# Fiber protection

## Introduction

With the continuous expansion of the scale of the power grid, the safe and stable operation of the power grid has become particularly important, and the requirements for relay protection are getting higher and higher. The application of optical fiber protection as the main protection of high-voltage lines in the power grid is becoming more and more common. Taking Guigang Power Supply Bureau as an example, there are currently 24 lines of 220kV and above voltage levels, equipped with 48 sets of main protection, of which 46 are optical fiber protection. , The optical fiber protection configuration rate reaches 96%. Optical fiber protection channel, as a channel for optical fiber protection to transmit data, is a prerequisite for the normal operation of optical fiber protection. The principle of optical fiber protection and optical fiber protection channel is analyzed, and how to better debug and maintain optical fiber protection channel is discussed for the reference of relevant personnel.

## Principle of optical fiber protection

Optical fiber protection uses optical fiber channel as a signal channel to transmit the comparison signal (electrical quantity or command signal) at both ends of the line, through calculation or logical judgment of the transmitted signal , Realize the full-line quick action function. At present, the principle of optical fiber protection for lines with voltage levels of 220kV and above is divided into the following two types.

1. Principle of optical fiber differential protection

Optical fiber differential protection uses optical fiber as the channel to transmit current information, and realizes the differential protection function by calculating the current on both sides. Realize full-line rapid movement. Take a 220kV line as an example. When an area fault occurs, the fault currents on both sides of the line flow to the fault point, and the vector sum of the currents on both sides becomes the action current. When a fault occurs in the area, there is a through current in the line, no action current is generated, only a braking current is generated, and the differential protection does not operate (note: the direction of the bus to the protected line is the positive direction).

2. Principles of fiber direction/distance protection

Optical fiber direction/distance protection is a longitudinal protection based on the direction of judgment, through the transmission of command signals, combined with the information on both sides for logic Judgment, to achieve full-line quick action. There are two types of logic judgments for longitudinal direction/distance protection: blocking type (no blocking signal is received, the side that meets the conditions will switch) and permissible type (after the side meets the conditions, it needs to receive the permission signal of the opposite side to trip. ).

## Principle of Fibre Channel

As the link between the protection information (current amount or command signal) on both sides of the line, Fibre Channel has always been a weak link in optical fiber protection. Once the fiber channel is interrupted, the corresponding main protection will be forced to quit operation, directly affecting the safety of the power grid.

There are two types of fiber channel connections: dedicated channels and multiplexed channels. The dedicated channel means that the devices on both sides of the line are directly connected through the fiber channel (that is, the protective pigtail is directly fused with the protection dedicated core of the optical cable or connected through the optical fiber distribution screen), and is mainly used for short circuits. Multiplexing channel means that the protection information is multiplexed to the PCM switch at a rate of 64kbit/s according to a certain protocol, and transmitted together with other information after multiplexing, or multiplexed to the E1 port of SDH at a rate of 2Mbit/s separately, and transmitted Protect data.

As an interface device that realizes the mutual conversion of optical signals and electrical signals, optical fiber protection communication interface equipment is mainly divided into two types: protection communication interface device (FOX-41A) and photoelectric conversion interface device.

The protection communication interface device FOX-41A is used for NARI RCS902 optical fiber distance or direction protection equipment. It uses optical fiber channel to transmit signals and can also be multiplexed with photoelectric conversion interface devices and communication equipment. It can be used for 64kbit. /S or 2Mbit/S transmission rate.

The photoelectric conversion interface device is divided into two types: one is the optical fiber differential protection device used for 2Mbit/S transmission rate and the SDH equipment interface multiplexing, such as MUX-2MC, GXC-2M, GXC-2M+ And so on, the second is the multiplexing of the optical fiber differential protection device used for the 64kbit/S transmission rate with the PCM machine, such as MUX-64B, GXC-64, etc.

## Fibre Channel Swap Method

Fibre Channel Swap mainly includes two parts: one refers to the protection device (optical difference protection), the photoelectric conversion device (MUX2M), and the protection communication interface (FOX41 ) And other devices to measure the optical power of the optical fiber transceiver port to ensure that the communication between the protection device, the photoelectric conversion device and the protection communication interface device is intact and the fiber attenuation is within the normal allowable range; the second is to verify the protection device The protection function. The following takes the RCS931 line protection device as an example to introduce the basic method of fiber channel swap.

1. Preparation: Modify the three control words related to the channel.

Master mode: Refers to whether the device is running in the master or slave mode. The protection devices on both sides must be the master on one side and the slave on the other.

Dedicated optical fiber: Set to 1 when using dedicated optical fiber, and set to 0 when multiplexing with PCM.

Channel self-loop or set the same side-to-side longitudinal link code: set to 1 during channel self-loop test, and set to 0 during normal operation.

2. Test the fiber channel data

For the channel wiring method of the dedicated fiber, the optical power of the transceiver port on the backplane of the protection device must be measured separately to verify the correctness of the fiber channel.

(1) Check whether the optical power level emitted by the protection device meets the requirements. If a dedicated optical fiber is used and the line is relatively long and the received optical power of the opposite side does not meet the receiving sensitivity requirements, the protection can be increased by jumpers The transmit power of the device.

(2) Check whether the optical power received by the protection meets the requirements, generally should be above -40dbm, if not, check whether the optical fibers are connected well, whether the optical fiber head is clean, and whether the attenuation of the optical fiber is consistent with the actual The line length is consistent (the attenuation of the pigtail is very small). For the channel wiring method of the multiplex fiber, in addition to testing the optical power of the above two points, it is also necessary to measure the optical power of the transceiver port of the photoelectric interface device.

(3) Measure the optical power level of the transmitting port of the photoelectric conversion interface device in the communication interface cabinet of the communication room, compare it with the optical power level received by the protection device, and detect the degradation between the two. The attenuation data varies according to the number of intermediate connectors, and there is not much difference.

(4) Measure the optical power level received by the photoelectric conversion interface device in the communication interface cabinet of the communication machine room, compare it with the optical power level emitted by the protection device, and detect the attenuation between the two , The attenuation data varies according to the number of intermediate joints, and there is not much difference. For multiplexed channels, a BER tester should also be used to test whether the multiplexed communication channels are good.

3. Main protection function verification

After completing the above inspection, restore the fixed value during normal operation, and at the same time restore the connection of the channel during normal operation, and put in the differential pressure plate to protect The device should not light up the abnormal channel light, and there should be no abnormal channel signal. The individual status counters in the channel status may occasionally increase. According to the different principles of the optical fiber protection device, the differential protection or direction (distance) protection function is debugged on both sides of the line.

## Resume the status before work

After the channel test and the protection function verification, the maintenance personnel set the device setting value according to the setting value sheet and put and return the pressure plate, and check the protection device and the photoelectric conversion interface The device has no abnormal alarm signal, and the protection device and the photoelectric interface device are restored to the state before the start of the work.

The test method of other types of optical fiber protection channels is similar to this, respectively measuring the receiving and sending levels of the protection device or the backplane of the protection communication interface, and the backplane of the photoelectric conversion interface device, compare them, and check the attenuation. Whether it is within the allowable range to determine whether the fiber channel is normal; verify the correctness of the protection logic by debugging the protection functions on both sides of the line.

## Operation and maintenance of fiber channel

In addition to regular preventive tests, fiber optic protection also needs to strengthen daily inspections. Under normal operation, the personnel on duty should pay attention to the following What time is it.

(1) Always record the data in the channel status to compare before and after and monitor the running status of the channel.

(2) Always observe whether the differential current is abnormal.

(3) Always check whether the warning light on the photoelectric conversion interface device is normal. The protection device and monitoring system have no "channel abnormality" alarm, and the "channel abnormality light" on the device panel does not light up.

## Summary

With the large-scale use of optical fiber protection, the problems of optical fiber protection channels are also increasing. It is recommended to strictly check the optical fiber protection before acceptance and put into operation to ensure the smooth flow of the protection channel. The correct protection function can improve the safety and stability of the optical fiber protection during operation.

This information was illegally obtained from 41021653

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