Conference Proceedings of CMD2010

Monitoring Insulator Leakage Current in South of Brazil: Different Approaches for Different

Requirements

Luiz Henrique Meyer1*, Graziano Cardoso1, Carlos Oliboni1, Hugo Almaguer1, Fernando Molina2

1 University of Blumenau – BRAZIL 2 CELESC – Centrais Elétricas de Santa Catarina - BRAZIL

*E-mail: meyer@furb.br

Abstract—The salt contamination over insulation surface is a problem that has to be monitored in order to avoid failure of the insulation systems, such as insulators, surge-arrester housing, bushing and switches. This type of contamination is a problem for many utilities in Brazil and has originated some work in order to better understand the problem. This work presents the development of leakage current monitor devices for different requirements, including quick development, insulation between high voltage and low voltage, and research.

Keywords – leakage current monitor, insulators, insulation systen, salt contamination.

I. INTRODUCTION

The problem of salt contamination of insulating systems (insulators, bushings, switches and surge arresters) in Brazilian coast is a problem that remains unsolved [1, 2]. No definite solution has been proposed and applied by the utilities. There have been many initiatives [3-5] though in order to reduce the problem caused by such contamination. The use of polymeric insulators with protected areas, the use of coatings and booster sheds for ceramic insulators are some of the initiatives. Some utilities carry out periodic maintenance procedures, such as washing, in order to reduce the interruptions of the distribution system. Some other initiatives are found on research field, as development of semiconducting glaze for ceramic insulators and use of nano-additives for silicone rubber coatings [6], both presenting application potential, but requiring further development for commercial use [7-9]. In this scenario, some developments have been made in order to better understand the problem of insulation contamination, and three different devices for leakage current monitoring were built. The first one is very simple and basically is a power quality monitor modified to record leakage current. A second device is more complex, based on a microcontroller and also records humidity and temperature. The third device in fact is a monitoring station, capable to simultaneously measure and record up to 40 insulation systems; also, there is a weather station, and an ESDD and NSDD assemblies. In this work, it is described the details of the devices built and main features.

II. EXPERIMENTAL

A. Quick development – LC Monitor A

To monitor leakage current, measure and record, basically, it is needed a shunt resistance, an acquisition system and a memory module. Except for the shunt resistance, the acquisition system and memory module is already built in a commercial power quality monitor. The modification of such device to work as leakage current monitor is easy to accomplish and, when quick development is required, this could be a solution. In figure 1 and the device is being installed in the field.

Figure 1. Installation of the power quality monitor as a leakage current monitor. The connections to the insulators at high voltage can be seen. The device is powered by the low voltage.

Another version of such device was developed, and can be seen in figure 2. The assembly is more compact, but still, there is an electrical connection between high voltage and low voltage.

B. Insulation Between High Voltage and Low Voltage – LC Monitor B

The main problems related to the use of the device described above are the bulkiness of the assembly, and mainly, the possibility of a discharge between high voltage and low voltage sides, where the safety is an issue.

The sponsor of this work are University of Blumenau – SC – Brazil, R&D Program from CELESC/ANEEL and CNPq, a Brazilian Research National Council.

Conference Proceedings of CMD2010

Figure 2. Assembly of a power quality monitor as a leakage current monitor. The small transformers provide some insulation, and still the device is powered by the low voltage of the distribution system.

To overcome this problem, a device that incorporates optical fibers was built. In this device, the power for its operation is provided by 12V batteries, and there is no electrical connection between high and low voltage sides of the distribution system. The device is run by a microcontroller and records the data in a memory card, and also has humidity and temperature sensors. A diagrammatic drawing of its connections and components can be seen in figure 3.

Local Unit A

Local Unit B

Local Unit C

Collecting ring

Optical fibers

Central Unit

Electrical wire

Figure 3. Diagrammatic drawing of the connections and components of the leakage current monitor, with insulation between high voltage and low voltage side. The units are powered by 12V batteries.

C. Research – Monitoring Station

An outdoor monitoring station was built in Itajai-SC-Brazil to study the performance of insulating systems, as insulators, bushings, and switches, at a voltage of 15 kV. Up to 40 insulating systems can be installed and have their leakage current monitored and recorded, in terms of peak, RMS and accumulated power loss. The acquisition system is based in a PC with a National Instruments cards, with LabView, and samples the current at about 16 kHz per channel. The system has a air conditioning device, communication system, weather station, and ESDD and NSDD assemblies. This monitoring system is built at about 1000m from the sea, and has little exposition to salt contamination, despite its

distance from the sea. A new station is being built in Laguna-SC-Brazil, which is recognized by the utility as a very harsh environment, with same features as the station built in Itajai. This new station faces the open sea and is about 50m away from water. North-east winds bring salt contamination to distribution lines and accelerate deterioration by dry-band arcing on polymeric insulators. These insulators have to be replaced sometimes twice a year and washing procedures are carried out frequently.

Figure 4. The monitoring station built by the beach. Two poles support the structure that holds up to 40 insulation systems, under applied voltage of 15 kV. In the ground, beside the right pole, there is a control cabinet. In detail the 10 kVA transformer and the wireless weather station are shown.

Figure 5. The main cabinet is composed by a PC running LabView that controls the acquisition card. Outside of the left wall there is a protection cabinet, and at the door, the signal conditioning system. The cabinet also holds a air conditioning device to control the internal temperature and a communincation system.

Conference Proceedings of CMD2010

To study the insulation performance, it is fundamental to have leakage current and weather variables available. The station started its operation since beginning of 2010 and it is accumulating data that can be already analyzed.

III. RESULTS

Some results from the different built devices are shown below.

A. LC Monitor A

The leakage current monitor shown in figures 1 and 2 was installed in a heavy salt contamination area, about 50m from the sea. The leakage current was recorded from hybrid design of ceramic and polymeric materials insulator, as seen as an insert in figure 6. The leakage current, of three of such insulators, is seen in the same figure 6, during one week period.

Figure 6. Leakage current of three hybrid design insulator (see insert) installed in a pole about 50m from sea. The fase to ground voltage is about 8 kV.

It can be seen that during night time the levels of leakage current increases due to the humidity present in the air. During daytime, the surface dries up and very little leakage current is recorded. It can be seen that in last three days there were higher levels of leakage current registered, which was observed to be due to rain during those days. It should be noted that the installation of the leakage current monitor required the intervention of live-line personnel. Despite of it, the whole process was quite simple and fast, as required by the time of installation.

B. LC Monitor B

As the device is new and it was not installed in the field yet, the results presented are from a salt fog chamber, where three different types of insulators were installed. These insulators

are seen in figure 7 and the recorded leakage current can be seen in figure 7.

Figure 7. Insulators tested as in figure 8.

Figure 8. Recorded leakage current of insulators installed in a salt fog chamber. This device was developed with optical fibers to provide insulation between high and low voltage.

From figure 8, it can be observed that the pin type developed larger current in the very beginning of the test, mainly because of its shorter leakage distance. As the insulators get wet, the protected surface of the pin type maintain the leakage current in same levels as the beginning of the test, while the post type ceramic develops larger currents. If the test was prolonged, the situation could have changed, as even the protected areas of the pin type would also get wet. The polymeric insulator maintains lower current levels than the other insulators for the entire test.

C. Monitoring Station

Some results from the monitoring station are presented in figure 9.

Figure 9. Recorded RMS leakage current for ceramic and polymeric insulators in the field, in the monitoring station.

Conference Proceedings of CMD2010

IV. CONCLUSIONS

This work presents three developed devices for measuring leakage current. Each device has a different approach, accordingly to some requirements. The very first leakage current monitor is in fact a modified power quality monitor, which demands little development and implementation time. On the other hand it has limitations regarding the size of the final assembly; also, its software is not open to allow for modifications. The second developed device is based on microcontrollers linked by optical fibers, which provides insulation between high voltage and low voltage side. The software was developed in house and it is easy to change and accommodate modifications. It is powered by 12V batteries and records its data to a memory card. The third device is in fact a monitoring station, for up to 40 insulators, and provides data mainly for research. The development of such devices is helping the utility to understand the performance of the insulation systems that they are using, reducing their costs and increasing the levels of their energy quality indexes.

ACKNOWLEDGMENT

The authors would like to thanks CELESC-Centrais Elétricas de Santa Catarina in helping to install the monitoring devices in their system.

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