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What are three ways you can increase the strength of an electromagnet?

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Description : What happens when you reverse the direction of the current in an electromagnet?

Answer : When  you  reverse  current  direction  in  an  electromagnet,  the magnetic  poles  will  also  change.

Description : What makes an electromagnet stronger than a solenoid?

Description : What is permanent magnet and electromagnet?

Answer : Permanent magnet: A permanent magnet is an object made from a material that is magnetized and creates its own persistent magnetic field. As the name suggests, a permanent magnet is 'permanent'. ... an electric current passes through the coil. If the current is interrupted, the magnetism is lost.

Description : State any two applications of electromagnet.

Answer : Applications of Electromagnet: Cranes, Motors, Generators, Transformers, Electromagnetic Relays, Circuit breakers, Traction, Measuring instruments, Electrical Bell etc.

Description : What is dielectric strength of an insulating material? What is its unit?

Answer : Dielectric Strength: The dielectric strength of an insulating material is the maximum voltage which the insulating medium can withstand without breakdown. Unit is volts per millimeter (V/mm), or kV/mm or kV/cm

Description : How can we increase the induced current?

Answer : Induced  current  can  be  increased by  reducing  no  of   windings  on  the  secondary  part   compared   to   primary.

Description : What will happen if you increase the current in the motor?

Answer : Increasing current means increasing frequency of the motor because current is directly proportional to rotations of the motor rotor

Description : Define : (i) Dielectric strength (ii) Breakdown voltage

Answer : (i) Dielectric strength: The voltage which a dielectric material can withstand without breaking down (without losing its dielectric property) is called its dielectric strength. It is represented by kV/mm ... or is no longer an insulator) for a specified thickness, is its breakdown voltage. 

Description : Give the relation between magnetic field strength, magnetic flux density and permeability.

Description : Define magnetic field strength and state its unit.

Answer : Magnetic field strength is the force experienced by a unit N-pole when placed at any point in a magnetic field is known as magnetic field strength or magnetizing force. Magnetising force or magnetic field ... unit of length is metre. So the unit of magnetic field strength is ampere turns per metre.

Description : What is dielectric breakdown strength?

Description : Reduction in core losses and increase in permeability are obtained with transformer employing?

Answer : Reduction in core losses and increase in permeability are obtained with transformer employing core built-up of laminations of cold rolled grain oriented steel.

Description : When a V-V three phase transformer system is converted into a Δ-Δ system, increase in capacity of the system is (A) 86.6% (B) 50% (C) 57.7% (D) 73.2%

Answer : When a V-V three phase transformer system is converted into a Δ-Δ system, increase in capacity of the system is 73.2%

Description : Define Dielectric Strength for transformer oil. State its value for new transformer oil.

Description : A magnetic circuit has effective iron length of 100 cm and it is wound with 800 turns of wire carries 1 A. Find the magnetic field strength.

Answer : magnetic field strength

Description : The electric breakdown strength of insulating materials depends on  (A) Nature of applied voltage (B) lmperfection of dielectric material (C) Pressure, temperature and humidity (D) All or these

Answer : The electric breakdown strength of insulating materials depends on  (A) Nature of applied voltage (B) lmperfection of dielectric material (C) Pressure, temperature and humidity (D) All or these

Description : The dielectric strength of transformer oil is expected to be?

Answer : The dielectric strength of transformer oil is expected to be 33 kV.

Answer :  The size of a synchronous motor decreases with the increase in flux density.

Description : For given applied voltage, with the increase in frequency of the applied voltage?

Answer : For given applied voltage, with the increase in frequency of the applied voltage eddy current loss will remain unchanged.

Description : Why does increase in current mean a decrease in voltage?

Answer : This is because current flows from high potential to low potential to bring the two diffrent potential to unity , thus  a reduced potential (voltage)

Description : how can we reverse the direction of rotation of three phase induction motor ?

Answer : The direction of rotation of three phase induction motor can be reversed by plugging i.e by changing any two out of three phases of the supply to the stator of the Induction motor terminal.

Description : List three important characteristics of an electric circuit.

Description : When three resistors with unequal values are connected in parallel, _______ A) The current across the resistors is the same  B) The voltage drop across the resistors is the same C) The voltage drops across the resistors is proportional to the resistance of each resistor D) None of these

Answer : When three resistors with unequal values are connected in parallel, The voltage drop across the resistors is the same

Answer : Three point starter can be used for both shunt and compound motor.

Description : Consider a circuit with three parallel branches connected across a DC supply. What is the ratio of the branch currents I1 : I2 : I3 if the branch resistances are in the ratio of 2 : 3 : 4 respectively? A) 2 : 3 : 4 B) 6 : 4 : 3 C) 4 : 3 : 2 D) None of these

Answer : Consider a circuit with three parallel branches connected across a DC supply. What is the ratio of the branch currents I1 : I2 : I3 if the branch resistances are in the ratio of 2 : 3 : 4 respectively? A) 2 : 3 : 4 B) 6 : 4 : 3 C) 4 : 3 : 2 D) None of these

Description : what is the difference between four point starter and three point starter?

Answer : The only difference is in the NO VOLT COIL connection in the starter, in three point starter NVC is connected to the field whereas in four point starter it is connected separately. The advantage of using ... (for above rated speed) and lead to DEENERGISE the NVC leading to turning off of the motor.

Description : Why is a capacitor used in a single phase motor and not in three phase motor ?

Answer : In 1-phase induction motor capacitor work is generate the auxiliary winding current than excite the main winding to rotor starts rotate. After rotor start rotating about 75% of their speed than auxiliary ... emf to start the motor.so,in 3-phase induction motor is self start induction motor.

Description : Why is a three phase denoted by R, Y, B ?

Answer : phase 1 ,R =Red colour cable terminal, phase 2 Y=Yellow colour terminal cable,Phase 3 B=Blue colour cable terminal, N =Neutral. For identification.

Description : State any four advantages of three phase induction motor. 

Answer : Advantages of three phase induction motor https://youtu.be/27OIOCKN05U

Description : Define balanced and unbalanced load in three phase circuit.

Answer : Balanced Load: When all the imedances of 3 phases are equal in magnitude and of same nature then load is said to be balanced.  Unbalanced Load: When all the imedances of 3 phases are not equal in magnitude and of different nature then load is said to be unbalanced.

Description : In a three-phase supply floating neutral is undesirable because it way give rise to?

Answer : In a three-phase supply floating neutral is undesirable because it way give rise to unequal line voltages across the load.

Description : What is mean by plugging in three phase induction motor?

Answer : Plugging in three-phase induction motor means interchanging of any two phases of a stator for quick stopping.

Description : What is a three phase connection?

Answer : RYB, 440 volt/phase

Description : List different starting methods of three phase synchronous motor. Explain any one of them.

Answer : Different Starting Methods of Three Phase Synchronous Motor: As synchronous motor is not self starting, different methods of starting are as follows: 1) By using an Induction (Pony) motor 2) ... . The rotor gets pulled into synchronism and starts running at constant speed as a synchronous motor. 

Description : Explain with neat circuit diagrams the procedures to perform no load and blocked rotor tests on three phase induction motor.

Description : Explain the need and steps to conduct the reduced voltage running up test on the three phase induction motor.

Description : State any four applications of three phase circuits.

Answer : The application of three phase circuits are 1. Three phase circuit is used for power transmission over long distances. 2. Three phase circuit can produce rotating magnetic field 3. Three phase ... three phase Motors and Transformers. 4. Three phase circuit is used for power converters circuits.

Description : Draw the waveform of three phase AC supply voltage.

Description : State advantages of three phase over single phase.

Answer : Advantages of 3-phase system over 1-phase system: -  1. More output: For the same size, output of poly-phase machines is always higher than single phase machines.  2. Smaller size: For ... are self- starting: The three phase ac motors are self starting, while single phase induction motor are not.

Description : The slip of 400 V, three phase, 4 -pole induction motor when rotating at 1440 rpm is 

Answer : The slip of 400 V, three phase, 4 -pole induction motor when rotating at 1440 rpm is 4 percent

Answer : A three point starter is considered suitable for shunt as well as compound motors.

Description : Three phase synchronous motor will have how many sliprings?

Answer : Three phase synchronous motor will have two sliprings.

Description : How is a three phase cage induction motor self starting?

Answer : Any type of induction motor is self starting. Because the reason for torqe production require two flux displaced by some angle theta.If theta is constant with time then torqe will be constant;if ... torqe also pulsating. In induction motor this angle theta is not pulsating.so it is self starting 

Description : Explain power relations in three phase circuit.

Description : Explain three phase half wave controller or three phase unidirectional controller.

Answer : Three phase half wave controller or unidirectional controller:

Description : Explain Three Phase Bidirectional Delta Connected Controller.

Answer : Three Phase Bidirectional Delta Connected Controller:

Description : Explain three phase bridge inverter.

Answer : Three phase bridge inverter: Three phase bridge inverter converts DC voltage input to three-phase variable frequency variable voltage output. DC voltage source can be a DC source or output of the rectifier. ... in proper sequence. The switch may be thyristor or IGBT etc.

Description : Explain three phase full wave controller.

Answer : Three phase full wave controller: Three phase full wave controller is also called as the three-phase bidirectional controller. Let the load is star connected so at each phase there are antiparallel connected SCRs. ... conduct at the same time and the third phase will be open.

Description : three phase to single phase cycloconverter

Answer : three phase to single phase cycloconverter

Description : Write short notes on 3 phase AC system.

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