Current Transformer Installation And Connection - ABB ESI-S Installation, Operation And Maintenance Instructions

6.12 Current transformer installation and connection

The location of the CTs is critical to ensure the proper operation of the inverter. The CTs
are the "eyes" of the inverter and it will react in accordance with the information supplied
by them.
WARNING: Special care has to be taken for the connection and location of the CTs:
wrong CT installation is the most common source of problems found at the
commissioning stage.
By default, the ESI-S is provided with CT terminals that are not shorted. A set of shorting
plugs is provided with the inverter. They should always be kept with the inverter and
accessible for service engineers.
WARNING: When connecting the CTs of a live system to the ESI-S, the secondaries of
the CTs have to be shorted. Failure to do so may result in CT explosion and consequent
damage to the installation. Once the connections to the inverter have been made, the
shorting links must be removed.
The basic rules for successful CT installation are given next (Cf.
- The three inverter CTs have to be positioned for closed loop control, i.e. the CT
must monitor the load current and the inverter current. In some cases,
summation CTs may be needed to fulfil the closed loop requirement (Cf.
examples further down this section).
- The CTs must be positioned in the correct direction around the power cable: the
K (P1) side should be in the direction of the supply and the L (P2) side should be
in the direction of the load.
- Each CT must have its own guard circuit, i.e. one terminal of each CTs secondary
terminal (k (S1) or l (S2)) should be earthed. Once a terminal is chosen (e.g. k-
terminal), the same terminal should be earthed for all the CTs.
The CT monitoring a phase should be connected to the inverter terminal
-
dedicated to the same phase. In practice this means that:
· The k (S1) terminal of the line 1 CT (L1, Red, U) must be connected to
terminal X21-1 of the inverter
· The l (S2) terminal of the line 1 CT (L1, Red, U) must be connected to
terminal X21-2 of the inverter
- The CT connection terminal X21 is located in the middle of the top plate of the
inverter (Cf. Figure 39).
Manual Energy Storage Inverter ESI-S ç Electrical design and installation 53
Figure 38):