Medium-voltage surge arresters — Siemens Energy product catalog

What surge arresters do and the Siemens Energy portfolio

Surge arresters protect electrical equipment — transformers, circuit-breakers, bushings, generators, motors, capacitors and complete switchgear — against overvoltages from direct or nearby lightning strikes, electromagnetic pulses, electrostatic discharge and switching operations. The surge current is diverted through the arrester, in most cases to earth; effective protection requires different arrester types depending on the application.

Siemens Energy has designed and manufactured medium- and high-voltage surge arresters since 1925. The portfolio spans high-voltage arresters for substation equipment up to 1,200 kV, medium-voltage arresters for systems up to 72.5 kV, gas-insulated metal-enclosed arresters for AC and DC applications from 72.5 kV to 800 kV, plus line and railway arresters.

Within medium voltage, the 3EK distribution-class family protects transformers, circuit breakers, MV switchgear/panels and distribution lines; the 3EJ Cage Design family adds higher energy discharge capability at a low protection level for rotating machines, arc furnaces, industrial transformers, airfield lighting, cable sheath, capacitor banks and drive converters; the 3EP-G porcelain-housed arrester serves generators and motors needing short-circuit current capability up to 300 kA; and the 3EH4 is a plug-in arrester for encapsulated switchgear and transformers.

MOV technology, standards and testing

The core of every Siemens Energy arrester is the gapless metal oxide varistor (MOV). Its highly nonlinear resistance gives low resistance during surges (limiting overvoltages), high resistance during normal operation, and sufficient energy discharge capability for stable operation. Silicone-embedded MOV columns provide high energy discharge capability with a very low protection level; the MOVs are characterized by their high long-duration current impulse withstand capability and are less prone to self-heating and thermal runaway, maintaining their characteristics throughout their lifetime.

Arresters are designed and tested to the latest IEC 60099-4, IEEE C62.11 and GB 11032 standards. All type tests are performed by independent, PEHLA-certified laboratories, and every arrester leaving the factory undergoes a routine test and ships with a routine test certificate. The in-house test field is certified by the Deutsche Akkreditierungsstelle (Germany's national accreditation body) per DIN EN ISO/IEC 17025. Siemens Energy meets ISO 9001:2008, ISO 14002:2004 and BS OHSAS 18001:2007, and its R&D experts sit on IEC TC 37 and the IEEE Surge Protective Device Committee.

How to select a suitable surge arrester

Selection balances two requirements that cannot be fulfilled independently: adequate protection margin (overvoltages must stay below the protected device's withstand voltage) and stable continuous operation. Step 1 fixes the continuous operating voltage: for solidly earthed neutral systems Uc,min ≥ Us/√3; for isolated or resonant earthed neutral systems Uc,min ≥ Us (earth fault factor k = 1.73, since these systems commonly run >30 minutes in single-phase earth fault). A factor of 1.25 then gives the minimum rated voltage Ur = 1.25 × Uc,min. Example, 24 kV solidly earthed: Uc,min = 13.9 kV, Ur,min = 17.3 kV, typical Ur = 18 kV; isolated neutral: Uc,min = 24 kV, typical Ur = 30 kV.

Step 2 selects the nominal discharge current In from the expected lightning amplitude, Imax = (2·Ufo − Upl)/Z (24 kV example: Ufo = 250 kV, Upl = 80 kV, Z = 450 Ohm gives Imax = 0.9 kA — a 10 kA arrester withstands far higher impulses). Step 3 checks protective levels: a lightning impulse protective level Upl,10kA,8/20µs < BIL/1.4 is adequate. Step 4 selects the energy class per IEC 60099-5 / IEEE C62.22 charge-transfer and energy equations (energy classes A–N span 3.0 to 30 kJ/kVMCOV two-shot ratings). Step 5 verifies the protective zone xs = (BIL/1.15 − Upl)·vtw/2s — for the 24 kV solid-earthing example (BIL 125 kV, Upl 47.7 kV) xs = 9.1 m; for isolated neutral (Upl 79.5 kV) xs = 4.4 m.

The catalog also tabulates recommended minimum clearances per arrester rated voltage Ur, reproduced below.

Typical rated voltages Ur for highest system voltages Us (IEC 60099-4)

The typically applied rated voltage depends on the system's neutral earthing. Values marked 1) require a high-voltage surge arrester. A companion table in the catalog gives typical duty-cycle voltages per IEEE C62.11 for 4.16–34.5 kV system L-L voltages.

Product range and main technical data (IEC 60099-4)

Siemens Energy offers multiple models of each surge arrester family. The selection overview per IEC 60099-4 spans distribution applications (3EK7, 3EK8), high-energy applications and protection of rotating devices (3EJ2, 3EJ3, 3EJ4, 3EJ0, 3EJ9, 3EP-G) and plug-in applications (3EH4). Designations range from DM (In 5 kA, Qth 1.1 C, Qrs 0.4 C) and DH (In 10 kA) through SL/SM/SH energy classes up to Wth 18 kJ/kVr at In 20 kA. Indoor versions are available for 3EK7, 3EJ4 and 3EJ9 (plus the indoor/outdoor IP66 3EH4). A parallel IEEE C62.11 table assigns energy classes A (3.0 kJ/kVMCOV), B (4.5), E (9.0), G (13), J (18) and K (21).

3EK distribution-class surge arresters with silicone rubber housing

The 3EK family combines cage design and wrap design construction: the MOVs are enclosed by a cage of fiber-reinforced plastic (FRP) rods, with silicone rubber molded directly onto the MOVs and rods. This total embedding — free of inclusions and gaps — provides an excellent seal against moisture ingress and avoids partial discharges. If the MOVs are ever overloaded, the arc escapes through the soft silicone housing without pressure buildup or ejection of internal parts. Silicone rubber is highly hydrophobic, tracking- and erosion-resistant, self-extinguishing and flame-retardant, giving maintenance-free service life.

A disconnector at the earth terminal separates a failed arrester from the system so the line section can be re-energized. Unlike most market designs that ignite a small explosive cartridge, Siemens Energy disconnectors do not use any pyrotechnics — safe handling, storage and installation without dangerous-goods regulation.

Two product lines cover distribution networks: 3EK7 for rated voltages up to 60 kV with very high mechanical performance, and 3EK8 for rated voltages up to 36 kV. The proven 3EK7 is also available as an indoor cage-design version. Accessories include line clamps (M11/M13), L-bracket (M12), NEMA/DIN metal and insulating brackets, bird protection caps (M81/M84), transformer and cross-arm mounting brackets, ground straps and insulated line/earth leads.

3EK7 specifications according to IEC 60099-4 (electrical characteristics)

Designation DH, nominal discharge current In = 10 kA, charge transfer rating Qrs = 0.5 C, thermal charge transfer rating Qth = 1.1 C for all types. Columns give maximum residual voltages (kV) at the stated discharge impulses. Mechanically, housings run 170–470 mm height with 372–1,420 mm creepage, rated short-circuit current 20 kA, lightning impulse withstand 104–281 kV, and arrester weights 1.5–5.1 kg. An SL variant (Qrs 1.2 C, Wth 4.5 kJ/kVr, up to 42 kV) and indoor IEC/IEEE versions are separately tabulated in the catalog, as are IEEE C62.11 ratings (energy class B, 4.5 kJ/kVMCOV).

3EK8 according to IEC 60099-4

The 3EK8 wrap-design distribution arrester covers rated voltages 3–36 kV. Designation DH, In = 10 kA, Qrs = 0.4 C, Qth = 1.1 C. Rated short-circuit current 20 kA. The catalog also lists IEEE C62.11 heavy-duty (3EK8 HD, energy class A, 3.0 kJ/kVMCOV) and riser-pole (3EK8 RP) variants. Height and approximate weight (without accessories) are appended below; creepage distances run 267–1,358 mm.

3EH4 medium-voltage plug-in arresters for distribution networks

The 3EH4 plug-in arrester protects transformers and switchgear (indoor and outdoor, IP66) against switching overvoltages and lightning. Its plug-and-socket connection comes in connector sizes 2 and 3, dimensioned to EN 50180 / EN 50181 for the inner-cone system; the arrester corresponds to class DH and suits operating voltages up to 52.5 kV. Because it shares the electrical characteristics of the 3EK family, it delivers the same protection levels. The silicone-coated MOVs are insulated against the grounded, corrosion-resistant, touch-proof aluminum housing, which is hermetically sealed; overload pressure is relieved via a corrosion-resistant pressure-relief diaphragm. Versions with insulated ground terminal enable monitoring devices.

The table below is the connector size 2, earthed-housing series (designation DH, In 10 kA, Qrs 0.4 C, Qth 1.1 C, rated short-circuit current 16 kA). Identical electrical values apply to the insulated connector size 2 series and to connector size 3 (heights 432 mm, housing insulation LIWV 250 kV / PFWV 100 kV, weights 6.5–7.1 kg).

3EJ surge arresters with high energy discharge capabilities

The 3EJ Cage Design family uses the same FRP-rod cage with directly molded silicone rubber as the 3EK, but with higher energy discharge capability in combination with a low protection level. It protects generators, motors, arc furnaces and arc furnace transformers, dry-type transformers, airfield-lighting systems, cable sheath, capacitors and capacitor banks, and converters for drives.

Five product lines differentiate by protection level: 3EJ2 up to 54 kV with medium energy discharge capability; 3EJ3 up to 54 kV with high energy discharge capability; 3EJ4 up to 54 kV with very high energy discharge capability; 3EJ0 up to 15 kV and 3EJ9 up to 12 kV with very low protection levels for switching-overvoltage protection. The 3EJ0 is normally used in cable systems up to 15 kV; the 3EJ9, with higher energy absorption and improved protection level, serves station service systems of power stations and extensive cable systems. The proven 3EJ4 is also available in an indoor version.

Key ratings of the smaller lines: 3EJ0 (designation DM, In 5 kA, Wth 1.0 kJ/kVr, Is 20 kA, 3.6–15 kV); 3EJ9 (SM: In 10 kA, Wth 4.0 kJ/kVr; SH: In 20 kA, Qrs 6.0 C; Is 50 kA; 3.6–12 kV). The 3EJ3 (designation SH) offers In 20 kA at Qrs 2.8/3.6 C, Wth 10.0/14.0 kJ/kVr, rated short-circuit current 65 kA across 1.4–54 kV — the highest short-circuit rating of the silicone family.

3EJ2 specifications according to IEC 60099-4 (electrical characteristics)

Designation SM, In = 10 kA, Qrs = 2.0 C, thermal energy rating Wth = 7.0 kJ/kVr. Mechanically: rated short-circuit current 50 kA, heights 166–481 mm, creepage 430–1,580 mm, weights 3.0–11.0 kg. IEEE C62.11 versions carry energy class E (9.0 kJ/kVMCOV, single impulse withstand 2.0 C).

3EJ4 specifications according to IEC 60099-4 (electrical characteristics)

The 3EJ4 offers the family's very high energy discharge capability: designation SH, In = 20 kA, Qrs = 6.0 C, Wth = 18.0 kJ/kVr. Mechanically: rated short-circuit current 50 kA, heights 188–496 mm, creepage 460–1,810 mm, weights 7.8–27.1 kg. Indoor IEC versions cover 3.3–30 kV; IEEE C62.11 versions carry energy class K (21.0 kJ/kVMCOV, single impulse withstand 6.0 C, Is 50 kA). The companion 3EJ3 IEC series (SH, In 20 kA, Qrs 2.8 or 3.6 C, Wth 10.0 or 14.0 kJ/kVr, Is 65 kA) spans 1.4–54 kV in the catalog with residual voltages from 2.5 kV (30/60µs 125 A at Ur 1.4 kV) up to 133 kV (8/20µs 20 kA at Ur 54 kV).

Figures & drawings

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