Speedtronic Mark VI control configuration and operation Part 1
Note: In part 1, the hardware configuration is explained.
GE’s SPEEDTRONIC Mark VI Turbine Control
The SPEEDTRONIC™ Mark VI turbine control is the current state-of-the-art control for GE turbines. It is designed as a complete integrated control, protection, and monitoring system for generator and mechanical drive applications of gas and steam turbines. It is also an ideal platform for integrating all power island and balance-of-plant controls.
The control system is mainly based on the Control Module, which is available in either a 13 or 21 slot standard VME card rack. Inputs are received by the Control Module through termination boards with either barrier or box-type terminal blocks, and passive signal conditioning. Each I/O card contains a TMS320C32 DSP processor to digitally filter the data before conversion to 32 bit IEEE-854 floating point format. The data is then placed in dual port memory that is accessible by the on-board C32 DSP on one side and the VME bus on the other.
The Control Module contains:
- I/O card,
- an internal communication card,
- a main processor card,
- flash disk card.
I/O data is transmitted on the VME backplane between the I/O cards and the VCMI card located in slot 1. The VCMI is used for internal communications between:
- I/O cards that are contained within its card rack,
- I/O cards that may be contained in expansion I/O racks called Interface Modules,
- I/O in backup
- I/O in other Control Modules used in triple redundant control configurations, and
- The main processor card
The main processor card executes the bulk of the application software at 10, 20, or 40 ms depending on the requirements of the application.
A QNX operating system is used for real-time applications with multi-tasking, priority-driven preemptive scheduling, and fast-context switching.
Communication of data between the Control Module and other modules within the Mark VI control system is performed on IONet. The VCMI card in the Control Module is the IONet bus master communicating on an Ethernet 10Base2 network to slave stations.
The Control Module is used for control, protection, and monitoring functions, but some applications require backup protection. For example, backup emergency overspeed protection is always provided for turbines that do not have a mechanical overspeed bolt, and backup synch check protection is commonly provided for generator drives. In these applications, the IONet is extended to a Backup Protection Module. The triple redundant version contains three independent sections (power supply, processor, I/O) that can be replaced while the turbine is running. IONet is used to access diagnostic data or for cross-tripping between the Control Module and the Protection Module, but it is not required for tripping.
Mark VI Triple Module Redundant (TMR) is derived from the basic architecture with three completely separate and independent Control Modules, power supplies, and IONets. Mark VI is the third generation of triple redundant control systems that were pioneered by GE in 1983. System throughput enables operation of up to nine, 21-slot VME racks of I/O cards at 40 ms including voting the data. Inputs are voted in software in a scheme called Software Implemented Fault Tolerance (SIFT). The VCMI card in each Control Module receives inputs from the Control Module back-plane and other modules via “its own” IONet. Data from the VCMI cards in each of the three Control Modules is then exchanged and voted prior to transmitting the data to the main processor cards for execution of the application software. Output voting is extended to the turbine with three coil servos for control valves and 2 out of 3 relays for critical outputs such as hydraulic trip solenoids. Other forms of output voting are:
- a median select of 4-20ma outputs for process control, and
- 0- 200ma outputs for petitioners.
Sensor interface for TMR controls can be either:
- triple redundant, or
- Combinations of redundancy levels.
There are two types of termination boards.
- 24-point, barrier-type terminal blocks that can be unplugged for field maintenance.
- Another type of termination board used on Simplex controls is mounted on a DIN rail and has one, fixed, box-type terminal block.
Discrete I/O: A VCRC card provides 48 digital inputs and 24 digital outputs. The I/O is divided between 2 Termination Boards for the contact inputs and another 2 for the relay outputs.
Analog I/O: A VAIC card provides 20 analog inputs and 4 analog outputs. The I/O is divided between 2 Termination Boards. A VAOC is dedicated to 16 analog outputs and interfaces with 1 barrier-type Termination Board or 2 box-type Termination Boards.
Temperature Monitoring: A VTCC card provides interface to 24 thermocouples, and a VRTD card provides interface for 16 RTDs. The input cards interface with 1 barrier-type Termination Board or 2 box-type Termination Boards. Capacity for monitoring 9 additional thermocouples is provided in the Backup Protection Module.
Speed (Pulse Rate) Inputs: Four-speed inputs from passive magnetic sensors are monitored by the VTUR card. another two-speed (pulse rate) inputs can be monitored by the servo card VSVO which can interface with either passive or active speed sensors. Pulse rate inputs on the VSVO are commonly used for flow-divider feedback in servo loops. The frequency range is 2-14k Hz with sufficient sensitivity at 2 Hz to detect zero speed from a 60-toothed wheel. Two additional passive speed sensors can be monitored by “each” of the three sections of the Backup Protection Module used for emergency overspeed protection
Synchronizing: The synchronizing system consists of automatic synchronizing, manual synchronizing, and backup synch check protection. Two single-phase PT inputs are provided on the TTUR Termination Board to monitor the generator and line busses via the VTUR card. Breaker Close command is pass via the TTUR. An external synch check relay is connected in series with the internal K25P synch permissive relay and the K25 auto synch relay via the TTUR. Feedback of the actual breaker closing time is provided by a 52G/a contact from the generator breaker (not an auxiliary relay) to update the database. An internal K25A synch check relay is provided on the TTUR; however, the backup phase / slip calculation for this relay is performed in the Backup Protection Module or via an external backup synch check relay.
Shaft Voltage and Current Monitor: The VTUR / TTUR can continuously monitor the shaft-to- ground voltage and current, and alarm at excessive levels.
Flame Detection: The existence of flame either can be calculated from turbine parameters that are already being monitored or from a direct interface to Reuter Stokes or Honeywell-type flame detectors. These detectors monitor the flame in the combustion chamber by detecting UV radiation emitted by the flame. The Reuter Stokes detectors produce a 4-20ma input. For Honeywell flame scanners, the Mark VI supplies the 335Vdc excitation and the VTUR / TRPG monitors the pulses of current being generated.
Trip System: A trip command issued either from the main processor card to the VTUR card in the Control Module(s) or from the Backup Protection Module. Hydraulic trip solenoids are wired with the negative side of the 24Vdc/125Vdc circuit connected to the TRPG, which is driven from the VTUR in the Control Module(s) and the positive side connected to the TREG which is driven from the VPRO in each section of the Backup Protection Module. A typical system trip initiated in the Control Module(s) will cause the analog control to drive the servo valve actuators closed, which stops fuel or steam flow and de-energizes (or energizes) the hydraulic trip solenoids from the VTUR and TRPG. If cross-tripping is used or an overspeed condition is detected, then the VTUR/TRPG will trip one side of the solenoids and the VPTRO/TREG will trip the other side of the solenoid(s).
Servo Valve Interface: A VSVO card provides 4 servo channels with selectable current drivers, feedback from LVDTs, LVDRs, or ratio metric LVDTs, and pulse-rate inputs from flow divider feedback used on some liquid fuel systems. In TMR applications, 3 coil servos are commonly used to extend the voting of analog outs to the servo coils.
Vibration / Proximitor® Inputs: The VVIB card provides a direct interface to seismic (velocity), Proximitor®, Velomitor®, and accelerometer (via charge amplifier) probes. In addition, DC position inputs are available for axial measurements and keyphasor® inputs are provided. Displays show the 1X and unfiltered vibration levels and the 1X vibration phase angle. -24vdc is supplied from the control to each Proximitor with current limiting per point. An optional termination board can be provided with active isolation amplifiers to buffer the sensor signals from BNC connectors. These connectors can be used to access real-time data by remote vibration analysis equipment. In addition, a direct plug connection is available from the termination board to a Bently Nevada 3500 monitor. The 16 vibration inputs, 8 DC position inputs, and 2 Keyphasor inputs on the VVIB are divided between 2 TVIB termination boards for 3,000 rpm and 3,600 rpm applications. Faster shaft speeds may require faster sampling rates on the VVIB processor, resulting in reduced vibration inputs from 16-to-8.
Three phase PT and CT monitoring: The VGEN card serves a dual role as an interface for 3 phase PTs and 1 phase CTs as well as a specialized control for Power-Load Unbalance and Early-Valve Actuation on large reheat steam turbines. The I/O interface is split between the TGEN Termination Board for the PT and CT inputs and the TRLY Termination Board for relay outputs to the fast acting solenoids. 4-20ma inputs are also provided on the TGEN for monitoring pressure transducers. If an EX2000 Generator Excitation System is controlling the generator, then 3 phase PT and CT data is communicated to the Mark VI on the network rather than using the VGEN card.
Optical Pyrometer Inputs: The VPYR card monitors two LAND infrared pyrometers to create a temperature profile of rotating turbine blades. Separate, current limited +24Vdc and –24Vdc sources are provided for each Pyrometer that returns four 4-20ma inputs. Two Keyphasors are used for the shaft reference. The VPYR and matching TPYR support 5,100 rpm shaft speeds and can be configured to monitor up to 92 buckets with 30 samples per bucket.