Statnett’s substation in GryttenRefurbishment of 132 kV switchgear

2 Statnett‘s substation in Grytten | ABB

ABB | Statnett‘s substation in Grytten 3

Grytten substation

The Grytten substation is a part of Statnett’s regional grid, and as the sole feeding point, provides electrical power to the area around Åndalsnäs.

The substation is situated in dramatic settings with the river Raumaälven just a stone’s cast away and surrounded by high mountains. With the popular tourist destinations Trollväggen, Trollstigen and the Raumabanan rail line, the area is one of Norway’s most-visited.

Grytten substation prior to refurbishmentThe old switchgear was traditionally designed with a double busbar system (A and B) and a transfer bus (C). The switchgear included in total six bays:

four line bays and two transformer bays, as well as the C bus circuit breaker bay and a disconnector bay for interconnecting of the B and C buses. Be-

cause the Grytten substation is the only feeding point in the Åndalsnäs area, the demands on availability are very high.

HistoryThe substation was built in 1965 with two lines and one transfor-mer. As was common at the time, it was built with a primary bus and a transfer bus. It was planned to subsequently expand the substation to include a double busbar system with transfer bus.

In 1972, one line and a feeder from Grytten hydro power plant as well as one transformer were added. At the same time, the switchgear was complemented with a second primary busbar to create a double busbar system with transfer bus.

The double busbar system was necessary to guarantee uninterrupted service during transformer and circuit breaker maintenance.

Maintenance and repairsDisconnectors and older circuit breakers were maintained at three- to five-year intervals. Moreover, the disconnectors’ main contacts were inspected using thermal imaging on a yearly basis to detect any overheating tendencies.

Three older circuit breakers have been replaced with modern SF6 circuit breakers. These were inspected after one year of service and a maintenance interval of 15 years was subse-quently established.

Just one voltage transformer and a few surge arrestors on the transformers have otherwise been replaced.

4 Statnett‘s substation in Grytten | ABB

A modern switchgear solution is created

Reasons for refurbishmentIn Statnett’s maintenance plans, the useful service life for dis-connectors had been set to 35 years and the disconnectors at the substation were accordingly scheduled for replacement. It had also been decided to replace the substation’s control equipment.

During subsequent planning, the question came up as to whether the replacement should be done device by device or whether a new all-embracing solution should be considered. Statnett had studied the solution at Norsk Hydro’s facility in Sundalsöra and therefore wanted to look at a solution with disconnecting circuit breakers.

Disconnecting circuit breakersDisconnecting circuit breakers satisfy the demands both for disconnectors and circuit breakers in one and the same de-vice. The primary component is an SF6-based circuit brea-ker that is also type-tested as a disconnector. Because the disconnector function cannot have a visible opening distance, there is an externally fitted, motor-operated grounding switch. By checking the position of this switch, it can be determined whether power has been turned off to the lower side of the circuit breaker.

Furthermore, a disconnecting circuit breaker is equipped with an interlocking and blocking system that prevents unintenti-onal operation. IEC 62271-108 is the applicable standard for disconnecting circuit breakers.

Operational requirementBecause the substation is the only feeding point for the area, a requirement was that at least one of the transformers had to be in service throughout the refurbishment project. This spoke for replacing device by device.

Technical descriptionThe old switchgear was designed with three lines and one feed from the Grytten hydro power plant as well as with two transformers. Moreover, there was a C bus circuit breaker and a disconnector between the B and C buses.

The new switchgear was to be planned to be within the same scope of connected objects.

The old solution with double busbar and transfer bus enabled maintenance to be carried out on any switchgear component, with one transformer still in service. This capability was also to be included in the refurbished substation.

Planning of new switchgearThe old switchgear had 81 single-pole disconnectors. This complicated operational switch-overs. Furthermore, lengthy periods with reduced service capabilities were necessary since portions of the switchgear had to be taken out of service to enable maintenance of these disconnectors. A simpler solution was therefore requested by maintenance personnel.

This led to an alternative that did not include disconnectors being discussed in the early planning stages. It was determi-ned that a proposal with disconnecting circuit breakers and a sectionalized single bus should be evaluated.

Proposals for single-line diagrams and layout drawings were prepared. Additionally, availability calculations were conducted for both a sectionalized single busbar system and for double busbar system with transfer bus. The calculations were inten-ded to show the theoretical annual downtime caused by the high voltage switchgear. The supply from the medium voltage switchgear on the transformers’ lower side was used as a reference point. Because downtime in both cases was close to zero, it was decided to move forward in planning with the al-ternative without disconnectors, but with a sectionalized single busbar. The question now was whether it would be possible to build an entirely new switchgear system while keeping the old one in service. It was then discovered that the existing C bus, with just a few changes, could be used as a busbar in the new switchgear. It had the correct length and was located at the most appropriate location, and there was even space for the sectionalizing breaker. Because a trans-fer bus is only used during circuit breaker maintenance, it could be disconnected from the rest of the switchgear without affecting operational capabilities.

The new switchgear could then be comple-tely assembled, and reconnection of lines and transfor-mers could be scheduled so that service did not need to be interrupted.

Motor Drive

To further reduce maintenance needs, Statnett chose Motor DriveTM as the

operating mechanism for the disconnecting circuit breakers.

The optimized design with just one moving part in the operating mechanism

reduces mechanical stress to a minimum. Electronically controlled operation is

accomplished without mechanical stopping, which means very quiet operation.

ABB | Statnett‘s substation in Grytten 5

132 kV A

132 kV B

132 kV C

VT x 3

VT

ES x 3

CTDS x 3

DSES

CT

VT

CB

DS x 3

DSES

CT

CT

SA

CB

TR

DS x 3

DS

DS

DS x 2

DS x 3

DSES

ES

CT

SA

CB

CB

VT

CT

DS

DS x 3

ES

CB

VT

CT

DS

DS x 3

ES

CB

CB

TR

132 kV

VT

VT VT VT

ES

ES ES ES

ES

VT

CT CT CT

SA

TR

DCB DCB DCB

VT VT VT

ES ES ES

CT CT CT

SA

TR

DCB

DCB

DCB DCB

Before refurbishment

After refurbishment

LegendCB Circuit breaker CT Current transformer GS Ground switch

DCB Disconnecting circuit breaker SA Surge arrester DS Disconnector

VT Voltage transformer TR Power transformer

6 Statnett‘s substation in Grytten | ABB

Refurbishment project

Turnkey contractAfter a customary procurement procedure, ABB was selected as the general contractor.

The equipment was ordered and work at the site was begun in the spring of 2007. As planned, the C bus was disconnec-ted and converted into a sectionalized single busbar system. A disconnecting circuit breaker was also used for section switching.

Once all the devices were installed, one line was connected to one of the sections. After this, one of the transformers could be moved over and the section could be powered up. The other devices were subsequently moved over and lastly, the old switchgear was removed.

Freed spaceThe new switchgear occupies about 30 percent of the space of the old switchgear. The freed space can now be used for any other needs that may arise in the future.

Maintenance requirementsIn practice, the only devices that require maintenance are the disconnecting circuit breakers. A 15-year maintenance interval was proposed for full inspection. Every other year, visual inspections of the devices will be conducted, but without removing equipment from service.

Increased availabilityOne of the sections can always be in service during circuit breaker maintenance. During maintenance of the sectiona-lizing breaker, power is first disconnected from one section, and this side of the sectionalizing breaker is disconnected by removal of a special connection link. The section is then po-wered up and power to the second section is disconnected. The sectionalizing disconnecting circuit breaker is then free for work. If work requires an interruption for a longer period, the breaker can also be disconnected from this section according to the same procedure. The sectionalizing breaker is then entirely disconnected and both sections can be in service. Disconnection and connection of the sectionalizing breaker is expected to take less than two hours.

ExperiencesStatnett’s experiences from the project have been very good. Statnett has obtained a new switchgear based on modern technology with a minimum of maintenance requirements. The substation, which is situated at an important location in the grid, has high availability and is very operationally forthcoming.

The short installation time and the well-planned switchover of operations enabled the entire refurbishment project to be per-formed without interrupting the power supply to customers.

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Technical data for ABB’s disconnecting circuit breakersRated voltage 50 - 420 kV

Rated current up to 4000 A

Rated breaking current up to 40 kA

There are reference installations for all voltage levels. Configurable switchgear solutions with integra-ted busbars can be provided for switchgear up to 300 kV.

Simple installation with ABB’s disconnecting circuit breakersIn conventional switchgear, there are normally four switching devices for each bay. If a solution, with a sectionalized single bus and disconnecting circuit

breakers, like the one chosen by Statnett is employed, there is only one switching device per bay. Because all of the devices require installation, connec-

tion and secondary cabling, it is easy to see that the time gained is considerable.

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ABB AB High Voltage ProductsSE-771 80 LUDVIKA, SWEDEN Phone: +46 (0)240 78 20 00 Fax: +46 (0)240 78 36 50 www.abb.com www.abb.com/highvoltage

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NOTE! ABB AB is working continuosly to improve the

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