Taking the Temperature of a Cable System

Taichung City is the center of activities for one of Taiwan’s three main science parks, the Central Taiwan Science Park. This area has already attracted approximately 92 foreign and local manufacturers, pledging a total investment of US$51 billion. The science park has played a key role in the development and advancement of high-tech industries in central Taiwan. Its objective is to push the high-tech industries to new heights and construct sustainable operations — by creating efficient and intuitive systems — to increase the stability of the electricity supply.

A brand-new substation built in Houli by the national utility, Taiwan Power Co. (TPC), will satisfy the rising demand for energy and establish a smart grid. TPC awarded a contract for an underground transmission cable system at this substation, complete with accessories and real-time monitoring.

Tdworld Com Sites Tdworld com Files Uploads 1 2

The 345-kV XLPE underground cable system is installed on a route that includes outdoor and basement sections, GIS switchgear and transformer terminations.

Project Components

The turnkey contract for the new 345-kV underground cable system at the Houli Substation was awarded to Brugg Cables. The installation included LIOS Technology’s distributed temperature-sensing (DTS) monitoring system with an integrated real-time thermal rating (RTTR) solution.

Technicians installed the complete substation cable system required for the installation of the 345-kV cross-linked polyethylene (XLPE) cable on a route that included outdoor and basement sections, gas-insulated switchgear (GIS) and transformer terminations. The cable route was installed in various locations where the ground and air temperatures differ. In addition, the thermal resistivity of the cable installation changed quite a bit. The ambient temperature in the tunnel was close to 30°C (86°F), while the ground temperature in the basement was about 20°C (68°F). These temperature and thermal resistivity differentials would impact the load capabilities of the cable.

The single-core cables were laid in trefoil with a rugged fiber-optic cable attached to each core with cable ties. The temperature-sensing cable was installed after the power cable. It was difficult to obtain accurate conductor temperature forecasts because of permanent structures along the cable route (for example, tunnels, basements and outdoor areas) as well as load variations on the cables.

Tdworld Com Sites Tdworld com Files Uploads Overviewof Houli345k V Power Cable Monitoring

Distributed temperature sensing allows conductor temperature to be calculated in real time.

DTS System

LIOS Technology’s DTS system with an integrated RTTR solution is designed to measure the temperature along the entire cable length using a fiber-optic cable. The distributed temperature profile, as measured at the fiber-optic cable location, is used to determine the real-time conductor temperature by means of complex extrapolation using International Electrotechnical Commission (IEC) and Institute of Electrical and Electronics Engineers (IEEE) standards.

In addition to the temperature in the fiber-optic cable, other parameters such as load in the extra-high-voltage cable and the thermal resistivity of the soil and environment also are considered during this process. Mathematical models are specifically prepared to meet individual requirements. DTS systems are successfully proven in critical applications for fire detection in road and rail tunnels as well as hazardous buildings, transmission cables and the monitoring of overhead lines.

Hot Spot Sensitivity

The optical frequency-domain reflectometry (OFDR)-based DTS system ensures high-temperature and spatial resolution measurements over long distances to meet the requirements of the operator. With this very high resolution, the system is able to detect hot spots (for example, high-temperature points at cable joints and terminations) as well as proximities with other cable systems.

OFDR technology differs from the optical time-domain reflectometry (OTDR) system, which employs a laser-pulse principle that is sensitive to dispersion effects and affected by a broadened spatial resolution at long measurement distances. Therefore, the measurement and accuracy of hot spot locations tend to degrade with distance.

Tdworld Com Sites Tdworld com Files Uploads Fig5 Screen Shot Enhanced View Houli

LIOS cabinet installed in 345-kV Houli Substation with enhanced view of the cabinet screen.

Real-Time Thermal Rating

Because the fiber-optic cable is attached to the sheath of the extra-high-voltage cable at the Houli Substation, the temperature measured at the fiber-optic-cable location is sheath temperature and not the conductor temperature. However, the DTS system, along with the RTTR calculation engine, can calculate the conductor temperature in real time.

Another positive feature of RTTR is the emergency operations calculation, which can evaluate current, time (duration) and temperature. The additional fiber-optic cables installed in the GIS basement and in both tunnels are also used to measure the ambient temperatures in these areas. This measurement helps to control the ventilation systems, keeping the basement and tunnels cool. A similar system is installed in Wufong, Taiwan.

DTS Software

Control room operators find the DTS software to be user-friendly as one of the available languages is traditional Chinese. The software provides temperature profiles and current values for multiple zones, which can be defined starting at the controller. Also, remote access enables operators to display several projects in different locations.

The operator can display the Houli Substation controller with all its channels and the current sensors connected to each circuit. The database provides TPC the opportunity to create temperature history profiles in addition to real-time profiles. The defined zones divide the entire power cable into several segments.

A fiber break alarm is included in the remote zone and provides protection for the entire cable. The controller sends alarm signals to TPC’s supervisory control and data acquisition (SCADA) system about the status of the alarm together with the minimum, maximum and average conductor temperatures.

The DTS software designed for the Houli Substation provides an improved schematic view in every type of background, together with color coding, which makes visualization easy for control room staff. The cable temperature information, ampacity of the circuits and all the information specified by TPC are shown on one main screen.

Acknowledgement

The author wishes to thank Claudia Herrmann and Omar Ciprietti of Brugg Cables and Patrick Nollmann of LIOS Technology for their help and support in the preparation of this article.

Lai-Jinn Chen ([email protected]) is deputy director of the power supply department at Taiwan Power Co. Chen has 27 years of experience in the power industry, specializing in power dispatching, substation equipment maintenance, diagnosis, automation and asset management. He holds a BSEE degree from the National Taiwan University of Science and Technology and a MSEE degree from the National Taipei University of Technology.