1. Application of Torsional Stress Relays GE Energy Dr. Daniel H. Baker March 12, 2010 g Imagination at work

2. The Difference Between “Mitigation” and “Protection” Protection Mitigation • Detects actual stress on the shaft itself, regardless of the cause • Responds to all causes of high stress, both known and unknown • Acts to prevent damage to the turbine-generator • SSR blocking filter or TCSC to reduce SSR caused by series capacitors • Series capacitor switching to avoid SSR • Auto transfer-trip to avoid certain operating conditions (HVDC terminal, series capacitors, steel mills) • Subsynchronous damping control (SSDC) on HVDC system Reduces Risk by avoiding Known Causes of high torsional stress Protects machine from All Causes of high torsional stress

3. Torsional Relaying Functions and Features • Measure instantaneous “stress” in limiting shaft for each torsional mode • Inverse time fatigue trip • Steady-state instability trip • Potential Primary and secondary trip circuits for • 1) tripping unit • 2) opening lines and/or bypassing series capacitors • Alarms to indicate when oscillations are present

4. Torsional Stress Relay (TSR)

5. Typical Fatigue Curve for One Shaft Section • Shows shaft torque magnitude vs. cycles-to-failure (crack initiation) • Function of material properties and dimensions • Used to calculate loss-of-life and relay trip settings

6. TSR Protection Curve for One Torsional Mode Generator Trip Optional Line Trip

7. Example Application of TSR Protection – Damping Torque

8. Example Application of TSR Protection – Worst Instability vs. Outages

9. Torsional Relaying Protection for SSR • No SSR problems for several contingencies (up to 3 in this example) • Possible Instability for multiple contingencies (5 or 6 in this example) • Torsional Relaying Protection Only is Adequate for this condition SSR problems with 2 contingencies or less would need Mitigation in addition to Protection