The system study, manufacture of main equipment , development of valve control, station control, DC protection, installation and commissioning have all been undertaken by domestic organizations.

该工程系统研究、主设备制造，阀控、站控，直流保护设备研制，安装及调试全部由国内单位承担。

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DC circuit breakers are the most important protection equipments for DC power system.

直流断路器是直流供电系统中极其重要的保护设备。

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With the rapid development of subway, it is necessary to consummate the protection for DC traction power supply system.

随着城市地铁的大力发展，研制更加完善的直流保护正是应时之需。

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Charles Bolden, the head of the US space agency, NASA,and Lisa Jackson from the Environmental Protection Agency,or EPA, came to this Washington,DC middle school to encourage these youngsters to focus on math and science careers.

VOA: standard.2010.05.10

DC, which has been campaigning for several years for greater protection for sturgeon in the Caspian Sea a body of water that is the source of about 90% of the trade in caviar.

ECONOMIST: Fishing (II): Conserving caviar | The

But inquiring minds will want to know who is paying for the extra secret service protection, the extra wait staff , the screeners and background checkers, and motorcades of the DC and Capital police.

FORBES: First Couple's Sequester Sacrifice: Date Nights