High-voltage surge arresters — Product guide

Definition and purpose of surge arresters

Surge arresters protect high-voltage equipment in substations — transformers, circuit breakers, bushings — against overvoltages caused by direct or nearby lightning strikes, electromagnetic pulses, electrostatic discharge, or switching operations. The current from the surge is diverted through the arrester, in most cases to earth, and effective protection requires different arrester types matched to the application.

Siemens Energy has been designing and manufacturing medium- and high-voltage surge arresters since 1925. The arresters serve insulation coordination in power systems and are available for any application from 3 kV up to 1,200 kV, including special applications such as high-voltage direct current (HVDC) and FACTS systems, and are designed for installation environments from arctic cold to desert heat and tropical dampness.

MOVs: the core of the arresters

The active part is built from nonlinear metal oxide (MO) resistors: low resistance during surges so overvoltages are limited, high resistance during normal operation, and sufficient energy absorption capability for stable operation. The nonlinearity of MO resistors is high enough that MO arresters need no series gaps.

Siemens Energy metal oxide varistors (MOVs) combine high energy absorption capability with a very low protection level. They are characterized by a high long-duration current impulse withstand capability — an indirect measure of single impulse energy absorption — making the arresters less prone to self-heating and thermal runaway, and keeping their characteristics stable throughout their lifetime. The guide includes the IEC power-frequency voltage vs. time (U-t) TOV characteristic with preheating to 60 °C prior to duty.

Housing materials: silicone rubber and porcelain

Siemens Energy has supplied silicone rubber housed arresters for more than 25 years and uses only HTV (high-temperature vulcanized) or LSR (liquid silicone rubber) elastomers. Genuine silicone rubber is the only polymeric material that maintains hydrophobicity throughout its lifetime — unlike EPDM alloy rubbers, which chalk, crack, and lose hydrophobicity. Its –Si–O– backbone gives better chemical resistance, UV resistance, and lower flammability (IEC 60707 / UL94 V-0, self-extinguishing), and it performs across an ambient range of −60 °C to +200 °C.

Porcelain-housed arresters feature a directional pressure relief device for maximum protection in the case of an overload. Both ends carry aluminum flanges cemented with sulfur cement — advantageous over Portland cement because it does not corrode aluminum and reaches nearly full mechanical strength directly after application. Flange and end-section design ensures the cement joint is mechanically stronger than the porcelain itself.

Three station class product families

Siemens Energy provides three surge arrester product families for standard and special AC applications from 3 kV up to 800 kV: 3EL silicone rubber arresters with Cage Design™, 3EQ silicone rubber arresters with composite hollow core design, and 3EP porcelain-housed arresters.

3EL (Cage Design): MO blocks are enclosed by a cage of prestressed fiberglass-reinforced plastic (FRP) rods with silicone rubber sheds molded directly onto the MO blocks and end fittings — no gaps or bubbles, no sealed shell, so no excess pressure can build up on overload and internal parts are almost completely prevented from ejection. Extremely lightweight, installable at any mounting angle (horizontal, vertical, or suspended as line surge arrester), for systems up to 550 kV.

3EQ (composite hollow core): silicone rubber molded onto an FRP hollow core tube with directional pressure relief devices at both ends. Shatterproof, retains at least 75 percent of mechanical strength even after pressure relief, suited to the highest mechanical demands (heavy seismic activity, extreme wind loads) and as post insulator replacement in substations up to 800 kV. 3EP (porcelain): ideal for high mechanical performance up to 800 kV with guaranteed seismic qualification of 0.5 g, directional pressure relief, and nonporous sulfur cement bonding.

Standards, testing, and quality assurance

All arresters are designed and tested in compliance with the latest IEC 60099-4, IEEE C62.11, and GB 11032 standards. All type tests are performed by independent, PEHLA-certified laboratories; reports are available on request. Every single arrester leaving the factory undergoes a routine test and is delivered with a routine test certificate. The test field is certified by the Deutsche Akkreditierungsstelle (DAkkS, D-PL-12072-04-01) according to DIN EN ISO/IEC 17025.

Siemens Energy meets ISO 9001:2008, ISO 14002:2004, and BS OHSAS 18001:2007. Its R&D experts are members of IEC TC 37 (IEC 60099-4, IEC 60099-8 EGLA, IEC 60099-9 HVDC, application guide IEC 60099-5) and the IEEE Surge Protective Device Committee (IEEE C62.11, application guide IEEE C62.22), and contribute to CIGRE.

How to select a suitable surge arrester

Selection balances two requirements: adequate protection (overvoltages at the protected device must stay below its withstand voltage with sufficient safety margin) and stable continuous operation. Step 1 sets the continuous operating voltage and rated voltage: for solidly earthed neutral systems Uc,min ≥ Us/√3; for isolated or resonant earthed systems Uc,min ≥ Us; the rated voltage follows as Ur = 1.25 · Uc,min. Step 2 selects the nominal discharge current In from Imax = (2·Ufo − Upl)/Z — e.g. for a 420 kV system with Ufo = 2.1 MV, Upl = 806 kV, Z = 350 Ω, Imax = 9.7 kA, so a 10 kA arrester suffices. Step 3 selects the line discharge class per IEC 60099-4 (classes 1–5, specific energy in kJ/kV vs. the Ures/Ur ratio).

Step 4 checks protective levels: the lightning impulse protective level should satisfy Upl, 10 kA, 8/20 µs < BIL / 1.4. Step 5 selects the housing: length driven by clearance and creepage requirements (specific creepage distances up to 20 mm/kV are standard; 25 mm/kV and 31 mm/kV for maritime, desert, or heavily polluted environments), then material and diameter per mechanical criteria (rated short-circuit current Is, specified long-term load SLL, specified short-term load SSL). If actual requirements are unknown, the table gives guideline static head loads.

Applications as line surge arresters

Surge arresters on hazardous stretches of a power line improve network protection and transmission system reliability. With low weight, outstanding strength, and safe overload behavior, 3EL arresters are ideally suited — reference installations include a 400 kV line in Bulgaria and a 550 kV line in Colombia, both NGLA solutions realized with 3EL2.

Two solutions exist: non-gapped line arresters (NGLA), installed directly on the insulators or on the tower, available in the 3EL1, 3EL2, 3EL3, and 3EL5 series; and externally gapped line arresters (EGLA) of the 3EV1, 3EV2, and 3EV5 series, whose series varistor units are based on the respective 3EL1, 3EL2, and 3EL5 product lines and whose external spark gap galvanically isolates the active part from line voltage under normal conditions.

Product range — main technical data

The selection table below shows the maximum values of the eleven product lines. Models within each family differ mainly in diameter, housing length, and MOV block size. Nominal discharge current / line discharge class / energy absorption combinations range from 10 kA / class 2 / 4.4 kJ/kVr / 550 A (3EL5) up to 20 kA / class 5 / 16.0 kJ/kVr / 3,200 A (3EP3, 3EQ4, 3EQ3).

Footnotes as printed: for 3EQ4 an increased rated short-circuit current of 80 kA is available on request; 3EP6, 3EP3, 3EQ4, and 3EQ3 list increased bending moments (second value).

Typical rated voltages by system earthing

The guide tabulates the typical minimum rated voltage Ur for the arrester depending on the highest voltage of the system Us and the type of neutral earthing, according to IEC 60099-4.

Product line datasheets — maximum values per family

Each product line has a technical datasheet with variants by nominal discharge current, line discharge class, and energy rating; the table below consolidates the datasheet 'Maximum values' columns. All lines protect transformers, circuit breakers, generators, motors, capacitors, bushings, and switchgear; the 3EL lines additionally cover traction vehicles and transmission lines.

Full 'Ratings and specifications' tables in the guide list, per rated voltage step: continuous operating voltage Uc, line discharge class, long duration current impulse (2 ms), maximum residual voltages at 30/60 µs 0.5/1/2 kA and 8/20 µs 5/10/20/40 kA impulses, arrester type code, and minimum housing size — for phase arresters and, on most product lines, neutral ground arresters (pages 31, 35–37, 42–45, 50–51, 57–59, 64–65, 72–74, 80–81, 88–89, 96–97, 104; 3EL5, 3EP3, and 3EQ3 list phase arresters only). Mechanical characteristics tables give per housing size: height, creepage distance, lightning/switching impulse and power frequency withstand voltages, SSL, SLL, grading ring diameter, maximum arrester weight, and flashover distance.

Order code system and ordering example

Every arrester is specified by a 16-position order code encoding product line, rated voltage (kV), long duration current impulse / energy absorption capability, application (L = line surge arrester, P = phase, S = neutral point), housing size and number of units, line discharge class, form of sheds and housing color, high-voltage terminal, nameplate language, mounting, and accessories (–Z suffix).

Ordering example from the guide: product line 3EL2 with rated voltage and energy rating gives 3EL2 096-2P.3.-…; selecting the minimum housing J yields 3EL2 096-2PJ31-…; selecting terminal, nameplate, and mounting completes the code as 3EL2 096-2PJ31-4XA1 (4 = upright mounting, X = DIN/NEMA flat terminal, A = English nameplate, 1 = insulated mounting, D = 200 mm); an optional D91 line clamp gives 3EL2 096-2PJ31-4XA1-Z D91, plus optional monitoring device 3EX5 080-0 ACM basic. Terminal options per line include metal plate, bolts (26–50 mm diameter in stainless steel, hot-dip galvanized steel, aluminum, or copper), and DIN/NEMA flat terminals; nameplates are available in German/English, French, Czech, Slovene, Russian, Spanish, Portuguese, Arabic, Brazil, and CFE (Mexico) versions.

Accessories and monitoring devices

Optional accessories are added to the order number by code, e.g. D51 earth terminal copper tin-plated, D71 DIN/NEMA earth terminal, D81/D82 adapters DIN/NEMA to double DIN/NEMA flat terminal with 2 line clamps, D91 line clamp, D92 eyebolt earth terminal, D93/D94 NEMA earth terminals (stainless steel / copper), D95 palm earth terminal aluminum, D96 earth terminal 2x D14 stainless steel, K02 N2 filling, K14 yellow cover panels for gas diverter, and K80 increased rated short-circuit current of 80 kA (3EQ4).

Operated within specification, arrester service life can reach up to 30 years without maintenance. Siemens Energy offers a complete line of monitoring devices for early fault detection: surge counters (3EX5 030-0, with auxiliary contact 3EX5 030-1), surge counters with leakage current meter 0–30 mA (3EX5 050-0/-1) and 0–50 mA (3EX5 050-2), Arrester Condition Monitor ACM basic (3EX5 080-0) and ACM advanced (3EX5 080-1, USB wireless module 3EX5 086), sensor (3EX5 060-1) and display (3EX5 062-1) with connecting leads from 3 m to 30 m, plus mounting bracket, connection cable, and earth lead.

Figures & drawings

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