Switching Technology
A new generation of smart meters demands new relay designs
As smart electricity meter roll-out accelerates across Europe, second and third generation meters are emerging with increased functionality to accommodate the exporting, storage and auxiliary utilisation of energy. Steve Drumm, European marketing, sales development and project management, Omron Electronic Components Europe, explains
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ountries that have yet to roll-out smart meters will move to the new generation immediately, and
countries where roll-out is already well advanced may replace their estates. Second generation meters are typically smaller than earlier units by about 20 percent and also draw less power. They also offer new ways of controlling for example, the charging of hybrid electric vehicles, allowing this kind of non-critical function to be carried out at times of excess capacity. New functions to manage small scale local generators such as solar panels are also included. Some also disconnect the AC supply to the smart meter by PLC or by wireless M2M communication such as SMS, GSM or LW.
Switching relays
These second generation meters continue to rely on electromechanical supply service control relays to manage the supply of electricity, for a number of compelling reasons. A relay provides a really strong
mechanical break in the circuit, with complete isolation between input and output. Solid state disconnection devices are unable to withstand the operating conditions or offer equivalent high dielectric strength, high overload capacity and high fault currents during switching without expensive additional protection. For local load switching and time of use functions, the relay is there to make rather than to break the circuit. Therefore, a latching relay is required, as it will stay in the ‘on’ position saving energy. A latching, single-pole electro-mechanical relay with a maximum current rating of up to 120A at 250V AC would meet the needs of a smart meter employed in a commercial, residential or light industrial environment.
New standards
Relays in smart meter applications are now subject to a new standard - IEC 62052-31:2015(E) launched in September 2015. This specifies product safety requirements for equipment for electrical energy measurement and control and replaces IEC 62055-31. It applies to newly manufactured metering equipment designed to measure and control electrical energy on 50Hz or 60Hz networks with a voltage up to 600V, where all functional elements, including add-on modules are enclosed in or form a single. It also applies to metering equipment containing supply and load control switches, but only those
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which are electromechanical in operation and is applicable to auxiliary input and output circuits.
Most smart meter manufacturers now
require Utilization Category 3 (UC3) compliance for latching relays whereas previously UC1 or UC2 was seen as sufficient. UC3 requirements entail that the relay should withstand higher short circuit or over-current events. Forward looking relay manufacturers are extending their latching relay portfolios to address the opportunity represented by the new generation of smart meters. They are reducing the profile of their latching relay devices and offering solutions capable of handling the potentially high inrush currents. Much effort is being made to improve the efficiency of relays where the key characteristics of switching capacity, switching endurance, coil type, load isolation and physical construction can have a notable impact on the overall energy efficiency. Design features that can facilitate this application include the use of twin contacts to improve overcurrent capability, enhancing safety. Twin contacts can also reduce power loss and suppress temperature rises within the component. Changing the orientation of the coil layout can also reduce contact welding,
Components in Electronics
improving over-current capability and electrical life. Features like this not only ensure true UC3 overcurrent protection but also reduce the energy consumed in the smart meter.
Tamper protection Whilst in the past smart meter manufacturers have relied on lever switches to detect the opening of the case, more sophisticated fraud methods have entailed new thinking on protection. Smart meter relays are now often fitted with screening, to reduce the effect of applying an external magnetic field. In the future it is likely integrated security features will be common place within the relay providing further resilience to tampering.
The Smart Meter opportunity The purely electronic solid state meter is still some way off. Latching power relays will remain a central feature of smart meter design for the foreseeable future. Relay manufacturers are responding to the opportunity with more efficient designs that fully meet the ever more stringent international standards, and support meter manufacturers in their efforts to address the perennial issues of fraud and tampering.
omron.eu December 2015/January 2016 31
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