Sub Synchronous Interactions (SSR, SSCI, SSTI)
Sub-synchronous interactions present severe risks of shaft torque fatigue and catastrophic turbine failure when power plants operate in proximity to series-compensated transmission lines or high-speed power electronic converters. MEPCO assesses Sub-Synchronous Resonance (SSR), Sub-Synchronous Control Interaction (SSCI), and Sub-Synchronous Torsional Interaction (SSTI) using detailed PSCAD/EMTDC simulation.
Figure 1: Multi-mass turbine-generator shaft string analyzed for sub-synchronous torsional torque stresses.
Technical Scope & Engineering Capabilities
MEPCO Engineering Projects brings specialized domain knowledge, rigorous modeling standards, and practical site experience to every assignment. Our scope covers:
- Sub-Synchronous Resonance (SSR): Analyzing the Induction Generator Effect (IGE) and Torsional Interaction (TI) between series-compensated transmission lines and turbine-generator mechanical shafts.
- Sub-Synchronous Control Interaction (SSCI): Simulating fast inner current control interactions of wind turbine converters (DFIG / Full Converter) and PV inverters with series capacitors.
- Sub-Synchronous Torsional Interaction (SSTI): Evaluating interactions between generator shaft mechanical natural frequencies and nearby HVDC converters or FACTS controllers.
- Multi-Mass Shaft Spring-Mass Modeling: Developing lumped spring-mass mechanical models (HP, IP, LP1, LP2, Generator, Exciter) to determine natural torsional modes.
- Electrical Damping Frequency Scans: Performing frequency scans to verify that total system damping remains positive across all sub-synchronous frequencies (5 Hz to 45 Hz).
- Mitigation & Protection Schemes: Sizing sub-synchronous damping filters, supplementary damping controllers (SSDC), and sub-synchronous protective relays.
Software Platforms & Computational Tools
Primary Tool: PSCAD / EMTDC (Electromagnetic Transient Simulation with non-linear multi-mass mechanical shaft models).
Analytical Tool: Frequency-domain impedance scan routines.
Applicable Standards & Grid Codes
SSR Guides: IEEE PES Subsynchronous Resonance Working Group Publications, CIGRE Technical Brochure on SSR/SSCI.
Methodology & Project Delivery Workflow
Our engineering delivery aligns with MEPCO’s structured 6-stage project execution framework, ensuring quality throughout input verification, design modeling, and client handover:
- Stage 01 — Scope & Criteria Definition: Establish study boundaries, utility tie-in data, single-line diagrams, and client objectives.
- Stage 02 — Data Audit & Modeling Assumptions: Collect, verify, and validate manufacturer datasheets, impedance tolerances, and site operating configurations.
- Stage 03 — Simulation Model Development: Build detailed, validated mathematical digital models in specialized power software.
- Stage 04 — Computational Analysis & Verification: Execute base-case and contingency scenarios, conducting rigorous internal peer reviews.
- Stage 05 — Client Review & Approval: Present study findings, address technical comments, and participate in technical clarification sessions.
- Stage 06 — Final Handover: Deliver formal certified engineering reports, executive summaries, and native simulation model files.
Figure 2: Converter-interfaced wind farms evaluated for sub-synchronous control interactions (SSCI) in series-compensated grids.
Completed Project References (From MEPCO Profile)
Selected project assignments delivered by MEPCO demonstrating our technical execution and regional client trust:
| Project Name | Client / Authority | Location | Tools / Mode | Scope Executed |
|---|---|---|---|---|
| Series-Compensated Thermal & Renewable Networks | Regional Power Authorities | Middle East | PSCAD/EMTDC | SSR / SSCI Assessment, Shaft Torque Stress Calculations, and Supplementary Damping Controller Design. |
Key Engineering Deliverables & Outputs:
- Comprehensive Sub-Synchronous Interaction Study Report.
- Natural Torsional Frequency Tables and Spring-Mass Shaft Model Data.
- Electrical and Mechanical Damping Curves across Sub-Synchronous Frequencies.
- Shaft Torque Transient Stress Curves under Network Faults.
- Mitigation Filter Specifications and Protective Relay Trip Logic.
Inquire About This Service
Contact MEPCO’s engineering team for technical proposals, study scope definition, or project consultations:
Email: m.khaled@mepco-tds.com | Phone: +20 11 2696 7082 | HQ: 5 Al-Ibrahimia Street, Cairo, Egypt