Definition
RTU (Remote Terminal Unit) collects primary equipment telemetry and telecontrol data in substations and executes remote adjustment and control. It is the foundation of grid dispatch automation. Traditionally, the main links are based on power private networks and synchronous fiber-optic digital systems. With the widespread adoption of auxiliary monitoring, online monitoring, and mobile inspections, some sites have introduced cellular networks as backup or supplementary links, especially during emergency communications and technical transition periods.
Dual SIM backup usually refers to having two IoT SIM cards from different operators or different network systems. The gateway automatically switches when the link quality degrades to avoid a single point of failure causing "blind control." The distinction between cold/warm backup, primary/secondary priority, and failback conditions must be clearly defined to prevent ping-pong switching that could trigger master station alarm storms.
Technical Features
Address NAT, DNS, and certificate verification failures and retries during switching moments; it is recommended that the session layer supports fast reconnection and data retransmission. In terms of cost, the primary and backup SIM cards may incur double monthly fees, which can be controlled by low-traffic plans plus event-triggered upgrades.
SimtoLink supports online monitoring at the SIM card level, regional restrictions, and remote deactivation, facilitating account closure when equipment is decommissioned. For classified substations, industry security standards must be followed, and cellular networks should only be used for non-control or approved limited services.
Use Cases
In remote substations, island microgrids, post-disaster repair command centers, and temporary mobile substations, dual SIM cellular networks can improve accessibility. For major urban substations, they mostly serve as heterogeneous backups to fiber main links.
In operations and maintenance, regular switching exercises should be conducted, verifying the source addresses and security policies on the main station side; the switching events should be included in the monthly operation report, continuously optimizing thresholds and operator combinations.
Deployment and Operation Recommendations
During the project implementation phase, enterprises should bind the IoT SIM card numbers to device serial numbers, installation locations, power supply methods, and maintenance responsible persons one-to-one, and sync this information into the asset and operation system to form a traceable link from card issuance, modification, activation, suspension to eventual cancellation. For equipment involving cross-province allocation or cross-border delivery, roaming charges, real-name registration policies, and local data compliance requirements should be evaluated in advance. It is recommended to choose solutions with predictable costs that support remote network switching or eUICC, reducing the frequency of on-site disassembly, and reserving spare cards and emergency replacement processes to shorten fault recovery time. For terminals received in bulk, it is recommended to perform sampling network verification covering connectivity and charges before activating the entire batch, to reduce rework costs.
In terms of cybersecurity, it is recommended to configure dedicated APN or VPDN tunnels for production or critical infrastructure terminals, converge north-south traffic to enterprise-controllable boundaries, and link with identity authentication, bastion host remote maintenance, and operation auditing; for remote control and parameter writing capabilities, hierarchical authorization, time windows, and dual-person review should be set. Regular drills for weak network and primary/backup link switching should be organized, recording latency, packet loss, and recovery time as technical references for MLPS (Multi-Level Protection Scheme) assessment, industry regulatory inspections, or internal risk control reviews. For third-party outsourced operations, minimum permissions, session recording, and key custody responsibilities should be clarified to avoid account sharing.
In daily operations, card management platforms should be used to continuously track online rates, abnormal traffic, dormant terminals, and data plan utilization, integrating alarms with the ITSM work order system to achieve automatic ticket assignment and closure. SimtoLink can split data pools for enterprises by factory, line, or business domain, providing bulk device suspension/resumption, API integration, and billing allocation capabilities, supporting visibility, control, and sustainable cost reduction at large-scale points, while aligning card management insights with project budgets and cost centers to improve transparency.