Over the last decade, turbine operators have been converting their mechanical trip systems to redundant electronic controls in order to improve the reliability of their trip systems and to reduce their exposures to turbine overspeed accidents during testing. This is a big improvement, but it has exposed another weak link in the trip chain: the hydraulic trip solenoid.
One solenoid valve can’t be tested without tripping the turbine. Two solenoids in series can be tested, but both solenoids must open to affect a trip. Some manufacturers offer a two-out-of-three voting arrangement that can be tested on-line, but not repaired on-line. And these triplicated arrangements depend on precision orifices and a narrow fluid viscosity range to be effective.
The Invensys Turbine Safety System provides a solution to all these problems. Consisting of a Trident Triple Modular Redundant (TMR) controller and a Quadvoter hydraulic trip block, the Invensys Turbine Safety System ensures that no single component failure can cause a trip and no single component failure can prevent a trip. All active components are testable and repairable online without bypassing trip functions.
The Quadvoter is placed in series with the hydraulic trip header to keep the steam trip valves open during operation. On detection of an over speed condition the Trident instructs the Quadvoter to dump the trip fluid to the reservoir during a trip action. The Quadvoter can be provided for dump-style systems or for systems requiring a pressure source.
In any safety system, the key component in reducing the system’s probability of failure on demand is testing. Interfacing directly to the Trident TMR controller, the Quadvoter provides both the means to test all the active components and instrumentation to judge the results. Pressure instruments monitor the state of each solenoid valve and during testing, they provide feedback to the control system to allow confirmation of the success of each step in the test. Optional proximity switches provide an additional level of redundancy and allow performance monitoring of each solenoid valve.
Isolation valves allow each pair of solenoid valves to be taken out of service and replaced without compromising the system’s ability to trip, if required.
The Trident executes test logic to fully automate the Quadvoter test sequence. Each step of the test procedure is monitored and can be recorded for test documentation. Testing can be initiated by the operator or it can be scheduled to proceed automatically.
Each step of the automated test sequence has a “pass” criteria. If any step in the sequence fails, the test is aborted and the operator is notified. Test failure details are presented to the maintenance personnel to allow quick troubleshooting.
The Trident includes the most sophisticated speed detection system available in the industry. The Trident pulse module not only provides the highest speed calculation accuracy, it is the only pulse module available that can detect missing teeth. One turbines that experience high vibration at high speeds, the probe gap can open up enough that some of the teeth are not counted. Ordinary pulse modules will interpret this as a reduction in speed. Not the Trident. It records the time of each tooth as it passes and can thereby compensate for missed teeth, allowing it to always calculate the correct speed.
An important benefit of installing a Quadvoter trip system is the use of industry-standard NFPA hydraulic components eliminating the reliance on expensive OEM trip system parts. High replacement parts prices and long leadtimes are eliminated.
The Invensys Turbine Safety System is the most reliable, most available and most testable turbine trip system available.
Product :
1. TS3410
2. TS3420
3. TS3000
4. TriLogger
5. TurboSentry Overspeed Trip Protection
