Metering equipment is a critical component of all parts of the electric delivery system and serves a variety of functions. Most importantly, it is used by market participants and service providers to determine who owes whom and how much. Without accurate and timely meter data, buyers cannot be billed and suppliers cannot be paid. It is also used by transmission and distribution operators to gather and record key operational data that is used to monitor and evaluate the status and health of the system and by end users to monitor their operations.
Revenue meters are installed at strategic points on the electrical system: where generators put power onto the grid, where utilities buy and sell power to other market participants, and where utilities deliver power to their own end-use customers. Additional meters provide system operation data in real time to system operators who use it to monitor and manage the grid and to system designers who use it to determine when system upgrades are required. Metering technology is currently undergoing a significant transition as the industry moves from electromechanically operated meters to solid state electronic meters, more commonly known as smart meters, that can record, communicate, and store increasingly complex types of data and are read remotely via a variety of both wired and wireless technologies. The development of this technology has drastically increased the amount of information that can be collected and analyzed from the electric system.
In addition, the means of collecting meter data is rapidly changing. Not long ago, only limited operational data was available via the utility’s Supervisory Control and Data Acquisition (SCADA) system. Other operational data, as well as most customer usage data, was collected periodically by sending employees into the field to manually read meters. Manual collection of meter data is rapidly being replaced by expanded SCADA systems that collect operational data and Automated Meter Reading (AMR) systems that collect customer usage data.
Categories of meters
There are several ways in which meters are categorized.
- By the type of electric service they measure, either single-phase or three-phase. Single-phase meters measure single-phase service while three-phase, or polyphase, meters measure three-phase service. The difference between the two is the number of meter elements or circuits contained in the meter. Single-phase meters have just a single element while three-phase meters contain either two or three elements depending on the type of three-phase service the meter is designed to measure.
- By operating technology, including the three primary metering technologies in use today – induction, hybrid, and solid state – as well as the means of communicating data. Data communications can be manual or remote, which is also referred to as automatic meter reading.
- By register type, meaning by what they measure. This can be energy, demand, time-of-use, power factor, or other electrical quantities.
- By voltage type, including transmission, primary, or secondary voltage.
- And by the type of installation in which they are used, either self-contained or transformer-rated. A self-contained meter does not require ancillary equipment while a transformer-rated meter does.
Each meter is labeled with information that describes the meter category and other important information. This typically includes the class which tells the maximum current rating of the meter, the maximum voltage rating, whether the meter is for three-wire or four-wire service, and other information on the meter specifics. The example below shows the class, voltage, service configuration (shown here as CL200 which means 200 amps), maximum voltage (240 V), and three-wire service.
Some of the same information is encoded in the meter form. This is an industry standard alphanumeric designation indicating the number of meter elements, connection configuration, and the meter base required to operate correctly.
Finally the meter label indicates the amount of test amps to be used by the meter technician testing the meter and the disk constant and register ratio that tell how to translate revolutions of the disk into actual usage in kWh. Many newer meters put this information into a bar code that can be directly scanned from the meter.