Efficiently starting compressors

Softstart (UK) was recently asked to undergo a survey at the efficiency of starting 2 x 6.6kV compressors and then to supply, install and commission for a brand new furnace and upgrade for a glass production facility in the UK, part of a multi-million pound upgrade and refurbishment programme. The compressors in question are rated at 900KW and 700KW respectively and are sited in the brand new MV switch room, as part of the major upgrade we investigated with the main contractor the effect of starting the compressors on the available power. During the upgrade we also supplied a brand new transformer starter for the main furnace, with our main contractor partner LSES (Norwich). Over a period of several days we commissioned the 11kV furnace boost transformer starter and the two 6.6kV soft starters. Eventually capping the full load starting current at 320% of In around 228A and integrate seamlessly with the Ingersoll Rand control system. Motor protection is built into the MV Soft Starters and is functional even the by-pass condition, the start time of the compressors is around 3.5 seconds at the new current limits. There was no requirement or benefit for VFD’s so the Soft Starters had a distinct advantage over either using DOL (high start current and reflected torque) or auto-transformers (heavy and large size), additionally the soft starters have a high degree of motor protection built in and additionally Ethernet for remote monitoring and diagnostics. Such as last start time, current etc. The Soft Starter also was measured during start and caused no effect on the supply or other equipment with harmonics during the start and of course the THD very rapidly falls away to zero after start and by-pass condition. Volt drop on the supply transformers is measured at below 2% even with all systems starting simultaneously or even with standby generator sets connected. We are looking forward to being involved in a further upgrade to the facility in the beginning of 2016, when a third compressor with a rating of 700KW will be introduced.

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