The following installation recommendations apply to the measurement of residual current with CSH120 and CSH200 Zero Sequence Current Transformers.

1. Observe the mounting and wiring directions for the toroid (see attached Install Sheet)
2. Make sure that the toroid is positioned perfectly concentrically with the cables (centre the cables in the toroid)
3. The cable diameter must not be more than half the toroid diameter, otherwise there is a risk of unintentional tripping with current peaks on start-up
4. In an existing installation, if this previous condition cannot be complied with, the problem can be overcome by adding a magnetic metal sleeve of a length equal to the diameter of the toroid
5. Remember to run the earthing cable for the shielding of the three MV cables through the toroid

If the diameter of three-phase cables is too large to fit inside a single toroid, you have two options:

Use a standard 1 A or 5 A CT appropriate to the cable diameter and add the CSH30 toroid adaptor to the secondary.

If there are multiple cables for each phase:

1. Divide them into N groups, each containing all three phases
2. Use a CSH120 or 200 for each group: maximum number = 5
3. Observe the direction of energy flow
4. Connect the CSHs in parallel directly to the Sepam using a single shielded twisted pair cable of the shortest possible length
5. Bear in mind the loss of measuring accuracy, estimated at -10% for two toroids or -25% for five toroids

All of this information can be found in the Sepam relay manuals.

Released for:Schneider Electric UK