Unexplained Downtime? It Could Be PQ Issues.

| Tom Hopkins

PQ Issues

Phantom Issues with Your Machines?

Are you having intermittent issues with your machines? Are things shutting down for no apparent reason, or strange glitches popping up at seemingly random times? You could be having PQ issues (power quality issues).

How is Your Power Quality?

My first question is always, “Have you tested your power quality?” Yup, power quality can have a big impact on reliability, and your equipment may be more sensitive than you may realize.

Let’s look at various sources of PQ issues.

Incoming from the Utility

Most people say, “No way! The utility gives us high uptime, and we don’t have any issues.” Yes, the utility gives you high uptime, but are you SURE about the quality of the power supplied?

Let’s talk real-world events. Consider a squirrel becoming a conductor to ground on a high voltage line 30 miles away from you or a car hitting a utility pole. We are all familiar that these events happen, but I bet you didn’t know that a short duration fault will send a ripple through the power distribution system for a long distance. Look at the below diagram showing what happens on the grid when a fault occurs. It covers a longer range than most people realize. 

PQ Issues Fault

The EPRI (Electrical Power Research Institute) did a study that monitored 300 sites for over two years. They found 96% of all PQ issues were voltage sags less than two seconds, and the majority of those were under 200 milliseconds. You certainly won’t detect these events without measuring equipment. But your power supplies, relays, and controllers may react adversely to a deep quick voltage sag. Switched-mode power supplies are especially sensitive to quick voltage changes. Have you noticed power supplies popping off? Relays and other controls may drop out due to sags, causing your machine to have phantom stoppages or worse.

It is believed that voltage sags have the greatest impact on productivity at automated sites and are responsible for 10-30% of unplanned downtime each year.

Internally Generated PQ issues

Just a few items in your plant that could be creating PQ issues:

  • Motors switching on/off causing voltage sags and surges. 
  • Motor drives causing noise and harmonics. 
    • Are your drives grounded correctly, or is that noise going through the plant wiring?
  • Operation of fuses and circuit protection.
  • Operation of welders.
  • Power factor correction capacitor banks.

Let Me Tell You a Story

I got a call from a good customer complaining about inductive proximities faulting in a location. Initially, their response was, “These proxes you are selling me are cheap and unreliable.” The issue was intermittent, causing headaches. 

As they described the issue to me and the flashing pattern on the proximity output LED, I could tell the proximity was responding to a surge and protecting itself. So, we placed a surge suppressor in the trouble location. PQ issues solved—the proximities didn’t fault anymore. What we came to realize was another piece of equipment on the same power branch was creating spikes.

This type of thing is more common than you might expect. Back in the day, components were more rugged and could handle PQ issues. Now circuit boards are a lot smaller and the gap between transistors is minuscule (i.e., it doesn’t take much to fry a circuit board). 

What Can You Do?

How can you solve a problem if you cannot see what is causing it? Let’s figure it out, and if it’s PQ issues, there are products to mitigate them.

STEP 1 Diagnosis

Let’s see what tools you have available to diagnose your problems.

i-Sense Voltage MonitorFor Utility Voltage Sags

Rockwell Automation® sells a product called an i-Sense® voltage monitor. This product will highlight and timestamp events coming into your plant. You can then correlate to downtime. Additionally, the system will compare to other meters on the grid to confirm there was a grid event. 

PQ Issues Start and End of Power Quality Event

For Internally Created PQ Issues

PowerMonitor 5000The PowerMonitor™ 5000 unit has three available versions for identifying everything from sags and surges to harmonics and transients. Some versions will even give you a waveform capture. And this device can be connected to your RSLogix™ software-based PLC controller to trend, time stamp, and more. 

Step 2 – Mitigation

Once you know what you have going on, there are many products to combat PQ issues, including:

  1. Voltage sags
    1. 1608 DySC Voltage Sag ProtectorA dynamic sag corrector (e.g., 1608 DySC® voltage sag protector) can be used for AC power. There are large versions to handle a whole section of the plant or small ones for just a control cabinet.
  2. Uninterruptable power supplies can be battery-operated or capacitor-based. 
    1. AC versions  
    2. DC versions – battery or capacitor-based sag correctors (called buffer modules)
  3. Voltage surges and noise. Various duty levels for both AC or DC.

Give us a call to help navigate which is best for your application. Contact us today!