Forward Power Supervision; Function Description - Siemens SIPROTEC 7UT613 series Manual

2 Functions
2.13

Forward Power Supervision

2.13.1 Function Description

Determining Real
Power
Time Delay, Logic
250
The forward power supervision monitors wether the active power undershoots one set
value or overshoots a separate second value. Each of these functions can initiate dif-
ferent control functions.
When, for example, with generators operating in parallel, the active power output of
one machine becomes so small that other generators could take over this power, then
it is often appropriate to shut down the lightly loaded machine. The criteria here is that
the forward power supplied into the network falls below a certain value.
In some applications it may be useful to give a control command when the issuing real
power exceeds a specific value. If only one of two parallel connected transformers is
active, the second one can be activated, as soon as the transferred power exceeds a
preset ratio.
When a fault in a utility network is not cleared within critical time, the utility network
should be split or for example, an industrial network with internal supply decoupled
from it. As criteria for decoupling, in addition to power flow direction, are undervoltage,
overcurrent and/or frequency. As a result, the 7UT6 can also be used for network de-
coupling.
The forward power supervision can only be used for three-phase protective objects.
This understands that the device is connected to a voltage transformer set and that
this voltage, together with an assigned corresponding current transformer, allow for a
logical calculation of the active power. This is therefore only possible for 7UT613 and
7UT633.
When the circuit breakers are deactivated, the P< stage should be blocked via exter-
nal signals.
The forward power supervision in 7UT6 calculates the active power from the symmet-
rical components of the fundamental waves of the voltages and currents.
There are two measurement methods:
• The "exact" measurement method averages the active power via the last 16 cycles
of the measured quantities. The evaluation of the positive phase-sequence systems
makes the active power definition independent of current and voltage asymmetries.
If an exact derivation of real power at high apparent powers (low cos ϕ) is desired,
it will be necessary to consider the angle error of voltage and current transformers.
The angle correction is performed by a correction angle ϕ
2.1.4).
• The "fast" measurement method calculates the positive-sequence components of
currents and voltage over a cycle. A short tripping time is hereby achieved. It is
therefore well suited in system applications where short tripping times are more
desired than high accuracy, e.g. used for purposes of network decoupling.
The P<-stage as well as the P>-stage each have a time delay. The respective
command is issued after end of the resulting delay and each can trigger a control ac-
tivity.
Every stage can be blocked separately via binary inputs; a another binary input blocks
the entire forward power supervision. The P<-stage is blocked internally when the
(see Subsection
corr
7UT613/63x Manual
C53000-G1176-C160-2