Fix transformer CM=2 magnetizing susceptance sign

src/pm_io/psse.jl

@@ -1004,21 +1004,34 @@ function apply_tap_correction!(
     return windv_value
 end
 
+# Two-winding records name their buses "f_bus"/"t_bus", three-winding ones
+# "bus_primary"/"bus_secondary"/"bus_tertiary"; both reach the warning below.
+function _transformer_bus_label(sub_data::Dict)
+    haskey(sub_data, "f_bus") && return "$(sub_data["f_bus"]) -> $(sub_data["t_bus"])"
+    return string(
+        sub_data["bus_primary"], " -> ", sub_data["bus_secondary"],
+        " -> ", sub_data["bus_tertiary"],
+    )
+end
+
 # Base Power has a different key in sub_data depending on the number of windings
 function _transformer_mag_pu_conversion(
     transformer::Dict,
     sub_data::Dict,
     base_power::Float64,
 )
-    if isapprox(transformer["MAG1"], ZERO_IMPEDANCE_REACTANCE_THRESHOLD) &&
-       isapprox(transformer["MAG2"], ZERO_IMPEDANCE_REACTANCE_THRESHOLD)
-        @warn "Transformer $(sub_data["f_bus"]) -> $(sub_data["t_bus"]) has zero MAG1 and MAG2 values."
+    if isapprox(transformer["MAG1"], 0.0; atol = ZERO_IMPEDANCE_REACTANCE_THRESHOLD) &&
+       isapprox(transformer["MAG2"], 0.0; atol = ZERO_IMPEDANCE_REACTANCE_THRESHOLD)
+        @warn "Transformer $(_transformer_bus_label(sub_data)) has zero MAG1 and MAG2 values."
         return 0.0, 0.0
     else
         G_pu = PSSE_MICRO_UNIT_SCALE * transformer["MAG1"] / base_power
         mag_diff = transformer["MAG2"]^2 - G_pu^2
         @assert mag_diff >= -ZERO_IMPEDANCE_REACTANCE_THRESHOLD
-        B_pu = sqrt(max(0.0, mag_diff))
+        # The magnetizing branch is inductive: MAG2 under CM=2 is the exciting current
+        # magnitude (positive by convention), so the susceptance it implies is the
+        # negative root, matching the already-negative MAG2 a CM=1 record supplies.
+        B_pu = -sqrt(max(0.0, mag_diff))
         return G_pu, B_pu
     end
 end

test/test_openapi_transformer_discriminators.jl

@@ -111,13 +111,14 @@ end
     @test d["br_x"] ≈ 0.05626483087470335
 
     # CM=2: MAG1 (80000.0 W) is no-load loss, MAG2 (0.005 pu) is exciting current;
-    # G_pu = 1e-6*MAG1/base_power, B_pu = sqrt(MAG2^2 - G_pu^2).
+    # G_pu = 1e-6*MAG1/base_power, B_pu = -sqrt(MAG2^2 - G_pu^2).
     g_pu = 1e-6 * 80000.0 / d["base_power"]
     @test g_pu ≈ 0.001
-    b_pu = sqrt(0.005^2 - g_pu^2)
-    @test b_pu ≈ 0.004898979485566357
+    b_pu = -sqrt(0.005^2 - g_pu^2)
+    @test b_pu ≈ -0.004898979485566357
     @test d["g_fr"] ≈ g_pu
     @test d["b_fr"] ≈ b_pu
+    @test d["b_fr"] < 0
 
     # tap: WINDV1/WINDV2 * (bus_J_base_kv/bus_I_base_kv) * (winding1_nominal_voltage /
     # winding2_nominal_voltage); NOMV1=0 -> winding1_nominal_voltage = bus_I_base_kv

test/test_parse_psse.jl

@@ -154,3 +154,83 @@ end
     @test length(shunt_101["y_increment"]) == 1
     @test shunt_101["initial_status"] == [0]
 end
+
+@testset "PSSE transformer CM=2 magnetizing susceptance is inductive" begin
+    # Under CM=2 a transformer record gives MAG1 as a positive number by convention, when
+    # the magnetizing branch is inductive (negative susceptance).
+    raw = read_fixture(FOURTEEN_BUS_FIXTURE)
+
+    # The fixture's transformers are all CM=1 with zero MAG1/MAG2. Flip one two-winding
+    # and one three-winding record to CM=2 and give them a loss/exciting-current pair.
+    # Record line 1 is `I, J, K, CKT, CW, CZ, CM, MAG1, MAG2, NMETR, NAME, ...`.
+    mag1_watts, mag2_pu = 3.0e4, 5.0e-3
+    cm2 = replace(
+        raw,
+        "   109,   104,     0,'1 ',1,1,1, 0.00000E+0, 0.00000E+0,2,'TRAFO 2W 3  '" => "   109,   104,     0,'1 ',1,1,2, 3.00000E+4, 5.00000E-3,2,'TRAFO 2W 3  '",
+        "   109,   104,   107,'1 ',1,1,1, 0.00000E+0, 0.00000E+0,2,'TRAFO 3W 2  '" => "   109,   104,   107,'1 ',1,1,2, 3.00000E+4, 5.00000E-3,2,'TRAFO 3W 2  '",
+    )
+    @test cm2 != raw
+    pm_data = parse_file(IOBuffer(cm2); filetype = "raw")
+
+    # SBASE1-2 is 100.0 for both records, so G is watts scaled to that base and B closes
+    # the right triangle against the exciting current.
+    expected_g = 1e-6 * mag1_watts / 100.0
+    expected_b = -sqrt(mag2_pu^2 - expected_g^2)
+    @test expected_b < 0
+
+    branch = only(
+        v for v in values(pm_data["branch"]) if
+        get(get(v, "ext", Dict()), "psse_name", "") == "TRAFO 2W 3  "
+    )
+    @test branch["g_fr"] ≈ expected_g
+    @test branch["b_fr"] ≈ expected_b
+    @test branch["b_fr"] < 0
+
+    transformer_3w = only(
+        v for v in values(pm_data["3w_transformer"]) if
+        get(get(v, "ext", Dict()), "psse_name", "") == "TRAFO 3W 2  "
+    )
+    @test transformer_3w["g"] ≈ expected_g
+    @test transformer_3w["b"] ≈ expected_b
+    @test transformer_3w["b"] < 0
+end
+
+@testset "PSSE transformer CM=2 zero MAG1/MAG2 warns on both winding counts" begin
+    # The zero check guards against a magnetizing branch with nothing to derive. It only
+    # runs under CM=2, so flip the same two records the sign test uses but leave their
+    # MAG1/MAG2 at the fixture's zeros. The three-winding record is the one that matters:
+    # its sub_data names buses "bus_primary"/"bus_secondary"/"bus_tertiary", so a warning
+    # reaching for "f_bus" would throw rather than warn.
+    raw = read_fixture(FOURTEEN_BUS_FIXTURE)
+    cm2 = replace(
+        raw,
+        "   109,   104,     0,'1 ',1,1,1, 0.00000E+0, 0.00000E+0,2,'TRAFO 2W 3  '" => "   109,   104,     0,'1 ',1,1,2, 0.00000E+0, 0.00000E+0,2,'TRAFO 2W 3  '",
+        "   109,   104,   107,'1 ',1,1,1, 0.00000E+0, 0.00000E+0,2,'TRAFO 3W 2  '" => "   109,   104,   107,'1 ',1,1,2, 0.00000E+0, 0.00000E+0,2,'TRAFO 3W 2  '",
+    )
+    @test cm2 != raw
+
+    # Collect the records rather than using @test_logs: a message that fails to build is
+    # still reported as a warning, and match_mode = :any accepts that stand-in, so assert
+    # on the rendered message text directly.
+    logs, pm_data = Test.collect_test_logs() do
+        parse_file(IOBuffer(cm2); filetype = "raw")
+    end
+    messages = [string(r.message) for r in logs if r.level == Logging.Warn]
+    @test count(m -> occursin("has zero MAG1 and MAG2 values", m), messages) == 2
+    @test any(m -> occursin("Transformer 109 -> 104 has zero", m), messages)
+    @test any(m -> occursin("Transformer 109 -> 104 -> 107 has zero", m), messages)
+
+    branch = only(
+        v for v in values(pm_data["branch"]) if
+        get(get(v, "ext", Dict()), "psse_name", "") == "TRAFO 2W 3  "
+    )
+    @test branch["g_fr"] == 0.0
+    @test branch["b_fr"] == 0.0
+
+    transformer_3w = only(
+        v for v in values(pm_data["3w_transformer"]) if
+        get(get(v, "ext", Dict()), "psse_name", "") == "TRAFO 3W 2  "
+    )
+    @test transformer_3w["g"] == 0.0
+    @test transformer_3w["b"] == 0.0
+end