Why Control Panels Can Be a Source of Risk in Retrofit Projects

The following tip is from the ISA book by Greg McMillan and Hunter Vegas titled 101 Tips for a Successful Automation Career, inspired by the ISA Mentor Program. This is Tip #29.

101 Tips for a Successful Automation CareerProject management is really just risk management, and a large source of risk to an automation project is the control panels. If these panels and the software can been fully tested before the team arrives on site, the only remaining unknown will be the field wiring. Here are some tricks to make sure your panels are ready to go.

Concept: A poorly designed or fabricated control panel can bring a retrofit project schedule to its knees during a start-up. Take the time to ensure that the panels are thoroughly tested and ready to go in advance.

Details: Most system integrators push the client to let them design and fabricate the panels at their shop so they know they can be thoroughly tested before arriving on site. A client is wise to agree to this arrangement, provided they are allowed to take part in the panel checkout and that the checkout occurs PRIOR to shipping the panels on site. This timing is important because if any problems are encountered during the checkout (wrong type or missing panel components, design problems, etc.), the client can get them resolved BEFORE the panels arrive on site. If the client does not get to review the panels in advance and problems are discovered after the panels are shipped, the client does not have much time to fix them and his negotiating position will be considerably weaker.

Here are some tips to consider when doing a panel test:

  • If the panel is to be fed with two independent sources of power (such as UPS and non-UPS), connect the panel to two power sources that are out of phase. (If undocumented or unplanned links occur between one power feed and the other, it will quickly become obvious!)
  • Tug (HARD) on every wire. This may seem like a colossal waste of time and can be a laborious task, but the odds are that you will find at least a couple of loose wires in the panel. If the wires are heavier gauge and jumpered, the copper tends to relax after the initial termination, and MANY wires will pull out. In addition, some electricians use an undersized screwdriver to do their terminations, and this becomes obvious when every other wire suddenly starts coming loose. (As a side note, most electricians get embarrassed when the engineer starts finding loose wires, and they will start torquing the wires hard from that point forward—which is a
    win-win for all!)
  • First check the power supply wiring, then gradually power up the panel. Always perform a resistance check before energizing a breaker or inserting a fuse. Once the 120VAC power is fully energized, test and power up the 24VDC system. If the power feeds are jumpered, be sure to check that power is available along the whole strip. A single loose jumper will keep half of the feeds from getting power.
  • Energize and establish communications. If fiber transducers are used, put them in the network and use fiber jumpers to simulate the field fiber cable. Try to include every component in the system so that its functionality can be proven.
  • Test each I/O point with real-world signals that actually draw some current. (A high resistance termination on a digital output will pass a voltage check but will fail under load.) Use a 2W/4W analog simulator to test each analog loop. Use a small relay to test digital outputs. Feed voltage into every digital point. Do not rely on the indicator lights on the card. Some failures will allow the card I/O to work and the lights to function, but the information still fails to get transferred to the software.
  • If the system has redundant power feeds (or 24VDC power supplies), test them individually and then test them with both sides energized. Trip each feed and make sure the system continues to function and the appropriate alarms sound.
  • With as many digital and analog outputs turned on as possible, trip the main power feed and then restore it. This tests the current inrush of the system. A poorly designed panel may trip the main breaker under this condition.
  • Once the panel is fully tested, REMOVE ALL F– USES (or at least those feeding the power supplies) BEFORE SHIPPING THE PANEL TO THE SITE! (See Watch-Outs below.)

Watch-Outs: Do not make the mistake of shipping a panel to the plant site with the fuses still in it. The electricians will hook up the power and will want to “smoke test” the system to make sure it works. If the power is hooked up incorrectly, they WILL smoke test the system, destroy several components, and then deny it ever happened. Or they will power up the system and proceed to blow every single I/O fuse as they pull and connect wires in the field. As a minimum, pull the fuses that feed the main power supplies and I/O power. If power is put on the system, it cannot get far enough to do much damage.

Exceptions: In some retrofit projects, there are existing cabinets that must be gutted and have the internals refitted with the new system. In this case, prefab the panels as much as possible, and size them to fit inside the existing cabinets. This will still allow the team to test the panels thoroughly and the change over at start-up should proceed faster because the team is just “ripping and replacing” the internals rather than trying to install panel components during the shutdown. Be sure to measure the internal dimensions carefully, including the size of the doors. Many replacement panels have been fabricated to the wrong dimensions and would not fit in the cabinet. Still others have been fabricated to the correct dimensions, but the team failed to realize that the DOOR OPENING was smaller so they could not get the new panel through the door!

Insight: In a retrofit project, the cabinet design and the logistics of changing it out will have a huge impact on the length of shutdown required. While there is a great desire to re-use cabinet designs, realize that one size rarely fits all in system retrofits. In many cases, the cabinets and/or panels must be specially designed to accommodate the shutdown schedule dictated by the plant.

Rule of Thumb: Always take the time to thoroughly test control panels prior to shipment from the fabricator. A checkout should include pulling on each wire, performing “real world” tests of the I/O, and load testing the power supplies to make sure that everything is ready for installation. Then remove the major fuses and ship the units to the installation team.

Print Friendly, PDF & Email

, , , , , , , ,

Pin It on Pinterest

Shares
Share This

Share This

Share this ISA post with your friends!