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Wednesday Write-up: Voltage Response Testing

The development of new technology: why do we need voltage response testing? - A non-technical perspective.

Disclaimer: The following is a very high-level information piece for non-specialists. If you find you need more information or find this explanation lacking the nuance you require in a discussion on this topic, (Hey, there isn’t a single acronym on the whole post!) we would invite you to read more of our technical information available here.

OneStep Power’s Generator Voltage Response Tester provides a system-wide indication of a facility’s capability to respond to transient voltage variations, including under-voltage and over-voltage.

Dynamic Positioning in a Nutshell

OneStep Power developed the technology in response to a need in the Dynamic Positioning sector. Dynamically Positioned vessels are a large subset of the offshore sector in both oil and gas and renewables. Dynamic Positioning systems are also present in several other maritime vessel classes. The key concept for dynamically positioned vessels is to remain on station.

These vessels “station-keep” around a fixed point using complex computer modeling, in combination with a series of thrusters, and position reference systems, such as sea-bed transponders and satellite positioning.

These vessels, (most vessels, really!) aren’t operating with an extension lead back to shore… They need to generate power onboard. Traditionally, that has been by diesel-electric engines. Other solutions are becoming popular, including liquified natural gas, battery hybrid, etc, but we will stick to diesel-electric today.

The power generated needs to be reliable. Mechanical/electrical failures must be managed in such a way that the vessel can stay in place even if there is a failure in the system. Station-keeping is vitally important to the success of a vessel operating in the offshore environment. Staying in one spot, or moving along a predetermined path is very important if you are laying subsea cable, performing operations with divers on the seabed, or drilling a well. It’s also important if you are supporting these activities. In-field vessel collisions are a serious threat to the safety of facilities, the performance of the work, and their personnel and the environment. The risk of these incidents must be mitigated as much as possible.

Testing for Failures

Vessel owners perform testing to prove the system can continue to maintain station even in the event of a failure. This testing, which can range from removing a cable from a wind sensor, or disconnecting a computer to shutting down engine-rooms, is a complex series of tests designed to prove the redundancy and reliability of the vessel.

One of the tests required for certain operating modes is the confirmation of a vessel’s ability to “ride through” a short circuit event. Short circuits, which may occur in a range of ways aboard vessels result in 3 immediate and unavoidable outcomes:

  • Very high current

  • Voltage drop to zero volts for the time to clear the fault

  • Transient over-voltage as the system recovers and corrects

A vessel must be able to keep station after these events. Very high current testing in the form of primary injection and secondary injection testing has long been an established power industry technique. We intend to provide some more information on that in future posts. The voltage responses, are trickier.

Short duration voltage drop to zero-volts has been achieved in the industry by using high-speed switching of circuit breakers. Typically the method has involved vendors making changes to protection settings on the vessel. There are risks associated with this method, but it’s possible.

The real elephant in the room is the transient over-voltage. The industry was unable to produce the voltage transients of a short circuit without actually doing a short circuit. This wasn’t an appropriate methodology for testing many of the vessels which required testing, and so the industry identified the need for alternative methods of proving fault ride through.

Thus, OneStep Power developed the Generator Voltage Response Tester.

For the first time, vessel owners can produce the voltage responses of a short circuit event, without actually having to perform the short circuit. In effect, completing the testing puzzle.

With the combination of OneStep Power’s Generator Voltage Response Tester, and our high-speed switching apparatus, ZeroDip, we can provide facilities with a way to demonstrate the ability to ride through the voltage drop and transient over-voltage of a short-circuit event without actually doing a short circuit.

But WHY?

This testing is required before vessels may operate in specific configurations. The following configurations may be required by power consumption, or for reducing emissions and other efficiencies:

  • Hybrid Battery Systems

  • Closed Bus Configurations

  • Other emission reduction solutions

Beyond the rule requirements, testing by inducing controlled failures to demonstrate a system response might make sense in other scenarios such as:

  • Pre-testing in advance of a short circuit to ensure the system will pass

  • Inducing safe system-wide failures to confirm responses

  • Assist in training crew and validating design

  • Demonstrate system operation to clients and stakeholders

  • Help in incident investigation

For more information, check out:

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