GVRT Testing or Short circuit?
Updated: Jan 21, 2021
OneStep Power's key technical differentiation is the ability to produce the voltage response of a short circuit without actually performing a short circuit. Why? And what's the point?
Back in 2016, OneStep Power was formed on the basis of developing testing tools to provide dynamically positioned vessels with assurance of the reliability of their power systems. The key technology, the Generator Voltage Response Tester (GVRT) was created to mimic the voltage responses of a short circuit - a voltage dip and a transient over-voltage. The goal of the GVRT was to provide a safe and realistic alternative to "short circuit" tests.
“For closed systems, in particular, fault ride through testing supplemented by validated computer simulation will play a crucial role as the industry begins to increase its use of closed bus configuration in light of requirements for lower emissions and fuel consumption,” Steven Mearns Cargill Technical Authority for Dynamic Positioning, DNV GL
Class societies such as DNV, ABS, BV, and Lloyd's Register have required fault ride through testing prior to closed bus operations for DP3 vessels, and increasingly, conversations regarding proving DP2 fault ride through has also been part of the industry.
The GVRT and associated technologies such as ZeroDip provide a safe test:
No changes to protection settings
No personnel in high-risk areas during testing
No damage to equipment
Invisible to the ship's system
But how does it stack up against a short circuit?
MTS's TECHOP_ODP_09 is the current industry guidance for fault ride through testing, and identifies the Need for Alternative Methods:
"The test methods described in this TECHOP are not suitable for all types of DP power plant. There will be a need to develop suitable methods, specific to the power plant design, to demonstrate fault ride through capability if it is intended to conduct critical DP operations with their diesel electric power plants configured as a common power system. "
Bolted short circuits, while possible on high voltage switchgear, are not viable for low voltage (690V or 480V) systems and may not be suitable for hybrid vessels, or vessels which were built prior to the "Built to test" guidance which became prevalent in 2017. This is primarily due to the high currents encountered during short circuit testing. These current spikes are not present using OneStep Power's technologies, presenting a safer solution for equipment throughout the power network.
Short circuits are not an easily repeatable test - should equipment not ride through the voltage transients, the test cannot be easily performed again. Further, a short circuit test can only validate one fault path. Without performing the test multiple times, it's impossible to use a short circuit test to validate the outcome of all possible fault locations. Conversely, OneStep Power's testing presents the fault to the full system, demonstrating the fault ride through capability of the integrated power system - from thrusters to DP controllers to lights.
Given the right vessel access, GVRTs takes only a day to install, and generally a day to test is all that is required. We test the system multiple times and can test a range of configurations to match all DP FMEA requirements.
Hate Acronyms? So do we...
ABS - American Bureau of Shipping
BV - Bureau Veritas
DNV GL - Det Norske Veritas group
DP - Dynamically Positioned (Or Dynamic Positioning)
DP2 - DP Class 2 (a vessel classification)
DP3 - DP Class 3 (a vessel classification)
FMEA - Failure Modes & Effects Analysis
GVRT - Generator Voltage Response Tester
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