By: Zack Smith & Allan Evora
ATS multi-circuit metering helps effectively manage load creep.
Emergency Power Supply Systems (EPSS) are the critical infrastructure that supports a hospital system during power outages. Regulations place a lot of emphasis on testing and maintenance of the EPSS system; however, all the maintenance in the world will do no good if the EPSS becomes overloaded.
EPSS experience load creep like normal power systems. Additionally, they run the risk of reduced capacity due to the addition of non-essential loads plugged in to designated red receptacles during extended outages. These loads may consist of diagnostic equipment or in some cases “comfort equipment” such as microwaves, heaters or coffee pots. Education and training can help ensure only approved loads are plugged in to EPSS.
Submetering is the only way to truly manage load creep and prevent EPSS overload.
You Can’t Manage What You Don’t Measure
The best way to manage your capacity is to submeter your loads. For some hospitals, this is easier said than done. While you may have submetering information at the generator switchgear or even downstream submetering at EPSS distribution switchgear, the ideal location to submeter for managing load creep is the load side of the automatic transfer switch (ATS).
Newer ATSs (installed within the last 10 years) either have digital controllers that incorporate submetering as an option, or engineers had the foresight to specify that OEMs install a separate third party submeter with the ATS. Unfortunately, older ATSs need to retrofit submeters to be able to measure the ATS load. This can be a costly proposition when considering hardware and installation costs. The combination of OSHA regulations, and the fact that the ATS is part of critical infrastructure, can make modifying equipment challenging.
A Cost-Effective Alternative to Conventional Circuit Monitoring
Within the last five years, a new type of electrical submeter has emerged and is an ideal solution for retrofitting ATSs with submetering capability. This meter type is referred to as the multi-circuit or multiple circuit meter. The concept is simple: Use one submeter CPU/circuit board to measure multiple loads.
A multi-circuit meter has only one set of inputs for a common voltage source, and multiple sets of current inputs for loads that share the common voltage source. Due to limitations on current transformer (CT: the instrument that provides current input to the meter) lead wire length, the multi-circuit meter is best suited for loads in which the CT installation locations for the loads are near one another (typically within 100 ft.).
Examples include: submetering all the circuits within a distribution panel, or all the distribution panels within an electric room, or feeder breakers on a unit substation. Since ATSs tend to be concentrated in electric rooms and typically share a common normal and emergency voltage source, they are great candidates for multi-circuit submeters.
What makes multi-circuit submetering so cost effective? The lower hardware and installation costs. Additionally, since there is only one CPU/circuit board, there is only one low-voltage communication connection.
Our general rule of thumb: whenever you have more than two loads to submeter that meet the criteria for multi-circuit metering, go with multi-circuit metering. Its costs will be lower when compared to individual meters.
Multi-Circuit Submeter Hardware
The Dent PowerScout 24 is a great example of an inexpensive yet accurate submeter that provides all the measurements necessary for monitoring ATS loads. Dent Instruments was one of the first companies to introduce the multi-circuit design.
The PowerScout 24 comes with its own enclosure, is powered via the voltage source and easily integrates to your SCADA or building automation system via Modbus or BACNet. It can measure up to 8 3-phase loads. List price for a PowerScout 24 with serial communication is $1,200. A Dent 3037 (the single circuit meter version) is $400.
Taking in to account installation costs, it is easy to see how the multi-circuit meter is a cost-effective solution when you need to meter more than two loads that meet the multi-circuit criteria. The cost savings are even more substantial as the number of loads increases. A fully provisioned PowerScout 24 will have approximately 66% lower hardware costs when compared to individual meters. Taking in to account labor savings, the total costs savings can be as much as 80-90%.
Turn That Data into Information
Submeters provide data. To make this data valuable, it needs to be turned into actionable information. To accomplish this, we recommend a few additional steps.
First, we recommend that submeter data be recorded. To be of benefit, the load profiles need to be analyzed over time using trending software within your SCADA or building automation system. If you don’t have an existing system, there are some very cost effective data logging devices that can store a large amount of interval data. This data can generally be exported and analyzed with a desktop application such as Microsoft Excel. We also recommend that the ATS switch position and generator run status also be recorded.
Using this information, it would be easy to analyze the data to check the load prior to the ATS switching to emergency, the load while on emergency, and the load after the ATS returns to the normal source. Using this analysis, it’s easy to identify loads added during a power outage and not removed when normal power is restored.
Another easy way to spot load creep is to trend year over year load growth. Using this analysis technique, load creep is easy to quantify.
Ultimately, multi-circuit submeters are an easily installed, inexpensive way for healthcare facility managers to conduct accurate load profiling and analysis.
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Zack Smith is an accomplished Field Services Manager at Affinity Energy, and as a Certified Control Systems Technician (CCST) with 20 years of experience, has responsibility for managing our dedicated team of field engineers and field technicians. While Zack spends most of his time developing and building the field services team, he is more than capable of rolling up his sleeves and leading by example.
As a member of the U.S. Navy Submarine force for eight years, Zack began his career by serving as a technician of the submarine-launched Trident ballistic missile. Over the next few years, he gained top secret clearance, made a handful of 4-month deterrent patrols during the Cold War, was decorated repeatedly, earned his associate’s degree in Industrial Electronics, and was selected to be a naval instructor within the submarine fleet.
Upon his honorable discharge, Zack pursued a career in industrial automation at manufacturing companies Sandvik and Delphi Automotive, and became an expert in programming industrial automation machinery and robotics. After spending six years as Head Applications Engineer at an industrial automation supplier, he joined the Affinity Energy team in 2010.
Zack’s contributions include major enhancements to SCADA systems at Carolinas Healthcare System, Chesapeake Bay Bridge and Tunnel, and the University of Virginia, along with numerous utility-scale PV integrations.
Allan D. Evora is a leading expert in control systems integration and president of Affinity Energy with over 20 years of industry experience working in every capacity of the power automation project life cycle. With a background at Boeing Company and General Electric, Allan made the decision to establish Affinity Energy in 2002. Allan is an alumnus of Syracuse University with a B.S. in Aerospace Engineering, graduate of the NC State Energy Management program, and qualified as a Certified Measurement & Verification Professional (CMVP).
Throughout his career, Allan has demonstrated his passion for providing solutions. In 1990, he developed FIRST (Fast InfraRed Signature Technique), a preliminary design software tool used to rapidly assess rotary craft infrared signatures. In 2008, Allan was the driving force behind the development of Affinity Energy's Utilitrend; a commercially available, cloud-based utility resource trending, tracking, and reporting software.
Allan has been instrumental on large scale integration projects for utilities, universities, airports, financial institutions, medical campus utility plants, and manufacturing corporations, and has worked with SCADA systems since the early ‘90s. A passion for data acquisition, specialty networks, and custom software drives him to incorporate openness, simplicity, and integrity into every design in which he is involved.