World Of Electrical

Induction Motor Interview Questions with Answers | Part-1 Induction Motor Interview Questions with Answers | Part-1 Q.1 The frame of an induction motor is made of (A) aluminium (B) silicon steel (C) closed grained cast iron (D) stainless steel (E) bronze Answer:  (C) closed grained cast iron Q.2 The stator frame is an induction motor is used to (A) hold the armature stampings in position (B) ventilate the armature (C) protect the whole machine (D) provide return path for flux Answer:  (A) hold the armature stampings in position Q.3 The stator core of a 3 phase induction motor is laminate in order to reduce the (A) eddy current loss (B) hysteresis loss (C) both hysteresis and eddy current loss (D) weight of the stator (E) windage and friction losses Answer: (A) eddy current loss Q.4 An induction motor works with (A) dc only (B) ac only (C) ac and dc both (D) none of these Answer:  (B) ac only Q.5 Which of the following statement associated with polyphase induction motor is...

Specifications Of 3 Phase Induction Motor Specifications Of 3 Phase Induction Motor Following specifications are required to start the design of 3 phase induction motor:  ✓ Rated output in H.P. or K.W. ✓ Three phases ✓ Frequency in Hz = f ✓ Voltage in volts = V ✓ Connections, star or Delta, Y or ∆ ✓ Speed in RPM = N ✓ Type Squirrel cage rotor or wound rotor ✓ Type of Duty (Continuous, intermittent etc.) ✓ Power factor ✓ Efficiency ✓ Class of Insulation ✓ Temperature rise ✓ Full load current ✓ Pull out Torque Following symbols will be used for design: Q = KVA rating of machine P = Rating of machine in kW Eph = Induced emf per phase in volts (Generally applied voltage per phase = Induced emf per phase) Iph = Current per phase in Amp Tph = Turns per phase D = Diameter of stator core in m. L = Length of stator core in m Ba = Average value of flux density over the air gap Wb/m2 ac = Ampere...

Design of Submersible Motor Design of Submersible Motor Submersible motor is used to drive the submersible pump. Submersible motor is also a squirrel cage type induction motor. Its principle and the general construction is similar to the squirrel cage type induction motor. It means there is laminated stator core and three phase winding in it and there is squirrel cage rotor. But as the whole motor is under water, special type of construction has to be employed. Mainly all the parts are made of the corrosion resistance type materials. Its diameter is less and the axial length is more. Instead of using the ordinary bearings the thrust bearings are used. There are two types of construction of the submersible motor. (1) Wet type submersible motor: This type of motor is completely filled with clean water or oil or emulsion of water and oil. (2) Dry type submersible motor: In this type of motor the stator winding is dry and...

Transformer Faults Transformer Faults There are many faults can occur in power transformer which is mentioned below: 1.Over heating of the core 2.Improper contacts on the tap changer 3.Failure of the cooling system 4.Phase to phase fault 5.Earth fault 6.Inter turn fault 7.Over load 8.Over voltage The effect of all Faults is described below: 1. Over heating of the core Transformer core gets over heated due to excessive loading, failure of the cooling system or fault in the core. e.g. shorting of lamination. Over heating of the core Due to this, the life of the insulation is reduced and so the life of transformer is reduced. 2. Improper contacts on the tap changer Arcing occurs and the insulation is damaged when the contacts of the tap changer are not proper. 3. Failure of the cooling system Cooling is affected when cooling fan stops working or there is fault in the circulating system. Due to this t...

Characteristics Of DC Shunt Motor Characteristics Of DC Shunt Motor Circuit diagram of DC Shunt Motor is shown in below image. Circuit Diagram of DC shunt motor We know that torque is directly proportional to the flux per pole and armature current. So, Ta proportional to Φ and Ish According to circuit diagram Ia = IL - Ish Ish = V / Rsh  V = Eb + Ia Ra   There are three characteristic s of DC Shunt Motor, which is mentioned below. Torque - Armature current ( T / Ia ) characteristics Speed - Armature current ( N / Ia ) characteristics  Speed - Torque ( N / T ) characteristics    1. Torque - Armature current characteristics We know that field current is remains constant because of supply voltage is constant in dc shunt motor. Here , for dc shunt motor flux is also constant because supply voltage is kept constant So,  Ta α Ia So torque is directly proportio...

There are three types of DC motor: Shunt wound Series wound Compound wound   1.  Shunt wound Motor Circuit diagram of this type of motor shown in below image. In this type of dc motor, Field winding is connected in parallel with armature. When voltage across shunt field winding is same as supply voltage, it's resistance is very high. So shunt field winding has many turns of thin wire. Here, shunt field winding is connected across the supply voltage, so Ish must be remains constant Here,  Ish = V / Rsh IL = Ia + Ish Eb = V - Ia Ra   Pi= V IL  Pm = Eb Ia    2. Series wound Motor  Circuit diagram of this type of motor shown in below image. In this type of motor field winding is connected in series with armature. When field winding is connected in series with armature winding it carries full load armature current.  It has few turns of thick wire , so it's resistance is ver...

DC motor is electrical machine which convert electrical energy into mechanical energy. Principal When current carrying conductor  placed between electric field so it experience mechanical force. The force direction is find by Fleming's left hand rule and it's magnitude is calculate by below formula. F = B I L N               where, B = flux density                          L = conductor length                          I  = current Circuit Diagram  Working When we apply supply voltage armature of dc motor start rotating in magnetic field. so armature conductor cuts the magnetic field. So, Due to principle of electromagnetic induction emf is induced in it. Induced emf direction is opposite of applied voltage, so it's called back emf. back emf value is always less than a...

There are two types of DC Generator Separately exited Self exited Separately exited DC Generator  In these types of generator, Energisation of field magnets is done by separate dc supply. Circuit Diagram Here, Ia  = IL            Eg = V +IaRa+ brush contact drop            Po = V Ia      2. Self exited DC Generator In these types of dc generator, Energisation of field magnets is done by their own field current, so I it's called self exited dc generator. There is small flux present initially due to residual magnetism. So when armature starts the rotate, it produced small emf and small amount of current, which is use for field magnets. According to field winding and armature winding connection dc generator are three types Shunt wound Series wound Compound wound      1. Shunt wound In this type of generator the field winding ...

Definition DC generator is device which converts mechanical energy to in form of electrical energy. Principal D.C. generator work on principal of electromagnetic induction. Whenever flux is cut by the conductor dynamically induced emf is produced in it. Basic component of d.c. generator are as below Conductor  Magnetic field For produce dynamically induced emf, three portions are needed Magnetic field   Conductors  Motion of conductor  Magnetic field produce magnetic flux in the machine. The dynamically induced emf produced in the conductor will cause a flow of electric current in it, if the conductor circuit is closed. Working The emf induced in the armature conductors of a DC generator is alternating in nature. It is converts AC into DC in the external load circuit by the split-rings or commutator. According to upper figure in first half rotation current flows through ABRCD. Here B1 brush is connected ...