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Locating Leaks in Self-Contained Oil-Filled Underground Cables

Tracer technology is applied effectively to low pressure self-contained oil-filled cables to accurately locate leaks.

In-Service Cable Testing

A tracer-based method to locate leaks is applied to high-pressure cables, pinpointing underground oil leaks within a few metres, without removing the cable from service. 

A tracer chemical, originally developed for atmospheric studies, is mixed into the cable oil. When a leak occurs some of the tracer leaks out too. The tracer evaporates from the oil, moves up through the soil where the cable is buried, and is detected in the air above the cable route. The profile of the tracer concentration along the route is used to determine the leak location. 

Although proven for high-pressure cables, the atmospheric tracer technology has seen little use for low-pressure cables.  Dissolved gases must be excluded more stringently than in high-pressure cables to prevent the formation of bubbles, which can lead to ionization, a breakdown in the insulation, and ultimately a fault in the cable. The tracer chemicals are compatible, both chemically and electrically, with the oil and other materials in low-pressure cables.

Innovative Application

There are three major requirements to apply tracer technology to self-contained oil-filled cables for leak detection:  (1) mix the tracer in cable oil, (2) inject the tracer into a cable reservoir, and (3) measure the concentration of the tracer in the air.  

Typically, when applied to low-pressure cables, the methods developed to mix and inject the tracer in cable oil, maintain the air concentration in the cable oil below acceptable levels.

During the mixing process, Kinectrics eliminated direct exposure with the atmosphere by evacuating the apparatus. This modified method for injection requires only a minor change to the standard procedure for adding oil to a cable, and does not expose the tracer-in-oil mixture to air in the process.  

To measure the tracer concentration in air, samples of air are filtered with adsorbent traps. The methods used to deploy and analyze the traps for low-pressure cable applications are identical to the methods developed previously to locate leaks in high-pressure cables. 

Leak Detection and Location – a Typical Project

Recently, three self-contained oil-filled cables, each about 3 km long, were found leaking. Two of the cables had been leaking for some time; whereas the third cable had only been leaking for a short period of time, but coincidentally along the same route as one of the other cables. 

The cables were treated with tracers and leak locations were identified for each cable.  An initial coarse search procedure determined a leak location for each cable within 100m. A fine search pinpointed each location. These leak locations were confirmed during the repair of the cables to be within 3m of the actual individual leaks.   

Major Client Benefits

With great success, Kinectrics applies atmospheric tracer technology to detect and identify leak locations in low-pressure self-contained oil-filled cables. The modified tracer technology pinpoints a leak within a few metres, thereby minimizing excavations and avoiding the need for freezes.  A leaking cable can remain in service during the entire leak detection and location process.