What is a high-frequency locked signal? What are the action conditions? How does it work?
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What is a high-frequency locked signal? What are the action conditions? How does it work? The blocking signal is the signal that triggers the blocking protection to trip; in other words, the absence of a blocking signal is a necessary condition for the protection to be able to trip. Protection takes effect on tripping only when both of the following conditions are met: (1) The local protection device operates ； (2) No lockout signal. In the event of an external fault, a blocking signal is sent from the end of the line closest to the fault site. When the relay protection device at the other end of the line receives this blocking signal, its protective components will activate, but no trip command will be issued. In the event of an internal fault, no blocking signal is sent from either end of the line, and neither end receives such a signal; once the protective device activates, a trip can be initiated.
High-frequency protection includes phase difference high-frequency protection and power direction blocking high-frequency protection. Phase difference high-frequency protection measures and compares the phases of the current values on both sides of the protected line, using carrier communication over the transmission line to transmit the phase information of the currents on those two sides. The power direction locking high-frequency protection compares the power directions on both sides of the protected line; it defines a positive power direction as being from the busbar to a certain line, and a negative direction as being from that line back to the busbar. In the event of an internal fault in the line, the power direction on both sides is from the busbar to the line, which triggers the protection to trip, with the signal transmission direction remaining the same
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