Watch for disruptions to systems that could lead to glitches or failures.
Moving or reconfiguring a production line can disrupt a complex and finely tuned system. Electrical distribution systems, variable frequency drives (VFDs), programmable logic controllers (PLCs), lighting, communication circuitry, controls, emergency stop systems, and more are susceptible to unanticipated changes ranging from glitches to outright failures.
Problems at the unit level may cause failures at the system level, such as unexpected tripping of conveyor drive systems, communication system failures, overheated equipment, an unsafe electrical system, and costly downtime.
Problems arising from a move may not be immediately visible when you return a line to service. In fact, symptoms of potentially serious problems may appear long after installation and setup are complete. These problems may crop up: motors are noisy or burn out prematurely; equipment shuts down for unclear reasons; sensors and detectors don’t function properly; and operator complains of ergonomic problems.
Many of the things that need to happen when you move or reconfigure a production line are obvious, but the less obvious include finding and correcting EMI problems; replacing worn-out and outdated equipment; upgrading equipment where it makes sense to do so; and ensuring motor drive systems are delivering clean power, free of harmonics, at the right voltage after the move.
Here’s a nine-step checklist that serves as a starting point to plan a production line move, keep it on track, realize the opportunities for replacements and upgrades, and help troubleshoot when the move is done.
1. Establish benchmarks for the existing production line. Take key voltage and current readings at panelboards and other supply points while the existing line is operating. After the move is complete, you can compare the pre-move to post-move readings to validate the new setup and troubleshoot if necessary. Look for any circuits at or near their limits, so you can add capacity to the new line or redesign as needed.
Even better than voltage readings, do a power quality survey for complete picture of the state of the electrical system, including any harmonics, voltage sags, and other problems. Look for existing problems in the initial power quality survey so you can correct them in the new layout.
Whether you choose key readings or the survey, be sure to look for voltage imbalances at panelboards. They can cause three-phase transformers and motors to overheat. You can use a handheld digital multimeter (DMM) or a power quality analyzer to check for variations between the phase voltages in a three-phase system. When using a DMM, any phase voltage reading that deviates by more than 1% to 2% from the average value warrants corrective action.
Power quality analyzers provide a more detailed analysis. The solution for unbalanced voltages is to distribute single-phase loads evenly across all three phases at panelboards and switchboards.
2. Review proposed electrical plans and drawings for the new production line. Are the plans the best they can be and do they meet your objectives? Ensure plans comply with electrical codes and verify the efforts of everyone involved in the project are coordinated.
3. Calculate the expected voltage drops for any circuits you are increasing in length or to which you are adding loads. Limit the voltage drop at the farthest equipment to 3%. Equipment may not operate properly below its design voltage. Computers may lock up, electronic equipment and controls may give spurious alarms or fail completely, and motors may overheat and fail well before reaching their expected 20-year lifespan.
If a branch circuit may has more than the recommended 3% voltage drop, consider increasing the size of the conductors. Although using larger wire costs more, it will be more than offset by the reduction in downtime. Upsizing conductors may require upsizing conduits. Check the Canadian Electrical Code. Limit the voltage drop for combined feeder and branch circuits to 5%.
4. Ensure you have the correct cabling between VFDs and motors. VFDs are the most common adjustable speed motor drives on plant floors. Because output is a series of sharp-edged voltage pulses (rather than the smooth sine waves of 50- or 60-hertz power), give special consideration to the length and type of cable that runs from the drive to the motor, and ensure the cabling is installed correctly.
Failure to do so can cause dangerous and destructive reflected waves in the drive cable.
Reflected waves cause higher voltages to appear at motor terminals – as high as 2,000 volts on a 480-volt motor – which is a safety hazard. They stress motor insulation, shorten motor life and can cause immediate motor failure.
VFDs may have been trouble-free but changes to the setup – especially to cabling – can introduce reflected waves. Do the following:
• Verify that manufacturers’ recommendations regarding VFD output cabling and lengths have been met.
• Use recommended cabling and add load reactors on VFD outputs as needed.
• Minimize electromagnetic interference in communications and control circuits.
• Properly ground all systems and equipment.
• Run VFD output cables and all control cables in separate conduits.
• Keep VFD cables at least a third of a metre away from shielded control circuits and a metre away from unshielded control circuits.
• VFD power and control cables that cross should do so at right angles.
5. Evaluate equipment for upgrades and replacement. New technologies may be available to improve productivity and reduce energy costs. As a rule, when capital equipment needs to be replaced, get a higher efficiency model.
Improvements that increase worker safety, comfort and the general work environment often result in higher productivity and worker satisfaction.
One of the biggest problems on automated production lines is small power glitches that damage PLCs, so consider adding PLC protection.
Adding VFDs to control centrifugal pumps and fans saves a lot of money. For example, at 9 cents per kilowatt hour, reducing the speed of a 25-horsepower motor from 1,800 rpm to 900 rpm reduces its hourly operating cost from $1.68 to $0.21, a reduction of more than 80%.
Moving a production line is a good time to upgrade the lighting system. Replacing older T-12 fluorescent fixtures and HID with newer T-8 and T-5 fluorescents reduces costs significantly. Consider change to LED lighting where appropriate.
6. After the move is complete, check all safety circuits and emergency stops. Understand and comply with the requirements of regulatory agencies, such as sounding warnings before conveyors start, having emergency stops at operator locations, and having emergency circuit resets. PLCs must de-energize outputs when an emergency stop is actuated, and motors must shut down if a PLC goes offline.
Verify that safety circuits and emergency stops are installed as specified in the electrical drawings.
Also verify correct operation of every circuit as part of the production line startup.
7. Verify grounding for safety, code compliance, and electrical noise reduction. An oscilloscope is the easiest way to detect electrical noise. Noise causes equipment to operate in an unexpected or less-than-optimal manner. For example, a VFD connected to a motor with unshielded cable can cause 80 volts or more of electrical noise to appear in nearby, unshielded communication wiring, and 10 volts or more of noise to appear in nearby shielded cables. Electrical noise creates operational problems on the plant floor, which may appear in the following ways:
• Bad communications, such as when noise affects the function of a 4-20 mA control loop signal.
• Sporadic shutdowns.
• Intermittent communications.
• PLCs that reset in a seemingly random fashion.
• Earth ground devices tripping.
• 5-volt supply level going up and down with sensitive equipment.
8. Complete a power quality survey after installation to identify potential problems and establish benchmark recordings for the electrical maintenance program. The power quality survey gives you a complete picture of the state of the electrical system, including any harmonics, voltage sags and other problems. Benchmark readings are valuable resources for establishing or maintaining an effective predictive maintenance program.
9. Test the line for correct operation. Before resuming production, thoroughly test the line for correct operation. This is a good time to bring in line operators and get feedback. Be sure everyone who was involved with the line move is present when you restart the line so they can assist with troubleshooting and final adjustments.
A checklist provides a map and an agreement about what needs to be done, and a reminder to check that all tasks are completed. This will go a long way to ensuring your new production line is safe and operating correctly when it goes back online.
This is an edited version of an article provided by Fluke Electronics Canada LP, a manufacturer of electronic test tools and software, based in Mississauga, Ont.