M-3425 Instruction Book
2–34
50/27 Inadvertent Energizing
The inadvertent energizing protection function (50/27)
of the relay is an overcurrent function supervised by
generator terminal bus voltage. Inadvertent or
accidental energizing of off-line generators has
occurred frequently enough to warrant the use of
dedicated protection logic to detect this condition.
Operating errors, breaker flashovers, control circuit
malfunctions or a combination of these causes
have resulted in generators being accidentally
energized while off-line. The problem is particularly
prevalent on large generators connected through a
high voltage disconnect switch to either a ring bus
or breaker-and-a-half bus configuration. When a
generator is accidentally energized from the power
system, it will accelerate like an induction motor.
While the machine is accelerating, high currents
induced into the rotor can cause significant damage
in a matter of seconds. Voltage supervised
overcurrent logic is designed to provide this
protection. (See Figure 2-16, Inadvertent Energizing
Function Logic Diagram)
An undervoltage element (all three phase voltages
must be below pickup) with adjustable pickup and
dropout time delay supervises instantaneous
overcurrent tripping. The undervoltage detectors
automatically arm the overcurrent tripping when the
generator is taken off-line. This undervoltage detector
will disable or disarm the overcurrent operation
when the machine is put back in service. Ranges
and increments are presented in Table 2-16.
N
O
I
T
C
N
U
F
E
G
N
A
R
T
N
I
O
P
T
E
S
T
N
E
M
E
R
C
N
I
)
7
2
/
0
5
(
g
n
i
z
i
g
r
e
n
E
t
n
e
t
r
e
v
d
a
n
I
)
0
5
(
t
n
e
r
r
u
c
r
e
v
O
p
u
k
c
i
P
A
0
0
.
5
1
o
t
0
5
.
0
)
A
0
0
.
3
o
t
0
1
.
0
(
A
1
0
.
0
)
7
2
(
e
g
a
t
l
o
v
r
e
d
n
U
p
u
k
c
i
P
V
0
3
1
o
t
0
4
V
1
y
a
l
e
D
e
m
i
T
p
u
k
c
i
P
s
e
l
c
y
C
0
6
1
8
o
t
1
e
l
c
y
C
1
y
a
l
e
D
e
m
i
T
t
u
o
-
p
o
r
D
s
e
l
c
y
C
0
6
1
8
o
t
1
e
l
c
y
C
1
Table 2-16
Inadvertent Energizing (50/27) Setpoint Ranges
Summary of Contents for M-3425
Page 1: ...Instruction Book M 3425 Generator Protection ...
Page 14: ... 13 M 3425 Generator Protection Relay Figure 1 External Connections ...
Page 33: ...x M 3425 Instruction Book This Page Left Intentionally Blank ...
Page 89: ...M 3425 Instruction Book 2 52 This Page Left Intentionally Blank ...
Page 125: ...1 3 A B C M 3425 Instruction Book 4 26 This Page Left Intentionally Blank ...
Page 187: ...M 3425 Instruction Book 6 50 This Page Left Intentionally Blank ...
Page 207: ...M 3425 Instruction Book C 4 This Page Left Intentionally Blank ...
Page 209: ...D 2 M 3425 Instruction Book Figure D 1 Volts Hz 24 Inverse Curve Family 1 Inverse Square ...
Page 210: ...Inverse Time Curves Appendix D D 3 Figure D 2 Volts Hz 24 Inverse Family Curve 2 ...
Page 211: ...D 4 M 3425 Instruction Book Figure D 3 Volts Hz 24IT Inverse Curve Family 3 ...
Page 212: ...Inverse Time Curves Appendix D D 5 Figure D 4 Volts Hz 24IT Inverse Curve Family 4 ...
Page 215: ...D 8 M 3425 Instruction Book Figure D 5 Definite Time Overcurrent Curve ...
Page 216: ...Inverse Time Curves Appendix D D 9 Figure D 6 Inverse Time Overcurrent Curve ...
Page 217: ...D 10 M 3425 Instruction Book Figure D 7 Very Inverse Time Overcurrent Curve ...
Page 218: ...Inverse Time Curves Appendix D D 11 Figure D 8 Extremely Inverse Time Overcurrent Curve ...
Page 223: ...D 16 M 3425 Instruction Book This Page Intentionally Left Blank ...