WinCC V7 Redundant Server Licensing: Sizing Client Licenses

Siemens WinCC V7.0 SP1 is a SCADA system commonly deployed in redundant server / multi-client topologies for power, water, and process plants. The licensing model combines a per-tag PowerTags count, per-station Runtime (RT) authorization, optional Runtime and Configuration (RC) authorization, an explicit Client License (replacing the legacy RT-128 tag license), and a server-side Redundancy License that pairs with the WinCC Server option. The interaction of these components is the most common source of confusion when adding new client stations to an existing redundant pair.

1. WinCC V7 Redundancy Architecture Overview

A redundant WinCC V7 system consists of two server stations that mutually monitor each other. Process data is acquired on both servers in parallel; one server holds the active role (process server) while the partner holds the standby role. On standby failure of the active server, the partner takes over within the configured switchover time without operator intervention.

Each server hosts a complete project; data is exchanged via terminal bus and the WinCC Redundancy option, while clients connect to whichever server is currently the process server.

1.1 Logical Components

1.2 Why Redundancy Requires a Dedicated License

Although both servers run the same project and tag database, the runtime must explicitly know that the local instance is participating in redundancy. This is what the Redundancy License (sometimes referred to as the WinCC/Redundancy option) authorizes. Without it, the server runtime behaves as a standalone server even if the WinCC Redundancy option is configured in the project.

2. License Components Required per Station

The reference deployment in this article uses the following license stack, which represents a typical industrial-scale SCADA:

2.1 Server A and Server B (identical stacks)

2.2 Client Station

3. RT vs RC vs Client License: A Precise Comparison

Three authorization grades exist for V7 clients. Mis-selecting the grade is the most common licensing defect encountered during commissioning audits.

Selection rule for V7.0 SP1: If the new client is a pure operator station, install the Client License. If the new client must be able to edit the server project (download configuration changes, modify graphics, add tags, deploy), install the RC license instead. The legacy RT-128 tag-constrained license still operates against V7 servers when present on the client, but new deployments should use the Client License grade.

4. PowerTags Allocation: Where the Tag Count Lives

PowerTags is a per-tag licensing metric. A "PowerTag" is an internal or external process tag the project reads or writes, not an alarm or an archive tag. Alarm logging and archiving are not counted against the PowerTags limit.

4.1 Tag Counting Rules

• Counted: WinCC tags, structure tag elements, indirect tags (each pointer instance is a tag), and tags inside user archives when those tags are also process tags.
• Not counted: Archive tags, alarm tags, internal WinCC system tags, and connection-point tags.
• PowerTags is allocated at the server; the client sees all configured tags regardless of its own license grade when the Client License is used.

4.2 Verifying the Tag Count

Open the WinCC Explorer on the server, right-click "Tag Management" and choose "Statistics". The displayed total must be less than or equal to the licensed PowerTags count. In the reference deployment, 8192 PowerTags on each server is the project envelope; clients add no tag count to the server.

4.3 Upgrading PowerTags

Siemens ships PowerTags license upgrades as cumulative counts (e.g. 128, 256, 512, 1024, 2048, 4096, 8192, 16384, 65536). Licenses are additive on a given server. The 8192 count shown above is reached by stacking the standard package with cumulative upgrades. Verify the cumulative sum in the Automation License Manager on the server; do not trust the printed certificate alone.

5. How Many Clients Can Be Added?

The number of clients in a WinCC V7 server-client topology is limited by the WinCC Server license and by the project's Max Clients setting, not by the server's PowerTags count.

5.1 Default and Maximum Client Counts

5.2 Single Client Reference Deployment

In the reference system described in the source, the project contains one client station. The system administrator can add up to 31 more clients (for a 32-client total) without acquiring additional server-side licenses, provided each new client installs a valid Client License (or RC license, depending on operator/engineering role). Each added client is a separate client PC with its own license key.

5.3 What Each New Client Requires

Adding a new operator-only client requires exactly one new authorization per client PC:

1. WinCC Client License (preferred for V7.0 SP1) — a single license, not stacked on tag count.
2. If a legacy RT-128 (or other RT-grade) license is already in stock, it is acceptable on the new client; it grants a tagged number of client-side subscriptions but functionally behaves as a client license for connection to a V7 server.
3. If the new client must configure the server project, use the RC license instead of the Client License.

The new client does not require PowerTags license, a WinCC Server license, or a Redundancy license. Those are server-side only.

6. Redundancy License Behavior in Detail

The WinCC Redundancy license controls whether the WinCC runtime on a given server engages in the partner-monitoring protocol. Both partner servers must hold the license; a single-server deployment with a Redundancy license will simply run as a standalone server, with the redundancy logic dormant.

6.1 Required Server-Side Configuration

Beyond the license, the project must be configured for redundancy on each server:

• In WinCC Explorer: Redundancy > Server tab: set the partner server name and IP address.
• Set the watchdog / life-bit interval (default 5 s).
• Define the switchover time (default 30 s for slow networks, 5-10 s for switched gigabit).
• Enable or disable the User Archives redundancy sync if User Archives is licensed.

6.2 Switchover Time Versus Tag Count

Switchover time depends on the data volume to be reloaded into the partner server's picture cache and on network latency. With 8192 tags and a clean gigabit terminal bus, switchover typically completes in 15-25 seconds; with a saturated 100 Mbit link and high archive replay, 30-60 seconds is common. Plan operator handover procedures for the worst-case switchover.

7. License Server Configuration with Automation License Manager

WinCC V7.0 SP1 uses the Siemens Automation License Manager (ALM) and, beneath it, the Flexera FlexNet publisher for license storage and checkout. Each PC participating in WinCC runtime requires a functioning local ALM service.

7.1 Single-Node License Storage

On a standalone server, the ALM service runs on the server itself and licenses are stored on a local license key (USB dongle or hard-disk license file). This is the simplest configuration and is sufficient for the reference deployment.

7.2 Central / Redundant License Server Topology

For deployments that span multiple physical PCs and where license keys must be shared, Siemens supports a centralized or redundant license server. The license server itself does not need to be the WinCC server — it can be a dedicated machine running the ALM service.

When you have multiple ALM license servers configured as redundant, the same license key can be installed on both. The WinCC runtime will check out its license from whichever ALM server responds first; the second ALM server is a hot-standby. This protects against a license-server failure interrupting the SCADA. The principle is similar to other vendor license server pairs and follows the Flexera FlexNet redundant server model: each license server holds an independent copy of the same license key, and clients transparently fail over to the surviving server.

7.3 Verifying the License Server Is Reachable

1. On the WinCC server, open the Automation License Manager.
2. Confirm the connected license server hostname (or localhost) in the title bar.
3. Open View > Licenses and verify each required WinCC license is present and not in "trial" state.
4. Check the WinCC runtime startup log (WinCC_Startup.log in the project directory) for lines beginning with LIC:<date> showing each license being checked out.

8. Commissioning Checklist for a Redundant WinCC V7.0 SP1 System

Use this checklist to verify the licensing of a new redundant deployment before process values are routed through it.

1. Each server has WinCC Server, RT, PowerTags 8192, Redundancy, and User Archives licenses present in the ALM.
2. Both servers show identical tag counts in Tag Management > Statistics.
3. Both servers connect to the same project directory (or mirror projects via redundancy-aware distribution).
4. The Redundancy option is enabled in the project on both servers and the partner address is correct on each.
5. At least one client has a Client License (or RC license) installed, with the correct server name configured in the client project.
6. The redundant ALM license server is reachable from both WinCC servers and from each client (if clients use a remote ALM).
7. Operator pictures, scripts, and alarm logging have been tested for switchover behavior — specifically, that the new client retains a working connection after the active server is forced to fail.
8. WinCC startup logs on all stations contain no LIC:ERROR entries and no "License not found" messages.

9. Common Licensing Errors and Their Meaning

10. Migration Notes: From RT-128 to Client License

Sites upgrading from WinCC V6.x to V7.0 SP1 often have RT-128 client licenses already deployed. These are valid against V7 servers and may remain in service. The only difference is the tag count cap: an RT-128 client cannot subscribe to more than 128 tags as the "source of truth" for its local caches, while a Client License has no such cap and simply subscribes to whatever the server publishes.

For a retrofit where a client is being moved from operator-only to engineering, the operator-grade Client License should be replaced by an RC license, not stacked on top of it. Stacking two licenses on one client is wasteful and does not unlock additional capabilities.

11. Best Practices for License Management in a Redundant Plant

• Maintain a license inventory sheet per server, including the Automation License Manager screenshot at commissioning and at every change.
• Store physical license keys (USB dongles) in a labeled, ESD-safe enclosure attached to the server. Loss of a dongle stops the server's runtime.
• For hard-disk licenses, back up the license container file and the corresponding license certificate on a media separate from the server.
• When using a redundant ALM license server, install the same license keys on both ALM nodes and verify automatic failover by stopping one node during a scheduled outage.
• When increasing client count, the server-side cap is 32 (or 64 with the upgrade option). Plan hardware and licensing for that ceiling before the 30th client connects.
• Do not mix client license grades unnecessarily. Use Client License for operator stations, RC only on engineering stations, and never both on the same PC.

12. Frequently Asked Questions