**3.2.3 The transducer**

The leakage current supplies energy enough to optically power a high efficient blue-green-LED (Marcou, 1997). The leakage current modulates the LED output power that is transmitted to the receptor by means of a specially protected POF. The emitted light from the LED is amplitude and wavelength modulated. In this work it was applied only amplitude modulation/demodulation technique.

Fig. 3.2.3. Picture of the POF-based leakage current sensor

The optical signal is detected by the receptor circuit, inside the Remote Station that performs the half cycle demodulation. Fig. 3.2.3 shows pictures of the transducer which was designed to be connect to the test-insulator. Calibration and measurement procedures of leakage waveforms were made under controlled laboratory conditions by a salt-spray chamber aiming to simulate the real conditions of the field.

Optical Fiber Sensors 17

The monitoring process is based on block dataset transference, which is related with values sampled from specific time interval. Figure 3.2.6 shows a set of data downloaded from the

Fig. 3.2.6. Results downloaded from the system's website. The upper trace is the ambient

The LED/POF technology applied in thr leakage current sensor presents some advantages over other techniques adopted in last years, i.e.: efficient, easy to handle, robust and reliable. Despite problems described on the literature, optical amplitude modulation technique applied to fiber optic sensing proved to be efficient enough to obtain the leakage current so that the use of frequency modulation technique proposed as alternative technique was not

The objectives of this project were reached, however, in order to this technique be of any usefulness to the company, it necessary to transform the data into information. This means to establish parameters which can determinate the real status of the insulator regarding the leakage current allowed to flow to the ground. After such parameter has been established, it will be possible to issue the "washing procedures" alarm, meaning that if the set of insulators were not washed immediately, a flashover may occur. The establishment of these parameters would produce the logistic insertion of this activity in company, reducing the risk probability of an insulator failing. To create these parameters it would be necessary to analyze a great diversified amount of data from different critical points of maritime pollution inside the company operation area. Thus, it would be possible to determinate the optimum point to intervention (washing of insulators). On the other hand, it could be possible to establish an analytical relationship between different kinds of insulators under same pollution conditions, aiming at the creation of a "performance indicator" to each insulator under the same conditions. This analytic methodology could supply most

temperature and the lower trace is the leakage current.

adequate insulator to specific geo-meteorological region.

**3.2.7 Discussion and conclusions** 

necessary (Culshaw& Dakin, 1989 and 1997).

**3.2.6 Results** 

system's website.
