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Case Study

Iron ore mine at Malmberget

SVC for voltage support, power factor control and power quality improvement

An SVC came on line in 2013 at LKAB’s underground mining facility at Malmberget in the north of Sweden, the second SVC for mining supplied to LKAB by Hitachi Energy in just a couple of years. It is a turnkey installation, rated at 21.5 kV, 0-41 Mvar capacitive, and with all indoor equipment housed in a pre-fabricated container. Its purposes are stabilizing the feeding voltage to the mine during varying load cycles, power factor correction as well as power quality improvement in conjunction with planned extensions of the ore mining capacity. The SVC has been designed to cope with an ambient temperature span of -40 to +40 deg. C.

As space is scarce in the substation, the SVC is located some distance away and connected to the 21.5 kV mine bus via 600 m power cables, a well proven solution in cases like this.

The load to be compensated by the SVC consists of six mine hoists connected to the 21.5 kV bus, four AC converter hoists each rated at 3.99 MW and two 6-pulse DC converter hoists rated each at 8.15 MW, altogether 32.3 MW. The duration of a load cycle is approximately 70 s and consists of an acceleration phase, operation at full speed, and retardation. During this time the load varies strongly, causing voltage variation on the feeding bus as well as at the PCC (Point of Common Connection). 

With the SVC in operation, a stabilization as well as increase of the mining bus voltage level have been established.

Main data
Commissioning year: 2013
Controlled voltage: 21,5 kV
Dynamic rating: 0-41 Mvar (capacitive), continuously controlled
Harmonic filters:  3rd harmonic / 7 Mvar
 7th harmonic / 18 Mvar
13th harmonic / 16 Mvar
Control system: - Closed loop control, based on power factor control or Mvar control,
- Open loop reactive power control
Thyristor valve: Water cooled, BCT type thyristors, indirect light firing