 # Electrical Engineering

## Electrical engineering is a field of engineering that deals with the study and application of electricity, electronics and electromagnetism.

###### 45,163 Questions
Electronics Engineering
Electrical Engineering

# Why in short circuit test iron loss is very less?

actually it is operated at (10-15)% of the rated voltage and as you know n case of low voltage low magnetic flux is produced and then there will be low magnetic field density(B). and we know hysteresis and eddy current losses depend on (B).as in case of :

hysteresis depends on B^1.2 and

eddy current depends on B^2

So if B is low then both losses(collectively called constant losses) will be very very low.

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# Which leg is 208 on 3 phase power?

On three phase 208 volts one leg does not have the potential of 208 volts. It takes two legs to provide the 208 volts. The potential is across AB, BC and CA. Voltage to the grounded neutral A-N, B-N and C-N will produce a potential of 120 volts. In a wye configured secondary three phase four wire you have the potential of 120/208 volts.

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Electrical Engineering
Electronics Engineering

# Is there any application of Lenz law in DC motor?

yes lenz law states that every current opposes the reason which cause the generation of that current . it is very useful for considering back emf in dc motor.

The lenz law also help us to determine the supply voltage of DC motor.

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Measuring Tools

# What instrument measures electrical current?

The instrument used to measure electrical current is called an ammeter, which is actually a shortened form of 'amp meter'. The current is measured in amperes. In scientific labs, a much more sensitive instrument called a galvanometer is used to measure very small currents.

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Circuits

# What is Ohm's law?

Ohm's Law states: "The current flowing through a conductor is directly proportional to the applied voltage, provided the temperature of the conductor remains constant."

It specifically refers to conductors and not resistors. And it takes into consideration the need to maintain a given temperature as the voltage and current vary. At the time, Georg Ohm already knew that allowing the temperature to vary would break the constant ratio.

Keep in mind that this was a historic new understanding that he had discovered was applicable to various conductors (metals).

Ohm's Law is by no means a universal law, and very few materials or electrical components actually 'obey' Ohm's Law. Those that do (some metals) are termed 'linear' or 'ohmic'; those that don't (most) are termed 'non-linear' or 'non-ohmic'.

Simply put, if the graph of voltage against current, plotted for variations in voltage, is a straight line, then Ohm's Law applies; if the graph is not a straight line, then Ohm's Law does not apply. And very few materials/devices produce a straight line graph. Based on this, you could say that 'Ohm's Law' is not a 'law' at all, but simply describes the behaviour of a limited range of materials.

So Ohm's Law doesn't apply to heated metals such as tungsten filaments, or to circuit components, such as diodes and to practically all other electronic devices.

The basic unit of electrical resistance was given the name 'The Ohm' in honor of Georg Ohm. The symbol for the unit is Î©, pronounced Omega. The ratio of a given voltage to resulting current will always tell us what the resistance happens to be for that particular instance. This is because the ratio of voltage to current is, by definition, resistance - however, this has nothing whatsoever to do with Ohm's Law, but is simply a definition of resistance!

E = I R

Voltage = Current times Resistance

As the alternate answers below clearly indicate, there is a widespread misunderstanding regarding Ohm's Law. Answer Resistance defines the relationships between (E) electromotive force in Volts and (I) current in Amperes. One ohm is defined as the resistance value through which one volt will maintain a current of one ampere. In other words, an ohm is a volt per ampere.

(I) Current is what flows on a wire or conductor like water flowing down a river. Current flows between points of different voltage. Current is measured in (A) Amperes, abbreviated: amps.

(E) Voltage is the difference in electrical potential between two points in a circuit. It's the push or pressure behind current flow through a circuit, and is measured in Volts.

(R) Resistance determines how much current will flow through a component. Resistors are used to control voltage and current levels. A very high resistance allows a small amount of current to flow. A very low resistance allows a large amount of current to flow. Resistance is measured in Ohms.

Answer The statement taught in electrical training is "Current is directly proportional to the applied EMF and inversely proportional to the resistance of the circuit".

Ohm's law: When there is a potential (Voltage-V) different between two ends of a conductor a follow of charges will be created (The current-I) through this conductor which is directly proportional to the voltage difference and inversely proportional to the resistance of the conductor (Resistance-R ).

I Î± Vdifference

I Î± 1/R

I=Vdifference/R : Current increases with increase of voltage, but decreases with the increase of the resistance

Answer Ohms Law states that the amount of current that passes through an object is directly proportional to the potential voltage across that object, and inversely proportional to the resistance, or electrical impedance, of that object. In other words: * as voltage goes up, the current goes up by the same proportional amount * as the impedance goes up, the current is reduced by the same proportional amount. Ohms Law can be stated mathematically as:

I = E/R Where: I is the current, E is the voltage, R is the resistance

As you can see from the above formula, if the voltage were to double, then so would the current. If the resistance were to triple, then the current would be one-third of its former value. You can use Ohms Law to calculate any value if you know the other two. These are expressed mathematically as: V = I x R (to calculate Voltage) R = V / I (to calculate Resistance) In the above calculations, V is measured in 'volts', I is measured in 'amperes' (or amps), and R is measured in Ohms.

Ohm's Law states Voltage = Current x Resistance. Except in unusual circumstances the resistance "R" is a constant. When you increase voltage, current increases.

-----------------------------------------------------------------------------------------------

Ohm's Law states that 'the current flowing through a conductor at constant temperature is directly proportional to the potential difference across that conductor'.

Ohm's Law is by no means a universal law, and onlyapplies to those conductors or devices where the ratio of voltage to current is constant over a wide range of potential differences. These materials are termed 'ohmic' or 'linear', whereas those materials and devices that do not obey Ohm's Law (and there are a great many!) are termed 'non-ohmic' or 'non-linear'. Examples of non-ohmic materials and devices include tungsten (lamp filaments), diodes, electrolytes, etc.

The ratio of voltage to current is termed resistance (R = E/I), and is derived from the definition of the ohm, and not (as many people think) from Ohm's Law. This equation can be applied to both ohmic and non-ohmic materials and devices, so applies whether or not Ohm's Law is followed.

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Electronics Engineering
Electrical Engineering

# What is dynamic resistance of diode?

The Current-Voltage relationship of a diode is not constant (not a straight line) and hence the resistance cannot be measured. Due to this non-linear nature of the the curve, there exists a unique value of resistance at every point of the curve which is called dynamic resistance (not static of constant resistance).

The dynamic resistance equals the change in voltage divided by the change in current, when the voltage is changed by a small amount. In other words it is the slope of the graph of voltage against current. The dynamic resistance is different at different current values.

About 30 years ago, and I do not remeber the brand or maker, there was a digital multimeter that DID measure dynamic resistance in diodes. It was a God Send for testing diodes in circuit. Diodes only conduct in one direction, so the device would show an open in one direction and a resistance under 1000 ohms on the other or a short (0 ohms).

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# 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)

<<>>

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.

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# Why hissing noise occur in transformer?

A: Hissing is because is overheating before it destroy itself. But other noises are caused by loose lamination of the core.

B: Hissing noise is produced due to this reason but here is another important point is about frequency (e.g for 50 Hz) the core lamination face attractive and repulsive forces fifty times in one

cycle because frequency is 50 Hz.

The original answer is unnecessarily melodramatic. Transformers are fitted with protective devices that will disconnect the transformer long before a rise in temperature will cause it to 'destroy itself'!

'Hissing', as opposed to 'humming', is usually caused by the ionisation of air in the immediate vicinity of the transformer's high-voltage bushings (hollow insulators). This also manifests itself, after dark, as a blue-coloured luminous discharge.

'Humming', on the other hand, is due to something called 'magnetostriction', a distortion to the core laminations -exactly as described in the original answer, except that the attractive/repulsive forces are twice that of the supply frequency (i.e. 100 times, in the case of 50 Hz), together with harmonics based on that frequency.

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# Clearance between phase to earth?

366

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# How many windings does a single-phase transformer have?

Generally a single-phase transformer will have twowindings. One of the Low voltage side and one on the high voltage side. North-American distribution transformers will have three: one high-voltage winding, and two low-voltage windings connected in series.

However...

...a single-phase transformer can also have several primary and several secondary windings. The primary windings can be connected in series or in parallel with each other, as can the secondary windings. For example, taking the primary winding as an example, it could consist of two 120-V rated windings: if connected in series, it could be supplied with 240 V without exceeding its voltage rating; if connected in parallel, it could be supplied with 120 V without exceeding its voltage rating. Multiwinding single-phase transformers allow for a variety of connections.

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# What are the types of bus bar arrangements?

There are various types of bus bar arrangements

1. single bus bar arrangement

2. double bus bar arrangement

3 Tie bus bar arrangement

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Simple Machines (engineering)

# What is a welding transformer?

A welding transformer is an electrical transformer used in welding power supply.

It pulls relatively low current drawn from the mains power (typically limited to 15 A to avoid tripping the circuit breaker) and converts it to the typical 50 A to 500 A used in arc welding and higher currents used in spot welding. The main difference between a Normal Step Down Transformer & a Welding transformer , is Not only to Step Down ( lower ) the outlet supply voltage and at the same time increase the Available Output Circuit Current, but to be also able withstand the Short Circuit Conditions on the Welding Output Side and especially for the Magnetic ( Iron Lamination Core ) Part of the Transformer. This Magnetic Path difference prevents the Supply side Electrical Circuit from Oveloading , espcially during the Striking of the Arc, when the Welding Electrode & the Welding Job touch to initiate an Arc, after which the Welding Electrode is lifted slightly by Experience, to maintain the required weld flow. A Normal Transformer of equivalent rating will not be able witstand this operation without burning out.

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# How many types of circuit breakers and their ratings in details?

There are several type of circuit breakers now a day we are using these are as follows:

1. M.C.B. (Miniature circuit Breaker)

Rating : 1, 2, 4, 6, 10, 16, 20, 25, 32, 63 Amperes

2. M.C.C.B. (Miniature current circuit Breaker)

Rating : 10, 16, 20, 25, 32, 63, 100, 200, 250, 400 Amperes.

3. A.C.B. (Air Circuit Breaker)

Rating : 400, 800, 1000, 1200, 1500, 1800, 2000 Amperes.

4. A. B. Switch (Air Breaker)

used in High tension line.

5. SF6 Breaker (Contact break in the Sf6 medium)

used in High tension line.

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The Difference Between

# What is the difference between motors and generators?

A motor converts electrical energy into mechanical energy and a generator converts mechanical energy into electrical energy.

The primary difference between a motor and a generator is that one converts electrical energy into mechanical energy (that's the motor) and the other converts mechanical energy into electrical energy (that's the generator).

In some cases of direct current (DC) machines, but not alternating current (AC) machines, there is so little difference that a single device (it might be called a motor-generator) can be used as either a motor or a generator.

A superb example of this would be the motor-generator that is used in electric vehicles: when the vehicle is accelerated, the batteries supply power to the motor-generator and it acts as a motor, driving the wheels. When the brake is applied, the motor-generator shifts function and the vehicle's inertia is used by the motor-generator to generate electricity and put some energy back into the batteries. This slows the vehicle down. The one device (the motor-generator) is being used in either capacity. The "handle" often applied to electric vehicles with this feature is dynamic braking.
They alike because they both have stators and rotors they are different in that the generator is driven by mechanical device that rotates the rotor, the rotor cuts through magnetic force fields and electricity is generated. The motor is driven by an input of electricity into the stator and the rotor is forced to turn by reaction with magnetic force fields.
Generator will provides current to load ......... but motor will drawn current............... generator is based on Flemming right hand rule but motor is based on left hand rule.

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# How much voltage in three phase wire?

There is no voltage in three phase wire. The ability of wire to carry voltage is dependant upon the insulation that surrounds the wire. The thicker the insulation the higher the voltage potential can become. Three standard insulation voltages are 300, 600 and 1000 volts.

First of all, there is no such thing as a voltage 'on' a wire. 'Voltage' is another word for 'potential difference', so a voltage can only exist between two wires. Voltages in three-phase systems are generally specified in terms of their line voltages-i.e. the voltage between any two line conductors. These depend on the electrical standards used in the country in which you live. In the UK, for example, three-phase transmission lines will have line voltages of 400 kV, 275 kV, or 132 kV, while distribution lines will have line voltages of 33 kV and 11 kV, and low-voltage distribution line voltage is 400 V.

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# How tall are power lines?

It depends on the voltage, the sag of the line, and the distance between towers. Generally there is a minimum height that the power line must be above the ground, defined by voltage level. If the geography requires there to be a great distance between structures (such as a river crossing), the towers will be made tall enough to accomodate this.

In general, the lower voltage lines may be as short as 25 feet, while taller ones can be over 200 feet.

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# What is meaning for transient in RLC series circuit?

In circuit analysis, there is steady state and transient conditions. transient conditions are how the circuit acts immediately following some action (such as turning on power, closing a switch, losing power, etc.). Steady state conditions is everything else.

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# How many ohm's is a 1M5 resistor?

The plural of 'ohm' is ohms, not ohm's.

The alpha-numeric code for identifying the resistance of a resistor is quite straightforward.

The letter is used as a multiplier. For example, k= x1000 and M = x1000 000. In other words, k represents kilo, and M represents mega.

The position of the letter represents the position of the decimal marker.

So,

• 1M5 represents 1.5 x 1000 000, or 1.5 megohms.
• 15M represents 15 x 1000 000, or 15 megohms.
• etc.

Similarly,

• 1k5 represents 1.5 x 1000, or 1.5 kilohms.
• 15k represents 15 x 1000, or 15 kilohms.
• etc.
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New Electrical Work

# How do you rewire a 110 220 volt motor from 110 to 220 with reversible rotation?

Answer for USA, Canada and countries running a 60 Hz power supply service.

If it is a 220 volt motor with split windings to run on 110 volts then there is usually a connection chart on the motor somewhere on or behind the motor wiring cover plate. There will be at least 4 lugs for running it in series for 220V or parallel for 110V and possibly a couple more terminals to reverse its direction.

Enter the model number of the motor on an Internet search engine and see if you can find a wiring diagram.

<><><>

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.
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# How do I test a capacitor when I cannot remove it out of circuit?

You cannot. It must be taken out of the circuit and then tested on its own.

That's not 100% true because, if it has wires at its ends, you can cut through one wire with an appropriate tool and then test the capacitor "out of circuit". If the capacitor is ok you can then re-join the two cut wire ends by applying a blob of solder carefully. (But, to avoid damaging the capacitor, use a suitable heat sink to shield the body of the capacitor from the heat of the soldering iron.)

With direct current a capacitor also works like a special type of resistance. Whilst being charged up, it will show low resistance. As it slowly (or quickly) charges, the resistance will grow larger and larger. Whenever I repair circuitry and I have doubts about a capacitor (in the uF area) I simply use my multimeter on its Ohms setting. If a capacitor has shorted, then the result will be 0 Ohm. If the capacitor is working, or partially working, the resistance will gradually increase until it is out of range of the multimeter.

Use an ohm-meter first to test the on-board capacitor and then use it to test a similar capacitor off-board, to see if the results sort of match up.

Most often they will not match completely as on-board you also measure the effect of all other components connected into circuit with the capacitor. It might point you in the right direction though.

On a separate thought, if you really cannot remove it, or disconnect one of its connections, then why test it at all? If it really can't be removed to replace it, then it makes no sense to test it!

A capacitor can be tested using multimeter without removing it from circuit. but in order to check it, its polarities should be noted and then keep the positive terminal of multimeter on positive of capacitor and negative terminal on negative. It is vital to note that the readings will be affected by the remainder of the circuit. To test for capacitor function in circuit demands a good understanding of the circuit operation.

Of course there are ways to test capacitors, both in circuit and out. While a truly accurate test involved taking the cap out of circuit, a basic test can certainly be done in circuit.

Out of circuit, one can either connect to a VM, or better yet, an oscilloscope, and measure the time for voltage to decay to zero across the capacitor. This time should equal the time given by the equation for the time constant, and is dependant on the values associated with that particular capacitor.

For RC circuits, this equation equals:

Ï„ = R Ã— C. It is the time required to charge the capacitor, through the resistor, to 63.2 (â‰ˆ 63) percent of full charge; or to discharge it to 36.8 (â‰ˆ 37) percent of its initial voltage. These values are derived from 1 âˆ’ e âˆ’ 1 and e âˆ’ 1 respectively.

It is important to keep in mind that one must apply a voltage across the capacitor at its rated value. Thus, if it is a 400V capacitor driving a tube amp, for instance, it must be driven at around 400V. Driving it at 12V will lead to useless results.

The only proper way to check for a capacitor value and or leakage is with a proper test bridge: set it to the capacitor's DC rating with it removed from the circuit completely. Any other way is just waste of time.

Additionally, a common in-circuit test for a electrolytic capacitor is to measure its Equivalent Series Resistance (ESR) which can be done with an ESR meter. This is a quick and easy way to locate failing electrolytic capacitors, especially in power supply circuits.

An effective method of testing any component in-circuit is with an in-circuit curve tracer. If you have an oscilloscope with X-Y input mode you can easily build one of these on your own. They do take some getting used to before you can use it effectively and are most useful for good board vs. bad boardcomparison.

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# Can you use ac ammeter to measure dc current?

It depends. If it's an inductive ammeter (the kind that clamps around a wire), it won't work at all. If it is the type of ammeter that is actually placed in the circuit, it will work but it won't be accurate.

Comment

Actually, modern 'clamp on' ammeters WILL measure d.c. currents. It uses the Hall Effect to measure the current.

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# What is the full form of AMF panel?

Auto Mains Failure

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Energy Conservation

# What is electric ghost power?

Ghost electricity, often called vampire power, phantom power, or idle current, is power wasted by devices when they're not in use or even turned on. Often, unused devices left plugged into your wall outlet contribute to higher electric bills.

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# How do you obtain phase 6 electrical craft practice questions?

A search on the Internet is probably your best bet.

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# How do you reduce 9V DC to 3V DC?

Use either DC to Dc converter or voltage regulators for the required voltages.

AnswerA common method is to use a voltage dividercircuit. This comprises a number of resistors, connected in series, across the power supply. This creates a series of voltage drops across each resistor and, by choosing resistors of appropriate value, the desired load voltage can be achieved.

For example, if three identical resistors are connected in series across 9 V, then the voltage across each resistor will be 3 V, and the load can be connected across any one of these resistors.

In practise, selecting the appropriate values of resistance is more complicated than this simple example, because (1) the resistors themselves mustn't overload the power supply, and (2) the load itself, being connected in parallel with one of the voltage divider resistors, affects the overall resistance of the voltage divider circuit and must, therefore, be taken into account when designing the circuit. This is called the 'loading effect' and, to put it simply, its effect is minimised providing the resistance of the load is VERY much larger than that of the voltage divider resistor it is connected across.

This sounds like you're trying to run a 3-volt device off a 9-volt battery. I would do it in one of three ways.

First way is if there's nothing in the circuit that needs 9 volts. Your best bet here is to replace the 9-volt battery clip with either a holder for two AAA cells or two A-76 button cells. Trying to reduce the output of a 9-volt battery to 3 volts will produce lots of heat. You'll get a fairly short battery life, too. AAA cells are about the same size as a 9-volt; button cells are way smaller. There is a 3.3-volt regulator called the 7803SR - Murata makes it - but they cost \$10 each.

Second way is if you need both 3v and 9v...in that case, I would install a pair of AAA cells alongside the 9v cell and wire the 3v supply to the circuit that needs it.

And third is if this is a flashlight. In that case it's even easier: replace the 3v bulb with a 9v bulb (yes, there are 9v flashlight bulbs) and be happy.

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