Monitored Data; Operation Principle - ABB RET650 Technical Manual

1MRK 504 135-UEN A
Table 151: OEXPVPH Non group settings (basic)
Name Values (Range)
GlobalBaseSel
VoltConn
9.4.6
9.4.7
Technical manual
Unit
1 - 6 -
Pos Seq -
UL1
UL2
UL3
UL1L2
UL2L3
UL3L1
Only PosSeq or UL1L2 should be selected for the VoltConn setting.

Monitored data

Table 152: OEXPVPH Monitored data
Name
TMTOTRIP
VPERHZ
THERMSTA

Operation principle

The importance of Overexcitation protection (OEXPVPH) function is growing as the
power transformers as well as other power system elements today operate near their
designated limits most of the time.
Modern design transformers are more sensitive to overexcitation than earlier types.
This is a result of the more efficient designs and designs which rely on the
improvement in the uniformity of the excitation level of modern systems. If an
emergency that causes overexcitation does occur, transformers may be damaged
unless corrective action is taken. Transformer manufacturers recommend an
overexcitation protection as a part of the transformer protection system.
Overexcitation results from excessive applied voltage, possibly in combination with
below-normal frequency. Such condition may occur when a transformer unit is
loaded, but are more likely to arise when the transformer is unloaded, or when a loss
of load occurs. Transformers directly connected to generators are in particular danger
to experience overexcitation condition. It follows from the fundamental transformer
equation, see equation 76, that peak flux density Bmax is directly proportional to the
induced voltage E, inversely proportional to frequency f, and turns n.
Step Default
1 1
- Pos Seq
Type Values (Range)
REAL -
REAL -
REAL -
Section 9
Voltage protection
Description
Selection of one of the Global Base Value
groups
Selection of measured voltage
Unit Description
s Calculated time to trip for
overexcitation, in sec
V/Hz Voltage to frequency ratio
in per-unit
% Overexcitation thermal
status in % of trip level
223