The Analysis And Solution Of Transmission Channel Interference In Relay Protection

Fiber channel has become the first choice of transmission channel in relay protection. In order to ensure the normal transmission of fiber protection signal, the higher demand is proposed by the relay protection to anti-interference capability of the transmission channel, and how to effectively solve the problem of fiber channel interference is the key of the right action of fiber protection. In this thesis, the reason to interfere with the normal transmission of fiber signal is identified through analyzing the twice fiber protection about not acting in Yunnan power grid and effective solutions are proposed to ensure stable and reliable operation of the relay.First, the situation of the application about fiber of the relay is described in this thesis. Second, the requirements of fiber protection and relay protection on the channel are researched, and the factors of leading to fiber channel interference are analyzed. Finally, through the detailed analysis of two events about not acting to protect in Yunnan power grid, the reasons about not acting to protect of is obtained as following, fiber channel interference is caused by ground potential difference, coaxial cable of the fiber channel is influenced by electromagnetic interference, fiber current differential protection is not synchronized sampling. Increasing the ground bronze to establish uniform grid about resolving the interference caused by ground potential difference, shorting the signal transmission distance of optical fiber to reduce electromagnetic interference in coaxial cable of the fiber channel and modifying the synchronous logic of the differential protection to achieve sampling synchronization is put forward. Meanwhile, in order to enhance the safety about the use of fiber channel, three kinds of line protection constitute programs consist of dual fiber current differential protection and public communication network, dual fiber current differential protection and high-frequency distance protection, dual fiber current differential protection and optical distance protection are put forward. Aiming at the interference of communication room, through analyzing the anti-interference function and the against over-voltage ability of the shield on secondary cable, four specific anti-interference measures are given as following, single shield coax cable grounding at both ends of the shield, double shielded or compound shielded secondary cable grounded at one end in the shield and at both ends outside the shield, one point grounding is used when the shield of the second cable has shielding effect and as a signal return circuit and secondary cable between substation control room and switchyard grounding at switchyard end through the appropriate resistance, the main control room connected directly to ground. The electromagnetic interference of equipments in communication room is effectively inhabited.