1. Project WECC-0100 Update Load Modeling Task Force
March 2016
Chuck Matthews

2. R1.1 Steady State Voltage Applicability – All applicable BES buses.
Criterion:
At all applicable BES buses
95% to 105% of nominal for P0 event,
90 to 110% of nominal for P1-P7 events
Discussion
Steady state voltage range for P0 event originates in ANSI C84.1 standard. No difference for 500 kV for simplification.
Wider range for P1-P7 events to allow for contingencies. Voltage regulators keep acceptable voltage to loads.
Discussed definition of nominal. In this case TP/PC can define nominal in their individual criterion if they need to for defining voltage limits for their system (e.g. 525 kV).

3. R1.2 Post-Contingency Voltage Deviation
Applicability - At each applicable BES bus serving load.
Criterion:
Post-Contingency steady-state voltage deviation at each applicable BES bus serving load (having no intermediate connection) shall not exceed 8% for P1 events
Discussion
The 8% for P1 events is based on some entities indicating a state regulatory need, and some entities allowing 8% voltage deviation for shunt reactive power device switching after an outage.
For P2-P7 events it was concluded by the SDT it would be acceptable to not have voltage deviation criteria that is more stringent than steady state voltage criteria in requirement R1.1.

4. R1.3-1.6 Transient Voltage Performance
Applicability - At each applicable BES bus serving load
Applies to P1-P7 events
R1.3 – Voltage recovery following fault.
R1.4 – Voltage dip following voltage recovery.
R1.5 – Same performance as R1.4 for contingencies without a fault, P2.1.
R1.6 – Oscillations required to show positive damping within 30 seconds.

5. R1.3-1.4 Transient Voltage Response Criteria
General philosophy of Criteria has changed from no loss of load to maintaining integrity of the BES.
Criteria developed to accomplish three goals:
Account for FIDVR
Consider impact of more explicit load modeling
Minimize loss of load that is non-consequential
R1.3 – Voltage recovery to 80% of pre-contingency voltage within 20 seconds
Consideration for FIDVR events based on experience and industry comments.
Recognizes load loss initiated during fault can’t be prevented
R1.4 – With a fault, following recovery above 80%,Vdip below 70% for 30~, below 80% for 2 seconds.
Guidance from IEEE 1668 Trial Use Recommended Practice for Voltage Sag and Short Interruption Testing for End Use Equipment. Type I and II tests seems reasonable since majority of transmission faults are non 3-phase.
Helps minimize load loss for subsequent swings.
Also within ranges specified in IEEE 1547 Interconnecting Distributed Resources

9. Impacts to Other Systems
WR2. – If an entity uses more stringent Criteria than WR1 shall apply that Criteria only to their own system.
WR3 – If an entity uses less stringent Criteria than WR1 shall allow others to have same impact to that part of system.
These requirements carry over from the previous Criteria requirement WR2 which allowed systems to apply different requirements than Table W-1.
Retains the philosophy of “allowable effects on other systems”.

10. WR4. Cascading and Uncontrolled Islanding
Threshold Criteria to identify potential for Cascading or uncontrolled islanding.
Criterion:
Post contingency analysis results in steady-state facility loading either exceeding 125% or the known trip setting.
Transient stability voltage response R1.3, voltage recovery longer than 20 seconds.
When unrestrained successive load loss or generation loss occurs.
Discussion
Since Cascading or uncontrolled islanding would manifest itself differently in different parts of the system, the SDT developed a threshold criteria where further investigation would be warranted.
Regarding unrestrained successive load or generation loss, it is anticipated this would be an iterative powerflow simulation process as determined by the entity.

11. WR5 Voltage Stability
Positive reactive power margin for the following:
For transfer paths 105% or 102.5% of path flow for P0-P1 or P2-P7 events respectively.
For load areas 105% or 102.5% of forecasted peak load for P0-P1 or P2-P7 events respectively.
Discussions
No technical justification to changing existing real power margins used in previous Criteria.
Concerns about specifying a particular methodology rather than a Criteria.
Path or load area assumed voltage stable by at least demonstrating the margins specified. Discussion this is a criteria for transmission Planning over the Planning Horizon, not a methodology to find system voltage stability limits beyond what the system is planned for.

12. WR6 Make Criteria Available
Entity that uses study criteria different from criteria in WR1 shall make their criteria available upon request within 30 days.

13. Frequency Dip Criteria
Frequency dip criteria is not included in this Criteria. A frequency dip criteria was included in Table W1 which was retired.
There is no good technical justification for frequency dip impact to load.
Under frequency concern is to protect generators. UFLS designed in coordinated fashion based on frequency excursion to prevent excessive gen loss, not based on frequency dip as defined by previous criteria.
PRC-006 Automatic UF Load Shedding defines requirements for PC’s developing UFLS Programs. WECC ONF Requirements.
Generator frequency capability requirements defined in NERC PRC-024

14. Questions?