Power supply monitoring

The power supply monitoring functions described in this section are available for the MDP92A power supply module, which has a connection to the supply system.

The MDE90A DC/DC converter module does not have an AC connection, which is why the power supply monitoring functions are not available with this device. If the MDE90A is configured as a module bus slave, it can receive the information about this from the module bus master in the event of a phase failure and respond in accordance with its configuration.

The line frequency of the connected supply system must be set correctly so that the line voltages can be measured correctly. This takes place using parameter "8809.20 Line frequency".

The power supply monitoring functions are called up at 1 ms intervals. The monitoring functions basically relate to the grid phase-to-phase voltage.

The following events are monitored and reported:

  • Line phase failure
  • In the device status, the flag of the failed phase is set to "0" in the grid condition. The line phase failure is not parameterizable. If a phase failure is detected, it is signaled, and the grid condition is adapted accordingly.
  • Power failure
  • All flags of the grid condition are set to "0" in the device status.
  • Line overvoltage
  • Line undervoltage

The following limit values are available for monitoring:

  • Parameter "8809.21 Power off threshold"
  • If all phase-to-phase voltages exceed this threshold, "Grid ON" is detected and grid monitoring starts. If one of the phase-to-phase voltages drops below the set value, averaging of each phase-to-phase voltage for 100 ms starts. If all phase-to-phase voltages fall below the set value while this averaging is taking place, a power failure is detected and the relevant fault "E6.2 Power failure" is signaled and the grid condition is adapted accordingly using parameter "8809.24". Monitoring starts from the beginning.
  • After 100 ms the mean value is checked on the basis of parameter "8809.23 Minimum line voltage" as described below and fault "E6.4 Line undervoltage" may be signaled. If no fault is detected, monitoring starts from the beginning, from the point detected as "Grid ON".
  • Parameter "8809.22 Maximum line voltage"
  • If one of the phase-to phase voltages exceeds the set value, the device signals fault "E06.3 Line overvoltage".
  • Parameter "8809.23 Minimum line voltage"
  • If "Grid ON" is detected, the 100 ms averaging starts. The averaging also starts if one of the phase-to-phase voltages has dropped below the value set here, and not only if it undershoots parameter "8809.21 Power off threshold". If the averaging process has been completed, it is checked whether one of the mean values has fallen below the set voltage. If this is the case, fault "E6.4 Line undervoltage" is signaled and the grid condition is adapted accordingly using parameter "8809.24".
  • If "DC 24 V Standby operation" is active, the AC monitoring system does not signal a fault.
  • This only applies if the device starts directly in "DC 24 V Standby operation" or is in this status. For more information, see also chapter Rapid undervoltage detection and DC link monitoring.
  • This means that the device reverts to this condition due to a power failure, for example, and the line fault is signaled correctly. After the fault has been reset, the monitoring must not signal any fault providing that the device is still in "DC 24 V Standby operation". In other words, a fault is not directly signaled if the grid is not yet available.