1. SSR Control of Power SystemsBy
Colin EJ Bowler
Instrumentation Technology Inc.
September 9, 2013
ERCOT

2. Electromagnetic Resonance Concerns
Causes
SSR from series capacitor application
Electrical self excitation
Torsional interaction
Transient resonance
Device dependent torsional interaction
Control design ramification for:
HVDC, SVC, UPFC
Excitation systems
Super synchronous resonance
Torsional modes too close to f0 and 2*f0 frequency
Strong coupling to generator torque
Negative sequence torque transients
Unbalanced transmission faults
Breaker high-speed reclosing

3. SSR Torsional Interaction Damping v.s. Series Compensation Level
An unstable electric & mechanical response
Limited by magnetic saturation or plasticity
A broad band phenomena 0->60 Hz
Occurs over a wide range of series compensation
Mitigated by damping or filtering

4. SSR Transient Response
Mostly a post fault phenomena – torsional interaction driven by post fault resynchronization
Mechanical response integrates the electrical response at resonance
Even when stable, event will produce severe shaft fatigue

5. Application RULES for SSR
Must be Base Case Stable
Probability of SSR should be low
N-2 or better at onset
Must NOT Operate near Resonance
Control Shaft Torque
Keep same as equivalent uncompensated system
SSR Relay Only Protection
Only when probability of SSR is very low
Backing up calculated expectation of stability
Backing up switching countermeasures
Load Dependent Capacitor switching
SSR Relay only for backing up primary SSR control

6. Quantification of SSR Level of Torsional Destabilization
Excess over positive damping
Turbine Positive Damping 0.05 to 0.1 rad/sec
Negative Damping due to SSR
500 kV – 3 Rad/sec
345 kV - 1 Rad/sec
Level of Shaft Torque
Excess over High Cycle Fatigue Torque
1 to 3 Times on uncompensated system
Do not exceed levels for uncompensated system

7. SSR Protection Options
Instantaneous electro-magnetic torque
Instantaneous three phase voltages
Instantaneous three phase line current
Subtract stator iR drops from voltage
Integrate to measure magnetic flux
Multiply flux by current
Instantaneous velocity response
Each end of TG set
Basic Elements of Torsional Protection & Monitoring
SSO – Subsynchronous Time over-current
SMF – Subsynchronous Time over-velocity
DMF – Subsynchronous Time over-acceleration
Monitoring internal stress and fatigue

8. SSR Relay Qualities Dependability Security Undependable Insecure
Always Trips when required
Security
Never False Trips
Undependable
Does NOT trip when required
Insecure
Trips when NOT required (FALSE)

9. SSR Relay Options Security and Dependability
Sensing Means
Time Delay to Trip
Relay Type
V/I
Velocity
T < 1
< 1 T < 10
T > 10
Points
SSO
3V/3I
I/U
S/D
SMF
0/0
1 or 2
SMF/DMF 2
Legend
Meaning
Description I
Insecure
FALSE Trips U
Undependable
NO Trip when Required S
Secure
Never False Trips D
Dependable
Always Trips when required
Subsynchronous Electrical Oscillations
Time over Current
Single Mode Frequency
Time over Velocity
DMF
Digital Mode Frequency
Time over Acceleration
Developed for SCE Mohave High Speed Trip required 3V
3 Phase voltage 3I
3 Phase Current
Rotor Velocity
Measure at one or two tooth-wheel locations on Turbine-Generator

10. SSR Countermeasure Selection Example
SEDC
SEDC/TCSC/SRF
Onset
Instability level
0.05
0.1
0.2
0.4
0.8
1.6
3.2
Radians/Sec
Contingency
Doubling Time
13.86
6.93
3.46
1.73
0.87
0.43
0.22
Seconds
AC/SSO
AC/SMF
AC/DMF 1 2
SSO
SMF 3
DMF
LEGEND AC
Active SSR Counter Measure
SSO Protection
SMF protection
DMF Protection
Supplementary Excitation Damping Control
TCSC
Thyristor Controlled Series capacitor
SRF
SSR Power Filter

11. Instrumentation Technology Experience
Original Developer of SMF Protection in US
Developed DMF Observer Protection
Commissioned by SCE
First use on Mohave Plant
Installed, Operating, Ordered - 24 systems
16 gas turbines
4 Nuclear
4 Fossil

12. The End THANK YOU Colin EJ Bowler President IT Inc.
(919) m
(919) p

13. DMF Protection for Combined Cycle Group
SMF & DMF Protection
Operator Interface
Velocity Target vs Mode
Acceleration Targets vs Mode
Trip Target
Shaft Torque Display

14. Post Event Data Evaluation
Enhanced replacement for generator oscillograph
120 Samples per cycle
32 Channels Analog
24 channels digital input
24 channels digital output
GPS Time synchronized
Available with phasor measurement sub-system
COMTRADE file generation
Arbitrary long events
Nonvolatile storage
Windows human interface
Independent from protection system
Easy to understand & use

15. SSR Protection Traditional methods - SMF Observer based methods – DMF
Filter modal response from velocity
Inverse time over-velocity
Cannot mitigate resonance due to filter delay
Observer based methods – DMF
Calculate response where inaccessible to direct measurement
Measure modal torque without filter delay
Inverse time over-velocity and acceleration
Can trip before max response is reached
Extremely Dependable & Secure
A class of both protection and mitigation for SSR
Valuable for super synchronous response observation
Eliminates false trip and high associated cost