In 2019 we were set the challenge: present a safer and more systematic method of producing the "bang-bang" test to confirm zero-volts ride-through capability. We delivered, and now, with several projects to its credit, we thought we should explain what exactly ZeroDip is, and how it improves on the original.
Why do we need it?
The requirement for a fault ride through test is described in the requirements of class for DP3 vessels. Testing isn't required for DP2; however, more vessel owners are choosing to operate in closed bus and need to ensure the safety of their system.
MTS, in their TECHOP-ODP-09 describe a typical short-circuit fault:
While the OneStep Power GVRT provides a test for the over-voltage without short circuit, the GVRT was initially unable to produce the zero-volts period immediately after the fault was generated. When we were asked to come up with a way to produce *both* the over-voltage and the zero-volts section in one test, we had to start thinking outside the box!
Why do we need a safer alternative?
Traditionally, vessel owners have worked with breaker OEMs to test the zero-volts section using a methodology referred to as "Bang-Bang". This test earned its name from the noise the breaker makes when it is opened then closed again in rapid succession.
"Bang-Bang" testing had the distinction of being the only method in the industry to simulate the zero-volts response of a short circuit without actually performing a short circuit. The test required the removal and disconnection of various protections which were put in place to prevent mal-operation of the breaker, and could only be performed with OEM supervision.
The biggest draw-back of "bang-bang" testing was the need to remove protections and then replace them again after testing. The industry has seen IMCA DP station-keeping incidents as a result of incorrectly reset protection settings. These statistics indicate an inherent threat in the "bang-bang" testing method. To prevent this, we developed the core value of not changing protection settings during testing.
Introducing the OneStep Power ZeroDip
So, you need rapid breaker control, but you don't want to change protection settings? You want it to be repeatable, and link to a transient over-voltage to replicate a short circuit voltage response? You need it to be safe, and you need it to be deployed quickly so you can get back to work? Also, it would be nice if it worked in a shipyard setting so you knew what system changes are needed before you left the yard.
Impossible? Almost, but not quite.
High-speed breaker control without changing protection settings was the largest leap of logic to overcome. Once we had a solution for breaker control, the rest was developed in conjunction with our existing technologies.
We developed dead-bus detection and other safeguards to ensure we maintained the safety of the vessel during and after testing. Then, we tied it to the same software protocols of the GVRT, to allow us to use both technologies in conjunction.
This means we are now able to offer the only repeatable zero-volts ride through and transient over-voltage test in the industry.
And, if that wasn't enough, our protocols mean we can vary the duration of the zero-volts test, and perform repeatable testing year after year. Our ZeroDip provides exact timing, rather than "0.5 to 1 sec" and much better resolution and control of the outputs. We provide graphs of the test with our much higher sampling rate.
Just another way we uphold our mission: to provide the best testing & engineering solutions to verify the reliability of power systems, in a ROBUST, RELIABLE, & REPEATABLE way.
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