Power Quality Monitoring

Selecting and configuring a power quality monitoring system requires energy but offers significant payback.

Power Quality Monitoring
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Power quality monitoring instrumentation can be compared to a home security system. If a home doesn't have one, consequences may never be suffered. However, if a situation does occur and there's no alarm system in place, the consequences could be grave.
Power quality monitoring is no different. If a business has it but never experiences a power shortage or sag, there is still the peace of mind that comes with knowing the operation is protected. However, in the event that a power event does occur, the investment made in the instrumentation can certainly be justified by the damage it may have prevented. Given that the cost of power quality monitoring devices has decreased significantly over the past decade, the investment has become far less severe and the return on the investment much quicker.
Modern power quality monitoring systems also provide the added benefit of simultaneously monitoring demand, energy and other parameters. For a myriad of reasons (i.e., being proactive, constant system vigilance, larger database), permanent monitoring may serve a business' purposes better than portable monitoring. The following guidelines should be followed when structuring a permanently installed power monitoring plan.
Where to monitor
The first, and perhaps most crucial step, is deciding where and what to monitor. One of the most popular places is the utility service entrance. Typically, the utility company is not fully aware of the quality of power that they are providing. Monitoring the supply they're feeding is an effective way to have a figurative leg up on the utilities. In fact, customers have often been able to prove utility failures and recoup losses to equipment and operational downtime thanks to a carefully designed monitoring system.
Generators can also be monitored, as can the switches that transfer the source of power between the utility and the generator. And, in certain facilities where computer usage is particularly critical (such as data centers or banking centers), there are often Uninterruptible Power Supplies (UPS) that not only supply power to the computers and other machines, but help negate the effects of voltage fluctuations or other problems unrelated to power. The system acts as the referee and ends finger pointing by providing quantitative information as to the source of the problem. A UPS is not guaranteed against failure though, so monitoring the input and output of this device can be very beneficial. Monitoring the UPS is also a guard against non-power related situations, such as server reboots.
Next are what might be termed second -tier locations where power quality is not a burning issue, but where measuring demand and energy might be sensible or is important enough to require monitoring.
Selection criteria
In order to choose an appropriate power quality monitoring system, there are a number of factors to consider. Naturally, compliance with the latest standards is a fundamental concern, with the most highly recognized standards being IEC 61000-4-30 and, domestically, IEEE 1559. Although not required in the US, Class A compliance with IEC 61000-4-30 indicates the system provides reliable and repeatable measurements that can be trusted.
User interface
It is important that the power quality monitoring system incorporates a standard browser interface such as Netscape Navigator or Microsoft Explorer, allowing users to share power quality information without costly dedicated workstations or user licenses. This is particularly crucial should a power event occur, since quicker problem resolution will result if the building owner, electrical contractor and others have simultaneous access to this information.
Security
Let's face it; you don't usually see rogue users hacking into power quality systems. Regardless, having a password-protected system will prevent unauthorized personnel from unintentionally, or intentionally, causing problems. Therefore, it's a good idea to choose a system that supports basic security features such as a username and password to enter the system.
Connectivity issues
Permanent power quality monitoring systems can record a lot of information that can be viewed by many users. Because more than one computer is generally used to collect data remotely, the Internet is by far the most efficient and cost-effective technology available for connectivity. If a company is utilizing old serial technology such as RS-232, it is likely that they are also using older, outdated instrumentation. Ideally, a newer system will have very flexible communications and will work on both hard wired and wireless Internet systems.
Notification
Systems now are capable of providing the end-user with data automatically via e-mail, cell phone, or pager that pushes important information to the users. Users can still be proactive if they desire and manually interrogate the system, but the need to be "eternally vigilant" is essentially eliminated. What's more, notifications can be set for different sensitivity levels with the delicacy of the data dictating the notification.
Data characterization
The oscillating wave shapes that basic systems record are of little use to anyone who is not an electrical engineer. A system that can characterize data with no need for complex interpretation is a major plus, allowing users of all levels to recognize and understand a power event. This simplicity is especially integral to the concept of directivity — that is, being able to identify the exact location of a problem. For example, when a problem is detected from a device positioned at a service entrance, it is important to determine if it is an "upstream" problem, for which the utility is responsible, or a "downstream" problem, which falls on the user. This applies to other locations within the monitoring system.
IT issues
In any reasonably large organization there are information technology (IT) concerns. If you intend to access the existing network when connecting the power quality instrumentation, you should work closely with the IT department. It may be a simple act of courtesy, as the instrumentation rarely interferes with network performance, but it also ensures that the devices enjoy the network's full connectivity. It is also possible to create a separate network for the instrumentation, a much easier task than in years past, given the availability of functional and user-friendly network products sold at retail electronic outlets.
Connections
Typically, there are two types of connections to be made: one for voltage and one for current. The voltage connection is a straightforward task, requiring simple, direct-wire connections. The optimal choice to make these connections is an instrument that does not need transformers or other ancillary equipment under 600 volts.
Current connections present a bit more of a challenge, as they require a special sensor or current transformer. Further, there is an issue as to whether the connections can be made "live" (power on) or "dead" (power off). A dead connection that allows for disconnecting the wires can use much less expensive current transformers and is far less expensive, but the idiosyncrasies of the specific business may preclude this option. The cost of the connection also rises substantially when clamp-on current transformers are employed. If existing current transformers can be used in piggyback fashion, a significant savings in both time and money can be realized.
Training and post start-up
Someone has to shoulder the responsibility of ensuring that the installation was completed correctly, and train the system users. It is an installation aspect that should be addressed early — even before the system is purchased.
Once the instrumentation is installed, users must determine how they will use it. Will they employ a reactive approach, allowing them to go back in time to see if an event occurred? Or will they be more proactive, allowing them to determine if something is deteriorating and may become an issue in the future and require corrective measures?
What happens if and when there is an actual power problem? Is there in-house expertise that can diagnose the predicament? Are there measures to mitigate the problem? Knowing in advance who to call if a problem arises can greatly reduce the time to get back up and running.
Maintenance
Typically, power quality monitoring instrumentation requires no maintenance other than yearly calibration. For companies that are ISO 9001 certified, calibration of all instrumentation is a requirement; consequently, the monitoring devices will fall under that aegis. The majority of reputable instrumentation manufacturers offer such services since many businesses don't have internal resources to perform the calibration.
While calibration should certainly be on the "to do" list, it is not the most critical matter when it comes to power quality monitoring. Many of these devices are extremely accurate, but should one be a bit out of whack, performance will not be significantly impacted. However, annual calibration ensures the continual health of a system and the reliability of data.
It is evident that the selection of proper equipment for power quality monitoring requires a significant amount of time, energy and education. Yet given the ramifications of having the wrong system or no system at all, it is just as evident that it is time well spent.
Ross Ignall is Product Manager, Systems Applications, for Dranetz-BMI, manufacturer of handheld, portable and permanently installed power quality and energy management instrumentation for utility, industrial, facility and electrical contractor customers. For more information visit www.dranetz-bmi.com
In Brief
Guidelines for structuring a permanently installed power monitoring plan.
Related Products: Power Quality Monitoring Systems; Generators; Transfer Switches; Uninterruptible Power Supplies; Current Transformer.
author: By Ross Ignall, Dranetz-BMI




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