Compensation of Reactive Power

Ensto has extensive experience in providing turnkey solutions for compensation of reactive power to underground cable networks, covering everything from needs assessment to commissioning and maintenance.

Management of Reactive Power Compensation

The need for reactive power compensation has increased due to the rise in medium voltage underground cabling. However, the reactive power produced by the network must remain within the limits set by the transmission system operator, which is why distribution system operators use compensation reactors to limit reactive power.

The reactive power produced by underground cables raises the voltage, especially when there is no load. Excess reactive power typically occurs in the summer when the network load is small relative to its capacity. Managing reactive power frees up network transfer capacity and promotes reliable network operation.

Ensto offers compensation reactors and comprehensive solutions as a turnkey service for compensation of reactive power, for both centralized and decentralized needs. The turnkey services include all from the needs specifications and devices to commissioning and maintenance services. The solutions are always carefully planned based on and configured to meet the customer’s needs.

Our Solutions

Centralized Compensation

Centralized compensation is an efficient and quick way to compensate for the increase in reactive power caused by the underground cable network. The centralized compensation reactor is usually installed at the primary substation, either in a shelter or in the immediate vicinity of the substation in an equipment shelter.

The centralized reactive power compensation reactor can also be equipped with an on-load tap changer and automatic regulator, allowing the equipment to independently maintain the correct level of compensation without user intervention.

Decentralized Compensation

In addition to centralized compensation, it is possible to use decentralized reactive power compensation on individual feeders or branches. Decentralized units on feeders also restrain voltage rise when the network operates at low load. This allows for reactive power compensation exactly where it is needed.

As network switching situations change, decentralized compensation facilitates network operation, as the feeder compensates for its own reactive power, regardless of where it is fed from. The compensation reactor can be placed in a substation or a separate equipment shelter, depending on the size of the device. Decentralized reactive power compensation units are also available as combination devices, which may include a distribution transformer and/or earth fault current compensation coil.

Combining Centralized and Decentralized Compensation

The best and reliable results are achieved by using centralized compensation at substations and decentralized compensation units placed in the network.

Compensation units are available as fixed or adjustable. The adjustment of the units can be implemented with the following adjustment methods:

Off-load tap changer
Off-load tap changer with motor drive
On-load tap changer
On-load tap changer with automatic control

It is important to consider the noise level and losses caused by the compensation reactor. A high-quality device, correctly installed, will last a long time in the network without causing harm or disturbance to other devices or the environment. The equipment should be equipped with the necessary surge protection to ensure durability in use and prevent harmful overvoltage spikes.

Equipment Shelters

The equipment shelter is a secondary substation-type building designed for compensation equipment and meets customer requirements excellently in terms of usability, ease, appearance, and cost-effectiveness.

The equipment shelter is more spacious than a secondary substation, making it easier to audit and maintain the equipment. The overall design of the shelter can always be defined according to the customer's needs. Available standard size models (foundation external dimensions):

2,4m x 5,8m
2,4m x 4,5m
2,4m x 2,65m

Sustainable Finnish Design

The design of the equipment shelter considers the maximum snow and wind loads prevailing in the north. Comprehensive strength calculations have been made for the structures, also considering the stresses caused by lifting the building. The equipment shelter is delivered to the site ready for use together with the foundation basin.

The foundation is a uniform and flat-bottomed concrete element basin, in which the equipment shelter can be freely placed. The foundation also serves as a fire-safe and durable oil collection basin. The foundation design also focuses on easy installation.

If necessary, the equipment shelters can be equipped with enhanced natural ventilation or blowers. The manufacture of equipment shelters is ISO 9001, ISO 14001, and ISO 45001 certified.