Safety factor of transmission line

[Mlmlzx]

Dear sirs,

I came across a literature of 220 kV DC overhead transmission line design with:

1. loading calculations for max deviation security condition (BWC) everyday temp 100% wind,
NC:1 ; BWC: 1 (safety factor)
2. loading calculation for min deviation security condition (BWC) everyday temp 100% wind,
NC:1; BWC:1 (safety factor)
3. loading calculation for safety condition (E and M)
NC:1; BWC:1 (safety factor)
4. loading calculation for reliability condition for min temp and 36% wind
NC:1; BWC:1 (safecy factor)
5. loading calculation for anti-cascading condition
NC:1; BWC:1
6. loading calculations (dead end with slack span condition max deviation)
reliability condition everyday temp 100% wind
NC:1; BWC:1
7. loading calculation (dead end with slack span condition min deviation
reliability condition everyday temp 100% wind
(NC:1, BWC: 1)
8. loading calculation (dead end with slack span condition max deviation
security condition (BWC)slack span broken
(NC:1, BWC: 1)
9. loading calculation (dead end+slack span min deviation security condition (BWC)
slack span broken
(NC:1, BWC: 1)


As i read through standards, safety factor should be 2.5 or at least 2.
(safety factor = working stress/ultimate strength)

Can somebody please tell?

Regards,