Manual Energy Storage Inverter ESI-S
Electrical design and installation 55
6.11 Selection of the current transformers
Each invert unit in a system may need to monitor the line current if harmonic mitigation
or load balancing are required. This is done by three current transformers (CTs). For
proper operation of the ESI-S standard accuracy CTs with the following minimum
specifications have to be used:
−
5 A secondary current rating.
−
15 VA burden for up to 30 meters of 2.5 mm² cable. For longer cables lengths refer
to the chart in
In case the CTs are shared with other loads, the VA
burden shall be adapted accordingly. Note that the burden requirement for a
complete inverter system (consisting of up to 4 inverter units) is 5 VA, excluding
connecting cables.
−
Class 1 accuracy
−
Primary side current rating sufficient to monitor the total line current (including
transient phenomena such as drive/motor starts …)
It is strongly recommended that the three CTs have the same characteristics.
WARNING: The connection of different inverter units in an ESI-S system, as well as
other loads, on the same CT must be in series.
In order to determine the suitable CTs for your application, please refer to the chart in
.
Remark: in some applications two or more power supplies exist (e.g. a network
transformer supply and a generator supply). When the current into both supplies has to
be filtered, summing CTs have to be used. All summing CTs must have the same ratio.
More information on how to install the summing CTs is given in next section.