Fail-safe operation (reactive power)

Last modified: 2026-03-23

About fail-safe operation for reactive power

Fail-safe operation prevents a power plant system from entering an undefined operation mode in the event of a communication error. 

You can configure fail-safe operation for reactive power to determine the behavior in case of:

• Communication failure with the grid operator interface.

• Communication failure with a meter.

You can configure plant behavior for each type of communication failure. The error behavior is only activated after a user-defined waiting time has elapsed for each type of failure. 

Communication failure with the grid operator interface

Depending on the configured setpoint command mode in reactive power control (see Reactive power (Hybrid EMS)), the blue'Log XC relies on receiving signals from the grid operator to determine the setpoint.

A communication failure between the grid operator and the blue'log XC triggers fail-safe operation.

The setpoint is now determined based on the error behavior mode you have configured. The following modes are available:

• Default value: Define a default value of the setpoint (Q or cos φ). Additionally, you can add a voltage limitation for Q.

• Hold last value: The controller maintains the original operation mode with the last valid signal received via the grid operator interface.

• Q(V): See Characteristic curve Q(V).

• Q(P): See Characteristic curve Q(P).

The remaining components of the Q controller (control value determination and control value dispatch) continue to operate as usual.

Communication failure with a meter

To perform reactive power control, the blue'Log XC relies on measured data from a connected meter.
If the meter fails or communication to it is lost, the blue’Log will enter the configured error behavior.

Since the feedback signal from the grid connection point is no longer available, the blue’Log always switches to open-loop operation and applies the configured error behavior as the control value.

There are two options for the error behavior:

• Default value: Define a default control value (Q or cos φ).

• Hold last value: The controller maintains the last valid control value.

The remaining component of the Q controller (control value dispatch) continues to operate as usual.

Configure fail-safe operation

Prerequisites

• Hybrid EMS license

Steps

1. Go to Power control > Reactive power > Fail-safe operation.

2. Under Setpoint failure, configure the desired error behavior for the plant.

3. Under Meter failure, configure the desired behavior for the plant.

4. Select Save.

Fail-safe operation is configured.