Fix zero sequence floating in some scenarios

power_grid_model_c/power_grid_model/include/power_grid_model/common/common.hpp

@@ -84,6 +84,8 @@ constexpr DoubleComplex y_link{g_link, g_link};
 constexpr double default_source_sk = 1e10; // 10 GVA 10^10
 constexpr double default_source_rx_ratio = 0.1;
 constexpr double default_source_z01_ratio = 1.0;
+// transformer low susceptance ratio for floating zero sequence
+constexpr double transformer_low_susceptance_ratio = 1e-8;
 
 // some usual vector
 using DoubleVector = std::vector<double>;

power_grid_model_c/power_grid_model/include/power_grid_model/component/transformer.hpp

@@ -258,6 +258,21 @@ class Transformer : public Branch {
             param0.ytt() = y0_series;
         }
 
+        auto const low_susceptance = -transformer_low_susceptance_ratio * sn_ / base_power_3p / uk_;
+        bool const zero_seq_available_from =
+            (winding_from_ == WindingType::wye_n && winding_to_ == WindingType::wye_n) ||
+            (winding_from_ == WindingType::wye_n && winding_to_ == WindingType::delta) ||
+            winding_from_ == WindingType::zigzag_n;
+        bool const zero_seq_available_to = (winding_to_ == WindingType::wye_n && winding_from_ == WindingType::wye_n) ||
+                                           (winding_to_ == WindingType::wye_n && winding_from_ == WindingType::delta) ||
+                                           winding_to_ == WindingType::zigzag_n;
+        if (!zero_seq_available_from && from_status()) {
+            param0.yff() += DoubleComplex{0.0, low_susceptance};
+        }
+        if (!zero_seq_available_to && to_status()) {
+            param0.ytt() += DoubleComplex{0.0, low_susceptance};
+        }
+
         // for the rest param0 is zero
         // calculate yabc
         ComplexTensor<asymmetric_t> const sym_matrix = get_sym_matrix();
@@ -269,6 +284,7 @@ class Transformer : public Branch {
             y012 << param0.value[i], 0.0, 0.0, 0.0, param1.value[i], 0.0, 0.0, 0.0, param2.value[i];
             param.value[i] = dot(sym_matrix, y012, sym_matrix_inv);
         }
+
         return param;
     }
 };

tests/cpp_unit_tests/test_transformer.cpp

@@ -92,6 +92,11 @@ TEST_CASE("Test transformer") {
     double const r_series = 100e3 * 10e3 * 10e3 / 30e6 / 30e6;
     DoubleComplex const z_series = r_series + 1.0i * std::sqrt(z_series_abs * z_series_abs - r_series * r_series);
     DoubleComplex const y = 1.0 / z_series / base_y;
+    auto const low_susceptance = -transformer_low_susceptance_ratio * input.sn / base_power_3p / input.uk;
+    DoubleComplex const low_admittance = 1.0i * low_susceptance;
+    ComplexTensor<asymmetric_t> y012;
+    y012 << low_admittance, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0;
+    ComplexTensor<asymmetric_t> low_admittance_asym = dot(get_a(), y012, get_a_inv());
 
     // sym
     std::vector<BranchCalcParam<symmetric_t>> vec_sym;
@@ -125,10 +130,15 @@ TEST_CASE("Test transformer") {
     vec_asym.push_back({{y1, -y1, -y1, y1}});
     // Dyn11
     vec_asym.push_back({{y2, y3t, y3, y1}});
+    vec_asym.back().yff() += low_admittance_asym;
     // Yd1
     vec_asym.push_back({{y2, y3, y3t, y2}});
+    vec_asym.back().yff() += low_admittance_asym;
+    vec_asym.back().ytt() += low_admittance_asym;
     // Yy12
     vec_asym.push_back({{y2, -y2, -y2, y2}});
+    vec_asym.back().yff() += low_admittance_asym;
+    vec_asym.back().ytt() += low_admittance_asym;
     // YNyn2
     vec_asym.push_back({{y1, y4, y4t, y1}});
 
@@ -469,8 +479,10 @@ TEST_CASE("Test Transfomer - Test grounding - Dyn11") {
 
     // Zero sequence
     DoubleComplex const z_grounding_to = (input.r_grounding_to + 1i * input.x_grounding_to) * base_y_to;
+    auto const low_susceptance = -transformer_low_susceptance_ratio * input.sn / base_power_3p / input.uk;
+    DoubleComplex const low_admittance = 1.0i * low_susceptance;
 
-    DoubleComplex const y_0_ff = 0.0;
+    DoubleComplex const y_0_ff = low_admittance;
     DoubleComplex const y_0_ft = 0.0;
     DoubleComplex const y_0_tf = 0.0;
     DoubleComplex const y_0_tt = (1.0 / (z_1_series + 3.0 * z_grounding_to)) + y_1_shunt;
@@ -578,8 +590,10 @@ TEST_CASE("Test Transfomer - Test grounding - Yzn11") {
 
     // Zero sequence
     DoubleComplex const z_grounding_to = (input.r_grounding_to + 1i * input.x_grounding_to) * base_y_to;
+    auto const low_susceptance = -transformer_low_susceptance_ratio * input.sn / base_power_3p / input.uk;
+    DoubleComplex const low_admittance = 1.0i * low_susceptance;
 
-    DoubleComplex const y_0_ff = 0.0;
+    DoubleComplex const y_0_ff = low_admittance;
     DoubleComplex const y_0_ft = 0.0;
     DoubleComplex const y_0_tf = 0.0;
     DoubleComplex const y_0_tt = (1.0 / (z_1_series * 0.1 + 3.0 * z_grounding_to));
@@ -687,8 +701,10 @@ TEST_CASE("Test Transformer - Dyn11 - tap_max and tap_min flipped") {
 
     // Zero sequence
     DoubleComplex const z_grounding_to = (input.r_grounding_to + 1i * input.x_grounding_to) * base_y_to;
+    auto const low_susceptance = -transformer_low_susceptance_ratio * input.sn / base_power_3p / input.uk;
+    DoubleComplex const low_admittance = 1.0i * low_susceptance;
 
-    DoubleComplex const y_0_ff = 0.0;
+    DoubleComplex const y_0_ff = low_admittance;
     DoubleComplex const y_0_ft = 0.0;
     DoubleComplex const y_0_tf = 0.0;
     DoubleComplex const y_0_tt = (1.0 / (z_1_series + 3.0 * z_grounding_to)) + y_1_shunt;

tests/data/power_flow/floating_zero_sequence/asym_output.json

@@ -0,0 +1,23 @@
+{
+  "version": "1.0",
+  "type": "asym_output",
+  "is_batch": false,
+  "attributes": {},
+  "data": {
+    "node": [
+      {"id": 1, "energized": 1, "u_pu": [0.96852205547155257, 1.0206083148508613, 0.98784175476403047], "u": [5591.764694425905, 5892.4848531631515, 5703.307030297653], "u_angle": [-0.040742566360496869, -2.1441345251331376, 2.0033567593816968], "p": [1314971.9340071543, 1691451.3014948303, 2993576.7644979917], "q": [989444.74610297778, -743175.16349568975, 263988.08450858196]},
+      {"id": 2, "energized": 1, "u_pu": [0.94750841657660867, 0.99621887552137245, 1.0263746319452911], "u": [5470.4423936994108, 5751.6723595405065, 5925.7767004301686], "u_angle": [2.5081331635193447, 0.47812215756400461, -1.688791344148733], "p": [1.2548582932767838e-08, 1.302774370913572e-08, 2.5285099200928076e-08], "q": [1.9214234326283912e-09, -2.5139098505749905e-08, 6.7944203835937232e-09]},
+      {"id": 3, "energized": 1, "u_pu": [0.95328569878941172, 1.0317279231128014, 0.98298950273421282], "u": [5503.7975481068734, 5956.6839413962934, 5675.2925401417415], "u_angle": [-0.07860954164747154, -2.1823201253199591, 1.8951713864745763], "p": [-999999.99999999907, -1000000.0000000133, -4000000.0000000075], "q": [8.0491169285323849e-10, 2.3166653780511599e-08, 7.1054273576010019e-09]}
+    ],
+    "transformer": [
+      {"id": 4, "energized": 1, "loading": 0.6498356896389379, "p_from": [1314971.9340071543, 1691451.3014948303, 2993576.7644979917], "q_from": [989444.74610297778, -743175.16349568975, 263988.08450858196], "i_from": [294.29822170602006, 313.53774185504125, 526.92132474738628], "s_from": [1645646.4057680501, 1847516.3947758083, 3005194.0958455205], "p_to": [-2308548.6844076109, -1006423.2333675779, -2685028.0822247765], "q_to": [-978312.09287856543, -60818.915340574335, 760155.06177346141], "i_to": [458.33362520409179, 175.29844576248311, 470.91844756917072], "s_to": [2507287.6937744003, 1008259.2251624847, 2790557.5644081375]},
+      {"id": 5, "energized": 1, "loading": 0.63061044833450686, "p_from": [2308548.684407624, 1006423.2333675909, 2685028.0822248021], "q_from": [978312.0928785674, 60818.915340549247, -760155.06177345454], "i_from": [458.33362520409406, 175.29844576248513, 470.91844756917453], "s_from": [2507287.6937744129, 1008259.2251624962, 2790557.5644081603], "p_to": [-999999.99999999907, -1000000.0000000133, -4000000.0000000075], "q_to": [8.0491169285323849e-10, 2.3166653780511599e-08, 7.1054273576010019e-09], "i_to": [181.69272965790074, 167.87864016931633, 704.80948280775453], "s_to": [999999.99999999907, 1000000.0000000133, 4000000.0000000075]}
+    ],
+    "asym_load": [
+      {"id": 6, "energized": 1, "p": [1000000, 1000000, 4000000], "q": [0, 0, 0], "i": [181.69272965790091, 167.87864016931411, 704.80948280775306], "s": [1000000, 1000000, 4000000], "pf": [1, 1, 1]}
+    ],
+    "source": [
+      {"id": 7, "energized": 1, "p": [1314971.9340071541, 1691451.3014948303, 2993576.7644979917], "q": [989444.74610297778, -743175.16349568986, 263988.08450858208], "i": [294.29822170602, 313.53774185504125, 526.92132474738628], "s": [1645646.4057680501, 1847516.3947758083, 3005194.0958455205], "pf": [0.79906104336759709, 0.91552708613450973, 0.99613424924413729]}
+    ]
+  }
+}

tests/data/power_flow/floating_zero_sequence/asym_output.json.license

@@ -0,0 +1,3 @@
+SPDX-FileCopyrightText: Contributors to the Power Grid Model project <[email protected]>
+
+SPDX-License-Identifier: MPL-2.0

tests/data/power_flow/floating_zero_sequence/input.json

@@ -0,0 +1,26 @@
+{
+  "version": "1.0",
+  "type": "input",
+  "is_batch": false,
+  "attributes": {},
+  "data": {
+    "node": [
+      {"id": 1, "u_rated": 10000},
+      {"id": 2, "u_rated": 10000},
+      {"id": 3, "u_rated": 10000}
+    ],
+    "transformer": [
+      {"id": 4, "from_node": 1, "to_node": 2, "from_status": 1, "to_status": 1, "u1": 10000, "u2": 10000, "sn": 10000000, "uk": 0.050000000000000003, "pk": 0, "i0": 0, "p0": 0, "winding_from": 1, "winding_to": 2, "clock": 7, "tap_side": 0, "tap_pos": 0, "tap_min": 0, "tap_max": 0, "tap_nom": 0, "tap_size": 0},
+      {"id": 5, "from_node": 2, "to_node": 3, "from_status": 1, "to_status": 1, "u1": 10000, "u2": 10000, "sn": 10000000, "uk": 0.050000000000000003, "pk": 0, "i0": 0, "p0": 0, "winding_from": 2, "winding_to": 1, "clock": 5, "tap_side": 0, "tap_pos": 0, "tap_min": 0, "tap_max": 0, "tap_nom": 0, "tap_size": 0}
+    ],
+    "asym_load": [
+      {"id": 6, "node": 3, "status": 1, "type": 0, "p_specified": [1000000, 1000000, 4000000], "q_specified": [0, 0, 0]}
+    ],
+    "source": [
+      {"id": 7, "node": 1, "status": 1, "u_ref": 1, "sk": 100000000, "rx_ratio": 0, "z01_ratio": 1}
+    ],
+    "fault": [
+      {"id": 8, "status": 1, "fault_type": 2, "fault_phase": 6, "fault_object": 3}
+    ]
+  }
+}

tests/data/power_flow/floating_zero_sequence/input.json.license

@@ -0,0 +1,3 @@
+SPDX-FileCopyrightText: Contributors to the Power Grid Model project <[email protected]>
+
+SPDX-License-Identifier: MPL-2.0

tests/data/power_flow/floating_zero_sequence/params.json

@@ -0,0 +1,7 @@
+{
+  "calculation_method": [
+    "newton_raphson"
+  ],
+  "rtol": 2e-07,
+  "atol": 1e-07
+}

tests/data/power_flow/floating_zero_sequence/params.json.license

@@ -0,0 +1,3 @@
+SPDX-FileCopyrightText: Contributors to the Power Grid Model project <[email protected]>
+
+SPDX-License-Identifier: MPL-2.0

tests/data/short_circuit/floating_zero_sequence_two_phase_short_circuit/input.json

@@ -0,0 +1,26 @@
+{
+  "version": "1.0",
+  "type": "input",
+  "is_batch": false,
+  "attributes": {},
+  "data": {
+    "node": [
+      {"id": 1, "u_rated": 10000},
+      {"id": 2, "u_rated": 10000},
+      {"id": 3, "u_rated": 10000}
+    ],
+    "transformer": [
+      {"id": 4, "from_node": 1, "to_node": 2, "from_status": 1, "to_status": 1, "u1": 10000, "u2": 10000, "sn": 10000000, "uk": 0.050000000000000003, "pk": 0, "i0": 0, "p0": 0, "winding_from": 1, "winding_to": 2, "clock": 7, "tap_side": 0, "tap_pos": 0, "tap_min": 0, "tap_max": 0, "tap_nom": 0, "tap_size": 0},
+      {"id": 5, "from_node": 2, "to_node": 3, "from_status": 1, "to_status": 1, "u1": 10000, "u2": 10000, "sn": 10000000, "uk": 0.050000000000000003, "pk": 0, "i0": 0, "p0": 0, "winding_from": 2, "winding_to": 1, "clock": 5, "tap_side": 0, "tap_pos": 0, "tap_min": 0, "tap_max": 0, "tap_nom": 0, "tap_size": 0}
+    ],
+    "asym_load": [
+      {"id": 6, "node": 3, "status": 1, "type": 0, "p_specified": [1000000, 1000000, 4000000], "q_specified": [0, 0, 0]}
+    ],
+    "source": [
+      {"id": 7, "node": 1, "status": 1, "u_ref": 1, "sk": 100000000, "rx_ratio": 0, "z01_ratio": 1}
+    ],
+    "fault": [
+      {"id": 8, "status": 1, "fault_type": 2, "fault_phase": 6, "fault_object": 3}
+    ]
+  }
+}

tests/data/short_circuit/floating_zero_sequence_two_phase_short_circuit/input.json.license

@@ -0,0 +1,3 @@
+SPDX-FileCopyrightText: Contributors to the Power Grid Model project <[email protected]>
+
+SPDX-License-Identifier: MPL-2.0

tests/data/short_circuit/floating_zero_sequence_two_phase_short_circuit/params.json

@@ -0,0 +1,8 @@
+{
+  "calculation_method": [
+    "iec60909"
+  ],
+  "rtol": 1e-07,
+  "atol": 1e-07,
+  "short_circuit_voltage_scaling": "maximum"
+}

tests/data/short_circuit/floating_zero_sequence_two_phase_short_circuit/params.json.license

@@ -0,0 +1,3 @@
+SPDX-FileCopyrightText: Contributors to the Power Grid Model project <[email protected]>
+
+SPDX-License-Identifier: MPL-2.0

tests/data/short_circuit/floating_zero_sequence_two_phase_short_circuit/sc_output.json

@@ -0,0 +1,26 @@
+{
+  "version": "1.0",
+  "type": "sc_output",
+  "is_batch": false,
+  "attributes": {},
+  "data": {
+    "node": [
+      {"id": 1, "energized": 1, "u_pu": [1.0999999999999999, 0.72758161054276271, 0.72758161054276194], "u": [6350.8529610858823, 4200.6943870428549, 4200.6943870428504], "u_angle": [2.512019772889243e-16, -2.4278682746450277, 2.4278682746450273]},
+      {"id": 2, "energized": 1, "u_pu": [0.96250000511909928, 0.96249999477409609, 0.27500000037381495], "u": [5556.9963705052814, 5556.9963107783778, 1587.7132424296924], "u_angle": [2.998245085844498, 0.14334756929664444, -1.5707963457989134]},
+      {"id": 3, "energized": 1, "u_pu": [1.0999999999999994, 0.5499999999999996, 0.5499999999999996], "u": [6350.8529610858805, 3175.4264805429393, 3175.4264805429393], "u_angle": [5.6520444890008018e-16, -3.1415926535897927, -3.1415926535897927]}
+    ],
+    "transformer": [
+      {"id": 4, "energized": 1, "i_from": [1.6705560276655585e-12, 2749.9999999999986, 2750.0000000000005], "i_from_angle": [3.1415926535897931, -3.1415926535897931, 5.9670114874447551e-16], "i_to": [1587.7132402714715, 1587.7132402714694, 3175.426480542942], "i_to_angle": [3.1415926535897931, 3.1415926535897922, 7.7513752992010926e-16]},
+      {"id": 5, "energized": 1, "i_from": [1587.7132402714719, 1587.7132402714703, 3175.426480542942], "i_from_angle": [4.1340668262405803e-15, -1.0335167065601461e-15, -3.1415926535897927], "i_to": [1.6412165780830384e-12, 2750.0000000000009, 2750.0000000000005], "i_to_angle": [1.552048524251098, -2.9835057437223771e-16, -3.1415926535897913]}
+    ],
+    "asym_load": [
+      {"id": 6, "energized": 0, "i": [0, 0, 0], "i_angle": [0, 0, 0]}
+    ],
+    "source": [
+      {"id": 7, "energized": 1, "i": [2.2886189511086415e-12, 2749.9999999999995, 2750.0000000000014], "i_angle": [-2.3421109143694845, -3.1415926535897927, 1.1934022974889508e-15]}
+    ],
+    "fault": [
+      {"id": 8, "energized": 1, "i_f": [0, 2750.0000000000009, 2750.0000000000009], "i_f_angle": [0, -3.1415926535897927, 4.4752586155835661e-16]}
+    ]
+  }
+}

tests/data/short_circuit/floating_zero_sequence_two_phase_short_circuit/sc_output.json.license

@@ -0,0 +1,3 @@
+SPDX-FileCopyrightText: Contributors to the Power Grid Model project <[email protected]>
+
+SPDX-License-Identifier: MPL-2.0

tests/data/short_circuit/single_phase_to_ground_c_maximum/params.json

@@ -1,6 +1,6 @@
 {
   "calculation_method": "iec60909",
-  "rtol": 1e-08,
-  "atol": 1e-08,
+  "rtol": 2e-06,
+  "atol": 1e-03,
   "short_circuit_voltage_scaling": "maximum"
 }

tests/data/short_circuit/single_phase_to_ground_c_minimum/params.json

@@ -1,6 +1,6 @@
 {
   "calculation_method": "iec60909",
-  "rtol": 1e-08,
-  "atol": 1e-08,
+  "rtol": 2e-06,
+  "atol": 1e-03,
   "short_circuit_voltage_scaling": "minimum"
 }

tests/data/short_circuit/two_phase_to_ground_c_maximum/params.json

@@ -1,6 +1,6 @@
 {
   "calculation_method": "iec60909",
-  "rtol": 1e-08,
-  "atol": 1e-08,
+  "rtol": 2e-06,
+  "atol": 1e-03,
   "short_circuit_voltage_scaling": "maximum"
 }

tests/data/short_circuit/two_phase_to_ground_c_minimum/params.json

@@ -1,6 +1,6 @@
 {
   "calculation_method": "iec60909",
-  "rtol": 1e-08,
-  "atol": 1e-08,
+  "rtol": 2e-06,
+  "atol": 1e-03,
   "short_circuit_voltage_scaling": "minimum"
 }