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            ARTEMiS/SSN OLTC



This block implements a 2-winding transformer with continuously variable turn ratio in SSN, with saturation. The model has a variable secondary inductance and resistance as well as turn-ratio which can be modified during real-time simulation.

The secondary winding is on the side marked with 'TAP' (with PM-port 'b' and 'd'). The tapped winding resistance and inductance are given as input signals to the block because they typically vary with the turn-ratio.

The saturation is specified as a 2-slope inductance with unsaturated and saturated regions.



Connection type: let the user select between 4 terminal transformer, 3 terminal (with either the primary or secondary tapped winding grounded) or 2 terminal transformer with both windings grounded on one side.

Primary winding resistance and inductance (Ohms ,H).

Core resistance (Ohms) :As seen from the primary

Enable saturation

Unsaturated magnetization inductance (H): As seen from the primary.

Saturated magnetization inductance (H): If Enable saturation is checked, this is the saturated core inductance when the flux is above the Flux Saturation Threshold specified by the user, as seen from the primary.

Flux Saturation Threshold (Wb): the core flux above which (in absolute value) the transformer goes into saturation.

Sample Time (s): sample time of the model in seconds.

Generate internal S-function code (Required once): pressing this button is required once to compile and generate the C code of the S-function builder SSN Custom User Code. (Note: this parameter is not present on the new version of SSN OLTC without S-function builder)

Input and Output signals

Simulink connection points

Signal inputs:

   1st signal: secondary winding resistance (Ohms)

   2nd signal: secondary winding inductance (H)

   3rd signal: transformer turn ratio n (V_secondary_tapped=n*V_primary)

   4th signal:  when set to 1, uses the Backward Euler method for solver. This can be used dynamically during simulation for example to damp numerical oscillations after switching events or after tap changes.

Signals outputs:

   1st signal: Primary and secondary windings currents in Amperes and transformer core flux (Wb)

Physical Modeling connection points

a,c: primary connection points.

b,d: secondary connection points (with TAP on the block).



ssn_oltc.mdl is an example that uses the SSN OLTC transformer in a current transformer application. Note the very low core inductance in this type of application. The model is designed to compare the SSN OLTC to an equivalent one made in SPS using switches. Typical real-life OLTC can have hundreds of switches attached to them and the method used by SPS cannot be extended in general. By opposition, the SSN OLTC is not composed of real switches as it simply recompute its equations according to the change in inductances and turn-ratio. It can therefore be used in real-time applications without any losses in computing performances.


  1. Dufour, J. Mahseredjian , J. Bélanger, “A Combined State-Space Nodal Method for the Simulation of Power System Transients”, IEEE Transactions on Power Delivery, Vol. 26, no. 2, April 2011 (ISSN 0885-8977), pp. 928-935

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