ABB Relion REQ650, Applications Manual

Page: 149 / 340

6.13.3 Setting guidelines
GlobalBaseSel : Selects the global base value group used by the function to define
( IBase ), ( UBase ) and ( SBase ).
Broken conductor check BRCPTOC must be set to detect open phase/s (series faults)
with different loads on the line. BRCPTOC must at the same time be set to not operate
for maximum asymmetry which can exist due to, for example, not transposed power
lines.
All settings are in primary values or percentage.
Set minimum operating level per phase IP> to typically 10-20% of rated current.
Set the unsymmetrical current, which is relation between the difference of the
minimum and maximum phase currents to the maximum phase current to typical
Iub>
= 50% .
Note that it must be set to avoid problem with asymmetry under
minimum operating conditions.
Set the time delay tOper = 5 - 60 seconds and reset time tReset = 0.010 - 60.000
seconds.
6.14 Directional over-/under-power protection
GOPPDOP/GUPPDUP
6.14.1 Application
The task of a generator in a power plant is to convert mechanical energy available as
a torque on a rotating shaft to electric energy.
Sometimes, the mechanical power from a prime mover may decrease so much that it
does not cover bearing losses and ventilation losses. Then, the synchronous generator
becomes a synchronous motor and starts to take electric power from the rest of the
power system. This operating state, where individual synchronous machines operate
as motors, implies no risk for the machine itself. If the generator under consideration
is very large and if it consumes lots of electric power, it may be desirable to disconnect
it to ease the task for the rest of the power system.
Often, the motoring condition may imply that the turbine is in a very dangerous state.
The task of the reverse power protection is to protect the turbine and not to protect the
generator itself.
Steam turbines easily become overheated if the steam flow becomes too low or if the
steam ceases to flow through the turbine. Therefore, turbo-generators should have
1MRK 505 291-UEN A
Section 6
Current protection
143
Application manual