Power Cable Monitoring

Buried and subsea cables form an integral and critical part of the transmission system. We cannot see them and tools available to assess their condition continuously, in real-time, are limited.

Alternative generation (distributed, renewable) and evolving patterns of energy consumption mean that a power cable may be subjected to fluctuating loads, flow reversal or other changes in its operation and environment. The effect these changes have on the power cable can be seen in its temperature.

Fiber Optic Distributed Temperature Sensing (DTS) uses optical fiber to provide invaluable insight into power cable behavior.

Decisions about increasing the current or deferring cable replacement are made, safe in the knowledge that the cable is operating within safe temperature limits.

When and where will cables fail?
How much more load can the cable handle?
Where are hotspots?
How can cable condition be monitored?
Are there any hot or cold spots on the new cable lay?
How can the data be used?

Condition monitoring

The temperature of the power cable is monitored continuously and in real time, along its entire length enabling hotspots and temperature anomalies to be located and investigated. The temperature information provides insight into the condition of underground Distribution, MV, HV and EHV as well as subsea power cables. As more wind and photovoltaic generation comes on stream, a resilient grid requires monitoring to help engineers decide how much more load (ampacity) a cable can safely handle. Offshore wind farm cables rely on fiber optic sensing to indicate unburial, a change in condition or if the cable is snagged.

For new installations, the passive and EMI immune fiber optic sensing cable can be integrated into the cable, laid alongside it or placed in an adjacent duct.

Existing installations can be monitored either using an unused fiber (dark fiber) contained within the power cable, or by deploying a new sensing cable into an adjacent duct.

Marmon Sensing Solutions can provide permanent monitoring or survey power cables on a regular, intermittent basis. Surveys are also ideal for installation design verification pre- and post- cable energization.

Performance optimization

The actual cable/route temperature profile identifies hot spots that can be mitigated to address temperature “bottlenecks”. These are often different from hotspots identified through calculations.

Additionally, Dynamic Cable Rating (DCR) also known as Real Time Thermal Rating (RTTR) is a software option that continually mines the data relationship between the known cable load and the measured temperature. Using this information, the time to an over-temperature event or the amount of current that can be supplied through the cable before overheating, can be predicted. This informs network investment planning as well as maintenance scheduling.

Outputs

The temperature of the cable can be visualized on the screen or shown as a profile.

The data, including alarms, can be sent to SCADA using most common protocols including IEC 61850

How is the sensing cable installed?

This depends on the requirement for the monitoring and what is already available. The fiber optic sensor can be:

Integrated into the power cable - Provides the most precise monitoring, can be used to infer the conductor temperature and with dynamic rating
Attached to the power cable - Provides ‘relative’ temperature information, which is important when making decisions about the cable and for knowing the cable’s condition and environment.
Placed in a duct close to the power cable - Ideal for retrofit, the temperature information is ‘relative’ informing decisions about the cable(s) and their environment.

Marmon Sensing Solutions is pleased to discuss the various installation options, contact us.

DTS is available on Marmon Utility cables: contact us.