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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 the function of an under voltage relay?
under voltage relay is used to protect the electrical equipment from the low voltage below the rated voltage till 80% of the network potential.
u/v relay is used to give a signal to emergency generator to start whenever the system voltage drops below (80%).
U/V relay number is (27) which is available in most electrical circuits to protect the following circuits by insulating them whenever the low voltage occurs:
LV/MV switch boards.
Motor feeders
Generator Circuits
Transformer circuits
u/v relay is considered to be one of the main protective relays in electrical design.
The value of the voltage (potential difference) across a conductor when a current of one ampere dissipates one watt of power in the conductor. It is also equal to one joule of energy per coulomb of charge, J/C. Unit conversion: V = W/A = (J/s)/A = J/As = J/C where V=volt, W=watt(power), A=ampere, s=second, C=coulomb(charge)
The speed of a synchronous motor with 60 Hz power supply is?
Speed (RPM) = 120 x f / p
f = frequency
p = number of poles.
2 poles, speed = 3600 RPM
4 poles, speed = 1800 RPM
What is negative phase current?
Negative Phase Sequence is Phenomena generally found in motors,
the formula for positive phase sequence is : Ip= Ir + a * Iy + a^2*Ib
the formula for negative phase sequence is : In= Ir + a ^2* Iy + a*Ib
As the name suggest the sequence of current or the mmf is in reverse order, a reverse order current in stator will produce a reverse order mmf, now this reverse order mmf is rotating in direction opposite to the rotor of the motor, thus the mmf cut is very high and so current induced in stator is considerably high; as for normal mmf it is in direction of rotor so mmf cut is very small thus current induced is very small.
this high current in your rotor leads to overheating of your motor and finally burning of your windings.
Comment
Negative phase sequence is not 'generally found in motors'. But one of the effects of negative phase sequence would be to cause a three-phase motor to reverse direction.
How does an earth-leakage circuit breaker or ELCB work?
An Earth Leakage Circuit Breaker - ELCB for short - was the first name given to what is now called a Ground Fault Circuit Interrupter (GFCI) .
The early, original, type of ELCB was designed only to detect a current flowing in the safety "ground" or "earth" wire.
Why was that important?
If there is no fault anywhere in a circuit supplying single-phase alternating power to a unit such as an electrical appliance, machine or other equipment, the current flowing to the unit at any instant in the "hot" or "live" wire should exactly match the current flowing away from the unit in the neutral wire. Similarly, there should be no current flowing in the unit's safety "ground" or "earth" wire.
It is a basic fact of electrical engineering design that all current flowing to an electrical appliance, machine or other equipment from the power generation station via its supply circuit's "hot" or "live" wire should only return to the power station via that same circuit's "neutral" wire.
So, as a result of that basic fact, if any current isflowing in the ground wire, it must be caused by a fault condition and the supply of current to the circuit needs to be stopped urgently.
Many years ago, before today's electronic RCDs or GFCIs were designed, much simpler electro-mechanical relays called Earth Leakage Circuit Breakers (ELCBs) were invented so that, if any such ground current exceeding just a few milliamps was detected, they would "trip" - meaning "operate" - to break the current supply to the circuits for which they were installed to protect.
The original type of ELCB did not check for any difference in current flowing in the live and neutral wires, which is another indication of a very serious fault condition - even if no current can be detected flowing in the ground wire - because the "missing current" may actually be flowing to ground via someone's body!
When RCDs were invented, most manufacturers of GFCIs adopted the same technology because it offers so much more protection to users than the original GFCI could ever give.
In the US and Canada such devices are still commonly known as "GFCIs" or "GFIs" even though they have the additional "residual current detector" functionality, whilst in Europe and elsewhere the more accurate name of "Residual Current Detector" or RCD has been widely adopted for general use instead of using the name of the much simpler GFCI device.
Another answer [Note: this is actually a description of a GFCI, not of an ELCB.]
An ELCB works by comparing the input current in the "hot" line feeding a load and the return current in the "neutral" line coming back from that load.
If the return current is less than the input current by a quite small amount - usually only about 30mA or less (mA = milliamps, which are thousandths of an amp) - it means there must be a leakage current.
That very small difference between the input and return currents is what the ELCB is designed to detect and cause it to trip so as to break the flow of current to the load.As the name itself indicates, an Earth Leakage Circuit Breaker device always checks for any leakage of current. The leakage may be either to the "earth" or "ground" wire or to something else such as the user of the equipment that is being protected by the ELCB device.
What will be the current flow of a 3 hp motor supplied with a 120 volt service?
1hp= 746Watts. So, now, we can take a simple power equation of
P= IV, Solve for I, I=P/V, and plug in 746 x 3 for Power, and 120V for V.
What is the difference between steam turbine and water turbine?
The difference is that geysers are way much hotter than the steam from hot springs. The geysers can give you 3rd degree burns. But so can the steam from hot springs if you're in there to long.
What is the simple device that opens and closes an electrical unit called?
A device that opens and closes a circuit is called a switch.
Where does the current flowing in the neutral wire go to?
In most power systems that I know of, the neutral bus bar is bonded to the ground bus bar in the distribution panel, so any current returning to neutral will go out to the service entrance (street power) along the ground conductor. This is the only time that current is permitted on ground, i.e. upstream of the distribution panel.
However, in a properly balanced split phase or three phase system, all of the various hot legs will balance each other out, resulting in very little actual current on neutral/ground. In this case, the ground connection is simply providing a tie point, so that hot leg voltage does not rise inappropriately high. If you were to explore, for instance, with a clamp on ammeter, you might discover that neutral current for one branch circuit is counterbalanced with neutral current for an opposite hot leg branch circuit, and that the net neutral/ground current going to the service entrance is very low. In this case, the neutral bus bar is simply a common tie point.
How do electrons work in a circuit?
1. heat. If it's hot enough, blackbody radiation (e.g. incandescent light bulb)
2. Electromagnetic radiation (radio waves, magnetic or electric coupling to adjacent conductors) if the current is changing.
Where can one find a neutral connection point?
A person can find a neutral connection point is testing the continuity of every neutral connection. This technique will enable a person to find a bad connection point.
How do you make your own transformer?
Usually the power provider will conned the wires to the transformer.
If your house if fed over head, your service will attached to an insulated attachment point on the house or service mast.
Then they will pass through the meter, and then into the main breaker in your electrical panel.
If your house is fed underground the service wire will be burred underground and enter the electrical meter from the bottom
If you can elaborate a little more I can give you a more precise answer
A closed circuit is a kind of electric circuit in which the path that the electrons follow forms a complete circuit.
What do you use to measure an electric current?
An ammeter, either shunt or inductive. A shunt is an inline resistor of a small, known resistance. Knowing the resistance and the voltage one can calculate the amperage by Ohms law, I=V/R. An inductive, or clamp on ammeter measures the magnetic field and using more complex calculations displays the current, typically on a digital display.
What measures the flowing in a circuit?
The flow in a circuit is called the electric current and it is measured by voltages. The number of volts that are present in the charge will determine the strength of the electric current.
Why field producing winding of 3 phase induction motor made stationary?
Because the motor is much simpler and easier to design when the electrical power is supplied to the stator, while the rotor is a short-circuited copper cage. It allows the motor to work with no commutator or slip rings, so induction motors are quiet and have a very long life.
What will happen if a transformer is operated without grounding the neutral?
It won't function, the circuit needs to be complete and the core is considered separate from the whole unit (electrically speaking); if you mean the 'bar' of the transformer, then it can build up a charge from action as well as vary the voltage output because of the charge.
When cells are connected in parallel then?
putting cells in series gives you a higher voltage but at the same current rating.
putting cells in parallel gives you the same voltage but at a higher current rating.
series parallel can give you both..
How is low voltage distinguished from high voltage?
To understand how voltage standards for motors are set it is important to know the basics of the power systems they operate on. In general, utilities that supply power in the USA, and most other 60 cycle countries, are required to provide power to the incoming point of a facility in multiples of 120 volts. Thus incoming equipment, such as circuit breaker panels, are rated in multiples of 120 volts. The common voltages are 120, 240, 480, and 600.
In addition, utilities are obligated by the regional governing authorities, (usually called Public Utility Commissions) to regulate the voltage within a fairly narrow range such as plus or minus 5%.
For example, in most single phase residential systems the voltage is 120/240. It is brought to the building with 3 wires, one being a neutral and the other two having voltages 120 volts different from the neutral wire. The voltage difference between the two "hot" wires is 240 volts.
In 3 phase systems the situation is a bit different. There are 3 phase, 3 wire, ungrounded systems where the voltage between the three wires is 240 volts. The big brother of that system is the ungrounded 3 phase, 3 wire 480 volt system. Ungrounded systems are usually found in older facilities.
In newer installations, the two most popular systems are called 4 wire grounded wye systems. The low voltage version is represented by a 120/208 volt system. The higher voltage version it is a 277/480 volt system. On both of these "grounded wye" systems, the low voltage portion (120 or 277 volts) is only available as single phase. The high voltage (208 or 480 volts) is available as either single phase or 3 phase. It should be noted that in the 4 wire grounded wye systems the high voltage is 1.73 times (the square root of 3) higher than the low voltage. These grounded wye systems are generally felt to be safer and more flexible than the older ungrounded systems. The flexibility comes from the ability to handle single phase lighting circuits, that operate at 120 volts or 277 volts, from the same system that feeds the 3 phase circuits for motors, equipment for heating, air conditioning, elevators, and industrial machinery.
The brightness of three bulb would be mare than one
To hold things inside of it. A trough for a farmer is for feeding animals. In engineering, they hold wires going from point to point.
What are the different phases in the mitocytosis phase?
Interphase - Cell growth + Normal cell functions (Large majority of time spent in this phase) G1 Phase - Cell growth + preparations for duplication
S Phase - DNA is duplicated
G2 Phase - Preparations for division
MITOTIC PHASES~
Prophase
Prometaphase (Sometimes included in prophase; "Late prophase"
Metaphase
Anaphase
Telophase
Cytokinesis
How do you find the current going into a resistor?
You can find the current by using an ammeter. The cheapest way (although more invasive) is to use a probe type ammeter or multimeter. To use, you need to insert the meter in the current path of the resistor (in series with the resistor). These meters are fairly cheap - as low as $8 if you shop around. If it is not feasible to break the circuit and insert the meter, and you have room around a wire going to the resistor, you could use a clamp on ammeter as well. These are typically more expensive.
If you understand resistor codes, you can also use a volt meter/multimeter to measure the voltage drop across the resistor (put the probe in parallel with the resistor). The current should be equivalent to I = V / R.
If you don't know resistor codes, do an online search to match colors with numbers. There should be three stripes. The first two are the resistance and the third is a magnitude. For example, if the first color matches the number 1, and the second matches 8, and the third matches 3, then this is a 18 x 1000 = 1.8k ohm resistor.
