Unit protection, with its advantage of fast selective clearance,.has been used for interconnections within power systems from the early stages in the development of generation, transmission and distribution. In these early stages, generation was local to the load, and distribution was the main function of the network. At this period, we find unit protection of cable interconnections an example of the first applica tions of the principle of unit protection. As the main network was underground, it was natural that the secondary interconnections necessary for unit protection should be by means of 'auxiliary' or 'pilot' cable laid at the same time as the primary cables required to be protected. Also, as the 'Merz-Price' or 'differential' principle was developed in this period, it was understandable that this principle should be used as the main basis of these early forms of unit feeder protection.

Chapter Contents:

• 10.1 General background and introduction
• 10.2 Some basic concepts of unit protection for feeders
• 10.3 Basic types of protection information channels
• 10.3.1 Pilot wires
• 10.3.2 Main conductors
• 10.3.3 Radio links
• 10.4 Types of information used
• 10.4.1 Complete information on magnitude and phase of primary current
• 10.4.2 Phase-angle information only
• 10.4.3 Simple two-state (off/on) information
• 10.5 Starting relays
• 10.6 Conversion of polyphase primary quantities to a single-phase secondary quantity
• 10.6.1 General philosophy
• 10.6.2 Interconnections of current transformers
• 10.6.3 Summation transformers
• 10.6.4 Phase-sequence current networks
• 10.7 Elementary theory of longitudinal differential protection
• 10.7.1 Longitudinal differential protection with biased relays
• 10.7.2 Phase-comparison principles
• 10.7.3 Nonlinear differential systems
• 10.7.4 Directional comparison systems
• 10.7.5 Current sources and voltage sources
• 10.7.6 Nonlinearity and limiting
• 10.8 Pilot-wire protection
• 10.8.1 Basic principles
• 10.8.2 Practical relay circuits
• 10.8.3 Summation circuits
• 10.8.4 Basic discrimination factor
• 10.8.5 Typical pilot circuits
• 10.8.6 Typical systems for privately owned pilots
• 10.8.7 Use of rented pilots
• 10.8.8 Typical systems for use with rented pilots
• 10.8.9 V.F. phase-comparison protection (Reyrolle protection)
• 10.9 Some aspects of application of pilot-wire feeder protection
• 10.9.1 General
• 10.9.2 Current transformer requirements
• 10.9.3 Operating times
• 10.9.4 Fault settings
• 10.9.5 Protection characteristics
• 10.10 Power-line carrier phase-comparison protection
• 10.10.1 Introduction
• 10.10.2 Types of information transmitted
• 10.10.3 Basic principles of phase-comparison protection
• 10.10.4 Summation networks
• 10.10.5 Modulation of h.f. signal
• 10.10.6 Junction between transmitted and received signals
• 10.10.7 Receiver
• 10.10.8 Tripping circuit
• 10.10.9 Starting circuits
• 10.10.10 Telephase T3
• 10.10.11 Contraphase PIO
• 10.10.12 Marginal guard
• 10.10.13 Checking and testing
• 10.11 Problems of application of phase-comparison feeder protection
• 10.11.1 General
• 10.11.2 Attenuation over the line length
• 10.11.3 Tripping and stabilising angles
• 10.11.4 Fault settings related to capacitance current
• 10.11.5 C.T. requirements
• 10.12 Directional comparison protection
• 10.12.1 General
• 10.12.2 Basic principles
• 10.12.3 Basic units
• 10.12.4 Directional relays
• 10.12.5 Fault detecting
• 10.12.6 Change of fault direction
• 10.13 Power supplies
• 10.13.1 General
• 10.13.2 Station battery supply
• 10.13.3 Separate batteries
• 10.14 Bibliography

Inspec keywords: interconnections; power cables; power system protection

Other keywords: carrier current systems; unit protection; feeder protection; pilot wire systems; cable interconnections; power system protection

Subjects: Power system protection