Siemens SIPROTEC 7UM62 - Page 147

Functions
2.17 Reverse Power Protection (ANSI 32R)
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
147
The pickup value 3102 P> REVERSE is set in percent of the secondary apparent power rating S
Nsek
= √3 · U
Nsec
· I
Nsec
. If the primary motoring energy is known, it must be converted to secondary quantities using the following
formula:
with
P
sec
Secondary power corresponding to setting value
S
Nsec
secondary rated power = √3 · U
Nsec
· I
Nsec
P
Mach
Machine power corresponding to setting value
S
N, Mach
Nominal apparent power of the machine
U
N Mach
Nominal Voltage of the Machine
I
N Mach
Nominal current of the machine
U
N prim
Primary Nominal Voltage of the voltage transformers
I
N prim
Primary nominal current of the current transformer
Pickup Seal-In Time
The 3105 T-HOLD pickup seal-in time serves to extend pulsed pickups to the parameterized minimum duration.
Delay Times
If reverse power without emergency tripping is used, a corresponding time delay must be implemented to
bridge any short reverse power states after synchronization or power swings subsequent to system faults (e.g.
3-pole short circuit). Usually, a delay time 3103 T-SV-OPEN = approx. 10 s is set.
Under emergency tripping conditions, the reverse power protection performs a short-time delayed trip subse-
quent to the emergency tripping via an oil-pressure switch or a position switch at the emergency trip valve.
Before tripping, it must be ensured that the reverse power is only caused by the missing drive power at the
turbine side. A time delay is necessary to bridge the active power swing in case of sudden valve closing, until
a steady state active power value is achieved. A 3104 T-SV-CLOSED time delay of about 1 to 3 s is sufficient
for this purpose, whereas a time delay of about 0.5 s is recommended for gas turbine sets. The set times are
additional delay times not including the operating times (measuring time, dropout time) of the protective func-
tion.