Gas production from the Ormen Lange Field on the Norwegian continental shelf started on 13th September 2007.
At the heart of this historic project, to deliver gas via the 1200km “Langeled” sub sea gas pipeline from Nyhamna in Norway to Easington on the UK east coast, are three 48MW export gas compressors driven by BRUSH MAX 2-pole synchronous motors.
Operating at speeds between 2,520 rev/min and 3,780 rev/min, these closed circuit air to water (CACW) cooled MAX motors are a derivative of the very successful BRUSH DAX range of turbogenerators. The motors are configured for variable speed operation powered by a load commutated inverter (LCI).
As part of the customer’s rigorous testing programme for these IP55 machines, certified for hazardous area operation, the motors were required to perform a 48 MW full load, full speed, back to back test with the project drive equipment. In addition, a variable speed, full load string test was carried out with the contract compressor equipment.
The project, seen as one of Norsk Hydro’s most successful development programmes, delivered on time and on budget, is the first project of its kind for BRUSH and, at its
peak, is expected to meet 20 percent of the UK’s gas requirements. Ormen Lange, which translated means “Long Snake”, is located 120 km off the northwest coast of Norway at a water depth of 800 – 1100 metres. It is Norway’s second largest gas field with estimated gas reserves of 395 billion cubic meters, and a forecast annual production of 20 billion cubic metres.
BRUSH sees this important first entry into this market as the initial “stepping stone” to a new trend towards “all electric” applications in the production, transport and storage of natural gas and liquefied natural gas.
The project is now operated by SHELL.
Motors for compressor drives
In the past, compressors driven by gas and steam turbines were used in the larger production facilities to transport gas through dedicated pipelines to consumers. In recent years, however, an increasing number of gas and steam turbine drives have been replaced by electric variable speed drives.
Besides the lower investment costs, electric variable speed drives are more efficient than gas turbines and require only a fraction of the maintenance. Apart from the obvious maintenance cost reduction, this results in a higher uptime. Other factors that influence the decision in favour of electric drives, are the high reliability and excellent control properties of the electronically adjustable AC drives as well as lower CO2 and NOx emissions.
The MAX 2-pole synchronous motor has two three phase 30° displaced 6.7 kV stator windings (for the 12-pulse inverter). Its main rotor field winding is fed via the shaft mounted three phase exciter and rotating diodes. Total efficiency of the VSD system, which consists of transformer, converter, motor and filters, at nominal power/speed is better than 96.5%.
Specification of motor
- 48 MW
Shaft speed (nominal / max)
- 3500 / 3780 rpm
- 58.33 / 63 Hz
Voltage per winding
- 6700 V
- 2325 A
- EEx P II T3
- Air-to-water / CACW
- Speed 2520 – 3780 rpm
- Shaft power 16 – 48 MW