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