Vector Group of Power-Transformer-Winding connection designations

                             Basic Idea of Winding

An ac voltage applied to a coil will induce a voltage in a second coil where the two are linked by a magnetic path. The phase relationship of the two voltages depends upon which ways round the coils are connected. The voltages will either be in-phase or displaced by 180 degree.
When 3 coils are used in a 3 phase transformer winding a number of options exist. The coil voltages can be in phase or displaced as above with the coils connected in star or delta and, in the case of a star winding, have the star point (neutral) brought out to an external terminal or not.

Six Ways to wire Star Winding:

Six Ways to wire Star Winding

Six Ways to wire Delta Winding:

Six Ways to wire Delta Winding

Polarity

An AC voltage applied to a coil will induce a voltage in a second coil where the two are linked by a magnetic path. The phase relationship of the two voltages depends upon which way round the coils are connected. The voltages will either be in-phase or displaced by 180 deg.
When 3 coils are used in a 3 phase transformer winding a number of options exist. The coil voltages can be in phase or displaced as above with the coils connected in star or delta and, in the case of a star winding, have the star point (neutral) brought out to an external terminal or not.

Additive and substractive polarity of transformer

When Pair of Coil of Transformer have same direction than voltage induced in both coil are in same direction from one end to other end. When two coil have opposite winding direction than Voltage induced in both coil are in opposite direction.

Winding connection designations

• First Symbol: for High Voltage: Always capital letters.
• D=Delta, S=Star, Z=Interconnected star, N=Neutral
• Second Symbol: for Low voltage: Always Small letters.
• d=Delta, s=Star, z=Interconnected star, n=Neutral.
• Third Symbol: Phase displacement expressed as the clock hour number (1,6,11)

Example – Dyn11

Transformer has a delta connected primary winding (D) a star connected secondary (y) with the star point brought out (n) and a phase shift of 30 deg leading (11).
The point of confusion is occurring in notation in a step-up transformer. As the IEC60076-1 standard has stated, the notation is HV-LV in sequence. For example, a step-up transformer with a delta-connected primary, and star-connected secondary, is not written as ‘dY11′, but ‘Yd11′. The 11 indicates the LV winding leads the HV by 30 degrees.
Transformers built to ANSI standards usually do not have the vector group shown on their nameplate and instead a vector diagram is given to show the relationship between the primary and other windings.

Vector Group of Transformer

The three phase transformer windings can be connected several ways. Based on the windings’ connection, the vector group of the transformer is determined.

The transformer vector group is indicated on the Name Plate of transformer by the manufacturer. The vector group indicates the phase difference between the primary and secondary sides, introduced due to that particular configuration of transformer windings connection.

The Determination of vector group of transformers is very important before connecting two or more transformers in parallel. If two transformers of different vector groups are connected in parallel then phase difference exist between the secondary of the transformers and large circulating current flows between the two transformers which is very detrimental.

Phase Displacement between HV and LV Windings

The vector for the high voltage winding is taken as the reference vector. Displacement of the vectors of other windings from the reference vector, with anticlockwise rotation, is represented by the use of clock hour figure.
IS: 2026 (Part 1V)-1977 gives 26 sets of connections star-star, star-delta, and star zigzag, delta-delta, delta star, delta-zigzag, zigzag star, zigzag-delta. Displacement of the low voltage winding vector varies from zero to -330° in steps of -30°, depending on the method of connections.

Hardly any power system adopts such a large variety of connections. Some of the commonly used connections with phase displacement of 0, -300, -180″ and -330° (clock-hour setting 0, 1, 6 and 11).
Symbol for the high voltage winding comes first, followed by the symbols of windings in diminishing sequence of voltage. For example a 220/66/11 kV Transformer connected star, star and delta and vectors of 66 and 11 kV windings having phase displacement of 0° and -330° with the reference (220 kV) vector will be represented As Yy0 – Yd11.
The digits (0, 1, 11 etc) relate to the phase displacement between the HV and LV windings using a clock face notation. The phasor representing the HV winding is taken as reference and set at 12 o’clock. Phase rotation is always anti-clockwise. (International adopted).
Use the hour indicator as the indicating phase displacement angle. Because there are 12 hours on a clock, and a circle consists out of 360°, each hour represents 30°.Thus 1 = 30°, 2 = 60°, 3 = 90°, 6 = 180° and 12 = 0° or 360°.
The minute hand is set on 12 o’clock and replaces the line to neutral voltage (sometimes imaginary) of the HV winding. This position is always the reference point.

Example

• Digit 0 =0° that the LV phasor is in phase with the HV phasor
  Digit 1 =30° lagging (LV lags HV with 30°) because rotation is anti-clockwise.
• Digit 11 = 330° lagging or 30° leading (LV leads HV with 30°)
• Digit 5 = 150° lagging (LV lags HV with 150°)
• Digit 6 = 180° lagging (LV lags HV with 180°)

When transformers are operated in parallel it is important that any phase shift is the same through each. Paralleling typically occurs when transformers are located at one site and connected to a common bus bar (banked) or located at different sites with the secondary terminals connected via distribution or transmission circuits consisting of cables and overhead lines.

Phase Shift (Deg)	Connection
0	Yy0	Dd0	Dz0
30 lag	Yd1	Dy1	Yz1
60 lag		Dd2	Dz2
120 lag		Dd4	Dz4
150 lag	Yd5	Dy5	Yz5
180 lag	Yy6	Dd6	Dz6
150 lead	Yd7	Dy7	Yz7
120 lead		Dd8	Dz8
60 lead		Dd10	Dz10
30 lead	Yd11	Dy11	Yz11

The phase-bushings on a three phase transformer are marked either ABC, UVW or 123 (HV-side capital, LV-side small letters). Two winding, three phase transformers can be divided into four main categories

Group	O’clock	TC
Group I	0 o’clock, 0°	delta/delta, star/star
Group II	6 o’clock, 180°	delta/delta, star/star
Group III	1 o’clock, -30°	star/delta, delta/star
Group IV	11 o’clock, +30°	star/delta, delta/star
Minus indicates LV lagging HV, plus indicates LV leading HV

Clock Notation 0 (Phase Shift 0)

Clock Notation 0 (Phase Shift 0)

Clock Notation 1 (Phase Shift -30)

Clock Notation 1 (Phase Shift -30)

Clock Notation 2 (Phase Shift -60)

Clock Notation 2 (Phase Shift -60)

Clock Notation 4 (Phase Displacement -120)

Clock Notation 4 (Phase Displacement -120)

Clock Notation 5 (Phase Displacement -150)

Clock Notation 5 (Phase Displacement -150)

Clock Notation 6 (Phase Shift +180)

Clock Notation 6 (Phase Shift +180)

Clock Notation 7 (Phase Shift +150)

Clock Notation 7 (Phase Shift +150)

Clock Notation 11 (Phase Shift +30)

Clock Notation 11 (Phase Shift +30)

Smart Grid Technology- A solution to the problems With Today's Electric Grid

                               Smart Grid Technology

What is the Smart Grid?

The Smart Grid is a network system that will allow the electric companies, electricity generators (coal plants, wind turbine plants, solar plants, etc.), businesses, houses, etc. be able to communicate back and forth in order to meet the necessary supply and demands of electricity.  This system will help avoid blackouts, reduce our carbon footprint, and save people & businesses money by being able to adjust the amount of electricity they use throughout the day.  This network is made up of hardware, software (data management and storage), and a communication system that ties it all together

                              

Smart grid technology includes sensors and specialized information communication systems to monitor, adjust, and optimize the flow of power through the electric grid. Ideally, smart grid technology helps utilities to minimize and meet peak demand for electricity. Smart grid technology, such as sensors, enables consumers to lower energy costs through demand pricing.

Smart electric grids intelligently optimize the flow of electricity and can help expand the contribution of renewable sources like wind and sunlight.

           

The following nine technologies play key roles in the expansion and development of smart grids:

#1) Batteries and other energy storage devices capture excess energy produced by wind or sunlight and retain it for later use. In addition to time-shifting energy from intermittent renewables, batteries and other storage devices help ensure that mission-critical systems continue to function even during an outage.

#2) Semiconductor switching enables remote and automated control of electrical power flow.

#3) Synchrophasors allow precise and rapid monitoring of electrical system function. This technology helps enable dynamic pricing of electricity.

#4) Smart meters sense and measure electric use by individual customers; they are a core element of AMI.

#5) Wireless and radio communications enable various parts of the grid to speak without needing wired communication transmission lines; communications are a core element of AMI.

#6) Meter data management systems include software and databases that can store and analyze electricity usage data coming in from smart meters; meter data management systems are a core element of AMI.

#7) Automated demand response (also known as automated or intelligent load shedding) tracks time-sensitive system data and automatically cuts power when necessary to stabilize the system and help prevent blackouts. Typically, automated demand response cuts power to select customers or sections of a system intentionally, to help maintain or optimize the larger system.

#8) Interoperability standards reflect efforts by industry experts to assure that all the equipment within a smart grid speaks the same language. This involves standardizing the way system data is stored and transmitted. One example of such a standard being researched is the Open Automated Demand Response Communications Specifications (OpenADR) data model, designed to communicate dynamic pricing to electricity customers.

#9) The Internet and cloud computing provide customers with online access to their smart meter readings. Web-based applications can also be used to remotely schedule and control appliance within homes or businesses linked to the smart grid.

                                    

(Source "Smart Grid Technology")

Current Problems

Problems With Today's Electric Grid

Key problems:*

• Lack of extra-high voltage transmission lines
• Inefficient grid operation features
• The grid is one large machine, which does not allow for small individual actions

In order to transport power, from wind for example, extra-high voltage lines are needed. Transmitting large amounts of power over lower voltage lines is too inefficient because of the excessive amount of power loss in the lines and potential to overload the lines. See the AC/DC section.

Procedures for grid operation need to be improved in order to handle adding other forms of energy. For example, more coordinated supervision, and better predictability of the state of the power system. Some blackouts in the past years have been linked to people not paying attention to the loads on the system as stations, sub-stations, etc. Upgrading our current grid system to the Smart Grid would help maintain the systems efficiency, understanding the issues in real time, and help to balance the supply and demand of electricity placed on the grid durring peak and off-peak times.

The grid is really one large, synchronized machine. The current grid, as discussed in the section titled The Grid, is set up in very large sections, such as the Western section that covers the whole western U.S. The section is all one system, so adding power in one part sends that power out to everything it is connected to. You cannot add more power in one spot and direct that power to one other spot; it goes everywhere. This created a problem when energy production was de-regulated; if someone bought a lot of power from a source far away, that power was put into the system and spread across everything it was connected to. The increase in "congestion" can cause the lines to heat up and be ruined, or trip breakers and cause a blackout. The same issue makes it difficult to build a large hydroelectric or wind plant and just hook it up to the grid. Transmission lines need to be built to handle the power and move it to where it will be used.

Energy efficiency – saving resources.Photovoltaic (solar cell) Systems--home made solar cell step by step

           Photovoltaic (solar cell) Systems

A continuously rising energy demand combined with increasingly limited natural resources are challenging energy suppliers, industry as well as consumers to rethink how we produce and use energy. Energy efficiency, smart energy use, and energy savings are keys to meeting this challenge in a sustainable way.

Solar cells convert sunlight directly into electricity. Solar cells are often used to power calculators and watches. They are made of semiconducting materials similar to those used in computer chips. When sunlight is absorbed by these materials, the solar energy knocks electrons loose from their atoms, allowing the electrons to flow through the material to produce electricity. This process of converting light (photons) to electricity (voltage) is called the photovoltaic (PV) effect.

Solar cells are typically combined into modules that hold about 40 cells; a number of these modules are mounted in PV arrays that can measure up to several meters on a side. These flat-plate PV arrays can be mounted at a fixed angle facing south, or they can be mounted on a tracking device that follows the sun, allowing them to capture the most sunlight over the course of a day. Several connected PV arrays can provide enough power for a household; for large electric utility or industrial applications, hundreds of arrays can be interconnected to form a single, large PV system.

home made solar cell step by step 

Materials you will need

                                                                            1

A sheet of copper flashing from the hardware store
A transparent CD case
Electric wire
Sodium bicarbonate or Table salt

An electric stove
hot glue
solder
Sheet metal shears for cutting the copper sheet

How to prepare copper                                 2

The first step is to cut a piece of the copper sheeting that is about the size of the burner on the stove. Wash your hands so they don't have any grease or oil on them. Then wash the copper sheet with soap or cleanser to get any oil or grease off of it. Use the sandpaper or wire brush to thoroughly clean the copper sheeting, so that any sulphide or other light corrosion is removed.

Next, place the cleaned and dried copper sheet on the burner and turn the burner to its highest setting.

Cooking the copper

cook the copper for at least 30 min.
As the copper gets hotter, the colors are replaced with a black coating of cupric oxide. This is not the oxide we want, but it will flake off later, showing the reds, oranges, pinks, and purples of the cuprous oxide layer underneath.
The last bits of color disappear as the burner starts to glow red.
When the burner is glowing red-hot, the sheet of copper will be coated with a black cupric oxide coat. Let it cook for a half an hour, so the black coating will be thick. This is important, since a thick coating will flake off nicely, while a thin coat will stay stuck to the copper.
After the half hour of cooking, turn off the burner. Leave the hot copper on the burner to cool slowly. If you cool it too quickly, the black oxide will stay stuck to the copper.

Prepare the cooked copper                               3

When the copper has cooled to room temperature (this takes about 20 minutes), most of the black oxide will be gone. A light scrubbing with your hands under running water will remove most of the small bits. Resist the temptation to remove all of the black spots by hard scrubbing or by flexing the soft copper. This might damage the delicate red cuprous oxide layer we need to make to solar cell work.
When you are finished cleaning the copper should be as in the photo

Assemble the cell

Cut another sheet of copper ,
Solder a wire to each copper plate
glue to insulate the soldering
glue the plate as in photo

Fill and seal the cell                                                   4 

seal the cell and fill it with a solution of baking soda (or cooking salt) and water

Test the cell

test the cell whit Sunlight
A note about power

 cell produces 58 microamps at 0.10 volts.

Don't expect to light light bulbs or charge batteries with this device. It can be used as a light detector or light meter, but it would take acres of them to power your house.