Independent editorial & reference on offshore wind dropper cables and preassembled connection systems
Working definitions for the terms that come up most often across our coverage of offshore wind dropper cables and connection systems. Written for procurement and engineering audiences — precise, not simplified.
The length of cable — sometimes called a tower cable or hang-off cable — that runs from the point where the submarine array cable enters the turbine foundation (typically through a J-tube) up to the switchgear or transformer inside the tower. Historically field-jointed by hand; the industry has shifted toward factory-preassembled, pretested cable and connector systems that plug directly into a preinstalled joint on site.
See What Is a Dropper Cable? .
A factory dielectric integrity test that detects insulation voids or defects in a cable or termination before it ships. Under IEC 60840, a properly manufactured HV cable assembly should show no detectable partial discharge above the test instrument’s background noise floor — typically held to a limit under 5 picocoulombs (pC) at the specified test voltage. Reynard tests every dropper cable and connector assembly this way before it leaves the factory, rather than relying on a datasheet rating.
The international standard governing design, testing, and quality requirements for extruded (XLPE-type) insulation power cables and their accessories rated above 30kV up to 150kV. It specifies type tests, routine tests, and sample tests — including the partial discharge test referenced throughout this glossary — that a cable assembly must pass before it’s considered compliant for service at these voltage classes.
Cross-linked polyethylene, a semi-crystalline thermoplastic insulation material. Dominant for fixed subsea array cables because of its low dielectric losses and strong performance under continuous, largely static loading. Less suited to components that flex or twist repeatedly, since it can develop micro-cracking under cyclic mechanical load at lower temperatures.
See EPR insulation is the material more commonly used in dynamic dropper cable applications instead.
A standardized, separable (plug-in) connector interface used on medium- and high-voltage switchgear and transformer bushings, commonly built to European interface standards such as EN 50181. It lets a factory-terminated cable end plug directly into a bushing without any on-site stripping, stress-cone building, or crimping — the mechanical basis for factory pre-termination.
Progressive mechanical degradation caused by repeated twisting, distinct from the fatigue mechanisms that affect a statically buried cable. In a dropper cable’s dynamic yaw loop, uneven or repeated rotation concentrates stress at the hang-off grip; in a conductor not built for dynamic service, this can shear individual strands over time, creating a resistive hot spot well before any external sign of damage appears.
See birdcaging .
An inter-array cable operating at 66kV rather than the 33kV that was standard a decade ago. A 66kV cable can carry roughly twice the power of a similarly-built 33kV cable, which is why most new offshore projects now specify it.
See 66kV vs. 33kV Offshore Array Cables for the full comparison, including what it changes about dropper cable and termination design.
The geometric insulation buildup at a cable termination that grades electrical field stress at the point where the cable’s shield or screen ends — the single most failure-prone step in a hand-built field joint, since it depends on workmanship performed under time and space pressure. Factory pre-termination replaces manual stress cone assembly with a tested, repeatable process performed under controlled conditions.