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”
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
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
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