Practical Power System Protection
Providing both the underpinning knowledge and basic calculations needed to understand, specify, use and maintain power protection systems, this book also covers the practical techniques required on a daily basis.
TABLE OF CONTENTS Practical Power System Protection
Chapter 14: Feeder Protection Cable Feeders and Overhead Lines
14.1 Introduction
Two commercially available systems have been chosen as typical examples to illustrate the concepts. However there are other similar products on the market using essentially the same technology.
14.2 Translay (see Figure 14.1)
Figure 14.1: Simplified connections illustrating principles of operation
14.2.1 Translay is a Voltage Balance System
Whilst the feeder is healthy, the line CTs at each end carry equal currents. Equal and opposite voltages are induced in the secondary windings 12 and 12a and no current flows in the pilots. No magnetic flux is set up in the bottom magnets 16 and 16a so the relays do not operate. Under heavy through-fault conditions there may be a small circulating current due to line CT mismatch. A restraint torque is produced by bias loop 18, which also stabilizes the relay against pilot capacitance currents. A fault fed from one end causes current to circulate in the pilots and the relay at that end will operate to trip. A fault fed from both ends will cause a current reversal in the remote CTs, making the circulating current additive so that both ends operate to trip.
14.3 Solkor Protection
Solkor unit protection is used where solid metallic pilot wires are available. The system is a differential protection system and is available as Solkor R/Rf. Optional equipment includes pilot wire supervision and injection intertripping systems.
Solkor protection can be configured in two modes. The R mode caters for systems where pilot/earth insulation levels are 5 kV or less. The Rf...
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