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Existing Instrumentation - In most cases the existing instrumentation on the turbine can be reused. No expensive electric valve upgrades are necessary since the system accepts OEM supplied LVDTs and servos. TDS can retain any level of redundancy in the instrumentation supplied by the OEM including LVDT, servo coils and magnetic pickup inputs. |
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Inlet Pressure Control - TDS has implemented algorithms designed to control the inlet pressure to the turbine. This is the preferred mode of operation as it will control drum pressure and stabilize the level. The turbine will use as much steam as is available from the boiler. This mode also maintains peak steam turbine efficiency. When several turbines are run in parallel the integral action of the controller will be disabled to allow the turbines to co-exist. |
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Rate - Initial Pressure Loss Control - TDS has implemented control algorithms to implement a Rate-Sensitive Initial Pressure Loss controller. This type of control forces the valves shut when the boiler pressure is decreasing at an accelerated rate. This is typically the result of the boiler loosing fire. During these conditions, there is an increased chance of water induction, therefore, the valves should close. |
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Extraction Pressure Control - TDS has implemented control algorithms necessary to implement extraction pressure control. This includes single and double automatic extraction control. The operator is able to control the pressure at the extraction and also implement a flow limit. The flow limit is implemented as a % of theoretical extraction flow. This scheme is fully integrated into the V1 control so that changes to V1 are feed-forwarded to the V2 & V3 valves in order to have a zero effect on extraction flow and pressure. |
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Admission Pressure Control - TDS has implemented control algorithms to control admission pressure. This algorithm can be combined with extraction pressure control to create admission/extraction control on machines that feature this type of control. |
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Exhaust Pressure Control - This type of algorithm is implemented on machines that are being used as letdown stations. It will control the pressure of the header (turbine exhaust) that it is discharging into. The integral action of this controller can be disabled in case there is more than one device controlling the pressure in the header at any point. |
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Speed Control - This type of control is implemented as a straight proportional controller with integral action when offline. The operator (or auto-start sequence) can input a speed target and ramp rate to instruct the control system to provide the desired speed and acceleration. This controller is the primary overspeed protection for the turbine and meets IEEE requirements. |
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Load Control - This type of controller is the default controller when the turbine is online. It is open loop control and is calibrated as percent of theoretical output. All control systems are equipped with this controller. |
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Megawatt Control - This controller is a closed loop load control. The feedback can come from a variety of sources. It can be a dedicated transducer (4-20mA) or from a digital protection relay that features Modbus communications. |
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Hydraulic Valve Control - The control system handles all hydraulic valve positioning internally with no need for external boxes and controllers. This simplifies the interface and increases reliability. Also, no expensive electric valve retrofits are required since all original parts are reused. |
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Individual Control Valve Actuator Retrofit - Many turbines have a camshaft actuated or torque tube actuated valves. These setups are reliable, however, the control valves cannot be tested online. Many users base load their machines but would like the ability to test the control valves. The control system is capable of supporting this type of control. TDS has the ability to retrofit steam turbines with individual actuators that can control each of the valves individually. This will allow the testing of the valves (see description below). In addition, this setup can give full arc capabilities on machines that lack a controlled stop valve (see description below). |
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Control Valve Testing - Some manufacturers outfitted their turbine with individually controlled steam valves. These valves have the ability of being tested on-line when operating at a low enough load. During this mode the turbine will be operating closed loop on inlet pressure (other feedbacks can be used). The control valves can be closed individually giving the user the knowledge that the control valves will close if needed. This procedure also exercises the valve stem helping to avoid excessive buildup. This is typically provided on units that are base loaded. |
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Stop Valve Testing - Most steam turbine manufacturers outfit their stop valves with a test mechanism. On turbines that feature two stop valves, there is usually a way to completely shut one stop valve to confirm full stroke operation. This procedure helps maintain the valve stem’s free motion. On machines that have only one stop valve, the stop valve only travels 15% of the stroke. This only confirms that the valve is free to move, not that it will completely shut. TDS can support both types of stop valves. |
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Bypass Valve Startup - Some stop valves feature a bypass valve meant to roll the turbine up in speed in full-arc mode. Typically this bypass valve is controlled manually by the operator. TDS can fully automate this valve so that speed is controlled automatically. If the valve has enough flow capacity, the turbine can also be placed online and loaded. This will further the benefits of full arc startups. |
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Intercept Valve Control and Testing - On reheat steam turbines there is an intercept valve that needs to be controlled and also, sometimes, a stop valve to be controlled. TDS can fully automate these valves. At low loads these valves can also be tested for proper operation. |
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Power Load Unbalance - On newer reheat steam turbines the power to rotor inertia ratio is very high. This can lead to overspeed situations based on traditional speed control schemes. On these machines the manufacturer included a power-load unbalance scheme where the intercept and control valves were fast closed when load, speed and crossover pressure criteria were met. This scheme successfully limits the speed overshoot on these machines. TDS can implement this type of scheme due to the fast scan rate of the TurboNet DASH 1. |
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Full Arc - Partial Arc (FAPA) Control – Many large machines have a scheme where the turbine can be started by admitting steam over the full first stage arc (full arc). This mode ensures that the shell and passages are warming evenly around the periphery and thus minimizing stresses. This can be done two ways: by modulating the steam bypass valve built into the stop valve or by using individually controlled control valves. Once the bypass valve reaches its flow capacity, the turbine needs to be swapped to partial arc. If using individually controlled valves, this would happen at a designated load point. Individually controlled control valves also have the advantage of valve testing (see description above) and the ability to switch from full arc to partial arc and vice versa at any load. |
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Speed Wheel Retrofit - On older MHC machines there is no speed wheel that can be used as a speed feedback. TDS is fully capable of retrofitting these machines with a speed wheel. If the original overspeed bolt scheme is retained this speed wheel can be located anywhere in the turbine shaft. If the overspeed bolt is to be removed then the speed wheel needs to be mounted on the free end of the turbine, typically the front standard. |
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Zero Speed Indication - The speed input modules have enough sensitivity to detect zero speed on the turbine. This can be used to engage the turning gear automatically and to inform the user that the turbine is not rotating. No external modules such as Bently Nevada speed modules are necessary to perform this function. |
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Electronic Overspeed Retrofit - TDS can retrofit the turbine with an electronic triple redundant overspeed trip system. This is built into the control system even though it is completely independent of the control processor. Each overspeed module drives a relay. The relays are wired in a two out of three configuration, where it requires two modules to indicate “ready to run” in order for the turbine to run. The status of these relays is fed back to the control system. Because of these features, this scheme can be tested online for proper operation. The overspeed setpoint of each module is lowered one at a time and the status of its relay verified to be correct. This ensures the complete system is operational. |
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Automatic Start - TDS can implement the logic from the startup and loading instructions supplied by the manufacturer in the control system. This will ensure that the turbine is started using the correct set of parameters every time. However the operator can pause the startup or completely take over if it is deemed necessary. |
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Pump Testing - TDS can implement all the pump controls into the control system. This not only provides improved diagnostics, but it also allows for the pumps to be monitored, rotated and tested from the control room. Timers can also be implemented to track operation time for maintenance purposes. |
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MOV/Drain Control - TDS can automate all the drains in the turbine. The drains will be operated correctly every time if the control system is in control. The operator can also operate the drains manually. |
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Excitation System Interface - The control system can be interfaced to a TDS provided exciter retrofit to form one complete package. All the relevant exciter data can be displayed and trended on the display in the control system. The control of the exciter can still be done by discrete contact inputs and outputs. |
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Generator Protection System Interface - The control system can be interfaced to a generator protection relay in order to bring in all the relay flags. This assists operators and engineers in understanding the cause of a generator trip. |
