Measuring Induced AC

Any site with induced AC voltage at levels that require mitigation needs a product that provides AC grounding, without compromising the cathodic protection voltage. The device must be suitable for conducting steady-state AC current while blocking DC current, when connected between the pipeline and ground. Dairyland products provide continuous AC grounding for pipelines with induced voltage, while leaving the cathodic protection voltage unaffected.

For more information on this application, refer to: AC Mitigation

Measuring Induced AC
In order to properly select a product to use on your AC mitigation project, it is critical to know the amount of induced AC current present on the pipeline. Steady-state AC current can be measured using a clamp-on ammeter at a temporary bond established between the connection points — the pipeline and grounding system. The current value can then be compared to the Dairyland product ratings. The Dairyland product rating for steady-state AC current should exceed the values measured on-site.

Procedure:

1. Using appropriate safety precautions, connect a temporary jumper between the pipeline and the grounding system.
   1. In the case of induced AC voltage at an insulated joint, where one side of the joint is grounded, connect the jumper across the joint.
   2. For underground transmission cable sheaths/casings, a grounding conductor will already be in place.
2. Using a clamp-on AC ammeter, read the AC rms current flowing in the conductor
   1. If this value fluctuates daily or seasonally, several readings should be taken over time, selecting the highest reading for the rating of a Dairyland product.
   2. If several readings are not possible, adjust the measured value upward to reflect the higher seasonal changes. One major variable is the power line load current, so the adjustment could be determined from a comparison of the load current at the time of measurement to the power company’s maximum expected load current. This would require coordination with the power company to acquire these values. Lacking any ratio information, include at least some margin between the measurement and the device steady-state AC current rating. For underground transmission cable sheaths/casings, consider imbalance and harmonics.

Sizing and Installing a Decoupler

When selecting a Dairyland decoupler for your application it is critical to size the device properly for steady-state current. Standard decouplers like the SSD and PCR line of products have a 45A continuous rating, which is suitable for most applications. If higher ratings are required, ask Dairyland about our optional 80A rated devices.