17-09-2014, 12:03 PM
INDUSTRY
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ABSTRACT
To automate the cooling activities of a power transformer using programmable logic controller (PLC). In our project we are redesigning the existing control circuit using PLC instead of electromechanical relays. By using this method we can change the control logic at site and communication with remote panel as per customer requirements.
TRANSFORMER HEATING:
The transformers are having the winding which is wound on the core. The flux links with core and the windings of the transformer.
The flux on the primary side winding links with secondary winding. This produces the heat because of the losses in the core.
The heat will be transferred to the winding and then to the transformer oil.
The transformer oil is provided in the transformer for the cooling and better insulation purpose.
The heat is than transferred to the transformer oil. The heat sinks are provided for the transformer walls cooling.
INTRODUCTION
High speed fans are provided with this type of cooling system.
All fans are automatically controlled, whenever the temperature of the transformer goes beyond the safe limit then all the fans are switched ON.
This method provides better performance than natural oil and air cooling, but there is an additional cost due to the fans.
EXISTING CONTROL SCHEME AND ITS DISADVANTAGES
Present method of cooling control of a power transformer is done by using electro-mechanical relays which is nothing but hardwired logic.
In case of fault, trouble shooting will be very tedious as the circuit is complex along with many wires.
There is a great chance that loose connections may occur in control wirings.
Also the power consumption is observed to be more and it accommodates more space.
Use of timers, contactors, relays in cooling control panel makes it very complicated.
PROPOSED CONTROL SCHEME
In order to overcome the disadvantages of the existing control scheme a programmable logic controller(PLC) can be used. PLC is user friendly software programmable device whose operation mainly depends on the program written in its memory. One of the common programming method used in PLC is the ladder program(LADDER Logic).
CIRCUIT EXPLAINATION
The above circuit diagram consists of mode selection switch manual selection switch, fan series, timer, stand by fan, temperature sensor.
The input to the PLC will be winding or oil temperature.
The automatic or manual selection process is carried out with the help of the mode selection switch.
When manual mode is selected we use three selection modes for controlling the cooling process. The three modes are ‘OFF’, ‘In service’ and TEST.
ADVANTAGES
WE CAN CHANGE THE CONTROL LOGIC & COMMUNICATION WITH REMOTE PANEL AS PER CUSTOMER REQUIREMENT.
REMOTE CONTROLING CAN BE DONE MORE EASILY.
IT TAKES LESS WIRING AND SPACE.
USING COMPONENTS OF HIGH RELIABILITY INCREASES THE OVERALL RELIABILITY OF THE SYSTEM.