Distributed Energy Resources (DER) and microgrid are typical ways to use renewables (e.g. wind, photovoltaic parks, etc.). They are fundamental elements of energy transition that form the pathway toward the global energy transformation to combat the global warming and the climate change. Take European Union as an example, the policy frameworks of EU 2020 Climate & Energy Package (COM/2010/0639), EU 2030 Climate & Energy Framework (COM/2014) and EU 2050 Climate-Neutral Economy (COM/2011/0885) have duly produced EU Climate Laws, EU Emission Trading Systems (ETS) and union strategy to stimulate the transformation. European member states interact with the European Commission to set up integrated National Energy and Climate Plans (NECPs). In many European countries, ENTSO-E grid code (RfG, DCC, HVDC) compliance guidelines for electricity transition framework are applied by energy and utility players with diverse focuses on the energy markets, system operation, and electricity connections.
Worldwide, for similar reasons, the renewable market is flourishing, as government and private sectors willingly encourage its adoption. With more DERs and microgrids maturing to participate in utility grid, their impact on the distribution networks need to be properly addressed. This contribution discusses the interconnection between renewables and the utility distribution network, and proposes the corresponding communication service requirements for protection mechanisms specifically.
Shown in Figure 5.16.1-1
is the ecosystem with existing DSOs and potential new stakeholders such as DER owners, DER operators, and/or DER aggregators. The focus of this paper is the interface for energy transport shown in red dashed lines. This interface includes both power interface (green line) and communication interface (blue line).
The "interface energy transport"
shown in Figure 5.16.1-1
could be embodied with a single Point of Common Coupling (PCC) illustrated in in Figure 5.16.1-2
, where the power grid could be a medium voltage (MV) substation, and the microgrid could be controlled by its own micro-Energy Management System (μEMS). μEMS communicates with the Distribution Management System (DMS) of a DSO. It is worth mentioning that when the microgrid in Figure 5.16.1-2
is replaced with a single DER, the interconnection with the utility power grid can be more precisely called the Point of Connection (PoC).
From the electrical system's safety and operation resiliency point of view, renewables are not just plugged in to feed the utility grid energy. Because of renewable generation's unpredictability (generation with increased variability), connecting DER or microgrid into the public distribution network need to fulfil a number of standards and requirements - to consider the fluctuating capacity flowing into the grid, more bidirectional flows at distribution level, issues like generator synchronization, and operation threshold conditions for voltage and frequency (i.e. under-/over-voltage, under-/over-frequency). Aside from possibly being used for power flow management (e.g. downward dispatch/curtailment trigger, etc.), PCC is also a control reference point for two power systems to interact, including the control of voltage magnitude and frequency regulation, injection and absorption of reactive power by DER, etc. Based on abnormal operation conditions, many regional and international standards have produced guidelines for measurements and specified conditions for triggering protection 
at the PCC interconnection. In this paper, the focus is on voltage and frequency protection. Tripping in this context is the action to clear abnormal conditions within a specific duration of time. Table 5.16.1-1
lists the required trip time values for different types of possible trips at PCC, based on a number of regional and international standards.
||Under Voltage Threshold 2
||Under Voltage Threshold 1
||Over Voltage Threshold 2
||Under Frequency Threshold 2
IEEE 1547 Cat I ||0.16||2||0.16||0.16|
IEEE 1547 Cat II ||0.16||10||0.16||0.16|
IEEE 1547 Cat III ||2||21||0.16||0.16|
IEC 63547 ||0.16||2||0.16||n.a.|
EN 50438 ||n.a||1.5||n.a.||n.a|
IEEE 929 ||0.1||2||0.03||n.a|
BDEW ||0.3||1.5 - 2.4||n.a||n.a|
It does not take much effort to notice that here the tripping time values for DERs are much more relaxed than those for a regular MV/HV substation. That is because for the PCC interconnect, protection functions are required to coordinate with other functions such as frequency ride-through and even ROCOF ride-through, meaning DERs are required to stay "on"
for much longer. Furthermore, two thresholds are introduced for DER tripping to prevent it from happening prematurely, which would compromise the stability of the bulk power system.
There are many available algorithms available for an IED to detect abnormal conditions and to further determine whether the tripping conditions are met. More algorithms are based on continuous measurements and comparison of local and remote measurement provided by PMUs. With renewables and DERs proliferating in the distribution networks, decisions on PCCs would need real-time measurements from multiple strategically chosen measurement points in the network.
Purely based on the values in Table 5.16.1-1
, it could be true that a PV-owner might opt for CS104 (or even OPC-DA, Profinet) that is simpler and cheaper to deploy. But these protocols are less flexible to support PMU multicast mode. That is where IEC 61850 adds value to the WAN protection mechanisms. In this case, multicast PMU data could be transferred via routable sampled values (R-SV) profile (IEC 61850-90-5). Similarly, the tripping command could be sent out by routable GOOSE (R-GOOSE) profile, or even as normal GOOSE provided the IED with protection functions and the circuit breaker for PCC are in the same LAN. When PMU data is multicast using R-SV profile, the transport should support source-specific advanced route path determination. This mechanism helps to mitigate the DDOS attacks known to multicast group addresses.
A number of wind and PV-parks are connected to the medium voltage substations of a utility DSO. Interfaces including PCCs are established between these systems. P class PMUs are installed at selected busses containing a load. PMUs and IEDs with control and protection functions are connected to the 5G network. The DSO also has a centralized Wide Area Monitoring Protection Automation Control (WAMPAC) application in the control centre. Depending on the control and protection functions, PMUs and WAMPAC can subscribe to different data such as synchrophasor, frequency, frequency and the rate of change of frequency (ROCOF) generated from a specific source PMU. The communication is supported by IEC 61850-90-5 standards.
Company U operates a large national grid. Thanks to U's existing IP/MPLS infrastructure, PMUs deployed in substations belonging to transmission grid are connected to this IP/MPLS network. The number of PMUs can range from a few hundred to tens of thousands. Each individual PMU continually streams measurement data to a number of PDCs located in control centers at different levels for monitoring and analysis performed by different teams (or analysis by IEDs - Intelligence Electronic Devices with e.g. protection functions). The network engineer Arjen configures in each IP/MPLS router, so that a dedicated VPN is used for transmitting R-SV (routed-Sampled Values) datagrams (Sampled Values can be generated by MU-Merging Unit, but here PMUs are able to generate Sampled Values too). Then, Arjen assigns IP addresses to PMUs from the IP/MPLS network. Due to the high number of PMUs, Arjen configures the IP/MPLS network to efficiently transfer the PMU data to destination PDCs. In the meantime, to improve security, Arjen uses the source specific multicast (SSM) feature to ensure the IP/MPLS network only forwards datagrams to receiving PDCs from only the source PMUs to which the receiving PDCs have explicitly joined. The multicast trees are static once the PMU application is up and running. Worth mentioning is that for each PMU, its corresponding multicast tree is built based on the WAN Smart Grid protection application logics. In other words, the multicast tree reflects where in the Smart Grid the R-SV measurement data from a particular PMU is needed.
With the renewables booming, the distribution grid of company U is connected to an increasing amount of PV parks and wind parks. At and around the interconnections, gradually more new PMUs are deployed. It is impractical to extend the IP/MPLS network physically to all these locations. Therefore, company U decides to make use of the 5G service from an operator KTT.
Now, for U's DERs and microgrids, Arjen again refers to the WAN Smart Grid protection application logics to configure the newly installed PMUs. The purpose is that these PMUs will virtually take part in the existing multicast trees in U's IP/MPLS network. Thanks to KTT's 5G_LAN service, these PMUs and control centre IP gateways are added to the VPN that Arjen previously configured in the IP/MPLS network. See as the extension of U's IP/MPLS network footprint, 5G delivers the PMUs' datagrams conforming the source-specific multicast a priori.
As a result, 5G network provides communication among the PMUs with PDCs in the control centres. A PMU produces a single source of R-SV measurements, and the 5G network delivers the measurements efficiently to the intended group of recipients.
Suddenly an outage of a distributed generator at a given site causes generation load imbalance (site 1). Similar conditions happen to another distributed generators connected nearby (site 2).
PMUs measure synchrophasors, frequency and ROCOF associated with the fundamental/primary components at various interconnections with DERs.
PMUs multicast measurement data to the subscribers, which could be other PMUs and the WAMPAC.
At abnormal site 1, based on the PMU's locally measured ROCOF, the protection function decides the problem to be a weak load imbalance. So the protection will not be triggered since the frequency is supposed to restore after some time. At other abnormal sites 2, similar decisions are made by the local protection functions.
However, the WAMPAC receives measurement from all of these PMUs. Based on its global view, it detects that area with prevalence of under frequency conditions spread among a number of DERs could potentially cause severe impact on the overall distribution grid. The WAMPAC decides to trip the generators in some of these problematic sites (treating the under voltage condition as severe imbalance), so as to prevent system collapse.
5G communication works properly. System collapse is prevented ensuring system resiliency. Additionally, with data measured by PMUs, the DSO has a good real-time view of operation states of DERs and how the energy flows throughout the networks.
The communication delay KPIs can be supported by the existing requirements.
The 5G system shall be able to deliver data originated by a UE to a group of recipient UEs distributed over a large geographical area.
The 5G system shall allow the originating UE to send data to several groups at the same time.
The 5G system shall enable recipient UEs to indicate their interest in receiving data from a specific originating UE.