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Home / Technical Articles / 8 Examples Of Transformer Differential Protection Using SIPROTEC Numerical Relays

Transformer Protection

The following examples show the application of SIPROTEC numerical relays for transformer protection. The individual functions are designated, using ANSI codes (Standard C37.2 – Electrical Power System Device Function Numbers).

8 Examples Of Transformer Differential Protection Using SIPROTEC Numerical Relays
8 Examples Of Transformer Differential Protection Using SIPROTEC Numerical Relays (photo credit: Siemens)

The integrated supplementary functions in each relay may be applied advantageously. It must however be noted that back-up protection functions for redundancy must be provided in a separate hardware (a further relay).

Therefore, the overcurrent protection included in the differential protection 7UT6 can only be implemented as back-up protection for external faults in the connected system.

The back-up protection for the transformer itself must be provided by a separate overcurrent relay (e.g. 7SJ600). The Buchholz (gas pressure) protection providing fast short-circuit protection is provided together with the transformer.


  1. Two-winding transformer protection
  2. Three-winding transformer protection
  3. Transformer protection with restricted earth-fault protection
  4. Transformer protection for 1-½ circuit breaker arrangements
  5. Auto-transformer protection
  6. Protection for a large transformer bank
  7. Protection of regulating transformers
  8. Protection of generator transformer units

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Edvard Csanyi

Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry facilities. Professional in AutoCAD programming.

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