IEEE DRAFT C37.91 : D7.0 2006

1 Overview
   1.1 Scope
   1.2 Purpose
2 Normative references
3 Definitions
4 Device Numbers
5 Philosophy and economic considerations
6 Types of failures in transformers
7 Relay currents
   7.1 Minimum internal faults
   7.2 Maximum internal faults
   7.3 Through faults
   7.4 Performance of CTs
   7.5 Reasons for mismatch
8 Electrical detection of faults
   8.1 Fuse protection and self-powered re-settable fault
        interrupters
   8.2 Differential protection
   8.3 Overcurrent relay protection
   8.4 Ground fault protection
   8.5 Fault detection for special purpose transformers
   8.6 Backup and external fault protection
   8.7 Temperature relays
   8.8 Miscellaneous relays
9 Mechanical detection of faults
   9.1 Gas accumulator relay
   9.2 Gas detector relay
   9.3 Pressure relays
10 Thermal detection of abnormalities
   10.1 Thermal relays for winding temperature
   10.2 Other means of thermal protection
   10.3 Testing thermal relays
11 Fault clearing
   11.1 Relay tripping circuits
   11.2 Circuit breakers
   11.3 Tripping of remote circuit breakers
   11.4 Circuit switcher
   11.5 Fuses
   11.6 Self-powered re-settable fault interrupters
12 Re-energizing practice
13 Gas analysis
14 Special protective schemes
   14.1 Overall unit generator differential
   14.2 Unit transformer of three legged core form type
   14.3 Grounding transformer inside the main transformer
        differential zone
   14.4 Unbalanced voltage protection for wye connected three
        legged core type transformers
   14.5 Differential protection of single-phase transformers
        connected in three-phase banks
   14.6 Differential protection of a bank of three single
        phase autotransformers with delta tertiary
   14.7 Differential protection of single-phase transformers
        in a three-phase bank with a spare transformer
15 Other considerations
Annex A (informative) Application of the transformer
        through-fault current duration guide to the protection
        of power transformers
Annex B (informative) Transformer failure statistics
Annex C (informative) Examples of setting transformer protection
        relays
      C.1 Electromechanical relays for protecting a step up
          transformer
      C.2 Setting relays for a network autotransformer
      C.3 Relay settings for a distribution transformer
Annex D (informative) Thermal overload protection
      D.1 General theory
      D.2 Winding temperature monitoring on transformer with OLTC
      D.3 Limitations of traditional winding temperature indicator
      D.4 Protection
      D.5 Digital relays for transformer thermal winding protection
      D.6 Measuring temperature with imbedded RTD sensors
Annex E (informative) Internal phase shift and zero sequence
        compensation in numerical relays
      E.1 An example
      E.2 Reasons for using internal compensation
      E.3 Differential current compensation connections
      E.4 Examples
Annex F (informative) BIBLIOGRAPHY
Annex G (informative) Additional sources of information
      G.1 General information
      G.2 Fault detection
      G.3 Pressure and gas analysis
      G.4 Overvoltage