Basler Electric BE1-51/27C - Manual (Page 62)

56 9137200998 Rev E
lower accuracy-class voltages. A neutral element pickup of 10 percent of the circuit rating is normally
enough to be above any non-fault unbalance for a solidly grounded system. Lower settings are
appropriate and safe for impedance-grounded systems or for ungrounded, protected-equipment
connections.
Undervoltage settings should be as high as possible without allowing operation under the worse no-fault
conditions. An 85 percent of rated voltage setting meets these requirements. If motor starting or motor
accelerating following a fault can severely depress the relay voltage, a setting of 75 percent or 80 percent
may be advisable.
Setting Example
Figure 36 illustrates generator relay elements that are to be set in this example. Plant 11 kV feeders are
supplied by a 115 kV system that is supplemented by two local 3,700 kVA generators. Line 1 is illustrated
completely; line 2 is the same as line 1 and only shows major components. Settings are provided for the
BE1-51/27C Time Overcurrent Relay with voltage control, BE1-51 Time Overcurrent Relay, and BE1-67
Phase Directional Overcurrent Relay.
Generator Backup (Breaker A)
•
BE1-51/27C (51/27), relay style number: T3E B6S B2C0F
•
Three-phase-and-neutral overcurrent
•
1.5 to 12 A phase (instantaneous trip is out of service)
•
0.5 to 4 A neutral (instantaneous is in service)
•
Very inverse timing (B6)
•
300/5 CTs
Feeder (Breaker F)
•
BE1-51 (51)
•
0.5 to 12 A
•
Very inverse timing (B6)
•
800/5 CTs
•
No instantaneous
•
Pickup set to 6 A
•
Time Dial set to 08
Phase Directional (Breaker L)
•
BE1-67 (67)
•
0.5 to 12 A
•
Definite timing (B3)
•
3,000/5 CTs
•
Pickup set to 0.5 A
•
Time Dial set to 02
Generator Reactance (Per Unit)
Sub transient ........... 0.18
Transient ................. 0.25
Steady State ........... 1.5
Tests and Adjustments BE1-51/27C