# Suggested Temperature Monitoring System for Distribution Transformers by Using Microcontroller Scheme

• El-Gawad, Amal F. Abd (Electrical Power and Machines Dept., Zagazig University)
• Accepted : 2015.06.19
• Published : 2015.09.01

#### Abstract

The paper presents a monitoring system for the cooling of distribution transformers. The suggested system is controlled by a microcontroller scheme. The system is designed to control the oil temperature. It gives a solution to improve the cooling system by adding a number of fans especially for indoor transformers that are placed in badly-ventilated rooms. Also, the paper includes an alarm system with the possibility of tripping the transformer if it is necessary. The monitoring system consists of acquisition temperature sensor, and on-site unit. The hardware and software of the on-site unit are demonstrated with sufficient illustrations. Small prototype is constructed in the laboratory. Some laboratory experiments are carried out for examining the designed circuit by using Proteus Virtual System Modeling as well as for testing the prototype monitoring system. Concerning this research point, a study is carried out to evaluate the economic feasibility. The results are recorded and associated with many recommendations that may be valuable to electrical distribution (utility) companies.

# 1. Introduction

For many years, there has been a good collaboration between the Electric Power and Machines Dept., Faculty of Engineering, Zagazig University, Egypt and the Electrical Distribution Company, El-Sharkia branch that is considered as the authorized utility company of Zagazig city. This collaboration may be demonstrated in scientific consultants, practical studies, student training, et al. At the summer of 2012, the utility company complained from a series of accidents and dramatic events in distribution transformers 11000/400 volts. Five transformers suffered from severe internal damages in their winding and other four transformers suffered from frequent tripping in rush hours. The utility company requested from the Electric Power and Machines Dept. to find a simple and economical solution. During the onsite observations, it was found that most of these transformers were indoor transformers classified as Oil Natural Air Natural Type. In addition, they were placed in badly-ventilated rooms.

Actually, for any transformer, some power is dissipated in the form of heat. For example, suppose a 10MVA transformer at a distribution substation that operates at an efficiency of 99%, then 1% loss corresponds to a staggering of 100 kW [8]. In general, smaller transformers like those on distribution poles are passively cooled by simply radiating heat away to their surroundings, sometimes assisted by radiator fans that maximize the available surface area for heat removal. Transformers with efficiencies less than 96% produce an excessive amount of heat and usually have an unsatisfactory temperature rise.

This paper suggests adding a number of fans to improve the cooling system, especially for indoor transformers that are placed in badly-ventilated rooms. Microcontroller technology is recently one of the most important applications that serve for control [6, 13, 16]. So, the suggested system is controlled by using a microcontroller scheme. The hardware is designed to control the oil temperature. First, it is required to sense oil temperature by LM35, which is an integrated circuit sensor that can be used to measure temperature in °C with an electrical output that is proportional to the temperature. Then, the suitable action is taken according to the following four sequential stages: Fan (1) operates at 55℃, fan (2) operates at 65℃, sound or light alarm operates at 95℃, finally, trip signal is sent at 100 ℃. The designed hardware is tested by Proteus Virtual System Modeling (off-line testing program). Then, it is implemented online at a small prototype that is constructed in the laboratory.

# 6. Future Recommendation

In the future, the suggested monitoring system can be modified to be suitable to SCADA system. The general packet radio service (GPRS) communication technology can be applied so that remote signal transmission is accomplished by wireless network [9, 12, 15]. As mentioned before, until now the distribution utility of Zagazig city doesn’t have SCADA system to communicate with the dispatch center. So, it is suggested to utilize temperature sensors (indicators). If the utility decides to use SCADA system, the suggested monitoring system can easily be modified to deal with SCADA system. Possibly, the modifications may include the hardware of on-site unit to be suitable for online managements and communications with the dispatch center. The heart of this unit is LPC2214, which is based on 32-bit ARM7 processor [5]. It has lots of integrated peripherals which bring great convenience to system design. After preparing the voltage signal that is obtained from temperature sensor indicator by using Analog to Digital (A/D) card, the processor transfers it to remote expert diagnosis system by GPRS. GPRS mobile network is based on the data packet commutation through the usable mobile network where the data quantity is charged not the duration of the connection. Having this in mind, a necessity is to choose the appropriate communication protocols and standards that would utilize that kind of data transfer in the most efficient way. Data is then sent to the SCADA application servers via IEC 60870-5-104 communication protocol. One of the points is to lower the cost of data transfer; other is to ensure that data is up-to-date (real-time data). The real-time data acquisition is the key to efficient distribution network management.

# 7. Conclusions

From the above contributions discussed in the present paper, it can be concluded that:

- The suggested monitoring system finds simple and inexpensive solution for cool problem of indoor transformers that are placed in unsuitable rooms with bad ventilation. - Utilizing temperature sensors (indicators) are the best choice in the present case as the distribution utility of Zagazig city doesn’t have SCADA system till now. - Experiments that were carried out in laboratory either examining the designed circuit by using Proteus or testing the prototype monitoring system granted a good design and operation. - In case of using SCADA system, the suggested monitoring system is still valid with minor modifications.

#### References

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