Prática de Shadowing: 17E058 - Back to Back Stations - Aprenda a falar inglês com vídeo

Hello everyone, I am Monika.

I am here to present back -to -back stations.

Let's see.

What is back -to -back?

Generally, in electronics and power electronics, if two bipolar components are connected in series with opposite polarity, then this pair is known as back -to -back system.

As same as in electrical, rectifiers and inverters are identical

and connected in series is known as back -to -back system from this diagram here rectifier

and the inverter are connected in series via a hvdc link

and it is also a hvdc back -to -back link a back -to -back hvdc link the hvdc system

which transfers energy between two ac buses at the same location is called as back -to -back system

or an hvdc coupling system in other words the converters

and rectifiers are installed and operates on high voltage DC in the same stations.

Hence there is no DC transmission line.

So it reduces the overall conversion cost and improve the reliability of the DC system.

Such type of system is designed for bipolar operation.

This picture shows the bipolar link of a back -to -back link.

A bipolar link has two conductors.

One is positive and the other one is negative.

This link has two converter stations at each end.

The midpoint of the converter station is connected to the air through the electrodes.

Next, we are going to see about the construction of back -to -back HPDC link.

The main components are converter station, converter unit, converter vaults, converter transformer,

filters, high frequency filter, reactive power source, smoothening reactors and then system port.

What do you mean by converter walls?

There are two types of converter walls.

One is the sending end converter and then receiving end converter.

The sending end converter act as a rectifier which converts AC into DC.

The receiving end converter act as a inverter which converts DC into AC.

What are converter transformers?

These are transformers

which are used before the rectification of ac in the hvdc system filters filters may be ac

or dc what is the use of high frequency filters these

are provided to suppress the high frequency currents what do you mean by smoothening reactors smoothening reactors are those

which is used on the dc side to smoothen the dc current as well as the production purposes

This shows the simple block diagram of back -to -back HPDC link.

From the system 1, AC current is converted into DC by means of rectifier

and current DC is supplied via DC link

and it is converted back again to AC by means of inverter and then distributed to the different grids.

It shows the simple block diagram.

Working principle of back -to -back link.

Two independent neighboring transmission systems with incompatible electrical parameters such as frequency

or voltage level or short -circuit power level are connected via a DC link.

The basic principle operation of HPDC linking system is based on the conversion of AC to DC

and vice versa by means of converter volts power from two

or more system is first converted into dc by means of power rectifier system

and then summed up after summing of the resultant power is

again converted into ac with the help of power inverter

and then supplied to different grids the process involved in here is simple only by theoretical

but in practical it is very much complex as it involves high voltages

and power semiconductor devices what are the needs for back -to -back stations we all know

that high voltage ac is used to transmit the electrical power for reducing power transmission losses

in a transmission system different grids are interconnected but sometime it might happen

that one or more grids or power systems may not be in synchronization with other grids

or there exist a weak link between different power systems due

to various factors to overcome these problems hvdc back -to -back system is created it also can be used

when two asynchronous ac system need to be interconnected for a bulk power transmission

and also for the stabilization processes these are the some examples of back -to -back stations mcnell hvdc back -to -back station,

HVDC back -to -back link commissioned between India and Bangladesh, Chandrapur HVDC back -to -back station, Vaisak back -to -back station, Windyashal back -to -back station.

We will see them one by one in the following slides.

McNeil HVDC Back -to -Back Station A back -to -back station

is a series of HVDC interconnectors between the unsynchronized eastern and western AC systems of United States and Canada.

It connects the power grids of Canadian provinces at Alberta and Saskatchewan.

The station was built by Geck -Alstom,

was commissioned in 1989, with the power capacity about 150 megawatt at a DC voltage of 42 kilovolt.

This picture shows the back -to -back station at Alberta.

Mechanical station was notable for operating with low short -circuit ratio.

What do you mean by short -circuit ratio?

Short -circuit ratio is a measure of how strong or weak the connected AC system is.

Most of the HVDC schemes uses line commutated converters with SCR about 3,

but McNeill's scheme was designed to operate with an effective SCR which is even less than 1 .0 on the SASCAT7 side.

So hence it was the only SCR with the lowest value

ever achieved with the line commutated hvdc converter it is also

considered as the first hvdc station to use three phase four winding converter transformer the transformer

which are connected at the 138 glow volt at alberta side

and 230 glow volt on the saskatchi one side the number of poles used in this link is about only one Next,

we are going to see about Indo -Bangladesh link, a SVDC back -to -back link commissioned between India and Bangladesh.

This Indo -Bangladesh link was commissioned by Siemens.

Here, two back -to -back links are installed.

The block one is in operation since 2013 with a capacity of 500 megawatts.

Siemens recently announced that in June 2020, it fully commissioned the second block of hvdc back -to -back

line in barhamara at bangladesh to connect the electricity supply network to india

and bangladesh with the transmission capacity of 500 megawatts hence a total capacity is up to 1000 megawatt

which is the highest reliable power capacity in bangladesh Siemens is a world leader in HVDC technology,

which has installed more than 55 projects worldwide with an overall capacity of 94 GW.

This picture shows the back -to -back stations at Biramara at Bangladesh.

This is the map which shows the back -to -back HVDC link between India and Bangladesh.

Here, from Biramara, at the western border of Bangladesh,

a 230 kV grid of the country will be connected via substation and OH lines to India's 400 kV grid,

which is located at Baharampur.

Next, we are going to see about Chandrapur back -to -back HVDC station.

It is a back -to -back HVDC connection between western and southern regions in India located close to the city of Chandrapur.

Its main purpose is to export power from the Chandrapur Super Thermal Power Station to the southern regions of Indian National Grid.

This picture shows the power station at Chandrapur.

It was owned by Power Grid Corporation of India and the installer for the substation is Gek Alstom and commissioned in 1997.

7 with a power capacity of 500 megawatts at a dc

voltage of 205 kilo volt at each pole next we are

going to see about why is a back -to -back hvdc

station why is a back -to -back hvdc station is a back -to -back hvdc station connection between the eastern

and southern regions in india located close to the city of Viswagapatnam in the state of Andhra Pradesh.

100

It was owned by Power Grid Corporation of India.

101

It has two substations namely VISAG -1

102

and VISAG -2 commissioned in 1999 by Alstom

103

and the latter in 2005 by ABB

104

which has a power capacity of 500 megawatts

105

and a DC voltage of 205 kilovolt at ysac 1 and 176 kilovolt at ysac 2.

106

It consists of two independent poles.

107

The station is no longer required for its original purpose of linking eastern and southern grids,

108

although it can be still used as an embedded power flow device to help control power flow within the AC system.

109

Next, we can see recent developments.

110

Power Grid Corporation of India has chosen Siemens to upgrade India's oldest HVDC link,

111

which is the India's oldest HPDC link.

112

Any guess, Vintiachal back -to -back HPDC link is the India's oldest link.

113

And Siemens has been chosen by Power Grid of India to modernize it.

114

Next, we can see some of the advantages of back -to -back HPDC link.

115

Power can be upgraded to desired frequency then two asynchronous systems can be joined successfully without loss of stability

116

stability of the system is increased as well as power flow can be maintained within the limits

117

more active power can be added where the ac system is

118

already at the limit of short circuit capability then it also

119

helps in the stabilization of weak ac signals weak ac links thank you

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Vocabulário e dicas de fala para esta lição

Esta aula de conversação usa o vídeo “17E058 - Back to Back Stations”. As palavras que mais se repetem: link, station, hvdc, converter, grid. Este vídeo tem 119 frases e 1512 palavras para praticar shadowing. A fala dura 11:21. O falante mantém um ritmo estável de cerca de 133 palavras por minuto, confortável para o shadowing. Apenas 76% das palavras estão entre as 3.000 mais comuns do inglês, por isso o vocabulário é exigente.

Vocabulário principal deste vídeo

15 palavras do vídeo que vale a pena aprender, com pronúncia e significado:

Palavra	Pronúncia	Significado
grid substantivo	/ɡɹɪd/	matriz, quadriculado
connect verbo	/kəˈnɛkt/	conectar
voltage substantivo	/ˈvəʊltɪd͡ʒ/	tensão, voltagem
transmission substantivo	/tɹænsˈmɪʃən/	transmissão
convert verbo	/kənˈvɝt/	converter, transformar
circuit substantivo	/ˈsɝ.kɪt/	circuito, volta
frequency substantivo	/ˈfɹiːkwənsi/	frequência
filter substantivo	/ˈfɪltɚ/	filtro, crivo
bipolar adjetivo	/baɪˈpoʊ.lɚ/	bipolar
hence advérbio	/ˈhɛns/	daqui
ratio substantivo	/ˈɹeɪ.ʃoʊ/	razão, rácio
pole substantivo	/pəʊl/	polo
locate verbo	/ˈloʊˌkeɪt/	localizar
diagram substantivo	/ˈdaɪ.ə.ɡɹæm/	diagrama
reactor substantivo	/ɹiˈæktɚ/	reator

Gramática neste vídeo

As estruturas que o falante mais usa, com as palavras exatas do vídeo:

Estrutura	No vídeo
Voz passiva be + particípio passado — o foco está no que acontece, não em quem faz	are connected · is known · is called
Present perfect have/has + particípio passado — uma ação passada que ainda importa agora	has installed · has chosen · has been chosen

Pronúncia para ficar de olho

Os sons de “th”: theoretical /ˌθi.əˈɹɛt.ɪ.kəl/, smoothen /ˈsmuːðən/
Os sons de “sh” e “zh”: transmission /tɹænsˈmɪʃən/, ratio /ˈɹeɪ.ʃoʊ/, conversion /kənˈvɝʒən/, substation /sʌbˈsteɪʃən/, stabilization /ˌsteɪ.bəl.ɪzˈeɪ.ʃən/
Palavras longas — acerte a sílaba tônica: electrical /ɪˈlɛktɹɪkəl/, stability /stəˈbɪlɪti/, electronics /ɪˌlɛkˈtɹɑ.nɪks/, successfully /səkˈsɛs.fə.li/, electricity /ɪˌlɛkˈtɹɪsɪti/

Sons difíceis para falantes de português:

Consoante final — sem acrescentar um “i” depois: grid /ɡɹɪd/, connect /kəˈnɛkt/, convert /kənˈvɝt/, circuit /ˈsɝ.kɪt/, installed /ɪnˈstɔːld/
/l/ final — a língua toca o céu da boca, não vira “u”: electrical /ɪˈlɛktɹɪkəl/, pole /pəʊl/, principle /ˈpɹɪn.sɪ.pəl/, practical /ˈpɹæk.tɪ.kəl/, mechanical /məˈkænəkəl/
s + consoante no início — sem um “i” antes: stability /stəˈbɪlɪti/, slide /ˈslaɪ̯d/, smoothen /ˈsmuːðən/, stabilization /ˌsteɪ.bəl.ɪzˈeɪ.ʃən/

Como praticar com este vídeo

Ouça o vídeo inteiro uma vez sem falar e anote as palavras que você não conhece.
Faça shadowing frase por frase na velocidade normal, repetindo cada uma até o seu ritmo ficar igual ao do falante.
Grave a sua voz e compare com o original, prestando atenção a palavras como grid, connect, voltage.

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