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Summary of The Role of Machinery Protection Systems



Summary of The Role of Machinery Protection Systems from Uptime Magazine April 6th to May 31st Edition, 2018

The article presents a case study that illustrates the importance of installing machinery protection systems consisting of vibration monitoring instrumentation in turbo machinery and the role they play when performing diagnostic testing in such environments. The problem in this article relates to a cogeneration generation plant. Although most of the turbo machinery comes with a set of protection systems already installed, this pre-existing protection system has to be incorporated into a routine program designed to analyze vibrations in order for technicians to identify specific types of faults that may occur.

In 2008, the technicians in one of the cogeneration plants decided to introduce a vibration analysis program that would help them monitor its condition. Initially, the focus was given to support equipment when analyzing the required instrumentation for performing monthly vibration analysis. After some considerations, however, it was decided that route-based analysis tools would be used to collect vibration data from the plant’s generator assembly and gas turbine since this would not alter in any way the monthly program cost. In the end, it emerged that the technicians had made a very important decision given that they were able to determine different fault types and monitor the condition of the machine with greater accuracy by analyzing the data collected.Summary of The Role of Machinery Protection Systems

The machine train being investigated consisted of a gas turbine, model GE Frame 7EA, and had three oil film bearings. It was directly connected to a generator operating at 60 Hz. Its protection system combined a gas turbine control and transducer sensor systems, which were used to collect data about the turbine’s thrust on a routine basis using proximity probes. The initial data collected did not indicate any significant changes. Consequently, no major repair items were isolated. A few months later, a major inspection was done during the normal preventative maintenance schedule of the machine. During this exercise, all bearing components in addition to the rotors of the machine were removed for inspection. Afterward, reassembly was carried out and the machine was put back into its normal operation. Soon, the vibration analysis team discovered that during the starting of the machine, a major difference had occurred in the vibration amplitude of the bearings of turbine number two. Surprisingly, the protection system of the machine did not give any alert.

By designing their own routine vibration analysis program that incorporated the machine’s preexisting protection system, the technicians could detect any vibration levels that exceeded 2.5 mils peak-peak. The case study presented in this article shows that machinery protection systems form an important component in today’s turbo machinery. However, it emerged that they cannot be used alone to cater for predictive maintenance of a machine. Competent technicians are needed to collect and analyze vibration data if faults are to be detected before they become detrimental to the health of a machine.