Reverse-Power Protection Application With Flexible Protection Function; Description - Siemens siprotec SJ62 User Manual

2.18 Reverse-Power Protection Application with Flexible Protection
Function

2.18.1 Description

General
Disconnecting Fa-
cility
SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015

2.18 Reverse-Power Protection Application with Flexible Protection Function

The flexible protection functions allow a single-element or multi-element directional
protection to be implemented. Each directional element can be operated on one or on
three phases. The elements can optionally use the active power forward, active power
reverse, reactive power forward or reactive power reverse as measuring quantity. The
elements can pick up on undershooting or on overshooting of the threshold. Table 2-
22 shows possible applications for directional protection.
Table 2-22 Overview of directional protection applications
Direction
P forward
reverse
Q forward
reverse
The following example depicts a typical application where the flexible function acts as
reverse-power protection.
The example in figure 2-91 shows an industrial substation with autonomous power
supply from the illustrated generator. All lines and the busbar have a three-phase
layout (with exception of the ground connections and the connection to the voltage
measurement at the generator). Feeder 1 and 2 supply the consumers on customer
side. Industrial customers usually obtain their power from the utility. The generator
runs only in synchronous operation without supplying power. If the utility can no longer
maintain the required supply quality, the substation is disconnected from the utility grid
and the generator assumes the autonomous supply. In the example, the substation is
disconnected from the utility grid when the frequency leaves the nominal range (e.g.
1 to 2% deviation from the nominal frequency), the voltage exceeds or falls under a
certain preset value or the generator feeds back active power into the utility grid. De-
pending on the user's requirements, some of these criteria are linked further. This
would be implemented using CFC.
Type of Evaluation
Overshooting
– Monitoring of the forward
power thresholds of equipment
(transformers, lines)
– protection of a local industrial
network against feeding energy
back into the utility grid
– detection of reverse energy
supply from motors
– monitoring of reactive power
thresholds of equipment (trans-
formers, lines)
– connecting a capacitor bank
for reactive power compensa-
tion
– monitoring of reactive power
thresholds of equipment (trans-
formers, lines)
– de-energizing a capacitor
bank
Undershooting
– detection of motors running at
no-load
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