Use these steps as a starting point when troubleshooting power quality problems. By organizing your approach, you'll ensure an effective investigation, proper data collection, accurate conclusions, and cost-effective recommendations.
Like all electrical and/or electronic equipment troubleshooting, site surveys rely on state-of-the-art diagnostic test equipment and the intuitive nature of the person using this equipment. Although most of us would like to think we are fully capable of doing such work, varying levels of expertise may prevent us from successfully resolving a power quality issue.
Whether you're a beginner or a seasoned veteran, you'll need to use a systematic approach when investigating power quality problems on a premises wiring system. This approach involves four key chronological steps.
Step 1: Receive the complaint. Before hooking up diagnostic meters, you must first define the real or perceived problem (usually done with a "walk-through"). The walk-through gathers basic facts by asking equipment operators or other personnel questions about any equipment operation and malfunction. Some questions you can ask are: * When did the problem start? * What type of equipment is experiencing problems, and what is the sensitivity of the device? (This will become important as you evaluate the results of on-site testing and make recommendations.) * What types of equipment malfunctions are occurring? * When do the problems occur? * What are the possible problem sources at the site, and what is their proximity to the affected equipment? * Has the addition of a power conditioning device reduced or eliminated the problem, or is it worse? * Are there any recent changes to the premises wiring?
You can gain further insight into the problem by gathering information from other people or groups directly, or indirectly, involved with the facility operation. They may include the equipment manufacturer, local electric or telephone utility, a qualified electrical maintenance person, and the equipment operator.
Step 2: Identify the power quality concern. After you've done the initial questioning, review the information to find what course of action best serves the site's needs.
The most difficult part of a power site survey is deciding where to begin. You can use varying levels of a site survey to investigate a power quality problem. Deciding which avenue to choose depends on the desired information and possible cost limitations. Most surveys will fall into one of the following categories:
Level 1 survey: This covers the visual inspection, testing, and analysis of the AC premises wiring and grounding system supplying the affected equipment. Remember: Unless the quality of the wiring and grounding system is tested and verified, the data produced by voltage quality monitors can be misleading.
Level 2 survey: This includes a Level 1 survey plus monitoring the applied AC voltage and load current of affected equipment. Voltage quality investigations usually take the shape of short- or long-term power line monitoring.
Level 3 survey: This consists of the Level 1 and 2 surveys plus monitoring environmental site conditions. A detailed look at possible radio frequency interference (RFI), electromagnetic interference (EMI), electrostatic discharge (ESD), and improper levels of temperature/humidity is more of a necessity where certain devices are sensitive to their surrounding environments.
Step 3: Organize and perform the site analysis. Organization is the key ingredient to a successful investigation. You'll need a large amount of advance preparation prior to doing a power site survey. Purchasing diagnostic equipment, attending safety training, and applying proper test methods are just a few items you must consider.
Here are some areas of concern you need to address prior to investigating.
Documentation: Make sure you provide a space in your documentation for each basic measurement taken. This allows you to use the documentation as log sheets to track any electrical expansion of distribution panels, transformers, and receptacles over an extended time period.
Test equipment: You may need the following diagnostic equipment during a survey: true rms-sensing voltmeter; true rms-sensing clamp-on ammeter; harmonics analyzer; power line monitor; oscilloscope with line viewer; earth ground resistance tester; and ground impedance tester.
Additional equipment may include devices providing accurate measurement of temperature and humidity, RFI, EMI, and power system demand (e.g., kVA, kW, etc.).
Type of tests to perform: The success of your approach to performing a survey (and prompt location of the problem's cause) usually depends on several factors: Your experience and intuition, and the type of industry, environment, and perceived problem.
Your investigation of power quality problems should include the grounding electrode system, electrical distribution panels, transformers, and receptacles/equipment locations. Here are just some of the tests and inspections you can do. * Grounding electrode (earthing) systems: visual inspection of connections and electrodes for corrosion; check tightness of connections; current measurement of grounding electrode conductors; earth ground resistance testing; and two-point bond testing. * Electrical panels: visual investigation; check tightness of connections; true rms voltage measurements; current measurements; ground and neutral impedance measurements; electrical noise measurements; voltage quality monitoring; and harmonic measurements. * Transformers: visual investigation; check tightness of connections; true rms voltage measurements; current measurements; voltage quality line monitoring; and harmonic measurements. * Receptacles: visual investigation; true rms voltage measurements; verify correct wiring; test for improper neutral-ground bond; test for properly installed isolated ground; and ground and neutral impedance measurement. * Electrical noise measurements.
Step 4: Evaluate results and provide cost-effective solutions. Brief the end-user on the results upon completion of the survey. This will give you the chance to tell your customer about potential safety hazards, suspected problem areas, and possible recommendations.
Be careful with your recommendations; make sure you follow these rules: * Weigh the gathered data and possible solutions with the needs and tolerances of the affected equipment. Many power quality investigators have found that offering general recommendations to particular problems came back to haunt them. One example of this is the general practice of recommending an IG wiring system to counter a perceived electrical noise problem affecting computer equipment. Electrical noise on a grounding system may, in fact, be the result of shared power distribution with non-sensitive loads, the length of branch circuits, or improperly wired outlets -none of which will be corrected by an isolated ground. * If you can, provide your client with more than one sensible solution to the problem. Remember, some solutions may have a higher initial cost but result in a long-term benefit. * Urge the resolution of any wiring and grounding deficiencies before applying power conditioning equipment. * Keep in mind you may have to provide some type of simulation for harmonics or transient analysis.
The most effective way to find power quality problems related to the wiring and grounding system may be through visual inspection. Improper neutral-ground bonds in branch circuit panelboards, incorrectly installed IG systems, overcrowded branch circuits, and poorly maintained earthing systems are just some of the conditions you can find if you're a trained observer. More importantly, you may find unsafe conditions for personnel and measurement equipment that you can correct.
Your best bet is to follow common sense rules. Most surveys that fail to produce acceptable results are due to not following one or more of the items below. * Safety first. Make sure you wear safety gloves and glasses, use your test equipment properly for the test being performed, and secure your test equipment if left unattended. * Don't assume anything. * Step back and take a look if things don't look right.