ONGC- An Overview
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Transcript of ONGC- An Overview
A Presentation on Summer Training in ONGC Mehsana Asset
-Ashish Patwal
B.Tech (EEE)
7th sem
ONGC- An Overview
ONGC (Oil and Natural Gas Corporation Limited) is India's leading oil & gas exploration company.Set up in 1955 by government of India to develop the oil & natural gas resources in the various regions of the country.India's highest profit making corporate 77 percent in India's crude oil production and 81 percent in India's natural gas production.
Topics
Three Phase Induction MotorThree Phase AC GeneratorAuto Transformer StarterGenerator StarterWelding Machine
Three Phase Induction Motor
Types- Squirrel Cage Induction Motors Slip Ring or Wound Rotor Induction
Motors95% Induction motors are of squirrel
cage type
Stator ConstructionBasic Layout is made up of number of stampings,
which are slotted to receive the windings.
three phase windings are placed on the slots of laminated core & these windings are electrically spaced 120 degrees apart.
windings either star or delta depending upon requirement
Insulations between the windings are generally varnish or oxide coated.
Rotor Constructionconsists of a cylindrical laminated core with
parallel slots for carrying rotor conductors,
which are thick, heavy bars of copper or aluminium or its alloys
end rings which are welded or electrically braced or bolted, also they are permanently short-circuited, hence it is not possible to add any ext. resistance in series
rotor conducting bars are usually not parallel to the shaft, but are purposely given slight skew
Double Squirrel Cage Rotorstarting torque was very poor because of
permanently shorted rotor conductors.
That’s why, two independent cages on the same rotor are employed
outer cage consists of bars of high resistance metal with low reactance to resistance ratio for maximum torque at starting
inner cage has low-resistance copper bars low resistance but high reactance to resistance ratio for normal running of motor
Separated Rotor of an Induction Motor
Cleaned stator slots of an Induction Motor
Stator winding Connections (Start to Start, End to End)
Roller Bearings
Ball Bearings
Establishing Rotor inside a Newly Wound Stator
Motor Testing Panel and Standby Induction motors
A1
RY BBYBY RR
C2B2
A2C1B1
R Y B
Single phase Start-to-Start, End-to-End Connection
Three phase Start-to-Start, End-to-End Connection
Three Phase AC GeneratorBasic Components of an AC generator are:
– Field– Armature– Prime Mover– Rotor– Stator– Slip Rings
Operation of AC Generator A simple AC generator consists of:
– (a) a strong magnetic field,– (b) conductors that rotate through that magnetic
field, and– (c) a means by which a continuous connection is
provided to the conductors as they are rotating
Losses in AC GeneratorHysteresis losses Rotational or mechanical losses
Efficiency
AC Generator Nameplate Ratings:
Types of AC GeneratorStationary field, Rotating armature Rotating field, Stationary armature
Stationary Armature 3-Φ AC Generator
Connections of AC Generator
Delta-Connected Generator
Star-Connected Generator
Skewed Rotor (Armature) of AC Generator
AC Generator (440 V) Unit (DC supply to stator is provided by a full wave rectifier energized by output of armature itself)
Slip Ring arrangement for an AC Generator
AC Generator (440 V) Unit (Irrespective of the previous generator, DC is supplied to the stator by an additional unit of rotor (shown in next slide) employed on the main shaft)
Additional Unit employed on main shaft to supply DC to the stator as shown in previous slide
Winding machine (used for fabrication of winding of heavy induction motors and AC generators)
Auto Transformer Starter
Although its an older method of starting motors, it is still widely used due to its simplicity & it is
economical
Offering max. starting acceleration & torque by overcoming 2 major limitations of on-line starters- high starting current & high starting torque
Classification is based on position where they are mounted under operation as shown below– Side/Wall Mounting Type– Floor Mounting Type
Due to the turn ratio advantages, primary line current is less than secondary motor current. A 3-coil auto transformer is connected in a wye configuration & connected to motor in such a way
as to supply reduced volt. to motor when the line volt. is applied to the Auto transformer. Several sets of taps are usually available to the user to provide different values of reduced volt.
Floor mounting type Auto Transformer from Workshop
Generator Starter
Working Operation-As DC is supplied across the given terminals in starter, the solenoid charges &
moves against the spring arrangement which pulls out the rotor of the DC starter motor. As soon as the drive gear engages the ring gear on the flywheel, the high starting torque provided by the DC series motor starts the diesel engine.
The series motor provides high starting torque and is able to move very large shaft loads when it is first energized.
Circuit diagram of series motor
Relationship between series motor speed and the armature current
Back EMF- When the armature begins to rotate, it will produce a voltage that is of opposite polarity to that of the power supply. This voltage is called back voltage, (electromotive force), or counter EMF
Welding Circuit
Basically it converts the typical high voltage - low current electricity into high current – low voltage
electricity.
Their designs are often bulky because they operate at the utility mains frequency of 50 or 60 Hz
Operation-electric arc welding utilizes electric energy to initiate and sustain an arc which is the source of intense heat sufficient to melt the materials to be joined and help them fuse together.
Thank you for Listening