Hackers, thieves, and the curiously mischievous may try to break into your remote electric utility metering equipment.The best way to protect equipment is to approach meter security from a layered perspective. In a metering environment, security begins with the design of the hardware and firmware platform. Meters with self-testing, high accuracy, and an innovative error detection system provide secure revenue protection.

QUALITY PROCESS IN DESIGN

To meet international standards, the meter must pass electromagnetic immunity tests for surge withstand, electrostatic discharge, radiated radio interference, and extensive environmental tests for heat, cold, dust, and vibration. Multiple levels of password protection help control who can read, reset, and program the meter, locally or remotely. This is the first step to avoid tampering.

INTERNAL METER SELF-TESTING

High-quality microprocessor-based revenue meters periodically perform a number of self-tests. These include dc offset on each input channel, internal power supply voltages, clock battery voltage, and internal temperature, as well as tests on RAM, ROM, and EEPROM. Depending on the severity of the condition, the meter issues a warning or declares a failure. Utilities can monitor these alarms through SCADA or other remote notification systems, or detect alarms locally and via output relays. Self-testing reduces the time required to find metering errors, which saves revenue.

REAL-TIME ERROR DETECTION

SEL has developed a unique way of detecting problems in real time at key meter locations. A pair of SEL-734 Meters is wired with their current inputs in series and voltage inputs in parallel. The two meters send KYZ pulses to each other via SEL MIRRORED BITS® communications protocol over a serial connection, on a cable or fibre pair. MIRRORED BITS communications provides a continuously monitored communications path for up to eight digital signals between two devices.

Using binary and comparison logic equations, each meter counts the pulses and compares its own pulse count with the other meter’s pulse count. If they differ, the logic will initiate alarms using one of the three standard output relays on each meter. A SCADA RTU or a radio-based remote notification device can then help detect the alarm. In just 12 ms, the meters can detect an accuracy problem, an auxiliary power problem, incorrect wiring, or a loss of communication between the meters, and then signal the alarm. This method also detects tampering with inputs or settings of either meter. The base price of the SEL-734 is $1444 and the cable connecting the two meters is $25. The complete redundant metering solution is under $3000. 

DATA COMMUNICATIONS

Advanced multifunction meters offer a variety of communications options, including serial EIA-232 and EIA-485, modem, fibre optics, and Ethernet. Typically, commercial and industrial revenue meters are read using a data collection system that periodically dials the meter on a telephone line, enters a password, and then reads the load profile data and energy registers. SEL serial encrypting transceivers (SEL-3021) work with existing modems to secure the meter’s communications. The SEL-3021 is designed to meet very high security requirements, using 128-bit keys. It supports DNP3, Modbus® RTU, and other metering and SCADA protocols. Using these new encrypting transceivers satisfies the need for both data and revenue security.

The SEL-734 provides security through design and continuous self-tests. In critical applications, two meters can monitor each other and provide real-time notification of tampering. The SEL-3021 provides secure communications to and from the meter, protecting valuable billing information and power quality data.