Selection Of The Power Cable Size - ABB ESI-S Installation, Operation And Maintenance Instructions

Further, the following rule should be respected: when the ESI-S consists of only one
enclosure, the enclosure's PE-point must be connected directly to the installation's PE-
point
6.6

Selection of the power cable size

Several types of power cable can be used to connect the inverter to the network. Local
regulations and habits often determine the user's choice. Note however that due to the
high frequency output inverter of the ESI, there is no radiated emission through the
feeding cables. Consequently, there is no need for special screening of the inverter
connection cables.
The following steps have to be followed to determine the section of the power cables
feeding the inverter:
1. Determine the RMS current rating of the enclosure for which the cable has to be rated
(Irms).
The rating is marked on the enclosure label.
Each enclosure has to be individually connected to the supply and bottom cable entry
has to be used. If required an optional cable connection box can be added to allow for
multi-cable termination.
The minimum cable section to be used for the power conductors is 16 mm².
The RMS current for which the cable has to be rated equals the current rating of the unit
to be connected to the supply.
2. Determine the factor X and the cable section required taking into account the skin
effect.
The multiplication factor X is a factor that takes into account that the current that will
flow through the inverter connection cables is predominantly a harmonic current, i.e. a
current of which the frequency of the most important components is higher than the
network base frequency. Due to the frequency being higher than the network base
frequency a physical phenomenon called 'skin effect' comes into play. This effect implies
that for higher frequencies the current will not flow through the complete cross section
of the cable but will have the tendency to flow at the cable surface. The result is that
although one may use a cable of A mm², the section through which the current flows is
only X*A m² (with X < 1). In order to compensate for this "loss of section", the cable has
to be oversized such that the total equivalent section through which the current flows
taking into account the skin effect is acceptable.
The multiplication factor X to be used depends on the cable material (e.g. copper [Cu],
aluminum [Al]) and on the base frequency of the network on which the inverter will be
installed. For a given installation its value can be determined using the following process:
Step 1: Determine in a conventional way (e.g. using cable manufacturer's tables) the
cable section A (mm²) for the RMS current Irms obtained in 1 above.
Manual Energy Storage Inverter ESI-S ç Electrical design and installation 41