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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
Which two port parameters are best suited for analyzing a series shunt feedback circuit?
h parameters
Why is it important that the core of a transformer pass through both coils?
If it doesn't, you don't have a transformer. The core is where the magnetic flux will pass, which induces voltage on the secondary (voltage applied to the primary winding induces a magnetic flux in the core, which induces a voltage on the secondary winding); If the core is not passed through one coil, it will not induce a voltage in that winding.
Leakage flux outside the core can result in some inductive coupling, but the job of the core is to couple the primary winding to the secondary winding.
How does electric servo motor brake work?
break is connected with parallel to motor winding if the brake is d.c. is supply it must be connected with rectifier unit,when motor in ideal position the brake holds the shaft which is connected with gear and when motor starts the break coil will energise and motor shat became free and motor will run like this brake work
What are the three ways in which voltage can be induced in a wire?
Voltage can never be induced in a straight open wire because flux through a wire is zero but a coil made up of a wire can have induced voltage.
Methods
Move a magnet to and fro through the coil, the magnitude can be changed by altering the relative velocities between them
Move the coil relative to he still magnet
Place the coil in a time varying magnetic field such that the flux linked through the coil changes with respect to time
Place the coil tn an uniform magnetic field and alter its area with respect to time
Explain why the parts of your model are like the real circuit components?
It is because there is a light bulb and things like that......
Explains why a 3-phase induction motor develops no torque when running at synchronous speed?
When rotor speed becomes equal to Synchronous speed in an induction motor, it means that the slip is zero. Which means that there is no cutting of magnetic lines by rotor bars and hence no torque is generated.
To generate Torque, rotor speed should always be less than the synchronous speed. That is why, you must have seen in your dailty life that all induction motors are rated below 3000 RPM(sync speed for a 2 pole machine).
Sync speed (Ns) = 120f/P
High AC voltages are usually measured with?
They are usually measured using potential transformers that lower the voltages so that normal metering equipment can be used. Potential transformers PT's are almost no different that regular transformers except they are designed to be extremely accurate since they are used for metering purposes.
How can I check IC good or not?
This depends on the IC. Visual inspection will only go so far. You will need to test it and compare the testing to the datasheet; if it is not testing as specified in the datasheet, then it is bad.
Sorry, there's no one easy answer for all IC's.
Maximum load current on a 140KVA, three phase transformer when the output voltage is 115 v phase to phase is:
140kva / sqrt (3) / 115 = 703 Amps.
frequency does not matter here.
What is the use of polarity test?
I will assume that your question is in reference to CT and transformer polarity.
In the case of a CT (Current Transformer) they have to be installed in the correct direction for proper metering. The polarity check is used to verify that they are installed correctly and that the polarity marks are correct (if the CT has them).
In the case of a transformer there are two types of polarity, additive and subtractive. If you are paralleling transformers you have to ensure that they are the same type polarity in addition to other attributes.
Hope this helps.
Alternative AnswerIn a new electrical installation, a polarity test is conducted to ensure that socket outlet terminals are correctly wired (line really is line, neutral really is neutral, and the protective conductor (earth/ground) really is protective conductor. It's also important, for example, that the centre pin on an Edison Screw lampholder is connected to line, and not to neutral.
What is limit load factor in aviation?
the maximum load factor without structural damage to the aircraft.
Load factor = 1 / (cos (angle of turn))
Why no electric shock from neutral line?
There is normally no voltage on the neutral line because the neutral line is grounded. However, and this is always important, do not assume that neutral is grounded, nor that there is not an elevated voltage on neutral or ground due to a possible ground fault.
What angle is the voltage increasing at its fastest rate?
This is a simple derivation problem. Take the derivative of the AC voltage waveform (I'll assume sin (t)), and set the derivative equal to the maximum value it can attain (which is 1):
cos (t) = 1, t = 0 degrees, thus for an AC waveform of y = sin(t), the fastest increase in voltage occurs at 0, 360, etc. degrees. The fastest decrease in voltage will occur at 180, 180 + 360, etc. degrees.
What affect does a changing magnetic field strength have on an ac generator power output?
By increasing the field current (current flowing through the rotor windings), the magnetic field generated by these windings will increase. This increased magnetic field will result in a larger current flow in the stator windings (the output of the generator). This in turn causes a larger pull against the rotation of the rotor, causing it to slow down. The governor will then kick in, allowing more steam/ power to the prime mover to keep speed steady.
Assuming all is working correctly, the output power will increase as the magnetic field is increased (to a limit).
What are Examples of open and closed loop systems in the home?
Closed loop:
1. Thermostat --> furnace (constant temperature)
2. Toaster setting (light/dark) --> toast (IF the toaster has heat sensors)
3. Refrigerator cold/hot setting --> refrigerator inside temperature (constant)
4. Temperature setting for oven (not stovetop) --> oven temperature constant
5. Clothes dryer with moisture sensor
6. Washing machine water level
Furnace.
Temperature sensors control when furnace is turned on. Heating sensors in furnace control when air blower is turned on, and when flames must be turned off.
Refrigerator.
Temperature sensors control when refrigerant cycle turns on and off.
Many TV functions, internal operation of disc playback and record, really ad infinitum.
The NPN transistor when used as an amplifier is operating in linear mode, and, when operating as a switch, in saturated mode.
In the following discussion, base currrent means base-emitter current, while the base is more positive than the emitter, and collector current means collector-emitter current, while the collector is more positive than the emitter. There is base-collector current, but we are going to ignore it for now - besides, we are going to discuss class A, common emitter, configuration.
The PNP transistor is very similar. Everything is backwards, including Vcc, which is now -Vcc, or appropriate reconfiguration. The rules are the same - just backward.
In switched or saturated mode, the ratio of base to collector current is far greater than beta-dc, or hFe, so the transistor is operating way out of its linear mode. We call that saturated mode, and the transistor is essentially either fully on or fully off, and therefore operating as an on-off switch.
The rest of this discussion will focus on linear or amplilfier mode.
If the ratio of base to collector current is less than beta-dc, or hFe and, if both base and collector voltage are greater than cutoff voltage, then the transistor is operating in linear mode. Well, sort of, for best linear mode, we look at the data sheet, or make empirical observations, and we pick the base and collector currents that are centered between the base knee and the collector knee, i.e. "in the middle of" the linear region.
In this mode, a very small base current can control a much larger collector current, and, most importantly, a very small change in base current can create a much larger change in collector current.
In the theoretical case, for example, where the emitter is grounded and where hFe is 100, then 1 mA of base current translates to 100 mA of collector current, and 2 mA of base current translates to 200 mA of collector current. Problem is, that hFe varies amongst even so called identical transistors, and hFe varies as a function of temperature as well.
So, in the practical case, an emitter resistor is added to stabilize the transistor and place limits on the need for hFe of a particular value. Done properly, this will yield predictable gain for various transistors and for various temperatures.
Now, lets look at how gain works in the practical sense. The base voltage is also a known delta above emitter voltage. Yes, temperature will affect this, but proper design can make this a negligable factor. The emitter current times the emitter voltage results in a known voltage. By Norton's current law, the base current and the collector current add up to be the emitter current, but by hFe, the base current is very much smaller than collector current, meaning that the really important part is that collector and emitter current are the same for all practical purposes.
So, now add a collector resistor. Ignoring base current, the collector/emitter circuit is a series circuit, and Norton's current law, reinterpreted for series circuits, says the two resistors have the same current. Think about what that means; if the current in both resistors is the same, then the ratio of the voltage across the two resistors is proportional to their value. The gain of the amplifier is collector resistor divided by emitter resistor. That is critical knowledge. Again, base current enters into the equation but, if hFe is high enough, it does not matter.
All that is left, then, is to bias the base. You want to pick a base voltage (current) that places the collector current in the center (or in an appropriate point) of the linear region. Choose a nominal hFe, divide by collector current, and you get an approximation of what base current bias should be. Choose a resistor divider to match, keeping in mind that the two resistors (base to Vcc and base to Gnd) in parallel will reflect your effective input impedance.
Review everything, particularly your power levels. To calculate the power through the collector/emitter junction subtract collector resistor voltage from emitter resistor voltage from Vcc, and you get collector/emitter voltage. Multiply that by collector current, and you get power dissipated by the transistor in nomial bias condition.
Play with the values until you have what you want. You could even set this up in a spreadsheet.
Last, but not least, there is a base bias voltage. If you are going to amplify something, you need to maintain that nominal bias voltage. Connect a series capacitor between the base and the input point and you will be able to operate from an AC signal that is zero referenced. Just pick the RC time constant appropropriate for your application.
Similarly, there is a collector bias, so, if you want an AC output zero referenced, use a series capacitor also in between the collector and the ouput.
This is an AC coupled, inverting amplifier. There are DC coupled non-inverting versions, but they are more complicated, requiring more than one transistor, and this answer does not address them. Good luck!
Advantages and disadvantages of polyphase circuit?
fewer ripples in a direct current when alternating is converted to direct current
What is hysteresis angle in transformer?
Generally th e current drawn by the transformer in no load condition is being utilised by the iron losses and the angle b/w voltage and current is known as hystresis angle.
How many amps does a 20HP motor draw at 415volt three phase?
Assuming a power factor of approx. 0.8 which depends on motor but this will error on the side of caution IL =S/1.73*VL S=P/pf 20hp= about 15000 W. S=15000/.8 = 18750 VA.
IL = 18750/1.73*415 = 26A
The motor would draw about 26 A. depending on Load and efficiency
Why is the number of turns in primary coil more than that of the secondary coil?
The number of turns or windings of a transformer can vary. There can be more in the primary, or more in the secondary, or there can be an equal number in a transformer that is simply used for isolation (an isoformer). More turns in the primary than secondary will create a step down transformer. More turns in the secondary are found in a step up transformer. The transformers on power poles have more turns in the primary to step the line voltage down for delivery to residential customers.
Differentiate between normal and reverse polarity?
It depends on the context. In a.c. circuits, 'reverse polarity' describes a situation in which a device, such as a socket outlet, is wrongly wired -with the line and neutral conductors interchanged.
A cycle is one complete revolution of the sine wave. Hertz is the frequency of the alternating current, how many complete cycles per second. 60 Hertz would have 60 cycles each second.
Explain overall organization of the MIPS RX000?
A sequential circuit is an interconnection of flip flop -------
