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Fix short-circuit source impedance scaling #1547

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Fix short-circuit source impedance scaling #1547

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3 changes: 2 additions & 1 deletion power_grid_model_c/power_grid_model/include/power_grid_model/calculation_parameters.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -300,7 +300,8 @@ template <symmetry_tag sym_type> struct StateEstimationInput {
struct ShortCircuitInput {
DenseGroupedIdxVector fault_buses;
std::vector<FaultCalcParam> faults;
ComplexVector source; // Complex u_ref of each source
ComplexVector source; // Complex u_ref of each source
DoubleVector source_admittance_scaling; // Multiplier for source y_ref in short-circuit calculations

@nitbharambe nitbharambe Aug 28, 2026

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I believe if we just do the cabs(input.source[source_number]) at short_circuit_solver directly, we wont need to add source_admittance_scaling right? Lets remove so if thats the case

};

template <typename T>
Expand Down
8 changes: 8 additions & 0 deletions ...l_c/power_grid_model/include/power_grid_model/main_core/calculation_input_preparation.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -311,6 +311,7 @@ prepare_short_circuit_input(main_model_state_c auto const& state, ComponentToMat
sc_input[i].faults.resize(state.components.template size<Fault>());

sc_input[i].source.resize(state.math_topology[i]->n_source());
sc_input[i].source_admittance_scaling.resize(state.math_topology[i]->n_source());
}

comp_coup = ComponentToMathCoupling{.fault = std::move(fault_coup)};
Expand All @@ -324,6 +325,13 @@ prepare_short_circuit_input(main_model_state_c auto const& state, ComponentToMat
return std::pair{state.components.template get_item<Node>(source.node()).u_rated(), voltage_scaling};
});

// Source::calc_param() returns c * exp(j * angle). sk is defined at rated voltage, so its source-equivalent
// impedance scales with c and the corresponding admittance scales with 1 / c.
for (auto& input : sc_input) {
std::ranges::transform(input.source, input.source_admittance_scaling.begin(),
[](DoubleComplex const& u_ref) { return 1.0 / cabs(u_ref); });
}

// only now do we know where the fault objects are placed => resize to used only
for (auto& input : sc_input) {
auto const is_unused = [](FaultCalcParam const& param) {
Expand Down
23 changes: 20 additions & 3 deletions ...id_model_c/power_grid_model/include/power_grid_model/math_solver/short_circuit_solver.hpp
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Expand Up @@ -92,13 +92,31 @@ template <symmetry_tag sym> class ShortCircuitSolver {
auto& diagonal_element = mat_data_[diagonal_position];
auto& u_bus = output.u_bus[bus_number];

detail::add_sources<sym>(sources, bus_number, y_bus, input.source, diagonal_element, u_bus);
add_sources(sources, y_bus, input, diagonal_element, u_bus);

add_faults(faults, bus_number, y_bus, input, diagonal_element, u_bus, infinite_admittance_fault_counter,
fault_type, phase_1, phase_2);
}
}

static ComplexTensor<sym> source_admittance(YBus<sym> const& y_bus, ShortCircuitInput const& input,
Idx source_number) {
assert(input.source_admittance_scaling.empty() ||
input.source_admittance_scaling.size() == input.source.size());
double const scaling =
input.source_admittance_scaling.empty() ? 1.0 : input.source_admittance_scaling[source_number];
return scaling * y_bus.math_model_param().source_param[source_number].template y_ref<sym>();
}
Comment on lines +102 to +109

@nitbharambe nitbharambe Aug 28, 2026

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Nitpick: Could you please move the above comment of calculation_input_preparation regarding the reason to this place?

I would like a explaining docstring here along the lines:
"source admittance is calculated on sk for a specific u_ref for powerflow solvers within PGM.
However for generic short circuit calculation, sk is defined at rated voltage, so its source-equivalent impedance scales with c and the corresponding admittance scales with 1 / c = 1 / cabs(input.source[source_number])"


static void add_sources(IdxRange const& sources, YBus<sym> const& y_bus, ShortCircuitInput const& input,
ComplexTensor<sym>& diagonal_element, ComplexValue<sym>& u_bus) {
for (Idx const source_number : sources) {
ComplexTensor<sym> const y_source = source_admittance(y_bus, input, source_number);
diagonal_element += y_source;
u_bus += dot(y_source, ComplexValue<sym>{input.source[source_number]});
}
}

void add_faults(IdxRange const& faults, Idx bus_number, YBus<sym> const& y_bus, ShortCircuitInput const& input,
ComplexTensor<sym>& diagonal_element, ComplexValue<sym>& u_bus,
IdxVector& infinite_admittance_fault_counter, FaultType const& fault_type, IntS phase_1,
Expand Down Expand Up @@ -303,8 +321,7 @@ template <symmetry_tag sym> class ShortCircuitSolver {
ComplexValue<sym> i_source_bus{}; // total source current in to the bus
ComplexValue<sym> i_source_inject{}; // total raw source current as a Norton equivalent
for (Idx const source_number : sources) {
ComplexTensor<sym> const y_source =
y_bus.math_model_param().source_param[source_number].template y_ref<sym>();
ComplexTensor<sym> const y_source = source_admittance(y_bus, input, source_number);
ComplexValue<sym> const i_source_inject_single =
dot(y_source, ComplexValue<sym>{input.source[source_number]});
output.source[source_number].i = i_source_inject_single - dot(y_source, output.u_bus[bus_number]);
Expand Down
39 changes: 39 additions & 0 deletions tests/cpp_unit_tests/math_solver/test_math_solver_sc.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -462,4 +462,43 @@ TEST_CASE("Short circuit solver") {
}
}

TEST_CASE("Short circuit source admittance follows the voltage factor") {
MathModelTopology topology;
topology.slack_bus = 0;
topology.phase_shift = {0.0};
topology.sources_per_bus = {from_sparse, {0, 1}};
topology.shunts_per_bus = {from_sparse, {0, 0}};
topology.load_gens_per_bus = {from_sparse, {0, 0}};

DoubleComplex const source_admittance{10.0 - 50.0i};
MathModelParam<symmetric_t> parameters;
parameters.source_param = {SourceCalcParam{.y1 = source_admittance, .y0 = source_admittance}};

YBus<symmetric_t> const y_bus{topology, std::move(parameters)};
ShortCircuitSolver<symmetric_t> solver{y_bus, topology};

DoubleComplex const solid_fault_admittance{std::numeric_limits<double>::infinity(),
std::numeric_limits<double>::infinity()};
auto const run_with_voltage_factor = [&](double voltage_factor) {
ShortCircuitInput input;
input.source = {voltage_factor};

@nitbharambe nitbharambe Aug 28, 2026

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Suggested change
input.source = {voltage_factor};
input.source = {{voltage_factor, 0.0}};

Good to be explicit

input.source_admittance_scaling = {1.0 / voltage_factor};
input.fault_buses = {from_sparse, {0, 1}};
input.faults = {
{.y_fault = solid_fault_admittance, .fault_type = FaultType::three_phase, .fault_phase = FaultPhase::abc}};
return solver.run_short_circuit(y_bus, input);
};

auto const low_voltage_minimum_output = run_with_voltage_factor(0.95);
auto const high_voltage_minimum_output = run_with_voltage_factor(1.0);
auto const maximum_output = run_with_voltage_factor(1.1);

CHECK(cabs(low_voltage_minimum_output.fault[0].i_fault - source_admittance) < numerical_tolerance);
CHECK(cabs(high_voltage_minimum_output.fault[0].i_fault - source_admittance) < numerical_tolerance);
CHECK(cabs(maximum_output.fault[0].i_fault - source_admittance) < numerical_tolerance);
CHECK(cabs(maximum_output.source[0].i - source_admittance) < numerical_tolerance);
CHECK(cabs(maximum_output.fault[0].i_fault - low_voltage_minimum_output.fault[0].i_fault) < numerical_tolerance);
CHECK(cabs(maximum_output.fault[0].i_fault - high_voltage_minimum_output.fault[0].i_fault) < numerical_tolerance);
}

} // namespace power_grid_model::math_solver
4 changes: 2 additions & 2 deletions tests/data/short_circuit/branch_source_single_phase_to_ground_c_maximum/sc_output.json
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Original file line number Diff line number Diff line change
Expand Up @@ -29,11 +29,11 @@
"id": 5,
"energized": 1,
"i_f": [
63508.52961085883410,
57735.026918962576,
0.0,
0.0
]
}
]
}
}
}
6 changes: 3 additions & 3 deletions tests/data/short_circuit/branch_source_single_phase_to_ground_c_maximum/sc_output_batch.json
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Original file line number Diff line number Diff line change
Expand Up @@ -30,7 +30,7 @@
"id": 5,
"energized": 1,
"i_f": [
63508.52961085883410,
57735.026918962576,
0.0,
0.0
]
Expand All @@ -43,7 +43,7 @@
"id": 1,
"energized": 1,
"u_pu": [
1.083914433075477,
1.0817685322751267,
1.1,
1.1
]
Expand All @@ -63,7 +63,7 @@
"id": 5,
"energized": 1,
"i_f": [
6257.9828971464731,
6245.59353309911,
0.0,
0.0
]
Expand Down
44 changes: 22 additions & 22 deletions tests/data/short_circuit/dummy-test-line-into-itself/sc_output_batch.json
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Original file line number Diff line number Diff line change
Expand Up @@ -6,24 +6,24 @@
"data": [
{
"node": [
{"id": 1, "energized": 1, "u_pu": [0, 1.1000077319762265, 1.1000098548415278], "u": [0, 6350.8976016714405, 6350.9098580399723], "u_angle": [0, -2.0944042236085978, 2.094402410425154]},
{"id": 2, "energized": 1, "u_pu": [0, 1.1003709155896784, 1.117158383518543], "u": [0, 6352.9944432413577, 6449.9169345187802], "u_angle": [0, -2.112990106753871, 2.0974639893699574]},
{"id": 3, "energized": 1, "u_pu": [0, 1.1003709152901693, 1.1171583831127465], "u": [0, 6352.9944415121408, 6449.9169321759127], "u_angle": [0, -2.1129901070564321, 2.0974639891599725]}
{"id": 1, "energized": 1, "u_pu": [0, 1.100008505188684, 1.1000108403504814], "u": [0, 6350.902065815646, 6350.915547878569], "u_angle": [0, -2.094405135749131, 2.094403141240517]},
{"id": 2, "energized": 1, "u_pu": [0, 1.10037169814409, 1.1171594117225554], "u": [0, 6352.99896132136, 6449.922870857413], "u_angle": [0, -2.112991042936463, 2.097464714857289]},
{"id": 3, "energized": 1, "u_pu": [0, 1.1003716978445806, 1.1171594113167584], "u": [0, 6352.998959592142, 6449.922868514544], "u_angle": [0, -2.112991043239024, 2.0974647146473044]}
],
"line": [
{"id": 4, "energized": 1, "i_from": [309.26652168666647, 728.9516101684294, 732.36548748962139], "i_from_angle": [-2.3422247532036535, -1.3419762083430138, -1.8295943660541507], "i_to": [436.49378866975974, 3.6564812397251591, 3.8271101981503142], "i_to_angle": [-1.0791563599686425, 2.6521928824986034, 0.26542148608168392]},
{"id": 4, "energized": 1, "i_from": [309.26720894741226, 728.95311410609, 732.3670692013686], "i_from_angle": [-2.342225010996923, -1.3419769001103916, -1.829594168056166], "i_to": [436.4947586585155, 3.65648296050423, 3.8271128254544378], "i_to_angle": [-1.0791566177619114, 2.652192140837011, 0.2654220381852178]},
{"id": 5, "energized": 0, "i_from": [0, 0, 0], "i_from_angle": [0, 0, 0], "i_to": [0, 0, 0], "i_to_angle": [0, 0, 0]},
{"id": 6, "energized": 0, "i_from": [0, 0, 0], "i_from_angle": [0, 0, 0], "i_to": [0, 0, 0], "i_to_angle": [0, 0, 0]}
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{"id": 9, "energized": 1, "i_from": [0, 3.656483779705358, 3.8271127964214253], "i_from_angle": [0, -0.4894005845110841, -2.8761706832415648], "i_to": [0, 3.656483779705358, 3.8271127964214253], "i_to_angle": [0, 2.6521920690787093, 0.2654219703482284]}
],
"shunt": [
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{"id": 8, "energized": 1, "i": [0.68295207957823156, 3.6564810900168685, 3.8271100083522671], "i_angle": [1.5502437165727303, -0.4893997316430107, -2.8761711433811832]}
{"id": 7, "energized": 1, "i": [0.665076023947669, 3.662123914711542, 3.7855694022618493], "i_angle": [1.5707934911319938, -0.47527611928440006, -2.8784813531611757]},
{"id": 8, "energized": 1, "i": [0.6829535972535181, 3.6564828107883494, 3.8271126356552787], "i_angle": [1.5502434587794647, -0.48940047330335473, -2.8761705912777473]}
],
"source": [
{"id": 10, "energized": 1, "i": [63508529.610858843, 731.32759227924817, 734.26006094063086], "i_angle": [-1.4711276743037347, -1.3381594964606927, -1.8340636301254731]}
{"id": 10, "energized": 1, "i": [57735026.91896259, 731.3290974137417, 734.2616450593654], "i_angle": [-1.4711276743037347, -1.338160194402424, -1.8340634245549368]}
],
"sym_load": [
{"id": 11, "energized": 0, "i": [0, 0, 0], "i_angle": [0, 0, 0]}
Expand All @@ -32,31 +32,31 @@
{"id": 12, "energized": 0, "i": [0, 0, 0], "i_angle": [0, 0, 0]}
],
"fault": [
{"id": 13, "energized": 1, "i_f": [63508331.109258644, 0, 0], "i_f_angle": [-1.4711239498504336, 0, 0]},
{"id": 14, "energized": 1, "i_f": [436.49378866976025, 0, 0], "i_f_angle": [2.0624362936211509, 0, 0]},
{"id": 15, "energized": 1, "i_f": [0.68295207957823156, 0, 0], "i_f_angle": [-1.5913489370170628, 0, 0]}
{"id": 13, "energized": 1, "i_f": [57734828.41702631, 0, 0], "i_f_angle": [-1.4711235773938323, 0, 0]},
{"id": 14, "energized": 1, "i_f": [436.49475865851304, 0, 0], "i_f_angle": [2.0624360358278855, 0, 0]},
{"id": 15, "energized": 1, "i_f": [0.6829535972535181, 0, 0], "i_f_angle": [-1.5913491948103287, 0, 0]}
]
},
{
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{"id": 1, "energized": 1, "u_pu": [0, 1.100008505188684, 1.1000108403504814], "u": [0, 6350.902065815646, 6350.915547878569], "u_angle": [0, -2.094405135749131, 2.094403141240517]},
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{"id": 9, "energized": 1, "i_from": [0, 3.656483779705358, 3.8271127964214253], "i_from_angle": [0, -0.4894005845110841, -2.8761706832415648], "i_to": [0, 3.656483779705358, 3.8271127964214253], "i_to_angle": [0, 2.6521920690787093, 0.2654219703482284]}
],
"shunt": [
{"id": 7, "energized": 0, "i": [0, 0, 0], "i_angle": [0, 0, 0]},
{"id": 8, "energized": 0, "i": [0, 0, 0], "i_angle": [0, 0, 0]}
],
"source": [
{"id": 10, "energized": 1, "i": [63508529.610858843, 731.32759227924817, 734.26006094063086], "i_angle": [-1.4711276743037347, -1.3381594964606927, -1.8340636301254731]}
{"id": 10, "energized": 1, "i": [57735026.91896259, 731.3290974137417, 734.2616450593654], "i_angle": [-1.4711276743037347, -1.338160194402424, -1.8340634245549368]}
],
"sym_load": [
{"id": 11, "energized": 0, "i": [0, 0, 0], "i_angle": [0, 0, 0]}
Expand All @@ -65,9 +65,9 @@
{"id": 12, "energized": 0, "i": [0, 0, 0], "i_angle": [0, 0, 0]}
],
"fault": [
{"id": 13, "energized": 1, "i_f": [63508331.109258644, 0, 0], "i_f_angle": [-1.4711239498504336, 0, 0]},
{"id": 14, "energized": 1, "i_f": [436.49378866976025, 0, 0], "i_f_angle": [2.0624362936211509, 0, 0]},
{"id": 15, "energized": 1, "i_f": [0.68295207957823156, 0, 0], "i_f_angle": [-1.5913489370170628, 0, 0]}
{"id": 13, "energized": 1, "i_f": [57734828.41702631, 0, 0], "i_f_angle": [-1.4711235773938323, 0, 0]},
{"id": 14, "energized": 1, "i_f": [436.49475865851304, 0, 0], "i_f_angle": [2.062436035827888, 0, 0]},
{"id": 15, "energized": 1, "i_f": [0.6829535972495371, 0, 0], "i_f_angle": [-1.5913491948103282, 0, 0]}
]
}
]
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