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Ring-Closing Operation: Definition & Importance in Power Grids

Source: Maxwell He 2025-08-14 16:47:24

Essentials of Ring-Closing: Seamless Load Switching in Loop Networks

          In electrical power systems, a ​ring-closing operation​ refers to the controlled closure of a normally open switch or breaker within a closed-loop network topology. Unlike interconnecting independent grids (synchronization), this technique operates exclusively within a single, strongly coupled system—such as feeders from the same substation or tightly bonded grid sections.

          Its primary purpose is to enable seamless ​load transfer​ during maintenance, fault recovery, or network reconfiguration without interrupting supply. For example, closing a tie switch between two parallel 10kV lines allows shifting loads from Line A (to be de-energized) to Line B. Critical technical prerequisites include validating ​negligible voltage difference​ (ΔU <5%), ​phase angle alignment​ (<5°), and pre-calculation of induced ​circulating currents​ to ensure thermal/mechanical safety. Modern grids use dedicated protection schemes and IoT sensors for real-time monitoring.

          While distinct from high-risk synchronization (parallel operation) between asynchronous systems, improper ring-closing can still cause Protection relay maloperation or equipment stress. Thus, utilities mandate rigorous simulation studies and standardized switching protocols under N-1 contingency criteria.

1. Ring-Closing Operation:Definition & Context​

          A ring-closing operation involves closing a disconnection point (e.g., switch, circuit breaker) in an electrically closed-loop network fed by a ​single power source​ or tightly coupled sources. This converts radial feeders into parallel paths, redistributing loads while maintaining grid integrity.

​2.Ring-Closing Operation: Operational Workflow​

​Pre-Condition Checks:

  • Voltage difference < 5% at closing point.
  • Phase angle deviation ≤ 5°.
  • Circulating current calculation (must not exceed equipment ratings).

​Action Sequence:

  • Close tie switch/circuit breaker.
  • Monitor transient currents.
  • Transfer loads by opening the original feeder.

​Safety Mechanisms:

  • Differential protection.
  • Overcurrent relays with directional logic.

​3.Ring-Closing Operation: Applications​

  • ​Load Transfer: Hot-switching circuits during maintenance (e.g., substation upgrades).
  • ​Fault Management: Isolating faulted sections while restoring supply via alternative paths.
  • ​Loss Reduction: Optimizing power flow to minimize resistive losses in congested feeders.

​4. Ring-Closing Operation:Technical Challenges​

  • Circulating Currents: Result from voltage imbalances, potentially overheating cables/transformers.
  • ​Protection Coordination: Risk of relay misoperation due to altered fault-current paths.
  • ​Grid Stability: Voltage fluctuations during transition, requiring reactive power support.

​5. Ring-Closing Operation:Comparison with Parallel Operation

6. Ring-Closing Operation:Safety Protocols​

  • ​Mandatory Simulations: EMT/PSCAD modeling to predict dynamic behavior.
  • ​Grid Code Compliance: Adherence to IEC 61970/IEEE 1547 for interoperability.
  • ​Live Testing: Phasor measurement units (PMUs) for real-time angle verification.

7. Ring-Closing Operation:Industry Use Cases​

  • ​Urban Distribution: Ring-main units (RMUs) in cities for N-1 redundancy.
  • ​Renewable Integration: Seamless switching between hybrid sources (solar/wind/grid).
  • ​Microgrids: Reconfiguring islanded/localized networks without synchronization.
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