Preventing overspeed has always been the primary focus for turbine safety design

Now, as the industry has become more aware of the need for a more comprehensive approach to turbine safety, a refinement is underway that’s reflected in recent changes to industry standards such as API612 (Special-Purpose Steam Turbines for Petroleum, Chemical, and Gas Industry Services) and API670 (Machinery Protection Systems). This new sensibility highlights the importance of considering the performance of all components in the “turbine safety chain.”

The following is a summary of our interpretation of the revised standards, as they apply to turbine safety, specifically, overspeed detection and trip systems.

API 612

  • Combining the turbine overspeed protection with the turbine shutdown system is allowed as long as the performance requirements can be met – controls must still be separate from the shutdown system and overspeed system.
  • A new annex (Annex D) is included that provides the equations and method for calculating overspeed excursions (based on ASME PTC 20.2)
  • The minimum requirement for trip oil system dump solenoids is two parallel, de-energize- to-trip valves. The standard recommends using a two-out-of-three or two-out-of-four arrangement to improve availability.

API 670

  • Combining the turbine overspeed protection with the turbine shutdown system is allowed as long as the performance requirements can be met – controls must still be separate from the shutdown system and overspeed system.
  • A new annex (Annex O) is included that provides the equations and method for calculating overspeed excursions for a steam turbine (based on ASME PTC 20.2)
  • The standard requires a SIL study to determine the required redundancy and testing intervals. IEC 61511 and 61508 are cited for guidance in conducting the studies.
  • A surge detection is required for axial compressors. This system must be separate from the anti-surge control system, but may be combined with the emergency shutdown system.
  • ESD system shall record and store events with a 1 ms time stamp, retain the data for 30 days (or 10,000 events) in non-volatile memory and employ a first-in, first-out retention sequence.

When it comes to protecting a critical turbine train, a TetraSentry hydraulic trip interface paired with a Braun dedicated overspeed detector, provides the most cost effective, online-testable and online-repairable safety system available.

Test Tetrasentry

TetraSentry

The TetraSentry is an online testable, online repairable hydraulic trip interface with SIL 3 reliability in an ultra-compact footprint that’s designed specifically for turbomachinery applications. The TetraSentry is completely configurable, which makes it not only the most reliable, but also the most adaptable hydraulic trip interface available.

For applications that don’t have a programmable logic solver with four outputs, a “manual test” configuration is available that allows the TetraSentry to interface with an independent “two or three output overspeed detection system.” The manual test configuration allows for full online 2 testing of the TetraSentry. Optional block valves make this configuration online repairable.

For applications that have a programmable logic solver (we recommend the TSx), the TetraSentry can be configured with the instrumentation to allow for automatic testing.

For applications where a dedicated, configurable, electronic overspeed protection device (EOSPD) is most appropriate, we recommend the Braun EOSPD with integrated TertraSentry testing.

If we’re providing a TSx for the electronic overspeed protection system, we’ll also program the TetraSentry testing logic. If we’re not supplying a TSx or Braun EOSPD, and the TetraSentry has been configured for automatic testing, we’ll provide a “narrative” that describes the test.

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TurboSafe

The TurboSafe is designed to replace a traditional mechanical trip bolt on steam or gas turbines, power turbines, and other rotating equipment. It’s purpose-built to provide reliable overspeed trip protection for rotating equipment using magnetic speed sensors to determine rotational speed. Like the other Tri-Sen configurable products, the TurboSafe includes an intuitive configuration interface, so it's easy to set-up and simple to operate.

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TurboSafe-big

Braun+Tri-Sen

For applications where the TurboSafe is not enough EOSD, we have partnered with Braun (GmbH) to provide an API 612 / 670 compliant, configurable, TUV certified (SIL3), electronic overspeed protection device (EOSPD) with integrated TetraSentry testing.

The Braun is also suitable as a cost-effective interface to “partial stroke pneumatic trip systems.”

In addition to TertraSentry testing, the Braun EOSPD also includes an integrated frequency generator to test the overspeed trip circuits, as well as supporting an HMI interface via Profibus communications protocol.

All active components (including the trip relays) on the Braun EOSD are directly located on the Monitors and can be replaced during operation.

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Braun E16A345 With Tri Sen

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