Why Should I Monitor the Cable System?
The availability of a power plant depends crucially on the reliability of major high voltage components such as the generator, isolated phase bus (IPB) and the generator step-up transformer (GSU). It is therefore important for power plants to have reliable cables. The key benefits to implementing online monitoring are
- Increasing safety for workers
- Reducing unexpected failures to increase plant reliability
- Reducing unplanned outages which saves time and money
Online condition-based monitoring collects data generated during the assets normal operating conditions to get real-time awareness of problems.
Manual Inspection vs Online Monitoring
The condition of generation assets are usually determined through periodic manual inspections during an outage. The disadvantage of periodic inspections is that the time interval between two maintenance activities is not always sufficient to identify developing issues prior to failure. Periodic maintenance is often performed when the asset is not in service or the plant is in outage and the actual state of the asset with respect to time and plant operation condition is often not available for diagnosis. Periodic maintenance frequently results in the maintenance of healthy assets, increasing maintenance costs, and the possibility of human error.
Online Monitoring for Cables
Monitoring for partial discharge (PD) in switchgear and cable systems is beneficial to extend the life of assets. Use of the standard configuration of coupling capacitors for every three cubicles will monitor the PD in MV switchgear. However, determining the location or direction of the PD activity can be precarious. By combining the use of the capacitors and RFCTs in every cubicle one can easily determine if the PD source is inside the switchgear or coming from the cable system by using polarity discrimination.
How “far” one can see down the cable can depends on the type of cable insulation and shield condition. If the shield condition is good, perhaps 650 to 1000 meters (2133 to 3281 ft.) maximum. If the condition and integrity of the shield is poor then most likely coverage will drop down to around 100 meters. Nine out of 10 cable failures are with the cable accessories such as splices and terminations.
Use Realtime Data with Cable Monitoring
Switchgear and Cable Monitor
The Switchgear and Cable Monitor (SCM) continually monitors partial discharge (PD), and stores and correlates operating dynamics. The SCM provides information on the health of the medium voltage insulation systems of switchgear, cables, bus duct and unit substations.
Coupling Capacitor Sensors
The sensor has been designed to be used like the bus support insulator of the Isolated Phase Bus (IPB) or as coupling capacitor. It consists of a “stacked-mica” capacitor sealed with a special epoxy resin suitable for operation in extreme industrial environments.
The Radio Frequency Current Transformer (RFCT) provides non-invasive, directionally sensitive PD detection on electrical equipment by detecting activity in the ground connection.
Comprehensive Partial Discharge Monitoring Approach
It is important to consider a comprehensive partial discharge monitoring approach. PD can occur in generators, isolated bus ducts, step up transformers, and switchgear. Comprehensive monitoring of the entire power train can greatly increase the ability to pinpoint problem locations. To learn more about comprehensive PD Monitoring, visit our overview page.