**3.2.4 Remote station**

The Remote Station contains the sensor interrogation system the CPU and the cell-phone transmitter. The electronic hardware is composed by the followings modules: CPU board associated to the datalogger system; power supply; battery and cell phone (see Fig. 3.2.4). The RS, designed to work under field conditions, is attached at the metallic structure located at medium height of the tower (see Fig. 3.2.2a).

Fig. 3.2.4. Electronic hardware inside of Remote Station: power supply, battery, datalogger, CPU and cell phone.

#### **3.2.5 The software**

The software is responsible for establishing the communication between RS (installed in field) and any authenticated computer connected to the Internet. The signals are acquired, processed and stored in memory. In another cycle, the data is sent to the remote computer via modem. Another program is responsible for remote updates of the local software. This feature is particularly important because the monitoring place is about 2000 km away from the Laboratory and very often a new update of the local program has to be installed in the system and this is done remotely. Fig. 3.2.5 shows the remote screen as seen in our laboratory.

Fig. 3.2.5. Main screen to be monitored by the Internet.

### **3.2.6 Results**

16 Modern Telemetry

The Remote Station contains the sensor interrogation system the CPU and the cell-phone transmitter. The electronic hardware is composed by the followings modules: CPU board associated to the datalogger system; power supply; battery and cell phone (see Fig. 3.2.4). The RS, designed to work under field conditions, is attached at the metallic structure located

Fig. 3.2.4. Electronic hardware inside of Remote Station: power supply, battery, datalogger,

The software is responsible for establishing the communication between RS (installed in field) and any authenticated computer connected to the Internet. The signals are acquired, processed and stored in memory. In another cycle, the data is sent to the remote computer via modem. Another program is responsible for remote updates of the local software. This feature is particularly important because the monitoring place is about 2000 km away from the Laboratory and very often a new update of the local program has to be installed in the system

and this is done remotely. Fig. 3.2.5 shows the remote screen as seen in our laboratory.

Fig. 3.2.5. Main screen to be monitored by the Internet.

**3.2.4 Remote station** 

CPU and cell phone.

**3.2.5 The software** 

at medium height of the tower (see Fig. 3.2.2a).

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 system's website.

Fig. 3.2.6. Results downloaded from the system's website. The upper trace is the ambient temperature and the lower trace is the leakage current.

#### **3.2.7 Discussion and conclusions**

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 necessary (Culshaw& Dakin, 1989 and 1997).

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 adequate insulator to specific geo-meteorological region.

Optical Fiber Sensors 19

by the former in the following manner: in ground potential a laser injects 830 nm light in a multimode ordinary telecommunications optical fiber. This fiber is directed to the high potential subsystem through a specially designed 138 kV polymeric insulator. At the high potential level, the laser light is converted into electric energy through a conventional silicon photodetector. This energy powers all electronic circuits embarked on the high voltage level: current and temperature sensors, microcontroller and fiber optic serial transmitter. The transmitter relays the data collected to the ground potential through another multi-mode

A Rogowski coil, a helical coil sensor uniformly wound on a relatively long non-magnetic strip [Tumanski, 2007], is used as a current sensor, which offers advantages compared to conventional current transformers, such as linearity and easy handling [Ward and Exon, 1993]. The cable temperature measurement is implemented through a conventional LM35 integrated circuit, which is very simple and inexpensive. The sensors' electrical output signals are digitalized and processed by means of a low-power microcontroller and sent to a receiving system located at the low-voltage region using a LED operating at 850 nm

All the circuits located in the high voltage area are optically powered; a laser module at the low-voltage area launches up to 1W optical power at 830 nm in another multimode 62.5/125-µm fiber, conducting the energy to the photovoltaic power converter remotely situated. Power and data channels can be combined into a single optical fiber linking both high and low voltage areas [Böttger et al, 2008]; however, in this monitoring system for TL an option for dedicated fiber cables was made [Tardy et al, 1995 and Pember et al, 1995]. A

Fig. 3.3.1. General view of the system, showing the circuits situated in high and low voltage

The system is comprised of the following sub-modulus: the laser module located at the low voltage region, 830 nm operating wavelength, and controlled by a driver which can manage

optical fiber that is also insulated by the previously mentioned 138 kV insulator.

wavelength, connected to a multimode 62.5/125-µm optical fiber.

general view of the system is presented in Fig. 3.3.1.

**3.3.3 Power over fiber link** 

regions.

#### **3.3 Hybrid optoelectronic sensor for current and temperature monitoring in overhead transmission lines**

#### **3.3.1 Introduction**

Transmission line (TL) capacity is determined by the maximum power transmitted from the source to the load. Since the line voltage is always fixed, this capacity is in fact the maximum current capable to flow in the TL. Normally, during the project, this maximum power is established and the whole project is built around this parameter. When the energy demands grow, technicians are worried to infringe standards of security and performance, such as wire temperature and sag (conductor-to-ground distance).

The sag is a very important parameter since it is directly related to the current: the higher the current, the higher the conductor temperature, and so thermal expansion, consequently decreasing the conductor-to-ground distance. Nevertheless, the conductor temperature does not depend only on the electrical current. It is strongly dependent on environmental features such as wind velocity and direction, ambient air temperature, pollution, cable construction, rain and snow conditions [Douglas and Thrash, 2007]. So, TL maximum sag characteristic is determined always considering the worst case aiming the best safety conditions.

With the increasing demand for electrical energy, especially in developing countries, the idea to utilize the full transmission capacity of already existing TL, instead of built new ones, is quite attractive. The idea behind this project, which will be confirmed by data collected from the system in the field, is that the temperature of the conductor depends on current and weather conditions, but the sag only depends on the conductor temperature, regardless the weather conditions.

The system operates in two stages. The first stage will provide the measurement of three parameters: line current, conductor temperature and sag. This system will be installed in one or two TL towers for sufficient period of time to acquire data at all possible situations. This information will make it feasible to establish a set of calibration curves which will relate sag distance with conductor temperature, and sag distance with line current. The sag will be measured by taken photographs of a target hung on the middle of the catenary. A neural network recognizes the target on the picture and calculates its distance from a background reference.

Since the sag is dependent on line current and conductor temperature, on the second stage of the project only current and temperature sensors will remain installed on the TL tower. Thus, technicians will be able to infer the sag value exclusively from the latter parameters. The conductor-sag distance, acquired using the digital processing of digital camera images, plus the data regarding conductor current and temperature, will enable the development of a catenary behavior estimation algorithm, for each monitored and calibrated TL conductor cable, hence eliminating the necessity of constant monitoring.

#### **3.3.2 System description**

The system is comprised of three monitoring sub-systems: a temperature sensor, a current sensor and a conductor-sag monitoring sub-system. These three sub-systems will be installed on a 138 kV transmission line tower, in order to monitor the sag between this tower and the next one, being this conductor sag a strategic and representative one. Once the effectiveness of this method is confirmed, the system will be reproduced and taken to monitor problematic sags in the company's transmission lines.

The current transformer and the temperature system are composed by two subsystems: the one in ground potential and the one in high voltage (138 kV); the latter is optically powered

**3.3 Hybrid optoelectronic sensor for current and temperature monitoring in overhead** 

Transmission line (TL) capacity is determined by the maximum power transmitted from the source to the load. Since the line voltage is always fixed, this capacity is in fact the maximum current capable to flow in the TL. Normally, during the project, this maximum power is established and the whole project is built around this parameter. When the energy demands grow, technicians are worried to infringe standards of security and performance, such as

The sag is a very important parameter since it is directly related to the current: the higher the current, the higher the conductor temperature, and so thermal expansion, consequently decreasing the conductor-to-ground distance. Nevertheless, the conductor temperature does not depend only on the electrical current. It is strongly dependent on environmental features such as wind velocity and direction, ambient air temperature, pollution, cable construction, rain and snow conditions [Douglas and Thrash, 2007]. So, TL maximum sag characteristic is

With the increasing demand for electrical energy, especially in developing countries, the idea to utilize the full transmission capacity of already existing TL, instead of built new ones, is quite attractive. The idea behind this project, which will be confirmed by data collected from the system in the field, is that the temperature of the conductor depends on current and weather conditions, but the sag only depends on the conductor temperature,

The system operates in two stages. The first stage will provide the measurement of three parameters: line current, conductor temperature and sag. This system will be installed in one or two TL towers for sufficient period of time to acquire data at all possible situations. This information will make it feasible to establish a set of calibration curves which will relate sag distance with conductor temperature, and sag distance with line current. The sag will be measured by taken photographs of a target hung on the middle of the catenary. A neural network recognizes the target on the picture and calculates its distance from a background

Since the sag is dependent on line current and conductor temperature, on the second stage of the project only current and temperature sensors will remain installed on the TL tower. Thus, technicians will be able to infer the sag value exclusively from the latter parameters. The conductor-sag distance, acquired using the digital processing of digital camera images, plus the data regarding conductor current and temperature, will enable the development of a catenary behavior estimation algorithm, for each monitored and calibrated TL conductor

The system is comprised of three monitoring sub-systems: a temperature sensor, a current sensor and a conductor-sag monitoring sub-system. These three sub-systems will be installed on a 138 kV transmission line tower, in order to monitor the sag between this tower and the next one, being this conductor sag a strategic and representative one. Once the effectiveness of this method is confirmed, the system will be reproduced and taken to

The current transformer and the temperature system are composed by two subsystems: the one in ground potential and the one in high voltage (138 kV); the latter is optically powered

determined always considering the worst case aiming the best safety conditions.

wire temperature and sag (conductor-to-ground distance).

cable, hence eliminating the necessity of constant monitoring.

monitor problematic sags in the company's transmission lines.

**transmission lines 3.3.1 Introduction** 

regardless the weather conditions.

reference.

**3.3.2 System description** 

by the former in the following manner: in ground potential a laser injects 830 nm light in a multimode ordinary telecommunications optical fiber. This fiber is directed to the high potential subsystem through a specially designed 138 kV polymeric insulator. At the high potential level, the laser light is converted into electric energy through a conventional silicon photodetector. This energy powers all electronic circuits embarked on the high voltage level: current and temperature sensors, microcontroller and fiber optic serial transmitter. The transmitter relays the data collected to the ground potential through another multi-mode optical fiber that is also insulated by the previously mentioned 138 kV insulator.

A Rogowski coil, a helical coil sensor uniformly wound on a relatively long non-magnetic strip [Tumanski, 2007], is used as a current sensor, which offers advantages compared to conventional current transformers, such as linearity and easy handling [Ward and Exon, 1993]. The cable temperature measurement is implemented through a conventional LM35 integrated circuit, which is very simple and inexpensive. The sensors' electrical output signals are digitalized and processed by means of a low-power microcontroller and sent to a receiving system located at the low-voltage region using a LED operating at 850 nm wavelength, connected to a multimode 62.5/125-µm optical fiber.

#### **3.3.3 Power over fiber link**

All the circuits located in the high voltage area are optically powered; a laser module at the low-voltage area launches up to 1W optical power at 830 nm in another multimode 62.5/125-µm fiber, conducting the energy to the photovoltaic power converter remotely situated. Power and data channels can be combined into a single optical fiber linking both high and low voltage areas [Böttger et al, 2008]; however, in this monitoring system for TL an option for dedicated fiber cables was made [Tardy et al, 1995 and Pember et al, 1995]. A general view of the system is presented in Fig. 3.3.1.

Fig. 3.3.1. General view of the system, showing the circuits situated in high and low voltage regions.

The system is comprised of the following sub-modulus: the laser module located at the low voltage region, 830 nm operating wavelength, and controlled by a driver which can manage

Optical Fiber Sensors 21

It has been shown that the proposed monitoring system for transmission line cables measurement of temperature and current provides reliable data. Since silica optical fiber cables are utilized in communications and power supply links, insulation between the sensor head and the user operation site is guaranteed, eliminating the use conventional

The measured values were compared with reference values, the latter being outfitted by commercial measurement laboratory instruments; and small errors were observed, for both current and temperature data. For an even more reliable study of the system accuracy, a

Future works include the system field installation, in Piracicaba TL, which requires the improvement of system mechanical robustness, and the addition of the sag monitoring subsystem. It is expected that the data collected, together with the sag information, will provide support for the development of an algorithm for the estimation of conductor-sag

**3.4 Optical high voltage sensor based in fiber Bragg grating and PZT piezoelectric** 

Electric power facilities, such as substations, rely on instrument transformers for their functionality and protection. They are divided into voltage transformers (VT) and current transformers (CT) for measuring and controlling voltage and current, respectively. The role of the instrument transformer is to provide accurate signals for protection, control and metering systems, including revenue metering. These requirements place stringent demands on the accuracy and reliability of the instrument transformer to guarantee the correct functionality for protection systems and precise measurement for metering

Created over a century ago, they are reliable for over-voltage and over-current protection; allow 0.2% revenue metering accuracy and their behavior is well known under both normal and abnormal conditions. Nevertheless, these pieces of equipment are made entirely of copper, ceramic and iron with all empty spaces filled with oil, which are weighty materials, producing bulky, heavy and clumsy equipment. On top of that, they tend to explode without prior warning, resulting in the potential destruction of nearby equipment by pieces

Optical voltage transducers offer many improvements on traditional inductive and capacitive voltage transformers such as linear performance and wider dynamic range,

The optical-fiber sensors industry has grown in recent years, and most of the efforts involving the sensors industry focused the use of Fiber Bragg Grating (FBG) as a sensor element. Among the parameters of interest most of the works found in the literature focus on temperature, strain, pressure, displacement, acceleration, vibration, voltage and

The behavior of optical current transformer (OCT) and optical voltage transformer (OVT) applied on electric power transmission system has been widely discussed in the literature because they present advantages when compared with conventional transformers. The innovations coming from the optical transformers circumvent problems such as the risk of explosion, high weight, electric safety, insulation oil, difficulty of installation, etc [Sawa et

of sharp ceramics and furthermore putting the substation personnel at risk.

lighter weight, smaller size and improved safety.

calibration using tracked instruments must be carried out.

**3.3.4 Conclusions** 

copper cabling.

values.

**ceramics** 

purposes.

current.

**3.4.1 Introduction** 

the launch of up to 1 W optical power; a 40m-long-62.5-µm multimode optical fiber to guide the optical power; and a photovoltaic power converter (PPC), which is an array of semiconducting diodes.

Optical attenuation is a key issue when photonic power is used. Fiber splices and connectors were implemented to incorporate the 40 m optical waveguide into the power-over-fiber link, including the isolator showed in Figure 3.3.1, between the laser and the PPC on the other end. The estimated losses for the fiber splices and the connector are 0.01dB and 0.30dB, respectively; the optical fiber attenuation for the first transmission window should also be considered, accounting approximately 0.12dB (forty meters long). Consequently, the total estimated attenuation in the power-over-fiber link is 0.43dB, which does not affect the system operation. Since the system is installed outdoors, according to the international standard IEC 60529, the circuits and optical connectors are allocated inside an IP66 rated enclosure, providing increased long-term functionality and greater protection against dust and humidity. The electronic system placed close to the conductor cable was designed to perform two main functions: provide electrical power to the sensors and data processing elements, carry out the digital-to-analog conversion and the communication between high and low voltage regions. The PPC provides 3.5 V that is raised to 5 V using a DC-DC converter. Another DC-DC converter provides the symmetric ±10 V to the Rogowski coil integrator circuit. A low-consumption microcontroller executes data acquisition, treatment and communication between low and high voltage areas. A RMS-to-DC operation is effectuated on the Rogowski coil integrator signal, which produces a sinusoidal function proportional to the current, prior to the microcontroller 10 bit analog-to-digital conversion. The data are serially transmitted at 9600 bps via a 850 nm LED (see Figure 3.3.2). The light signal is coupled to a 40-m-62.5-µm optical fiber, dedicated for data transmission.

Fig. 3.3.2. High voltage area circuit general view: (Left) microcontroller inputs and voltage levels, Right) communications schematic.

The low voltage area circuit, located at a base station, performs the optical-to-electrical conversion by a high speed PIN photodiode, operating in photovoltaic mode, using the technique suggested by Werneck and Abrantes [2004]. Before the serial transmission to the instrumentation computer, the signal is converted to EIA-232 levels. Fig. 3.4.1 shows the low voltage area schematic for the monitoring system communications section. Energy to drive the laser for photonic power, which is also situated at the low voltage area, and for the data treatment circuits, after the optical-to-electrical conversion, will be provided by solar energy. Batteries, charged by a solar panel, supply electrical power to the circuits.

the launch of up to 1 W optical power; a 40m-long-62.5-µm multimode optical fiber to guide the optical power; and a photovoltaic power converter (PPC), which is an array of

Optical attenuation is a key issue when photonic power is used. Fiber splices and connectors were implemented to incorporate the 40 m optical waveguide into the power-over-fiber link, including the isolator showed in Figure 3.3.1, between the laser and the PPC on the other end. The estimated losses for the fiber splices and the connector are 0.01dB and 0.30dB, respectively; the optical fiber attenuation for the first transmission window should also be considered, accounting approximately 0.12dB (forty meters long). Consequently, the total estimated attenuation in the power-over-fiber link is 0.43dB, which does not affect the system operation. Since the system is installed outdoors, according to the international standard IEC 60529, the circuits and optical connectors are allocated inside an IP66 rated enclosure, providing increased long-term functionality and greater protection against dust and humidity. The electronic system placed close to the conductor cable was designed to perform two main functions: provide electrical power to the sensors and data processing elements, carry out the digital-to-analog conversion and the communication between high and low voltage regions. The PPC provides 3.5 V that is raised to 5 V using a DC-DC converter. Another DC-DC converter provides the symmetric ±10 V to the Rogowski coil integrator circuit. A low-consumption microcontroller executes data acquisition, treatment and communication between low and high voltage areas. A RMS-to-DC operation is effectuated on the Rogowski coil integrator signal, which produces a sinusoidal function proportional to the current, prior to the microcontroller 10 bit analog-to-digital conversion. The data are serially transmitted at 9600 bps via a 850 nm LED (see Figure 3.3.2). The light

signal is coupled to a 40-m-62.5-µm optical fiber, dedicated for data transmission.

Fig. 3.3.2. High voltage area circuit general view: (Left) microcontroller inputs and voltage

The low voltage area circuit, located at a base station, performs the optical-to-electrical conversion by a high speed PIN photodiode, operating in photovoltaic mode, using the technique suggested by Werneck and Abrantes [2004]. Before the serial transmission to the instrumentation computer, the signal is converted to EIA-232 levels. Fig. 3.4.1 shows the low voltage area schematic for the monitoring system communications section. Energy to drive the laser for photonic power, which is also situated at the low voltage area, and for the data treatment circuits, after the optical-to-electrical conversion, will be provided by solar energy.

Batteries, charged by a solar panel, supply electrical power to the circuits.

levels, Right) communications schematic.

semiconducting diodes.
