Power system security assessment

Power system security is the ability of the system to remain in a secure operating state and keep supplying load when sudden disturbances (contingencies) occur, such as loss of a generator, line or transformer, or a fault. A secure system meets the N-1 criterion.

Vital components of security assessment

1. System monitoring

   • Real-time measurement of voltages, currents, power flows, breaker status and frequency through SCADA/EMS and PMUs.
   • State estimation filters bad data and gives the best estimate of the system state.

2. Contingency analysis

   • "What if" studies of credible outages (lines, units, transformers).
   • Uses fast load flow (DC or AC) to check overloads and voltage violations after each outage.
   • Contingencies are ranked by severity (performance index).

3. Security control / corrective action

   • Preventive: generation rescheduling, security-constrained optimal power flow so the system stays N-1 secure.
   • Corrective: load shedding, switching, tap changes, reserve activation when limits are violated.

4. Stability assessment (dynamic security)

   • Transient, voltage and frequency stability studies after large disturbances.

5. Reserve and protection assessment

   • Adequate spinning reserve, under-frequency load shedding and coordinated protection.

 SCADA data -> State estimation -> Contingency
                                     analysis
                                        |
           Secure? --yes--> Normal operation
              |
              no -> Preventive / corrective control

Operating states

Normal → Alert → Emergency → In extremis → Restorative; security assessment aims to keep the system in the normal state.