Large steam turbines employ a suite of supplementary measurements not found on other types of rotating machines. These measurements are known as Turbine Supervisory Instrumentation (TSI) and are the focus of vibro'meter's new "Practical Guide for Understanding Turbine Supervisory Instrumentation".
Whether you are a rotating machinery engineer, reliability specialist, maintenance practitioner, control room operator, or instrumentation professional, understanding what you are measuring and why is always important. As the world shifts away from steam turbines to gas turbines, it is reasonable to ask whether knowledge of steam turbine instrumentation is really even necessary or will eventually become just a largely extinct bit of knowledge – like hieroglyphics or the finer points of constructing feather quill pens – of little practical use and of interest to only a curious few.
But the truth is that steam turbines will be with us for a long time to come. And therefore, measuring their conditions will remain important for a long time to come.
Even as the world relies more and more on electric motors where smaller, single-stage steam turbines were once used for mechanical drive applications, coupled with an increasing dependence on gas turbines and renewable sources for electricity generation, steam turbines – particularly large steam turbines – will remain a vital part of the mix for several reasons.
First, although the efficiency of simple-cycle gas turbine plants may outperform similar thermal plants using only steam turbine generators, they still waste considerable energy up the exhaust stack – energy that can be used to boil water and generate additional power through a steam turbine as part of combined-cycle operation. Compare the efficiency of today’s best simple-cycle gas turbine plants at less than 45% with the 55 to 60% achievable in combined-cycle plants by simply adding a steam turbine and a Heat Recovery Steam Generator (HRSG). It really is like getting a free lunch: no additional fuel yet up to 50% more electricity production.
Second, combined-cycle plants are not the only place where steam turbines will continue to see application. Nuclear plants will continue to employ gargantuan steam turbine generators – some capable of producing the same power output in a single machine train as would require more than 640 average-sized wind turbines, all while consuming 500 times less real estate. And pure thermal plants using gas, coal, or oil will likewise continue to see use to help meet peak demand even as renewables such as hydro, wind, and geothermal form a larger percentage of capacity and cleaner sources of generation from gas turbines become the go-to sources for meeting baseload demand. In fact, as thermal plants become more and more relied upon for peak demand rather than base demand, the mechanical stresses on machines that were originally intended for continuous, baseload operation but are now running up and down multiple times per week becomes acute. The instrumentation on these large steam turbine generator trains becomes more important than ever because cyclic mechanical and thermal stresses are being incurred for which the machines were never originally intended.
A typical steam turbine generator train in a thermal power plant. These machines range in size from less than 100MW to as much as 1200MW. The steam turbine cases in this photo are blue, the piping that routes the steam from the HP/IP turbine sections to the LP turbine section is silver, and the generator/exciter is yellow. Originally designed for a continuous baseload operation, many thermal plants today are used to supplement baseload during periods of peak demand, placing additional wear and tear on machines that were not intended to run up and down so frequently. Comprehensive monitoring has thus become more critical – not less – on such machines.
Because these steam turbines are so large, their casings and rotors expand thermally at different rates, entailing special measurements to ensure rotor-to-casing rubs do not occur. In addition, the massive rotors can sag due to gravity if allowed to come to a complete standstill during times when the turbines are not operating. This entails another set of important measurements. And, because both the casings and the rotors of these machines can undergo substantial vibration, the normal assumptions that only shaft-relative vibration measurements are required may not apply. Can you name all of these measurements, the variations in how they are made, and why they are made? You’ll find the answers in our comprehensive new TSI - Practical Guide.