The newly-developed vertical Connex transformer connectors for up to 52 kV connect the transformers and switchgears in a touch-proof system spread over several levels. The latest additions to the Connex family allow several vertical MV cables to be inserted for the first time.
North Zurich, Eduard-Imhof-Straße. The Oerlikon substation would have been virtually invisible, had ewz not decided to erect a network base above its three underground levels. The above-ground constructions, which include a warehouse, repair shop, and social facilities, are used by up to 45 ewz employees involved in grid expansion and maintenance activities. ewz is one of the ten largest utility companies in Switzerland and has been providing Zurich and parts of the Canton of Grisons with power since 1892.
Oerlikon is a forward-looking substation built using space-saving connection systems that free up additional space in the city center. The installation is also sustainable as SF6 gas is not used for the gas-insulated high and medium-voltage switchgear, but instead an environmentally-friendly gaseous mixture. ewz likewise places a very demanding set of requirements on the technology and systems used as Pascal Müller, who headed the construction project for the substation and grid base, explains: “When and if a component malfunction occurs, it will almost definitely have to do with the interface point. To minimize this inherent design risk, we view the quality of the connection systems integrated as playing an equally important role.” This is why Connex connections from Pfisterer are used. The engineer has done his homework when it comes to the total costs of component quality as in 2003 he was part of a team of authors who presented a new computational model for determining the cost efficiency of investments made in electric and electrical operating equipment. The article focuses on failure scenarios that can be directly attributed to the quality of the components used. Alongside the anticipated expenditure, the model also takes incident-related costs into account. “This includes managing and troubleshooting faults as well as follow-up costs such as lower revenue and the effects of a tarnished image”, explains Müller. In calculating these costs for a 170 kV power circuit breaker and a substation, it was determined that they can increase dramatically and account for a considerable portion of the overall lifecycle costs in more vulnerable products. Yet if the components are of high quality and are reliable, these costs are virtually negligible.
Extremely compact system connection
The Connex system used in the ewz network has already proven itself to be a reliable cable connection technology in a wide range of systems. “We have been using Connex systems and components for over ten years and have found them to be excellent. At the new Oerlikon substation, all of the high-voltage and medium-voltage connections in the two switchgears and three transformers use CONNEX” states Müller during a tour of the substation, opening a signal-red sliding panel. “Here you can see it at work, with a new addition to the product family.” A 50-MVA power transformer from ABB, 6.6 m high, 5.5 m long, and 4.1 m wide, is the dominating first impression. The new, size 3, straight MV-Connex transformer socket (TAT) for 2,200 A or 3,150 A depending on the connection type and 52 kV protrudes over its cover. Inside, three cables equipped with MV-Connex separable connectors are inserted right next to each and reach up to the ceiling. The extremely compact, vertical cable connection is one of many advantages of the new connection for Mr Müller: “As you can see, its fourth connection point is not in use. Here, we could connect a Connex earthing set without having to access the interior of the system and keeping the enclosure intact. We can determine the voltage conveniently via the integrated voltage tap, which is directly connected to a Pfisterer continuous voltage indicator. In addition, the enclosure of every Connex cable termination reduces the system’s vulnerability to failures and also makes every system interface touch-proof. Our maintenance staff can therefore carry out their work in complete safety without barriers – a key aspect with space-saving design.”
Ultra-compact system connection
The transformer cell is used to the max. With a room volume of 280 m3 and covering an area of 35 m2, it houses more than simply the transformer which weighs a total of 80 t. It is also coupled with heat exchangers on each of its short sides. These cool the transformer oil and use its heat to heat air and water – one of several measures that ewz uses to keep its energy requirements for supplying heat to the building as low as possible. It is possible to hazard a guess at how much installation space the new substation saves in total by taking a look from the balcony of the neighboring building. Behind the new network base, an air-insulated, high-voltage substation stretches across the ewz site. This is part of the old Oerlikon substation, which has been supplying the Zurich districts of Oerlikon, Seebach, and Neu-Affoltern with electricity since 1949, and has now reached the end of its technical service life. It is to be replaced by the new substation, which was successfully put into operation in August. The new system will be integrated into the ewz network in stages, set for completion by 2018. Up to this point, the air-insulated substation will ensure reserve supply, and then finally be decommissioned. The old substation is considerably larger than the new construction in its entirety. Müller adds to the impression with a fact: “The new substation and its more advanced technical equipment only take up 30 percent of the space originally needed.” When the old substation is removed, a valuable building plot will become available again. Specifically, ewz plans to sell back approximately 5,200 m2 to Zurich, which will cover the added outlay for the underground construction.
Vertical integration for up to four cables
The straight MV-Connex transformer socket (TAT) for up to 52 kV is the latest addition to PFISTERER’s Connex cable termination system. It enables up to four cables to be connected vertically in a very compact space. This means that even transformers and GIS installed at different levels can be linked together in a touch-proof manner. “Over the last five decades, substations have become more and more compact. With the introduction of the Connex system and its continuous expansion, we have also helped to shape this lasting trend in a solution-oriented manner” states Reto Aeschbach, Sales Manager at Pfisterer Sefag AG.