powerfactory emt model3

8/10/2019 PowerFactory EMT Model3

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- Polynomial: the saturation curve is approximated by a polynomial of user-defined

order. The polynomial fits asymptotically into the piecewise linear definition.

- ,M sati Magnetizing Current pu

-M Magnetizing Flux pu

-M

L Linear Reactance pu

-0 This parameter is automatically calculated to

that the polynomial characteristic fits the

saturated reactance in full saturation and

transits steadily in to the piece-wise linear

characteristic at the knee point. Pu

- ksat Saturation exponent, i.e. polynomial degree pu

Figure 4.23 Two slope and polynomial saturation curves


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Parameter Description Unit

Knee Flux Knee-point of asymptotic piece-wise linear characteristic.Typical value around 1.1 to 1.2 times the rated flux.

p.u.

Linear (unsaturated)

Reactance

Magnetizing reactance for unsaturated conditions Lunsa.

In p.u. values, the linear reactance is equal to the

reciprocal of the magnetizing current (reactance part of

the exciting current)

p.u.

Saturated Reactance Magnetizing reactance for saturated condition Lsat. p.u.

Saturation Exponent

Exponent of polynomial representation (ksat). Typical

values are 9, 13, and 15. The higher the exponent thesharper, the saturation curves.

-

- Current/Flux values: The user can also define the saturation curve in terms of

measured current-flux values and select between a piecewise linearor spline interpolation.

The base quantities of the p.u. values in the current-flux table are also referred to the peak

values of the corresponding nominal variables:

3[ ][ ] 2 103 [ ]

base

basebase

S MVAI A

U kV=

3[ ] / 3[ ] 2 102 [ ]

basebase

base

U kVV s

f kHz =

The zero sequence magnetizing reactance strongly depends on the construction

characteristic of the transformer core (three-legged, five-legged, shell-type, etc.) and its

vector group. Figure below shows the equivalent circuit for the zero sequence.

Table 4.2 Basic data of the two-slope and polynomial saturation characteristics

Figure 4.24 Equivalent circuit for the zero sequence


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Transformer with delta-connected windings

If the transformer has delta-connected windings, then any zero sequence excitation

approximates a zero-sequence short-circuit, as the delta-connected winding short-circuits the

zero sequence current. In that case there is no need to represent zero sequence saturation.

Transformer without delta-connected windings

If the transformer type does not have delta-connected windings, then the zero-

sequence excitation current results generally higher than the positive-sequence excitation

current and strongly depends on the core type.

To account for the higher zero-sequence linear exciting current when no delta-

connected winding is available, PowerFactory allows for the definition of linear (unsaturated)

zero-sequence magnetizing impedance. This zero-sequence magnetizing impedance and its

R/X ratio is defined in the load flow page (TypTr2nLoad flow); the parameters are made

available depending on the vector group (i.e. hidden in case of delta-connected winding).

To account for the core type dependency of the zero-sequence saturation

characteristic, the transformer model supports the following two options in the EMT-

simulation page:

3 Limbs core: use this option for three-legged core designs. In this core type, the

fluxes are roughly equal in the three legs and must therefore return outside the core through

the air-gap and the tank. Because of the fact that the air-gap and the tanks are no-magnetic,

the zero-sequence magnetizing current is nearly linear and therefore the model uses the linear

zero-sequence magnetizing impedance defined in the load flow page. In other words, it does

not consider zero-sequence saturation effects.

5 Limbs core: use this option for five-legged and shell-type cores. As the zero-

sequence fluxes return inside the core, the model uses the saturation characteristic (of the

positive sequence) in the zero-sequence magnetizing reactance as well.

4.3.4.2.

Three-winding Transformer (3-phase)

In PowerFactoryeach winding of a transformer can have taps, however only one of

the tap changers can be controlled in the load-flow calculation. The adjustment of the taps


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can be set in the load-flow of the transformer type or can be enabled for automatic control

before run load-flow solution.

For a three-winding transformer, the third winding is referred to the minimum rated

power of the other two windings. For example, for a 60/60/10 MVA, 132/22/11 kV

transformer, a value of 10% is specified both for the HV-MV and LV-HV positive-sequence

short-circuit voltages. The impedance value (referred to HV-side) of the impedance between;

- the HV and MV terminals is;

( )2

1320.1 29.04

60

kVprimary

MVA =

- the HV and LV terminals is

( )2

1320.1 174.24

10

kVprimary

MVA =

Figure 4.25 PF Positive-sequence model of the 3-winding transformer, taps modelled

Figure 4.26 PF Positive-sequence model of the 3-winding transformer, taps modelled


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The model diagrams Figure 4.10 and Figure 4.11 and input parameters in Positive,

Negative and Zero sequence models will be list in table below:

Parameter Unit Description

Ur,T,HVUr,T,HVUr,T,HV

kV Rated Voltage on HV/MV/LV side

Sr,T,HVSr,T,HVSr,T,HV

MVA Rated Power for the windings on HV/MV/LV side

usc,HV-MVusc,MV-LVusc,LV-HV

% Relative short-circuit voltage of paths HV-MV, MV-LV, LV-HV

PCu,HV-MVPCu,MV-LVPCu,LV-HV

kW Copper losses of path HV-MV, MV-LV, LV-HV

ur.sc,HV-MVur,sc,MV-LVur,sc,LV-HV

%Relative short-circuit voltage, resistive part of paths HV-MV, MV-

LV, LV-HV

X/RHV-MV

X/RMV-LVX/RLV-HV

Relative short-circuit voltage ratio, X/R ratio of path HV-MV, MV-

LV, LV-HV

i0 % No-Load current, related to rate current at HV side

PFe kW No-Load losses

It is possible to use manufacturers or any other available measurement data for load-

flow calculation.

Table 4.3 Positive and Negative sequence in put parameter

Figure 4.27 Measurement data input page for three-winding transformer

powerfactory emt model3

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