Stability Limits

Stability related transmission limits

Stability Limits by PJM (p60, Revision 67)

The PJM RTO established stability limits for preventing electrical separation of a generating unit or a portion of the PJM RTO. PJM recognizes three types of stability:

• Steady State Stability - A gradual slow change to generation that is balanced by load.
• Transient Stability - The ability of a generating unit or a group of generating units to maintain synchronism following a relatively severe and sudden system disturbance. The first few cycles are the most critical time period.
• Dynamic Stability - The ability of a generating unit or a group of generating units to damp oscillations caused by relatively minor disturbances through the action of properly tuned control systems.

PJM will operate the facilities that are under PJM operational control such that the PJM system will maintain angular and voltage stability following any single facility malfunction or failure.

In general, stability is not a limiting constraint on the PJM RTO.

Stability Related Transmission Limits by PJM (p40, Revision 67)

In addition to the thermal limits referenced in Section 2, PJM operates the PJM RTO considering voltage and stability related transmission limits as follows:

• Voltage Limits – High, Low, and Load Dump actual voltage limits, High and Low emergency voltage limits for contingency simulation, and voltage drop limits for wide area transfer simulations to protect against wide area voltage collapse.
• Transfer Limits – The MW flow limitation across an interface to protect the system from large voltage drops or collapse caused by any viable contingency.
• Stability Limits – limit based on voltage phase angle difference to protect portions of the PJM RTO from separation or unstable operation.

Stability Limits by PJM (p82, Revision 133)

The ability of a generating unit or a group of generating units to maintain synchronism following a system disturbance can be identified using real time and study applications such as the PJM Transient Stability Analysis (TSA) tool. Based on results from TSA, stability limits will be established and logged within PJM’s TO Connection. For real power (MW) stability limits only, TO Connection stability limits will be translated into a corresponding generator output constraint (in MW) for a single generator or a group of generators.