Overexcitation Protection Oexpvph (24) - ABB RET670 Applications Manual

1MRK504116-UUS C
Name Values (Range)
CCrv2 0.0 - 1.0
DCrv2 0.000 - 60.000
PCrv2 0.000 - 3.000
CrvSat2 0 - 100
3.8.4
3.8.4.1
Application manual
Unit Step
- 0.1
- 0.001
- 0.001
% 1

Overexcitation protection OEXPVPH (24)

Function description
Overexcitation protection
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"
occuring at disturbance where high voltages and/or low frequencies can occur.
Overexcitation can occur during start-up and shut-down of the generator if the field
current is not properly adjusted. Loss-of load or load-shedding can also result in
overexcitation if the voltage control and frequency governor is not functioning
properly. Loss of load or load-shedding at a transformer substation can result in
overexcitation if the voltage control function is insufficient or out of order. Low
frequency in a system isolated from the main network can result in overexcitation if the
voltage regulating system maintains normal voltage.
According to the IEC standards, the power transformers shall be capable of delivering
rated load current continuously at an applied voltage of 105% of rated value (at rated
frequency). For special cases, the purchaser may specify that the transformer shall be
Default Description
0.0 Parameter C for customer programmable
curve for step 2
0.000 Parameter D for customer programmable
curve for step 2
1.000 Parameter P for customer programmable
curve for step 2
0 Tuning param for programmable over voltage
TOV curve, step 2
IEC 61850 IEC 60617
identification identification
OEXPVPH
SYMBOL-Q V1 EN
Section 3
IED application
ANSI/IEEE C37.2
device number
24
U/f >
529