Distributed Generation and
Power Quality-Continued
1
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.
2
Typical interconnection requirements for
customer-owned DG
• No voltage regulation while interconnected
unless by special agreement
• Anti-islanding frequency and voltage
control (IEEE Standard 929-2000)
• 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)
3
Typical requirement to detect faults on utility system
and disconnect after delay (60 Hz system):
Condition
Max delay
V  50%
10 cycles
50% < V  88%
2.0 sec
110% < V  120%
1.0 sec
V > 120%
10 cycles
f < 59.3 Hz
10 cycles
f > 60.5 Hz
10 cycles
4
ANSI C37-2 Device Numbers
21 Distance Relay
25 Synchronizing Device
27 Undervoltage Relay
32 Directional Power Relay
49 Thermal Relay
50 Instantaneous Overcurrent Relay
51 AC Time Overcurrent Relay
52 AC Circuit Breaker
5
ANSI C37-2 Device Numbers
59
67
Overvoltage Relay
AC Directional Overcurrent
72
76
79
DC Circuit Breaker
DC Overcurrent Relay
AC Reclosing Relay
81
Frequency Relay
86
87
Lockout Relay
Differential Relay
6
Small DG:
Relays added to normal
protection (overcurrent,
etc.) for interconnection
81 OU
load
DG
27/59
27: undervoltage
59: overvoltage
81: frequency (O=over, U=under)
7
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)
8
50/51
46
27/59 81 47
O/U
25
46
87
51G
32R
DG
59I
59N
50/51
40
resistance grounded to limit ground
fault current
1-10 MW DG showing typical protection
9
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)
10