The term used in this e-book for this style of instrument is 'big gun', this being the fully fledged power quality recorder. These are the type that are coupled to appropriate test points and then record absolutely anything of value to the power quality and/or electrical engineer. In simple terms one could think of these as being a 'one-stop shop' approach to the collection, reporting, and interpretation of relevant information.
The most useful feature in these recorders is the ability to capture the waveform of the offending incident allowing you, as the user, to interpret the results. I have seen systems where the software attempts to interpret the event. Personally, I am a little wary of them especially in light of the fact that books are still being written on the subject of interpreting power quality issues. It is felt these spoon-fed results carry with them a possibility of incorrectly interpreting what happened.
Having the waveform substantiates the main reason for employing such 'big guns' being the ability to detect the direction of a disturbance. Having power quality impacted by two possible reasons i.e. did the load affect the source or vice versa, means having instrumentation that assists with determining the direction will go a long way to detecting and curing power quality issues.
There are two general categories of instruments. The first is what can be called the "power quality digital storage oscilloscope". The second is known as the "full disclosure recorder".
"There are very few PQ issues a customer may be having that a good multimeter and well-trained tech can not locate and repair"
I completely agree, except, how much longer will it take because the tech cannot see what the real issue is. And, there are certain PQ issues a multimeter just cannot display!
PQ-DSOs are, as the category suggests, instruments that are handy when trying to locate a problem while watching for it i.e. designed for "cause and effect" analysis.
Having the nature of an oscilloscope, these are fitted with 'trigger levels' that must be adjusted to each and every situation. Because of this they usually have a limited number of channels (usually a max of 4), although this in itself is not a bad thing! A display is fitted for viewing waveforms and relevant data, as well as immediate viewing of any captured transgressions. They usually have limited memory, but do allow at least a few events to be captured and stored.
With these instruments, the minimum requirement is that the type and magnitude of the fault is known. The modus operandi will be to set the instrument up to a point where normal operational deviations and/or noise don't 'trigger' an event capture, and to then wait for the abnormal one that is causing concern - this may be provoked by operating other equipment to see any effects they may be introducing.
Although many engineers are known to do this, these instruments are not designed to be adjusted to 'acceptable limits' and then, if nothing happens, call the supply 'perfect'. An oscilloscope is not operated in this way, and the same applies to a power quality oscilloscope.
These instruments are not suited to situations where there is a simple complaint of "I think it's the power". Furthermore, they are not good for comparative surveys. The pure fact they have adjustable levels make them unsuitable for this type of work. It's bad enough having to remember the settings from one survey to the next, but the instrument too can act differently from survey to survey. Trying to keep track of any changing characteristics of a site over time is nigh impossible.
These are, simply, designed to record absolutely everything. The main aim is to measure all aspects of power and its quality in one instrument. These would be employed when either doing a survey or an investigation but the actual cause or condition is unknown. It is favourable that the need to program thresholds has been removed as one would not know what to program for.
Other handy aspects (seeing as you're doing a survey or investigation) would be an ability to measure all phase and ground currents simultaneously, create trend graphs of all significant harmonics on all voltage and current channels (50th is called for in G5/4, but a personal limit is at least 65th), and, if possible, the source and load impedances in order to trace resonance.
As these recorders are designed for long-term work, they are fitted with large hard-drives (more modern ones have flash) and can be left for weeks to pickup everything of interest to the power quality investigator.
Although expensive, the return on capital outlay is quickly seen through being able to have systems operating at peak efficiency, the early detection and causes of transients, sags, surges and outages which reduce productivity, and other causes of disruption, downtime and damage. One is simultaneously able to keep watch on harmonics which arise from the use of computers, adjustable speed drives and energy saving technologies which stress conductors, capacitors, transformers and switchgear.
'Ownership' of the cause i.e. who is causing the power problem, is done quickly, correctly and completely and therefore assists in determining the best technical and economic solution. Being able to log all power measurements simultaneously and thus troubleshoot and forecast future problems is what gives this category of instruments their edge.
With such an avalanche of data it also proves pointless having a display on the recorder itself. As is, these are likely to be connected up to a customer's site and a display will often prove a tempting plaything for someone thus invalidating any recording that was done (meaning it will all need to be redone!). What I like about the split recorder-display arrangement is the ability to have the recorder in a noisy part of a site, while sitting in a nice quiet office reading the data. If this is across the globe, then even better!
© 26.01.03 / 04.11.04