High-voltage surge arresters — Siemens Energy product guide (online edition)

Portfolio: three arrester designs for any requirement

Surge arresters protect high-voltage equipment in substations — transformers, circuit breakers, generators, motors, capacitors, traction vehicles, bushings and complete switchgear — against overvoltages caused by 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 according to the application.

Siemens Energy has designed and manufactured medium- and high-voltage surge arresters for standard and special applications since 1925. Arresters 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 as well as all kinds of compensation systems, and are designed for installation environments from arctic cold to desert heat and tropical dampness.

Three designs have emerged from technology development and practical experience: surge arresters with porcelain housings, with silicone housings, and with metal enclosures. Each is offered in several versions to meet specific demands such as high mechanical stability for outstanding seismic safety, extremely reliable pressure relief behavior for areas requiring special protection, and excellent pollution layer characteristics for coastal, desert or heavily polluted regions. All Siemens Energy arresters feature a superior sealing system that reliably prevents moisture ingress. This brochure describes the three station-class product families for standard and special AC applications from 3 kV up to 800 kV: 3EL (silicone housing, Cage Design), 3EQ (silicone housing, composite hollow core design) and 3EP (porcelain housing).

MOVs: the core of the arresters

An arrester must protect equipment from overvoltages while having no negative effect on the power system during normal operation, and must withstand typical surges without damage. Nonlinear resistors fulfill these requirements: low resistance during surges so that overvoltages are limited, high resistance during normal operation, and sufficient energy absorption capability for stable operation.

Nonlinear metal oxide (MO) resistors have proven especially suitable. Their nonlinearity is so high that MO arresters do not need series gaps. Siemens Energy metal oxide varistors (MOVs) provide high energy absorption capability at a very low protection level — they absorb a high amount of energy while avoiding thermal runaway — and are characterized by their high long-duration current impulse withstand capability, an indirect measure of single-impulse energy absorption capability. Siemens Energy arresters are less prone to self-heating and consequent self-destruction, and maintain their characteristics throughout their lifetime. The guide includes the IEC power-frequency voltage-versus-time (U-t / TOV) characteristic with preheating to 60 °C prior to duty.

Housing materials: silicone rubber and porcelain

Siemens Energy has provided silicone rubber-housed arresters for more than 25 years and uses exclusively HTV (high-temperature vulcanized) or LSR (liquid silicone rubber) elastomers. Silicone rubber is highly hydrophobic and — unlike EPDM-based alloy rubbers — maintains its hydrophobicity throughout the entire service life; hydrophobicity even returns after a corona discharge. Its –Si–O– backbone has a higher bonding energy than the –C–C– backbone of EPDM, giving inherently better chemical, physical and UV resistance and lower flammability: flame-retardant properties comply with IEC 60707 and UL94 V-0 (self-extinguishing, no burning drips). Silicone rubber resists all common cleaning agents and solvents and performs across an ambient temperature range of –60 °C to +200 °C.

Porcelain-housed arresters feature a directional pressure relief device that ensures maximum protection in an overload case. Both ends of the housing carry aluminum flanges cemented with sulfur cement, which — unlike the Portland cement common in the insulator industry — can contact aluminum without causing corrosion and reaches almost full mechanical strength directly after application. Flange and end-section design ensures the cement joint is mechanically stronger than the porcelain itself, so the porcelain's full strength can be used when specifying permissible mechanical head loads.

The three station-class families: 3EL, 3EQ, 3EP

3EL Cage Design: the 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 — total embedding free of bubbles and gaps, preventing partial discharge and moisture ingress. Cage design arresters are among the mechanically strongest polymer arresters on the market at minimal material use and very low weight. With no sealed shell or hard wrapping, no excess pressure develops on overload: the arc escapes directly through the soft silicone housing and ejection of internal parts is almost completely prevented. 3EL arresters serve station and line applications in systems up to 550 kV and can be installed at any mounting angle (horizontal, vertical, or suspended from the line as line surge arrester).

3EQ composite hollow core design: silicone rubber is molded directly onto an FRP hollow core, with directional pressure relief devices and a special flange sealing at both ends. The design combines cost savings with very high safety — on overload the arc escapes through the directional pressure relief devices, no parts are ejected and the housing does not break; the arresters are shatterproof and retain at least 75 percent of their mechanical strength even after pressure relief. They support high bending moments, suit heavy seismic activity and extreme wind loads, can be mounted directly over a transformer to support connectors, and are the perfect choice for replacing existing post insulators in substations up to 800 kV.

3EP porcelain: the ideal choice for high mechanical performance requirements up to 800 kV, with a guaranteed seismic qualification of 0.5 g up to 800 kV. A specially designed directional pressure relief device lets the arc escape easily on overload — no internal pressure buildup, no ejected parts. The MO blocks are enclosed by a rigid reinforced FRP-rod cage, and nonporous sulfur cement bonding protects the MO blocks and prevents aging effects. Thanks to their safety, 3EP arresters can be installed in close proximity to costly system components.

Standards, testing and quality assurance

Siemens Energy surge 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 with reports available on request, and every arrester leaving the factory undergoes a routine test and is delivered with a routine test certificate. The in-house test field — whose generator supplies impulse voltages of 1.2/50 µs and 250/250 µs and impulse currents of 8/20 µs and 30/60 µs — is certified by the Deutsche Akkreditierungsstelle (Germany's national accreditation body) according to DIN EN ISO/IEC 17025.

Siemens Energy meets all requirements of ISO 9001:2008, ISO 14002:2004 and BS OHSAS 18001:2007, and all suppliers must be ISO-certified or are audited by Siemens Energy. Siemens Energy R&D experts are members of IEC Technical Committee 37 (which develops IEC 60099-4, IEC 60099-8 for EGLA, IEC 60099-9 for HVDC and the application guide IEC 60099-5) and of the IEEE Surge Protective Device Committee (IEEE C62.11 and application guide IEEE C62.22), and contribute to CIGRE.

How to select a suitable surge arrester (steps 1–5)

Selection balances two requirements that cannot be fulfilled independently: adequate protection with sufficient safety margin, and stable continuous operation under all long-term, temporary and transient stress. Step 1 fixes the continuous operating voltage and rated voltage: Uc,min ≥ Us/√3 for solidly earthed neutral systems; Uc,min ≥ Us for isolated or resonant earthed neutral systems (earth fault factor k = 1.73, since such systems commonly operate more than 30 minutes in single-phase earth fault). A factor of usually 1.25 then gives the lowest necessary rated voltage Ur = 1.25 · Uc,min.

Step 2 selects the nominal discharge current In from the expected maximum lightning amplitude Imax = (2·Ufo − Upl)/Z. Example for a 420 kV system: Ufo = 2.1 MV, Upl = 806 kV, Z = 350 Ω gives Imax = 9.7 kA — a 10 kA arrester readily withstands higher amplitudes. Step 3 selects the line discharge class, presently the only way of specifying energy-handling capability per IEC 60099-4; the standard's diagram relates specific energy in kJ/kV of rated voltage (classes 1–5) to the ratio of switching impulse residual voltage Ures to rated voltage Ur. Step 4 checks protective levels: a lightning impulse protective level Upl,10kA,8/20µs < BIL/1.4 is adequate.

Step 5 selects the housing: length, creepage distance and material determine the rated short-circuit current Is, the specified long-term load SLL and the specified short-term load SSL. Specific creepage distances up to 20 mm/kV give the shortest housings, while 25 mm/kV and 31 mm/kV play an important role and maritime, desert or heavily polluted environments require even more. If no information on actual mechanical service stress is available, the catalog gives the guideline static head loads below.

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

The typical minimum rated voltage of the arrester depends on the highest voltage and the earthing of the system. Fidelity note: for Us of 245 kV and above the printed table leaves the isolated-neutral, impedance-earthed and resonant-earthed columns empty (such systems are solidly earthed at these levels); those cells are reproduced empty below. The right-hand column gives the rated voltage for neutral-protection arresters.

Applications as line surge arresters and equipment monitoring

Surge arresters on hazardous stretches of a power line improve network protection and increase transmission system reliability. Siemens Energy provides two line surge arrester solutions. Non-gapped line arresters (NGLA) offer high mounting flexibility — installed directly on the insulators or on the tower — and, thanks to their high energy absorption capacity, a very high level of protection against lightning and network-generated switching impulse currents; the 3EL1, 3EL2, 3EL3 and 3EL5 arresters are available as NGLA types. Externally gapped line arresters (EGLA) of the 3EV1, 3EV2 and 3EV5 series place an external spark gap in series that galvanically isolates the active part from line voltage under normal conditions; on lightning the gap ignites, the overvoltage is discharged through the arc, and the active component limits the follow current so the arc extinguishes within the first half-cycle. The series varistor units (SVU) of the 3EV1/3EV2/3EV5 EGLA lines are based on the respective 3EL1, 3EL2 and 3EL5 product lines.

Operated within specification, surge arresters can reach a service life of up to 30 years without any maintenance, but overloads can occur that cause arrester failure and even endanger network safety. Equipment monitoring records operating states and remaining service life, providing asset management data and enabling immediate assessment of network state. Siemens Energy provides a complete line of monitoring devices — from simple surge counters and condition indicators to periodic analytic condition monitoring and a future live condition monitoring system — detailed in the accessories section below.

Order code system and product range — main technical data

Every arrester is specified by a 16-position order code (example 3EL2 096-2PJ31-4XA1-Z D91): positions 1–4 product line, 5–7 rated voltage in kV, 8 long-duration current impulse / energy absorption capability, 9 application (L = line surge arrester, P = phase, S = neutral point), 10 housing size, 11 line discharge class, 12 number of units, 13 form of sheds and color of housing, 14 high-voltage terminal, 15 nameplate language, 16 mounting, plus Z-codes for optional accessories and monitoring devices.

The selection table on page 26 summarizes the main technical data of the eleven product lines, transposed below. Its central matrix additionally marks which of ten nominal-discharge-current / line-discharge-class / energy / long-duration-current-impulse combinations each line offers, ranging from In 10 kA, class 2, 4.4 kJ/kVr, 550 A (3EL5 only) up to In 20 kA, class 5, 16.0 kJ/kVr, 3,200 A (3EP3, 3EQ4, 3EQ3). Footnotes: 1) increased rated short-circuit current of 80 kA available on request (3EQ4); 2) increased bending moment (second value).

3EL5 electrical characteristics — phase arresters (complete, IEC 60099-4)

The 3EL5 is the compact Cage Design line for systems up to 72.5 kV: nominal discharge current 10 kA, line discharge class 2, energy absorption capability 4.4 kJ/kVr, long duration current impulse (2 ms) 550 A, rated short-circuit current 20 kA, high current impulse 100 kA, dynamic bending moment 0.5 kNm. It protects transformers, circuit breakers, generators, motors, capacitors, traction vehicles, bushings, switchgear and transmission lines. The complete phase-arrester ratings table is transcribed below (residual voltages in kV at the stated impulses); the highest system voltage groups of the original are flattened by repeating Us per row. Mechanically, housings B through 2xH span 170–840 mm height, 372–2,460 mm creepage, lightning impulse withstand 104–484 kV and arrester weights 3.6–10.2 kg.

3EL1, 3EL2 and 3EL3 — ratings overview and 3EL2 mechanical characteristics

3EL1 (systems up to 252 kV, Ur up to 198 kV) comes in two energy variants: line discharge class 2 (I2ms 750 A, Eth 5.0 kJ/kVr) and class 3 (800 A, 6.0 kJ/kVr, up to 170 kV / Ur 156 kV), both with In 10 kA, Is 65 kA and 1.2 kNm dynamic bending moment. Its phase-arrester table spans Ur 3–198 kV with residual voltages from 5.9 kV (30/60 µs 0.5 kA at Ur 3 kV) up to 646 kV (8/20 µs 40 kA at Ur 198 kV); neutral ground arrester versions (S) are separately tabulated.

3EL2 (up to 420 kV, Ur up to 360 kV) offers four variants: class 2 (1100 A, 5.0 kJ/kVr, In 10 kA), class 3 (1100 A, 8.0 kJ/kVr, In 10 kA), class 3 (1200 A, 8.0 kJ/kVr, In 20 kA) and class 4 (1200 A, 10.0 kJ/kVr, In 20 kA), all with Is 65 kA and 4.0 kNm. Its phase table runs Ur 9–360 kV — at Ur 360, class 3: residual voltages 677 kV (30/60 µs 0.5 kA) to 1,066 kV (8/20 µs 40 kA) on minimum housing 3xJ. 3EL3 (up to 550 kV, Ur up to 468 kV) offers class 4 (1600 A, 10.0 kJ/kVr) and class 5 (2000 A, 14.0 kJ/kVr), In 20 kA, Is 65 kA, 10.0 kNm; at Ur 468 residual voltages reach 874–1,253 kV on minimum housing 4xK.

The 3EL2 mechanical characteristics table is transcribed below as representative of the family (grading ring diameter '-' means none fitted). The maximum arrester weight can vary depending on rated voltage and line discharge class.

3EP porcelain product lines — datasheet maximum values

The four porcelain lines cover 123 kV (3EP5) through 800 kV (3EP6, 3EP3) systems, each protecting transformers, circuit breakers, generators, motors, capacitors, bushings and switchgear. The table below combines the 'Maximum values' header table of each product-line datasheet (one row per catalog variant, values verbatim). Dual bending-moment figures give standard/increased bending moment.

3EQ composite hollow core product lines — datasheet maximum values

The three composite hollow core lines cover 300–362 kV (3EQ1) up to 800 kV (3EQ4, 3EQ3) systems. 3EQ4 housings are additionally orderable with increased SSL variants, and its rated short-circuit current of 65 kA can be increased to 80 kA on request (accessory code K80); the 3EQ3 carries 80 kA as standard — the highest of the portfolio — together with the highest dynamic bending moment (42/72 kNm). Values below are verbatim from each datasheet's 'Maximum values' table, one row per variant.

Accessories and monitoring devices

Arresters can optionally be equipped with accessories added as Z-codes to the order number (example: 3EL2 096-2PJ31-4XA1-Z D91): earth terminals in copper tin-plated, DIN/NEMA, NEMA stainless steel or copper, palm aluminum and 2xD14 stainless variants (D51, D71, D93–D96), adapters DIN/NEMA to double DIN or double NEMA flat terminal including two line clamps (D81, D82), line clamp D91, eyebolt earth terminal D92, N2 filling K02, yellow cover panels for gas diverter K14, and increased rated short-circuit current of 80 kA (K80).

Building on over 85 years of arrester experience, the monitoring line ranges from simple surge counters and condition indicators to periodic analytic condition monitoring (ACM) and a future live condition monitoring system, matched to voltage level, network situation and customer requirements. The sensor/display system requires a connecting lead, orderable in lengths from 3 m to 30 m (order number 3EX5 063- plus a length code). Main order numbers are transcribed below.

Figures & drawings

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