February 1996 Volume 2 Issue 2
DO YOU HAVE ELECTRICAL QUESTIONS
The Energy and Minerals Section has test equipment that allows us to do out-of-the-ordinary electrical measuring and monitoring. We can, for instance, visit Island plants and
· measure and record three-phase voltage (V), current (A), power (kW), kilovolt-amps (kVA), and power factor (%) over a 24-hour period using a recording wattmeter;
· create a 24-hour electrical demand profile of either the plant-as-a-whole or a particular piece of equipment;
· create a 24-hour power factor profile of either the plant-as-a-whole or a particular piece of equipment;
· monitor the electrical service entrance or individual plant power circuits for voltage transients or power-frequency harmonics.
These are our measurement capabilities; how can we use them to benefit you? There are two types of circumstances where this kind of metering could be valuable to your operation, and we stand ready to help in both of them:
1. When you are trying to understand how your plant uses electricity.
2. When you are trying to track down the cause of an electrical problem.
UNDERSTANDING HOW YOUR PLANT USES ELECTRICITY
With the light-weight, portable test equipment we have available, it is easy to come to your plant, set up the equipment, and make a 24-hour recording of volts, amps, kW, kVA, kWh, and power factor. As shown below, the measuring equipment is connected directly to the three phases to monitor voltage, and magnetically-coupled probes are clipped onto the phase wires to monitor current.
If the point of attachment is the electrical service entrance, the entire plant becomes the LOAD, and the electrical behaviour of the plant-as-a-whole is recorded. Sometimes, however, measuring whole-plant electrical use does not give a sufficiently detailed picture. Particularly in larger facilities it may be necessary to monitor individual pieces of high-demand equipment for 24-hour periods, and create demand profiles for each of them.
Although we probably visited your facility some time ago and took measurements of this kind, it may make sense to ask us to return. Perhaps:
· You’ve made additions to your plant, or changes within it, and want the new situation to be assessed.
· Your facility’s electrical demand or consumption has just gone up and the reason isn’t clear.
are thinking of implementing one or more retrofit measures to reduce your
plant’s electricity bill, but before you can do that you need to have some
assumptions verified or some missing information supplied.
If it will benefit you, we would be pleased to bring our measuring equipment back to your facility, attach it, and help you analyze the data that it collects.
TRACKING DOWN THE CAUSE OF AN ELECTRICAL PROBLEM
Many types of electrical problems can be diagnosed with ordinary voltmeters and clip-on ammeters, or by a “recording wattmeter” that monitors Volts, Amps, kW, kVA, and power factor over a period of time. There are, however, other kinds of problems that this traditional measuring equipment cannot help solve. These are problems connected with power quality, such as the presence of power frequency harmonics, and the presence of transient voltage spikes.
With the more widespread use of solid-state industrial equipment such as variable speed motor drives, production controllers, and computers, power quality has become an increasing concern. Fluorescent and High-Intensity Discharge (HID) lighting systems, arc welders, variable-speed-drive motor controllers, computer power supplies, and some other types of power-consuming equipment all introduce power-frequency harmonics. Continuous high-amplitude harmonics can cause power factor correction capacitors to overheat or fail, and harmonics can raise havoc with the functioning of sensitive electronic equipment such as production controllers, computers, and monitoring equipment.
High-voltage spikes are the other major power-quality problem. Insulation breakdown and short circuits within the electric utility’s distribution system sometimes cause short-duration voltage spikes thousands of volts in amplitude to appear on the low voltage lines entering a plant. Smaller amplitude (but also troublesome) voltage transients can be generated within a plant. This can happen, for example, when high-power equipment cycles on and off. Voltage spikes are a problem because they can damage the solid-state devices in computer power supplies, variable-speed motor drives, and other electronic equipment. And like harmonics, even when they don’t actually destroy anything, voltage spikes sometimes cause equipment malfunctions.
These new problems are often difficult to analyze and solve. For one thing, the conditions that cause them are often of short duration. A semiconductor-damaging voltage spike may come only rarely, and last only milliseconds. Fortunately, our monitoring equipment can record these short-duration spikes, and can measure the amplitude of power-line harmonics.
GIVE US A CALL
If you think our electrical monitoring and measuring equipment might help you
· better understand how your plant uses electricity, or
· track down the cause of a stubborn electrical problem,
call Mike Proud or Ron Estabrooks at 368-5010 (toll free).