Types of Prosumer electrical installation according to IEC 60364-8-82
IEC 60364-8-82 (2022 edition) defines prosumer's electrical installation (PEI) as:
- low-voltage electrical installation connected or not to a distribution network able to operate:
- with local power supplies, and/or
- with local storage units,
- and that monitors and controls the energy from the connected sources delivering it to:
- current-using equipment, and/or
- local storage units, and/or
- distribution networks
IEC 60364-8-82 (2022 edition) defines 3 types of Prosumer electrical installation (PEI)
- Stand-alone PEI
- Grid connected PEI
- Islandable PEI
Note: IEC 60364-8-82 is the new standard number since its 2022 edition. The first edition (2018) was IEC 60364-8-2.
A stand-alone PEI is a PEI permanently not connected to a distribution network (IEC 60364-8-82 2022 82.3.15).
There are no new specific requirements for such installation that are existing for a long time (typically building far from any distribution network in a remote area such as mountain refuge) .
For a stand-alone PEI, voltage and frequency shall be set by a grid forming source (for example one rotating generator or one grid forming converter).
Grid connected PEI
A grid connected PEI is a PEI intended for operating only when connected to a distribution network (IEC 60364-8-82 2022 82.3.14).
Protective measures against electric shock inside the installation rely on the connection to the distribution network. Operation and control can be quite simple, nevertheless a grid connected PEI needs an Electrical Energy Management System (EEMS) to ensure proper functioning of the installation, and achievement of energy efficiency objectives (when a local renewable source such as PV production is not working properly, the installation is still supplied by the distribution network: with no EEMS, the loss of the renewable source is not detected, which may impact the carbon reduction goals).
Interaction with the distribution network is set by regional, national or local grid codes.
In case of loss of mains or if voltage, frequency or other power quality values are out of their tolerances as defined by the Distribution Network operator, no local power supply shall remain connected to the distribution network nor to the installation. Although this may at first seem counter-intuitive, it addresses a serious safety concern. In case of utility supply loss, installations with local generation are required to guarantee that they do not inject power into the grid to keep utility workers safe. Additionally, if the prosumer installation is not designed to operate disconnected, protective measures against electric shock inside the installation may be not effective anymore as well.
An islandable PEI is a PEI intended for operating either being connected to a distribution network or being disconnected from the distribution network: An islandable PEI is in a connected mode or an intentionally island mode. (IEC 60364-8-82 2022 82.3.16)
For islandable PEIs in island mode, voltage and frequency shall be set by a “grid forming” source (for example one rotating generator or one grid forming converter). Other “grid following” sources may be added in parallel
Photovoltaic installations cannot ensure standalone operation of the electrical installation in off-grid mode because the solar energy produced is volatile, predictable but unplannable, and has limited control capabilities. To provide an islanded operation, photovoltaic installations must be associated with another major and stable source such as energy storage or a generator.
Operation of such an electrical installation in both grid-connected and islanded mode is more complex, and will require a specific electrical installation design, an additional control system, and an effective protection plan for each operating mode. See Calculation rules when integrating solar and storage.
Such a PEI shall be connected to the distribution network through a “Switching device for islanding” (SDFI) as described in IEC 60364-8-82 184.108.40.206.3.
Islanded mode can start
- automatically in case of loss of mains and/or
- intentionally on building operator request
The SDFI opening will initiate islanded operation meaning for AC system:
- Create local neutral to earth link if necessary.
- Change control mode of a “grid forming” source to start voltage and frequency regulation.
- Manage loads according to local production and storage capacity
During islanded operation the closing of this SDFI shall not be possible except when voltages of PEI and Distribution Network are synchronized.
Return to grid connected mode can be done without power interruption with synchronization of islanded PEI voltage system and distribution network voltage system or with a power outage (switching of local sources, opening local neutral to earth link if any, closing the SDFI, restarting the local sources in grid following mode).
Return to grid connected mode may need Distribution Network Operator’s allowance in some cases.
Islandable PEI may have to be combined with a back-up generator.
Operation of Electronic Power Converter sources such as PV and battery in parallel with generator requires special attention for the stability of the system.
Loss-of-mains protection (or Anti-islanding)
Grid connected and islandable PEI shall be protected against “Loss of mains”: In case of loss of mains or if voltage, frequency or other power quality values are out of their tolerances as defined by the Distribution Network operator, local sources shall be disconnected from the distribution network. Detection of such situation is specified by regional, national or local “grid code”.
Detection of such situation is usually based on phase undervoltage and phase overvoltage protections; and underfrequency and overfrequency protections. Optionally other protections may be required such as: rate of change of frequency protection, reverse power protection.
The settings are generally defined by Distribution Network operator specifications or local regulations. These settings are defined to meet several requirements in particular "LVRT" and "FRT" requirements
- Low voltage ride through (LVRT) is the capability of local sources to stay connected for a short period of time where the frequency is out of specified tolerance.
- Frequency ride through (FRT) is the capability of local sources to stay connected for a short period of time where the frequency is out of specified tolerance.
The selectivity of the loss of mains protections with short-circuit protections or other foreseeable disturbances such as voltage drop inside the PEIs should be ensured as far as possible.
This "Loss of mains" protection is called "anti-islanding" protection by the distribution network operator. The unwanted situation for the distribution network operator is to have a part of its distribution network energized by a prosumer during grid outage.
Some national regulations (see for example Switzerland RR/IPE-NR 7 – CH 2020) requires redundancy of the disconnection means in case of loss of mains.
This redundancy is ensured either by: - two switching devices in series controlled by the loss of mains (or anti-islanding) relay - one switching device AND all local sources controlled by the loss of mains (or anti-islanding) relay
Loss of mains (or anti-islamnding) relay and related switching devices need to be controlled independently of the main power to withstand low voltage ride through requirements. So dedicated auxiliary supply with a short storage capability is required.