Underground Cable Advanced Diagnostics (UCADS)
- Underground Systems, Inc.
Advanced technologies to enhance performance of the nation’s electricity delivery system have been proposed over the past decade by many organizations. The objective of enhancing the performance is to safely and reliably transport more electrical energy through the power transmission system. While improving transport capability, the system must operate within thermal limits and system stability must be maintained; each alone is necessary but not sufficient for reliable system operation. Although the United States power grid has maintained a high level of reliability for decades, it is rapidly running up against its limitations. A changing supply mix, expanding power quality needs, and continuing demand growth are stressing an aging, congested electricity infrastructure, and thus challenging system reliability. While the Nation’s lights may remain on, the risks and complexity of achieving sufficient power supply are growing every day. Remote monitoring technologies can optimize the utilization of transmission and distribution (T&D) assets and improve their operational efficiencies through a smart-grid-enabled infrastructure. During the Underground Cable Advanced Diagnostic (UCADS) project USi has been conducting R&D for monitoring and diagnostic systems in the lab while designing and testing the systems to be deployed in the field. The researched Phase II instrumentation package uses “state of the art” components. The modular design supports future growth, reduces the maintenance function and supports modifications as technology advances. Much of the effort was directed to developing monitoring and diagnostic systems for high voltage High Pressure Fluid Filled (HPFF) pipe type cable systems as they continue to be the major portion of the US high voltage underground transmission grid. The UCADS project was divided into five project tasks. The R&D challenges of the various tasks ranged from high risk / high reward to low risk adaptation of existing technologies. Overall System Design and Development as shown in Task 1 is central to the UCADS concept integrating the overall components. It is based on a proven systems and communications architecture deployed in existing USi monitoring, diagnostic and control systems. The novel sensors and black boxes developed under this project can be connected to a central UCADS CPU. Information, solutions or alarms generated by the CPU will then be transmitted to a utility SCADA system. Cyber Security requirements set by the utilities will be met and incorporated into the overall system. The largest project effort was applied to Partial Discharge (PD) Detection in High Pressure Fluid Filled (HPFF) pipe type cable systems. Very little previous research work had been done on this topic due to the complexity of the system and inherent high system signal attenuation. The research was a high risk, key R&D component of the UCADS project and covered PD generation, propagation within the cable and along the pipe as well as its detection inside the pipe. The work started with a full scale pipe mockup to prove that PD signals can actually leak from the inner dielectric to inside the pipe. This was followed by a characterization of the actual PD signals. The main part of the lab testing was a full scale, 40 ft long pipe mockup with full size 230kV transmission cables and joints in an actual 3 phase configuration to test propagation properties within a HPFF system pipe. Three field tests on utility pipe cable circuits evaluated the long range signal propagation under real life conditions. The research shows that PD signals can be transmitted from within the cable insulation to the space between the cables and the steel pipe. They can be easily detected within the HPFF cable system close to the PD source making joints the prime detection locations. However they are attenuated significantly when they propagate along the HPFF cable. Thus it is difficult to detect PD originating within the cable insulation far from the joints and manholes. A supposition at the beginning of the project that a largely loss free waveguide signal transmission would enable PD pulses to travel from the PD site to the end of the circuit over many thousand feet or even several miles proved not to be achievable. Our research results nevertheless contributed significantly to the understanding of PD signal propagation and detection in HPFF pipe-type cable systems. HPFF cable systems are robust and reliable due to their laminar paper oil dielectric. It takes time for defects in the dielectric to propagate across the insulation and cause failures. This process can take months or even years. During that time the degradation process releases key gasses into the dielectric fluid that can be used to detect and possibly locate incipient failures before the cable fails and causes an actual outage. While periodic DGA for cables has been used in static systems to detect defects in joints and terminations this technology has drawbacks. Due to the periodic nature of the measurements it can only identify high levels of gas concentrations, cannot be reasonably used in circulating systems and the cable length between joints is very difficult to monitor. With the proposed online DGA monitoring system developed and evaluated in task 3 it is now possible to apply DGA to circulating and forced-cooled HPFF systems by trending low levels of gas concentrations. Several different commercial DGA monitors developed for power transformers were evaluated. Some of these techniques while suitable for transformers cannot be directly applied to HPFF systems due to physical properties of their gas analyzers. A hydraulic system to sample, depressurize and analyze dielectric fluid from a HPFF pipe with the help of suitable commercially available transformer DGA monitors was developed and tested in the lab and in a short field test. More extensive field testing to determine the full range of operating parameters has been proposed and funded by NYSERDA at a host Utility. USi’s expertise in real time rating and material aging assessments has been applied to create a solution for Task 4. An online, continuous loss-of-life module was developed as part of the UCADS solution suite to be included into an overall advanced diagnostic system for underground cable systems. The model algorithm is based on the thermal aging of paper-oil cable insulations. The key parameter for the algorithm is the temperature of the cable conductor that is a direct function of the cable loading. Thermal aging becomes significant when cables are operated close to or above their rated normal ampacity. This diagnostic tool will provide the operator with increased confidence when cables are loaded close to their maximum rating over a long period of time and it will enable the user to determine the loss of life when the cable asset is exposed to emergency overload operation conditions. This diagnostic tool is useful for cable systems that are operated with both static and dynamic ratings. In Task 5 we have developed and demonstrated a robust Remote Monitoring Device suitable for service in electric utility substations and potentially for use in remote locations. The unit was designed and tested specifically to resolve reliability issues with prior monitoring technology. These units were (1) particularly sensitive electrical transients that caused failure of the device and (2) were incapable of detecting the very low potentials resulting from CP current flow through very short section of pipe that can be used to monitor and better characterize the CP system behavior. These objectives have been achieved. In addition to laboratory testing, a prototype unit has been deployed in a Gas Insulated Substation environment prone to electrical transient and has been performing reliably for over one year. This monitoring system consists of, 1) analog signal input and digital conversion, 2) microprocessor control and 3) a choice of communications technologies. Our challenge is to integrate the components into a “system” that would demonstrate the concept and test utility interest in 2019. The system has application well beyond Cathodic Protection but there is growing interest in CP and several characterization tools have already been used effectively. It is therefore a good starting point.
- Research Organization:
- Underground Systems, Inc.
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- SC0004280
- OSTI ID:
- 1574143
- Type / Phase:
- SBIR (Phase IIB)
- Report Number(s):
- DOE-USi-4280
- Country of Publication:
- United States
- Language:
- English
Similar Records
Underground Cable Advanced Diagnostics (UCADS)
The 345 kV underground/underwater Long Island Sound cable project