ATP-EMTP Cable Modeling Skill

Python-automated ATP-EMTP cable sheath voltage and transient analysis tool.

Memory (read first)

SKILL_DIR = {home}/.claude/skills/tool-atp-emtp/.

Always read <SKILL_DIR>/atp-memory.md before answering or running anything. It holds the current phase, the validated solver results (phasor + Bergeron vs the 12 CYMCAP reference cases, including which cases legitimately xfail and why), the hard-won key learnings (e.g. the coupled-RL backward-Euler instability and the Bergeron traveling-wave fix), and known issues. Without it you will re-derive solved problems or quote stale validation numbers.

Update it at the end of the session when any of these change: the phase, a validation result, a new key learning, or a known issue that got solved. Keep the existing shape — status snapshot at the top, dated results, then learnings. Say so in one line when you've updated it.

Triggers

User Says	Action
"run ATP" / "ATP simulation"	Run ATP simulation for cable case
"ATP sheath voltage"	Steady-state sheath voltage via ATP
"transient analysis" / "switching surge"	Transient template simulation
"lightning impulse" / "lightning study"	Lightning impulse simulation
"compare solvers" / "ATP vs OpenDSS"	Three-way comparison (ATP vs OpenDSS vs CYMCAP)
"validate ATP" / "ATP validation"	Run 12 CYMCAP reference cases through ATP
"ATP report"	Generate report with tables and charts

Prerequisites

1. ATP installed on Home PC (Windows 11, RTX 4070 Ti SUPER)

   • ATP_HOME environment variable set to ATP installation directory
   • tpbig.exe accessible from PATH or ATP_HOME
   • EEUG membership required (free non-commercial): https://atp-emtp.org

2. Python packages: pip install numpy pandas matplotlib

   • Optional: pip install pyatp (pdb5627/pyATP) for .pl4 binary parsing

Check ATP status:

# On Home PC
echo %ATP_HOME%
where tpbig.exe

Commands

1. validate — Run 12 CYMCAP reference cases

cd "30_Resources/Electrical-Engineering/Software-Tools/atp-emtp"
python validate_cymcap.py

Runs same 12 cases from opendss-cable-sheath/validate_cymcap_1310.py:

• GROUP A: 3 cases, 1500A, DLF=0.57
• GROUP B: 9 cases, 1310A, DLF=1.0
• Cable: 132kV 2000mm² Cu Milliken, corrugated Al sheath

2. compare — Three-way solver comparison

python compare_solvers.py

ATP vs OpenDSS vs CYMCAP side-by-side for all 12 cases.

3. sheath-voltage — Single case steady-state

from atp_core import generate_atp_file
from atp_runner import run_atp
from atp_parser import parse_lis_sheath_voltages

# Generate .atp file
atp_file = generate_atp_file(
    positions=[(-0.35, 1.16), (0.0, 1.16), (0.35, 1.16)],
    phases=['A', 'B', 'C'],
    cable=CableGeometry(),
    I_load=1310,
    section_length_m=1000,
    model_type="pi"
)

# Run and parse
result = run_atp(atp_file)
voltages = parse_lis_sheath_voltages(result['lis_path'])

4. switching — Switching surge analysis

from transient_templates import switching_surge_template

atp_file = switching_surge_template(
    cable=CableGeometry(),
    positions=[(-0.35, 1.16), (0.0, 1.16), (0.35, 1.16)],
    cable_length_km=10.0,
    closing_time_ms=50.0,
    timestep_us=1.0,
    duration_s=0.1,
)

5. lightning — Lightning impulse study

from transient_templates import lightning_impulse_template

atp_file = lightning_impulse_template(
    cable=CableGeometry(),
    positions=[(-0.35, 1.16), (0.0, 1.16), (0.35, 1.16)],
    I_peak_kA=10.0,
    front_us=1.2,
    tail_us=50.0,
)

6. report — Generate report

from report_generator import generate_validation_report
generate_validation_report(output_dir="./reports")

Reference Files

File	Purpose
opendss-cable-sheath/validate_cymcap_1310.py	CableGeometry dataclass, 12 TestCase definitions, CYMCAP reference values
opendss-cable-sheath/cable_sheath_core.py	Z-matrix impedance method (for PI section model)
opendss-cable-sheath/CYMCAP-Reference-Cases.md	Canonical test case definitions

Tool Location

All scripts: 30_Resources/Electrical-Engineering/Software-Tools/atp-emtp/

Key Technical Notes

ATP .atp File Format

• Fixed-column FORTRAN format — column positions are critical, off-by-one = silent failure
• Bus names limited to 6 characters: SRCA, SRCB, SRCC, LDAA, LDAB, LDAC, SHTA, SHTB, SHTC
• Sections separated by BLANK CARD lines
• Timestep: 10-50μs for steady-state, 0.1-1μs for transients

Two Model Types

1. PI section: Inject pre-computed impedance matrix from analytical formulas — simpler, faster
2. LCC (Line/Cable Constants): ATP's built-in routine with physical cable dimensions — proper frequency-dependent model

Steady-State from Time-Domain

• ATP is a time-domain solver — need 10+ power frequency cycles for transient decay
• Extract RMS from last 5 cycles for steady-state comparison
• Simulation: 0.2s (10 cycles @50Hz) minimum for steady-state

Related Notes

• [[CYMCAP-Reference-Cases]] - Canonical test cases
• [[OpenDSS-Cable-Sheath-Tool]] - Existing sheath voltage calculator
• [[CYMCAP]] - CYMCAP software reference
• [[Cable bonding method]] - Bonding theory