1 Distributed Generation and Power Quality-Continued

2 Siting Distributed Generation # Distributed Generation provides some capacity relief on the substation. # Distributed Generator should be sited away from the substation. # Distributed Generator (diesel genset) might be sited near the tie-point between two feeders.

3 Typical interconnection requirements for customer-owned DG No voltage regulation while interconnected unless by special agreement Anti-islanding frequency and voltage control (IEEE Standard ) Relaying to detect resonant conditions in susceptible applications Fault detection: relaying to detect faults on utility system and disconnect after delay. Direct transfer trip (costly)

4 Typical requirement to detect faults on utility system and disconnect after delay (60 Hz system): ConditionMax delay V  50% 10 cycles 50% < V  88% 2.0 sec 110% < V  120% 1.0 sec V > 120%10 cycles f < 59.3 Hz10 cycles f > 60.5 Hz10 cycles

5 ANSI C37-2 Device Numbers 21Distance Relay 25Synchronizing Device 27Undervoltage Relay 32Directional Power Relay 49Thermal Relay 50Instantaneous Overcurrent Relay 51AC Time Overcurrent Relay 52AC Circuit Breaker

6 ANSI C37-2 Device Numbers 59Overvoltage Relay 67AC Directional Overcurrent 72DC Circuit Breaker 76DC Overcurrent Relay 79AC Reclosing Relay 81Frequency Relay 86Lockout Relay 87Differential Relay

7 load DG 27/59 81 OU 27: undervoltage 59: overvoltage 81: frequency (O=over, U=under) Small DG: Relays added to normal protection (overcurrent, etc.) for interconnection

8 Small DG: Relays would trip DG breaker if not used for backup. Relays would trip main breaker if used for backup, so that continued operation is possible (must coordinate with controls on DG)

9 DG 46 50/ MW DG showing typical protection 27/59 81 O/U 4759I 59N 50/ R G resistance grounded to limit ground fault current

10 25: synchronizing device 27: undervoltage 32R: reverse power 40: loss of field 46: negative sequence current 47: negative phase sequence 50: instantaneous overcurrent 51: time overcurrent 51G: ground overcurrent 59I: inst. overvoltage (if resonance is problem) 59N: overvoltage (on corner of broken delta) 87: differential (main generator overcurrent)