New Developments In Inductive And Capacitive Underwater Electrical Connectors (1988)

ABSTRACT More efficient and smaller inductive and capacitive couplers have evolved from novel approaches. These couplers are applicable in complex networks where in the past their poor efficiency would have been prohibitive. They facilitate installation and maintenance and, under certain conditions, they allow for live disconnection. Hence they offer great flexibility to the underwater system designer. Moreover, they provide excellent reliability. Prototype testing of both types is discussed. INTRODUCTION Because of poor experience in the past, underwater mateable electric connectors (also referred to as couplers) have gained a reputation for being critical items in the reliability of underwater electric and electro-hydraulic systems. This reputation is fortified by the delicate treatment generally required during installation (Ref. 1). Because of the poor accessibility of underwater control systems, any improvement of the reliability and any simplification of the installation requirements will have considerable cost benefits. Various principles of underwater connectors are known (Ref. 2). The most familiar and oldest category is that of the pin-and-socket type underwater connector. The inductive coupler, basically an electrical transformer with separable primary and secondary, has been around for some time. Over a thousand coupler-years of field experience have demonstrated its outstanding reliability in the lower power range (&lt;500 VA). Disadvantages of currently available inductive couplers are their limited efficiency and their large size and weight. However, substantial improvements are possible by a coaxial, rather than the more common face-to-face, coupler design operating at an increased frequency (Ref. 3). Recently the capacitive connector was introduced (References 4 and 5), which is a cheap, small, efficient and reliable alternative. This paper presents recent developments, such as the testing of a prototype of an improved inductive coupler and the upgrading of the capacitive connector for larger power levels and wider applicability. It is discussed how inductive and capacitive couplers can be disconnected while the system is under power. The use of circuit breakers to achieve this is considered in more detail. INDUCTIVE COUPLERS The majority of inductive couplers applied today are of the face-to-face type, comprising a magnetic core built up of two identical halves, both provided with copper coils. It has been shown theoretically, however (Ref. 3), that a coaxial coupler design (Fig. 1) can be substantially more efficient than the more common face-to-face coupler design in more complex power distribution networks. Such a coupler shape was already known to offer advantages in rotational couplings (Ref. 6) and further because of its good gap tolerance and large bandwidth (Ref. 7). Additional advantages of this coupler are the greater tolerance to misalignment and the simpler installation requirements. Prototype construction A prototype of a coaxial 1 kVA coupler has been built and tested. A frequency of operation of 400 Hz was chosen. This frequency is considered to be a good compromise between coupler size and efficiency (the higher the frequency the smaller the size, but the lower the efficiency). A difficulty with this design is that it cannot be constructed from laminated transformer iron because of its rotational symmetry.