Measured Voltage - ABB Relion Technical Manual

Section 9
Voltage protection
9.4.7.1
9.4.7.2
304

Measured voltage

A check is made if the Selected voltage signal is higher than 70% of the rated phase-to-
ground voltage. When below this value, OEXPVPH (24) exits immediately and no
excitation is calculated.
The frequency value is received from the pre-processing block. The function operates for
frequencies within the range of 33-60 Hz and of 42-75 Hz for 50 Hz and 60 Hz
respectively.
• OEXPVPH (24) can be connected to any power transformer side, independent from
the power flow.
• The side with a load tap changer must not be used, since the tap changer can change
the relative excitation (M)
Operate time of the overexcitation protection
The operate time of OEXPVPH (24) 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.
×
0.18 TD
=
=
t
op
2
æ ö
M
-
ç 1 ÷
è ø
PUV Hz
ANSIEQUATION2298 V2 EN
where:
M the relative excitation
Pickup1 Operate level of over-excitation function at no load in % of (/f
TD is time multiplier for inverse time functions, see figure 140.
The relative excitation M is calculated using
×
0.18 TD
2
overexcitation
equation90
1MRK 502 048-UUS A
(Equation 89)
)
rated
Technical manual