Application - ABB 615 series Technical Manual

1MAC059074-MB A
4.8.3.5
615 series ANSI
Technical Manual
mode which selects the blocking mode. The BLOCK input can be controlled by a binary
input, a horizontal communication input or an internal signal of the protection relay's
program. The influence of the BLOCK signal activation is preselected with the global
setting Blocking mode.
The Blocking mode setting has three blocking methods. In the "Freeze timers" mode, the
operation timer is frozen to the prevailing value. In the "Block all" mode, the whole
function is blocked and the timers are reset. In the "Block TRIP output" mode, the function
operates normally but the TRIP output is not activated.

Application

Use of distributed power generating units (PGU) is rapidly increasing due to liberalized
markets (deregulation) and the global trend to use more renewable sources of energy. As
the capacity of these generating units increase, they are connected directly to medium
voltage networks. Until recent years it had been a practice by grid operators to disconnect
the distributed power generator from the network in case of fault in the network.
If there is a considerable loss in the power generation, it may affect the system's ability to
recover. To ensure power system stability, various grid codes have revised their
requirements and therefore require that the distributed PGUs have to make a contribution
to network support. In case of network faults, the distributed power generator should not
be immediately disconnected from the network. Instead, as a matter of principle,
generating plants connected to the medium-voltage network must be capable of
participating in steady-state voltage control and dynamic network support. However, if
the generators stay connected, it must be ensured that they do not take reactive power from
the network because this may lead to collapse of the grid. 32Q-27 is used for detecting
such situations, that is, simultaneous undervoltage and reactive power (under excited
generators) and trip the generators.
The protection function 32Q-27 is developed considering various grid codes. For
example, in the BDEW Technical Guideline "Generating Plants Connected to the
Medium-Voltage Network" (June 2008 issue, Germany), it is stated that if all three phase-
to-phase voltages at the grid connection point decrease and remain at and below a value
of 85% of the rated and if reactive power is simultaneously consumed at the grid
connection point (under-excited operation), the generating facility must be disconnected
from the network with a time delay of 0.5 s.
Section 4
Protection functions
737