ABB REC670 Applications Manual page 561

1MRK 511 401-UUS A
Bay control REC670 2.2 ANSI
Application manual
Winding to oil temperature gradient differs from winding to winding depending on
current density in the winding, physical dimensions, cooling system etc., This value
can be between 10 to 20 ̊ C for both distribution and power transformers. For low
current density winding it can be 10 ̊ C and for high current density winding it can be
20 ̊ C. The settings given below are also used for the calculation of winding time
constant.
WdgToOilGrad1: Winding to oil temperature gradient for the winding 1 at rated load.
WdgToOilGrad2: Winding to oil temperature gradient for the winding 2 at rated load.
WdgToOilGrad3: Winding to oil temperature gradient for the winding 3 at rated load.
CuLossW1: This setting is used to set the winding loss at rated load for the winding 1.
CuLossW2: This setting is used to set the winding loss at rated load for the winding 2.
CuLossW3: This setting is used to set the winding loss at rated load for the winding 3.
MassW1: This setting is used to set the mass of the winding 1.
MassW2: This setting is used to set the mass of the winding 2.
MassW3: This setting is used to set the mass of the winding 3.
Loss ratios at different tap positions are required for the calculation of top oil
temperature, especially when the transformer is using online tap changer. This loss
ratio is the ratio between load losses to no-load loss. It may vary from 6 -7 for
distribution transformer and 4-8 for power transformer. Normally it varies from 3 to 11.
The function has the following settings related to loss ratio calculation.
RLRated: This setting is used to set the ratio of load losses to no-load loss at principal
tapping position.
RLHighRated: This setting is used to set the ratio of load losses to no-load loss at
principal tapping +1 position.
RLMaxTap: This setting is used to set the ratio of load losses to no-load loss at
maximum tap position where maximum voltage is possible.
RLMinTap: This setting is used to set the ratio of load losses to no-load loss at
minimum tap position where minimum voltage is possible.
RatedVoltTap: This setting is used to set the position number of tap changer at rated
voltage.
HighVoltTap: This setting is used to set the position number of tap changer at possible
maximum voltage.
Section 17
Monitoring
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