Living in a direct current world

New edition of key standard for industrial switches

By Catherine Bischofberger

Many IEC Standards are paving the way for a direct current (DC) world. The most recent edition of IEC 60947-1 is a foundational standard for industrial switches and controlgear, which includes much improved testing specifications for DC.

Switchgear Switches are adapting to a DC world (Photo: Siemens)

Most of the devices we use in our homes, offices, healthcare facilities, greenhouses or data centres can operate on direct current (DC).  As renewable energies such as sun and wind produce DC power, several technologies are seeking to use DC from generation right through to consumption, without ever converting to alternating current (AC). This includes battery-operated equipment, electronics, computers, LED lighting, electric vehicles and more. In a conventional electricity network, power is transmitted over long distances using alternating current (AC). But DC is becoming a viable alternative, as more and more distributed power systems emerge to complement the uni-directional transmission from power station to end-user. Moving from DC to DC without converting electricity to AC is more energy efficient. Little or no loss of energy is experienced, contrary to what occurs when converting one form of current to another.

New specifications for DC

IEC Technical Committee 121 is about to publish a new edition of a foundational standard for low voltage switchgear and controlgear, IEC 60947-1, which, among its many improved features, includes comprehensive testing for DC switchgear and controlgear.

“All the DC devices we use, as well as the increasing reliance on renewable energy, require voltage switchgear with DC capabilities. This edition of IEC 60947 can be used for DC testing – in that sense it is a performance standard - but it also deals with safety aspects, when it comes to materials testing and insulation coordination, for instance. It is a generic publication, which means that every product standard in the IEC 60947 series can refer to it. Having such a generic standard avoids the multiplication of individual specifications”, explains Karl Hiereth, the Convenor of the working group responsible for publishing and updating general rules standards inside TC 121.

One of the factors that requires testing is insulation for DC electricity transmission, which has to be different than for AC. “We used to think we could apply AC insulation to DC but our experts have decided that we need to test specific insulation requirements for DC”, Hiereth adds.

Working with other technical committees

The standard is also updated for electromagnetic compatibility (EMC) requirements. “We liaise closely with IEC TC 77, which prepares standardized requirements and test methods in order to reduce EM emissions to an acceptable level and ensure sufficient EM immunity for electrical and electronic devices and systems. When they change certain standards, we must change ours as well. IEC TC 121 standards must also stay in line with EU regulations”, Hiereth says.

The IEC 60947 series of standards is widely used around the world by manufacturers of switchgear equipment for industrial purposes as well as by electric power utilities. “Around 50 participating members are involved in preparing this and other switchgear standards from all around the world, including South Africa and Egypt”, says Hiereth.

IEC TC 121 also works with IEC TC 111: Environmental standardization for electrical and electronic products and systems, notably when it comes to materials declaration. “We refer to IEC 62474, which is a key generic standard for materials and substance declaration. We use the example of a circuit breaker to show people how to proceed.”

Maintenance of the standard will continue. Hiereth expects a future edition to deal with topics such as terminals for aluminium connections and harmonized measurement for power losses.

Portrait 2016-08 Karl Hiereth