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  1. LMSANZ

    Zero Sequence Current - Homopolar current Relay Transformer Feeder

    Hi, we have a 30/0.4kV, 1600KVA Dyn11 transformer. After checking for imbalances in the primary phase currents, we connected relay software and noticed the presence of homopolar (zero sequence) current. I suspect that our power cable supplying the transformer could be starting to develop a...
  2. LMSANZ

    ABB REF610 CT ratio configuration problem ?

    Have you tried with ABB software PCM600?. Usually CT ratio is included during the setup process and most of the time, password protected to modify it.
  3. LMSANZ

    Transformer 30/0.4kV unbalanced currents

    Well, the transformer has taps, +/- 2.5%, 5%, but the tap is common for the three phases. I understand that Zero sequence can't pass through delta winding, in the case of earth fault in secondary. But what happen if there is a starting fault in any of the primary windings of the transformer...
  4. LMSANZ

    Transformer 30/0.4kV unbalanced currents

    I found this paper from IEEE, where it seems that the protection 51N can start detection false trips due to the unbalance currents. So it seems to me that 51N zero current calculations don't distinguish between ground fault or unbalance current...
  5. LMSANZ

    Transformer 30/0.4kV unbalanced currents

    Hi, I'm trying to get a power analyzer so we can check the phase angles of the secondary loads. We have another transformer feeding similar loads, and the overall PF is around 0.88. I am also in contact with Schneider for checking the CTs so we can be sure that there is nothing wrong in the...
  6. LMSANZ

    Transformer 30/0.4kV unbalanced currents

    yes, it is a same physical CT but with two secondaries. Don't know if there is sth wrong with that CT. In case there is a fault, it does make sense that the unbalance increase with the load?
  7. LMSANZ

    Transformer 30/0.4kV unbalanced currents

    Thanks for the answers. Well, the relay seems that start detecting I0 current from 4A, (10% of primary CT 50/1), because when the load increase the I0 start detection immediately from 4, and increases little by little acc to the demanded load. For example with primary currents L1=10.8, L2=...
  8. LMSANZ

    Transformer 30/0.4kV unbalanced currents

    Well, we don't have the equipment at field. But we are going to check completely the 03 CTs of that panel: - Insulation resistance test - Ratio and Phase deviation test. - Excitation (Saturation) Test - Winding resistance Test - Burden Test - Polarity test Hope the problem is at CT level. I...
  9. LMSANZ

    Transformer 30/0.4kV unbalanced currents

    Well, the primary CTs are 50/1, they are Merlin Gerin type TCF4F/N2. I think the secondary load is almost balance, only 6% unbalance between phase L1 and L3. It seems that the unbalance current in primary side increases when the load increases, and decrease when the load decreases. I am...
  10. LMSANZ

    Transformer 30/0.4kV unbalanced currents

    I don´t think so. The feeder has two sets of CT, one goes to protection relay SEPAM, and the other one goes to the Power meter. Both give us similar values for the unbalanced currents. The unbalance seems to be around 2-3A, but when the demanded load increase the difference between phase L1...
  11. LMSANZ

    Transformer 30/0.4kV unbalanced currents

    Primary voltage looks balance. See Attached Picture. Yesterday we've measured the secondary currents and we had: L1 1065A, L2 1015A, L3 1008A. Transformer is 30kV Delta 400V Star, neutral solidly grounded.
  12. LMSANZ

    Transformer 30/0.4kV unbalanced currents

    Hi, We have a distribution transformer 30/0.4kV 1.6MVA, which has the primary currents unbalanced. Secondary currents looks balanced +/- 80A. The transformer supply to MCC which has motor an single phase loads. We've made insulation test 5000V 1 min, on primary side and the results are GOhms...
  13. LMSANZ

    Neutral distribution

    Hi GG, well the loads connected to PT-504 (750kVA Xfmr) are basically all single phase. The transformer give service to a Restaurant and living quarters in the plant. The loads are quite well balance and only few of them are three phase. On the other hand, all loadas connected to MCC are pure...
  14. LMSANZ

    Neutral distribution

    Well, the transformer is 750 KVA so is almost half size of the distribution transformer 1600 kVA. In any case, all the auxiliary circuit connected to this transformer are properly protected through a Main CB and Outgoing CB with Ground protection. The goal of distribute the neutral is to...
  15. LMSANZ

    Neutral distribution

    Hi everyone, I've been recently involved in a brown field project. It is a 25 years old plant which was powered by generator at first "stage 0" and later on a electrical overhead line was built so they included a distribution transformer. As you can See under Stage 0, we have two generators...
  16. LMSANZ

    Medium Voltage switchgear panel fault

    hi everyone, we have under our facilities a 6kV swgr UNIGEAR ZS1, ABB made. Recently we had a fault in one of our motor starter panels (Fuse contactor VD4 type). The rear part of the contactor compartment is quite damaged. In the same swgr we have a spare panel identical to the faulty one...

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