Practical Uses of the Isolation Switch

Overview
The Isolation Switch was designed and introduced by Dairyland to allow safe disconnection and reconnection of a Dairyland decoupling device without causing exposed arcing. The following article discusses some of the primary uses of the Isolation Switch.

When should the Isolation Switch Be Used?

The primary need for the Isolation Switch occurs when there is the potential for AC voltage across the decoupler terminals, which can make it difficult to disconnect the decoupler without causing an arc.  For this reason, applications where induced AC is present, or may be present in the future, are strong candidates for the Isolation Switch.

Practical Uses of the Isolation Switch

Decoupler Testing
While the performance of Dairyland decouplers over the last 30 years has been impeccable, some users are required to perform periodic testing of decoupling devices to ensure proper operational condition of the Dairyland device. Some field tests recommended by Dairyland require temporary disconnection of the decoupler from the pipeline. 

In situations where AC voltage might be present, safe disconnection of a decoupler could be a concern.  The fault-current-rated Isolation Switch eliminates safety concerns, and makes safe disconnection/reconnection a routine procedure.

Decoupler isolation from close interval survey (CIS) operations
In some instances, decouplers on well-coated pipelines can affect off-potential readings during close interval survey testing.  The Dairyland PCRX, designed specifically to solve this challenge, is the perfect solution for these applications.  For a detailed discussion of this issue and the PCRX, check out our technical article, Utilizing the PCRX to Address Capacitance Issues During CIS Testing.

However, in some cases, the decoupler must be disconnected from the circuit. The simple operation of the Isolation Switch makes it easy for personnel doing CIS to quickly and safely disconnect and reconnect the Dairyland decoupler during testing.

Isolation of high frequency signals from locators and coating defect instrumentation
Certain test equipment used on pipelines emits a frequency or uses rectifier cycling to perform its function.  Examples include pipe locators, and ACVG and DCVG coating defect test equipment.  The Dairyland decoupler will appear as a low impedance to 60Hz and higher frequencies (which is how it can perform AC mitigation) and will shunt this current to ground or to the other connected structure.  Similar to the CIS discussion above, rectifier cycling can cause some small current flow in the decoupler during the on-off transition, and appear to ACVG and DCVG equipment as a coating defect.  In cases of such decoupler effects, one or two decouplers on either side of the test location may need to be disconnected via the Isolation Switch.