ABB Relion 670 series - Overexcitation Protection OEXPVPH (24)

CrvSatn: Set tuning parameter for step n. When the denominator in the expression of the
programmable curve is equal to zero, the time delay will be infinite. There will be an
undesired discontinuity. Therefore, a tuning parameter CrvSatn is set to compensate for
this phenomenon. In the voltage interval Pickup> up to Pickup> · (1.0 + CrvSatn/100) the
used voltage will be: Pickup> · (1.0 + CrvSatn/100). If the programmable curve is used
this parameter must be calculated so that:
0
100
CrvSatn
B C× - >
EQUATION1448 V1 EN (Equation 514)
HystAbsn: Absolute hysteresis for step n, set in % of VBase. The setting of this parameter
is highly dependent of the application. The hysteresis is used to avoid oscillations of the
PICKUP output signal. This signal resets when the measured voltage drops below the
setting level and leaves the hysteresis area. Make sure that the set value for parameter
HystABSn is somewhat smaller than the set pickup value. Otherwise there is a risk that step
n will not reset properly.
10.4 Overexcitation protection OEXPVPH (24)
10.4.1 Identification
Function description
IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Overexcitation protection OEXPVPH
U/f >
SYMBOL-Q V1 EN
24
10.4.2 Application
When the laminated core of a power transformer is subjected to a magnetic flux density
beyond its design limits, stray flux will flow into non-laminated components not designed
to carry flux and cause eddy currents to flow. The eddy currents can cause excessive
heating and severe damage to insulation and adjacent parts in a relatively short time.
Overvoltage, or underfrequency, or a combination of both, will result in an excessive flux
density level, which is denominated overfluxing or over-excitation.
The greatest risk for overexcitation exists in a thermal power station when the generator-
transformer block is disconnected from the rest of the network, or in network “islands”
Section 10 1MRK 506 369-UUS -
Voltage protection
580 Line distance protection REL670 2.2 ANSI
Application manual