Follow Joulz online

Joulz op Facebook Joulz op LinkedIn Joulz op Twitter Joulz op YouTube

Middelharnis 150kV substation successfully commissioned

Joulz successfully put the newly-built Middelharnis 150kV substation into service for TenneT on 3 November 2017. Thanks to good cooperation and the efforts of the entire team, Joulz was able to commission the Middelharnis substation after seventeen months of construction work. 


The growing supply of energy on the Dutch island of Goeree-Overflakkee necessitated getting the existing 150/50/10 kV Middelharnis substation ready for the future and increasing its capacity. It was also necessary to create a way of connecting a 150 kV cable to a large wind farm near the Krammer Locks and to meet a request from grid administrator Stedin to provide two extra connections for power transformers of more than 100 MVA.

Old situation

Stedin’s 150 kV transformers at the Middelharnis substation were connected by two cables to the TenneT 150 kV high-voltage grid at the Geervliet Noorddijk substation. The two cables were installed in 2015 to increase the connection capacity on Goeree-Overflakkee. Laying the two 19 km cables for this route involved boring below the Haringvliet inlet of the North Sea. Viewed from Geervliet Noorddijk, Middelharnis was in the kick-off situation a double regional network operator connection which on the tertiary 10 kV transformer winding had a reactive power shunt compensator to compensate for the reactive power.


New situation

The substation was enlarged in two phases. First, a new TenneT substation was built on an adjacent site, with various civil engineering modifications. The new substation, with 11 bays, has the following bay structure:

  • two cable feeder bays (inbound from Geervliet Noorddijk)
  • two transformer bays
  • a double busbar system that is ready for four future bays

After the substation had been constructed, there was the takeover and unbundling from Stedin. The work was performed under a strict planned unavailability regime. Before work started everything had been worked out in detail by means of pull planning.

User tests

User tests were conducted before the substation went into service. The user test was performed to check all parts that play a role in the controls, status reports and alarms in the primary and secondary installations of the substation, the transmission equipment and the EMS of TenneT. The user test zooms in on elements of the EMS such as functionality, correct nomenclature, displays and grid diagram.


After testing, the 150kV substation was put into service step by step in a controlled manner. The cables from Geervliet were first powered up and then the A/B busbars were ‘coupled’ (to close the ring) by means of the cross-connect bay. This was followed by the start-up of the Stedin power transformers and the powering up of the wind farm.

Published: 07 November 2017


Copyright © 2015-2019 Joulz Energy Solutions