IEEE DRAFT C37.108 : D6 98

1 Introduction
1.1 Scope
1.2 References
2 General background
2.1 Network development
2.2 Application considerations of adding protection to spot
       network vaults versus grid network vaults
3 Operation of a network transformer vault under fault
       conditions
3.1 Primary feeder faults
3.2.1 High-voltage switch faults
3.2.2 Transformer faults
3.2.3 Protector faults
3.2.4 Low-voltage bus faults
3.2.5 Low-voltage faults in customer supply cables and bus
3.2.6 Other faults
3.2.7 High voltage cable faults
4 Methods available to provide improved network transformer
       protection
4.1 Electrical detection of faults
4.1.1 Transformer differential relays
4.1.2 Overcurrent relays and fuses
4.1.3 Ground-fault relays
4.1.4 Compensator distance relays
4.1.5 Network protector relays
4.2 Mechanical detection of faults
4.2.1 Sudden-pressure relay (gas)
4.2.2 Sudden-pressure relay (gas/oil)
4.3 Thermal detection of faults
4.3.1 Heat detection
4.3.2 Smoke detection
4.4 Ultraviolet detectors
5 High-voltage fault interrupting devices
5.1 Circuit breakers
5.2 Remotely located circuit breakers with transfer tripping
5.3 Fault interrupters
5.4 Power fuses and current-limiting fuses
6 Low-voltage fault interrupting devices
6.1 Network protector
6.2 Low-voltage fuses
7 Distributed source generation
8 Network distribution SCADA
9 Bibliography
Appendixes
Appendix A Response of network relays to system faults
A1 Tripping characteristics
A2 Balanced faults
A3 Tripping operations on unbalanced faults
A4 Reclosing characteristics
Appendix B Example: 12.5 kV/277Y/480 V spot vault network
                      transformer protection
NOTES for fig B1, B2, B3
Appendix C Other concepts being investigated
C1 Low-voltage arcing fault detection
C2 Microprocessor based current differential relays
C3 Current-limiting fuses and three-phase load break
            switch
Figure 1 Typical network system
Figure A-1 Typical closing characteristics of master and
            phasing relays
Figure A-2 Typical tripping characteristics of master relay
Figure B-1 Example of a network transformer vault protection
            scheme
Figure B-2 High voltage coordination
Figure B-3 Low voltage coordination

Guide is intended to aid engineers who have reevaluated problems associated with faults within network vaults, particularly for those network vaults situated within or near highrise buildings. Also identifies currently available devices that are being used in network transformer protection schemes.