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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 a starting current in a DC motor very high?
A rotating d.c. motor generates a back-emf which opposes the supply voltage and reduces the current drawn by the motor. When the motor is stationary, it cannot generate this back emf and, so, the only opposition to current is the resistance of its windings which is relatively low. So, on startup, the current is large; as the machine starts to run, the resulting back emf, acts to reduce the current.
The relation between resistance R, Current I and voltage V is:
R= V/I
Therefore: 60 = 12 / I <=> I = 12 / 60 = 0.2 amp
How can you identify which one is step up or step down transformer?
A transformer has two windings, termed the 'primary winding' and the 'secondary winding'. The primary winding is the winding connected to the supply, while the secondary winding is connected to the load.
The secondary voltage of a 'step up' transformer is higher than the primary voltage; the secondary voltage of a 'step down' transformer is lower than the primary voltage.
The simplest way to determine whether a transformer is a step up or step down, is to measure the primary and secondary voltages. If you are simply looking at a transformer, then the transformer's insulated bushings will give you a clue -the higher voltage bushings are much bigger than the lower voltage bushings. If you have access to the inside of the transformer, then the higher voltage windings are thinner and have a greater number of turns than the lower-voltage winding.
How do you assumed power factor?
Power Factor is a maximum of one when the voltage and current in an AC waveform are in phase. Since power in watts is equal to voltage x current x power factor, you get maximum wattage with power factor = 1. This occurs with a pure resistive load. When you power an inductive load like a motor the power factor decreases and so does the delivered power. That is why motors are typically rated in VA, or volt-amperes rather than watts. So y Ou can assume power factor = 1 when you have a load measured in watts like a light bulb or space heater and perhaps in the .75 range for an inefficient motor.
What use of conservator tank in transformer?
To enable the oil in the transformer tank to expand and contract with temperature changes.
Why you use 400Hz frequency instead of 60Hz?
50 Hz has an edge over 60 Hz as it will have less skin effect and therefore line resistance will be less. Therefore, voltage drop as well as unwanted loss of energy in the line will be less. That means dip in supply voltage at user end will be less and efficiency will be more.
Answer
The difference in 'AC resistance' due to the effect of skin effect between 50/60 Hz is insignificant, just as the increase in inductive reactance, or the decrease in capacitive reactance is insignificant.
The answer to your question is that the two frequencies simply resulted from the independent development of electricity distribution networks in different parts of the world, and there is no inherent advantage of one frequency of the other.
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Transformers for 60 Hz are smaller than for 50 Hz, assuming a given power rating. That is because the iron magnetic core can be reduced in size by 20% for 60 Hz, for the same peak magnetic flux density.
How do you convert 3phase connection to 2 phase?
Any two legs of a three phase system can be classed as a single phase supply.
Alternative AnswerAs the above answer points out, connecting a load between any two line conductors of a three-phase supply will give you a single-phase load. But you must, of course, take into account the voltage rating of the load you wish to connect.
In Europe, three-phase low-voltage distribution is normally by means of a four-wire system, comprising three line conductors and a neutral conductor, operating at 400 V (line-to-line) and 230 V (line-to-neutral).
Your single-phase load's voltage rating must, of course, match either the single-phase supply's line-to-line or line-to-neutral voltages. In Europe, most single-phase loads are rated at 230 V so, for a residential three-phase, four-wire system, it is usual to obtain a single-phase supply by connecting the load between any one of the line conductors and the neutral conductor.
But, if you have a non-standard, 400-V single-phase load, then connecting that load between any two line conductors will also give you a single-phase supply.
Why watt-meter is required to measure real power delivered to a purely resistive load?
A wattmeter (not 'watt-meter') will always measure the true power of a load, regardles of whether that load is purely resistive or not. This is because a wattmeter effectively measures the in-phase component of the load current.
What are the five advantages that PLC's have over a relay logic solution?
Reduces the Hardware wiring
The System can be made compact
Contact Failure rate is very less
Speed of opeartion is very high
Easy for Trouble shooting
Reduces the Maintainance cost
Easier way of Making logics
The rms value of sinusoidal 200v peak to peak wave is?
You can work this out yourself. For a sinusoidal waveform the rms value is 0.707 times the peak value. As you quote a peak-to-peak value, this must be halved, first. Incidentally, the symbol for volt is 'V', not 'v'.
What is Fla on motor nameplate?
FLA: Full Load Ampere.
Its the current drawn by the motor when the motor is running at full load
FLA = kW / (1.732*V*pf*efficiency*100)
What are the four major load control functions found on a load lift?
Many lifts have the same functions. Thus, the four major load control functions found on a load lift are lift, lower, forward, and backward. Joystick Control Functions. 3-4. Joystick Control Functions (Button Pushed). 3-5. Service Brakes. 3-6 ... major contribution to safety if you, as the equipment users and operators: 1. ... Know that the machine can safety lift each load before attempting to lift. These are ...... Any problems discovered in the steps.
What is the relationship between total resistance and the resistance across each load?
There is no such thing as 'resistance across' a load! The correct term is 'resistance of a load'.
To answer your question, it depends on how the loads are connected. If they are connected in series, for example, the total resistance is equal to the sum of the individual resistances. If they are connected in parallel, then you must use the following equation: 1/R = 1/R1 + 1/R2 + 1/R3 + etc.
For any other connection, you will have to work it out individually.
How wattmeter is connected in circuit?
A wattmeter has two coils: a current coil and a voltage coil. The current coil is connected in series with the load, while the voltage coil is connected in parallel with the load (just in the same way an ammeter and a voltmeter are connected). The wattmeter's polarity markings must be observed while making these connections -if the wattmeter reads 'downscale' (backwards), then the connection to either one (but not both) of the coils must be reversed.
What is resin impregnation process?
In resin impregnation, any porous material is made impervious by filling its pores with the resin.
What is power factor of an R L series circuit?
Power factor in any circuit is the ratio of the load's true power to its apparent power. It's also the cosine of the phase angle. In L-R circuits, it's described as a 'lagging power factor', because the load current lags the supply voltage.
Steel is not used as an electrical conductor because, although it is a conductor, it's not a very good conductor -as is copper and aluminium, for example. A steel-wire core is used, however, to reinforce aluminium conductors on transmission tower lines
Does a toaster use a neutral phase?
There is no such thing as a 'neutral phase'. 'Live' or 'hot' conductors are called 'lines', whereas the neutralconductor is at approximately earth (ground) potential.
So, a toaster would be connected between a line and a neutral conductor.
Does the impedance of an RL series circuit varies inversely with the frequency?
The simple answer is no. The impedance of an R-Lcircuit is the vector sum of the circuit's resistance and its inductive reactance. Resistance is determined by the length, cross-sectional area, and resistivity of the conductor (although its 'a.c. resistance' is proportional to the frequency squared), whereas the inductive reactance is directly proportional to the frequency of the supply.
What is the function of spacer in electrical transformer?
Spacers insulate the transformer tank from the mechanical vibrations of core & the windings.this results in reduced noise emisions.
What is the effect of inductive load in distribution system?
Inductive load where current lags voltage to keep the power factor low thus increasing the consumption of more electrical units of supply provider. This is since an inductive load draws reactive power as well with active power. Reactive component is watt less power drawn from the source. We use only active part of the source. But pays from active+reactive parts. This low power factor also effects the other systems in the circuit virtually making the cables under sized by heating them
What will happen if field rheostat of dc shunt motor is kept at maximum position while starting?
First remember this rheostat is connected in series with the armature to increase the total resistance to limit the starting current, thus achieving max starting torque from the motor
