by Scott Laster
We often hear the terms smart meter and smart grid tossed around, but what does this really mean? Some would say it's a meter with wireless communications to integrate into an advanced metering infrastructure. Some would require features such as time-of-use or other self-read capabilities to support complex rates and automation within the meter. Others would consider power quality features such as sag/swell or transient detection a must in a smart meter. But, to truly be smart, a meter needs to have a flexible, programmable logic engine available, along with multiple communication ports supporting a variety of protocols.
The more basic functions just mentioned should, of course, be intuitive and easy to set up. Setting the reference (nominal) voltage, for example, should be all it takes to enable all of the power quality functions. Requiring the user to enter each trigger point is not a good practice because this is prone to user error. Instead, the smart meter should monitor power quality according to standards or recommended practices such as Institute of Electrical and Electronics Engineers (IEEE) 1159, IEEE 519 or International Electrotechnical Commission (IEC) 61000-4-30. Other settings such as time-of-use should also be easy to set up, using setup software. Configurations should be portable so that setting up a profile and deploying it to hundreds of devices is efficient.
Where a meter really gets to be smart is when you give it the ability to gather and process information, and even take action based on conditions. Take, for example, a generator facility with an auxiliary transformer and a generator step-up transformer (GSU); the losses in such a transformer can be significant, and to get a proper net-to-grid value requires subtracting the station load from the generator output.
Consider the simple situation of a single generator and auxiliary feed. If there is already metering on the generator and auxiliary feeds, then it is easy to add net-to-grid-without losing the raw generator and auxiliary data. Adding more generators and/or auxiliary feeds to a facility may seem like it complicates the situation, but it doesn't.
Each of the meters is connected to a common voltage bus and provides its voltage and current phasor measurements to a Modbus map. Leveraging Ethernet communications, the master meter polls other devices in the network to retrieve their real-time data. The measurements are combined in the master to obtain the net resultant phasors for each phase of current. From that point, there is a virtual metering point that can be treated as any other. Calculate the losses on the transformer and you have another metering point (high side). Calculate the losses in a section of transmission line on the high side of the GSU and you have another metering point-all without adding cost to the project.
Do you have a generation site with multiple generating units but a shared load such as a coal handler or a stack scrubber? Use a smart meter to allocate that shared load to each unit. How about a high voltage ring bus or a breaker-and-a-half bus? Do you need to calculate the power flowing in the lines that feed the station? A smart meter will do the job. Each meter is connected to the breaker's bushing CTs, monitoring the power flow through the breaker. Each meter communicates to the meter on the next breaker and calculates the power flowing in the line between them.
What about contractual agreements, which are common with renewables such as wind farms and solar fields? While it is true that losses are based on physical characteristics, it is also true that contracts trump physics. Based on real-time conditions, a truly smart meter can perform necessary calculations and log data according to a legal agreement between two or more parties. This may include something such as enforcing transformer losses in one direction of power flow, but not in the opposite direction-or anything else the lawyers come up with.
With a flexible logic engine embedded in a smart meter, coupled with communications, and digital and analog I/O, the possibilities are endless. Monitor breaker status to enable a function. Calculate totalized or net consumption. Control capacitor banks. Use a meter as a low-cost remote terminal unit for small substations. Read Modbus data from any device, and map points to a Distributed Network Protocol (DNP) map as a data concentrator.
When you start to think outside the meter glass, you see the possibilities of a truly smart meter are endless.
About the author: Scott Laster has been programming ION advanced meters for 20 years and has developed many solutions to complicated metering applications. Born in Ohio and educated at Purdue University, Scott lives in Indiana where he represents Schneider Electric as a metering subject matter expert to the utility market.