Monitored Data; Operation Principle - ABB REG650 Technical Manual

Section 8
Voltage protection
Table 147: OEXPVPH Non group settings (basic)
Name
GlobalBaseSel
VoltConn
8.4.6
8.4.7
238
Values (Range) Unit
1 - 6 -
Pos Seq -
UL1
UL2
UL3
UL1L2
UL2L3
UL3L1

Monitored data

Table 148: 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 most
of the time near their designated limits.
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. Thus, if
emergency that includes overexcitation does occur, transformers may be damaged
unless corrective action is promptly 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 on load, but are more likely to arise when it is on open circuit, or at a loss of load
occurrence. 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 induced voltage E, and inversely proportional to frequency f, and
turns n.
= × × ×
E 4 44 . f n Bmax A
EQUATION898 V2 EN
Step Default
1 1
- Pos Seq
Type Values (Range)
REAL -
REAL -
REAL -
×
1MRK 502 034-UEN -
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
Technical Manual
(Equation 76)