The PCRX represents the next leap forward in solid-state decouplers. It features camouflage technology, which addresses issues related to slow interrupted response associated with the capacitance of traditional decouplers.
Customers have been looking for a solution to capacitive effects during interrupted survey testing for a long time. With the addition of the PCRX to Dairyland’s product line, customers have had a wide variety of questions about this new, innovative technology. Our technical support team took time to answer the most frequently asked questions.
Dairyland Tech Support: We are always available and happy to discuss these questions or help customers to decide what products are right for their applications. We hope people will reach out to us if they have additional questions.
Let’s jump in with the first question everyone asks: with this new camouflage technology, how does the PCRX overcome capacitive effects?
The PCRX utilizes a proprietary technology that has been developed over the last decade of design and testing. The PCRX uses this technology to recognize when an interruption cycle has been started on a CP system and it is able to very rapidly reduce the capacitive effects that are found on traditional decouplers.
Does the PCRX still perform normal decoupler functions for faults, steady state voltages and lightning?
Yes. Like our other decouplers, the PCRX is a solid-state, maintenance-free device, designed to simultaneously provide DC decoupling and AC continuity/grounding when used with cathodically protected structures. The PCRX continuously provides an effective ground path for steady state AC, AC faults and lightning, even during the off cycle of the interrupted circuit. It performs the same functions you are used to with the SSD or the PCR.
What about product ratings? Folks who have used the SSD and PCR for a long time are used to certain fault current ratings, blocking thresholds etc. Are the PCRX product ratings the same?
The ratings for the PCRX will be familiar to our customers, although there are some differences. The ratings for fault current and lightning should be relatively familiar to most PCR and SSD users. The PCRX is being offered with fault current ratings of 5ka, 10kA and 15kA for AC faults, and a lighting rating of 100kA crest (8 x 20 µs waveform) — these are similar ratings to our PCR product line.
The PCRX is available with two blocking voltage threshold ratings of -4.5V to +3.5V and-5.5V to +2.5V. Similar to the blocking voltage threshold options on PCR and SSD models, the PCRX blocking voltage threshold rating is the total voltage across the device’s terminals and consists of the DC voltage plus the peak AC voltage. Total AC and DC voltage at or above the device’s blocking threshold, for a given polarity, will put the unit into conduction and the device will begin to pass all current as it performs its protective function of clamping voltage.
For more specific information on PCRX ratings, please consult the Technical Literature. This document will give more details on the blocking thresholds, DC operating voltage ranges, device impedance at varying levels of AC current through the PCRX and special considerations during low AC current scenarios.
I noticed you have two blocking voltage threshold ratings. Do you have recommendations on when to use one versus the other?
Yes – these two blocking threshold voltage ratings are aligned to be used with the most common types of grounding materials for AC mitigation or station grounding, namely zinc and copper. Due to the operating characteristics of the PCRX, application of these two models can generally be categorized for either zinc (-4.5V / +3.5V) or copper (-5.5V / +2.5V) mitigation. For more specific information on these blocking voltage ratings, please consult the Technical Literature. If there are questions on the choice of the model for your operating conditions, please contact Dairyland Technical Support for further guidance.
Thanks for clarifying some of the details around product ratings and camouflage technology. How does someone know if they need it?
Well, certainly existing users who have experienced the capacitance effect on their pipeline should consider the PCRX. In most cases, customers find that the PCRX will save them time and money when it comes to disconnecting decouplers or altering interrupted survey methods to address capacitance related issues.
For new installations though, it is trickier to predict the overall capacitance of the circuit. Due to the wide variety of factors, it is not currently possible to predict with certainty which sites will experience this issue. But site conditions play a significant role in whether or not you might have this capacitive effect during interrupted surveys with traditional decouplers. We prepped a simple chart that shows a sliding scale indicating the likelihood of this effect occurring based on site conditions. This can’t be used as a definitive indicator, but it can give you an idea of the types of conditions where these issues are likely to appear.
That explains the capacitance issue, I have also heard that the amount of AC current is also a factor in deciding the applicability of PCRX?
That is true – in addition to considering the amount of capacitance effect present, it is important to know the amount of AC current and voltage present at the proposed installation location. An important factor in applying the PCRX is understanding what level of steady state AC current and AC voltage are present at the PCRX terminals. For more specific information on the ratings at varying levels of AC current and AC voltage, please consult the Technical Literature. This document will give more details on the blocking thresholds, DC operating voltage ranges, device impedance at varying levels of AC current through the PCRX and special considerations during low AC current scenarios.
In regards to capacitance, what about a more certain, definitive test? Is there anything customers can do to be more certain?
Yes. For many users we think the predictive scale above may be enough to support the decision to choose the PCRX. For others though, there is a more definitive test approach using a test device CAD-270. People who are interested in learning more about it can explore our Knowledge Base paper here, or they can always contact us and we can assist.
The CAD-270 test device will allow the end-user to test how much capacitance will be present on an installed pipeline system that has the mitigation grounding system installed as well. These economical test devices replicate the capacitance typical of a PCR or SSD product.
Once people have a PCRX, they might still have questions about performing interrupted surveys on their pipeline. Could you comment on the recommended on/off cycle to use with the PCRX?
In general, each circuit is different, and we recommend that waveform analysis be completed prior to completing a CIS survey to determine the proper off cycles. But, typically, for a properly isolated pipeline segment, the measurement should be taken approximately 300 to 500 milliseconds after the instant off-potential has been initiated. This is the amount of time the PCRX decoupler needs to react to the off cycle. Therefore, the off cycle length should exceed the required PCRX response time, as determined by visual examination of the site waveform results.
Are there circumstances where a longer interrupted cycle, say 2 seconds, might be needed?
The accuracy of the instant off-potential measurement will always be affected by interference from other current sources, such as uninterrupted rectifiers bonded to the pipeline being tested or traditional decouplers that remain connected to the pipeline. Pipelines that are not isolated from other systems that contain traditional decouplers will take longer to reach an acceptable off-potential reading than a system with only PCRX decouplers. Remember that shorts, bonds, and failed-shorted isolation joints will tie systems together, possibly affecting these results. If you can, it is best to isolate the pipeline from segments that may still have standard decouplers or replace all the standard decouplers with PCRX units.
Do customers still need to use disconnect switches like the SWX-100 with the PCRX?
You certainly can use Dairyland disconnect switches with the PCRX. While the PCRX removes the need to disconnect devices during testing related to the capacitance issue, there are still circumstances where customers may want to install a disconnect switch.
Specifically, we would still recommend the installation of a disconnect switch for locating, current surveys, or ACVG coating surveys. The Dairyland decoupler will appear as a low impedance to 50Hz-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. This could give false readings or locating errors unless a very low frequency is used. In these circumstances use of a disconnect switch is desirable in that it makes disconnection fast and safe.
What about monitoring capabilities? Can customers install additional monitoring on the PCRX to monitor the AC current being drained without interfering with the functionality of the PCRX?
There are multiple methods to obtain the current value flowing onto the grounding system. Remote monitoring vendors have varying technology on this. For example, an AC current-sensing transformer or transducer can be installed onto the wire to the grounding system and the AC current is monitored by their RMU device. (RMU vendors may also offer the ability to monitor the AC current density on a coupon placed near the pipeline.) If you are out in the field and want to perform a one-time test of the current being drained, an AC clamp-on ammeter can be used to check the AC current flowing through the positive or negative cables.
Placing a shunt in series with the PCRX conductors as a means of measuring AC current flow should be avoided, due to the excessive safety issues related to such a component failing as an open circuit.
To answer the question directly, none of these monitoring devices will interfere with the functionality of the PCRX.
How do I determine decoupler spacing on new AC mitigation?
Often, customers ask about how many decouplers to apply, and where to locate them. The variables between decoupler installations are dependent on the overall AC mitigation design for that pipeline and the unique components involved. We recommend having an AC mitigation study performed to determine where to place decouplers and to design grounding systems that effectively mitigate the AC voltage and AC current density to acceptable levels. Various engineering firms provide services of this type.
One last question about installing the PCRX: what do customers need to know?
There are several things to keep in mind. First, the PCRX is not recommended for below grade installation. Unlike the SSD and PCR, there isn’t currently an option for a submersion rating for the PCRX. Additionally, the PCRX is designed to fit into our standard MTP-36 or MTP-48 mounting pedestals giving them a secure, protected enclosure. These are the most standard mounting accessories but there are a few other options available as well. In addition, the PCRX will perform in any mounting orientation to fit your application needs. Please note however, that the stainless-steel enclosure is internally bonded to the positive terminal. Ensure that the PCRX enclosure is mounted in a manner that provides isolation between it and the cathodically protected structure.
Our tech support team is always available and happy to answer any questions you may have regarding products or applications. if you have additional questions or would like our assistance determining if you need a PCRX, reach out to us here.
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