Transformer Residual Flux Evaluation Trafoswt; Identification; Functionality - Hitachi Relion 650 Series Technical Manual

1MRK 511 557-UEN Rev. A
12.20

Transformer residual flux evaluation TRAFOSWT

12.20.1

Identification

Function description
Transformer residual flux evaluation
12.20.2

Functionality

To mitigate inrush currents, a power transformer is ideally energized at a phase angle where the
dynamic flux (from the source voltage) matches the residual flux in the core. TRAFOSWT estimates
the residual fluxes in the core(s) of a three-phase power transformer by integrating the voltage on the
windings during de-energization. Based on the estimated residual fluxes and other parameters of the
transformer and the power system, it provides optimal target making angles, for the next energization
to the receiver functions.
AC
source
IEC21000982 V1 EN-US
Figure 144: Example- single-line diagram of controlled switching system for power transformer
As an example,
power transformer can be connected to the high voltage grid (represented by a three-phase AC
source) through circuit breaker CB
measures the load side voltage or the transformer LV side voltage. For controlled switching of the
transformer, CB
When CB
Using the output signal of VT
the limb voltages. Based on these residual fluxes, the TRAFOSWT function provides switching
angles for the next controlled closing operation.
Technical Manual
Bus 1
CB
1
VT
1
Figure 144 shows a simple single-line diagram of a power system. A three-phase
is assumed open, that is, the LV side of the transformer is in no-load condition.
2
is opened a certain residual magnetic flux will remain in each core of the transformer.
1
, TRAFOSWT estimates the residual fluxes by numerical integration of
2
© 2021 Hitachi Energy. All rights reserved.
IEC 61850
identification
TRAFOSWT
Power
Transformer
HV LV
. The source voltage is measured using VT
1
GUID-846AA953-A27B-439E-83FA-6B327C254281 v1
GUID-33B6B021-7657-4733-9991-8790D4CF8948 v1
GUID-CF20E3B4-90D7-4C91-8A2D-C930EC1A689A v1
Bus 2
CB
2
VT
2
whereas VT
1
Section 12
Monitoring
2
321