Elektromotive, a UK provider of technology and engineering solutions for electric vehicle recharging, has selected residual current devices (RCDs) from Moeller to provide key safety and usability functions in its new Elektrobay on-street charging stations.
The product of six years of intensive development work, the Elektrobay stations are already installed and in regular use at 80 locations in London, as well as in diverse other locations around the UK. With the rapid growth in popularity of electric vehicles, additional Elektrobay stations are being installed almost daily.
"Elektrobay stations take the form of an attractively styled cylindrical column that's usually mounted on the edge of the pavement adjacent to a parking bay," said Greg Simmons, Technical Director of Elektromotive, "and they're designed to be used by anyone who drives an electric car. No special knowledge or expertise is needed."
"In most locations, there will be no one around to provide advice or assistance when the stations are being used," he continued, "so it's essential that the stations are as safe as it's practicable to make them, and that they are very straightforward to use."
To achieve their safety objectives, the engineers at Elektromotive knew Elektrobay stations would need to include RCDs to guard against any possible risk of electric shock injury to users if, for example, they were to inadvertently use a damaged connecting lead to link the station to their vehicle.
Ordinary RCDs were not an appropriate choice for this project, however, as the Elektrobay stations essentially provide a 230 V AC supply to the battery charging equipment fitted in the user's vehicle.
The exact arrangement of the charging system varies for different types of vehicle and some types superimpose a pulsed DC current on the normal AC supply waveform. This can adversely affect RCD operation. RCDs in the PFIM range from Moeller are, however, available in versions with Type A characteristics, and are specifically designed to give effective protection in applications of this type.
A further special requirement for this project was that no manual reset should be needed for the RCD. An objective of the Elektromotive design team was that the Elektrobay stations should be entirely free of pushbuttons and switches – these items not only have the potential to cause confusion, they can also, unless special and potentially expensive measures are taken, prove to be design weak points that are prone to failure and attractive to vandals.
A convenient solution was provided by fitting the RCDs with a Z-FW-LP automatic reclosing devices, which are standard accessories in the Moeller range. Following an RCD trip, the Z-FW-LP waits for a short period, then automatically attempts to reset it. If the fault is still present and the RCD trips again, the process is repeated, in principle up to a maximum of five times. The internal control logic of the Elektrobay stations, however, limits the number of resetting attempts to three in this particular application.
"This auto-resetting is ideal for us," said Greg Simmons, "as it means we can fit the Elektrobay stations with sensitive residual current protection to ensure maximum safety, while also being completely confident that they won't be taken out of service unnecessarily if a spurious trip occurs."
"Some types of electric vehicle, for example, have an unbalanced inrush current when first connected to the supply, and this can cause an RCD to trip. It doesn't happen often but, without the auto-reset feature, it would be often enough to be a nuisance. In effect, auto-reset makes it easier for the RCD to discriminate between real faults and transient effects. And, of course, automatic resetting meets our key requirements of having no reset button, and of making the operation of the stations as simple as possible."
In service, the Moeller RCDs are performing exactly as anticipated, and are proving to be completely dependable, even though the Elektrobay stations, which are almost invariably installed out of doors, have to operate reliably over a very wide ambient temperature range.
A final but by no means insignificant benefit of using Moeller RCDs and accessories is that they are supported worldwide, something that is becoming increasingly important for Elektromotive, as its innovative products are starting to attract a lot of interest in many overseas markets.
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