Knowledge is power. But what do you really know about your power? Can you take action on useful information, or do you merely have a flood of data?
Today's nonlinear loads, uptime demands, and power quality commitments all conspire to create a demanding environment. In this environment, operating without useful information on the condition of your power is like driving the Indy 500 with plywood for a windshield. Fortunately, putting a power monitoring and control package into place is like replacing that plywood with a real windshield. If you do it right, you can see exactly where you're going.
Your power monitoring system must address your individual power subsystems, as well as the system as a whole. Fortunately, advances in digital technology allow you to tailor power monitoring in ways that empower you-instead of drowning you in rivers of data.
Information or data? New features abound in power monitors. Many are useful, but beware of the "feature race." If you have doubts about rapid obsolescence, look at the computer industry. The "improve-by-adding-features" approach leads to some problems:
Disjointed systems with incompatible features;
Groups of devices that cannot communicate with each other; and
Much data requiring extensive processing.
Imagine driving a car with a voice that constantly says: "Your oil pressure is fine." That's useful, but wouldn't you rather know only when your oil pressure is not fine? The same concept applies to power monitoring. You need useful information, not a flood of useless data.
Suppose you want 3-phase voltage, current (individual and total), power factor (PF), and breaker status from 50 metering locations. A traditional SCADA system using simple transducers may obtain 10 data each second from every metering point. For this to happen, the communications channel and central computer must each manage 500 data per second. This translates into 43 million data per day. You end up with tons of mostly useless data. Sure, the meters are inexpensive, but you waste your investment in equipment and operations. You spend most of your resources on non-value-added activity.
Intelligent electronic devices (IEDs) extract good information early in the monitoring process, thus maximizing the system's value. An IED can monitor critical quantities, interpret data in the field, and send minimum data containing maximum information to the host computer (See Fig. 1, on page 42, original article). Don't record all aspects of every parameter. In any but the smallest power monitoring systems, this approach will fail. It relies on a huge amount of data. You must communicate, store, and filter your data for the possibility of finding a few drops of information. It's better to store and forward only the data you need.
Object-oriented metering. As Bill Gates noted in the book "The Road Ahead," computer makers once built each machine for a specific purpose. If you wanted to do something else, you had to build a new machine. That's no longer the case today. The computer is successful as a tool, largely because it works with a wide range of objects we can link together to form a system. Each object gives predictable behavior; thus, you can use these objects as building blocks to accomplish many purposes.
This is the basic strength of object-oriented technology. This approach allows you to keep from getting on the "out-with-the-old, in-with-the-new" treadmill. If you've had to retrofit non-object-oriented systems to accommodate new information, you probably understand how expensive this can be.
An object-oriented system could have simple modules that calculate the minimum/maximum voltage level on a feeder. Or, it could include complex modules that determine the positive sequence components of the current flowing through a motor load.
This modularity is innovative. Suppose you need to record only the harmonic distortion at a distribution transformer under high load conditions. You can use just the modules that give you the third, fifth, and seventh harmonic currents when they exceed a preset value (See Fig. 2, original article). You can add a module to transfer some load and send an alarm once you pass a heat threshold. You can add another module to capture a waveform sample. With this approach, you receive important information with no unnecessary data. And you can reconfigure the modules when you need to, instead of ripping out existing hardware and installing new. If you're thinking: "This sounds like the move from hard-wired relays to PLCs," you understand a major advantage of object-oriented systems.
Integrating objects over a computer network. If you pan for gold in that river of data and find flecks in the sand, how do you manage the information efficiently? Doing so requires the right kind of software and communications infrastructure. Take the World Wide Web, for example. The Web makes a wide range of information available to many users with a common interface: Web pages. A few vendors use fully networkable software. Such software makes it possible to obtain, store, and share power system information with a wide audience using a simple, flexible, user interface. The result is a system you can expand and enhance as needed. Then you can devote your energies to improving your power infrastructure and your career.
Sidebar: Do You Need a Permanent Power Monitoring System?
If you answer "yes" to any of these questions, you'd probably benefit from a permanent power monitoring system.
- Are you paying a demand penalty on your electricity bill?
Look for a "ratcheting clause" that may affect your demand penalty. Such a clause means even if you run some equipment for only half an hour, you may pay the penalty every month for a year! Power monitoring lets you know your load profile during a typical day, so you can move your energy-intensive activities to off-peak periods.
- Are you scheduling maintenance per manufacturer's specs?
You may be overspending on equipment maintenance. You may be missing an opportunity to avoid costly downtime on equipment suffering from the stress that often results from poor power quality.
- Are you relying on protection devices for power information?
Don't assume they will give you the additional power quality information and logging you need for system planning, cost control, and troubleshooting. Digital trip units and "smart breakers" can give a rough indication of your consumption patterns. However, they may not be at the right location for good cost allocation, and they may use lower accuracy, protection-class current transformers (CTs).
- Are you in a service area with severe weather or variations in supply, or at a facility with on-site generation?
Portable test equipment rarely helps you find the cause of equipment failure due to a random event, like a lightning strike. A power monitoring system gives you the "flight recorder" information you need to find the cause of downtime so you can make sure it doesn't happen again.
- Are you in a jurisdiction undergoing deregulation?
The more information you have about your consumption trends and power quality requirements, the better the supply agreement you'll be able to negotiate. Without this knowledge, you'll probably end up paying too much.
If you are in any one of the following situations, you may not need a permanent system:
Your concerns are temporary; for example, your lease is about to run out, and your business will relocate soon.
You contract with an outside service that pays penalties to you for downtime and equipment damage.
Your production equipment is inexpensive, and your schedule allows you to make up downtime rapidly.
Unexpected loss of power or unexpected power quality events will not result in damage to equipment or delays in product delivery.
Your facility does not use any switching power supplies, SCRs, motors, or other equipment that present power quality concerns.