Operate Time Of The Overexcitation Protection - ABB RET650 Technical Manual

Section 9
Voltage protection
9.4.7.2
226

Operate time of the overexcitation protection

The operate time of OEXPVPH is a function of the relative overexcitation.
The so called IEEE law approximates an inverse-square law and has been chosen
based on analysis of the various transformer overexcitation capability characteristics.
They match the transformer core capability well.
The inverse-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 100.
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 100, can be modified (limited) by a special definite delay
setting tMin, see figure 99.
×
0.18 k
2
equation82
U f
measured rated
= ×
UBase f
measured
1MRK 504 135-UEN A
(Equation 81)
UBase /f
)
rated
(Equation 82)
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