Operate Time Of The Overexcitation Protection - ABB REG650 Technical Manual

1MRK 502 034-UEN -
8.4.7.2
Technical Manual

Operate time of the overexcitation protection

The operate time of OEXPVPH is a function of the relative overexcitation.
The so called IEEE law approximates a square law and has been chosen based on
analysis of the various transformers' overexcitation capability characteristics. They
can match the transformer core capability well.
The square law is according to equation 81.
×
0.18 k
=
=
t
op
2
æ ö
overexcitation
M
-
1
ç ÷
è ø
V Hz>
IECEQUATION2298 V2 EN
where:
M the relative excitation
V/Hz>
Operate level of over-excitation function at no load in % of (
k is time multiplier for inverse time functions, see figure 123.
The relative excitation M is calculated using
æ ö
U
measured
ç ÷
è ø
f
measured
=
M
æ ö
UBase
ç ÷
è ø
f
rated
IECEQUATION2404 V1 EN
Inverse delays as per figure 123, can be modified (limited) by a special definite
delay setting tMin, see figure 122.
×
0.18 k
2
equation121
U f
measured rated
= ×
UBase f
measured
Section 8
Voltage protection
(Equation 81)
UBase /f
)
rated
241