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Low-power instrument transformers to enable GIS digital substations

Low-power instrument transformers (LPIT) and IEC61850-9-2 process bus

Hitachi Energy's LPIT for gas-insulated switchgear (GIS) use Rogowski coils to measure the current. The primary voltage is measured by capactive voltage sensors. The measured values are digitally processed by the secondary converters and sent to the merging unit, which provides the values according to IEC 61850-9-2 LE to protection, control and revenue metering equipment. The CP-MU merging unit was the world‘s first to be conformance certified by UCA International Users Group. With multiple Ethernet ports and connections to LPIT, it offers high flexibility to system design.  


  • Protection, measurement and metering for digital substations

Why Hitachi Energy?

  • One combined multi-purpose electronic current transformer (ECT) and electronic voltage transformer (EVT) for protection, measurement and metering for all applications 
  • Wide-band calibration enables future proof design without the need to replace cores or to open gas compartments
  • More compact than current transformer (CT) or voltage transformer (VT), hence reducing SF6 weight and the footprint of the GIS 
  • Software configurable and digital, no burden calculation required
  • Conventional secondary cables and their engineering are replaced by IEC 61850 process bus, risk for electrical hazards reduced to a minimum
  • Primary sensor designed for GIS lifetime, secondary converter (sensor electronics) can be replaced during operation, with no calibration necessary 
  • No project specific dimensioning and manufacturing resulting in reduction in cost  
  • Higher availability of primary equipment and improved safety

Brief performance data

GIS with LPIT CP04 CP14 CP3
Rated voltage [kV] up to 170 up to 300 up to 550
Rated short-duration power-frequency withstand voltage [kV] 325 460 740
Rated lightning impulse withstand voltage [kV] 750 1050 1675
Rated current  [A] 3150 4000 6300
Rated short-time withstand current [kA] 63 63 63
Accuracy class ECT 5TPE/0.2 (0.2S) 5TPE/0.2 (0.2S) 5TPE/0.2 (0.2S)
Accuracy class EVT 3P/0.2 3P/0.2 3P/0.2
Number of Rogowski coils 1 or 2 2 2
Number of capacitive voltage sensors 1 or 2 2 2

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