Presentation · EN — 31-slide Siemens Energy sales presentation (October 2024, 'Unrestricted') on Low-Power Instrument Transformers (LPIT) for high-voltage GIS. The LPIT replaces the conventional inductive voltage transformer and current transformer with one capacitive voltage divider and two Rogowski coils integrated into a single gas-tight cast resin partition, shrinking an 8DN8 145 kV bay from 4.1 m to 3.5 m and an 8VN1 bay from 5.5 m to 3.7 m (5.8 t to 4.3 t). The deck walks through the partition components, the sensor physics (Rogowski coil per IEC 61869-10, capacitive divider per IEC 61869-11, Low Energy Analog output per IEEE C37.92-2023), the two integration paths into protection and control (directly to LPIT/LEA-input relays or via redundant SIPROTEC 5 / SEL-700MU merging units on the IEC 61850-9-2 process bus), testing with commercially available equipment, the path to EU MID revenue-metering certification planned for 2025, the preliminary technical data for the four variants LPIT-145 (8DN8), LPIT-145 (8VN1), LPIT-170 (8DN8) and LPIT-420 (8VQ3), the global track record (51 projects, 319 units since 2017, more than 3,000,000 operating hours by 7/2024), and the generation roadmap up to Generation 2 (2025) with availability for 8DN8-5, 8VM3, 8VN1, 8DN8-6 and 8VQ3.
In a conventional GIS bay, voltage and current are measured by two separate gas compartments: an inductive voltage transformer (VT) and a current transformer (CT). The LPIT replaces both with one capacitive voltage divider and two Rogowski coils, cast into a single gas-tight resin partition with integrated voltage and current sensors.
At the 8DN8 145 kV GIS this shortens the bay from 4.1 m to 3.5 m at the same 2.6 m height. At the 8VN1 Blue GIS the comparison is 5.5 m / 5.8 t for the bay with conventional instrument transformers versus 3.7 m / 4.3 t with LPIT.
The benefits slide quantifies the savings for two 8DN8 ratings (values as printed; the slide also shows the 8VN1 Blue GIS 145 kV with clean air at -30% bay length and -25% weight):
| Parameter | 8DN8 145 kV conventional CT / VT | 8DN8 145 kV with LPIT | 8DN8 170 kV conventional CT / VT | 8DN8 170 kV with LPIT |
|---|---|---|---|---|
| Bay length | 4.1 m | 3.5 m (-15%) | 5.6 m | 4.3 m (-25%) |
| Weight | 4 t | 3.2 t (-20%) | 5.4 t | 4 t (-25%) |
| SF6 | 90 kg | 70 kg (-20%) | 145 kg | 110 kg (-25%) |
An exploded view of the partition identifies the building blocks: the 3-phase contact system, the sensor rings with Rogowski coils and capacitive divider, the gas-tight cast resin partition into which the sensors are integrated, the metal flange, and a connection box for each phase.
Installed in the 8VN1 Blue GIS, the LPIT is a combined electronic voltage and current transformer according to IEC 61869. It is redundant — two current sensors and one voltage sensor in each bay, connected to a redundant protection system — and multi-purpose, with one device serving both protection and measurement.
It is standardized (the same device is used for every possible rated current) and flexible, allowing installation everywhere in the GIS. The analog signals run from the GIS cast resin partition to a SIPROTEC 5 device with IO240 (control and protection, or 'merging unit', e.g. inside the local control cubicle), with fully redundant digital connections: station bus IEC 61850-8-1 and process bus IEC 61850-9-2 / IEC 61869-9, plus digital output to third-party protection such as busbar protection.
Current is measured by a Rogowski coil (IEC 61869-10) on a sensor ring with middle electrode around the primary conductor on high-voltage potential; voltage is measured by a capacitive divider (IEC 61869-11) formed between the conductor and ground potential. The output is a Low Energy Analog (LEA) signal according to IEEE C37.92-2023.
Typical transformation ratios as printed: LPCT 130 to 200 mV/kA; LPVT 10,000:1 or 100,000:1 (divider voltage measurement) or 10 µA/kV or 1 µA/kV (displacement current measurement).
The Siemens Energy LPITs use additional correction mechanisms for crosstalk and temperature dependence, to be standardized by the new IEC 61869-7 and -8: IEC-standardized correction for metering, and protection accuracy without correction (with Generation 2 hardware).
There are two integration paths: the LPIT's interoperable analog interface (signals according to IEC 61869 / IEEE C37.92-2023) can be wired directly to a protection device, or connected via a redundant merging unit that publishes IEC 61850-9-2 Sampled Values on the process bus for Main 1 / Main 2 protection, busbar protection, digital fault recorder and the substation controller on the IEC 61850 station bus. Third-party protection connected to the SIPROTEC merging unit should preferably be compatible with IEC 61850 Ed. 2.1.
To avoid unnecessary wiring and cabling effort, at least one merging unit should be installed locally inside the GIS local control cubicle (LCC).
The deck recommends splitting the two redundant measurement channels by application: LPIT channel 1 feeds Main 1 protection, busbar protection and the fault recorder (protection current) plus control, measurement and power quality (measurement current); LPIT channel 2 feeds Main 2 protection and a second busbar protection plus revenue metering. Revenue metering is typically subject to national legislation and requires approval, and the SEL-700MU can provide redundant voltage measurements.
Two worked examples show a protection, automation and control system (PACS) based on SIPROTEC 5 — busbar protection 7SS85 and feeder protection / bay control 7SX85 (Main 1 + busbar protection; Main 2 and bay control with synchro-check; busbar coupler control and busbar voltage distribution) — tested with equipment from Omicron and SecuControl. Conventional and LPIT-based chains are compared for primary and secondary injection tests on both the analog and the digital side.
A dedicated slide lists third-party equipment for the Siemens Energy LPIT, with the note that test magnitudes below 2 kV and below 100 A require IO240 hardware revision 2 or the SEL-700MU. At the CIGRE Paris Session 2024, the 420 kV LPIT was exhibited with the SEL merging unit (test block from SecuControl), the Siemens merging unit (test block from Phoenix Contact), primary injection and accuracy testing with a meter test device from MTE, and a PACS demo including HMI with a simulated transformer bay.
Certification of the LPIT metering chain as an EU MID meter is planned for 2025. The approach follows IEC 62052-11, which the deck quotes: meters designed for operation with LPITs (as defined in the IEC 61869 series) may be tested for compliance together with their LPITs as directly connected meters — the 'black box' approach. IEC/IEEE 61869-21 covers accuracy tests including on-site testing with lower test magnitudes, with the deviation between results at rated values and at the lower test points added to the uncertainty of the test setup. Benefits listed: based on the existing meter standard, no special test devices, and convenient on-site accuracy verification.
According to the German verification authorities, this simplified test procedure using lower test values can be used provided it is verified and described in the type examination certificate (module B), then implemented in module D (or in principle module F); calibration authorities check the metering system on the same basis.
A linearity verification shows the power error at different load points with only 0.04% uncertainty introduced by the reference instrument transformers. For on-site accuracy verification of the whole metering chain, primary injection via the earthing switch with 480 V and 50 A is sufficient.
An earth fault on 29 July 2021 in Norway (utility not named in this entry) demonstrated the sensors' bandwidth: directional earth fault protection (ANSI 67Ns) is used in non-earthed grids, and the fault caused a significant voltage swing with heavy harmonic content while the fault current stayed very small since no load was connected to the busbar. The transient earth fault was nevertheless detected in the forward direction — the operator had not expected this fault to be detected at all, and definitely not with conventional CTs and VTs.
Ratings for the four LPIT variants as printed on the technical data slide (marked 'preliminary'). Slide callouts: same device for 50 Hz and 60 Hz; accuracy-at-harmonics class WB1 up to 3 kHz is a new accuracy class extension defined in IEC 61869-1, with SIPROTEC 5; 0.2% accuracy from 200 A to maximum continuous thermal current; accuracy requirements for protection (composite error and instantaneous error) are fulfilled up to Ith — 2TPM is equivalent to conventional TPZ but with 2% instead of 10% error; multipurpose LPVT accuracy class with higher requirements compared to 0.2 / 3P; excellent overvoltage performance with no disconnection during tests.
| Parameter | LPIT-145 (8DN8) | LPIT-145 (8VN1) | LPIT-170 (8DN8) | LPIT-420 (8VQ3) |
|---|---|---|---|---|
| Rated insulation level | 145 / 275 / 650 kV | 145 / 275 / 650 kV | 170 / 325 / 750 kV | 420 / 650 / 1425 kV |
| Rated frequency fr | 50 Hz / 60 Hz | 50 Hz / 60 Hz | 50 Hz / 60 Hz | 50 Hz / 60 Hz |
| Rated short-time thermal current Ith | 50 kA (3 s) | 50 kA (3 s) | 63 kA (3 s) | 80 kA (3 s) |
| Temperature range | -30 °C / +55 °C | -30 °C / +55 °C | -30 °C / +55 °C | -30 °C / +55 °C |
| Weight | 100 kg | 185 kg | 185 kg | 100 kg |
| Accuracy at harmonics | WB1 (up to 50th) | WB1 (up to 50th) | WB1 (up to 50th) | WB1 (up to 50th) |
| Applied standard | IEC 61869 | IEC 61869 | IEC 61869 | IEC 61869 |
| LPCT — Rated primary current Ipr | 200 A | 200 A | 200 A | 200 A |
| LPCT — Rated extended primary current factor Kpcr | 15.75 | 15.75 | 20 | 31.5 |
| LPCT — Nominal current range | 200 A to 3150 A | 200 A to 3150 A | 200 A to 4000 A | 200 A to 6300 A |
| LPCT — Rated accuracy class | 0.2S / 5P250 / 2TPM | 0.2S / 5P250 / 2TPM | 0.2S / 5P315 / 2TPM | 0.2S / 5P400 / 2TPM |
| LPCT — Rated symmetrical short-circuit current factor Kssc | 250 | 250 | 315 | 400 |
| LPVT — Rated primary voltage Upr | 66 to 138 / √3 kV | 66 to 138 / √3 kV | 66 to 154 / √3 kV | up to 400 / √3 kV |
| LPVT — Rated accuracy class | 0.2 P | 0.2 P | 0.2 P | 0.2 P |
| LPVT — Rated voltage factor FV and permissible duration | 3 / 2000 h | 3 / 2000 h | 3 / 2000 h | 3 / 2000 h |
Proven: more than 250 units installed and more than 3,000,000 hours of operation. Ready for control and protection (compatible with IEC 61850-9-2; interoperable control and protection devices available from different manufacturers), for metering (compatible with Landis+Gyr E880; certification for revenue metering to be discussed), and for special applications: power quality up to the 50th harmonic, circuit-breaker wear monitoring, and point-on-wave switching via SIPROTEC 5 functions.
Easy to test (LPIT and C&P testing devices commercially available; no VT disconnection during HV tests), to maintain (the partition is maintenance-free; electronics can be changed without recalibration) and to engineer (one standard device for all applications and nominal currents). Flexible: installation 'anywhere' in the GIS, and mixing of conventional instrument transformers and LPITs is possible. Durable: completely passive sensors, no active electronics close to the primary parts of the GIS. Safe: no dangerous overvoltages at terminals. Future-proof: the nominal current can be increased via parameter change.
Worldwide projects since 2017 (order intake till 10/2023): 51 LPIT projects with 319 LPIT units, in Finland, France, Germany, Norway, Switzerland, UAE, India, USA, Oman, Netherlands, Denmark, Argentina, Sweden and Colombia — more than 3,000,000 hours in operation by 7/2024. No individual customers or projects are named on the slide.
For the 8VQ3 420 kV clean-air GIS, the LPIT-420 replaces the conventional VT and CT with redundant current and voltage measurement, is compatible with all IEDs with LPIT/LEA inputs, and reaches class 0.2 accuracy with the Siemens IO240 and the SEL-700MU. Back-up slides add a second-generation LPIT for 8DN8-5 and 8VM3 and a 420 kV comparison of a 1 1/2-circuit-breaker tie-breaker arrangement with LPIT versus conventional instrument transformers.
The roadmap spans three generations: Generation 0 (2016), an integrated system based on SIPROTEC 4 with the SIPROTEC 4 merging unit; Generation 1 (2019) for 8DN8-5, 8VN1 and 8DN8-6 (indoor) with SIPROTEC 5 MU, SIPROTEC 5 protection and control and the SEL MU — IEDs including correction mechanisms for highest accuracy, redundant voltage measurements with the SEL MU; and Generation 2 (2025), where no correction mechanisms are required for control and protection applications and all relays with LPIT/LEA inputs can be used. Generation 2 availability as printed: 8DN8-5: 2025; 8VM3: 2025; 8VN1: 2026; 8DN8-6: 2026; 8VQ3: 2027 (outdoor).
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