Ocean Sentinel Instrumentation Buoy Used for WEC Testing

A novel Ocean Sentinel instrumentation buoy has been developed by NNMREC and AXYS Technologies for WEC testing.

The Ocean Sentinel is a surface buoy, based on the 6-meter NOMAD (Navy Oceanographic Meteorological Automatic Device) buoy design. This instrumentation buoy facilitates open-ocean, stand-alone testing of WECs with average power outputs of up to 100 kW. Deployment is typically at a NNMREC test site that is approximately 2.5 nautical miles offshore from Yaquina Head, north of Newport, Oregon.

WECs under test are moored approximately 125 meters from the instrumentation buoy and connected by an umbilical cable. Power generated by the WEC is controlled by switchgear and power conversion equipment located on-board the instrumentation buoy and dissipated in an on-board load bank. Wave data recorded by a wave measuring buoy is also transmitted to the Ocean Sentinel, via wireless telemetry.

The primary functions of the Ocean Sentinel instrumentation buoy are as follows:

1. Provide stand-alone electrical loading and power conversion for the WEC under test.

2. Measure and record WEC power output.

3. Collect and store data transmitted from the TRIAXYS wave measuring buoy moored nearby.

4. Transmit collected data to a shore station via a wireless telemetry system.

5. Conduct environmental monitoring.

The Ocean Sentinel power conversion and load bank system provides a stand-alone load for the WEC under test. This system provides generator control for WECs in early stages of development that do not include onboard generator power conversion. A switchgear enclosure that includes the contactors along with an electrical disconnect, current and voltage sensors, and fuses is installed below deck in the forward compartment of the Ocean Sentinel, together with the power converter. Two 50 kW, air-cooled load banks are installed above deck. This system is controlled by a National Instruments CompactRIO based data acquisition system developed by NNMREC, which is also used to record WEC power and measured wave data.

Because NNMREC anticipates testing WECs with different power outputs and generator configurations, the Ocean Sentinel loading system has been designed for a high degree of flexibility and is reconfigurable via terminations in the switchgear enclosure. The air cooled load bank can be reconnected for different voltage and power levels, and can be controlled by either contactor switching, converter control, or a combination of the two. WECs with output current to 125 A continuous can be accommodated, for a power capability of 100 kW at 460 V or 50 kW at 230 V.

An on-board power system developed by AXYS Technologies can supply up to 400W of 24 Vdc and 120 Vac power to the instrumentation and power conversion equipment installed on the Ocean Sentinel, and to the WEC via the umbilical. Primary power is provided by 40x sealed lead acid batteries (2000 Amp-hours at 24V), which are maintained through the use of a 1 kW wind generator, 2x 210 W solar panels and a 3.2 kW standby diesel generator. The system can provide 400 W throughout a 3 month deployment period without refueling. This power system is controlled and monitored by a Watchman 500 data acquisition and control system.

Two independent cellular telemetry systems are used between the Ocean Sentinel and shore, one for the Watchman 500 that controls and monitors the power system, and the other for the CompactRIO system that provides control and data acquisition for WEC testing.

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July 5, 2013