety (pdf), a rotating machinery engineer describes how his power station used a wireless vibration transmitter to avoid shutting down a turbine producing 200MW of electricity.
Online vibration monitoring, running continuously, coupled with analysis tools helps power station personnel to identify changes, however slight, to understand when to schedule maintenance, or predict when a failure may occur. It:
…can help to predict when a failure will occur and alert maintenance as to the health status of the equipment. Early warning of impending failures can prevent process shutdowns that lead to lost production.
The engineer, Travis Culham, noted that ideally, all rotating machinery should have continuous vibration monitoring permanently installed, but this practice would be cost prohibitive. As a result, critical assets have permanent monitoring.
The issue driving the need for a wireless vibration transmitter was a starter motor for a turbine generator. This motor was not already monitored, due to:
…no available cable infrastructure in place… not possible to cost-effectively add continuous vibration monitoring. Instead, manual readings were taken using a handheld collector and then downloaded for analysis.
An issue was detected with the motor through this manual analysis. However, the generating capacity was needed and a shutdown of the unit would take around 36 hours for the motor overhaul. This downtime was estimated to cost £50,000 in lost revenue.
If the unit was to continue to run, it was critical to continuously monitor this motor to be able to take action the generator offline if the motor were about to fail. Safety was the top concern:
A CSI 9420 wireless vibration transmitter provided a way to temporarily monitor the motor. The power station had an existing IEC 62591 WirelessHART network that was being used to collect valve diagnostics and send them back to the station’s Ovation control system. The spot where this wireless transmitter would be mounted posed challenges, since it was:
…cannot allow personnel to enter areas like this where a potential safety situation may arise. The question therefore was how could we monitor this motor and assets like it in critical situations?
…located within a gas turbine auxiliary compartment, which effectively acts like a faraday cage [hyperlink added]. The placement presents a tough environment for wireless and it was thought that a repeater transmitter would be needed to bridge back to the network. However, having installed the device during a period of downtime, it instantly joined the network and transmitted data without any problems. The smart wireless network is extremely robust and the performance in this application exceeded our expectations.
By being able to add this continuous monitoring, it provided time to schedule the motor repair when the 200MW capacity would not be required due to market conditions.
Information from the wireless transmitter:
…was transmitted from the motor, via a wireless gateway, directly into our existing Ovation™ expert distributed control system data historian. This enabled us to monitor vibration during operation, and by trending the data we were able to determine when the motor was going to fail. The wireless transmitter provided continuous visibility to the health of the motor enabling it to be run with confidence.
…encouraged us to use the wireless vibration transmitter as a mobile device to monitor various types of rotating equipment, where and when it is required. Generally the equipment we are monitoring with the wireless transmitter is deemed less critical to the process. The assets can often be found in hard-to-reach locations and do not currently have permanent health monitoring in place, but the transmitter provides us with the opportunity to perform very accurate continuous monitoring of such assets.
This is a great story of applying technology to improve safety and overall process uptime.