problems in modeling a three-phase four-winding transformer YNyn0yn0+d5 with three "multi-winding transformer" in zero sequence component

I want to model a three-phase four-winding transformer YNyn0yn0+d5 with two low voltage windings (yn0yn0) and a compensation winding (d5) using Simscape Electrical. The transformer is a 5 limbs transformer. Since the transformer has four windings, I had to connect three single-phase transformers (model in Simulink: multi-winding transformer) in star and delta configurations respectively.

From the transformer test report, I have calculated the parameters of the T-equivalent circuit diagram. Here, I had to calculate the longitudinal impedances of the compensation winding using the measurement of zero sequence component, because it was not measured in the short-circuit test.

The simulated values of the open-circuit and short-circuit tests in the positive sequence component agree very well with the values from the transformer test report.

My problem:

In the measurement of zero sequence component, I only get matching values for the measurement that I used for the calculation of the compensation winding (HV supply, compensation winding short-circuited). In the further zero sequence measurements (additionally, one LV winding short-circuited), the short-circuit voltage is five times too high.

Questions:

Is there possibly a coupling in the transformer only in the zero sequence component?

Or does anyone already know this problem?

Or does anyone have an idea of how I can model the transformer using other Simulink models?

Answer 1

[Umar]

Hi Ria,

The behavior described by you where measurements align when using the compensation winding but deviate when other windings are short-circuited, suggests the presence of coupling effects. Coupling in transformers can occur due to various factors such as mutual inductance between windings, leakage inductance, and inter-winding capacitance.

So, my suggestion would be analyzing the transformer's coupling characteristics. One approach i will suggest is to simulate the transformer model in MATLAB to understand the coupling effects better. By modeling the transformer with its winding configurations and parameters, you can simulate different scenarios and observe the impact of coupling on zero sequence measurements. Here is an example of code to help you further.

% Define transformer parameters

L1 = 0.1; % Inductance of winding 1

L2 = 0.2; % Inductance of winding 2

M = 0.05; % Mutual inductance between windings

% Create transformer model

A = [L1 M; M L2]; % Mutual inductance matrix

[V, D] = eig(A); % Eigen-decomposition for coupling analysis

% Display results

disp('Eigenvalues (Coupling Effects):');

disp(diag(D));

disp('Eigenvectors (Coupling Modes):');

disp(V);

Analyzing the eigenvalues and eigenvectors of the mutual inductance matrix, you can gain insights into the coupling effects and their influence on zero sequence measurements. Understanding these coupling phenomena can help in interpreting the discrepancies observed in your measurements and devising appropriate corrective measures.

Hope this will help resolve your problem.

Answer 2

[Umar]

To answer question about does anyone have an idea of how I can model the transformer using other Simulink models?

Here is a simple example of how you can model a transformer in Simulink using an ideal transformer block:

% Create a Simulink model

model = 'Transformer_Model';

open_system(new_system);

% Add an ideal transformer block

add_block('powerlib/Ideal Transformer', [model '/Ideal Transformer']);

% Connect input and output ports

add_line(model, 'In1/1', 'Ideal Transformer/1');

add_line(model, 'Ideal Transformer/1', 'Out1/1');

% Set parameters like turns ratio, resistance, etc., in the block parameters

set_param([model '/Ideal Transformer'], 'turns_ratio', '1:2');

% Save and simulate the model

save_system(model);

sim(model);

If you follow this approach and customize the parameters as needed, you can effectively model a transformer in Simulink using other Simulink models.