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 under fault
conditions
3.1 Primary feeder faults
3.2 Network equipment 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
4 Methods available to provide improved network
transformer protection
4.1 Electrical detection of faults
4.1.1 Differential relays
4.1.2 Overcurrent relays and fuses
4.1.3 Ground-fault relays
4.1.4 Compensator distance 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 Bibliography
Figure
1 Typical network system
Appendices
A Response of network relays to system faults
B Example
C Other concepts being investigated
Appendix Figures
A1 Typical tripping characteristics of master relay
A2 Typical closing characteristics of master and
phasing relays
B1 Example of a network transformer vault protection
scheme
B2 High voltage coordination
B3 Low voltage coordination