Description

Current transformer.

Table of Contents

Mask and Parameters

General tab:

General Parameters

Parameter	Description
Flux-current characteristic model	Model saturation only or saturation with hysteresis
Iteration Enable	Enable or disable iteration to achieve more accurate results at the expense of computation time when the saturation segment changes
Base primary voltage (rmsLL)	Base value pour PU conversion (kV)
Base power (total)	Base value pour PU conversion (MVA)
Base frequency	Base value pour PU conversion (Hz)
Rsn	Secondary side leakage resistance (ohm or pu)
Lsn	Secondary side leakage inductance (henry or pu)

Stray Capacitances

C1p, C2p: Values of the stray capacitance on the primary side before and after the leakage impedance (farad or pu)

Primary Winding Parameters

Np	Number of turns (default: np = 1)
Rp, Lp	Leakage resistance (ohm or pu) and inductance (henry or pu)
Rm	Resistance (ohm) representing magnetization losses

Secondary Winding Parameters

Ns	Number of turns (default: ns = 5000)
Rs, Lis	Leakage resistance (ohm or pu) and inductance (henry or pu)
Cs	Stray capacitance (farad or pu)
Rsc	Resistance in parallel with Cs (ohm or pu)
Rsa, Lsa	Load resistance (ohm) and load inductance (henry or pu)

Tertiary Winding Parameters

Nt	Number of turns (default: ns = 8660)
Rt, Lt	Leakage resistance (ohm or pu) and inductance (henry or pu)
Ct	Stray capacitance (farad or pu)
Rtc	Resistance in parallel with Ct (ohm or pu)
Rta, Lta	Load resistance (ohm) and load inductance (henry or pu)

Saturation tab:

Saturation parameters:

Number of points	Number of segments of the current-flux saturation curve; only the positive part of the curve must be specified, the negative part being completed by symmetry
Saturation current	The peak value of the current (in ampere or pu) for each segment of the saturation curve. The origin (0.0,0.0) is implied. The number of segments must be equal to the parameter “number of points”
Saturation flux	The peak value of the flux (in volt-second or pu) for each segment of the saturation curve. The origin (0.0,0.0) is implied. The number of segments must be equal to the parameter “number of points”

Note that in this model, the saturation branch is located on the primary side of the transformer. Therefore, the saturation current and flux parameters should be referred to that side.

Configuration tab:

Configuration parameters:

Model type	Select either "Transducer" or "Network elements" model type
Transformer windings connection	Select the type of windings connection as show in the figure: "Secondary Yg", "Secondary Delta lag", "Secondary Delta lead", "Secondary Yg+Res. Ld" or "SecondaryY+Tert. Dg"
Polarity criterion	When the Transformer windings connection is "SecondaryY+Tert. Dg", select either "Current" or "Voltage" as the polarity criterion

Hysteresis tab

Hysteresis Parameters

The main hysteresis cycle is characterized by four parameters. It is measured in DC so as not to include the Foucault losses, which are considered by the parallel resistance (Rm). The initial trajectory is characterized by only one parameter, the initial flux. Two other special parameters serve to minimize the generation of internal nested loops, and their corresponding trajectories, saved in memory (e.g. the loops that are too small will be ignored and their trajectories modelized by a straight line segment).

This is useful since their number must be limited (100 which suffices in most simulated cases). Above this cycle (limited to ±Is), the saturation zone is entered. The saturation is then characterized either by a series of points on the curve or by an inductance that the curve approaches asymptotically. In this last case, the model generates automatically segments (in the positive and negative saturation zone) of equal length (Is).

Saturation data type	Determines if the saturation curve is calculated by the model or defined by a series of segments (Equation, Curve)
Air core inductance	Value of the saturation inductance that the curve approaches asymptotically (henry or pu)
Slope at Ic	Flux slope at coercive current (henry or pu)
Coercitive current - Ic	Positive coercive current at null flux (A or pu)
Saturation current - Is	Current value of the first point in the saturation zone (A or pu)
Current tolerance	Special parameter limiting the generation of minor nested loops. When the magnetizing current values at the last inversion point and the preceding inversion point are closer than the specified tolerance (in % of Ic), it is assumed that there is a displacement on a trajectory represented by a straight line segment.
Remnant flux - Φr	Positive remnant flux at null current (V.s or pu)
Saturation flux - Φs	Flux value of the first point in the saturation zone (V.s or pu)
Flux tolerance	Special parameter limiting the generation of minor nested loops. When the flux values at the last inversion point and the preceding inversion point are closer than the specified tolerance (in % of Φs), it is assumed that there is a displacement on the current loop.
Initial flux (peak)	Initial flux determining initial trajectory which is calculated by supposing that it has an inversion point on the main cycle (V.s or pu)
Number of points	Number of segments of the current-flux saturation curve; only the positive part of the curve must be specified, the negative part being completed by symmetry
Saturation current:	Current for each segment of the saturation curve; the first value must be equal to Is (A or pu)
Saturation flux	Flux for each segment of the saturation curve; the first value must be equal to Φs (V.s or pu)

Ports, Inputs, Outputs and Signals Available for Monitoring

Ports

Net_1	Primary winding connection (supports only 3-phase connections)
Net_2	Secondary winding connection (supports only 3-phase connections)

Inputs

None

Outputs

None

Sensors

IPRIM(a,b,c)	Primary current for each phase (A)
VMAG(a,b,c)	Voltage in magnetization branch (V)
IMAG(a,b,c)	Magnetization current (A)
FLUX(a,b,c)	Mutual flux in the transformer (V.s)
VLOADSEC(a,b,c,n)	Load voltage on the secondary
ILOADSEC(a,b,c,n)	Load current on the secondary
ILOAD TERT(0)	Ground current on the tertiary

Note that in the current implementation, the polarity (sign) of the current measured by sensor IPRIM is reversed with respect to an external sensor measuring the current going into the primary windings.

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