C135 PCS 7 (PCS7)
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Diagnosing 'System State Changed to FAULT' and @RedundancyState Errors in SIMATIC PCS 7 WinCC

Diagnosing 'System State Changed to FAULT' and @RedundancyState Errors in SIMATIC PCS 7 WinCC

In SIMATIC PCS 7 WinCC, the runtime popup 'System state changed to FAULT' indicates that the internal redundancy tag @RedundancyState has transitioned to value 3 (FAULT). This failure occurs when an OS Server project configured for redundancy is launched on an Engineering Station or test PC where the redundant partner connection is missing, or when the Terminal Bus network card lacks a valid static IP address (such as using DHCP or suffering a disconnected physical link). To resolve it, assign a static IP to the Terminal Bus adapter, ensure the network link is active, and if converting a redundant server project into a Single Station for testing, remove redundant startup applications from Computer Properties > Startup.

Table of Contents

Executive Summary

High availability in SIMATIC PCS 7 Operator Stations is provided by redundant server pairs that cross-monitor heartbeats and synchronize process archives. However, automation engineers performing factory acceptance testing (FAT) or software debugging routinely test OS Server projects directly on an Engineering Station (ES) using the 'Allow runtime on ES' setting. When activating runtime on the test machine, an alarming system popup frequently appears: 'System state changed to FAULT', and the internal WinCC tag @RedundancyState transitions to 3. While engineers often assume a critical database corruption or software failure, this fault typically stems from invalid network adapter configurations (such as DHCP on the Terminal Bus) or residual redundant startup processes executing in a non-redundant environment. This technical guide outlines the root causes and resolutions.

WinCC Redundancy Architecture and the @RedundancyState Tag

WinCC Redundancy continuously evaluates server health via the Redundancy Control service (CCRedServer.exe):

  • Heartbeat telegrams are exchanged across two independent channels: the Terminal Bus (network adapter) and an optional serial / network Redundancy Link.

  • System health is exposed through the internal system tag @RedundancyState:

  • 0 = Not initialized or single station project.

  • 1 = Server is Master (active operational server).
  • 2 = Server is Standby (synchronized passive backup).
  • 3 = Server is in FAULT state.

Root Cause 1: Inconsistent Project Type Conversion (Redundant to Single Station)

When engineers attempt to convert a multi-user redundant server project into a standalone test project by simply unchecking 'Activate Redundancy' in the Redundancy editor, residual configuration artifacts remain:

  • Background tasks in Computer Properties > Startup still attempt to launch CCRedServer.exe or redundancy handlers.
  • Internal tags expecting a partner server fail to resolve, causing the redundancy state machine to enter FAULT state.

Root Cause 2: Terminal Bus Network Link and DHCP Configuration Faults

WinCC's communication kernel requires strict, deterministic network addressing:

  • DHCP Instability: If the Terminal Bus network card is configured for DHCP, lease renewals, gateway query delays, or missing DHCP servers cause Windows to assign an APIPA address (169.254.x.x), triggering immediate redundancy network failure.
  • Disconnected Cable (Media Disconnect): If the physical network cable is unplugged, Windows drops the link state; WinCC interprets the loss of network carrier as a fatal hardware fault.

Redundancy State and Error Condition Matrix

The following table categorizes @RedundancyState values, trigger conditions, and engineering responses:

Tag ValueOperational StateMeaningTrigger ConditionEngineering Response0None / SingleNon-redundant stationNormal for Single StationNo action required.1MasterActive Primary ServerNormal operationPrimary server servicing clients.2StandbySynchronized BackupNormal operationStandby server tracking master archives.3FAULTSystem FailureNetwork link down, DHCP issue, or crashed serviceCheck WinCC\Diagnose logs; verify static IP.

Step-by-Step Procedure to Resolve Redundancy FAULT Errors

Method 1: Configuring Deterministic Static IP on Terminal Bus

  1. Open Windows Network Connections (ncpa.cpl).
  2. Right-click the dedicated Terminal Bus adapter and select Properties.
  3. Select Internet Protocol Version 4 (TCP/IPv4) and click Properties.
  4. Change from 'Obtain an IP address automatically' (DHCP) to Use the following IP address.
  5. Assign a valid static IP (e.g. 192.168.1.10) and subnet mask (255.255.255.0).
  6. Ensure the network cable is connected to an active switch (or use a loopback connector during isolated mobile testing).

Method 2: Cleanly Converting Project for Non-Redundant ES Testing

  1. Open the project in WinCC Explorer on the ES.
  2. Open the Redundancy editor; uncheck Activate Redundancy.
  3. In WinCC Explorer, right-click the computer node and select Properties.
  4. Switch to the Startup tab.
  5. Review the Additional Tasks/Applications list; remove any entries referencing CCRedServer.exe.
  6. In the General tab, ensure the computer name matches the local PC's actual Windows hostname.
  7. Restart WinCC Runtime; confirm that the FAULT popup no longer appears.

Verification

To verify that redundancy errors are resolved:

  1. Tag Value Inspection: In WinCC Runtime, open a Tag Status view or APDIAG. Verify that @RedundancyState evaluates to 1 (if running as valid single master) or 0 (if non-redundant).
  2. Diagnostic Log Audit: Open C:\Program Files (x86)\Siemens\WinCC\Diagnose\WinCC_Sys_01.log. Confirm that no REDSVC: Partner not reachable or System state FAULT messages are logged.
  3. Popup Absence: Confirm that runtime activates cleanly without operator warning dialogs.

Limitations and Operational Precautions

  • Never Disable Redundancy on Production Servers: Modifying redundancy parameters on a live production OS Server pair destroys automatic failover and archive synchronization.
  • Dual NICs Recommended: Always utilize distinct physical network adapters for the Terminal Bus and Plant Bus to prevent traffic congestion and cross-talk.
  • Diagnostic Log Retention: Always archive the contents of WinCC\Diagnose before restarting services to preserve root-cause forensic data.

Engineer FAQ

Can a loopback adapter be used to test WinCC runtime without a physical network cable?

Yes, installing the Microsoft KM-TEST Loopback Adapter with a static IP allows testing WinCC Runtime on an isolated laptop.

Why does WinCC show FAULT when only the serial redundancy cable is disconnected?

If serial redundancy is configured as mandatory in the Redundancy editor, losing the serial link triggers a redundancy warning.

Does the @RedundancyState tag generate process alarms automatically?

Yes, PCS 7 APL and basic OS configurations link @RedundancyState to system alarms that annunciate on operator overview screens.

Technical References

Related Articles

Related Tags

  • https://industrialautomation.net/search?query=simatic-pcs7
  • https://industrialautomation.net/search?query=wincc
  • https://industrialautomation.net/search?query=redundancy
  • https://industrialautomation.net/search?query=troubleshooting
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