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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
Why is power factor is cos of angle between voltage and current?
Power factor is the ratio of true power to apparent power -if you refer to the so-called 'power triangle', these correspond to the adjacent and hypotenuse of a right-angled triangle. The cosine of the angle between them is the ratio of hypotenuse (apparent power) to adjacent (true power). As the power triangle is derived from the voltage/current phasor diagram, this is exactly the same angle as that between load current and supply voltage.
What is leakage current in transformer?
In low voltage and electronics Leakage Current is any current that flows when the ideal current
Why digital multimeter fails to read low resistance values?
They read low resistance values very well. I measured several dead shorts today accurately with a digital voltmeter.
However, when attempting to measure LARGE amount of resistance, the current generator in a standard digital voltmeter may fail to effectively penetrate the medium being measured. It is for this reason that Meggers (Mega-Ohmmeters) are used to measure high amounts of resistance. They usually employ a hand crank to develop the current needed to effectively flow through the medium being measured.
Sometimes digital voltmeters can be very inaccurate if they are measuring something that matches the impedance of the meter (loading effects of the voltmeter), but that is another story.
What is the power dissipated in the Ohm resistor?
Power dissipated is always Volts times Amps.
W= V*I
because of ohm's law, V=I*R, you can substitute either the voltage or amperage with the other value;
W= V^2/R or
W= I^2*R.
What makes the armature in the electric motor rotate?
from Faraday's law of electromagnetic induction :
when a current carrying conductor cuts the magnetic field an E.M.F (electro motive force) is produced and it sets up in such a direction so as to oppose the cause of it.
the stator winding of a motor which produces the R.M.F (rotating magnetic field) serves as the magnetic field and the armature winding is the current carrying conductor which cuts the magnetic field , thus an EMF is induced in the armature which again produces a force to oppose the emf produced in the armature winding.
What is meant by neutral grounding reactor?
Neutral-earthing reactors or Neutral grounding reactors are connected between the neutral of a power system and earth to limit the line-to-earth current to a desired value under system earth fault conditions.
What is the purpose of auto transformer?
Helps with the starting of large electric motors.
AnswerAn autotransformer is a transformer with a single winding, rather than two separate windings. It can be used as a step-up or as a step-down transformer, provided there is no requirement for electrically-isolating the secondary circuit from the primary circuit.
What are peripheral effects of power electronics equipments?
The operations of power electronic converters are mainly based on the switching of power semiconductor devices. Due to this the converters introduce voltage and current harmonics into the source as well as load. These harmonics can cause problems of distortion in the output voltage and current and also electromagnetic interference with the neighboring systems. To reduce these harmonics to an acceptable level it is necessary to introduce filters on the input and output of the converter. To evaluate the performance of the converter the quality of the waveform (voltage and current) needs to be measured using factors such as total harmonic distortion (THD), harmonic factor (HF) and input power factor (IPF). The implementation of proper control algorithm in the controller, generation of harmonics and distortion in the output waveform can be reduced. The switching of the power devices in power electronic converter can cause radio frequency interference due to electromagnetic radiation as a result gating circuits may generate erroneous control signals. This interference problem can be avoided by the use of grounded shielding.
What is the power of an electrical appliance?
It depends on the appliance. All appliances are required to have a 'nameplate' which contains information on their power and voltage ratings.
As we know that P=VI, and P is a constant value for any particular motor, so if the voltages will drop current will increase so that the product of V and I be the that particular constant value for any particular motor
What is the effective value of an AC sine wave current having a peak-to-peak value of 8 amperes?
The rms value of a sine wave current is 0.707 Imax. So the answer to your quesion is 0.707 x 4 = 2.83 A.
What are the effect of electrical cable joint?
A cable joint is the term used in the UK for what, in North America, is called a cable splice.
In the case of high- and medium-voltage underground cables, if they are done correctly, there is no adverse affect and joints should last as long as the cable itself. A great deal of care is taken replacing the insulation after jointing the conductors themselves, and to ensure that the cable remains waterproof and any armouring is replaced. HV and MV cable jointers are highly-skilled tradesmen who have completed an apprenticeship in cable jointing.
More_Information:">More Information:The connection of wires is typically called a splice (North American term). If the splice involves two different types of wire like copper and aluminum you would have to use special connectors made for this purpose and perhaps a compound made for the purpose. In the normal connection of two or more wires of the same type you need to make sure the ends of the wires are clean and that the connection is firm so as to reduce resistance at the joint. You also need to make the splice in a junction box for power wiring applications; and that bare wire isn't exposed which could cause shock or shorting situations. Underground splices pose yet another problem with moisture and varmints chewing on the splice.
What is an equipotential surface?
It's a surface over which electric charges are evenly distributed, caused by the mutual repulsion between charges of the same polarity.
What are brushes with reference to DC motors?
Bushes, with reference to DC motors is a brushed DC motor which is a motor that designed to run from a direct current (DC) power source. This type of motor is an internally committed electric motor.
Transmission power cables are designed by current carrying capacity.
The Linear Variable Differential Transformer is a type of electrical transformer used for measuring linear displacement. A counterpart to this device that is used for measuring rotary displacement is called a Rotary Variable Differential Transformer.
Why shunt resistance used in ammeter and why is it connected in parallel?
An ammeter's coil requires very little current for full-scale deflection (fsd). So, to measure a current above its fsd value, most of that current must be allowed to bypass the coil. This is achieved by placing a very low value shunt resistance in parallel with the coil ('shunt' is an archaic word for 'parallel').
What is the acceptable value of contact resistance in 415V air circuit breaker?
415v air circuit breaker acceptable value of 0.01 ohms and lessthan
Can alternating current be switched using normally open switch relays?
Yes. In fact, induction motor 'starters' work using normally-open relays, controlled by low-current control circuits -although we call these heavy-duty relays 'contactors'.
How do you reduce induced voltage in control cables?
You can reduce induced voltage in control cable by applying the following methods.
1. While laying control cable keep a minimum distance 300mm from the power cable.
2. If possible try to lay control cable on the separate cable tray.
3. Earth the Armour/ screen of the control cable on both side of the cable or at-least at one side.
Some times it is not important to reduce the the induced voltage in control cable, but it's effect on relay or contactor as the contactor or relay does not pick-down even after the removal of the control supply. In that case it is recommended to use two relay/contactor in parallel and use the contacts in series or parallel for control circuit interlocking.
