Browsing by Author "Ehtisham Ismail"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Microprocessor based numeric relay
    (2010) Ehtisham Ismail; Ali Akbar
    Relaying voltages and currents at are passed through Isolation Transformers. Since analog to digital conversion is usually performed on voltages, the current signals are converted to representative voltages by passing them through a known resistance. All the signals are then filtered using simple analog Anti aliasing Filters. Since ADCs are expensive it is common to use only one in a numeric relay. Our relay utilizes built-in ADC of PIC 16F877A Microcontroller. Software level Multiplexer is used, under microprocessor control, sequentially to select the required signal into ADC. Since an ADC takes a finite conversion time usually 25usec, it is necessary to hold the incoming signal for the duration of conversion. This is achieved by a Sample and Hold amplifier. Having been manipulated by the ADC the signal can be fed to Microprocessor which in our case is PIC 16F877A. There may be one or more processors, one for running algorithm ad another for scheme logic. The relaying program will be located in ROM and a RAM will be used for storing sampled quantities and intermediate products in relaying algorithm. Relay settings can be stored in EEPROM or they can be defined in program as in our case for fixed application. A Power Supply is also incorporated to supply a regulated and constant power to relay electronics. These are typically 5V or 12V. Switched mode supplies are generally used as they are more efficient. Voltage and current values of all three phases are continuously being displayed and updated on LCD separately. LCD also shows particular operation of relay in case of fault.
  • No Thumbnail Available
    Item
    Microprocessor based numeric relay
    (UMT, Lahore, 2009) Ehtisham Ismail; Ali Akbar
    Relaying voltages and currents at are passed through Isolation Transformers. Since analog to digital conversion is usually performed on voltages, the current signals are converted to representative voltages by passing them through aTcnown resistance. All the signals are then filtered using simple analog Anti aliasing Filters. Since ADCs are expensive it is common to use only one in a numeric relay. Our relay utilizes built-in ADC of PIC I6F877A Microcontroller. Software i^wf^TMultiplexer is used, under microprocessor control, sequentially to select the required signal into ADC. Since an ^ ADC takes a finite conversion time usually 25usec, it is necessary to hold the incoming signal for the duration of conversion. This is achieved by a Sample and Hold amplifier. Having been manipulated by the ADC the signal can be fed to Microprocessor which in our case is PIC 16F877A. There may be one or more processors, one for running algorithm ad another for scheme logic. The relaying program will be located in ROM and a RAM will be used for storing sampled quantities and intermediate products in relaying algorithm. Relay settings can be stored in EEPROM or they can be defined in program as in our case for fixed application. A Power Supply is also incorporated to supply a regulated and constant power to relay electronics. These are typically 5V or 12V. Switched mode supplies are generally used as they are more efficient. Voltage and current values of all three phases are continuously being displayed and updated on LCD separately. LCD also shows particular operation of relay in case of fault