IEC 60071

[nitin36537]

In IEC 60071 ,why there are multiple values for one system voltage. For example for 220 Line.
System highest voltage = 245 KV
Short duration power frequency withstand voltage 360,395,460
Lightening withstand impulse voltage 850,950,1050.

May be silly question , As I am Civil engineer.

Thanks
Nitin Patel

 

[7anoter4]

It is not-at all-a silly question. If you could see the paragraph no. 3.8 and 3.9 there are explanations for "nominal"[rated] [in Latin nomine=name ] Un it is not an actual value but an approximate one employed in order to "identify “the System. Us is the highest voltage -actual one-possible in the System any time and any where in usual operation without any damage.
The other two are test voltages.
The System could be exposed to overvoltage at rated frequency and from experience for each nominal [rated] level a system should be tested at a certain overvoltage in a limited duration.
The System has to withstand a lightning hit also. A standard form of lightning wave is used and a very high peak value is recommended for each system nominal voltage [Lightning Impulse Test].