ABB REG650 - Operate Time of the Overexcitation Protection

9.4.7.2 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
89.
op
2
2
0.18 0.18
t
M
1
V Hz>
k k
overexcitation
× ×
=
-
=
æ ö
ç ÷
è ø
IECEQUATION2298 V2 EN (Equation 89)
where:
M the relative excitation
V/Hz> Operate level of over-excitation function at no load in % of ( UBase /f
rated
)
k is time multiplier for inverse time functions, see figure 140.
The relative excitation M is calculated using equation90
measured
measured rated
measured
measured
rated
M
U
U f
f
UBase
UBase f
f
= = ×
æ ö
ç ÷
è ø
æ ö
ç ÷
è ø
IECEQUATION2404 V1 EN (Equation 90)
Inverse delays as per figure 140, can be modified (limited) by a special definite delay
setting tMin, see figure 139.
Section 9 1MRK 502 048-UEN A
Voltage protection
280
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