08-16-2017, 09:34 PM
basic avr working principle
Basically the AVR or Automatic Voltage Regulators function for generator is to ensure voltage generated from power generator running smooth to maintain the stable voltage in specified limit. It can stabilize the voltage value when suddenly change of load for power supply demand.
If the generator running in parallel condition,the AVR can controlled the voltage that it produce to ensure of equal value for reactive load sharing.
For the big system of interconnected power distribution with parallel design,it must have a full controlled and transient stability particular must added for requirement to the Automatic Voltage regulator for generator.
What is Automatic Voltage Regulator (AVR)
The AVR can operated in two condition controlled.It is from manual control or automatic control with standard limited parameter that required for generator.This controlled must be provided if it not available for the generator system to ensure it smooth running without any problem.Basic principles for AVR A signal proportional to generator terminal voltage obtained from the rectified output of a voltage transformer is compared to a stabilized reference voltage obtained within the regulator.If it detected any abnormal,different or error signal, it will amplified and control the excitation supply, increase or decrease the input to the main field winding or exciter field.The main purpose is to reduce the error signal to zero or an acceptable value.
Adjustment of the set voltage is obtained either by adjustment of the reference voltage or by adjusting the proportion of machine voltage compared to the reference voltage. The stabilizing loop is included to prevent hunting.
A voltage regulator is a voltage stabilizer that is designed to automatically stabilize a constant voltage level. A voltage regulator circuit is also used to change or stabilize the voltage level according to the necessity of the circuit. Thus, a voltage regulator is used for two reasons:-
To regulate or vary the output voltage of the circuit.
To keep the output voltage constant at the desired value in-spite of variations in the supply voltage or in the load current.
When the input supply voltage Vin increases the output voltage Vload also increases. This increase in Vload will cause a reduced voltage of the transistor base emitter voltage Vbe as the zener voltage Vzener is constant. This reduction in Vbe causes a decrease in the level of conduction which will further increase the collector-emitter resistance of the transistor and thus causing an increase in the transistor collector-emitter voltage and all of this causes the output voltage Vout to reduce. Thus, the output voltage remains constant. The operation is similar when the input supply voltage decreases.
The next condition would be the effect of the output load change in regard to the output voltage. Let us consider a case where the current is increased by the decrease in load resistance Rload. This causes a decrease in the value of output voltage and thus causes the transistor base emitter voltage to increase. This causes the collector emitter resistance value to decrease due to an increase in the conduction level of the transistor. This causes the input current to increase slightly and thus compensates for the decrease in the load resistance Rload.
The biggest advantage of this circuit is that the changes in the zener current are reduced by a factor and thus the zener effect is greatly reduced and a much more stabilized output is obtained.
The output voltage of the series regulator is Vout = Vzener Vbe. The load current Iload of the circuit will be the maximum emitter current that the transistor can pass. For a normal transistor like the 2N3055, the load current can go upto 15A. If the load current is zero or has no value, then the current drawn from the supply can be written as Izener + Ic(min). Such an emitter follower voltage regulator is more efficient than a normal zener regulator. A normal zener regulator that has only a resistor and a zener diode has to supply the base current of the transistor.