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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 size resistor is needed to drop 12 volt dc to 3 volt what is the formula?
The "size" (value or the power capacity) of the resistor can not be defined unless the power of the 3 volt bulb is known. If you tell me how many amps would the bulb draw from a 3 volt source, I will tell you exactly how many ohms of resistance, and how many watts of power capacity will be required of the resistor.
How do you check a capacitor to see if it is good or bad?
There are many ways. FIRST: short the terminals to ensure it is not charged. Many of the digital meters today also have a capacitance check setting, simply use that setting. It not only checks for faults, but also will give you a reading of the capacitance value itself. For most non-electrolytic capacitors a quick check (definately bad vs. maybe good) can be done with an analog VOM. Use the highest resistance scale to measure across the terminals. When first connected there should be a short needle jump that slowly drops back to infinity. Reverse the leads and do it again, should have the same effect. Any resistance highter than infinity indicates a shorted capacitor. Lack of needle jump may indicate an open capacitor (or one of very little capacitance). Electrolytics can also be checked with a VOM, but polarity must be observed, and the drop back to infinity may take a very long time. Alternatively, for electrolytics and larger capacitors is to charge them with a low voltage source (e.g. 9V battery) and measure with multimeter to see if they hold the charge.
Does a photovoltaic cell produces AC electric current?
The panel itself produces DC and if it is connected to mains electricity it needs a separate converter to change the current to AC.
How arc take place in circuit breaker?
All circuit breakers try to achieve the same thing: ensure that the rate of increase of dielectric strength exceeds the rate of increase of potential gradient across the gap between the separating contacts.
Explained in another way, the rate at which energy is developed by the arc must be exceeded by the rate at which energy is dissipated through heat transfer.
This can be achieved in numerous ways:
- reduction in arc temperature -which reduces vapourization of contact metals and ionisation of insulating medium.
- reduction in potential gradient -increasing contact separation distance.
- constriction of the arc -by insulating medium pressure, which reduces cross-sectional area of arc, and increases its resistance.
- increasing medium dielectric strength -by replacing contaminated insulation medium.
- speed of operation -minimising energy build up (I2Rt).
- utilising 'current zero' -utilising the natural cut-off point for a.c. current.
All practical circuit breakers utilise a combination of the above methods.
Why are step-down transformers used?
A step-down transformer is a reverse-wired step-up transformer. You can take a 110/220 transformer and feed 110 to step up to 220 or feed 220 to step down to 110.
step down transformer is a device which reduces voltage .
What is excitation and why is it needed for start up in an AC generator?
An alternator is just another name for a synchronous generator. Excitation is needed to create a magnetic field in the rotor. When to rotor is spun with excitation the magnetic field will cut through the stator field and produce an AC voltage in the stator field. In terms of an alternator with built in rectifier the stators AC voltage in the rectified to DC. The strength of excitation will determine the alternators output voltage. The AVR Automatic Voltage Regulator built into almost every alternator controls field current to maintain a constant output voltage.
Table 314.16(A) and (B): a 4" square x 1 1/2" deep box is good for 21"^3 and #12AWG takes up 2.25"^3
21/2.25 = 9.33333
9 wires can fit.
<<>>
The Canadian electrical code, Table 23, will allow 12 - # 12 wires in a 344 mL box.
What is open circuit fault of transformer?
A fault causing a difference between the primary and secondary currents of a power transformer. Usually a leakage to earth from somewhere in a winding. Such errors are caught by a protective circuit comprising two current transformers for transformation of the primary and secondary currents respectively, in a common scale typically 0...1 or 0...5 A and bringing them together in a loop. A transverse branch in the middle of the loop collects the differential current set up in case of a fault, the so called 'spill' current. The differential branch uses this current to operate the operating winding of the protection relay and through this the alarm and trip contacts. The protection circuit thus simulates what is happening in the power circuit in an under graded and more direct issue.
The relationship for current and voltage in a series circuit?
current is the rate of flow of charge: colombs per second or amps
voltage is the amount of energy in one colomb of charge: volt or jouls per colomb
voltage times current is the power.
Gunn diodes are used in GUNN oscillator over high frequency application. its work on the transfer electron effect TET and the scientist J.B Gunn observe it so the phenomenon is named by gunn effect. the diode are made from GaAs material.because silicon is not suitable low forbidden energy gap 1.21eV only.
What does not reduce resistance in a copper wire?
-- winding the wire into a coil
-- changing its price
-- tie-wrapping it to the outside of a conduit
-- shining a flashlight on it
-- exposing it to loud noises
-- changing the color of its insulating jacket
Resistance will only be reduced by changing the thickness / physical dimensions (15 small wires wound together vs 1 big one, etc.) of the wire, or the wire's temperature. It's apparent impedance can be changed by placing it in an electric field as well.
How you convert the value of single phase power to value of 3 phase power?
Electric power is measured in watts. It does not matter if it is single phase or three phase. All things being equal, for the same load, the power measured in a single phase circuit or a three phase circuit, will be the same.
How the moving coil actuator work?
A loudspeaker produces sound by converting electrical signals from an audio amplifier into mechanical motion. Sound is created from the forward and backward motion of the loudspeaker cone, which is a concave plastic or paper disc. The cone is mounted and centred on a concave metal frame by a ring of flexible rubber. Glued to the centre of the cone is a hollow cylinder of thin, lightweight aluminium. A length of thin, insulated wire is wound upon the bobbin to form the voice coil; both ends of the voice coil wire are connected to the voice coil terminals on the frame. The voice coil is positioned inside a narrow cylindrical groove or air gap in the centre of a magnet. The coil is suspended in the air gap by a flexible fabric disc. An audio amplifier is connected to the voice coil terminals. The coil emits a magnetic field as audio signals from the amplifier travel through the voice coil wire. The voice coil field alternately pulls and pushes the coil, bobbin and cone assembly towards and against the magnetic field from the magnet, which causes the forward and backward cone motion.
A relay circuit is typically a smaller switch or device which drives (opens/closes) an electric switch that is capable of carrying much larger current amounts. Or a circuit which operates the coil or electronic actuator from one source and uses a separate power source to drive an isolated device. Generally speaking, a relay circuit is a circuit that uses a small mechanical switch or a semiconductor device (with associated circuitry) to energize a relay, which will then close a contact set to complete another circuit. This system is used by most people on a daily basis, and it is used to start a motor vehicle. The key switch (ignition switch) is turned to "start" and 12 volts (approximately) is applied to the starter solenoid (which is a big relay). The coil is energized, it shuts contacts, and the battery voltage is delivered through the heavy contact set (for high current capacity) to the starter motor. There are variations on this theme to which the term relay circuit can be applied, but the idea remains the same: a small switch of some kind controls switching in another (usually higher voltage and/or current) circuit. It could be argued that the telegraph is a relay circuit. Remember those old westerns? When a telegraph key is pushed down (thus completing the circuit), a remote (relay) coil is energized. The magnetic field created by energizing that coil pulls down an armature with the objective being to make a "click" instead of it being to close some electrical contacts. An early and dramatic application of the simple relay circuit, the telegraph, yes? A RELAY CIRCUIT DOES NOT IMPLY MASSIVE CURRENT SWITCHING. It is a means to isolate one source to another.
Why are transformers helpful when using alternating current?
The transformer in the least complex manner can be depicted as a thing that means up or ventures down voltage. It is fundamentally a voltage control gadget that is utilized broadly in the conveyance and transmission of rotating flow power.
Trutech Products is a leading Transformer Manufacturers In Pune
Your standard light bulb where a filament is heated by a current passing through it. The heated filament then gives off light.
How do you calculate 3 phase kWh from measuring the total phase current current?
In a balanced 3-phase system, if the three loads are star connected, the line current is equal to the load current. If the loads are delta connected, the line current is less than the load current by a factor of 1/sqrt(3).
What are the uses of induction coils?
1. Transformer
2. DC/ AC Motors
3. Solenoid valves
4. Contactors/ Relays
5. Amplifiers
Air has less quenching effects when a breaker breaks on load or on a fault. Air circuit breakers are not suggested for very high rating current and high voltage application. It is ok for Low voltage application. Oil is cumbersome to use and maintain. But Hv or EHV application oil is used for breaker quenching application.
These days SF6 or vacuum circuit breakers are more popular for HV, EHV application.
What are disadvantages of bldc motors?
1. A squirrel cage Induction motor is lesser costlier than electrical drive because of using coverters and control circuits .
2. Technology for dc drives is improved compared to ac drive
3. It is not reliable
Two black wires to a single fuse or breaker lug is called?
This condition is commonly known as a "Double Tap", and is only permitted if the breaker specifically allows it. Some Square D breakers and possibly other manufacturers allow terminating two wires under the screw, and if the breaker allows it, it will be identified as such on the label.
If your specific breakers do not allow two wires terminating under one screw, you will need to install another appropriately sized breaker for that circuit, assuming your panel has the space available for the additional breaker.
As always, if you are in doubt about what to do, the best advice is to call a licensed electrician. Before you do any work yourself on electrical circuits, equipment or appliances, always use a test meter to ensure the circuit is, in fact, de-energized.
IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOB
SAFELY AND COMPETENTLY
REFER THIS WORK TO QUALIFIED PROFESSIONALS.
How do you find cable size with given kilowatts?
To select the proper cable size you need to know all of the following:
circuit ampacity needed
ambient temperature
length of circuit from point 1 to point 300
number of conductors in the raceway or cable
type of insulation being used
voltage: whether above or below 380 volts
and for some pieces of equipment, the manufacturer's instructions.
How much current flow in 1 watt bulb?
Everything Depends on the voltage supply ......
Current flow (Amp) = Watt / Voltage
the Current flow will be 1 amp if voltage is 1 V
the Current flow will be 0.5 amp if voltage is 2 V
the Current flow will be 0.25 amp if voltage is 4 V
and so on.......
Is the resistance of a resistor the same as voltage changes?
Yes and no. As voltage changes, current changes, causing power to change, with the end result that temperature changes. Most resistors have a small temperature coefficient, so their resistance will change slightly as the voltage changes.
