Medium voltage directive
The medium-voltage directive (full designation: directive for the connection and parallel operation of generation systems on the medium-voltage network ) applies to energy generation systems (including solar systems , biogas generators or wind power plants ) in Germany with a peak output of more than 100 kW that feed their output into the medium-voltage network. It serves to ensure the quality of care .
history
The guideline was drawn up in 2008 by the German Association of Energy and Water Management (BDEW) and has been complied with since January 1st, 2009. However, transition periods apply. Generating plants installed before this date are not affected by the directive.
The requirements that the medium-voltage directive places on energy generation systems mean a fundamental change in direction in the function of the inverters that connect the generation system to the public grid. Generating plants must now be able to participate in voltage maintenance in a regulating and stabilizing manner during the grid feed-in. A distinction is made between static and dynamic network stabilization .
In 2018, the MS directive was replaced by the VDE application rule (FNN) VDE-AR-N 4110 (technical connection rules for medium voltage).
| Technical requirement | to be adhered to (the date of the application counts) |
|---|---|
| Static voltage maintenance | July 1, 2010 |
| Dynamic grid stabilization (limited) | July 1, 2010 |
| Certification obligation | July 1, 2010 |
| Dynamic grid stabilization | January 1, 2011 |
conditions
Static network stabilization
At the request of the network operator, inverters must be able to feed inductive or capacitive reactive power into the network in order to balance the reactive power balance in the network and to keep the network voltage in the medium-voltage network stable.
In addition, it must be possible to automatically reduce the active power depending on the grid frequency . This happens via a characteristic curve called statics (40% per Hz) from leaving the normal frequency band at 50.2 Hz (upper frequency limit of the primary control) up to the shutdown of the generating unit at a frequency greater than 51.5 Hz. This behavior has been assigned to the TransmissionCode Taken in 2007 so that medium-voltage systems behave in the same way as power plants on the transmission network with regard to the global size of the network frequency.
Dynamic grid stabilization
The dynamic grid stabilization ensures that the voltage is maintained in the event of small, controllable grid faults in order to prevent unintentional simultaneous shutdown of the feed-in power and thus entire grid failures . In the event of faults in the network, the generating plants must not simply switch themselves off and must provide a defined short-circuit current in the event of a short circuit in the public network .
This driving through a fault is known under the abbreviation FRT for Fault Ride-Through . In addition to simply driving through, i.e. not disconnecting and feeding in immediately after a fault has been cleared, a contribution to the short-circuit current is also required. The system must feed a defined reactive current to the fault in order to help clarify the fault and trigger the protective devices . In the event of a voltage drop of 50%, a maximum short-circuit current equal to the nominal current is required. In order to give the manufacturers of the generating units the time they need to carry out these complex developments, the requirement for a "restricted run-through" without reactive power feed to the fault has been in force since July 2010. Full functionality has been required since the beginning of 2011.
Certification
As part of the new medium-voltage directive, certification of power generation systems, such as B. photovoltaic systems, prescribed. In the certification process, a distinction is made between two different certificates: the certificate for the entire system and the certificates for the generating units, i.e. the inverter. The respective manufacturers provide the certificates of the generating units.
The units and systems are certified by a certification body accredited by the German Accreditation Service (DAkkS) according to DIN EN ISO / IEC 17065 and approved by the BDEW, which confirms the conformity of the system properties with the requirements of the medium-voltage directive.
Directive-compliant inverters
Although the guideline has been in effect since January 1, 2009, inverters that meet their requirements did not appear on the market until mid-2010.
Web links
- BDEW (Ed.): Technical Guideline for Generating Plants on the Medium-Voltage Network (PDF; 2.4 MB), Berlin, June 2008.
- BDEW (Ed.): Regulations and transition periods for certain requirements in addition to the BDEW MS Directive 2008 , Berlin, February 2011.
- BDEW (Ed.): Technical connection conditions for connection to the medium-voltage network (TAB Medium-voltage 2008; PDF; 850 kB), Berlin, May 2008.
- KACO new energy: The medium voltage directive. From feeding in to network management. , Neckarsulm, December 2010.
- SMA: SMA shifts the phase - Why reactive power is important and correct, October 2009.
Individual evidence
- ↑ Technical connection rules for medium voltage (VDE-AR-N 4110). FNN, May 17, 2017, accessed July 15, 2018 .