AC & DC Schematic Protection

Objectives
• Understand the difference between AC (current/voltage) and DC (control/trip) schematics.
• Learn to trace protection circuits from CT/VT terminals to relay inputs.
• Analyze DC tripping circuits, including coil supervision and anti-pumping.

Key Topics
• AC Schematics: CT circuits (star/delta connections), VT circuits (open delta, phase-neutral), summation CTs.
• DC Schematics: Trip circuit architecture, relay output contacts, breaker 52a/52b aux contacts, trip coil supervision.
• Circuit breaker control: Close/trip logic, anti-pump feature, local/remote selection.
• DC supply distribution and MCB/mini-switch coordination.

Practical Focus
• Guided review of a complete AC & DC schematic for a distance protection relay.
• Fault-finding exercise: Identifying why a breaker fails to trip based on the DC schematic.

Key Takeaways:
• Proficiency in reading and interpreting detailed AC/DC protection schematics.
• Understanding of critical design elements like DC supply security and circuit supervision.

Suggested Diagrams
• Typical AC schematic for a transformer differential protection (87T) showing CT connections.
• DC schematic for a circuit breaker trip circuit with trip relay and supervision.

Standards & References
• IEC 60617 – Graphical Symbols for Diagrams.
• IEEE 242 – Recommended Practice for Protection and Coordination.

Certification & Delivery
• Certificate of Completion awarded.
• Delivery Mode: Online (On-demand).
• Corporate and customized training available on request.