The transition to 66 kV cables, transformers and switchgear have long been touted as a necessary step for the wind industry. In the space of a few short years progression has been very quick as the industry attempts to streamline every aspect of wind farm construction and energy production to realize reductions in the Levelized cost of energy. Larger capacity offshore turbines in the 6 MW and 8 MW range will apply more pressure on 33-kV array cabling and would require an increase in transformer capacity – or more transformer substations to cope with the increased demand. 66 kV cabling, in principle, will allow wind farm developers to maintain a conventional string of five wind turbines and negate the need to introduce further transformer substations.
There are, of course, many challenges en route to such an outcome. Some industry experts have called it a ‘systematic issue’, whereby the whole supply chain and whole system must go along for the 66 kV ride. Transmission losses are lower at 66 kV but if gains are offset by increased cost of cable production and/or installation, there is little benefit. However, there have been significant developments over the last year in terms of testing, validation, and implementation. While not without obstacles, the future of wind energy looks set to embrace 66 kV technology.
One of the key challenges over the last year has been testing and validation of 66 kV array cables, something JDR Cables has worked on in collaboration with the UK’s Offshore Renewable Energy (ORE) Catapult. The high voltage electrical laboratory based in Blyth, Northumberland, has been upgraded to provide enhanced testing capabilities to facilitate the shift to 66 kV for future offshore wind electrical systems.
This upgrade to the adjustable HV reactor involved an automated control system and an increase in the power rating of the 600 kV resonant transformer to 150 kW of power. The reactor, therefore, according to ORE Catapult, has the required high voltage and power capacity to carry out automated step-breakdown testing of 66 kV cable systems using water terminations.
The electrical testing laboratory is capable of exerting 20 times the operating pressure and stresses on the cable. Highly Accelerated Lifetime Tests (HALT) such as this enable qualification of new wet-type cable systems and the assessment of degradation of cable insulation systems. JDR Cables has cited the collaboration with ORE Catapult as a crucial enabler towards the completion of 66 kV cable type test approval to IEC60840, CIGRE 623 & 490; including coilable cable, factory flexible joint, connectors, and repair joints.
Full scale 66 kV accelerated wet-age testing has been performed in saline conditions at 3Uo 500Hz for 3000 hours, and Weibull assessment of step-break down results gives a lifetime prediction of more than 40 years, according to JDR’s product development director Jeremy Featherstone.
For the Siemens report on 66-kV cables: https://goo.gl/MndSt8
Filed Under: Projects