ABB Relion 670 Series Technical Reference Manual page 539

1MRK505222-UUS C
8.4.2.2
Technical reference manual
• 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.
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.
×
0.18 TD
=
=
t
op
2
æ ö
M
-
1
ç ÷
è ø
PUV Hz
ANSIEQUATION2298 V2 EN
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
æ ö
V
measured
ç ÷
è ø
f
measured =
=
M
æ ö
VBase
ç ÷
è ø
f
rated
ANSIEQUATION2404 V1 EN
×
0.18 TD
2
overexcitation
equation141
V f
measured rated
×
VBase f
measured
Section 8
Voltage protection
(Equation 140)
(Equation 141)
533