Single Fault Tolerance

In this article:

1. What is Single Fault Tolerance?
2. What's the Business Case for SFT Validation?
3. What does a comprehensive SFT Validation program look like?

We are assuming the reader has a grasp of marine engineering concepts and basic electrical knowledge.

What is Single Fault Tolerance?

The MTS DP Committee defines Single Fault Tolerance as "The ability of a system to continue its function, following a single failure, without unacceptable interruption." (MTS DP Vessel Design Philosophy Guidelines Rev2 - Apr21)

The concept of Single Fault Tolerance (SFT) comes from the practice of performing Failure Modes Effects Analysis (FMEA). This analysis systematically considers the exposure of a complex system to a single fault, ensuring that the fault does not propagate beyond the established boundaries of the system. It is expected that upon completion of an FMEA, and it's associated proving trials, a vessel would be able to withstand a single fault without loss of systems beyond that of the design, thereby maintaining station.

To expand on this further, let's consider a basic 2-split ship arrangement:

In this "entirely segregated" scenario, a reasonable Worst Case Failure Design Intent (WCFDI) could be the loss of a bus, with the resultant loss of 2 thrusters. Provided the vessel was able to maintain station with only 2 thrusters remaining, this vessel would be considered single fault tolerant due to the "ability of the system to function" (station-keep)... "without unacceptable interruption".

Of course, an entirely segregated arrangement is not as easy to build as it is to draw on a flowchart. A range of cross-connections and interconnects exist onboard modern vessels, including:

• Battery-on-board and other battery hybrid solutions
• Closed bus-ties
• Cross-fed control system power supplies
• Control system networks
• Fuel storage
• Emergency systems (emergency stops, fire & gas detection & suppression)
• Auto-transfers of thrusters and other key equipment

In these situations, where segregation cannot be relied upon, verification of Single Fault Tolerance is more challenging.

What's the Business Case for SFT Validation?

1. Go Green

Fully segregated vessels are no longer desirable, in terms of cost and emissions.

There are a range of efficiency measures being deployed in the maritime sector, from batteries to fuel cells. These technologies are under heavy scrutiny from regulators, and SFT Validation is a key enabler for you to deliver greener shipping.

2. Stop Blackouts

Power loss at sea can be extremely detrimental in terms of financial and reputational losses. A comprehensive SFT validation program will decrease the risk of complete power loss, and provide your crews with an understanding of how to operate their vessel safely, and within its capabilities.

The UK P&I club estimates that "main engine failures or electrical blackouts now amount to 7% of its third party claims property damage in US$ terms. Many were enormously expensive and in some cases amounted to millions of dollars."

3. Get on Contract

A SFT Validation program can speed up the marine assurance element of your new charter. Providing evidence of the vessel's safe operation can be a secret weapon in the rapid delivery of a vessel. Paired with additional concepts like high-quality power monitoring and pre-installed test points, getting your vessel on charter has never been faster.

What does a comprehensive Single Fault Tolerant Validation program look like?

OneStep Power Solutions Inc. has been developing and performing Single Fault Tolerance Validation programs for nearly a decade. We have a standardized program that allows us to quickly assess a facility's capability, and then build the tests needed to verify its specific arrangement.

The testing falls into 12 broad categories:

1. Protection setting audit (inc. version control)
2. Fuelling Testing
3. Excitation Testing
4. Over-Voltage Testing
5. Earth Fault Testing
6. Relay & Protective Device Testing
7. Current Sensing Testing
8. Load application & Rejection Testing
9. Phase Failure Testing
10. Blackout Recovery Testing
11. Harmonic Distortion Testing
12. Fault Ride Through Testing for voltage transients

We use a range of technologies, including high-speed measuring, to induce faults and monitor the outcomes aboard your ship.

We suggest performing the testing in two phases, which allows us to work with shipyard schedules and your ship's contracts.

Who is OneStep Power Solutions?

OneStep Power Solutions Inc. is an independent power validation service based in Houston, Texas. We support ship owners, their clients, and crews to understand and de-risk their complex power systems.

Our mission: Independent assurance to accelerate the future of clean power.

Read More:

This is an introductory article, more information is available at the following:

https://www.onesteppower.com/equivalent-integrity