Showing posts with label voltage. Show all posts
Showing posts with label voltage. Show all posts
Wednesday, March 1, 2017
Tuesday, February 14, 2017
Why are DC high voltage transmission lines replacing AC high voltage transmission lines at some places
Why are DC high voltage transmission lines replacing AC high voltage transmission lines at some places
With AC systems the peak voltage is 2^0.5 (1.4142) times the RMS (nominal) voltage. At transmission voltages that additional .4142 x voltage makes the insulation systems much more critical, lengthening the insulator strings and so increasing the cost of the insulators and poles required to separate the lines.
With DC systems the peak voltage is the nominal voltage, so the insulator strings need only deal with the nominal voltage reducing capital and maintenance costs (washing from helicopters etc.).
With very high voltage transmission where maximum voltage is limited by available technology, this fact is used to increase the nominal voltage on a given insulation type, resulting in a system which would be operated at 750,000 volts nominal (RMS) AC being used for 1,000,000 volts actual DC with 25% additional capacity for the same amperage (cable) design.
The other factors are
With DC systems the peak voltage is the nominal voltage, so the insulator strings need only deal with the nominal voltage reducing capital and maintenance costs (washing from helicopters etc.).
With very high voltage transmission where maximum voltage is limited by available technology, this fact is used to increase the nominal voltage on a given insulation type, resulting in a system which would be operated at 750,000 volts nominal (RMS) AC being used for 1,000,000 volts actual DC with 25% additional capacity for the same amperage (cable) design.
The other factors are
- In HVDC no corona loss is there as incase of HVAC.
- For longer distance,HVDC system is very economical as compared to the HVAC system.
- Allowing power transmission between unsynchronized AC distribution systems.
- HVDC increases the capacity of an existing power grid in situations where additional wires are difficult or expensive to install.
- For DC frequency is 0.Therefor there is no inductive reactance drop, result of it is improve voltage regulation.
- There is no problem of stability as in AC.
- There is no skin effect in DC.
- AC require 3 wire for transmission but DC require only 2 .
- There is no ferranti effect in DC{it doesnt mean that capacitance is absent in DC,capacitance act as open CKT for DC}
Available link for download
Tuesday, October 11, 2016
What is a Voltage Follower
What is a Voltage Follower
What is a Voltage Follower ?
A voltage follower (also called a unity-gain amplifier, a buffer amplifier, and an isolation amplifier) is a op-amp circuit which has a voltage gain of 1.
This means that the op amp does not provide any amplification to the signal. The reason it is called a voltage follower is because the output voltage directly follows the input voltage, meaning the output voltage is the same as the input voltage. Thus, for example, if 10V goes into the op amp as input, 10V comes out as output. A voltage follower acts as a buffer, providing no amplification or attenuation to the signal.
What is the Purpose of a Voltage Follower
An op amp circuit is a circuit with a very high input impedance. This high input impedance is the reason voltage followers are used. This will now be explained.
When a circuit has a very high input impedance, very little current is drawn from the circuit. If you know ohms law, you know that current, I=V/R. Thus, the greater the resistance, the less current is drawn from a power source. Thus, the power of the circuit isnt affected when current is feeding a high impedance load.
Lets look at both illustrations below:
The below circuit is a circuit in which a power source feeds a low-impedance load.
In this circuit above, the load demands and draws a huge amount of current, because the load is low impedance. According to ohms law, again, current, I=V/R. If a load has very low resistance, it draws huge amounts of current. This causes huge amounts of power to be drawn by the power source and, because of this, causes high disturbances and use of the power source powering the load.
Now lets look at the circuit below, connected to an op-amp voltage follower:
This circuit above now draws very little current from the power source above. Because the op amp has such high impedance, it draw very little current. And because an op amp that has no feedback resistors gives the same output, the circuit outputs the same signal that is fed in.
This is the reason voltage followers are used. They draw very little current, not disturbing the original circuit, and give the same voltage signal as output. They act as isolation buffers, isolating a circuit so that the power of the circuit is disturbed very little.
Voltage followers are important to buffer or isolate a low impedance load from a voltage source. This means that rather than connect a relatively low value of load resistance across the terminals of the power source, the op amp can be used to eliminate any loading that might occur. Thus, the power source will not be loaded down. The circuit acts as an ideal voltage source with nearly zero internal impedance, since it barely uses any current, yet outputs the full voltage.
Inverting amplifier and non-inverting amplifier both are negative feedback op-amp circuits
Non-inverting amplifier the input signal is applied to non-inverting pin
Inverting amplifier the input signal is applied to the inverting pin
Voltage follower is a negative feedback op-amp circuit with unity gain
Source : http://www.learningaboutelectronics.com/Articles/Voltage-follower
Available link for download
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