Why copper is called variable loss & core loss is constant loss?
Latest Answer: Iron loss-When an electric current flows through a copper conductor (or any conductor), some energy is converted to heat. i(square)*r...this equation is obvious that iron loss depends on flowing current. Core loss-Magnetic loss...composed of hysterisis ...
Iron loss-When an electric current flows through a copper conductor (or any conductor) some energy is converted to heat. i(square)*r...this equation is obvious that iron loss depends on flowing current.
Core loss-Magnetic loss...composed of hysterisis loss eddy current loss...
Doesnt depend on electrical component....The losses same even with or without load. hence know as constant losses.
Core loss-Magnetic loss...composed of hysterisis loss eddy current loss...
Doesnt depend on electrical component....The losses same even with or without load. hence know as constant losses.
Actually current is nothing its simply flow of charges.earthing is a wire which is common to all the points in a circuit used to complete the circuit it is compulsory .while grounding is used to pass leakage of charges to the ground it is used for safety measure but not compulsory.
Earthing is connecting the neutral point in 3 phase circuits to ground.
Grounding is connecting an electrical equipment individually to ground.
Grounding is connecting an electrical equipment individually to ground.
| Change in Frequency | ||||||||||||||||||||||||||
| Why do we maintain 50hz frequency? What happens when we change this frequency to any other value? If the question is for changing the frequency of Power supply to Induction Motors then it will lead to (1) Increased Iron losses (2) run at a differenct speed close to its new synchronous speed (120F/P) (3) lead to reduction in Torque capacity. It has been set as standard 50Hz for india and 60Hz at many other places. Either you believe this or not but FREQUENCY IS NEVER CONSTANT. It keeps on changing with load at the generation unit. As the load increases freq decreases this is only because of the change in torque angle due to change in load to fulfill the requirement of the load we provide more input and hence freq. changes normal to 50Hz. this constant frequency is useful for parallal operation of generators such as in power grids. Any change in freq. of two units will cause harmonics and heavy transients which may cause critical damage! To avoid this all the power generation units or power plants are synchronized with each other having const freq 50 Hz. if any power plant looses its synchronism it is notified immediately or it will be disconnected from every other unit!! to avoid losses! An Inductive Load say Induction Motor connected to an Alternator requires Active (KW) & Reactive Power (KVAr) both. This Motor receives Apparent Power (KVA --> KW + KVAr) from the Alternator. Active Power is what the Motor is delivering through its shaft and the reactive Power is what it is consuming internally to deliver the rated Output. So if Motor Power Factor is 0.8 then it is said that Motor is coverting 80 of its Input Apparent Power into Mechnical Output consuming remaining 20 Apparent Power internally. So the motor is demanding 20 reactive power being generated by the alternator. If the Power Factor of Motor is improved to 0.95 by means of External Capacitor then it should be understood that out of 20 of reactive Power required by the Motor 15 is supplied by external Capacitor and remaining 5 is being supplied by Alternator. so the Apparent Power Output of the Alternator reduces whereas Active Power Output remains constant as Motor KW. The alternator is always generating the real power along with the reactive power. This will never consume the reactive power. The induction generator only consume the reactive power. The output reactive power of the alternator is decided by the type of load. . . RE: Reactive Power Relation with Alternator If syn m/c is under excited that means it is not able to produce reactive power itself which is required so it will take reactive power i.e. act as induction generator. why frequency is 50 hZ Hi The frequency of the generated voltage basically depends on: 1). The speed of the Rotor (Field Winding) of the generator/alternator 2). No. of Poles of the alternator. By increasing both factors we can increase the generated frequency of the system but in increasing the frequency cost also increasees thats why both factors are limited by the other physical factors and cost. As explained: 1). The speed of the Rotor is limited by the capacity of the 'Prime Mover' which is revolving it and by the strength of the material by which Rotor is made of (otherwise it may bent at high speeds) 2). The no. of Poles are limited by the growing size of the machine. But simulteneously we can't take very low frequency also as the AC has quite large advantages over DC system. So The conclusion is that the frequency band of Around 50-60 Hz is an optimized value of the frequency in both respects i.e. Cost of generation and advantage of frequency. EDDY CURRENT LOSSES As frequency increases eddy current and hysteriss losses increasesand hence power loss also increases. Alternator Why alternator is operated at lagging power factor? How alternator responses with changing the load? Since the Synchronous generator having the property of supplying the reactive power along with the real power this can be operated in lagging power factor only. Suppose if it want to work with leading power factor means it should absorbed reactive power supplied by the capacitive load. The induction generator only having the property of observing the reactive power for its excitation purpose. If the load of the generator changes suddenly means from that instant itself the generator will take care of that load. But to balance the power the generator speed either increase or decrease. This reduction in speed will affect the frequency. What is the diffrence between Altrnator & Generator? Outline its working principal. 1.Alternators are used in automobiles to charge the battery and to power all the car's electric systems when its engine is running. Alternators have the great advantage over direct-current generators of not using a commutator which makes them simpler lighter and more rugged than a DC generator. The stronger construction of alternators allows them to turn at higher speed allowing an automotive alternator to turn at twice engine speed improving output when the engine is idling. The availability of low-cost solid-state diodes from about 1960 allowed auto manufacturers to substitute alternators for DC generators. Automotive alternators use a set of rectifiers (diode bridge) to convert AC to DC. To provide direct current with low ripple automotive alternators have a three-phase winding. 2.Alternator puts out voltage when it needed. But generator puts out voltage all the time. 3.Alternator produces Alternating Current.But Generator produces Direct Current. 4.Alternator consist no commutator and due to absense of commutator it's simpler than generator. 5.Alternator construction is more stronger than dc generator. 6.Alternator use only those energy which is needed.So it save energy.Where Generator use all those energy which is supplied.There is no save of energy.So using alternator is more profitable than generator in the purposes. Transformer Sound Why do you get a typical sound when the transformer is put into operation? Transformer noise is caused by the phenomenon magnetostriction. When a piece of any magnetic sheet is placed in the magnetic field it gets magnetised and elongate. But when the magnetic field is removed it is again comes to its original shape and because of this elongating and again coming back to shape produces noise which in known as transformer noise this phenomenon occurs in the core of a transformer which produces noise. If we are connecting a 50 hz transformer to a 60 hz transformer then there hystersis and eddy current both losses increases considerably (for detail check effect of frequency on transformer losses). Explain why the secondary terminal of current transformer should not be lift open circuited. Normally in a potential transformer the primary current depends on the secondary side load. But in current transformer the primary current does not depends on the secondary side load of current transformer. That will purely depends on the line where it is connected in series. So to equalise the primary MMF and secondary MMF of the current transformer there should be a load in the secondary of current transformer. Suppose in the case of no load condition there will be a heavy repeated accumulation of MMF will be restrained in the current transformer core. This will provide a heavy shock if anybody touches the secondary of current transformer. If the secondary of CT is left opened there wont be any current flow in secondary thus increasing iron loss (eddy hysteresis). This results in wastage of power in form of heat in th core. It also leads to saturation of the core. Why there is 220v in 1-phase but 440v in 3-phase? The Phase voltage of an generator is 220 - 230 V but the Phase to phase voltage (Line Voltage) will be 400 V. Voltage of R - Phase-230 Y - Phase-230 B - Phase-230 but RY-400V BY-400V RB-400V Because Line Voltage will be Root3 Times of the phase voltage In case off 3 phase Equipments we will take only line voltage for operating mode. But in single phase will take only Phase voltage Lightening is an an electricity charge that happens when two different charges clash in the clouds. This contains no current because it discharges to the nearest low resistance objects. Sub-Station Label Why the Substaions are labled as 11KV/33KV or 66/11KV etc instead of label with the POWER TRANSFORMERS Rating (In MVA/KVA)? All electrical equipments operated depend on voltage. In substations we can get same ratio transformers with various power ratings. Ex: 400/200KV with 800MVA 315 MVA Power ratings are depend on load. If we have small rating TR we connect less load High rating means we can connect high load So the substations are labeled like 132/11kV like that. | Power factor is the ratio of Active ppwer to apparent power in sysytem,It is an index to see how much of the energy is actually being utilized to do useful work | We know power factor(ie.Current lags or leads behind voltage by some angle and cos of that angle is power factor)...If the power factor drops below 1 the current consumed increases with the decrease in power factor...(for instance load with pf 0.2 consumes more current than that with 1)...This lagging or leading of current is mainly due to the storage of charges by the capacitors and inductors.... | Power factor is useful because they are helpful in analysying the percentage of useful power of all the power supplied... | Power factor also gives the idea about the active power and recative power. If power factor is high its active power is higher in comparision with reactive power also if power factor is higher then the corresponding current rating will be lower so for same rating of machine we need lower current rating coil. |
