Basler Electric BE1-50/51B-244 - Manual (Page 33)

9252000793 Rev C BE1-50/51B-244 Installation 4-5
Application Coordination
In a typical application coordination scheme, a BE1-50/51B-244 is used to provide primary protection for a
radial distribution feeder. An electromechanical overcurrent relay with extremely inverse timing provides
protection for the transformer and bus. To improve coordination with the electromechanical relay, the
BE1-50/51B-244 is configured with the following settings:
• Integrating reset enabled (SW3-4 ON)
• Westinghouse CO type curves selected (SW3-3 OFF)
The feeder reclosing relay is set for two reclose attempts at 3 and 15 seconds after the initial trip. If a
permanent fault occurs (magnitude 10 times pickup), calculate the feeder breaker trip time for each of the
three operations. Refer to Appendix A for the characteristic curve constants and definition of the terms
used in the following time characteristic curve equations.
From the time characteristic curve equation:
K BD
C M
AD
T
N T
+ +
−
=
028 . 0 ) 2 02758 . 0 (
1 10
2 7624 . 7
0938 . 2
+ × +
−
×
=
= 0.209 seconds
From the reset characteristic curve equation:
1 M
RD
T
2
R
−
=
M equals 0 if current goes to zero. A negative result indicates reset time.
seconds 15.5
1 0
2 7.75
2
− =
−
×
=
Result: Full trip = 0.209 seconds and full reset = 15.5 seconds if current goes to zero.
In Figure 4-7:
T
A
= 0.209 seconds (relay was at reset)
T
B
= value<T
A
because rewind has not gone to zero
T
C
= value<T
A
because rewind has not gone to zero
Figure 4-7. Coordination Timing Diagram