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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 are the End effects in linear induction motor?
due to the finite length of primary core and windings of linear induction motor, the phenomenon so produced is called as end effect.
this can be categorized further as dynamic end effects and exit end effects.
How many amps are available in a three phase 225 amp panel?
In a three phase 225 amp panel, there would be a total of 225 amps available for each phase, making it a total of 675 amps for all three phases combined. This means that you could have up to 225 amps of current flowing through each phase simultaneously.
Make motor circuit how to calculate range of MCB?
To calculate the range of an MCB (Miniature Circuit Breaker) for a motor circuit, you need to consider the full load current of the motor in amps and select an MCB with a rating above this value to ensure it can handle the starting current and any potential overload conditions without tripping. It is recommended to select an MCB that is rated at least 1.5 times the full load current of the motor to provide a safety margin and prevent nuisance tripping.
How do you measure power factor?
Use a voltmeter and an ammeter to measure the supply voltage and load current; the product of these two readings will give you the apparent power in volt amperes. Use a wattmeter to measure the true power of the load, in watts. Divide the true power by the apparent power, and this will give you the power factor.
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Try using an osciloscope, connect the voltage to one channel and the other to the current (CAUTION: provide proper shunting) You'll see the two wave forms, the distance between them would give you the angle between the voltage phasor and the current phasor, the cosine of this angle in degrees is the power factor.
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You can calculate the power factor if you have a meter that measures voltage in volts and current in amperes and have access to a wattmeter that measures power. Power factor can then be calculated by this formula:
Pf=P/S , S=V*I where S is apparent Power.
Power Factor, simply put is the relationship between real power (Watts) and reactive power (VARS). It isn't related to efficiency, at least not in terms of the ratio of output power/energy to input power. A motor might have a power factor of 0.87 (30 degree phase angle), but an electrical efficiency either *more* than 87%, or *less* than 87%.
Since the input power to a motor should properly be measured as *real* power, the power factor is not considered in calculations. One reason is that the motor's power factor (which is most likely inductive) can readily be corrected back to unity (1.0) by either adding a parallel capacitor (as is done for the inductive ballast coils in fluorescent lights), or by installing a synchronous motor in the circuit and adjusting the amount of excitation.
Strangely enough, a synchronous motor can be made to appear either inductive (like other motors) or *capacitive* according to its excitation power. Such motors are often used for constant-service applications such as airconditioning.
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THIS DOESN'T MATTER IN HOUSEHOLD ELECTRICITY. If a factory has a Power Factor of 95 %, then it will draw 105 % of the current it would draw if it were at 100%, or a Power factor of 1 (also called unity).
The electric company charges a customer more for ineffecient systems, i.e. Power Factor lower than 1 (100 % efficient).
The "Power Factor" is the ratio of volt-amps to watts. To get volt-amps, you also multiply volts times amps. With a resistive load, such as an incandescent lamp, volts times amps equals watts. All of the power gets dissipated heating up the lamp filament to make it glow. In this case, volt-amps is equal to watts, giving a ratio of 1:1, or 100 %. With inductive loads like transformers, electric motors, fluorescent lamps, etc., there is very little resistance. Something called "reactance" limits current flow. Larger currents flow with little power being dissipated. With a power factor of 50 %, double the current would flow. For example, a 40 watt incandescent lamp draws 0.33 amps. (40 watts / 120 volts = 0.33 amps) This bulb, being a resistive load, has a power factor of 100 %. A single tube fluorescent lamp rated at 40 watts may draw double the current of the 40 watt incandescent, but still only use 40 watts of power. This fixture has a power factor of 50 %.
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Home meters
Electrical meters for homes measure only resistive (real, apparent, or actual) power. They do not measure reactive power.
In the study of alternating current, it will be observed that there are alternating waves of both voltage and current. In a circuit with purely resistance load, the waves of current and voltage are in exact phase relationship to each other. This means that when the voltage is at its peak, the current flow is at its peak as well. An inductive load (that is, a coil) causes the current wave to lag or fall behind the voltage wave, so that the peak current flow is some time after the voltage wave is at its peak level. A capacitive load (that is, a capacitor) causes the current wave to lead or advance ahead of the voltage wave, so that the peak current flow is some time in advance of the peak of the voltage wave.
The consequence of this is that the AVAILABLE REAL POWER is the relationship between the current and voltage waves.
Resistive circuits have a power factor of 1.0, or unity, because the waves are in phase.
The more out of phase the relationship between voltage and current, the less efficient the use of available power, the more "waste" energy.
The less efficient the use of energy, the larger the size of transmission and generating equipment required to provide for energy needs and the more costly the operation of utilization equipment.
Scroll down to related links and look at "What is reactive power?"
No improvement to these good answers. I would just add that single phase power will rarely veer from unity. If you are dealing with household electrical service, you are likely to be at or near unity.
"... likely to be at or near unity..."
Umm... no.
Motors use magnetic windings, and are therefore inductive. Inductive components reduce the power factor below the ideal value of 1.0. Old style fluorescent lights use ballast chokes, which are also inductive. A correction capacitor in the housing will correct the PF back to 1.0, but if the capacitor is faulty/has been removed, the fluoro will also give an inductive power factor. In fact, *most* loads, other than heating elements, are inductive.
So you start up the washing machine, dishwasher, benchtop mixer and electric drill. It is unlikely that any of these appliances is power-factor-corrected. Your PF will drop to less than 1.0. Our electricity supplier does all of their house load calculations based on a PF of 0.8.
"...waste energy..." Yes and no. The extra current does cause extra resistive loss in transformers, cables and switches, but the real problem is back at the generator, where more current must be generated than would be needed by a system with a perfect PF of 1.0.
What is the conclusion of overheat protection of induction motor?
If the overload protection is set correctly to the motors full load amperage, any overloading of the motor will trip the protection and take the motor off line. Once the reason of the overload has been established and rectified, the overload protection is reset and the motor can be brought back on line.
How is current lost in a circuit?
Current can be lost in a circuit due to resistance in the conductive materials used, such as wires or components. This resistance causes some of the energy carried by the current to be converted into heat. Additionally, poor connections or faulty components can also lead to current loss in a circuit.
What are the types of tap changing transformer?
The simplest type of tap-changing mechanism is a rotary switch which allows the distribution company to select one of several 'tapping' (connection) points on the high-voltage side of a transformer. This enables the turns-ratio of the transformer to be adjusted to slightly elevate or reduce the output voltage if required. This type of tap changer is termed an 'off-load' tap changer, because it cannot be operated when the transformer is energised because the winding is temporarily disconnected as the mechanism's contacts move from one tap to the next. Off-load tap changers are operated manually, using a handle located outside the transformer -after the transformer has been de-energised, isolated, and safety earths (ground) applied.
More complicated is the motor-driven 'on-load' tap-changing mechanism. It, too, alters the turns-ratio of a transformer, but this is done (usually) automaticallyaccording to changes in load. Unlike the 'off-load' mechanism, the high-voltage winding is never temporarily disconnected as the mechanism's contacts move from one tap to the next. This is because a pair of contacts is involved. One contact moves to the new tap position while the second remains at the first tap connection; when this has been done, the second contact follows the first onto the new tap position -so there is no break in the circuit. Additionally, there might be surge-suppressors fitted, to limit current surges during the tap-changing operation.
Tap changers are always fitted to the high-voltage windings, where the current is lower -thus enabling smaller contacts to be used.
Why can't a transformer step up the voltage in a direct current?
In order to induce a voltage into the secondary winding of a transformer, there must be a continuously-changing magnetic flux within the magnetic circuit (core) linking the secondary and primary windings. This is only possible if the primary current is also changing -hence the reason why transformers require an a.c. supply.
There is an exception to this rule -an automobile's ignition coil is a transformer, supplied from the battery -i.e. a d.c. source. But to provide a changing flux, the d.c. current in the primary winding must be continously switched on and off -in older vehicles, this was done by the contact-breaker driven by the distributor.
Compare lumen's per watt in incandescent vs LED?
To determine the answer you need to know the efficacy (luminous flux) of the LED light which may range from 30-90. You can use 60 for an average.
Multiply the watts from an incandescent bulb - what you are familiar with - say 40 watts x the LED luminous flux 60 = comparable lumens of about 2400 to see the same brightness.
Motor efficiency refers to the ratio of the mechanical power output of a motor to the electrical power input. It indicates how effectively a motor converts electrical energy into mechanical energy, with higher efficiency values indicating less energy loss during operation. Efficient motors help reduce energy consumption and operating costs.
The efficiency of a transformer is calculated by dividing the output power by the input power, then multiplying by 100 to get a percentage. In this case, the efficiency would be: (580 VA / 600 VA) * 100 = 96.67%. This means the transformer is operating at around 96.67% efficiency.
Faraday's law of electromagnetic induction states that a voltage is induced in a circuit whenever there is a changing magnetic field that links the circuit, and the magnitude of the induced voltage is proportional to the rate of change of the magnetic flux.
How many homes can 3000 megawatts power?
The number of homes that 3000 megawatts can power depends on the average electricity consumption per home. On average, a home consumes around 10,972 kilowatt-hours per year, which is approximately 1.25 kilowatts. Therefore, 3000 megawatts could power around 2.4 million homes.
What is the difference between using 100 watts for 2 hours or 50 watts for 4 hours?
Using 100 watts for 2 hours consumes a total of 200 watt-hours, while using 50 watts for 4 hours consumes the same 200 watt-hours. The difference lies in the power output over time: the 100-watt appliance will consume power more quickly compared to the 50-watt appliance, but they both consume the same total energy.
Different between locked rotor current and starting current?
Locked rotor current is the current drawn by a motor when the rotor is prevented from turning, usually occurring during a fault condition. Starting current, on the other hand, is the initial surge of current required to start the motor and overcome inertia. Locked rotor current is typically higher than starting current.
What size wire would you use for a 70KW 240 vac single phase generator?
To calculate the wire size you would have to find the amperage. I = W/E, 70000/240 = 291.67 amps. The wire size according to code has to be up sized to 125%. 291.67 x 125% = 364.6. 500MCM copper wire with an insulation factor of 75 and 90 degrees C is rated at 380 and 395 amps respectively. If parallel conductors were used the wire size for 75 degree wire would be 3/0 rated at 200 amps. Parallel conductors for 90 degree wire would be 2/0 rated at 185 amps.
How you calculate 3 phase generator required for 20 hp 3 phase motor?
22 x 277 x 3 or 1.73 x 480 x 22 or more accurately: 22 x 277.1283 x 3 = 18.29 kW or 1.7320508 x 480 x 22 = 18.29 kW ---------------------------------------------------------------------------- Theory: S = Va Ia* = |Va| | Ia| = {|Vab| / }| Ia| = S Thus, S3 = 3 S = 3 {|Vab| / }| Ia| = |Vab| | Ia| ------------------------------------------------------------------------------- S = Va Ia* = |Va| | Ia| and S3 = 3 S ; 22 x 277.1283 x 3 = 18.29 kW or |Vab| | Ia| = 1.7320508 x 480 x 22 = 18.29 kW
Motor shaft speed refers to the rotational speed of the motor's output shaft in revolutions per minute (RPM). It indicates how fast the motor is rotating and is a key parameter in determining the mechanical power output of the motor. Motor shaft speed is influenced by the frequency of the electrical power supplied to the motor and the motor's design specifications.
Power conversion formula for single phase to three phase conversion?
To convert single-phase power to three-phase power, you can use the formula: P = √3 x V x I x cos(θ), where P is the power in watts, V is the voltage, I is the current, and cos(θ) is the power factor. This formula assumes balanced loads.
Why do inductors resists a change in current?
An inductor charges and discharges. When an alternating current come up, the positive signal of the current quickly charges up the inductor. when the negative signal part of the same cycle comes up the inductor develops a potential to opposes it. this is because any charge developed opposes if there is a change or break or whatever for that matter, in supply. so, the negative signal which is basically a change in signal when approaches the inductor the charge developed across it opposes it and as the charge developed thanks to the positive part of the signal is used up to oppose the negative part of the same signal, basically the charge is zero. thus an alternating current or high frequency current for that matter, does not pass through an inductor.
CommentI think the above answer has confused inductance for capacitance! No charges are involved with inductors.
Whenever current changes in an inductive circuit, a voltage is induced into that circuit. The magnitude of the induced voltage depends on the rate of change of current. The direction of the induced voltage is such that it opposes the change in current -for example, if the current is reducing in value, then the induced voltage will try to maintain that current.
Can all circuit breakers interrupt large fault currents?
All Circuit Breakers have a current rating and a FAULT current rating. The current rating refers to the current at which the circuit breaker is designed to 'break' the circuit and this is generally shown in Amperes (A). FAULT current rating is generally alot higher rating and is therefor shown in kilo Amperes (kA). This kA rating refers to the amount of current which a circuit breaker is designed to handle under fault conditions and can still maintain operation and 'break' contact.
Most household circuit breakers are around 7.5 kA, so any fault over 7,500 Amperes could potentially damage the circuit breaker contacts to the point which it can not open the circuit. Larger fault ratings are found in larger applications such as MCC's on plants, minesites or power stations.
Can DC power interfere with the Ethernet?
In extremely high amperages it can(as it will be radiating energy), but most normal installations of DC will not affect ethernet copper cabling. AC will almost always due to its alternating states. I'm not 100% sure on this, but in my office (Telecom Provider Central Office) we run ethernet and DC copper close to each other, but with AC with put them in a different tray and run them in plastic electrical tubing to help shield.
The symbol for 'kilowatt' is 'kW', not 'Kw'.
The kilowatt is used to measure power, whereas the ampere is used to measure current. These are different quantities, so you cannot simply convert one to the other. It's a little like asking "How do you convert kilometres per hour into newtons per metre?"!
However, if you know that the power-rating of a kettle is 3 kW, and the supply voltage is 230 V, then you can find out the resulting current by dividing the power by the voltage. In this example, the current would work out at 13 A.
2 Can generation time be calculated from any phase of the growth curve?
No, generation time is usually calculated during the exponential growth phase of the growth curve, where the population is growing at a constant rate. During this phase, the time it takes for the population to double is used to determine the generation time.
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