Transformer Tripping Problem

Lot to read:

using i characteristics to troubleshoot transformer differential relay

Or: IEEE Xplore - Using transformer differential relay IOP characteristics

So your transformer trips every time any transmission line attached to it also trips? You haven't supplied any of the important information like a single line diagram, the size and connection type of the transformer, or the type of breakers and relays, loading, etc. making it a bit tough to be precise.

Absent all that information (and more) I'd say that your CTs may not be matched closely enough, the breaker interpole opening times are too great, or the relays aren't set properly. There's a lot more to look at, loose connections, polarities, etc., especially since it's so consistent. You might also consider getting someone out there who knows what they're doing.

Differential protection is an unit protection and should remain stable for faults outside the measuring zone. Assuming the power flow is from 132 KV side, the relay should not even sense any fault unless the fault lies insider the zone CT's. For 2 way flow of power or grid interconnected system, the relay should sense it as a through fault and remain stable. All the points mentioned by RAMConsult to be checked. Carrying out stability checks in offline mode involving all the CT's, 132/33 kv transformer etc., will confirm whether system requirements of zone protection scheme are met. You will need the services of an experienced power systems commissioning engineer to trouble shoot the problem.

http://cr4.globalspec.com/thread/85270/Transformer-Tripping-Problem

gb477 has provided additional information-

Referencing previous post regarding transformer tripping through differential relay-(MAKE-SIEMENS 7UT) TR. NAME -BHEL INDIA RATING-80 MVA 132\33kv power tr. CTR-132kv 800\5A 33 kv 1500\5A Max load 55MVA TR. DGR. STAR- DELTA Addl. info. 132 kv grid system.4 nos. line. 3 nos trs in parallel rating 80MVA SIEMENS MAKE and 50MVA BHEL MAKE TWO BUS SYSTEM ONE MB AND TB