Star Delta Starter Line Diagram and Its Working Principle

Fig: Three Phase Motor connection diagram with a star-delta starter.

What is Star Delta Starter for Motor Starting?

Star-Delta starter is an electrical motor starting device, generally uses in big size motors to overcome some technical limitations. Star and Delta mean here 2 separate states of motor running, first Star connection and then Delta connection.

The starting current of any heavy electric motor can be more than 4 times the normal load current it draws when it has gained speed and has reached its normal running condition. 

To overcome this initial high current enchanting problem, such arrangement needs Star connection at starting time and if Star connection has sufficient torque to run up to 75% to %80 of full load speed, then the motor can be connected in Delta mode.

When the motor is connected to the Delta configuration the phase voltage increases by 173% and phase currents increase by the same ratio. The line current increases three times its value in star connection.

What Problem Starting Motor without Star-Delta?

We already know, if the motor starts simply when connected in Delta, the starting current would be huge just to be able to start the motor, not to running condition. To do this would require -

Sponsored:

v Large capacity circuit breakers to allow the start-up surge current to pass without immediately shutting the motor off.

v Oversized 3-phase power service cables require just for starting time, but the normal running time is not necessary.

v Large size of coils and contacts on the relays or contractors need to control the motor, but normal running time needs smaller sizes of them.

Sometimes, utility company also do not permits the big motor to start without a Star-Delta starter because of system instability due to switching transients. 

How Wiring a Star-Delta Starter for Motor?

Following the figure below, the power connection between magnetic contact for Main, Star, Delta and motor is shown in the schematic line diagram and wiring diagram for easy wiring.

Star-Delta Starter Connection with Control wiring

What is Important During Star-Delta Transition Period?

It is important that the break between the Star contractor switch OFF and the Delta contactor switch is ON because the Star contactor must be reliably quenched before the Delta contactor is activated. During the transition period of switch-over, the motor must be free running with little deceleration. It is also important that the switch over pause is not too long, it may generate a voltage of its own and this may add to or subtract from the applied line voltage.

That’s all for the Star-Delta starter for today; here in this article, we discussed only motor starting by 3 magnetic contracts Star-Delta, solid-state motor starters from different companies also are available in the market now.

Read: All Bangla News Paper

Feeder Booster for Electrical Transmission Lines and Its Functions

A feeder booster is an important piece of equipment for electrical energy transmission lines, especially for long feeders of transmission lines where the voltage dropped a the endpoint due to some technical limitations of transmission lines that are not easy to eliminate as required.

Basically, a booster is a generator whose function is to add to or inject into a circuit, a certain voltage that is sufficient to compensate for the IR drop in the feeders etc. IR drop means the voltage drop due to the resistance (R) of the transmission conductor when flowing current (I) through the conductors.

In an electrical transmission network system, it is not possible to keep the feeder length equal or uniform load distribution for all; in that caseload and voltage becomes unbalanced in the system network. In a d.c. the system, it may sometimes happen that a certain feeder is much longer as compared to others and the power supplied by it is also larger. In that case, the voltage drop in this particular feeder will exceed the allowable drop of 6% from the declared voltage. This can be remedied in two ways:

1. by increasing the cross-section of the feeder conductor, so that its resistance and hence IR drop is decreased;
2. or by increasing the voltage of the station bus bars.

The difficulty for both cases is that increasing the conductor means the cost of transmission lines will increase a few times and it is not economical for the utility companies without increasing the per unit electricity cost; on the other hand the bus-bar voltage increasing is not easy technically for a certain feeder.

The second method is not practicable because it will disturb the voltage of other feeders, whereas the first method will involve a large initial investment towards the cost of increased conductor material.

To avoid all these difficulties, the usual practice is to install a booster in series with this longer feeder as shown in the Figure above. Since it is used for compensating drops in a feeder, it is known as a feeder booster. It is a (series) generator connected in series with the feeder and driven at a constant speed by a shunt-motor working from the bus bars. 

The drop in a feeder is proportional to the load current, hence the voltage injected into the feeder by the booster must also be proportional to the load current, if exact compensation is required. In other words, the booster must work on the straight or linear portion of its voltage characteristic.

Example: 

A 2-wire system has the voltage at the supply end maintained at 500. The line is 3 km long. If the full-load current is 120 A, what must be the booster voltage and output in order that the far end voltage may also be 500 V.

Take the resistance of the cable at the working temperature as 0.5 ohm/kilometre.

Solution: 

Total resistance of the line is = 0.5 × 3 = 1.5 Ω

Full-load drop in the line is = 1.5 × 120 = 180 V

Hence, the terminal potential difference of the booster is 180 V (i.e. 180/120 = 1.5 volt per ampere of line current).

Booster-output = 120 × 180/1000 = 21.6 kW

 A Feeder Booster adds voltage to the feeder and compensates for the voltage drop. Hence it increases the efficiency and reliability of the system. That is why it is one of the important devices in power systems.

Engineering: Electrical and Electronic

What Should I Know as an Electrical Engineer?

1. Electric Current and Ohm’s Law

2. DC Network Theorems 

3. Work, Power and Energy

4. Electrostatics

5. Capacitance 

6. Magnetism and Electromagnetism

7. Electromagnetic Induction

8. Magnetic Hysteresis

9. Electrochemical Power Sources 

10. Electrical Instruments and Measurements

Classification of AC Motors;

Induction Motor: General Principal;

Construction Squirrel-cage Rotor;

Phase-wound Rotor;

Production of Rotating Field;

Three-phase Supply;

Mathematical Proof;

Why does the Rotor Rotate?

Slip;

Frequency of Rotor Current;

The relation between Torque and Rotor Power Factor;

Starting Torque;

Starting Torque of a Squirrel-cage Motor;

Starting Torque of a Slip-ring Motor;

Condition for Maximum Starting Torque;

Effect of Change in Supply Voltage on Starting Torque;

Rotor E.M.F and Reactance under Running Conditions;

Torque under Running Condition;

Condition for Maximum Torque Under Running Conditions;

Rotor Torque and Breakdown Torque;

The relation between Torque and Slip;

Effect of Change in Supply Voltage on Torque

and Speed;

Effect of Change in Supply Frequency Torque

and Speed;

Full-load Torque and Maximum Torque;

Starting Torque and Maximum Torque;

Torque/Speed Curve;

The shape of the Torque/Speed Curve;

Current/Speed Curve of an Induction Motor;

Torque/Speed Characteristic Under Load;

Plugging of an Induction Motor;

Induction Motor Operating as a Generator;

Complete Torque/Speed Curve of a Three-phase Machine;

Measurement of Slip;

Power Stages in an Induction Motor;

Torque Developed by an Induction Motor;

Torque, Mechanical Power and Rotor Output;

Induction Motor Torque Equation;

Synchronous Watt;

Variation in Rotor Current;

The analogy with a Mechanical Clutch;

The analogy with a D.C. Motor;

Sector Induction Motor;

Linear Induction Motor;

Properties of a Linear Induction Motor;

Magnetic Levitation;

Induction Motor as a Generalized Transformer;

Rotor Output;

Equivalent Circuit of the Rotor;

Equivalent Circuit of an Induction Motor;

Power Balance Equation;

Maximum Power Output;

Corresponding Slip.

11. A.C. Fundamentals

Generation of Alternating Voltages and Currents;

Equations of the Alternating Voltages and Currents;

Alternate Method for the Equations of Alternating Voltages and currents;

Simple Waveforms;

Complex Waveforms;

Cycle;

Time-Period;

Frequency;

Amplitude;

Different Forms of E.M.F. Equation;

Phase;

Phase Difference;

Root Mean Square (R.M.S.) Value;

Mid-ordinate Method;

Analytical Method;

R.M.S. Value of a Complex Wave;

Average Value;

Form Factor;

Crest or Peak Factor;

R.M.S. Value of H.W. Rectified A.C.;

Average Value;

Form Factor of H.W. Rectified;

Representation of Alternating Quantities;

Vector Diagrams Using R.M.S. Values;

Vector Diagrams of Sine Waves of Same Frequency;

Addition of Two Alternating Quantities;

Addition and Subtraction of Vectors;

A.C. Through Resistance, Inductance and Capacitance;

A.C. through Pure Ohmic Resistance alone;

A.C. through Pure Inductance alone;

Complex Voltage Applied to Pure Inductance;

A.C. through Capacitance alone.

12. Complex Numbers 

Mathematical Representation of Vectors;

Symbolic Notation;

Significance of Operator j;

Conjugate Complex Numbers;

Trigonometrical Form of Vector;

Exponential Form of Vector;

Polar Form of Vector Representation;

Addition and Subtraction of Vector Quantities;

Multiplication and Division of Vector Quantities;

Power and Root of Vectors;

The 120° Operator.

13. Series A.C. Circuits

A.C. through Resistance and Inductance;

Power Factor;

Active and Reactive Components of Circuit Current-I;

Active, Reactive, and Apparent Power;

Q-factor of a Coil;

Power in an Iron-cored Chocking Coil;

A.C.Through Resistance and Capacitance;

Dielectric Loss and Power Factor of a Capacitor;

Resistance, Inductance, and Capacitance in Series;

Resonance in R-L-C Circuits;

Graphical Representation of Resonance;

Resonance Curve;

Half-power Bandwidth of a Resonant Circuit;

Bandwidth B at any Off-resonance Frequency;

Determination of Upper and Lower Half-Power Frequencies;

Values of Edge Frequencies;

Q-Factor of a Resonant Series Circuit;

Circuit Current at Frequencies Other than Resonant Frequencies;

Relation Between Resonant Power P0 and Off-resonant Power P.

14. Parallel A.C. Circuits

Solving Parallel Circuits;

Vector or Phasor Method;

Admittance Method;

Application of Admittance Method;

Complex or Phasor Algebra;

Series-Parallel Circuits;

Series Equivalent of a Parallel Circuit;

Parallel Equivalent of a Series Circuit;

Resonance in Parallel Circuits;

Graphic Representation of Parallel Resonance;

Points to Remember;

The bandwidth of a Parallel Resonant Circuit;

Q-factor of a Parallel Circuit.

15. A.C. Network Analysis 

Kirchhoff's Laws;

Mesh Analysis;

Nodal Analysis;

Superposition Theorem;

Thevenin’s Theorem;

Reciprocity Theorem;

Norton’s Theorem;

Maximum Power Transfer Theorem-Millman’s Theorem.

16. A.C. Bridges 

A.C. Bridges;

Maxwell’s Inductance Bridge;

Maxwell-Wien Bridge;

Anderson Bridge;

Hay’s Bridge;

The Owen Bridge;

Heaviside Campbell Equal Ratio Bridge;

Capacitance Bridge;

De Sauty Bridge;

Schering Bridge;

Wien Series Bridge;

Wien Parallel Bridge.

17. A.C. Filter Networks

Applications of Filter Networks;

Different Types of Filters;

Octaves and Decades of frequency;

Decibel System;

Value of 1 dB;

Low-Pass RC Filter;

Other Types of Low-Pass Filters; 

Low-Pass RL Filter;

High-Pass R C Filter;

High Pass R L Filter;

R-C Bandpass Filter;

R-C Bandstop Filter;

The-3 dB Frequencies;

Roll-off of the Response Curve;

Bandstop and Bandpass Resonant Filter Circuits;

Series-and Parallel-Resonant Bandstop Filters;

Parallel-Resonant Bandstop Filter;

Series-Resonant Bandpass Filter;

Parallel-Resonant Bandpass Filter.

18. Circle Diagrams

Circle Diagram of a Series Circuit;

Rigorous Mathematical Treatment;

Constant Resistance but Variable Reactance;

Properties of Constant Reactance But Variable Resistance Circuit;

Simple Transmission Line Circuit.

19. Polyphase Circuits

Generation of Polyphase Voltages;

Phase Sequence;

Phases Sequence At Load;

The numbering of Phases;

Interconnection of Three Phases;

Star or Wye (Y) Connection;

Values of Phase Currents;

Voltages and Currents in Y-Connection;

Delta (D) or Mesh Connection;

Balanced Y/D and D/Y Conversions;

Star and Delta Connected Lighting Loads;

Power Factor Improvement;

Power Correction Equipment;

Parallel Loads;

Power Measurement in 3-phase Circuits;

Three Wattmeter Method;

Two Wattmeter Method;

Balanced or Unbalanced load;

Two Wattmeter Method-Balanced Load;

Variations in Wattmeter Readings;

Leading Power Factor;

Power Factor-Balanced Load;

Balanced Load-LPF;

Reactive Volt amperes with One Wattmeter;

One Wattmeter Method;

Copper Required for Transmitting Power Under Fixed Conditions; Double Subscript Notation;

Unbalanced Loads;

Unbalanced D-connected Load;

Four-wire Star-connected Unbalanced Load;

Unbalanced Y-connected Load Without Neutral;

Millman’s Theorem;

Application of Kirchhoff's Laws;

Delta/Star and Star/Delta Conversions;

Unbalanced Star-connected Non-inductive Load;

Phase Sequence Indicators.

20. Harmonics

Fundamental Wave and Harmonics;

Different Complex Waveforms;

General Equation of a Complex Wave;

R.M.S. Value of a Complex Wave;

Form Factor of a Complex Wave;

Power Supplied by a Complex Wave;

Harmonics in Single-phase A.C Circuits;

Selective Resonance Due to Harmonics;

Effect of Harmonics on Measurement of Inductance and Capacitance;

Harmonics in Different Three-phase Systems;

Harmonics in Single and 3-Phase Transformer.

21. Fourier Series 

Harmonic Analysis;

Periodic Functions;

Trigonometric Fourier Series;

Alternate Forms of Trigonometric Fourier Series;

Certain Useful Integral Calculus Theorems;

Evaluation of Fourier Constants;

Different Types of Functional Symmetries;

Line or Frequency Spectrum;

Procedure for Finding the Fourier Series of a Given Function;

Wave Analyzer;

Spectrum Analyzer;

Fourier Analyzer;

Harmonic Synthesis.

22. Transients 

What is Transients;

Types of Transients;

Important Differential Equations;

Transients in R-L Circuits (D.C.); 

Short Circuit Current;

Time Constant;

Transients in R-L Circuits (A.C.);

Transients in R-C Series Circuits (D.C.);

Transients in R-C Series Circuits (A.C);

Double Energy Transients.

23. Symmetrical Components

The Positive-sequence Components;

The Negative-sequence Components;

The Zero-sequence Components;

Graphical Composition of Sequence Vectors;

Evaluation of VA1 or V1;

Evaluation of VA2 or V2;

Evaluation VA0 or V0;

Zero Sequence Components of Current and Voltage;

Unbalanced Star Load form Unbalanced Three-phase Three-Wire System; 

Unbalanced Star Load Supplied from Balanced Three-phase Three-wire System;

Measurement of Symmetrical Components of Circuits;

Measurement of Positive and Negative-sequence Voltages;

Measurement of Zero- sequence Component of Voltage.

24. Introduction to Electrical Energy Generation

Preference for Electricity;

Comparison of Sources of Power;

Sources for Generation of Electricity;

Brief Aspects of Electrical Energy Systems;

Utility and Consumers;

Why is the Three-phase A.C. system Most Popular?;

Cost of Generation;

Staggering of Loads during peak-demand Hours;

Classifications of Power Transmission;

Selecting A.C. Transmission Voltage for a Particular Case; Conventional Sources of Electrical Energy;

Steam Power Stations (Coal-fired);

Nuclear Power Stations;

Advantages of Nuclear Generation;

Disadvantages of Nuclear Generation;

Hydroelectric Generation;

Non-Conventional Energy Sources;

Photo Voltaic Cells (P.V. Cells or SOLAR Cells);

Fuel Cells;

Principle of Operation;

Chemical Process (with Acidic Electrolyte);

Schematic Diagram;

Array for Large outputs;

High Lights;

Wind Power.

MATERIALS HANDLING AND STORAGE IN A PROJECT

Materials Handling and Storage: Ensure Maintenance & Construction Project Safety Code

The material handling and storage procedure for maintenance and construction project is intended to define the requirements, storage, take care & custody, issue & receive, etc, to ensure the responsibilities and obligations to the objective of safety induction.


The general requirements of maintenance and construction projects are to store materials in a planned and organized way that does not endanger employees’ safety.

It’s must be ensured that all the stacks, rows, and piles are stabled and stacked to aided safe handling and loading. Hazardous and chemical materials must be stored and handled in accordance with the individual requirements and MSDS should be available near the hazardous materials.

Methods of materials storing in open-yard store and warehouse

Typical materials storing places are both indoor and outdoor; especial attention required for in open-yard storage is combustible materials, access way, overhead electric power lines, and fire protection facilities, etc and for indoor storage to easy access, fire prevention, and protection facilities, floor loading capacities and overhead hazards.

The optimized storing methods and types are selected depending on the material's nature, size, weight, amount of materials and the space are of the store. This article’s most important focal point is employees’ safety and productive work output. The common and effective material storing methods are as follow:

· Case Piling up;
· Ground storing or Floor Storing;
· Plate stacking;
· Cross-wise Stacking;
· Stepped Stacking;
· Pyramid Stacking;
· Offset Stacking;
· Boxed Storing;
· Pallet Storing or Skid Storing;
· Vertical Stacking;
· Hanger Storing;
· Hooked Nail Storing;
· Bag Piling.

Tips to safe materials handling and storage Sponsored:

Following points onto safe materials handling and storing procedure may effective and productive to your any project especially in construction and maintenance project, if it a practice to discuss in a group regularly just before start your works. The most common tips are as below:

All materials shall be properly stored on racks or pallets;
Gangways shall be left to allow easy access to all materials, either by personnel or mechanical lifting equipment as appropriate;
Adequate firefighting equipment must be provided; such equipment must be readily accessible and not obstructed by the materials;
Manual handling and lifting must be done correctly, using a straight back and bending the legs;
Only trained and competent operators shall use forklift trucks;
Volatile and flammable materials shall be stored in a separate secured place, well ventilated building away from the main stores;
Compressed gas cylinders shall be stored in accordance with standard safety procedures;
Mechanical lifting equipment shall be used within its rated capacity;
When opening wooden packing cases ensure that all nails are either pulled or bent over;
Always wear work gloves when handling materials.

For better practice in materials handling and storing in your maintenance and construction project to ensure safety code and conduct, as the first step keep your work and storage areas clean and orderly and in a sanitary condition then keep stairways, access ways, and exits free from scrap, supplies, materials, or equipment.