0
Electrical Engineering
Electrical engineering is a field of engineering that deals with the study and application of electricity, electronics and electromagnetism.
23,056 Questions
How do you tell the difference between AC and DC 3 phase generators and alternators?
The very first thing to do is look at the nameplate. There it will tell you what the voltage is. On a three phase generator there is usually no places to plug any equipment into. Three phase generators usually have the coil ends brought to terminal points in the generators junction box. From a second set of terminals the feeder wires go to the top end of the generators main disconnect breaker. Different voltages can be obtained by positioning jumpers between different terminals within the junction box.
Is high electrical resistance good or bad?
electrical resistance is when something resists the electrical current .. eg rubber
hope it helped
What is difference between amplitude and peak value?
It is the highest value of the amplitude, called the peak value. Scroll down to related links and look at "RMS voltage, peak voltage and peak-to-peak voltage". Look at the figure in the middle below the headline "RMS voltage, peak voltage and peak-to-peak voltage".
Why is it thatFET is called a voltage operated device?
since in an FET the value of the current depends upon the value of the voltage applied at the gate and drain...so it is known as voltage controlled device.. for example..in a mosfet..the current from drain to source depends upon the width of the depletion layer..which in turn depends upon the voltage applied on the gate.. so that is the reason
What is volage ratio of potential transformer?
The voltage ratio of a potential, or voltage, transformer (PT or VT) depends upon the primary voltage to which it is connected. Accordingly, its voltage ratio varies considerably, as there is huge variety of system voltages throughout the world.
Typically a VT's secondary voltage is standardised at 110 V which will match the full-scale deflection of a voltmeter connected to it (although it can also supply protective relays), while its primary voltage is then matched to the voltage of the system to which it is connected: in the UK, for example:
- 11-kV:110 V
- 33-kV:110 V
- etc.
What size motor do you need to operate a 200 kw generator?
A kilowatt is a unit of power, and energy is measured in kilowatt-hours, in other words 1 kilowatt flowing for 1 hour is one kWh of energy.
For an ordinary heat engine it is normal to use a round-number estimate of consumption as half a pound of fuel for one horse-power-hour, which is 0.746 kWh.
How would you measure a relays contacts resistance?
The voltage drop across a relay coil will be the same as the coil supply voltage. If you are trying to see if the coil is good or not, remove one of the voltage supply leads and check for continuity by using an ohm meter across the coil leads. A reading will tell you that the coil is intact and not open.
When is a voltage drop calculation considered when determining the cable size?
The voltage drop in a cable is the current multiplied by the resistance. For a twin-wire cable the resistances of the two wires are added. Cable resistance for different sizes of cables can be looked up in wire tables.
More detailed answer for USA, Canada and countries running a 60 Hz supply service.
Voltage drop and cable size can be calculated by looking at tables that are available in the National Electrical Code. Some of these tables are difficult to understand and will require you to seek assistance. You can also determine the amount of voltage drop over a distance by finding the resistance of the cable for a specific temperature(given in ohms/1000ft)from the cable manufacturer or electrical wholesaler. If you know the largest amount of current that will flow in the cable, then use the formula:
Vdrop = Current X Distance(Ft) X 2 X Ohms per 1000Ft x 0.001
[Note: the 0.001 fixes an earlier error in the formula where the contributor didn't divide out 1000 ft by using R/1000ft!]
<><><>
Voltage drop is a complicated calculation done by electricians. I don't know what you're trying to run but let me just give you the rule of thumb. If you run out over 200 feet of wire for the job in hand, you should jump up a wire size in order to have sufficient voltage at the other end. For example. Let's say you are going to wire and out building for your workshop and you need only 120 volt receptacles at the shop end to run your power tools. Power tools run at the nominal voltage of 120 volts, but they operate within a range, say 108 to 128. This allows for how close your are to your distribution companies source. I don't know what your starting voltage is so that's why the rule of thumb. To your outbuilding you only need #12 to carry 20 amps for your tools and lights etc. If you have to exceed that distance, then you would jump up to #10 in order to have sufficient voltage at the other end. If you are starting at 115 volts at your house, and are running 100 feet, I would still up the wire size. You can't go wrong by going one size bigger on your wire. When in doubt, always consult a qualified electrician.
<><><>
Many electricians wire for no more than 5% voltage drop. This is usually fine since appliances and power tools are made to operate over a range of voltages. For a more expensive way to wire a house, you can try wiring for no more than 2% voltage drop. In this case, if you are running 20 amps, you need to up the wire size to #10 if you go more than 35 feet. In general, the percentage voltage drop decreases with a higher starting voltage. To see this, play around with the formula for voltage drop given in terms of resistance. The resistance of various sizes of wires can be found in the CRC handbook. Practically, this means you lose less power to voltage drop if you choose a 240 volt appliance instead of a 120 volt one. And you lose a lot with low voltage lighting running on 10 or 12 volts.
<><><>
The formula for voltage drop is Vd=KIL/CSA where Vd stands for voltage drop, K stands for the resistivity factor of the material [I think copper is around 7 and aluminum 11], I is the current in Amperes, L is the round trip length of conductor, CSA is cross-sectional area of the conductor in circular mils
You can get the CSA values from chapter 9 table 8 of the NEC
CSA for 14 is 4,110; 10 is 10,380; 8 is 16,510; 6 is 26,240
<><><>
As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed.
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 does an isolator switch work?
An SPN isolator switch is a circuit breaker; they are a device, which when used can automatically switch off the flow of electricity. They are used to protect a piece of machinery or equipment from damage by an overload of electricity.
What should you do before using electrical equipment?
Any test equipment that your life may depend on when using it must first be tested before being used. These types of test equipment usually have internal apparatus that can verify that the equipment is working perfectly before it is used by personnel. Linesmen use this type of test equipment before working on primary voltage lines.
Voltage frequency inverter dc or ac output?
An inverter changes a d.c. input to an a.c. output.
Inverter is a device to change low
volt DC to high volt AC
12 Dc to 220 Ac volt
So many type of inverter of watts
500 watt 1000 watt 5000 watt
How a rotaing magnetic field is generated in an induction motor?
The magnet is the stator part of the motor, either as a permanent or an electromagnet. It draws the rotor past of the motor towards it causing the rotation. As it does this the brushes of the motor now lose contact with that section of the rotors many coils and switch to next segment on the commutator (copper segments the brushes run on). This new coil becomes magnetised and is again drawn to the stator magnet and so on.
Where can you purchase DC power supplies?
There are a number of places where one can purchase direct current (DC) power supplies. Metric Test, EMCO High Voltage , and CY Power are three sources of SC power supplies.
What is the voltage drop through a resistor of 6 ohms(2amps)?
Assuming the these resistors are connected in series, the voltage drop across each resists can be calculated simply using V = IR. In a series circuit, the same current must flow through each resistor. So, 2*i + 2*i + 2*i = 6 volts. or i * 6 = 6, or i = 1. So, the voltage drop across all resistors i*r is 2 volts.
What is specific resistance how is it diff from resistance?
Electrical resistivity is a measure of how a material opposes the flow of electric current. Copper is used for electrical lines because it has a low resistance relative to its cost. Gold and silver also have a low resistance, but imagine how expensive the power cord for your computer would be if it were made of gold!
How many watts equal 35 lumen's?
There is no direct conversion for this, because these are two separate things. Watts is actual power usage. "Lumens" is how much light is provided from a specified amount of power. The typical light bulb converts some of the electricity driven through it into light, and the rest into heat. The more efficient the light bulb, the less power per lumen will be required.
That is why newer bulbs can be purchased that are 13 watts and advertised as equivalent to 60 watt incandescent bulbs - the light output is roughly equivalent (lumens), but the power usage is substantially different.
The output voltage from a PC power supply are?
Generally, there will be a 12+ volt rail, a 5+ volt rail and often a 3+ volt rail.
What is the full form of ac and dc voltage?
Full Form of A.C. and D.C. supply is :
A.C.= Alternating Current
D.C.= Direct Current
Direct Current and Alternating Current are two methods for transmitting electricity. In Direct Current, the individual electrons start at the power source and travel all the way to and through the load (such as a light bulb) and all the way back to the opposite terminal of the power source. This technique works well for small applications where the electricity is not being transmitted over any great distance, and relatively small voltages are being used.
When distance and high voltage are required, Alternating current is used. In Alternating Current, the direction in which the electrons travel is flipped, usually sixty times per second. This results in each of the electrons moving only a small distance before being pulled the opposite way. This technique of transferring electricity is much more efficient because each electron only moves across a small distance, making the maximum power that can be transmitted dependent upon how many ambient electrons are in a wire. While in Direct Current, the maximum power that can be transmitted is limited by how many electrons a wire can transport around the entire circuit.
How do you test dc voltage from a transformer?
On TRANSFORMER OIL BREAK DOWN VOLTAGE test is carried out which is done on field while filling the oil in transformer. This process is also called oil filtration.
1.Take sample from top of Transformer before filtration.
2.The BDV of oil should withstood min 50 KV
3.The gap between the test electrodes sample to be 2.5mm maintained
4.At least 5 sample(top/bottom) should be checked separately while filtration.
5. The samples should withstand 50 kv for 1 min.
5. Take the average of all the samples timings.You will get value.
7.Procedure
a.Voltage should be gradually increased from 0.
b. At one point Flash will take place and that point is
termed as Bread down Voltage
The break down characteristics depends upon initial moisture content of transformer & oil. The electrical strength of oil depends upon the water content in transformer & temperature gradient. The electrical strength of oil is reduced if the water content is more than 2%.
===============================================================
There are several standard test, specific components are needed to conduct these tests, although, like a car's motor oil, a visual inspection can determine the amount of oxidation, and broken-down mateial in the oil. See the related links for typical tests.
i would like to add here, regarding tests. we can do various test like dissolved gas analysis(DGA), check for furan compounds- it shows damage to the insulation, etc to check the transformer oil and take various actions.
Another Answer:
There are a variety of tests offered by Utility Testing Laboratoies that track dielectric oil quality including:
Dissolved gas
Dielectric strength
Acid number
Color
Interfacial tension
All tests are performed according to ASTM methods. Standard turnaround for sample testing is 2 weeks. Utility Testing Laboratories can be contacted by phone 8:30am-6:00pm (MST) M-F at (801) 458-891 or find them online at http://ut-labs.com/index.html
Can you wire a 3 phase 690 volt delta star motor to 480 volt 3 phase with out harming the motor?
Depends on the motor and the load on that motor. If the motor is loaded to its capacity, it will draw the same amount of power as it would on 690 volts - which will result in ( 690/480 = ) 144% of normal current, which will thermally damage the motor, or will trip overload protection.
How is electrical energy made from an alternative form of energy?
There are different types of energy that are considered "alternative". The details depend on the type of energy.
Why should an ohmmeter never be used on an energized circuit?
Because an ohmmeter works by putting a potential difference (voltage) across a load and measuring the resulting current (the current will be inversely proportionate to the resistance). In a live circuit there is already current flowing through the load so (at best) the reading will be inaccurate, at worst the meter will be damaged.
What is the full load amperage of a 500 HP motor at 380 volts?
1HP =746 watts power(watts)= current times voltage ... 746x500=373000. 373000/380= 981.58 so 981.58 amps
AnswerYou have not supplies sufficient information to answer the question.
The load current depends upon the type of motor(d.c./a.c./ single-phase/ three-phase), and the efficiencyof the motor. Before you can calculate the current, you need to determine the input power to the machine, which is always greater than its output power, which you have described as being 500 hp. Once you have determined the input power, and the type of motor, only then can you can calculate the load current
