Current Differential Relay Specification

1. Current Differential Relay Specification WECC M&VWG June 18,2014 Amos Ang

2. Agenda • Purpose • Background • Relay Model Specification • Next Steps

3. Purpose • To get approval from M&VWG for model specification • To model relay behavior in transient stability analysis • To satisfy the new TPL standards of modeling the actions of protection relays for compliance • Facilitate modeling interactions between RAS and Protection relays • To facilitate transfer of information from System Protection to Transmission Planner • Established a phased approach to implementing more functionality

4. Background • One of MSRATF sub group was tasked to deal with relays • Members of the sub group included input from Planning and Protection engineers • Identified current differential relay as one of the most used primary protection for 200 kV and above

5. Current Differential Relay Specification

6. Functional requirement of Relay • Model can be applied to branches i.e. lines and transformers and also apply to multi-segmented or multi sectional lines • Model can be applied to three terminal lines / three winding transformers • Model will open only the branch(es) within its zone of protection • Monitor only mode • Can be applied to a specific set of branches through the zone/kV/area/owner specifications • Can be applied to specific branches to override the general specifications stated above

7. Model Simplification • Details for detecting a fault within the zone of protection as done by the current differential relay is not necessary • Additional details does not add any more value • No known interactions from other system events so this is immune to power swings, etc. • In simulation, the fault is applied by the engineer and so the initiating event for the model is the application of the fault on the branch • After fault is applied, then associated breaker times, communication times, and relay delay times will open the appropriate branches

8. Modeling • 2 Types of Current Differential Relay Model • A generic / general current differential model DIFFRLYG • Applies to a set of branches by a priority list of kV range then a logical AND combination of Area / Zone / Owner • Tripping and timings applies to all branches that meet the criteria and from bus to bus • A specific current differential model DIFFRLYS • Applies to a specific branch or branch set • Overrides the DIFFRLYG model • Correctly defines the zone of protection that the DIFFRLYG cannot for such things as: • 3 terminal lines • 3 Winding Transformers • Multi-segmented and multi-sectional lines

9. Zone of Protection • Correctly defining the zone of protection is important for this relay so the following are illustrations of what is defined as the zone of protection

10. Zone of Protection (cont.)

11. DIFFRLYG *Clearing time is the sum of Tcb and TcC

12. DIFFRLYS *Clearing time is the sum of Tcb and TcC

13. Next Steps • Phase 2 • Apply to bus differential protection – once node-breaker model is used in WECC base cases

14. Any Questions?