N112-133 TITLE: Innovative Approach to Automatically Detect Ground Faults in Shipboard Control System

TECHNOLOGY AREAS: Information Systems, Electronics

ACQUISITION PROGRAM: PMS 400D, DDG 51 New Construction Program

OBJECTIVE: Development of an innovative, advanced fault detection/isolation/coordination methodology to increase the operational efficiency, robustness and reliability of the Machinery Control System (MCS).

DESCRIPTION: The Navy wishes to mitigate the amount of time a ship is inoperable or at a reduced operating capability due to the execution of the MCS fault detection, mitigation, isolation and repair process. This "downtime" is variable and is a simple function of when the troubleshooting effort begins and how quickly the troubleshooter is able to find the fault(s) within the system. The MCS design is based on an ungrounded or floating ground power supply design. There is no direct connection between the console circuits and hull ground. The design specifications require that the signal wires and their associated shields be isolated from the ship�s hull by more than 250K Ohms to ensure accuracy of the monitored signal. This configuration provides improved signal fidelity, resistance against EMI problems and against damage to electronic components as a result of stray voltages. However, it has become apparent that grounds to ship�s hull can introduce stray voltages and EMI in the MCS system, and cause the MCS circuits to vary in voltage relative to ground. Additionally, the presence of faults in the MCS system can result in the generation of inaccurate system information as well as a higher component failure which, in turn, can lead to equipment shutdowns and periods of system inoperability.

In general, the Navy machinery control system consists of five consoles that have roughly a total of 5500 control and monitoring signals directly wired to control points and sensors. The signal and return lines are typically two or three twisted wires with a shield. The signal shield is tied to the signal return at the MCS console. Many signal sets (50 or more) are cabled together and connected to the MCS console with an overall cable shield to reject EMI. This cable shield is tied to ships ground. The signal shield is isolated from the cable shield, and ship ground, to provide for a clean signal. Each signal set may have many termination points as it traverses from the console to the control point, through shipboard junction boxes. Individual signal returns and shields maintain continuity through the junction boxes. The cable shields are tied to ground at each junction point. If the signal return becomes grounded, signal value accuracy is affected, and un-commanded system operation may occur due to corrupted signal.

Currently, the Navy�s fault isolation detection process consists of taking the console off-line and, using a handheld analog meter, the user measures the resistance between the power supply return and ship�s hull. When less than 250K Ohms is measured, the user performs a manual trial and error method to locate the ground fault(s). This process usually starts at the console where the ground has been indicated and will continue cable by cable downstream of the console until the fault is identified. This is a very laborious and time consuming process and can lead to the introduction of additional grounds, additional component failures, and breaking pins due to removing and re-attaching the ribbon cables and the cannon plugs. Though another widely used method in the commercial industry to locate ground faults by injecting signals into the system. This is not considered a viable solution due to concerns of a potentially adverse impact on the operation of the MCS Control System.

This topic seeks to explore the development of an innovative, fault detection/isolation/coordination methodology and the associated technology(ies) to provide ship�s force with the ability to quickly and accurately identify a grounded condition as well as the ability to localize the affected cable(s) and/ or components. Specifically, proposed concepts should address the ability to detect and determine the location of the ground (including signal returns and signal shields connected to ship�s hull), multiple simultaneous grounds, between the MCS system and ship�s hull with attention to signal cables, sensor cables, and components, such as relays, sensors, transducers, contact closures, and other floating ground components. The proposed concept should be able to function while the system is in operation, with a noninvasive, nonintrusive approach, and should be able to provide fault indication and location of problems, such as: intermittent fault conditions, multiple faults on the same phase and/or inverted ground faults. An innovative, easy to implement concept that requires little training and utilizes minimal ship�s force to execute is of particular interest. The increased mission capability and potential savings on the materials and manpower associated with the development of this capability could be significant. Proposed concepts should employ open architecture principles and be able to interface with the currently used MCS and Integrated Condition Assessment Systems used onboard naval ships. It is envisioned that a key technical challenge is going to be in the development of a non-intrusive, detection and localization process that provides real-time or near real-time detection.

PHASE I: Demonstrate the feasibility of improved, innovative, fault detection/isolation/coordination methodology and the associated technology(ies) to provide ship�s force with the ability to quickly and accurately identify a grounded condition and localize the affected cable(s). Establish performance goals and metrics to analyze the viability of the proposed solution. Develop a test and evaluation plan to contain discrete milestones for product development to be utilized for verify performance and suitability.

PHASE II: Develop, demonstrate and fabricate a prototype as identified in Phase I. In a laboratory environment, demonstrate that the prototype system meets the performance goals established in Phase I. Verify and provide results for final prototype installation methodologies in a representative laboratory environment. Develop a cost benefit analysis for Total Ownership Cost, as well as Phase III testing and validation plan.

PHASE III: Construct a full-scale prototype based on the Phase II results for testing in a shipboard environment. Working with government and industry, install onboard a selected DDG 51 class ship and conduct extended shipboard testing.

PRIVATE SECTOR COMMERCIAL POTENTIAL: A means of quickly detecting a fault can dramatically improve the life of the system components that are subjected to large stresses during the fault periods. This method of fault detection may be applied to any system utilizing a floating ground.

REFERENCES:
1. C. Wood and P. Clark. FADES: An Expert System for Fault Analysis and Diagnosis. TIRM 87-024, Turing Institute, 1987.

2. Baldwin T., F. Renovich, Jr., L. F. Saunders, and D. Lubkeman; Fault Locating in Ungrounded and High Resistance Grounded Systems; IEEE Transaction on Industry Applications, Vol. 37, No. 4, July/August 2001; pp. 1152-1160.

3. Bascom III E. C., D.W. Von Dollen, H.W. Ng, "Computerized underground cable fault location expertise," Proceedings of the IEEE Power Engineering Society Transmission and Distribution Conference, Chicago, IL, USA, Apr. 10�15, 1994.

4. MIL-STD-1310 "Standard Practice For Shipboard Bonding, Grounding and other Techniques for Electromagnetic Compatibility and Safety" section 5.1.2.1.4 - (https://assist.daps.dla.mil/quicksearch/)

5. MIL-SPEC-901D," Shock Tests, High Impact Shipboard Equipment, Machinery, and Systems" -(https://assist.daps.dla.mil/quicksearch/)

KEYWORDS: MCS; ICAS: Ground Fault Detection; Fault Isolation; Ungrounded Systems

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