Medium-Voltage Surge Arresters — Product Catalogue

Definition of surge arresters

Surge arresters protect electrical equipment — transformers, circuit-breakers, bushings — against overvoltages caused by incoming surges from direct or nearby lightning strikes, electromagnetic pulses, electrostatic discharge, or switching operations in the supply system and in devices. The surge current is diverted through the arrester, in most cases to earth. Because some overvoltages carry very high energy, effective protection requires selecting the right arrester type for each application.

Portfolio overview

Siemens Energy offers surge arresters for every application from 3 kV up to 1,200 kV, including HVDC, FACTS and compensation systems, and for installation conditions from arctic cold to desert heat and tropical damp. The full portfolio spans high-voltage arresters up to 1,200 kV, medium-voltage arresters up to 72.5 kV, gas-insulated metal-enclosed arresters from 72.5 kV to 800 kV, line surge arresters, and arresters for railway applications.

Within medium voltage, product families map to applications: the 3EK distribution-class family protects transformers, circuit breakers, medium-voltage switchgear/panels, and distribution lines; the 3EJ Cage Design family combines higher energy discharge capability with a low protection level for rotating devices (generators, motors), arc furnaces and their transformers, industrial transformers, airfield-lighting systems, cable sheath, capacitors and capacitor banks, and drive converters; and for generators and motors requiring very high short-circuit current capability, the 3EP-G porcelain-housed arrester provides up to 300 kA.

MOVs, standards and testing

The core of every Siemens Energy arrester is the nonlinear metal-oxide (MO) resistor: low resistance during surges so overvoltages are limited, high resistance at continuous operating voltage so the power system is unaffected, and sufficient energy discharge capability for stable operation. The nonlinearity of MO resistors is so high that MO arresters need no series gaps. Siemens Energy MOVs provide high energy discharge capability with a very low protection level, are characterized by high long-duration current impulse withstand capability, are less prone to self-heating and self-destruction, and maintain their characteristics throughout their lifetime.

All arresters are designed and tested to the latest IEC 60099-4, IEEE C62.11 and GB 11032 standards. Type tests are performed by independent PEHLA-certified laboratories with reports available on request, 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 according to DIN EN ISO/IEC 17025. Quality assurance meets ISO 9001:2008, ISO 14002:2004 and BS OHSAS 18001:2007. Siemens Energy R&D experts sit on IEC TC 37 and the IEEE Surge Protective Device Committee, which develop IEC 60099-4/-5/-8/-9 and IEEE C62.11/C62.22.

How to select a suitable surge arrester

Selection balances two coupled requirements: adequate protection (overvoltages at the protected device must stay below its withstand voltage) and stable continuous operation. Both operating points are linked through the MOV voltage–current characteristic — lowering the protective level raises the continuous electrical stress and vice versa.

Step 1 — continuous operating voltage and rated voltage: Uc,min must equal the continuous phase-to-earth voltage ('continuous' meaning any voltage applied for more than 30 minutes). For solidly earthed neutral systems Uc,min ≥ Us/√3; for isolated or resonant earthed systems Uc,min ≥ Us (earth fault factor k = 1.73). A factor of 1.25 gives the minimum rated voltage Ur = 1.25 × Uc,min. Example, 24 kV solidly earthed system: Uc,min = 13.9 kV, Ur,min = 17.3 kV, typical Ur = 18 kV. Same system with isolated neutral: Uc,min = 24 kV, Ur,min = 30 kV, typical Ur = 30 kV.

Step 2 — nominal discharge current In: calculated from the maximum expected lightning current amplitude, Imax = (2·Ufo − Upl)/Z. Example for a 24 kV system with Ufo = 250 kV, Upl = 80 kV, Z = 450 Ohm: Imax = 0.9 kA. A 10 kA arrester readily withstands lightning impulses of higher amplitude without severe damage.

Step 3 — protective levels: assessed via the lightning impulse protective level (residual voltage at nominal discharge current). A protective level equal to the standard lightning impulse withstand voltage of the protected device divided by 1.4 is adequate: Upl,10kA,8/20µs < BIL/1.4.

Step 4 — energy class: IEC 60099-5 gives Qs = (Urp − Ups) × 2 × L / c·Zs and Ws = Ups × Qs for charge transfer and absorbed energy during line switching; IEEE C62.22 estimates discharged energy as J = 2·DL·EA·IA/v with IA = (ES − EA)/Z. The selected arrester must have charge and energy ratings above the accumulated values expected on the system. Per IEEE C62.11 the energy rating is not fixed — the higher the discharge voltage, the less energy the arrester absorbs during a line discharge.

Step 5 — protective zone: protection is only guaranteed for short arrester-to-equipment distances due to travelling-wave effects. Maximum separation: xs = (BIL/1.15 − Upl) · vtw / 2s, with front steepness s in the range of 1000 kV/µs and vtw = 300 m/µs on overhead lines. Example, 24 kV solidly earthed, BIL 125 kV, Upl 47.7 kV: xs = 9.1 m; isolated neutral with Upl 79.5 kV: xs = 4.4 m.

Clearances

Minimum clearances by rated voltage, phase-to-phase and phase-to-ground, as specified in the selection guidance.

Typical rated voltages

Typical rated voltages Ur for the highest system voltages Us according to IEC 60099-4, by neutral earthing type. Entries marked ¹ are served by high-voltage surge arresters. The catalogue also tabulates typical IEEE C62.11 duty-cycle voltages: e.g. Us 4.16 kV → Ur 3 kV (four-wire multi-grounded wye), 12.47 kV → 9 or 10 kV, 13.8 kV → 10 or 12 kV, 34.5 kV → 27 kV; three-wire low-impedance neutral: 4.16→6, 12.47→15, 34.5→36 kV; three-wire high-impedance neutral: 6.9→9, 13.8→18, 23→30 kV.

Product range and selection data

Cross-family main technical data according to IEC 60099-4. IEC arrester class designations: DH/DM = distribution high/medium duty (rated by thermal charge transfer Qth in C and charge transfer rating Qrs in C); SL/SM/SH = station low/medium/high duty (rated by thermal energy rating Wth in kJ/kVr and Qrs). 3EK7 is offered as DH (Qth 1.1 C, Qrs 0.5 C) and SL (Wth 5.0 kJ/kVr, Qrs 1.2 C); 3EK8 as DH (Qth 1.1 C, Qrs 0.4 C); 3EJ2 as SM (Wth 7.0, Qrs 2.0); 3EJ3 as SH (Wth 10 or 14, Qrs 2.8 or 3.6); 3EJ4 as SH (Wth 18, Qrs 6.0); 3EJ0 as DM (Qth 1.1, Qrs 0.4); 3EJ9 as SM (Wth 4.0, Qrs 2.0) and SH (Wth 4.0, Qrs 6.0); 3EP-G as SM (Wth 7.0, Qrs 2.0); 3EH4 as DH (Qth 1.1, Qrs 0.4). Note: the catalogue's per-product detail tables differ slightly from this overview in three places (3EK7 SL is listed there with Wth 4.5 kJ/kVr, 3EK8 with Is 20 kA, and 3EJ0 with Qrs 0.5 C) — both readings appear in the source document.

Per IEEE C62.11, energy classes are: 3EK7 class B (10 kA, 4.5 kJ/kVMCOV, 0.5 C), 3EK8 class A (10 kA, 3.0, 0.4 C), 3EJ2 class E (10 kA, 9.0, 2.0 C), 3EJ3 classes G (15 kA, 13, 2.8 C) and J (20 kA, 18, 3.6 C), 3EJ4 class K (20 kA, 21, 6.0 C); maximum rated voltage 36 kV for all five IEEE lines; rated short-circuit currents 20/21/50/65/50 kA respectively.

3EK distribution-class surge arresters (silicone rubber housing)

The 3EK cage-design and wrap-design families protect distribution networks. The MOVs are enclosed by a cage of fiber-reinforced plastic (FRP) rods for high mechanical strength, and silicone rubber is molded directly onto MOVs and rods, embedding all components free of inclusions and gaps — an excellent sealing system against moisture ingress that avoids partial discharges. If MOVs are overloaded, arcing cannot build critical internal pressure because there is no sealed mechanical shell: the arc escapes through the soft silicone housing and ejection of internal parts is almost completely prevented. The silicone housing is highly hydrophobic throughout its service life, tracking- and erosion-resistant, self-extinguishing and flame-retardant, giving maintenance-free service.

A disconnector at the earth terminal separates a failed arrester from the system; without one, in a solidly earthed neutral system the line section could not be re-energized. Unlike common designs that ignite a small explosive cartridge, Siemens Energy disconnectors use no pyrotechnics, offering safe handling, storage and installation.

Two product lines are offered: 3EK7 for rated voltages up to 60 kV with very high mechanical performance (also in an indoor cage-design version), and 3EK8 for rated voltages up to 36 kV. Ordering example 3EK7 360-4CH4: 360 = rated voltage 36 kV, 4 = LD class 1 (5 = LD class 2), C = IEC, H = housing type (H = 400 mm), final 4 = alternating sheds (0 = shedless indoor); suffix -Z adds accessories such as M11 line clamp, P12 NEMA insulating bracket, M81 bird protection cap.

The table below gives the outdoor 3EK7 IEC 60099-4 DH line (all versions: In = 10 kA, Qrs = 0.5 C, Qth = 1.1 C, rated short-circuit current Is = 20 kA). Residual voltages at the full set of test impulses (30/60 µs at 125 A and 500 A; 8/20 µs at 1, 3, 5, 10, 20 kA) are printed in the catalogue; the two headline protective levels are shown here. The catalogue additionally tabulates the 3EK7 SL line (In 10 kA, Qrs 1.2 C, Wth 4.5 kJ/kVr, 3–42 kV), the 3EK7 IEEE class-B line (3–36 kV, 4.5 kJ/kVMCOV), and indoor (shedless) IEC DH, IEC SL and IEEE variants with reduced creepage and weight.

3EK8 and 3EK accessories

The 3EK8 covers rated voltages 3–36 kV in a compact, lightweight silicone-housed design (0.5–2.8 kg). All IEC versions are class DH with In = 10 kA, Qrs = 0.4 C, Qth = 1.1 C and Is = 20 kA. IEEE variants are offered as 3EK8 HD (heavy duty, class A, 3.0 kJ/kVMCOV, 3–36 kV) and 3EK8 RP (riser pole, 3–27 kV). Ordering example 3EK8 360-1CW4: 1C = IEC, W = housing type (H = 332 mm), 4 = alternating sheds; without -Z the terminals are M12 internal thread; -Z accessories include M50/P50 bolts M12x53 and M81 bird protection cap.

A full accessories program serves 3EK7 and 3EK8: line terminals (M11 line clamp ø8–18 mm, spare 3EX4 063-0A/-0C; M12 L-bracket 3EX4 071; M13 line clamp 3EX4 101-1A/-1C), bird protection caps (M81 for 3EK7 3EX4 128-0A d=75 mm, for 3EK8 3EX4 068-0C d=65 mm; M84 XL 3EX4 103 d=92 mm), metal brackets (P11 NEMA 3EX4 061-0A/-0C, P21 DIN 3EX4 062), NEMA insulating brackets P12 for Ur ≤ 15 kV and > 15 kV (3EK7: 3EX4 080-1x/-2x; 3EK8: 3EX4 120-1x/-2x), DIN insulating brackets P22 (3EX4 086-1C/-2C), pyrotechnic-free ground-lead disconnectors (3EK7: 3EX4 065-7A/-7C; 3EK8: 3EX4 065-8/-8C), transformer brackets Q11 8.7"/221 mm, Q12 11"/279 mm, Q13 12.25"/311 mm, Q14 14.5"/368 mm (3EX4 075-0A/-0C/-0B/-0D), Q51 cross-arm bracket (3EX4 073-0A), and leads (P52 ground strap 305 mm 3EX4 078-0A/-0C; R51 insulated line/earth lead 455 mm 3EX4 074-0A/-0C; R61 line/earth lead 3EX4 121-3A). Packing data per housing size covers pieces per pallet and per 20'/40' container.

3EH4 medium-voltage plug-in arresters

The 3EH4 plug-in arrester protects transformers and switchgear (indoor and outdoor, IP66) against switching overvoltages and lightning. Its protection performance is aligned with the impulse withstand voltage of encapsulated switchgear and transformers, so overvoltages from travelling-wave reflection and switching are also limited. It shares the electrical characteristics of the 3EK family. The plug-and-socket connection is available 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. Silicone-coated MOVs insulate against the metal housing; on overload a corrosion-resistant pressure-relief diaphragm provides controlled pressure reduction. The grounded, corrosion-resistant aluminum housing is touch-proof and hermetically sealed, protecting the MOVs from moisture. New versions with insulated ground terminal enable monitoring devices. Compliance: IEC 60099-4, with type tests in independent PEHLA-accredited laboratories.

The table shows connector size 2 with earthed housing (all rows: designation DH, In = 10 kA, Qrs = 0.4 C, Qth = 1.1 C, Is = 16 kA). The same electrical values apply to the insulated-housing size-2 variants (housing codes J/K, e.g. 3EH4 300-1JC14) and to connector size 3 in earthed (D, H = 432 mm, housing insulation 250/100 kV) and insulated (L) versions. Ordering example 3EH4 300-1BC14: 300 = 30 kV, -1 = connector size 2, B = housing size 1 earthed (H = 335 mm), C = MO resistor type, 1 = indoor application, 4 = protection class IP66. Packing dimensions: housing B 150×150×504 mm, housings C/D 200×200×632 mm; insulated housings J 150×150×554 mm, K/L 200×200×682 mm.

3EJ surge arresters with high energy discharge capabilities

The 3EJ Cage Design family serves applications needing high energy discharge with a low protection level: generators, motors, arc furnaces and arc furnace transformers, dry-type transformers, airfield-lighting systems, cable sheath, capacitors and capacitor banks, and drive converters. Construction mirrors the 3EK cage design: MOVs held in an FRP-rod cage with silicone rubber molded directly on, giving inclusion-free sealing, no critical internal pressure buildup on overload, hydrophobic self-extinguishing housing, and maintenance-free service life.

Five product lines differentiate by protection level and energy: 3EJ2 (up to 54 kV, medium energy discharge), 3EJ3 (up to 54 kV, high energy), 3EJ4 (up to 54 kV, very high energy; also as indoor version), 3EJ0 (up to 15 kV, very low protection levels against switching overvoltages, normally used in cable systems up to 15 kV), and 3EJ9 (up to 12 kV, very low protection levels with higher energy absorption and improved protection level, used for station service systems of power stations and extensive cable systems). IEEE C62.11 lines: 3EJ2 class E (9.0 kJ/kVMCOV), 3EJ3 classes G and J (13/18 kJ/kVMCOV), 3EJ4 class K (21 kJ/kVMCOV), all up to 36 kV duty cycle voltage.

Ordering example 3EJ2 010-5CC31-4: 010-5 = rated voltage 10.5 kV, C = IEC, C = housing type (H = 211 mm), 3 = energy class Wth = 7 kJ/kVr, 1 = one unit, -4 = alternating sheds (-0 = shedless indoor; 3EJ9 suffix A = exchange for 3EF3-0). Detailed IEC and IEEE tables in the catalogue list per-rating residual voltages from 125 A (30/60 µs) to 20 kA (8/20 µs), heights, creepage distances, withstand voltages, mechanical loads (SSL up to 10,630 N for 3EJ4) and weights. 3EJ accessories include L-bracket 3EX4 500-1L, flat DIN/NEMA terminal 3EX4 500-1X, and insulated or grounded mountings from Ø190–260 mm to 310×310 mm (3EX4 500-2A…2D, 3EX4 500-3A…3D).

3EP-G porcelain surge arresters and glossary

For generators and motors requiring very high short-circuit current capability, the 3EP-G porcelain-housed arrester offers a rated short-circuit current of 300 kA. A specially designed directional pressure relief device lets the arc escape easily in an overload or arrester short-circuit: no pressure builds inside the arrester and no internal parts are ejected, preventing damage to surrounding equipment. The sealing system prevents moisture ingress for decades of trouble-free service; nonporous sulfur cement (instead of corrosive Portland cement) bonds and protects the MO resistors against aging. As in the polymer families, the MO resistors sit in a rigid FRP-rod cage whose high tensile strength holds them tightly in place.

All 3EP-G ratings share: Is = 300 kA, In = 10 kA, Qrs = 2.0 C, Wth = 7.0 kJ/kVr, height 665 mm, creepage 1035 mm, LIWV 206 kV, power frequency withstand (wet) 78 kV, SSL 51,120 N, SLL 20,450 N. Ordering example 3EP3 030-2GA31-2ZA9-Z K83 P2G R2G: 3EP3 = tube design porcelain housing heavy, 030 = 30 kV, -2 = resistor type, G = generator protection, A = housing type (H = 665 mm), 3 = energy class Wth 7 kJ/kVr, Z-options K83 enhanced short-circuit performance 300 kA, P2G terminal plate 13 mm, R2G insulated mounting. Packing: single 80×80×130 mm, triple 150×80×130 mm.

The catalogue closes with a glossary defining continuous operating voltage Uc, creepage/leakage distance, discharge and residual voltage, duty cycle voltage and rated voltage Ur (10 s or 100 s application), highest system voltage Us, lightning impulse classifying current and nominal discharge current In, MCOV, protective level (lightning 8/20 µs, switching 30/60 µs, steep current 1/2 µs), rated short-circuit current Is, specific creepage distance (mm/kV of Us), and temporary overvoltage (TOV).

Figures & drawings

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