跟讀練習: 17E058 - Back to Back Stations - 通過影片學習英語口語

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Hello everyone, I am Monika.

大家好，我是莫妮卡。

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

我在此為大家介紹背靠背站點。

Let's see.

我看看。

What is back -to -back?

什麼是背對背交易？

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.

通常，在電子學和電力電子學中，如果兩個雙極型器件以相反極性串聯連線，則該組合被稱為背對背系統。

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.

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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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本課的詞彙與口語要點

這節口語課以影片“17E058 - Back to Back Stations”為素材。影片中反覆出現的詞有：link, station, hvdc, converter, grid。這段影片共有 119 個句子、1512 個單詞可供跟讀。講話部分時長為 11:21。說話人語速平穩，每分鐘約 133 個詞，很適合跟讀。只有 76% 的單詞屬於英語最常用的 3,000 詞，詞彙難度較高。

影片中的重點詞彙

影片中 15 個值得學習的單詞，附發音和釋義：

單詞	發音	釋義
grid 名詞	/ɡɹɪd/	網格 /網格, 格子
connect 動詞	/kəˈnɛkt/	連線 /連線
voltage 名詞	/ˈvəʊltɪd͡ʒ/	電壓 /電壓
transmission 名詞	/tɹænsˈmɪʃən/	傳輸 /傳輸
frequency 名詞	/ˈfɹiːkwənsi/	頻率 /頻率, 頻度 /頻度
filter 名詞	/ˈfɪltɚ/	過濾器 /過濾器, 濾過器 /濾過器
hence 副詞	/ˈhɛns/	從這裡 /從這裡, 從這兒 /從這兒
ratio 名詞	/ˈɹeɪ.ʃoʊ/	比, 比例
pole 名詞	/pəʊl/	極 /極
diagram 名詞	/ˈdaɪ.ə.ɡɹæm/	圖 /圖, 圖表 /圖表
reactor 名詞	/ɹiˈæktɚ/	反應器 /反應器
principle 名詞	/ˈpɹɪn.sɪ.pəl/	原理, 原則 /原則
component 名詞	/kəmˈpoʊ.nənt/	元件, 部件
stability 名詞	/stəˈbɪlɪti/	穩定性 /穩定性, 穩定 /穩定
electronics 名詞	/ɪˌlɛkˈtɹɑ.nɪks/	電子學 /電子學

影片中的語法

說話人最常用的結構，並附上影片中的原話：

結構	影片中的用法
被動語態 be + 過去分詞 — 強調發生了什麼，而不是誰做的	are connected · is known · is called
現在完成時 have/has + 過去分詞 — 過去發生但與現在仍有關聯的事	has installed · has chosen · has been chosen

需要注意的發音

“th” 音: theoretical /ˌθi.əˈɹɛt.ɪ.kəl/, smoothen /ˈsmuːðən/
“sh” 和 “zh” 音: transmission /tɹænsˈmɪʃən/, ratio /ˈɹeɪ.ʃoʊ/, conversion /kənˈvɝʒən/, substation /sʌbˈsteɪʃən/, stabilization /ˌsteɪ.bəl.ɪzˈeɪ.ʃən/
長單詞——注意重音位置: electrical /ɪˈlɛktɹɪkəl/, stability /stəˈbɪlɪti/, electronics /ɪˌlɛkˈtɹɑ.nɪks/, successfully /səkˈsɛs.fə.li/, electricity /ɪˌlɛkˈtɹɪsɪti/

中文母語者容易讀錯的音：

/v/ — 不要讀成 /w/，上齒輕觸下唇: voltage /ˈvəʊltɪd͡ʒ/, convert /kənˈvɝt/, conversion /kənˈvɝʒən/, involve /ɪnˈvɑlv/, overcome /ˌəʊ.vəˈkʌm/
詞尾子音 — 要讀清楚，後面不要加母音: grid /ɡɹɪd/, connect /kəˈnɛkt/, voltage /ˈvəʊltɪd͡ʒ/, convert /kənˈvɝt/, circuit /ˈsɝ.kɪt/
/r/ 和 /l/ 的區別: electrical /ɪˈlɛktɹɪkəl/, principle /ˈpɹɪn.sɪ.pəl/, electronics /ɪˌlɛkˈtɹɑ.nɪks/, practical /ˈpɹæk.tɪ.kəl/, electricity /ɪˌlɛkˈtɹɪsɪti/

如何用這段影片練習

先完整聽一遍影片，不要開口，記下不認識的單詞。
用正常速度逐句跟讀，每句重複到你的節奏與說話人一致為止。
錄下自己的聲音並與原聲對比，特別注意 grid, connect, voltage 這類單詞。

什麼是跟讀法？

跟讀法 (Shadowing) 是一種有科學依據的語言學習技巧，最初開發用於專業口譯員的培訓，並由多語言者Alexander Arguelles博士普及。這個方法簡單而強大：您在聽英語母語原聲的同時立即大聲重複——就像是一個延遲1-2秒緊跟說話者的影子。與被動聽力或語法練習不同，跟讀法強迫您的大腦和口腔肌肉同時處理並模模擬實的講話模式。研究表明它能顯著提高發音準確性，語調，節奏，連讀，聽力理解和口語流利度——使其成為雅思口語備考和真實英語交流最有效的方法之一。

影子跟讀法: 閱讀完整分步指南 →

跟讀練習: 17E058 - Back to Back Stations - 通過影片學習英語口語

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