Not long after the ITS system arrival in 1982, GE offered its first fully-computerized control system.. Continuing the theme, it was called Speedtronic™ Mark IV. See Fig. 16-1 below.
The Mark IV system lasted most of the decade of the eighties. It included a Triple Modular Redundant (TMR) concept that was a significant departure from the Mark I and Mark II systems of the 1970s. Mark IV offered three main controllers that “voted” when assessing critical operations. In many decisions, 2/3 voting was required to trip the gas turbine and shut it down. In earlier Mark I and Mark II, most systems were “simplex” in concept; others were redundant but were “either/or” in operation. For instance, if one of the overspeed sensors measured excessive speed on a Mark II, the turbine would shutdown.
In Mark IV, all of the controllers (known then as microprocessors) had to be “healthy” to allow the turbine to start initially. However, the turbine could operate on just one controller, if necessary. The three controllers were called “R”, “S” & “T”. This was written <RST> when a function involved all three processors. Also, so-called Communicator <C> was required; it permitted communications between <RST>. If a function applied to only one controller, the R processor for instance, it might be just written <R>.
Note: Many engineers (I being one of them), and some clients too, thought the TMR system was “overkill.” particularly for peaking power plants. This is because the turbines were only rarely operated (emergency and peak demand situations) and that failures more frequently occurred with field sensors and wiring rather than with one of the three computers.
Fig. 16-2 above depicts an engineer working at a factory test panel. Unlike the Mark I which was 36 inches wide, the Mark IV panel was 54 inches across with double (French) doors. This permitted better and safer access to the processors and other circuits inside the panel.
Note: If the Occupation Safety and Health Administration (OSHA) existed in the 1960s – 1970s, they would have likely closed down the production of GE’s 36-inch panels as unsafe for electricians, technicians and turbine operators (in my opinion). There was insufficient room to work safely inside this “phone booth” of a control panel.
Mark V became the Speedtronic™ control system of the 1990s. There was an operator interface system called <I> on turbines at the beginning of the decade. It was a I-DOS based system and utilized a desktop PC to display operating conditions and significant data. Competitors of GE, particularly those in the upgrade business on GE turbines, were offering Microsoft Windows based interfaces, forcing GE to become more creative in their screen offerings. In early 2000, GE offered a human machine interface <HMI> like the one shown in Fig. 16-3 below. This was a marked improvement over previous HMI. Also, GE offered an “historian” option to record data for further analysis.
The HMI concept offered more creativity in displaying data and graphics, including a facsimile of a turbine on the screen and data points corresponding to their physical locations on the unit (see green object in Fig. 16-3 depicting a gas turbine). The TMR system of Mark IV was continued in Mark V, again using 2/3 voting of three process controllers <RST>.
Should the PC computer or its screen fail during turbine operation on the Mark V system, the control panel also was equipped with an auxiliary display where basic gas turbine operations can be monitored and controlled. Fig. 16-5 shows one such typical display for an early Mark V turbine. The turbine’s most important operating data could be “called up” from the Backup Operator Interface <BOI> and many of the basic functions ccould be initiated. Example: Raise/Lower Power Output (megawatts). A default screen shows the most important data: speed, FSR, Turbine Exhaust Temperature.
The screens in Fig. 16-6 show the difference between touch screen interfaces.
Around the turn of the century, GE offered the Speedtronic™ Mark VI system, which was continued in production to around 2008. Currently the Mark IVi is available (an “i” for internet variation), as a continuation of the Speedtronic™ trademark. Turbines with this system could be monitored back at GE’s headquarters in Atlanta, GA.
Note: Companies that offer alternatives to the GE Speedtronic™ systems were certainly driving forces to make General Electric “keep pace” with the available technology. Most of these companies, however, do not think it is necessary to offer TMR systems. One main processor, and hence a Simplex system, is all that is required; however, redundant sensors (like speed pickups, thermocouples, etc.) are appropriate.
Innovative Control Systems (ICS), HPI and Petrotech are competitors of GE in the controls alternative business. We have worked with all of them and have concluded that, in the turbine controls retrofit business, all of them offer reliable products in competition with General Electric.