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Electrical Engineering
Electrical engineering is a field of engineering that deals with the study and application of electricity, electronics and electromagnetism.
23,056 Questions
You can say DC voltage has a frequency of zero Hz.Because it is unidirectional in nature (may be positive or negative)
Applications of a ac generator?
Applications of DC Generators:
1. DC shunt Generator
The terminal voltage of DC shunt generator is more or less constant from no load to full load .Therefore these generators are used where constant voltage is required.
- For electro plating
- Battery charging
- For excitation of Alternators.
2. Series Generators:
The terminal voltage of series generator increases with load current from no load to full load .Therefore these generators are,
- Used as Boosters
- Used for supply to arc Lamps
3. Compound Generator:
- Differential Compound generators are used to supply dc welding machines.
- Level compound generators are used to supply power for offices ,hostels and Lodges etc.
- Over compound generators are used to compensate the voltage drop in Feeders.
4. Separately Exited Generator:
- As a supply source to DC Motors ,whose speed is to be controlled for certain applications.
- Where a wide range of voltage is required for the testing purposes.
Electrikals..
What are the common problems of a transformer?
winding tempareture and oil temp. both are high level than x'mer is burn.
What are the disadvantages of differential amplifier?
A:from a single ended none main concern is offset voltages and current offset and for some latch-up
Further explanation:
A differential amplifier is actually a very advanced (and good!) amplifier - it (at a minimum) consists of two transistors and biasing schemes, and in a basic form has two inputs and two outputs - one output is inverting, the other is non inverting, thus the two outputs can be used together to provide a 3dB (2 x) gain over using a single output.
From a signal to noise ratio, a differential amplifier is also a cut above if implemented correctly and designed well. For the best results, a positive and negative signal should be transmitted to the amplifier. One goes to either input of the amplifier, with the other to the other input. Noise inherently will be added onto both of these lines, but the noise will tend to be in the same direction for both. A differential amplifier has a high "common mode rejection", which means if the same voltage is applied to both inputs, the output will not change (it only amplifies the difference between the inputs). This is why sound boards and a lot of other A/V equipment use differential amplifiers.
If these features are not important for your design, then the added complexity of circuitry (usually requiring a positive and negative voltage, multiple transistors, etc.) becomes a disadvantage. Also, if you are just starting out, designing one well may be a bit over your head (a clear disadvantage when you don't know what's going on in the circuit - it becomes very difficult to trouble shoot).
What is the Difference between voltage controlled device and current controlled device?
The difference between a current control device and voltage controlled device is that for current controlled device, the current is constant and the voltage is variable while for a voltage controlled device, the voltage is constant and the current is variable.
Depends on the cell/battery chemistry.
The most common voltage for a cell is 1.5V, but you can have anything from 1.2(Ni-Cd, NiMH) to 3.7(Li-Po, Li-Io).
An automotive battery cell produces 2.2 volts.
According to Ohm's law of resistance in parallel, 1/RT=1/R1+1/R2+1/R3... so 1/RT=1/12+1/4=1/12+3/12=4/12=1/3 and 1/(1/3)=3.
The total resistance of the two devices is 3.
There is a simpler special case formula for two resistances in parallel:
* RTot = (R1R2) / (R1 + R2) In this case this it would give us (12 x 4) / (12 + 4), or 48 / 16 which equals 3 ohms.
3 ohms
What is the relation between KW and HP?
When calculating kW, power factor is brought into the equation
Formula for single phase kVA = I x E/1000,
3 phase kVA = I x E x 1.73/1000
Formula for single phase KW = I x E x pf/1000,
3 phase kW = I x E x 1.73 x pf/1000
Alternative AnswerWhen an AC current flows through a purely resistive circuits, its temperature increases above the ambient temperature, and energy is lost to the surroundings through heat transfer. This energy transfer is irreversible. The rate at which this energy loss is taking place is called the true power of the circuit, and is expressed in watts (symbol: W).
When an AC current flows through a purely reactive (i.e. inductive or capacitive) circuit, during the first quarter-cycle, energy is stored in the magnetic or electric field, and returned to the circuit during the next quarter cycle. So, although energy transfer is taking place, there is no net loss of energy. The rate at which this energy transfer is taking place is called the reactive power of the circuit, and is expressed in reactive volt amperes(symbol: var).
However, most practical circuits are inductive-reactive circuits. So, when AC current flows through an inductive-reactive circuit, some energy is permanently lost while some energy is transferred from and back to the circuit. In other words, most circuits exhibit a combination of true power and reactive power. The vector sum of true power and reactive power is called apparent power, and is expressed in volt amperes (symbol: V.A).
To summarise:(Apparent Power)2 = (True Power)2 + (Reactive Power)2
From the above equation, in a purely resistive circuit, the apparent power will be equal to the true power. For resistive-reactive circuits, the apparent power will always be larger than the true power.
Read more: What_is_KW_and_KVA
Thévenin's theorem for linear electrical networks states that any combination of voltage sources, current sources, and resistors with two terminals is electrically equivalent to a single voltage source V and a single series resistor R #wikipedia
actually i will explain you the way to solve problems applying this theorem consider a large network and in that network assume any resistance R about which you are asked o find the current and voltage-drop. now follow the steps below carefully
1. remove the specific resistor from the circuit (open the resistor) and find the voltage across both the points(or even parallel to both the points) where the resistor is opened this is called VTH (this is called thevenin's voltage).Also dont forget to open the current sources if present.
2. now to calculate the effective resistance as seen from the opened resistor short all the voltage sources and open all the current sources. and assume an arbitrary voltage V in the place of the opened resistor find current through the branch by mesh analysis and the ratio of voltage and current gives you the effective resistance fo the circuit as seen from the opened resistor. this is called Rth (thevenin resistance).
now , after getting the values of VTH,RTH construct a circuit in which the given resistance R and RTH arein series with the voltage source VTH , and the so called found current is the current flowing through R in the actual circuit
What can be done to minimize eddy current losses?
Changing magnetic field causes to produce eddy currents that are confind within the core of transformer. these are like circulating whirls inside the core. these can be eliminated by making the core of thin layers. "Eddy current losses occur whenever the core material is electrically conductive. Most ferromagnetic materials contain iron: a metal that has fairly low resistivity (roughly 10-7 Ω m). The problem is intuitively obvious if you consider that the magnetic field is contained within a 'circuit' or loop formed by the periphery of the core in the same way as it is contained within a turn on the windings. Around that periphery a current will be induced in the same way as it is in an ordinary turn which is shorted at its ends"
Why are the equipotential lines near conductor surfaces parallel to the surface?
For conductors, the electric field perpendicular to its surface and no field exist within the conductor. As a result the equipotential lines are found near the surface. They are parallel to the surface since equipotential are perpendicular to field lines.
Why input resistance of voltage amplifier is infinity?
For the successful amplification of the input signal the opamp should have ideally infinite input impedance . It should act like a buffer amplifier
BUFFER amplifier--------------------->
1.input impedance infinity
2.output impedance zero
the reason is that
Any signal source will have source impedance
for the signal not to get lost and dropped across source impedance we ideally insert infinite impedance in series with it which makes the whole drop across the infinite impedance but not across the source
similarly at the output zero impedance is used where in no part of the signal should be left behind in the op amp as a drop
What is the OHMS law formula for power?
There is no Ohm's Law formula for power. Ohm's Law simply states that the current flowing in a circuit is directly proportional to the applied voltage, providing external factors, such as temperature, remain constant. No mention of power, I'm afraid!
What is difference between line current and phase current?
A phase current is the current passing through a phase, whereas a line current is the current flowing through a line.
In the case of a balanced delta-connected load, IL = 1.732 IP. In the case of a balanced star-connected load, IL = IP.
For unbalanced loads, these relationships don't hold true, and must be individually calculated.
What is difference between stab shunt dc motor and shunt dc motor?
A series motor respond by decreasing its speed with small increase in current for a given load torque. A shunt motor holds its speed nearly constant with large increase in input current for same amount of load torque
What is ohm's law expressed as a formula?
Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference across the two points, and inversely proportional to the resistance between them
Why is it said that generator is a motor working in reverse?
because working principle of both the things are same.
The motor converts electrical energy in to mechanical via magnetic induction and generator do the exact opposite of this.
And yes,you should use 'electricity generator' not only 'generator'.
What will happen to the ammeter reading if the resistance is increased?
The current decreases due to I=V/R.
The ammeter reading will decrease as R is increased.
Difference between amplifier and power amplifier?
Voltage amplifiers are genrally used to amplify voltage signals to a certain db and amplification is a linear process. In power amplifiers it is not required to amplify voltage it is not significant and genraly equal to input voltage. It is significantly used to produce a large current at the output.
Why you use capacitors in power supply?
You use a capacitor to store electrostatic energy. You use an inductor to store electromagnetic energy. You use a resistor to dissipate electrical energy.
What is the difference between rectifier diode and zener diode?
A: They are both diodes. The difference lies in the application. A rectifier is used to rectify AC current into pulsating current. The zener diode is used to regulate a voltage source to the zener voltage when connected in the reverse direction.
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If you look at the characteristic curves of a rectifier diode and a zener diode, you will see that they are similar, but the reverse curve of the zener has a much sharper bend at what is called the "knee".
It is at this point on the zener's curve at which it operates.
It is an advanced power electronic device to start the motor with a very smooth starting curve. It is next generation starter compared to DOL or star Delta starter
What is the formula to find reading of ammeter?
V=I x R
Voltage= Current x Resistance
to make it easier you could rearrange the formula so it looks like this:
I=V/R
