Condition-based maintenance keeps a facility up and running

On Jul 5, 2023

Figure 1: Performing a predictive/preventive insulation test on a transformer. Courtesy: Megger

What if there was a way to protect facility assets and ensure little to no downtime of plant machinery?

Learning Objectives
• Explore what condition-based maintenance is and how it works with your equipment maintenance strategy.
• Gain a broader understanding of the different ways data is collected through a condition-based maintenance program depending on what type of machinery you are monitoring.
• Learn how condition-based maintenance not only decreases downtime, but also saves your facility time & money.

Condition-based maintenance insights

Condition-based maintenance lowers maintenance costs and decreases downtime of a manufacturing plant.
Selecting the correct equipment can ease the challenges of condition-based maintenance.

No matter the industry, when it comes to equipment and machinery, the goal is to keep it up and running with little to no downtime. When equipment fails, so does your production and ultimately your bottom line. Preventive maintenance, while good, isn’t always good enough.

Maintenance needs are predicted in advance and maximum downtime of equipment can be reduced, but oftentimes equipment that is on a scheduled maintenance routine is getting “maintained” when it doesn’t need to be. This is a waste of company time and resources. In truth, preventive maintenance has companies overspending on maintenance when they don’t need to. What if there was a way to protect assets and ensure little to no downtime with another maintenance strategy? What if time and money wasn’t being wasted? This is an opportunity for condition-based maintenance (CBM).

Figure 2: Heat-detecting camera pinpoints hot spots for impending breakdown. Courtesy: Megger

What is condition-based maintenance?

CBM is a maintenance strategy that monitors the real-time condition of an asset to determine what maintenance needs to be performed. Unlike preventive maintenance, which is based on some sort of schedule, CBM dictates that maintenance only be performed when real-time indicators set up on the asset being monitored show irregularities or signs of decreasing performance. Its goal is to continuously monitor equipment to spot impending failure. By doing this, maintenance teams are given enough time to react before failure occurs.

Because CBM is done by taking real-time measurements, maintenance is only done as needed while machinery is running. Because of this, there are fewer unplanned downtime events, which is extremely beneficial for production efficiency and resources.

Data can be collected in several different ways through a CBM program depending on what type of machinery being monitored. Some include vibration analysis, infrared thermography, ultrasonic analysis, oil analysis, electrical analysis and pressure analysis. By collecting information this way, it is remarkably precise, indicating not just that the machine is failing, but also exactly what is wrong with the asset by identifying the root cause. Electrical analysis is key in condition-based maintenance.

Electrical analysis in CBM

Electrical analysis is extremely important when it comes to large industrial machinery, like those found in petrochemical, mining and pulp and paper. Interruptions in production or reduction in output are extremely costly — for example, losing barrels of oil or tons of minerals in the petrochemical industry. CBM isn’t just to head off breakdown in machinery at the pass. It is also used to slow down loss of capacity.

By constantly monitoring the electrical condition of critical equipment, engineers and plant managers can hold production losses to a minimum or even to zero. In addition, conditions that could lead to catastrophic failure later can be spotted early and corrected with minimal or no loss of production.

An example would be if an unrecognized moisture source in a nearby industrial process causes a motor to fail. If a CBM program is in place, someone could recognize that insulation values were dropping at a rate beyond normal wear. This would allow them the time to look for the source of the problem and remedy it before it is too late.

Insulation resistance & ground testing

Monitoring for insulation resistance is paramount in CBM and is very easy to test. It monitors the condition of equipment in that it can alert the tester to water ingress, contamination and physical breakdown from things like vibration & electrical disturbances, as well as general long-term wear.

With a good quality tester, test results are easy to interpret because the range of measurement is vast — from Tera-Ohms continuously down to Megaohms. The person reading the measurement has a window that can be easily checked at any time and provide a look at where the equipment is on its life cycle. This allows for an early warning of anything happening beyond normal wear — like excess moisture ingress.

Figure 3: Testing wind farm collector transformer with Megger TTRU3. Courtesy: Megger

Ground testing is easily overlooked by many because the grounding system seems to be a passive part of the electrical plant, unlike motors and lights. However, a corroding or eroding ground can affect everyday operation in a plant. Failure to ground can cause noise interference and lightning strikes. So, ground testing needs to be a part of a condition-based maintenance plan.

For ground testing a four-terminal tester is needed because there is a good chance a resistivity test may be necessary at some point in order to install another ground or to improve what is already in place. Generally speaking, a clamp-on tester for continuous testing is not the best option; however, it may be useful to have on hand to use for a quick backup test.

A quick and easy way to regularly check for different kinds of problems on an electrical system is using a thermal camera. They are particularly good for production lines because the operator can find hot spots where some flaw or problem is interfering with current flow. Once found and isolated, the issue can be readily corrected before it interferes with production or ignites a fire.

Transformer testing

The performance of a transformer is rated by and critically dependent on the ratio of turns in the primary and secondary. Electrical stresses cause insulation breakdown, possibly no more than a tiny pinhole, where current can short across from one turn to an adjacent turn. This effectively reduces two turns to one and the cumulative effect can significantly change the transformer’s rating.
Industry standard is tight; no more than 0.1% change from rated is allowed before the transformer should be serviced. In this same area are winding resistance testers. These are applied to both transformers and motors. Winding resistance changes along with turns ratio. An ordinary ohmmeter is not useful because it lacks the power to readily overcome the capacitance and inductance of large windings. A dedicated winding resistance tester is required to produce the power necessary to test quickly and efficiently.

Figure 4: Checking for partial discharge on medium- & high-voltage equipment provides an early warning of future breakdown. Courtesy: Megger

Partial discharge is also a concern, especially in transformers. Deterioration of bushings and other components can cause electrical leakage to the atmosphere. Partial discharge testers are specifically designed to meet this challenge, identify and localize partial discharge. These can be used in CBM.

CBM is well worth the time, effort and money spent in implementing it. It helps to improve system reliability as well as increases productivity. CBM lowers maintenance costs and decreases downtime of a plant. It is a much quicker and more efficient way to diagnose problems within a system.

(Contributed by Megger India Pvt. Ltd.)

Website: www.megger.com/in