DC logger for traction AT stations

In the Netherlands, two different traction energy supply systems are in use on mainline railways. The standard supply voltage for railway lines is 1500 Vdc. The newly built Betuweroute freight line and the high-speed line Amsterdam-Rotterdam-Antwerp however have been electrified with 25 kV, 50 Hz. It was anticipated that under specific fault conditions, stray currents from a DC line could flow in the return circuit of a nearby AC line, exposing for example transformers to DC effects. Prolonged exposure to DC effects may damage the transformers of the traction power system. In order to monitor such phenomena, ProRail has ordered EMPEQ to supply four DC logging systems to be placed in the return cables of four autotransformers. The autotransformers have been selected based on stray current exposure calculations.

The instrument is equipped with a high-precision Direct Current Transformer (DCCT). The return connections of the two autotransformer windings are passed through the DCCT in opposing directions. As a results, the DCCT effectively measures the magnetizing current of the autotransformer. Any DC effect would lead to a DC component in this magnetizing current.

The instrument logs the DC component in 10-second intervals. It is equipped with a GSM modem to transmit measured data to a remote server and to send an alarm SMS if a pre-set level of DC is exceeded.

Technical specifications:

Supply voltage 60 Vdc
Type of DCCT LEM IT 700-s
Max. net current 700 Arms
Overload capability 3500 A / 100 ms
DC accuracy ± 100 mA
Logging interval 10 seconds

The instrument has been successfully tested against the following EMC standards:

EN61000-6-4:2007  Generic emission standard for industrial environments

EN61000-4-2:1995  Electrostatic discharge immunity

EN61000-4-3:2006  Radiated electromagnetic field immunity

EN61000-4-4:2004  Electrical  Fast Transient (EFT)  immunity

EN61000-4-5:2006  Surge Transient immunity

EN61000-4-6:1996  Conducted Radio-frequency disturbances immunity

EN61000-4-8:1993  Power frequency magnetic field immuity

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