15-09-2017, 01:18 PM
The relay is an electrical switch. Generally it works on electromagnetic principle for the action of the switching. The overcurrent relay (OC) is a type of relay that performs its switching action based on an input current. When the input current exceeds a certain recovery value, the relay operates. Microcontroller-based relays are gaining popularity as these have no mechanical contacts. These can operate at very high speeds. Any kind of features can be obtained by using these. In a typical relay based on a microcontroller there is a current transducer, a controller, current transformer and a circuit breaker. The microcontroller reads the load current through CT, transducer and ADC. When the current is above the pickup, it signals the switch to trip.
An "overcurrent relay" is a type of protection relay that operates when the load current exceeds a preset value. In a typical application, the overcurrent relay is used for overcurrent protection, connected to a current transformer and calibrated to operate at or above a specific current level. This model will attempt to design and fabricate an overcurrent protection relay using the PIC microcontroller. The PIC microcontroller will cause the circuit breaker to trip when the current of the load current reaches the setting value on the PIC microcontroller. In order to design it, it is first necessary to measure the load current to monitor it using the current sensor, including checking the fault (overcurrent) and when such a condition occurs, it will be isolated in the shortest possible time without damaging the other electrical devices The basic idea of this model is to compare the value of the current detected by the ADC of the microcontroller and compare it with the reference value of the set. To make this comparison, the program can be written in Embedded C language and can be loaded into the microcontroller.
To detect the current, first convert the AC current value to DC using a precision rectifier + and then feed it to a converter from I to V. Since the analogue port of the microcontroller detects the DC value, we need to perform this conversion . Once the conversion is done, the signal is now sent to the ADC port of the PIC microcontroller, where the signal is compared after the analog to digital conversion with the reference value of the current set in amps. If this detected value is greater than the reference, one of the microcontroller ports becomes HIGH, and the relay controller starts to operate, thus triggering the circuit breaker and disconnecting the device from the rest of the power system. To perform this operation, we have taken ULN2003 as a relay controller. For the purpose of testing and simulation we have taken a simple incandescent light bulb as device to be protected. The complete model was simulated in PROTEUS and satisfactory results were obtained. In order to change the value of the incoming AC current, a rheostat is connected in series to test different values of line current. Programming is done in mikroC, a popular compiler for PIC microcontrollers. In the same way the model can be configured for a transformer differential protection scheme. Here the two currents allow I1 and I2 of the two ends of the apparatus to be taken, converted into DC and then fed to the ADC channels of the PIC microcontroller.
An "overcurrent relay" is a type of protection relay that operates when the load current exceeds a preset value. In a typical application, the overcurrent relay is used for overcurrent protection, connected to a current transformer and calibrated to operate at or above a specific current level. This model will attempt to design and fabricate an overcurrent protection relay using the PIC microcontroller. The PIC microcontroller will cause the circuit breaker to trip when the current of the load current reaches the setting value on the PIC microcontroller. In order to design it, it is first necessary to measure the load current to monitor it using the current sensor, including checking the fault (overcurrent) and when such a condition occurs, it will be isolated in the shortest possible time without damaging the other electrical devices The basic idea of this model is to compare the value of the current detected by the ADC of the microcontroller and compare it with the reference value of the set. To make this comparison, the program can be written in Embedded C language and can be loaded into the microcontroller.
To detect the current, first convert the AC current value to DC using a precision rectifier + and then feed it to a converter from I to V. Since the analogue port of the microcontroller detects the DC value, we need to perform this conversion . Once the conversion is done, the signal is now sent to the ADC port of the PIC microcontroller, where the signal is compared after the analog to digital conversion with the reference value of the current set in amps. If this detected value is greater than the reference, one of the microcontroller ports becomes HIGH, and the relay controller starts to operate, thus triggering the circuit breaker and disconnecting the device from the rest of the power system. To perform this operation, we have taken ULN2003 as a relay controller. For the purpose of testing and simulation we have taken a simple incandescent light bulb as device to be protected. The complete model was simulated in PROTEUS and satisfactory results were obtained. In order to change the value of the incoming AC current, a rheostat is connected in series to test different values of line current. Programming is done in mikroC, a popular compiler for PIC microcontrollers. In the same way the model can be configured for a transformer differential protection scheme. Here the two currents allow I1 and I2 of the two ends of the apparatus to be taken, converted into DC and then fed to the ADC channels of the PIC microcontroller.