For the first one hundred years of humanity’s use of electricity, the meter served as a cash register.  This cash register was traditionally electromechanical and then later electronic. But the basic function of the device remained the same – record the amount of energy consumed so that the customer can be billed. The evolution of the distribution networks first began with Advanced Meter Reading (AMR).  AMR added one-way communication to the meter providing remote meter reading. This capability enabled utilities to read the meters more frequently and cost effectively. The next step in the evolution of the electricity distribution networks was the Advanced Metering Infrastructure (AMI) typically defined by the bi-directional communication capabilities of the meter and corresponding infrastructure. With the deployments of AMR and AMI systems, meters have been transformed from simple counters of energy to smart meters performing the function of a network sensor in addition to its traditional role as an energy counter.

Communication capabilities have increased the demands on the metrology capabilities of metering ICs for industrial, commercial, and residential meters. Powered by near real-time communications, smart meters are integrating reactive energy measurements, harmonic analysis and advanced diagnostic features.  Previously these measurements were found on the transmission lines and electrical substations. 

Improving accuracy and dynamic range

Industrial and commercial meters have an active energy accuracy reading that often exceeds 0.2%.  Active energy, also referred to as real energy, is energy used by the load to do real work. Utility companies bill customers based on their consumption of active energy, thus accuracy is critical as it directly translates to revenue and costs. While 0.2% accuracy may seem extremely high, in the context of a gigawatt, 0.1% is a megawatt, enough power for 20-30 modern homes. In a world where energy costs are rising rapidly, accurate measurements are paramount for suppliers and consumers.

In addition to accuracy, wide dynamic range is critical in smart meters. Dynamic range refers to the ratio of the largest and smallest signal that can be measured. State of the art metering ICs offer industrial and commercial grade accuracy over the dynamic range of 3000:1. Thus, a meter that can measure energy with 0.2% accuracy at 300 Amps, can measure energy with the same accuracy when currents are just 10mA. 

Power quality

Reactive energy results from the phase shift between the current and voltage waveforms.  Reactive energy is typically present due to the capacitive and inductive loads in the network. Reactive energy is necessary and unavoidable for operation of loads such as motors. However, the presence of a large amount of reactive energy in the network leads to increased losses in transmission and distribution.  For this reason electricity providers are monitoring reactive energy of large consumers.  Industrial and commercial consumers of electricity are often contractually required to monitor and limit reactive energy. Recent advancements in energy measuring ICs allow reactive energy measurements with the same accuracy as active energy measurements.

The focus on energy efficiency is evident everywhere, such as lighting, power supplies, and motor control drives.  At the same time due to the non-linear nature of these devices they have a potential to add undesired harmonics to the power grid.  Harmonics are frequencies on the power line other than the fundamental frequency.  Fundamental frequency is 50Hz or 60Hz depending on the country standard – the UK operates at 50Hz.  Harmonics power pollution is undesirable as it can interfere or degrade performance of sensitive equipment.  In some cases, large harmonic content can even damage or reduce the life of power equipment, like transformers, due to over-heating.

Metering ICs are able to measure the fundamental as well as total (fundamental plus harmonic) energy. This capability enables smart meters to act as advanced distributed sensor networks detecting power quality at every point on the grid. With this functionality the health of the grid can be monitored in near real time often allowing preventative maintenance instead of responding to costly and disruptive catastrophic failures.

Tamper proofing and fault detection

Tampering with electricity distribution networks can lead to substantial unbilled losses of electricity. In some parts of the world, it is estimated that tampering accounts for losses of over 30% of all generated energy. As a response, metering ICs have evolved to include mechanisms for detecting and often continuing proper operation under tamper attacks. For example, Analog Devices’ ADE7868 and ADE7878 incorporate neutral current measurement capability. Neutral current is compared to the sum of the phase currents. A significant difference in values can be an indication of either tampering or improper wiring. As a diagnostic tool, neutral current measurement can be used to detect phase imbalances.  Phase imbalances lead to excess losses in 3-phase power transmission and distribution. 

In addition, these devices include low power modes that enable the metering IC to continue monitoring current while the meter is operating from a backup battery. This feature combats a common method of tampering with the meter that disables the meters primary power supply. Phase angle measurements and phase sequence detection also permit the meter to detect mis-wiring.  Furthermore, the ADE7868 and ADE7878 devices can internally remap signals reconstructing the proper phase sequence without physical rewiring thus thwarting a potential tamper attack.

Phase angle measurements also play a vital role in connecting alternative power sources to the smart grid. More green energy sources like wind and solar are connected to the grid every day.  hese sources have to be tightly synchronized with the grid to ensure proper and efficient operation.

Analog Devices’ 3 phase metrology ICs

Analog Devices has developed the industry’s first ICs that can enable reactive power measurements with 0.1% accuracy over 1000:1 dynamic range, and 0.2% accuracy over 3000:1 dynamic range.  Recognising the need for advanced metrology, Analog Devices expanded its portfolio of metering ICs with four new ICs addressing evolving needs of smart meters. ADE78xx family of parts enables 3 or 4 wire, Delta or Wye energy metering and monitoring. In addition to the energy measurements, ADE78xx measures RMS current and voltages. These parts are digitally configured and calibrated. Power quality features include: line voltage period measurement, angles between phase voltages and currents, phase sequence, sag and peak detection, over current and over voltage.

While ADE7854 measures active energy only, ADE7858 and 2 other parts, include reactive energy measurements with the same accuracy and dynamic range as active energy. ADE7868 and ADE7878 include anti-tamper features as well as low power modes. ADE7878 is the flagship part of the family adding the capability to simultaneously measure fundamental only energy and total energy.

Vitaly Goltsberg, Marketing Manager, Metering Components group, Analog Devices

Printer friendly version

Email this article to a friend