ABB SPAF 140 C User Manual And Technical Description page 9

Example of
application
Example:
Frequency relay
SPAF 140 C used
for generator and
turbine protection
Normally, the frequency of the generator is de-
termined by the external network. If power con-
sumption exceeds the power generated, there
will be a power deficiency and, as a result, a fre-
quency decline. As the frequency drops, the
regulator tries to boost the capacity of the gen-
erator prime mover, causing the frequency to
return to normal. Correspondingly, if power
consumption is smaller than power generation,
the frequency of the network increases.
Unless it is possible to increase the capacity of
the prime mover so that it correspond to the
load, the power deficiency remains permanent
and the network frequency starts declining.
Under normal conditions, the rate of the fre-
quency drop automatically slows down, and may
even stop, because power consumption gener-
ally decreases as the frequency falls (compare
A
N
n
a
X0 63 13 14 16
U3
Fig. 4. Frequency relay SPAF 140 C used for the protection of a generator and a turbine.
pump and squirrel-cage motor). Sometimes, for
instance in island operation, the network fre-
quency can drop to a level that is hazardous to
the turbine of the generator. Mechanical vibra-
tion of the turbine blades due to underfrequency
may break the blades.
A moderate level of overfrequency does not
damage the generator but, for instance, a sud-
den load disconnection may cause the system
to accelerate so fast that the speed regulation
does not respond fast enough, and the genera-
tor and the prime mover reach dangerous rota-
tional speeds.
The frequency relay SPAF 140 C can be used
to protect the generator and the turbine against
both overfrequency and underfrequency.
d
1 0
-
U
aux
BS4 BS3 BS2 BS1
48 47 46 45 23 22 11 10
62 61
~ _
=
+ -
U2
U1
4
f
4
BS1
df/dt
BS2
BS3
BS4
BS5
0
+
1
+
-
+ (~)
- (~)
Alarm
IRF SS1 TS1
+
70 71 72 68 69 85 86
+ + +
IRF
SS1
TS1
SS2
TS2
SS3
TS3
SS4
TS4
I/O
Rx Tx
Alarm
SERIAL
TS2
PORT
(SPA)
87 88
+
9