top of page


Testing Venn_Opaque.png
EI Service

Demonstrate Single Fault Tolerance

Traditionally dynamic positioning vessels have operated in open bus configurations which reduces fault propagation paths between redundancy groups and subsequently reduces the risk of losing position. Modern strengthening of environmental and emissions standards have prompted vessel operators to move to closed bus configurations. While beneficial, closed bus configurations can lead to loss of DP capability if the power system is unable to ride through certain faults. 

The industry standard solution is the use of live short circuit tests to prove fault ride through capability during closed bus operations. However there is also commentary regarding the danger, difficulty, and potential damage that such testing involves. Live short circuit testing is only possible on some systems due to the fault currents associated with this test, and in many situations are not suitable for the vessel design. This has resulted in a broad range of regulatory and charterer requirements which generally allow alternative methods to be considered.

OneStep Power has encouraged the dynamic positioning sector to consider power system testing holistically. OneStep Power has developed tools to fill the missing gaps in the industry, not to replace existing best practices. These new and traditional practices are combined to create OneStep Power's"Equivalent Integrity Protocol". The DP industry also refers to this as "Single Fault Tolerance".

OneStep Power’s Equivalent Integrity Protocol is a full testing package that, when completed, provides assurance of a vessel’s Single Fault Tolerance for closed bus operations. The protocol has the following minimum requirements: 

  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 (Including Phase Back & Load Shedding)

  9. Phase Failure Testing

  10. Blackout Recovery Testing

  11. Harmonic Distortion Testing

  12. Fault Ride Through Testing for voltage transients GVRT + ZERODIP

We also provide project management support, delivering a single-source solution, including working with your DP FMEA practitioners for review and technical support for DP FMEA upgrades, and supporting testing scheduling around your vessel's activities.

03 Comprehensive Testing.png

Case to Operate

OneStep Power can also assist with assembling all required elements into a single, fully integrated deliverable for demonstrating single fault tolerant closed bus operations. This "Case to Operate" includes:

  • Functional Description

  • Protection Briefing

  • Equivalent Integrity Demonstration

  • Risk Assessment

and is a great source of closed bus information for Crew familiarization and Charterer acceptance.


Applicable Rule sets

IMO MSC Circ. 645 (1994) IMO MSC Circ. 1580 (2017) Class DP Rules

Equivalence Study

EI case study

Case Study

Contact Us

If you have questions, please reach out

bottom of page