POWER SHARING OF TRANSFORMER WITH OVERLOAD PROTECTION

Abstract

Generally, the transformer is meant for distributing power up to certain region. When the load exceeds the limit automatically the transformer will be broken down. To avoid this problem our project is implemented. This project monitors the control of the transformer continuously and is displayed in the LCD display unit. In the display unit we can view the continuous information about what reason particular transformer is failed to operate. In this project work for the demonstration purpose a small step-down transformer of 12V is considered and these two parameters are carried out over this small transformer. These transformers are connected with the relay which is controlled by the embedded controller. The voltage and current parameters are measured and these values are given to analog to digital converter which converts analog values to digital values. The values are compared with the preset values in the controller, if excess in any parameter occurs the relay will trip the transformer upon overloading. The voltage and current values are displayed in the LCD.

Existing System

The microcontroller based system was used in existing system. Power supply to the Loads from a single transformer under normal condition and a standby transformer is connected in parallel through a circuit breaker. A current transformer measures the load current continuously and send it to the microcontroller by converting it to a corresponding digital value in order to compare with the reference value set by the user. Whenever the load current more than reference value, the controller gives output signal to the relay which energizes the relay coil. The relay coil thus sends a tripping signal to the circuit breaker. Then standby transformer is directly connected to the main transformer. Thus the load is shared by the transformers equally. The current transformer continuous measures the load current and compares it with the reference value. Whenever the load current goes below reference value one transformer is shut down. If the load value increases further beyond the capacity of two transformers, load will be cut-off from the main supply based on the priority level set by the user. This is done to provide un-interrupted power supply to higher priority loads. The load parameters are continuously displayed in the LCD. Due to this we can show the peak load time duration.

Proposed System

The system consists of microcontroller, transformers, circuit breakers, relay, Current Sensor, GSM, LCD Display and keypad. The transformers are step down transformers in which only one transformer is operating under normal condition. The input to the transformer is fed through a circuit breaker to which a relay is connected. The circuit breaker is in closed position for transformer which is operating. Here the transformer feeds five loads which are provided with individual circuit breakers for protection. A stand by transformer is connected in parallel to the main transformer through a circuit breaker. In order to measure the current through the transformer a current transformer is connected to the secondary of the operating transformer. The current transformer measures the load current continuously and is fed to the microcontroller through a rectifier circuit. The output from the current transformer can also be fed directly to inbuilt ADC pins of controller, instead of using a rectifier. The microcontroller continuously compares the current sensor value with the maximum limit entered. The maximum load limit is entered to the controller through a keypad. Whenever the current exceeds the maximum limit, the main transformer gets overloaded and the second transformer shares the total load equally. When there is a further increase in load beyond the rated capacity of two transformers, microcontroller will give control signal to the circuit breaker of respective load to open, based on the priority level set by the user. When the load decreases and comes to normal value which is less than the maximum limit, the first transformer will shut down automatically. The GSM modem will send a message to the control room about the load sharing and a display will be shown in the LCD display.

Architecture

BLOCK DIAGRAM