Basler Electric BE1-11t - Manual (Page 483)

9424200995 Rev H 471
The K factor gives the time that a generator can withstand 1 per unit negative sequence current. For
example, with a K factor of 20, since (I
2
) 2 becomes 1 at 1 per unit of current, the generator can withstand
the condition for 20 seconds. Typical values for generator K factors are in the 2 to 40 range. The BE1-11t
uses the “nominal current” setting of the BE1-11t to determine what corresponds to 1 per unit current in
the generator.
When curve 46 is selected, the BE1-11t changes the range of the allowed time dial to 1 to 99 (instead of
the time dial range of 0.1 to 9.9 for all the other curves). The user should enter the “K” factor of the
generator into the time dial field.
BE1-11t Equation
When the 46 function is used, the BE1-11t uses the K factor (i.e., 46 time dial setting), 46 minimum
pickup setting and generator full-load current to create a constant Z (see Equation 29).
𝑍 = 46 𝑇𝑖𝑚𝑒 𝐷𝑖𝑎𝑙 �
𝐼
𝑁𝑜𝑚 𝑆𝑒𝑡𝑡𝑖𝑛𝑔
46 𝑃𝑖𝑐𝑘𝑢𝑝 𝑆𝑒𝑡𝑡𝑖𝑛𝑔�
2
Equation 29
The time to trip equation used in the BE1-11t is:
𝑇
𝑇
=
𝑍
𝑀 2
+ 0.028 𝑠𝑒𝑐𝑜𝑛𝑑𝑠
Equation 30
where:
𝑀 =
𝑀𝑒𝑎𝑠𝑢𝑟𝑒𝑑 𝐼
2
46 𝑃𝑖𝑐𝑘𝑢𝑝 𝑆𝑒𝑡𝑡𝑖𝑛𝑔
Equation 31
which, when M > 1, reduces to:
𝑇
𝑇
= 46 𝑇𝑖𝑚𝑒 𝐷𝑖𝑎𝑙 �
𝐼
𝑁𝑜𝑚 𝑆𝑒𝑡𝑡𝑖𝑛𝑔
𝐼
2
𝑀𝑒𝑎𝑠𝑢𝑟𝑒𝑑�
2
Equation 32
BE1-11t Time Curve Characteristics