FEATURE SWITCHES & RELAYS
THE SMARTER WAY TO SPECIFY RELAYS
Steve Drumm, business development manager – Energy, Omron Electronic Components Europe, explores the main areas where relays are used in smart meters and solar panels, and considers the relevant issues in the selection of a suitable relay
T
he growing markets for smart meters and solar panels have very specific
design challenges and there are some distinctive considerations that apply when selecting relays and switches for inclusion in these designs. Each successive generation of meters is typically smaller than earlier units and also draws 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. Implementation of these functions normally entail the use of a relay. Relay manufacturers are maximising the benefits of smart metering by continually raising standards of accuracy, safety and reliability. By offering cost-effective relays, switches, photomicrosensors and connectors, they help to save power in electricity metering systems. So, what are the considerations for designers? Relays in Smart Meter applications are now subject to a new standard: IEC 62052-31:2015(E). 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 50 Hz or 60 Hz networks with a voltage up to 600 V, 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 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
22 MAY 2017 | ELECTRONICS
circuit or over-current events. Manufacturers are now extending their
latching relay portfolios to address the opportunity represented by smart meters. They are reducing the profile of their latching relay devices and offering solutions capable of handling the potentially high inrush currents. Efforts are also being focused on efficiency improvements to relays, where the key characteristics of switching capacity, switching endurance, coil type, load isolation and physical construction can impact on energy usage. 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, 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. Clearly, the power consumption of the
smart meter itself is a concern to designers, and latching relays which are only energised while switching and use less power than non-latching designs are therefore popular. Although the wattage is normally quite low, if you multiply this small number up across the millions of meters in use on the grid, it does add up. A self-latching relay is recommended, which only uses power during the switching process and doesn’t have to be electro-magnetically held open.
In battery management applications, the G9EJ-1-E is capable of interrupting 15A at 400VDC yet draws only 1.2W while switching
The two key areas for relays in a smart
meter are AC disconnect, for disconnecting the supply, and auxiliary load management, allowing the consumer or the utility to switch in and out non time critical loads depending on the time of day and the level of load on the grid. AC disconnect relays can have an impact on power consumption, as the high load currents can bring about self-heating which is inefficient. They can also be open or closed for extended periods, so really a latching design should always be used here. Designers should consider a relay such as the Omron G9T which employs a proprietary double contact architecture which minimises self-heating. For local load switching and time of use
functions, the relay is there to make, rather than to break, the circuit. 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 in a commercial, residential or light industrial environment. For higher loads up to 16A, solutions like
Omron’s G2RL which is just 15.7mm high, are a popular solution. Despite its low profile, the G2RL meets VDE0700 requirements for household products according to VDE0110. Latching designs such as Omron’s G5RL-
Relays can be installed close to a PV panel or other renewable source, to disconnect it quickly in an emergency, to permit maintenance or in response to utility requests
U and the G5RL-K can switch up to 16A and are capable of dealing with high inrush currents of up to 150A. For lower loads even more compact solutions are available. Advanced construction makes the 10A G5Q-EU smaller than comparable designs, with an overall case size of just 20.3mm x 10.3mm x 15.8mm. Designed to switch 10A loads at the prevailing European 250VAC mains, Omron’s G5Q- EU compact single pole relay features a low power coil to save power supply size and cost, and tracking resistance that meets or exceeds CTI250. Omron has also developed relays for the
specific challenges found in solar PV grid protection, solar panel disconnection and battery management.
Omron Electronic Components
www.omron.eu T: 01438 758800
/ ELECTRONICS
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