ABB RELION REX640 Technical Manual page 1279

1MRS759142 C
REX640
Technical Manual
Load factor
I_A
calculation
I_B
I3P
parameter
I_C
TOIL_TEMP
calculation
AMB_TEMP
BLOCK
RESET
RST_AVGAGING
GUID-203CBDD6-9F2A-4533-B7B1-DB82C759B1E4 V1 EN
Figure 696: Functional module diagram
Load factor calculation and parameter selection
The transformer top oil and hot-spot temperatures are dependent on the load factor, the
winding conductor properties and the cooling oil properties of the transformer. This
module calculates the load factor based on the measured phase currents and selects the
transformer parameters based on user defined settings.
Load factor calculation
Load factor is a ratio of the load current to the rated current. Since the thermal content
of all the three phase currents influence the temperature inside the transformer, the
load factor is calculated as a ratio of the root of sum of squared phase currents to three
times the rated current.
2 2
I A _ I B _ I C _
+ +
K
=
2
3 I
⋅
rated
GUID-72BE9E6B-5034-43E9-8838-E31E3185940C V1 EN
Where
K
I_A, I_B and I_C
I
rated
If Transformer type is set to "Single phase", the denominator consists only of I
2
instead of 3×I .
rated
Equation 286 assumes that voltage is constant and tap changer position is not
considered.
Condition monitoring functions
and
selection
Top oil
Hotspot
Level
temp temp
detector 1
calculation
Ageing
and
loss of life
calculation
2
Load factor
RMS value of input phase currents (Amperes)
Rated current (Amperes)
Section 7
ALARM
WARNING
Level
ALM_AGE_RATE
detector 2
HOTSPOT_TEMP
TOPOIL_TEMP
(Equation 286)
2
rated
1273