Challenge

The customer required a converter station capable of converting the energy from a public 220 kV 50 Hz grid to a level required for the railway-operated 110 kV 16.7 Hz distribution grid. The key objectives of the project were to achieve the highest conversion efficiency, reliability and system availability at the lowest possible cost.

System overview

The Mannheim station consists of a single independent converter block. It connects to the 220 kV 50 Hz 3-phase grid through an oil-immersed transformer (ONAN cooling system) and feeds the German Railway owned and operated 110 kV 16.7 Hz single phase distribution network via a step up single phase transformer.

Converter system

The power part of the converter block consists of one converter system based on the proven MV 7000 converter type. The converter is rated at 150 MVA and is located in a single building. A single converter includes 3 x 5 medium voltage inverter units, each with the following main components:

• An input 3-phase pulse controlled sub-inverter
• A DC link with a 33.4 Hz filter
• An output 1-phase 4QS sub-inverter 

The core components in each sub-inverter are the press-pack IGBT modules organised in two phase-segments and fitted with a patented pull-out mechanism including the IGBT control amplifiers.

Providing the interface to the distribution grid

Cooling system

The converter block has its own dedicated cooling system with a mix of glycol and water. The power electronics as well as other components of the inverter units are directly cooled with this fluid. The advantage here is compact design and small space requirements. The heat is then dissipated in a water-air heat exchanger. Two water pumps are installed (100% redundancy) to provide continuous circulation. All systems are monitored and the pumps are switched over every 24 hours. To reduce the space required, the heat exchangers are located on the roof of each converter block.

Additional air-conditioning is provided for the house premises.

Control system

Internal converter control enables the following operation modes:

• Standard control in all 4 quadrants (according to the P/f, Q/U characteristic)
• Phase shift operation (supply of reactive power to the railway grid only)
• Parallel operation with rotary frequency converter
• Black Start-Up of rail grid

The control system allows for either local or remote operation via a user-friendly HDM interface.

Our SFC technology brings multiple advantages to the operator

Static frequency converter for railway application

Challenge

To increase speed and capacity on a segment of ca. 50 km along the European Corridor CE30 from Knappenrohde, Germany to the system interface at the polish border, Deutsche Bahn extends and electrifies an existing rail line. As part of this project, a static converter station to feed the 16.7 Hz 15 kV overhead catenaries was contracted as a turn-key project in Lohsa, Germany to a consortium lead by Power Conversion & Storage. The key objectives of the project were to achieve the highest conversion efficiency, reliability and system availability at the lowest possible cost.

System overview

The Lohsa station consists of three independent blocks operating fully redundantly. It connects to the 110 kV 3-phase grid through an oil- immersed transformer (ONAN cooling system) and feeds the 15 kV 16.7 Hz overhead catenary system directly as well as through a system of auto transformers. For maximum efficiency, each block employs air-core reactors on the 15 kV rail electrification side (transformer-less design). Connection of a 50 Hz filter is not necessary thanks to the innovative converter concept and control algorithm. On the 15 kV rail side, only a small passive filter is required to meet the strict harmonics requirements of DB.

Converter system

Each block employs three converters based on the proven MV 7000 type, with the main components being:

• An input 3-phase pulse controlled sub-inverter
• A DC link with an integrated 33.4 Hz filter and a fast discharge/ earthing device
• An output 1-phase 4QS sub-inverter 

Each sub-inverter contains press-pack IGBT modules organised in phase-segments and fitted with a patented pull-out mechanism including the IGBT control amplifiers.

Providing the interface to the distribution grid

Cooling system

Each converter block has its own dedicated closed-circuit cooling system with a mix of glycol and water. The power electronics is directly cooled with this fluid, to achieve compact design and small space requirements. The heat is then dissipated in a water-air heat exchanger. Two SFC-controlled water pumps are installed (100% redundancy) to provide continuous circulation. All systems are automatically monitored and the pumps are regularly switched over. Additional secondary air-cooling is provided for the E-house in each block.

Control system

Internal converter control enables the following operation modes:

• Standard control in all 4 quadrants (according to the P/f, Q/U characteristic)
• Reactive Compensation/ STATCOM (supply of reactive power to the railway grid only)
• Parallel operation with other generation units integrated on the 15 kV line
• Isolated mode (creating independent rail grid), with automatic synchronization to three-phase grid before reconnection
• Remote control by sinusoidal reference signal (Pilot Mode) or Autonomous Mode based on asynchronous
  telemetry reference signal can be provided as well.
• Black Start-Up of rail grid

Remote short circuits are handled reliably by the control algorithms. The control system allows for either local or remote operation via a user-friendly HDM interface and integration to SCADA according to IEC 61850 (IEC 60870-105-4 can be provided as well).

Our SFC tecnology brings multiple advantages to the operator

Static frequency converter for railway application