🎓 Lesson 17
D5
CYME Relay Coordination Module: Best Practices & Pitfalls
CYME Relay Coordination Module is a software tool that helps engineers set up protective relays so they trip in the correct order during faults—like making sure only the closest breaker shuts off, not the whole power system.
🎯 Learning Objectives
- ✓ Analyze time-current curves (TCCs) to identify miscoordination points between upstream and downstream relays
- ✓ Calculate minimum coordination time intervals (MCTI) for inverse-time overcurrent relays using IEEE C37.112 guidelines
- ✓ Design relay pickup and time-multiplier settings to achieve selective coordination across three-tier protection schemes
- ✓ Apply fault current attenuation modeling to validate coordination margins under worst-case system configurations
- ✓ Explain the impact of CT saturation and relay operating tolerance on coordination reliability
📖 Why This Matters
In mining and remote industrial power systems—where single-point failures can halt production, endanger personnel, or trigger cascading blackouts—relay coordination isn’t theoretical: it’s the difference between an isolated feeder outage and a complete mine shutdown. The CYME Relay Coordination Module transforms abstract protection principles into validated, auditable, field-deployable settings—ensuring safety compliance (e.g., MSHA Part 46/48), minimizing downtime, and meeting utility interconnection requirements.
📘 Core Principles
Relay coordination rests on two pillars: selectivity (only the nearest relay to the fault operates) and sensitivity (relays detect faults reliably below their pickup thresholds). CYME implements this via time–current curve (TCC) overlay analysis, where each relay’s TCC is plotted against fault current magnitude and duration. Coordination requires a minimum time separation—called the Minimum Coordination Time Interval (MCTI)—between adjacent relay curves, accounting for relay operating tolerance (±10%), CT ratio error, and circuit breaker clearing time. CYME models these non-idealities using built-in device libraries (e.g., SEL, GE, Siemens), system impedance-based fault studies, and dynamic load-flow–integrated short-circuit analysis—enabling validation under both maximum and minimum fault current scenarios (e.g., utility tie-in vs. generator-only mode).
📐 Minimum Coordination Time Interval (MCTI)
MCTI ensures sufficient time separation between relay operations to guarantee selectivity. It accounts for relay tolerance, CT saturation delay, breaker interrupt time, and system uncertainty. IEEE C37.112-2018 mandates MCTI ≥ 0.2 s for electromechanical relays and ≥ 0.1 s for modern digital relays—but CYME recommends ≥ 0.3 s for mining applications due to harsh environmental conditions and aging infrastructure.
💡 Worked Example
Problem: Given: downstream relay (Feeder 7) has total clearing time = 0.28 s at 5× pickup; upstream relay (Substation Bus Tie) has operating tolerance ±7%, breaker interrupt time = 0.06 s, CT saturation delay = 0.02 s, and system uncertainty factor = 1.15.
1.
Step 1: Compute worst-case upstream total clearing time = (relay operating time × 1.07) + breaker time + CT delay = (0.45 s × 1.07) + 0.06 s + 0.02 s = 0.5415 s
2.
Step 2: Apply system uncertainty: 0.5415 s × 1.15 = 0.6227 s
3.
Step 3: Subtract downstream clearing time: 0.6227 s − 0.28 s = 0.3427 s
Answer:
The calculated MCTI is 0.343 s, exceeding the recommended 0.3 s margin for mining systems—coordination is validated.
🏗️ Real-World Application
At the Red Lake Gold Mine (Ontario, Canada), CYME Relay Coordination Module identified a 0.09 s overlap between the 13.8 kV feeder relay (SEL-751) and the main substation bus differential relay during a minimum-generation fault scenario. Field testing confirmed nuisance tripping during motor starts. Engineers revised the feeder relay’s time-multiplier setting from 0.8 to 1.1 and added a 0.25 s intentional delay on the bus relay’s backup overcurrent element—verified in CYME with updated CT saturation models and verified on-site using DFR recordings. Post-implementation, fault isolation success rate improved from 68% to 99.4% over 18 months.
🔧 Interactive Calculator
🔧 Open Power System Protection Coordination Calculator📋 Case Connection
📋 Data Center Tier IV Electrical System Protection Coordination
Need for zero downtime during faults while maintaining selective tripping across 4-level distribution (230kV → 13.8kV →...
📋 Hospital Emergency Power System Coordination
Critical life-support loads (ICU, OR, imaging) required <100ms transfer and no false trips during generator paralleling...
📋 Utility-Scale Solar Farm DC Side Protection Coordination
Lack of standardized DC overcurrent protection leading to fire risk, inconsistent fuse-blower coordination, and inverter...
📋 Substation Automation Retrofit for Selective Coordination
Legacy electromechanical relays caused 3–5 second fault clearing times, exceeding SEMI F47 ride-through requirements for...
📋 Offshore Wind Farm Collector System Coordination
High capacitance causing charging currents >50% of nominal, leading to false earth-fault trips and inability to distingu...