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| A publication of the National Electronics Manufacturing Center of Excellence | April 2005 |
 An operational requirement for new ship and carrier construction is automatic monitoring and control of the electrical systems, such as generators, power converters, load centers, and circuit breakers. Present current and voltage sensors are large and heavy, which will result in significant increases in weight and space if legacy sensors are used. One of the EMPF goals is to evaluate fiber optic sensors and related networks to monitor power levels and to provide input to be utilized by a condition based maintenance system. Specifically, this will demonstrate the feasibility of fiber optic technology for use in monitoring the shipboard power conversion module (PCM). The ultimate goal is to produce a fiber optic condition based maintenance system (CBM) that will be integrated into the Navy’s Integrated Mission Support System (IMSS) and Automated Maintenance Environment (AME) System. These systems have been developed, demonstrated, and deployed by the Navy.
As an elaboration of further work, the EMPF will concentrate on the integration of fiber optics and sensor connectors into a CBM system. The EMPF will utilize technical resources from the Pennsylvania State University’s Applied Research Laboratory (ARL) and NASA’s Manufacturing Technology Transfer Center. The goal is to understand the latest technologies and best practices available for fiber optic cable selection, termination, and repair as applied to CBM. Following an investigation of the current state of fiber optic technology, device parameters will be identified that are most suitable for using fiber optic technology in high power shipboard applications. A fiber optic network will be designed to route multiple signals to/from a monitoring station. A selection of suitable fiber optic technology connectors/connector technology will be made. In relation to CBM, an optically compatible sensor will measure parameters which are defined. A sensor failure for any reason should not cause a failure in the PCM. All failure modes must be considered, and a Failure Modes and Effects Analysis (FMEA) will be performed. Isolation from the sensor to the backplane should not be less than 5 kV DC. Furthermore, the specification states that the CBM system must be immune to a single point of failure. A failure in the CBM system cannot cause a reduction in PCM unit performance or cause it to shut down. To support this (while focused on sensing voltage and current), the sensor will provide data for the following parameters:
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The need for improvement of the CBM is based on the operational demands and high procurement costs of the system in applications which require a high degree of uptime and reliability. Unexpected failures are costly to correct. Through its programs, the Office of Naval Research (ONR) aims to create a growth environment for CBM technology and applications that will return multifold benefits, such as the following:
The fiber optics effort will identify best methods for implementation within the electric generation and distribution systems of ships. The first phase of the fiber optics task will focus on specification development and system design. The EMPF will concentrate efforts on the fiber optic and sensor control module packaging. The second phase will involve the production and testing of a prototype system to demonstrate the feasibility of fiber optic technology for use in the monitoring of shipboard power systems. The current plan will take the two fiber optic sensors (current and voltage) from high power applications through a series of development, miniaturization, and ruggedization. A detailed schematic diagram of the network will be generated. At the present, the current sensor is at a higher level of technical readiness than the voltage sensor, which requires more development. Within the sensor system community, standards need to be developed for interfaces, interconnects, and power consumption. CBM requires constant monitoring of hardware, so that imminent failures of components and sub-assemblies can be promptly addressed, reducing downtime and system maintenance costs. The EMPF has chosen the fiber optic current sensor produced by Airak, Inc. A benefit of the Airak current sensor is that the size is independent of current range. In general, current transformers, transducers, and related sensors must be sized according to the magnitude of the current which they monitor and the magnitude of the system voltages in which they are installed. The Airak sensor (due to isolation of the optical fiber) does not require any special packaging or insulation below 19.2 kV. Overall size and weight of the transducer do not change as a function of measurement range. Since the Verdet constant of a dielectric material varies with temperature and wavelength of the optical source, the measurement may be affected by environmental perturbations such as temperature fluctuations and wavelength noise of the light source. Frequency response is limited only by the signal processing electronics. Traditional transducers are incapable of providing both high measurement range and high frequency response. This is a limitation in high voltage or high current applications such as transmission and distribution (T&D) monitoring or fault location. Wire-wound transformers and other related devices rated for 1000 A are typically limited to less than a 25 kHz response. Hall effect devices are limited to 250 kHz. Airak’s design is fundamentally limited by the signal processing electronics and not the transducer, which suggests that it is an ideal magnetic field and current sensor for T&D monitoring, fault-current location systems, power electronics applications, and other high power, closed-loop control and monitoring systems. Transducer packaging supports automated manufacturing (reduces labor and material costs). The cylindrical symmetric design of the transducer supports automated assembly and calibration, enabling a tremendous advance in the state of the art for fiber optic sensors, repeatability in calibration, and improvement in overall sensor reliability. At the end of this project, a formal report detailing the requirements for implementing fiber optic technology for condition based maintenance in high power shipboard applications will be provided. The first part of the report will provide detailed recommendations for the overall system design, including fiber selection, installation, connector technology, repair, and maintenance. The second part of the report will detail the results from production and testing of a fiber optic sensor network built to monitor a stand-alone PCM module. |
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| ACI Technologies, Inc. - - www.aciusa.org - - (610)362-1200 |  |
Fiber optic sensor systems offer several advantages over traditional electrical transducer-based measurement techniques. Because of their inherently dielectric nature, fiber optic sensors are an appealing choice for measurement of electric and magnetic fields and electrical current and voltage. They provide galvanic isolation of the sensor head from the ground potential and provide a superior safety profile. The biggest advantage relevant to Navy ships is that fiber optics are immune to EMI effects. In addition, fiber optic sensors are much lighter and smaller than existing transducers. The result is a significant weight and volume reduction on all Naval platforms, with response times equaling legacy systems. Installation and repairability will be enhanced. Typical figures of 180 current nodes and 133 voltage nodes will apply a volume reduction of 98.4% and a weight reduction of 96.8% over conventional sensors. Therefore, using fiber optics to control and monitor PCM units is an important consideration, and applying fiber optics to a CBM system is a logical choice.