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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
What is synchronization of alternators?
The frequency of a large electric power distribution system is established by the speed of rotation of many powerful alternators all connected by various tie-lines in the total network. The collective inertia and power of these generators is so great that there is no single load or disturbance which would be large enough to change their speed of rotation. The frequency of an electric system is, therefore, remarkably stable. An alternator can only deliver power to an existing electric power system if it operates at the same frequency as the system. A system whose frequency is 50 Hz cannot receive power from an alternator operating at 50.01 Hz. They must both operate at exactly the same frequency. This is not as difficult to achieve as may appear at first, because (when an alternator is connected into an existing system) automatic forces come into play to keep its frequency constant. Synchronization of an alternator with a large utility system, or "infinite bus' as it is called is comparable to matching a small gear to another of enormous size and power. If the teeth of both gears are properly synchronized upon contact, then the matching will be smooth. But should the teeth edges meet shock would result with possible damage to the smaller gear. Smooth synchronization of an alternator means first that its frequency must be equal to that of the supply. In addition, the phase sequence (or rotation) must be the same. Returning to our example of the gears, we would not think of trying to mesh two gears going in opposite directions, even if their speeds were identical. The next thing to watch for when we push gears together is to see that the teeth of one meet the slots of the other. In electrical terms the voltage of the alternator must be in phase with the voltage of the supply. Finally, when matching gears we always choose a tooth depth which is compatible with the master gear. Electrically, the voltage amplitude of the alternator should be equal to the supply voltage amplitude. With these conditions met, the alternator is perfectly synchronized with the network and the switch between the two can be turned on. Ref aus lab script
The megawatt is equal to one million watts.or it can be 1000 kilo watt. it means 1 kilo watt is equals to 1000 watt.hope now it is clear.
Another Answer
A megawatt (MW) is used to measure power, i.e. the rate of energy consumption. A unit, on the other hand, is another term (in the UK, at least) for a kilowatt hour, which is used to measure energy. The watt and the unit are used to measure two different quantities, so cannot be converted one to the other.
Difference between alkalized and galvanized batteries?
The old galvanic power cells that we used in our flashlights, and so forth, actually had a thin wrap of zinc alloy as one of the two electrodes. The other electrode was composed of thin sheet material with an acid paste applied to it and wrapped round and round with the zinc.
(Plating something with zinc to make it rust-proof is called "galvanizing", which has nothing to do with your question, other than to explain where the term comes from)
Alkaline power cells use an alkaline or basic 'paste' rather than an acid one, in a structure that is much more delicate than the glavanix cells, but with much more surface area, to create a much longer-lasting cell.
(PS, they are not batteries until 2 or more power cells are connected. It's like a battery of psychological tests, a battery of heavy naval guns, or the old baseball term, 'battery', which meant the pitcher and catcher working together as a team.
Would an mild electric shock cause nerve damage?
Yes it would cause a nerve damage but it depends on where and how long you give mild electric shock to somebody. i think so?
What is the use of a 100 mfd capacitor in an arc welder?
A capacitor is a storage device like a battery it will however discharge at a rate of 63% for one RC time constant .so it is there to provide more initial force.
Code 51 also refers to the throttle position sensor. You need to test the sensor - a factory repair manual will give the procedure and specs for testing.
A control system that appears to be self-regulating. Closed-loop systems employ feedback and a reference of correctness (norm or set point). Deviations from the norm are detected and corrections made in order to maintain a desired state in the system. Closed loop systems provide the homeostatic mechanism of many physiological functions (see negative-feedback) and also control some movement patterns, where feedback from proprioceptors and other receptors play an important part. Compare open-loop-system.
Single phase power from a L-L voltage of 208 volts is calc'd:
P = V(phase to phase) * I (individual phase current) / sqrt(3)
Total power from all three legs is the above P * 3.
P is in watts; continuous sampling will result in watt hour measurements; 1000 x this is kWh's.
Difference between steady state and transient analysis?
In steady state analysis, you assume anything that changes with time is 0. ie: d*rho/dt = 0. In transient, you keep all your d/dt terms. Steady state simplification is a handy tool to make many differential equations solvable, by reducing their "dimension", as x-direction, y-direction, z-direction, and time are each dimensions.
What is the KWh for 500 kw induction motor on idle running?
on idle, probably 0.
KWh = KW x time (hours) . eg. 20KW for 5 hours = 100KWh
(edit. ignore this answer i do not know what exactingly a idle motor is)
How to calculate power in an inductive load?
Inductive load power is reactive, it is given by the formula:
pL(t)=VL(t)IL(t),
in time domain (instant power);
PL(s)=VL,RMS(s)IL,RMS(s),
in Laplace transform domain (RMS denotes root mean square amplitude).
VL is the voltage across the inductor L and IL is its current (current enters in the "+" voltage reference pin, by applying user convention in which absorbed power is positive).
Power is reactive since voltage and current are always in quadrature:
VL(s) = s L IL(s),
in Laplace domain (derived from the time-domain formula vL(t)= L diL(t)/dt).
A real-life inductor will also show an active power term, which arises from parasitic resistance non-ideality; it can be modeled as a resistance DCR in series with the inductor itself:
pACT(t)=DCR IL(t)
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An inductive load such as an induction motor draws power from the supply with a power factor of less than 1.
Power = voltage x current x power factor.
This happens because the current reaches its peak in the ac cycle after the voltage, so that for a small part of the cycle power flows back into the supply from energy stored in the motor's internal magnetic field. The time-lag is measured in degrees and called the phase difference. 360 degrees denotes one complete cycle.
The power factor is the cosine of the phase difference, so that (for example) a resistive load has no phase difference so that the power factor is 1, while for a pure inductor the phase difference is 90 degrees and the power factor is zero.
If the rms voltage and current are expressed in complex-number form, also known as vectors or phasors, the real power is the real part of VI*, where the asterisk denotes the complex conjugate.
Another way to calculate the real power is to calculate the average value of the instantaneous power V x I. If the voltage is Vcos(wt) and the current is Icos(wt+phi) then those expressions can be multiplied together and trigonometry formulas used to show that the power factor is cos(phi) as stated.
Real power is measured from the average value of volts times amps with an instrument that contains a voltage coil and a current coil. The force produced is equal to the instantaneous power, and the instrument measures its average value muliplied by the time.
How do you calculate the current carrying capacity of cables?
if you know the gauge of the wire you can learn its current carrying capacity
How do i convert a Ramp Wave to its peak value for example 15vRMS?
Do you mean a "saw-tooth" wave? Also, a "peak value" is not an RMS value (by definition), it is simply the highest value attained (positive or negative) over the period of analysis.
We don't get shocked when we touch neutral and ground because neutral is grounded back at the distribution panel, so the effective voltage between neutral and ground is very low. It won't be zero, because there is current flowing on neutral, causing a voltage difference between the load and the distribution panel, but it is low enough, assuming there is no malfunction, to not cause a shock.
In the case of touching hot and neutral, or hot and ground, you will get shocked because there is line voltage between hot and neutral, and because neutral and ground are connected together, there is also line voltage between hot and ground.
Note, however, that connecting a load between hot and ground is a violation of the code and the intent of the design, because ground is not rated to carry current except in short term fault conditions - you must always connect a load between hot and neutral, or between hot and hot, as the case may be.
Why you need back emf in dc motor?
A back emf is DC machines ability to protect itself from over speed. From Farads' Law you can recall that emf is induced into a conductor immersed in a magnetic field.
In dc machines there is a magnetic field flow from one pole to another. As the conductor cuts through this magnetic field emf is induced into it. The amount of emf induced into the conductor depends not only at the strength of the magnetic field but also the rotational speed at which the conductor cuts through magnetic field.
Hence higher the motor speed, higher the back emf.
The back emf can be described by the following equation:
E = (Flux * angular speed of motor * number of poles in machine * (N/a)) / pie
Where N/a = series turns in the armature winding.
Does current ever flow in the neutral wire?
In 120 VAC circuits, the neutral wire carries all the return current from the hot wire. In a single phase 120 VAC circuit, such as found in US homes, the neutral wire carries exactly the same amount of current as the hot wire (unless there is a fault in the device). The difference is that the neutral wire is connected to the ground bus in the load center (also called "breaker box" in the Southern US).
In a three phase circuit, as was pointed out by another person, the neutral wire will carry any current that results from an imbalance in the phases. If the three phases are perfectly balanced, for example when connected to a motor, there will be no current in the neutral conductor. (In fact, in a three phase delta connection, there is no neutral. But I will not attempt to explain that here, beyond simply mentioning it.)
Nevertheless, anything that causes an imbalance in the phases of a three phase system will cause neutral current to flow. The amount of neutral current in a three phase system may be calculated using the phase relationships of the three phases, provided the imbalance is known, or simply measured with a standard AC current meter. (However, I must qualify this by saying that three phase systems are complex and hard to understand. It is easy to be fooled when working with such a system, and I would not undertake it without a thorough review of the principles involved. They do not behave in a simple and obvious manner.) However, I do believe that the neutral wire in a three phase system is often much smaller than any of the phase wires, because it is not called upon to carry the full current, but only the relatively small currents resulting from load imbalances.
In a 240 VAC system, such as is used to supply power for an AC unit in the US, again typically the neutral will not carry current unless there is some sort of problem. Rather, the current flows in the two hot wires. As before, the neutral wire is connected to ground at the load center, and is usually connected to the metal chassis of the device being powered, whether it be an air conditioning system, electric range, or hot water heater. This is to provide safety for the user, and also will help to trip the breaker if there is an insulation breakdown within the device.
Modern 120 VAC systems in the US have three wires. A safety ground wire has been added, and this is always connected to the metal chassis, except in certain devices that have extra insulation, such as power drills and most lamps. This ground wire is only for safety purposes, and normally does not carry any current. While the neutral wire is also connected to ground at the load center, it is a current carrying wire in a 120 V system, so is not usable for grounding the chassis as in the 240 VAC system. However, if there is an insulation breakdown problem in the device, the safety ground will conduct current and trip the breaker at the load center.
Interestingly, the fact that the neutral carries the same current as the hot wire in a 120 VAC system is used as the operating principle for Ground Fault Detectors. An electronic circuit in the GFD device compares the current in the hot and neutral wires. If they are not equal, the device trips a relay, removing power from the device. If the hot and neutral currents are not equal, this indicates an insulation breakdown, where some of the current is leaking to an improper place within the device. The Ground Fault circuit detects this and shuts down the device very quickly, preventing electric shock and potential loss of life.
How a bms control system is working?
the bms system is working through the logic created and controlled by the controller and the sensors based on the return air sensor in hvac bms system
Magnetic inrush current in power transformer with waveforms?
The mgnetic inrush current is the current drawn by the transformer when power is applied to the primary winding
Sorry, this question is unanswerable in the form you ask it. In order to answer it would be necessary to know what is meant by "a 1cm by 1cm square center leg at 14 volts". I have been an electronics engineer for 30 years and I don't know what you mean. Do you mean the ferrite core is 1 centimeter by 1 centimeter, with a center-tapped leg, the direct current voltage being 14 volts at that leg, 28 volts direct current total, irrespective of the waveform changing at 100 kilohertz? It would also be necessary to know the gauge of the wire, the type of the ferrite, the waveform, etc. Also, where are you measuring the strength of the magnetic field in Tesla units, one Tesla = 10000 gauss, at the center of the coil or some distance away?
Resistors placed in series create a total resistance that is found by simply adding the values of the resistors. (Knowing the applied voltage isn't necessary to solve this problem.) Rt = R1 + R2 + R3 = 2 ohms + 4 ohms + 6 ohms = 12 ohms
Electrical transformers physical description?
It has coils of wire wound around a metal core or frame. The amount of coiled wire depends on what voltages are to be increased or reduced (or 'transformed'). also known as the "turns ratio". The physical size is generally determined by what amount of voltage and current it is intended for. It can be open, or be enclosed in a metal can. It can be air, water or oil cooled.
Circuit diagram of stand by earth fault relay?
earth fault relay is similar like earth leakage ralay,but the 2nd one is more sensitiv.
