A Supervisory Approach towards Cyber- Secure Generator Protection

Transcription

1 A Supervisory Approach towards Cyber- Secure Generator Protection CPS WEEK, CPSR Workshop, VIENNA, April 2016 RAJESH G. KAVASSERI, Y. CUI AND N. R. CHAUDHURI DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING NORTH DAKOTA STATE UNIVERSITY Support from NSF CPS # gratefully acknowledged (*) 1

2 Context Modern system protection largely served by microprocessor-based relays; Multifunctional role for relays besides protection - control/automation/metering Network/remote access to multiple parties: relay technicians, protection engineers, control engineers, corporate groups and vendors.

3 What s at stake? A lot! The heart (sanctum sanctorum) of a relay lies in its settings. Incorrect settings (intentionally or otherwise) can be severely detrimental to system operation. How do we safeguard these settings? In this multi-party, multi-access scenario? Current practice: access restrictions, privileges, relay recommissioning,..

4 SETTINGS Example (from [1])

5 Example (from [2], BPA) Synchrophasor Vector Processor SETTINGS

6 Focus: Out of Step (OOS) Events for Synchronous generators OOS: generator exhibits undamped power swings with (potential) loss of synchronism Protection solutions based on settings a) Rate of change of positive sequence impedance seen at generator terminals (implemented by impedance relays/blinders) b) More recently, slip and acceleration based relays requiring PMU inputs used by SEL

7 Example/Relay characteristics TRIP Settings: (R,X) center, radius, blinder positions, separation timers 7

8 Example/characteristics (from [2]) Settings: Discriminating lines Compromised settings will impact protection potentially reversing TRIP and BLOCK decisions! 8

9 Key Idea Can we computationally supervise this relay through an independent path? For OOS, the key variable to monitor is the rotor angular separation

10 Challenge The voltage angles can be directly measured, but not the rotor angle The apparent impedance is used to approximate the angular separation between the rotor angle and voltage angle (Device 78) Immeasurable Measurable Solution: * Estimate the angular separation using Dynamic State Estimation (DSE) * Kalman filter-based methods can be used; but here, we use particle filters for robustness and accuracy 10

11 Dynamic State Estimation (DSE) Generator model Exciter, turbine model Measurement model Local PMU DSE V, θ I, φ Phasor information and resultant product (e.g. power output) δ, ω, E d, E q, E ff, T m Supervisory Scheme Estimated dynamic states 11

12 Particle Filter Approach We have x k = f k x k 1, u k 1, w k 1 y k = h k x k, u k, v k System Equation Measurement Equation We solve for p x k Y k = pdf of x k (sssss vvvvvv) given a set of measurements At each time step k: The a priori particles are computed from the system dynamics (f()) and the known pdf of the process noise. For m measurements, the probability of a priori particles conditioned on the measurement is given by: The probabilities are normalized and the a posteriori are resampled. 12

13 Case Study: New England System G1 37 G8 38 G G G G Self-clear fault on line G G G G7 System summary: 10 generators 39 buses 46 branches Prime-mover, excitation controllers and power system stabilizers are all modeled 13

14 Sample of Tracking Results Summary of 100 Monte Carlo trials 14

15 Sample of Tracking Results Summary of 100 Monte Carlo trials 15

16 Detection Method 16

17 Consistency Test: Stable Case 17

18 Consistency Test: Unstable Case 18

19 Misinterpretation due to Faulty Setting Stable swing leads to a mis-trip Unstable swing goes undetectable 19

20 Angular separation by DSE for generator mis-trip case Angular separation = rotor angle voltage angle of HV side of the transformer 20

21 Conclusions An alternative pathway is proposed to monitor the swing stability independently Simulation results show that the proposed approach complies with conventional relay decision The alternative pathway can provide supervisory supplement on detecting anomalous operation since it does not rely on the same set of settings and directly reflect angular separation

22 Sources [1] Technical Report/SEL Publication: Advanced Real-Time Synchrophasor Applications Edmund O. Schweitzer, III, David Whitehead, Armando Guzmán, Yanfeng Gong, and Marcos Donolo, Schweitzer Engineering Laboratories, Inc. [2] Schweitzer, E. O., Guzman, A., Altuve, H. J., and Tziou-varas, D. A., Real-Time Synchrophasor Applications for Wide-Area Protection, Control, and Monitoring, Tech. report., Schweitzer Eng. Laboratories, 2009.

23 Danke! (*) The views and opinions of authors expressed herein do not necessarily state or reflect those of the NSF or any government agency thereof.