Answer MET Question 15
Question: Explain What is meant by, and the significance of, four of the following terms. I. Voltage Stabilization, II. Filter choke; III. Impedance, IV. Rectification, V. Grid bias voltage.
Answer:
I.
Voltage stabilization means that the output voltage remains nearly
constant even when there are variations in load or input voltage.
Voltage fluctuations are unavoidable when operating electrical supply
networks. While the rotating mass of power generators seems to remain
unfazed by load changes, every change in current causes voltage
fluctuations, of greater or lower severity. The effects of this
occurrence are especially noticeable in inefficient supply networks and
at the end of long branch lines.
The operation of certain, often complex, electrical equipment frequently requires the provision of an operating voltage with narrow tolerances and a high degree of long-term stability, to ensure uninterrupted, reliable operations.
Voltage Stabilizer is an electrical appliance which is designed to deliver a constant voltage to a load at its output terminals regardless of the changes in the input or incoming supply voltage. It protects the equipment or machine against over voltage, under voltage, and other voltage surges.
The common types of voltage stabilizers include manual operated or switchable stabilizers, automatic relay type stabilizers, solid state or static stabilizers, and servo controlled stabilizers. In addition to the stabilizing function, most stabilizers come with additional features such as input/output low voltage cutoff, input/output high voltage cutoff, overload cutoff, output start and stop facility, manual/auto start, voltage cutoff display, zero voltage switching, etc.
In a voltage stabilizer, voltage correction from over and under voltage conditions is performed through two essential operations, namely boost and buck operations. These operations can be carried manually by switches or automatically through electronic circuitry. During under voltage condition, boost operation increases the voltage to a rated level while buck operation reduces the voltage level during over voltage condition.
The concept of stabilization involves in adding or subtracting the voltage to and from the mains supply. For performing such task stabilizer uses a transformer which is connected in different configurations with switching relays. Some stabilizers use a transformer with taps on winding to provide different voltage corrections while servo stabilizers use an auto transformer to have wide range of correction.
The operation of certain, often complex, electrical equipment frequently requires the provision of an operating voltage with narrow tolerances and a high degree of long-term stability, to ensure uninterrupted, reliable operations.
Voltage Stabilizer is an electrical appliance which is designed to deliver a constant voltage to a load at its output terminals regardless of the changes in the input or incoming supply voltage. It protects the equipment or machine against over voltage, under voltage, and other voltage surges.
The common types of voltage stabilizers include manual operated or switchable stabilizers, automatic relay type stabilizers, solid state or static stabilizers, and servo controlled stabilizers. In addition to the stabilizing function, most stabilizers come with additional features such as input/output low voltage cutoff, input/output high voltage cutoff, overload cutoff, output start and stop facility, manual/auto start, voltage cutoff display, zero voltage switching, etc.
In a voltage stabilizer, voltage correction from over and under voltage conditions is performed through two essential operations, namely boost and buck operations. These operations can be carried manually by switches or automatically through electronic circuitry. During under voltage condition, boost operation increases the voltage to a rated level while buck operation reduces the voltage level during over voltage condition.
The concept of stabilization involves in adding or subtracting the voltage to and from the mains supply. For performing such task stabilizer uses a transformer which is connected in different configurations with switching relays. Some stabilizers use a transformer with taps on winding to provide different voltage corrections while servo stabilizers use an auto transformer to have wide range of correction.
II.
Choke filter consists of an inductor connected in series with rectifier
output circuit and a capacitor connected in parallel with the load
resistor. The output pulsating DC voltage from a rectifier circuit
passes through the inductor or choke coil.
The inductor has low DC resistance and extremely high AC reactance. Thus, ripples get filtered through choke coil. Some of the residual ripples if present in filtered signal from inductor coil will get bypassed through the capacitor. The reason behind this is that capacitor allow AC and block DC.
The inductor has low DC resistance and extremely high AC reactance. Thus, ripples get filtered through choke coil. Some of the residual ripples if present in filtered signal from inductor coil will get bypassed through the capacitor. The reason behind this is that capacitor allow AC and block DC.
III.
Impedance is the effective resistance of an electric circuit or
component to alternating current, arising from the combined effects of
ohmic resistance and reactance.
If an a.c supply of RMS voltage V and frequency f is applied to a circuit containing resistance R, capacitance C and inductance L each component offers,some opposition to the current. The total opposition is called the Impedance Z and is measured in ohms. $\displaystyle \small \mathrm{Z=\sqrt{R^2+(X_L-X_C)^2} }$.
The RMS current is given by $\displaystyle \small \mathrm{I=\frac{V}{Z}}$, If the impedance is shuch that inductive reactance is more that capacitive reactance, then circuit power factor will be lagging. If the capacitive reactance is more than the inductive reactance, then the power factor of the Circuit will be leading.
If an a.c supply of RMS voltage V and frequency f is applied to a circuit containing resistance R, capacitance C and inductance L each component offers,some opposition to the current. The total opposition is called the Impedance Z and is measured in ohms. $\displaystyle \small \mathrm{Z=\sqrt{R^2+(X_L-X_C)^2} }$.
The RMS current is given by $\displaystyle \small \mathrm{I=\frac{V}{Z}}$, If the impedance is shuch that inductive reactance is more that capacitive reactance, then circuit power factor will be lagging. If the capacitive reactance is more than the inductive reactance, then the power factor of the Circuit will be leading.
IV.
Rectification:Rectification is the conversion of alternating current to
direct current. Rectification is performed by a diode that allows
current to flow in one direction but not in the opposite direction.
Direct current that has only been rectified, however, has various
changes in voltage (ripples) lingering from the alternating current.
Capacitors are used to smooth the currentand make it even. When
comparing with the dc power sources such as storage batteries the
retification and supplying dc through a rectifier is highly economical
and contineous.
V.
Grid Bias: Increasing the plate voltage or decreasing the grid-bias The
six methods most commonly used to bias a tube are illustrated in
Figure.
Fig.A: Bias cell(battery) is connected in series with the control grid.
Fig.B: The tube is self-biased by the use of a resistor connected in the cathode circuit.
Fig.C: The circuit is also a form of self-bias; however, the bias voltage is obtained by the use of a grid capacitor and grid-leak resistor between the control grid and ground.
Fig.D: The bias voltage is developed by grid-leak resistor and capacitor in parallel, connected in series with control grid.
Fig.E: Combination bias and consists of self-bias and battery bias. The resultant bias voltage is the negative voltage of the battery, and the bias created by the self bias resistor in the cathode circuit.
Fig.F: The bias battery is connected in series with grid leak resistor.
The bias voltage at the control grid is that developed by the battery and the self bias created by the combination of the grid resistor and capacitor. If the control becomes positive with respect to the cathode, it results in a flow of current between the control grid and the cathode through the external circuits. This condition is unavoidable because the wire of the control grid, having a positive charge, attract electrons passing from the cathode to the plate. It is important that the control-grid voltage is kept negative, reducing grid current and distortion.
Fig.B: The tube is self-biased by the use of a resistor connected in the cathode circuit.
Fig.C: The circuit is also a form of self-bias; however, the bias voltage is obtained by the use of a grid capacitor and grid-leak resistor between the control grid and ground.
Fig.D: The bias voltage is developed by grid-leak resistor and capacitor in parallel, connected in series with control grid.
Fig.E: Combination bias and consists of self-bias and battery bias. The resultant bias voltage is the negative voltage of the battery, and the bias created by the self bias resistor in the cathode circuit.
Fig.F: The bias battery is connected in series with grid leak resistor.
The bias voltage at the control grid is that developed by the battery and the self bias created by the combination of the grid resistor and capacitor. If the control becomes positive with respect to the cathode, it results in a flow of current between the control grid and the cathode through the external circuits. This condition is unavoidable because the wire of the control grid, having a positive charge, attract electrons passing from the cathode to the plate. It is important that the control-grid voltage is kept negative, reducing grid current and distortion.
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