Real Time Monitoring and Controlling Of Transformers
Transformers are basic design of electrical device which provide power transmission by
transforming induced current from one circuit to another. The induced current can be converted
step up or step down of current or voltage. This application mainly concentrates on the three-phase
transformers which are used in between electric poles and the Power transformers. The real time
controlling is done on the basic features like gas level, oil aging and regulation of overload and
temperature maintenance. These features are essential for effective power transmission and long
life of industrial transformers. The monitoring and control of the transformer is done by using
ARM7 processor, RF transmission for wireless communication and sensors which check the level of
gas, aging of oil, overload and maintain temperature by regular observation. There are various
transformer maintenance techniques but this paper gives a real time monitoring and controlling
of transformers by using ARM7 processor which replace the bulky computers making it as
embedded system. The design is to sense the features of transformer and send the information
regularly to the processor, the processor in turn will makes the transmission through RF to the
client. So, this design makes possible to attain real time control and monitoring of oil, gas, overload
and temperature range in the transformer.
Received: October 17, 2012;
Accepted: December 26, 2012;
Published: January 14, 2013
In Electrical power transmission systems, transformers represent one of the
key components in utility systems. Since, it is an integral part of the substation,
strategic bottle necks occur if we fail to monitor the transformer (Bashi,
2005). Regular monitoring of the crucial roles of a transformer before causing
ruining the system due to arising faults (Haron et al.,
2012). This can allow for a change from periodic to condition-based maintenance.
Some parameters of the transformer operation are (1) Temperature of oil, (2)
Moisture level, (3) Level of floats, (4) Operation of cooling fans, (5) Electrical
load levels and (6) Gas sensors (Bashi et al., 2007).
This study shows the Real time Monitoring and control of systems using sensors
for reading the value of different parameters of transformers.
The reason for using ARM7 processor devices are cost effectiveness, small size, robust and reduced power consumption which helps in the use of minimum power. So the basic features of ARM can be used for an industrial application like controlling of Transformers in a real time. The RF communication needs a base band processor which will provide a wireless mode of communication between a monitoring embedded device and the client by instant messaging about transformers features in regular intervals.
So, the combination of ARM7 processor and the RF communication provides with best performance, compatibility of sensors and security. The life of a transformer also plays an important role, as extended life of a transformer may in turn cut costs.
For monitoring transformers many methods have been adopted (Maizana,2012).
In earlier works Oil level, float level, Temperature level, overload has been
measured manually (Abaci et al., 2007; Zhao
et al., 2004). These levels should be checked periodically by the
operating personnel which will be tedious and inefficient way of monitoring.
For better monitoring of transformers several works like, Transformer controlled
with a microcontroller and sending data through serial communication to a host
computer has been implemented (Sun et al., 2011;
Sudha and Anbalagan, 2009). Also, several electrical
transformers are allowed to communicate with host computer within a closed network
(Devidas and Ramesh, 2010). Other works include capacitor
sensor which can sense the di-electric signals for detecting moisture level
inside transformer pressboard (Li and Gao, 2009).
Monitoring of distribution transformer using GPRS communication provides an
effective monitoring making use of wireless communication and broadband transmission
(Mao, 2010). The online monitoring of transformer features
and controlling of transformers from a remote region using web service technology
(Leger et al., 2001; Shertukde
and Shertukde, 2002; Ahmad and Rashid, 2007). The
analysis of gases dissolved in transformer oil is made through semiconductor
sensor array (Cao et al., 2008; Severo
et al., 2010; Moghaddam et al., 2012).
Thus, the earlier works shows various protection measurements of transformers
and power supply but all those systems lack in providing a robust and sophisticated
embedded system which can maintain transformers in real time and improve the
transformers life (Kouzou et al., 2010; Bashi
et al., 2008; Ahmad, 2010).
The block diagram shown in Fig. 1 depicts the hardware configuration of the complete system. General faults in a transformer can be grouped as: (1) Mechanical, (2) Contacts erosion and (3) Contact coking leading to high resistance and overheating. In order to reduce some internal failures like risk of fire and explosions, several standards and protective devices have been installed. There are several parameters which will affect the working of the transformer. The four main parameters that are mainly concerned here are gas, temperature, overload and oil.
The centre ARM7 processor handles the monitoring and controlling process of transformer along with transmission. ARM processors are a 32-bit embedded processor. It can even support thumb instruction set. It has a RISC architecture which uses load and store properties. It executes instructions in fixed width and efficient in ease of decoding and pipelining by the use of thumb instructions. The execution of an instruction will have high code density and ARM executes instruction as single bit. It supports all the operating systems depending upon the applications and the web browsing performance using ARM processor is same as any other advanced processor like Intel atom processor. All this features of ARM will give best performance to develop leading edge technology in a broad range of applications like mobiles, networking, consumer, industrial automation. If any discrepancies occur it will identify, control that and inform it to the user through wireless transmission.
Inside a transformer formation of many gases takes place. They are listed as:
Atmospheric gases: Hydrogen, Oxygen, Nitrogen; Oxides of carbon: Carbon monoxide
and carbon dioxide; Hydro carbons: Acetylene, methane, ethane.
|| Block diagram of the entire system
Formation of gas inside the transformer is a major problem which is formed
due to decomposition of oil, insulation overheating, corona, arcing of the transformer,
etc; all this change of information will be continuously sensed by the gas sensor
and sent to the processor and this will be intimated to the operator by parallely
switching on the exhaust fan.
In larger transformers part of the design problem is the removal of heat. If under any circumstances temperature rises above the desired level which in turn will affect the transformer working condition. The processor will indicates this temperature rise to the receiver and eventually control the process by switching on the cooling fan.
Overload on the transformer will automatically cause the transformer to shut down, instead if the processor detects overload condition from voltage divider, will send the information to the receiver and shares the load to another transformer along with an indication through an alarm. The transformer oil acts as a lubricant, coolant, as well as insulator for the windings. To check the oil aging here the Conductivity test (Resistivity test) is performed. The process uses two electrodes; the conductivity between these two is inversely proportional to the oil thickness. High resistivity shows the fewer amounts of free ions and conductive contaminants. If the processor detects the current flow then it will send the information to the user through wireless communication.
The gas sensor used in measuring the gas detection process is developed by NSK electronics products. The sensor detects the different gases by varying the resistance of all gases produced in an industry. The graph above Fig. 2 shows the resistance range versus pressure of gas. We can see that Hydrogen gas exists in centre of the graph. Every gas sensor will detect the presence of a gas by its varying resistance. This is directly proportional to the output showing gas detection by its pressure.
The temperature sensor used is LM 35 shown in Fig. 3. The
sensor has three pins, Vi is the input voltage pin which acts at 5V, Vo is the
output voltage gives the display provided to it. GND pin is the ground pin.
|| Graph shows the resistance ratio versus pressure of the gases,
Rs/Ro: Resistance range
|| The temperature sensor LM 35 pin diagram
The output voltage is directly proportional to the varying resistance. If temperature
rises above the desired level, cooling fan will be automatically switch ON.
This reduces the raised temperature of the transformer. Generally, by using
ARM7 processor the use of cooling Fan inside the industrial transformers is
greatly reduced. The output of Temperature sensor is displayed in LCD display
showing the detected temperature value. The Flow chart for the entire process
is explained as shown in Fig. 4.
||Initially sensors will sense the transformer conditions
||The sensed information is sent to ARM7 processor
||Depending on the sensed information processor will send respective signals
to the Peripherals to act
||The sensed data is sent to the operator by processor
RESULTS AND DISCUSSION
The experiment is performed by considering the two parameters of a Transformer like gas detection and temperature range. The general ranges of transformer values are executed and sent to the RF receiver from RF transmitter.
|| Flow chart shows the step by step process
|| Snapshot of ARM 7 LPC 2148 board
The Fig. 5 shows the snapshot of LPC 2148 board where all
the peripherals will be interfaced in it. It is interfaced with temperature
sensor LM35, Gas sensor, etc., for sensing temperature and gas detected in the
surroundings, along with cooling fan to reduce the heat inside the transformer
and an exhaust fan to expel the gases outside the transformer, respectively.
Figure 6-8 shows the snapshots of transmission
||Module of temperature sensor with exhaust fan and alarm unit
||Transformer (12v-5 A range) with cooling fan
||RF transmitter module along with gas sensor
The Fig. 9 shows the receiver unit for RF transmission. The
RF receiver is connected to the microcontroller for displaying the output in
the LCD. The RF transmission process is visualized by simple 16x2 LCD display
as shown in Fig. 10. The stimulation output is shown in Fig.
11. The emulation output is also shown in Fig. 12 and
13 using ISIS Emulator.
|| Receiver module of RF transmission
|| LCD display of test performed for transformer parameters
|| KEIL stimulator snap shot shows the debugging unit
||Snap shot of ISIS emulator indicating the transmission of
“rise in temperature” to the receiver
||Snap shot of ISIS emulator indicating the transmission of
“rise in gas level” to the receiver
CONCLUSION AND FUTURE WORK
This study gives remedies from the faults occurring in transformer and it overcomes the drawbacks of previous working methods. The paper focuses much on the efficiency of controlling process of the transformer and mainly through wireless communication that eliminates the use of large cables which are of high cost, low reliability and maintenance.
The RF Transmission helps in better way of communication which enhances the improvement steps in this process.
So, use of ARM processor makes the system real time embedded system and aids
very much in industry needs. This work can also be extended to handle several
numbers of transformers on industrial units by assigning RFID tags to each transformer
which in turn is monitored and controlled by a single ARM processor.
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