Medium-voltage connections

As a rule, connections over 15 MVA are connected to the high-voltage distribution network. The power limits mentioned above are indicative and may be deviated from for justified reasons. Electricity delivery for a medium-voltage connection is at 20 kilovolts.

When planning a medium-voltage connection, it is advisable to contact Caruna as early as possible. Once the power demand is known, Caruna performs a connectivity assessment to determine whether the connection can be made to Caruna’s network at the desired location and prepares a preliminary plan for implementation. The preliminary plan also defines the delivery time and the immediate expansion costs resulting from connecting to the electricity network. Caruna determines a feasible connection point to the nearest technically connectable point in the medium-voltage network.

For preliminary planning and connectivity assessment, information is needed on the maximum power of consumption and equipment, the type of consumption, and whether a backup connection is required. The customer must provide Caruna with a site plan showing the planned location of the substation or equipment to be connected and the planned cable routes, if known. For production plants, information is required on the type of plant, maximum production power, and the need for a backup connection.

It is in everyone’s interest to review the implementation of the connection during the planning phase so that the actual construction can be carried out according to agreed solutions. This helps align the connection construction with the project schedule.

The connection point is located at Caruna’s substation or at a switching station built as the connection point. The customer both owns and pays for the equipment beyond the point of connection and is responsible for the connection cable and excavation work.

Connections under 5 MVA are generally connected to Caruna’s switching station, which requires a location on the customer’s property. We primarily prefer an outdoor switching station. If no outdoor location is available, the switching station can also be built indoors in a dedicated switchgear room, provided Caruna has free access to it.

The customer is responsible for building the connection cable from the switching station to their own 20 kV switchgear. The connection point is at the cable terminals of the connection cell in Caruna’s switching station. Energy metering for the connection is located in the customer’s switchgear.

Connections over 5 MVA are mainly connected via the customer’s connection cable to Caruna’s substation at the 20 kV switchgear cell. The customer is responsible for building the 20 kV connection cable from the substation to their own switchgear. In this case, the connection point is at the terminals of the connection cell at the substation. Energy metering for the connection is also located in the customer’s switchgear.

Modifications to existing 20 kV connections are reviewed on a case-by-case basis. If the customer’s medium-voltage switchgear is renewed, the technical solution follows the principles of a new connection. Changes from low-voltage connections to medium-voltage connections are carried out according to the principles of a new connection. When modifying connections, it is advisable to review the lifecycle of the connection and replace parts of the electrical system that are nearing the end of their service life.

The price of a medium-voltage connection consists of immediate network construction costs and a capacity reservation fee. For increasing the size of a medium-voltage connection, the customer is charged for the immediate network expansion costs and a capacity reservation fee based on the difference between the new and old connection capacity. When changing the voltage level, the low-voltage connection right is credited as power corresponding to its ampere size.

The connection is built based on the connectivity assessment and after the connection agreement has been signed. The construction schedule must be aligned with the building project.

The customer is responsible for building the connection from the point of connection to their own switchgear. Caruna constructs its own 20 kV network and switching station through its network construction partners, who prepare detailed implementation plans together with the customer. Caruna’s contractor connects the customer’s connection cable to Caruna’s switching station or substation. The insulation resistance measurement of the customer’s 20 kV connection cable and the continuity measurement of the grounding must be carried out together with Caruna’s representative before commissioning the connection.

The customer’s electrical contractor orders the commissioning of the connection (voltage is applied to the connection cubicles and connection cable) using the general information form available on Caruna’s website.

The customer must provide Caruna with network documentation and all necessary information for commissioning well in advance of the connection and commissioning.

For network documentation, the following must be provided:

• Final main diagram of the customer’s electrical network at the connection point voltage level (including ownership boundaries if applicable – customer / network company)
• Location data of the customer’s connection cable (dwg/tky), length of the connection cable, and connection date
• Type of the customer’s connection cable (electrical data, data sheet: cross-section, resistance, reactance, operating capacitance, 1s short-circuit withstand, maximum load current)
• Identification of the customer’s network in the field (switching devices, substations/disconnector stations)
• Generators: rated power, rated voltage, type of generation, short-circuit current feed capability (%), power factor, efficiency, grounding method (grounded = yes/no)
• Magnitude of the customer’s earth fault current compensation (A)

For commissioning, the following must be provided:

• General information form
• Commissioning and testing reports for the customer’s 20 kV equipment
• Relay testing reports if the equipment is protected by a relay-controlled circuit breaker
• Route/locking instructions or diagrams showing the locations of any key safes, etc.
• Report on the earth fault current produced by the customer’s network and its compensation
• Measurement documentation: circuit diagram, burden calculation for current transformers, and loss calculation for voltage transformers

In addition, the customer must appoint an operations manager and provide their contact details (name, phone number, and email address) to Caruna no later than three months after commissioning the medium-voltage connection.

The point of connection defines the ownership and responsibility boundary between the customer and Caruna. Wires, cables, and equipment beyond the point of connection are the customer’s responsibility for maintenance and fault repair.

Maintenance and repair of components owned by the customer (e.g., cable terminations) located at Caruna’s network sites must be carried out by a contractor approved and trained by Caruna, using appropriate materials. Before doing any work, the customer must ensure that electrical tasks can be performed in compliance with safety regulations and that the work has been agreed upon with Caruna.

Outages required for maintenance and testing of Caruna-owned network components are agreed upon in advance with the customer.

Detailed instructions for operation can be found in the attachment below.

The requirements for real-time data exchange are based on Fingrid’s system technical requirements and Caruna’s needs for network monitoring and management. These requirements apply to all customers connected to the medium-voltage and high-voltage networks.

More information about real-time data exchange can be found at the link below.

If an outage is needed at the customer’s substation, it must be ordered from Caruna at least six working days before the planned outage date. Caruna is responsible for managing the connection state in the distribution network and performs the necessary switching operations at the switching station and substation to which the customer’s connection is linked.

An outage can be ordered using the general information form or by sending the outage request form by email to kytkennat@caruna.fi. In the email subject line, include the following details: Municipality, Medium-voltage connection outage, customer name, and outage date.

Detailed instructions for ordering outages can be found in the MV and HV connection operation file (in Finnish).

If there are multiple measurements under a medium-voltage connection, they should primarily be implemented as sub-measurements (i.e., measurements whose consumption is not included in the main measurement of the connection’s primary metering point). In this case, the main measurement does not show the consumption of sub-measurements, and sub-measurements are not included in the customer’s main measurement.

On the medium-voltage side of the connection, there is only one network operator’s meter, which for new connections is located in the customer’s switchgear. Energy metering follows Caruna’s energy metering guidelines.

For back measurements, the customer is responsible for necessary switchboard modifications and wiring, and sub-meters are always placed on the low-voltage side of the medium-voltage connection. It is especially important to ensure that:

• Measurements of low-voltage connections are each connected to their own riser cable
• Measurements of low-voltage connections must not be in series connection
• Meters must be placed  and organized consistently by stairwells or floors in the same location unless they are all in the same room
• The network operator must be able to disconnect each electricity usage point individually without affecting other customers
• Sub-measurement customers receive a network agreement based on fuse size. Consumption from sub-measurements is deducted from the main measurement. If reactive power billing applies to a sub-measurement customer, reactive power is also deducted from the main measurement.