Voltage support
Switzerland’s extra-high-voltage grid has a voltage of 220 kV and 380 kV respectively. Swissgrid maintains the voltage within narrow limits. Voltage support is one of Swissgrid’s core tasks.
In Switzerland, the voltage is primarily regulated by power plants that feed electricity directly into the transmission grid. Their generators allow them to produce or absorb reactive energy to influence the voltage. There are also distribution grids that control their reactive energy exchange, similar to power plants, and thus allow them to actively influence the voltage. Swissgrid also has the option of tapping transformers between the 220 kV and 380 kV voltage levels in order to control the flow of reactive energy and influence the voltage.
The existing voltage support concept has been in force since January 2020. It provides for two types of voltage support, mandatory and extra-mandatory voltage support. All power plant operators, distribution grid operators, neighbouring system operators and the operators of customer systems connected to the transmission grid are required to participate in the mandatory voltage support. Here, a distinction is made between active and semi-active voltage support. Only power plant operators can participate in extra-mandatory voltage support.
The following figure shows the active and semi-active nodes in the Swiss transmission grid.
General voltage support documents
Active voltage support
Active participation in voltage support for the transmission grid is mandatory for the following participants:
- All power plants directly connected to the transmission grid which are in operation (production, pump mode or synchronous/phase shifting mode), within the scope of their available reactive power that can be exchanged with the transmission grid without compromising the active power.
- Distribution grids and end customers directly connected to the transmission grid that have declared their active participation, within the scope of their available reactive power that can be exchanged with the transmission grid without compromising the active power. This obligation exists regardless of their operating status and is considered permanent.
Where necessary, active participants are obliged to use the available reactive power, without compromising the active power mode, for the purpose of voltage support in the transmission grid. This necessity is deemed to exist for as long as the prescribed setpoint voltage value according to the voltage plan is not reached at the respective transmission system node. The voltage plan must be implemented by means of continuous adjustments to the reactive power exchange between the plant and the transmission grid. The plant operator is responsible for the specific technical implementation; implementation can take place automatically or manually.
Successful prequalification is a condition for active participation in voltage support in the transmission grid. Upon successful prequalification, the participant receives an attestation. The attestation is valid for five years after which, it must be renewed. The prequalification also has to be renewed in the event of significant changes to the equipment necessary for voltage support within the five-year period.
Active participants undertake to deliver reactive energy in compliance with the requirements. The exchange of reactive energy with the transmission grid is deemed to be compliant if it contributes towards the attainment of the specified setpoint voltage. The reactive energy exchanged every 15 minutes is compensated at the Remuneration rate for active participants for reactive energy supplied according to requirements, if the following requirements are met:
- Power plants: the power plant must be online and in production, pump or phase shifter mode during the relevant 15-minute period.
Active distribution grids: the distribution grid must have at least one online transformer/line at the outflow point . - the reactive energy exchange must be financially compliant during the relevant 15-minute period.
- the exchange must be compliant with the requirements during at least 80% of the meter intervals during the month in question.
For non-compliant reactive energy exchanged every 15 minutes, the active participant is billed according to the Individual AS tariff for reactive energy for active participants non-compliant with requirements plus a penalty.
Active voltage support documents
Semi-active voltage support
Semi-active participation in voltage support for the transmission grid is mandatory for the following participants:
- All distribution grids directly connected to the transmission grid
- All customer systems directly connected to the transmission grid
- All neighbouring system grid operators directly connected to the transmission grid
If they meet the technical requirements, they can prequalify for active voltage support.
Participants in semi-active voltage support do not take on any obligations with regard to active voltage support in the transmission grid. However, semi-active participants receive financial incentives for the (compliant) exchange of reactive energy that is beneficial to the system. Participants in semi-active voltage support receive a voltage plan from Swissgrid. Conformity is calculated based on the setpoint voltage, the actual voltage and the direction of the reactive energy exchange. Compliant exchange with the transmission grid is compensated at the Remuneration rate for behaviour of semi-active participants beneficial to the system and non-compliant exchange is billed according to the Individual AS tariff for reactive energy for semi-active participants non-compliant with requirements. An area for the free exchange of reactive energy also exists.
Extra-mandatory voltage support
Besides the obligations relating to mandatory voltage support, power plants directly connected to the transmission grid can also reach bilateral agreements with Swissgrid on the provision of extra-mandatory reactive power.
A participant wishing to offer extra-mandatory voltage support must prequalify for this voltage support and provide a reactive power band of at least ±5 Mvar. The entire available reactive power in operation at the feed-in point as a phase shifter must be able to be fully utilised within a maximum of 15 minutes, if necessary, in order to comply with the required setpoint voltage.
Swissgrid compensates the start-up of the generator, the operating hours as well as the exchanged reactive energy at the Remuneration rate for active participants for reactive energy supplied according to requirements.