The purpose of any DLM is not to protect wiring or electrical system, but to optimize the use of available grid connection capacity. All EV chargers must be equipped with suitable automatic fuses and RCDs to comply with electrical safety regulations in case of critical overload or short-circuit. That being said, here are some considerations of Virta DLM:
DLM with static limit
When using Virta DLM 1.0 with static grid connection limit, there is no possibility to exceed the limit. The Virta system recalculates the maximum current limit of each station when a new charging transaction is started or stopped. In the event that the internet connection is lost, the previously set current limits for all stations on the site are preserved. Therefore, the total maximum site current consumption is kept at the set limit.
DLM with dynamic limit
When using Virta DLM 2.0 with dynamic grid connection limit, there is an external current measurement device at the grid connection point to measure the whole site’s loads. This data together with meter values from the chargers is used for recalculating available charging power. In case of power peaks, the charging power from the chargers is decreased so that the main supply’s maximum capavity is not exceeded. The measurement-recalculation cycle for available charging power is about 5 seconds. In case that the connection is lost to the external current measurement device, the site’s chargers power is limited to a defined safe level until the connection is re-established.
If the site is known for very poor or intermittent internet connection, there is also possibility to operate non-cloud -based charging point specific hardware DLM in conjunction with the Virta platform. However, this approach restricts the use of different charger brands at the same charging site and requires additional cabling.