Download Sepam T81 Relays for 64REF and Ground Fault (4

Sepam T81 Relays for 64REF and Ground Fault (4-Wire Low Voltage Panels)
1. As shown in the Sepam 80 manual, when the 64REF function is used on a low-voltage transformer winding
where the neutral conductor is distributed, the CCA634 CT adaptor must be used. The combination of the
CCA630 + CSH30 cannot be used.
So, the first step should be to double-check with the customer that the existing Neutral CT inside the
transformer is indeed mounted at the correct position, before the Neutral conductor is distributed. We should
request the detailed transformer datasheet and the internal wiring drawings. The transformer supplier should
be able to provide this information.
Once this has been verified, the original (existing) wiring on site should be modified to use a CCA634 adaptor,
as explained in the Sepam 80 manual.
After the wiring has been modified, we should ask the customer to run unbalanced loads downstream of the
transformer, and verify that the 64REF function does not trip, even in case of significant unbalance. If trips are
still occurring in case of unbalanced LV loads, this would be due to a CT secondary wiring error at the Sepam
terminals.
2. The original requirement for the project (with regards to the Sepam T81 panels protecting the 11kV to
0.42kV transformers) was for both a 64REF function and a separate Ground Fault function to check for
downstream earth faults in the low-voltage system.
This could make the wiring requirements slightly more complicated, since the Sepam 80 has specific
requirements for CT secondary wiring for the case of 4-wire low-voltage systems.
2a) the best-case scenario is that we can install a Ground Fault CT on the neutral-to-earth link of the
transformer, as shown below. This CT cannot be the same Neutral CT used for the 64REF function.
If this Ground Fault CT can be installed, then the Sepam T81 relay does not need to be changed to a Sepam
T87 relay.
We would inform the customer and get their confirmation that the low-voltage ground fault function would not
be done with a sum of the 3 phases plus the neutral current. The protection would be made by directly
measuring the ground current through the neutral-to-earth link of the transformer.
2b) this second case applies if either of the following are true:
i) the customer requires that the low-voltage ground fault protection should use the 3 phase CT’s and the
neutral CT. or
ii) it is not possible to install a Ground Fault CT at the position shown in the diagrams above (i.e., on the
neutral-earth link of the transformer, after the neutral conductor has been brought out for distribution).
In this case, we need to change the Sepam T81 to a T87 Application Type by changing the cartridge.
Then, 2 of the CCA634 adaptors must be used for each of these low-voltage transformer panels, because the
first CCA634 adaptor will be dedicated to the 64REF function only.
And, in this case, it will be necessary to wire the secondary circuits for the 3 phase CT’s in series, so that the
Phase CT output can be measured by both CCA634 adaptors.
Conceptually, the wiring will be as shown below.
Inside the panel, we will need to make a series link between the Phase Current inputs on the 2 CCA634
adaptors. This is because the B1 adaptor is dedicated to 64REF only. The B2 (2nd) CCA634 adaptor would be
used for the Ground Fault.
Again, please note that this is the worst-case scenario. If we can install a ground fault CT as shown above,
then this option is not necessary.