• OEXPVPH (24) can be connected to any power transformer side, independent
from the power flow.
• The side with a possible load tap changer must not be used.
8.4.2.2 Operate time of the overexcitation protection
The operate time of OEXPVPH (24) is a function of the relative overexcitation.
Basically there are two different delay laws available to choose between:
• the so called IEEE law, and
• a tailor-made law.
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 140.
op
2
2
0.18 0.18
t
M
1
PUV Hz
TD TD
overexcitation
× ×
=
-
=
æ ö
ç ÷
è ø
ANSIEQUATION2298 V2 EN (Equation 140)
where:
M the relative excitation
Pickup1
is maximum continuously allowed voltage at no load, and rated frequency, in pu and
TD is time multiplier for inverse time functions, see figure 273.
Parameter TD (“time delay multiplier setting”) selects one delay curve from the family of curves.
The relative excitation M is calculated using equation141
measured
measured rated
measured
measured
rated
M
V
V f
f
VBase
VBase f
f
= = ×
æ ö
ç ÷
è ø
æ ö
ç ÷
è ø
ANSIEQUATION2404 V1 EN (Equation 141)
1MRK505222-UUS C Section 8
Voltage protection
533
Technical reference manual
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