Single-Pole Tripping; Overview - GE L60 Instructions Manual

SINGLE-POLE TRIPPING

The L60 can be programmed to perform an automatic check-back. Under normal system conditions, a relay can initiate
transmission and modulate the analog signal to exchange small amounts of information. The ability to abort in cases of
system faults is a key to successful deployment. This feature can replace the guard signal when the latter is not available.
Furthermore, it provides a more comprehensive communications check from one center of relaying intelligence in the
microprocessor at one end to its companion at the other line terminal. This covers all links in the chain of communications,
not just the carrier part of the system.
The advantages of the L60 implementation of phase-comparison relaying with more pure and secure digital calculations
are summarized as follows. The following methods are critically important to the effectiveness of the new 87PC element.
• Separated CT inputs from multiple breakers feeding the line enables proper handling of bus through faults at a line
terminal, as explained
• Developing comparison signals from each breaker separately, and combining with the logic explained, eliminates
security risks caused by combining the breaker currents before calculating the comparison signals
• Treating channel receiver inputs as analog signals and sampling the waveform at high speed enables processing of
the receiver outputs that overcomes misbehaviors of the channel that fooled earlier phase-comparison
implementations, as explained
9.2 Single-pole tripping

9.2.1 Overview

9.2.1.1 Introduction
Single pole operations make use of many features of the relay. At minimum, the trip output, recloser, breaker control, open
9 pole detector, and phase selector must be fully programmed and in service; and either protection elements or digital
inputs representing fault detection must be available for successful operation. When single pole trip-and-reclose is
required overall control within the relay is performed by the trip output element. This element includes interfaces with
pilot-aided schemes, the line pickup, breaker control, and breaker failure elements.
9-36
Figure 9-27: Trip integration logic (relay COMTRADE record)
CHAPTER 9: THEORY OF OPERATION
L60 LINE PHASE COMPARISON SYSTEM – INSTRUCTION MANUAL