S2 : in the future additional services could be delivered by DER because distribution networks will no longer be designed following the "fit & forget" principle.
DER installed in medium and low voltage could deliver balancing services to the Transmission System Operator today. When “distribution” includes high voltage networks, other services can also be delivered, like for example voltage – var control. In the future, additional services will become necessary in Medium Voltage and even in Low Voltage distribution networks.
What type of services could be delivered to TSOs and DSOs in the future by DER installed in distribution networks?
For the sake of clarity it is important to distinguish “thick” from “thin” distribution networks
Transmission and distribution are not organised similarly in the different countries. Roughly speaking two types of organisations exist concurrently.
In the first one, TSO activities are limited to the upper layer of the system, which comprises of one layer, as in England and Wales with 380 kV or 275 kV or of two layers, as in Germany with the 380 kV and the 220 kV networks; the rest is considered as distribution. In these systems, distribution is made of at least 3 layers (“thick” distribution): high, medium and low voltages.
In the second type of organisation, distribution is only made of medium and low voltage networks (“thin” distribution); all other networks from high voltage up to ultra-high voltages being operated by the TSO.
Services will develop from “aggregated DER” to “integrated DER” as SmartGrid concept develops. Services for TSO and DSO
concern control “C”, emergency control “E.C.”,
congestion management “C.M” like implicit services such as those implanted via PowerMatcher, or during “N-1” conditions,
DR during restoration phase
In a “thick” distribution system the range of services that can be delivered today (or soon)
In the case of a “thick” distribution system a larger range of services can be proposed because the DSO operates high voltage networks, where big units can be installed that are often also referred to as DER. Services from these units are, in decreasing order of importance, voltage control or reactive power compensation; contribution to security of supply; power flow management services and eventually quality of supply services.
In a “thin” distribution system the range of services that can be delivered is limited to balancing active power
In the case of a “thin” distribution system, as considered within EU-DEEP, services are mainly supplied to the TSO because the distribution services are currently built to be unconditionally “adequate”. This means that no congestions can take place in normal situations as well as in the case of single contingency.
In the future, the range of services deliverable by DER will increase because MV and LV distribution networks will lose their unconditional adequacy
The proposed “UoS” tariffs tend to recognise the value of DER as “network replacement”. This will lead to the progressive disappearance of unconditional adequacy of distribution networks.
One can expect distribution networks to remain adequate when under normal operation and subject to limitation following “N-1” contingencies. This means that, at least for certain circumstances and probably during “N-1” situations, contributions from DER could be required to maintain the operating point within acceptable limits.
In the longer-term the number of services that could be delivered by DER to MV and LV distribution networks will increase
Assuming a design based on security in “N”, depending on the loading conditions, the distribution network could be at risk in the case of “N-1” contingency (note that these circumstances correspond to a low number of hours per year).
The management of these cases could rely on services coming from local DER. This could correspond to two different services: those where no limitation of the active power takes place and those where a reduction of active power injection is necessary.
The first ones can be implemented using “light” contribution of voltage control or reactive power compensation for releasing the less demanding power flow management services. For the more critical constraints, like power flow management in “N-1” situations, the corrective action could correspond to a sharp reduction of power injection (incidentally this is more a temporary constraint than a service brought to the system).
Quality of supply services could also be developed if the use of power electronics in generation as well as on the load side degrades power quality.
- Jacques DEUSETractebel EngineeringTechnical Director - WP2 Leaderemail
- Christine SCHWAEGERLSIEMENS PTDWP2email
- Vladimir CHUVYCHINRTUWP2email