15 Feb Three Levels of a PQ/Grounding/Bonding Investigation – Part 1 (Overview)
Over the next few months, iGround will be presenting a series of blogs to address the methods of approaching the various levels of Power Quality site surveys, depending on the location to be investigated.
This installment focuses on a high-level view regarding the three levels of a survey as you begin to troubleshoot.
Let me begin by stating that every power quality site survey is different. There are a variety of reasons as to why and when we begin the task of an electrical system investigation. Sometimes, it’s to find a known problem. In other cases, it may be a suspicion that a problem exists. Some of us utilize a site survey to confirm NO problem exists!
As an instructor, I’ve struggled with the best methods to teach people how to do a site survey. I find it’s better to impart the knowledge of how I approach one. To those just beginning this path of their career, PQ/Grounding/Bonding site surveys can be very intimidating, especially with large sites; campus or high-rise building, for example. But the best way to look at surveys, from an overview, is to see how they’re broken down…and why.
Level 1 Survey (Visual, Mechanical, Wiring, & Grounding/Bonding)
A Level 1 survey covers the visual inspection, mechanical inspection, testing, and analysis of the ac premises wiring and grounding system that is supplying the equipment.
Figure 1 illustrates where the Level 1 surveys would take place, given the highlighted areas. This may change depending on the type of investigation you are doing. For example, if you are doing a Quality Assurance (QA) inspection, you will likely look at ALL areas within the electrical distribution. However, if you are troubleshooting at an equipment location, you should rarely have to go further than the secondary side of a transformer.
The concept of verifying proper wiring and grounding systems has been labored upon many times. I can sound like a broken record to some people on the importance of this. But just last week, I encountered yet another example of where an investigative team ignored the contribution of wiring and grounding to PQ disturbances, costing their customers value time and money. Power quality problems caused by improper wiring and grounding can be misdiagnosed, especially if the wiring condition problem is masking itself as a voltage quality condition.
In all likelihood, unless the quality of the wiring and grounding systems is tested and verified, the data produced by voltage quality monitors (or any other meter for that matter) will be useless. If possible, all premises wiring and grounding deficiencies should be identified and corrected BEFORE engaging in Level 2 or 3 surveys.
Key Point: In 95% of cases, a Level 1 survey locates and corrects the problem.
If a Level 1 survey does not readily identify the cause, the investigation progresses to a Level 2 survey or Level 3 survey, if needed.
Level 2 Surveys (Voltage Quality)
This survey level focuses on the monitoring of the ac applied voltage, power system transients, and load current for the electrical distribution. Figure 2 shows where typical VQ investigations will be concentrated (blue dashed boxes).
Voltage quality problems can be difficult to pinpoint and may require different levels of power line monitoring. Thus, it requires a lot of patience! Not my best attribute…but it does pay off eventually.
The investigations take the shape of either short-term or long-term power line monitoring. Short-term monitoring may last from one to seven days (complete business cycle). This type of monitoring is usually done at the facility’s electrical service entrance to determine the electric utility’s contribution (if any) to the voltage quality problem.
If you have only one power line monitor, it is recommended that voltage quality monitoring be done at the equipment location, FIRST. This will give an investigator a better knowledge of the quality of voltage delivered to the equipment. Unless the disturbance is readily apparent through the short-term monitoring, it may be necessary for a more extensive analysis of the power system, where the long-term monitoring can last for several weeks or months.
Key Point: <5% of all problems are found/corrected with a Level 2 survey.
Level 3 Surveys (Environmental)
This survey consists of monitoring the environmental site parameters. Figure 3 is straightforward…all environment monitoring will be done at the equipment location of the equipment that is being directly affected, especially if it is the ONLY device being impacted. Power quality investigations rarely get to the Level 3 but, if it does, a new world of complexity and intrigue awaits. I liken Level 3 surveys to carnival funhouses…a series of illusions where nothing is ever what it seems and, in the end, hardly makes sense.
The detailed evaluation of the following may be necessary to determine an affected device’s sensitivity to its environment:
- Electromagnetic interference (EMI), including Radio Frequency Interference (RFI).
- Electrostatic discharge (ESD).
- Thermograph signatures.
- Psychrometric evaluation (temperature/humidity).
Key Point: <0.4% of all problems will be found/corrected via a Level 3 survey.
And, because of the ‘key point’ above, there are only three things I can write here as words of advice:
- Know the tolerances of your equipment via operating specifications. This will help with voltage quality, for sure, but the only way you’ll know ‘operating temperature/humidity’, electromagnetic compatibility requirements, and such will be to review them in the spec’s.
- If you’ve reached a Level 3 survey in order to troubleshoot (with the exception of temperature/humidity)…you’ve overlooked something on the Level 1 or 2 survey.
- Even if you FIND a problem on a Level 3 survey, it is likely that you’ll have to just live with it. Very often, the environment is the last thing we’d have the ability (or money) to change.
Viewing surveys with the three different levels is a good starting point. And, knowing WHERE those surveys will take place is just as important.
In our next blog, I’ll provide insight on the kind of checklists I give customers when they suspect a power quality issue. Even if they don’t fill them out, they’re good discussion points on how/where a company like iGround approaches it. Our upcoming blogs will be addressing each of the areas (panelboards, grounding electrode systems, transformers, telecommunications systems, data centers, and receptacles) with their own checklists and measurements for Levels 1-3 surveys.