Flyer · EN — Four-page Siemens Energy flyer introducing the 3FT composite post insulator family for station post and line post applications, suitable for both AC and DC systems. It covers the six core-diameter classes (3FT2–3FT7, 63.5–150 mm, SCL 18–150 kNm), key construction features (HTV silicone housing, ECR fiberglass core, overmolded end fittings), applicable IEC/ANSI standards, electrical field validation up to 800 kV, application types (station post, line post, spacers, CICA crossarm), available shed profiles and end fittings, and a full type overview table with SCL, MDCL, length range, lightning withstand and creepage factor per type.
The 3FT post insulator is designed for a wide range of applications in station environments (station post) and on overhead transmission lines (line post). It combines high mechanical strength with superior electrical insulation and a long service life, even under demanding environmental conditions.
A distinguishing advantage of the family is that it is suitable for both AC (Alternating Current) and DC (Direct Current) applications. With the 3FT portfolio, Siemens Energy completes its insulator, transmission-line-arrester and monitoring offering for both transmission lines and substations.
Flexible product length up to 5.5 m, configurable in 12.5 mm increments to match project requirements. SCL classes range from 18 to 150 kNm.
The housing is HTV (High Temperature Vulcanized) silicone applied by multi-shot injection molding, giving outstanding aging resistance, excellent hydrophobic properties and superior UV resistance. The core is ECR (Electrical and Corrosion Resistant) fiberglass for maximum mechanical strength and corrosion resistance.
End fittings are overmolded, which prevents moisture ingress and ensures the lowest possible electrical field stress at the triple point. A dedicated adhesion process — an extensively tested primer system with continuous monitoring and strict quality control in production — bonds silicone housing, fiberglass rod and end fittings for long-term performance.
The insulators are fully tested according to IEC and ANSI standards, and customers can opt to conduct Factory Acceptance Tests (FAT) in both Asia and Europe.
The family spans six core-diameter classes from 3FT2 to 3FT7, each with a corresponding SCL (Specified Mechanical Load) rating.
| Type | Core diameter | SCL |
|---|---|---|
| 3FT2 | 63.5 mm (2.5") | 18 kNm |
| 3FT3 | 76.2 mm (3.0") | 32 kNm |
| 3FT4 | 88.9 mm (3.5") | 46 kNm |
| 3FT5 | 100 mm (3.9") | 50 kNm |
| 3FT6 | 120 mm (4.7") | 78 kNm |
| 3FT7 | 150 mm (5.9") | 150 kNm |
The 3FT range is designed and tested to the relevant composite post insulator standards: IEC 61952 (composite line post insulators), IEC 62231 (composite station post insulators for substations), ANSI C29.17 (composite insulators — transmission line post type) and ANSI C29.19 (composite insulators — station post type). Shed profiles follow IEC 60815-3 for AC and IEC 60815-4 for DC.
Extensive electrical field simulations validate operational reliability up to 800 kV system voltages. For higher system voltages, larger corona rings are required and are offered as part of the portfolio.
For line post applications, Siemens Energy can calculate combined load curves using EPRI (Electric Power Research Institute) calculation tools and provide these load curves already at the offer stage.
Station post insulator: support for busbars in high-voltage substations, and support insulator below other high-voltage equipment.
Line post insulator: inclined post insulator, brace insulator, and jumper support configurations.
Interface and interline spacers: phase-to-phase separation in high-voltage installations to maintain electrical clearance.
Composite Insulator Crossarm (CICA): the most compact design of insulator strings for compact lines or line uprating.
Core diameters run from 63.5 mm up to 150 mm, with lengths from 0.5 m to 5.5 m in a single unit; insulators can be stacked to achieve greater total height. Two shed profiles are available (creepage factor 3.6 and 4.2) and four different end fittings can be specified.
Four end-fitting styles are offered: tapped flange, through-holes flange, drop hole tongue, and flat & gain bendable base. Drop hole tongue and flat & gain bendable base variants are available for the 3FT2 and 3FT3 sizes. Flange options are designated by bolt count and size together with a flange diameter figure (e.g. 4x M16 D127, 8x D18 D254), as listed per type below.
| Type | Tapped flange | Through holes flange | Drop hole tongue | Flat & gain bendable base |
|---|---|---|---|---|
| 3FT2 | 4x M16 D127 | 4x D18 D127 | Yes | Yes |
| 3FT3 | 4x M16 D127 | 4x D18 D127 | Yes | Yes |
| 3FT4 | 4x M16 D127 / 4x M20 D127 | 4x D18 D178 | – | – |
| 3FT5 | 4x M16 D127 | 4x D18 D178 / 8x D18 D178 | – | – |
| 3FT6 | 8x M16 D127 | 8x D24 D225 | – | – |
| 3FT7 | – | 8x D18 D254 | – | – |
The type overview lists SCL (Specified Mechanical Load, equivalent to ceramic breaking load), MDCL (Maximum Design Cantilever Load), available length range, lightning withstand voltage and creepage factor (creepage/arcing) per type.
| Type | SCL (Specified Mechanical Load*) | MDCL (Maximum Design Cantilever Load) | Length | Lightning withstand | Creepage factor creepage/arcing |
|---|---|---|---|---|---|
| 3FT2 -4 | 18 kNm | 9 kNm | 0.5 – 3.0 m | > 1600 kV | 4.2 |
| 3FT3 -4 | 32 kNm | 16 kNm | 0.5 – 3.0 m | > 1600 kV | 4.2 |
| 3FT4 -4 | 46 kNm | 23 kNm | 0.5 – 4.0 m | > 2150 kV | 4.2 |
| 3FT5 -4 | 50 kNm | 25 kNm | 0.5 – 5.5 m | > 3050 kV | 4.2 |
| 3FT6 -3 | 78 kNm | 39 kNm | 0.5 – 5.5 m | > 3050 kV | 3.5 |
| 3FT6 -4 | 78 kNm | 39 kNm | 0.5 – 5.5 m | > 3050 kV | 4.2 |
| 3FT7 -4 | 150 kNm | 75 kNm | 1.0 – 5.5 m | > 3050 kV | 4.2 |
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