My first review for MDPI Sensors (ISSN 1424-8220) Journal

The manuscript Wei, J.; Hao, Y.; Fu, Y.; Yang, L.; Gan, J.; Li, H. Experimental Study on Glaze Icing Detection of 110 kV Composite Insulators Using Fiber Bragg Gratings. Sensors 2020, 20, 1834 was reviewed by me for MDPI Sensors (ISSN 1424-8220) Journal.

In this paper, are consider a glaze icing detection as an essential part of the security and stability of power grids. Conventional methods suffer from difficulties in harsh weather, undoubtedly. The influence of high voltage electric (and magnetic) field also contributes to difficulties of glaze icing detection. In summary, intelligent sensing technologies are one of the core foundations of the sensing layer in power networks. The paper contains experimental results of glaze icing and icicles detection. The experiment and its results description are very interesting and useful.

I made three comments

• In the Figure 2с given distribution diagram of three fibers and FBGs along them. Fourteen FBGs are inscribed in #1 and #2 fibers and thirteen is inscribed in #3 fiber, But only nine FBGs are shown in Figure 2c, schematically. It will be better to draw a temperature sensor also.

• The FBG strain sensor placement, shown in Figures 2b and 4, is above the big shed. The hanging weight on a big shed for simulating icicle load leads to the central wavelength increasing of the FBG strain sensor. Similar dependence is shown in Figure 8, also. The maximum negative central wavelength shift observed when angles of icicles and FBG are matched, both equal to 0. The wavelength shift dependencies on force shown on the (8)-(12) formulas show negative dependence. It is not clear to understand.
  The Fg applying on the side of the big shed will lead to stretching above the FBG strain sensor, the period of FBG will increase, and as a result, will increase its central wavelength. Look at the picture be-dependencies low.

Hence, the relations between simulated load and FBGs central wavelength shift show the negative dependence. The load force increasing leads to decreasing of FBGs central wavelength shift. It is obscure.

It will be useful to give the forces application scheme on the above FBG strain sensor with the Fg force applying on the big shed side for better understanding.

• The central wavelength shift dependence on temperature, shown in Figure 6, demonstrates very similar character (such as the slope or gradient and the y-intercept) for each line. All our own experiments, connected with FBG temperature sensors designing, do not allow make the conclusion that central wavelength shift dependence on temperature can be similar for two different sensors. But the dependence shown in Figure 6 demonstrates absolutely identical dependencies for 39 independent sensors embedded into external matter.

I can suggest some not obligate recommendations, such as:

Even high elasticity of the ceramic pipe module may not necessarily prevent the effects of tension/compression FBG during, for example, bending of this ceramic tube. It would be nice to give a detailed explanation of its use.  Only one temperature compensation sensor is used for each optical fiber (optical channel). The insulation length of FXBW-110/100 (Table 1) is very large (more than 1000 mm), there is now conviction that a temperature at the one end is equal to the temperature at the second one end of FXBW-110/100. A mathematical model and a location algorithm development will be very useful for next science academic investigations. But it seems very bulky approach to glaze icing detection task solving to use it in practice. At first, it requires a lot of sensors on each insulator (more than 39). At second it requires 3 independent fiber channels on each insulator. Third, a lot of sensors require a very complex interrogation system.  It seems, that the task can be solved by using one sensor per insulator. It is important to include in model a wind and windflaw influence on measurements, also.