Surge arresters 15 kV low and medium voltage

1 Purpose

The purpose of this document is to provide the necessary basis for the technical approval of surge arresters for Bane NOR’s (hereinafter referred to as BN in this document) high-voltage installations, as well as the approval of suppliers. It shall describe objective requirements for surge arresters so that the supplier can design, manufacture, test, and deliver in accordance with BN’s requirements. Scope of delivery is defined in this documents Appendix.
The specification shall apply to tender documentation, production, and delivery of surge arresters for high-voltage installations to BN.

2 Scope

Section 3 of this specification is informative and introduces the use of surge arresters for high-voltage installations at BN. Section 4 provides technical requirements for surge arresters, while Sections 5 and 6 refer to references and appendices.
Section 7 is a checklist providing an overview of all specified requirements. The supplier shall indicate whether each requirement is met and include references to supporting documentation. If the supplier responds “no” to any of the items, this shall be justified in the comments field. The comments field may also be used for any additional remarks the supplier may have.

3 Function

3.1 Terms and abbrevations

Nominal voltage (U_n)
value of the voltage by which the electrical installation or part of the electrical installation is designated and identified

[SOURCE: IEV 826-11-01]

Rated insulation voltage (U_Nm)
rated value of the rms withstand voltage assigned by the manufacturer to the equipment or to a part of it, characterizing the specified permanent (over 5 min) withstand capability of its insulation

Note 1 to entry: U_Nm is a voltage between a live part of  equipment and earth or another live part. For rolling stock, earth referes to the vehicle body.

Note 2 to entry: U_Nm For circuits, systems and sub-systems in railway applications this definition is prefered to "highest voltage for equipment" which is widely used in international standards.

Note 3 to entry: U_Nm is higher than or equal to the working voltage. As a consequence, for circuits directly connected to the contact line, U_Nm is equal to or higher than U_max1 as specified in EN 50163.

Note 4 to entry: U_Nm  is not necessarily equal to the rated voltage which is primarily related to functional performance.

[SOURCE: IEV-312-06-02, modified - "(long-term)" has been replaced with "permanent (over 5 min)" and note 1 has been replaced with four new  notes as defined in EN 50124-1:2001]

Impulse withstand voltage (U_Ni)
highest peak value of impulse voltage of prescribed form and polarity which does not cause breakdown of insulation under specified conditions

[SOURCE: IEV 442-09-18]

Creepage distance
shortest distance or the sum of the shortest distances along the surface on an insulator between two conductive parts which normally have the operating voltage between them

Note 1 to entry: The surface of cement or of any other non-insulating jointing material is not considered as forming part of the creepage distance.

Note 2 to entry: If a high resistance coating is applied to parts of the insulating part of an insulator, such parts are considered to be effective insulating surfaces and the distance over them is included in the creepage distance.

[SOURCE: IEV 471-01-04 ]

Discharge current (I_n)
pulse current which flows through the surge arrester

[SOURCE: IEV 614-03-52]

Residual current (I_Δn)
algebraic sum of the values of the electric currents in all live conductors, at the same time at a given point of an electric circuit in an electrical installation

[SOURCE: IEV 826-11-19]

Residual voltage (U_res)
peak value of voltage that appears between the terminals of a surge arrester during the passage of the discharge current

[SOURCE: IEV 614-03-53]

Steep current impulse
current impulse with a virtual front time of 1 μs with limits in the adjustment of equipment such that the measured values are from 0.9 μs to 1.1 μs and the virtual time to half-value on the tail is not longer than 20 μs.

Note to entry: The limit to half-value on the tail is not critical and may have any tolerance during residual voltage type tests (see 8.3)

[SOURCE: EN 60099-4:2014, Clause 3.66]

Lightning current impulse
8/20 current impulse with limits on the adjustment of equipment such that the measured values are from 7 μs to 9 μs for the virtual front time and from 18μs to 22 μs for the time to half-value on the tail

Note to entry: The time to half-value on the tail is not critical and may have any tolerance during residual voltage type tests (see 8.3)

[SOURCE: EN 60099-4:2014, Clause 3.31]

Switching current impulse of an arrester
peak value of discharge current having a virtual front time greater than 30 μs but less than 100 μs and a virtual time to half-value on the tail of roughly twice the virtual front time

[SOURCE: EN 60099-4:2014, Clause 3.68]

Temporary transient overvoltage (TOV)
temporary overvoltage with a duration of a few milliseconds or less, oscillatory or non-oscillatory, usually highly damped

Note 1 to entry: Transient overvoltages may be immediately followed by temporary overvoltages. In such cases the two overvoltages are considered as separate events.

Note 2 to entry: IEC 60071-1 defines three types of transient overvoltages, namely slow-front overvoltages, fast-front overvoltages and very fast-front overvoltages according to their time to peak, tail or total duration, and possible superimposed oscillations.

[SOURCE: IEV 614-03-14, modified -  "temporary" has been added to the beginning of the term to be more suitable for this specification]

3.2 Application

Surge arresters are used to protect components in high-voltage installations and adjacent facilities against overvoltage’s caused by lightning strikes, switching operations, or induction.
Surge arresters are installed in a single-phase power system, where one of the conductors is connected to the rail. In the overhead contact line system, surge arresters are installed in connection with auto transformers, booster transformers, auxiliary transformers, and cables. 

3.3 Implementation

The neutral point of the surge arrester shall be as short and direct a connection to earth as possible. The earth electrode shall be designed as a crow’s foot shown in Figure 1, or equivalent, to achieve the best possible characteristics for the discharge of impulses (steep waves). The neutral point and the conductor routing to earth shall be insulated from the overhead contact line mast.
Surge arresters shall also be capable of being used in combination as support insulators. Therefore, both mechanical and electrical requirements are imposed on the surge arresters. Figure 2 is an excerpt from an arrangement drawing showing an overhead contact line mast with a 15 kV conductor for an autotransformer, switch, cable termination, and a surge arrester used as a support insulator.
The overhead contact line system in which the surge arresters are to be installed is a single-phase system where one phase is connected to earth. A ground fault will therefore correspond to a full short circuit and will consequently be quickly disconnected.
A schematic diagram for the use of surge arresters at a transformer in an overhead contact line mast is shown in Figure 3. The figure is provided in BN’s technical regulations Joint electricEkstern lenke, and the references indicated in the diagram refer to these regulations.
Due to special grounding rules at BN, it is standard practice not to ground cable screens at both ends. There are requirements for insulating and marking the ungrounded cable end to ensure safety. If the cable is so long that it is necessary to use surge arresters at both ends, the grounding of the surge arrester at the insulated end shall be carried out using a voltage limiting device [SOURCE: IEV 811-29-41] or equivalent (“open grounding”). Figure 4 shows a schematic diagram of this solution.

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3.4 Interface with the traction power supply's retun circuit

Surge arresters installed in overhead contact line masts are simultaneously accessible to touch together with the traction power supply’s return circuit, as the masts have equipotential bonding to the rails. Surge arresters shall have a low-impedance and short connection to earth. As this may cause interference with track circuits, a requirement has been introduced that the neutral point of the surge arrester shall be kept insulated from the traction power supply’s return circuit. This can, for example, be achieved by installing an insulating “block” between the neutral point of the arrester and the mounting bracket on the mast.
The potential of the return circuit is normally at or close to earth potential and shall not exceed a level that ensures touch safety. However, there may be a need to establish a temporary equipotential bonding connection between the surge arrester electrode and the traction power supply’s return circuit (see “temporary working earth” in Figure 2).
The principle of isolating the surge arrester from the traction power supply’s return circuit is relatively new, and there are therefore cases where the arrester and the return circuit are not insulated from each other.

4 Requirements

4.1 Quality and maintainability

4.1.1 Quality system

The supplier shall operate in accordance with a quality system that complies with ISO 9002 or equivalent. When submitting a tender in connection with technical approval, a copy of the quality manual shall be provided to BN together with the tender. If subcontractors are used for the partial production of components, it is the supplier’s responsibility to verify the subcontractor’s quality system. BN shall have the right to visit both the supplier and any subcontractors.
In connection with the submission of a tender for surge arresters, the supplier shall prepare a quality plan describing the main activities related to manufacturing, including the supplier’s proposed test procedures and expected results. The quality plan shall include references to specifications and standards.

4.1.2 Lifetime

Surge arresters shall be designed for a service life of at least 50 years. This shall be reflected in the supplier’s choice of details, surface treatment, and testing.
Information regarding parts that are subject to wear and require frequent replacement shall be provided by the supplier with the tender submission.
Any limitations in service life shall be described in the tender submission.
Surge arresters shall be designed in such a way that installation, dismantling, adjustment, and maintenance can be carried out without reducing their service life.

4.1.3 Interchangeability

Surge arresters intended for the same purpose shall be interchangeable and have identical characteristics.
Where possible, standard off-the-shelf components shall be used.

4.1.4 Protection breakdown

The probability of failure of a surge arrester under various external stresses shall be stated by the supplier in the tender.

There shall be clear indication in the event of a failure.  

4.1.5 Disconnector

Surge arresters with an extremely low probability of failure shall be supplied without a disconnector.
However, a separate offer shall also be provided for surge arresters with a disconnector.
Insulation and voltage data for the disconnector shall be specified in the tender.

4.2 Mechanical requirements

4.2.1 Mechanical properties

Surge arresters shall have mechanical properties such that they do not change their geometric shape or strength in the event of electrical failure.
The minimum breaking force for deflection of the surge arrester shall be specified.

4.2.2 Labelling and traceability

Surge arresters shall be provided with durable marking showing identification and classification in accordance with [EN 60099-4:2014], Section 4.1.
In accordance with BN’s technical regulations Joint regulationsEkstern lenke,  Contact Lines - MaintenanceEkstern lenke, and Traction Power Supply - Design and buildingEkstern lenke, surge arresters shall also be traceable to the manufacturer/supplier and shall, as a minimum, be marked with the manufacturer’s name, year of production (or date), and component type/number.

4.2.3 Safety against interruption

To minimize the risk of operational disturbances (including disturbances caused by vandalism), materials and designs should be selected with properties that minimize damage.
Connection bolts shall be adequately dimensioned to withstand the currents that may occur. The connection bolts shall have metric threads.

4.2.4 Material for the resistive elements in the surge arrester

The resistive elements in surge arresters shall be of the metal oxide (ZnO) type.

4.2.5 Insulating material

The insulation housing shall be made of polymer material.

4.2.6 Electical attachment points

The attachment points of the surge arrester shall be made of aluminum, galvanized steel/cast steel, or stainless steel.

4.3 Electrical requirements

4.3.1 System parameters for the 15 kV installation

The surge arrester shall operate under the following system parameters:

Maximum voltage according EN 50163:

4.3.2 Insulation level in outdoor 15 kV installations

For new installations, the following applies:

• Nominal insulation level (U_Nm) shall be 36 kV
• Short term retaining voltage for the casing at operating frequency (t<60 sec., 16 ⅔ Hz) shal be at least 70 kV (wet)
• The lighning impuls withstand voltage (U_Ni) of the sheat shall be at least 170 kV

However, the surge arrester shall also be suitable for use in existing installations with a lower lightning impulse withstand voltage (e.g. U_Ni = 145 kV). As a general principle, one single type of surge arrester is preferred for use in both new and existing installations; however, the option of offering two different types is acceptable if this provides improved protection in existing installations.

4.3.3 Creepage distance

For standardization purposes, the most severe pollution class shall be applied, and the minimum creepage distance shall be 747 mm. (43.3 mm/kV, ref. 17.25 kV) [IEC TS 60815-3]

4.3.4 Discharge current

The nominal discharge current (current class), I_n, shall be 10 kA.
The line discharge class (see EN 60099-4:2014, Annex L) shall be Class 1 or Class 2.

4.3.5 Residual current

For new installations, the maximum permissible residual voltage, U_res, shall be 50% of the lightning impulse withstand voltage, i.e. 85 kV.

The maximum residual voltage, U_res, shall be type-tested and specified for:

• Steep current impulse (EN 60099-4:2014, Clause 8.3.2)
• Lightning current impulse (EN 60099-4:2014, Clause 8.3.3)
• Switching current impulse (EN 60099-4:2014, Clause 8.3.4)

Any deviations from these requirements shall be clearly stated by the Supplier in the tender submission.

4.3.6 Temporary transient overvoltage (TOV)

The TOV curve shall be included in the tender submission.

4.4 Environment

4.4.1 Working conditions

The surge arrester shall be designed to operate under normal service conditions in accordance with EN 60099-4:2014, Clause 5.4, and under abnormal service conditions in accordance with EN 60099-42014, Annex A.

In addition, the surge arrester shall be designed to operate under service conditions specific to railway installations, see EN 50125-2, including:

• Altitudes above sea level up to 1,400 m (Class A1)
• Polluted environments due to dust and other contaminants, including brake dust from trains, tunnels, and coastal climatic conditions
• Abnormal mechanical stresses (vibration caused by train traffic and ice loading under Norwegian conditions)
• A power system frequency of 16 ⅔ Hz

4.4.2 Weather conditions

The surge arrester shall be robust and reliable under all weather conditions.

Surge arresters installed in overhead contact line systems shall be capable of operating at wind speeds of up to 30 m/s. In addition, the surge arrester shall continue to operate normally and shall not sustain damage after exposure to wind speeds of up to 50 m/s. See Contact Lines - Design and buildingEkstern lenke.

4.4.3 Humidity

The surge arrester shall be suitable for operation in all Norwegian outdoor and indoor environments, including tunnels, and shall comply with all requirements at relative humidity levels of up to 100%.

4.4.4 Corrotion

The materials selected shall be resistant to corrosion. Steel components shall be protected by hot-dip galvanizing.

• The zinc coating thickness of galvanized parts shall comply with NS EN ISO 1461
• The zinc added to the galvanizing bath shall have a purity of at least 98%
• Zinc drips shall be removed to eliminate any risk of personal injury

The Supplier shall assess whether additional corrosion protection is required. If supplementary corrosion protection is necessary to achieve the specified service life, this shall be stated and separately priced in the tender submission.

4.4.5 Dust

The surge arrester shall not lose its functionality or performance because of contamination or the accumulation of dust deposits generated by railway traffic.

4.4.6 Vibration

The surge arrester shall be designed to withstand vibration without sustaining damage or degradation of performance.

4.5 Installation and commissioning

4.5.1 Installation

The surge arrester shall be suitable for installation in vertical, horizontal, and inclined orientations. All metallic mounting components shall use metric dimensions.

Mounting accessories shall be designed to meet all mechanical and electrical requirements specified for the surge arrester.

4.5.2 Storage and transport

Measures shall be taken to ensure that no damage occurs to the surge arrester during handling and transportation. The surge arrester shall be supplied in suitable protective packaging.

4.5.3 Spesial tools

The surge arrester shall be capable of being installed, maintained, and operated without the use of special tools. If special tools are required, this shall be stated in the tender submission, and such tools shall be included with each delivery.

Where necessary, the Supplier shall provide procedures for the use of any special tools.

4.6 Tests

4.6.1 Type tests

Type tests in accordance with EN 60099-4:2014, Clauses 8.1, 8.2, 8.3, 8.4, 8.7, and 8.9 shall have been carried out by an accredited testing laboratory.

Relevant type test certificates are mandatory and shall be issued by the accredited testing institute. The Supplier shall provide copies of the test certificates as part of the tender submission.

4.6.2 Routine tests

Routine tests shall be carried out at the Supplier’s manufacturing facility in accordance with EN 60099-4:2014, Clauses 9.1a, 9.1b, 9.1c, 9.1d, 9.1e and 9.1f (including the residual voltage test) on all units.

A routine test report, with particular emphasis on compliance with the specified limit values, shall be provided upon delivery.

Upon request, the Supplier shall also be able to provide a routine test report that includes all measurement results.

4.6.3 Acceptance test

Upon request by BN, the Supplier shall carry out tests in accordance with EN 60099-4:2014, Chapter 9, Sections 9.2.1 and 9.2.2.

4.6.4 Other relevant tests

NOTE: If any other relevant tests, standards, specifications, guidelines, or instructions are used that are not explicitly referenced in this specification, these shall be identified and brought to the attention of the Purchaser by the Supplier.

4.7 Documentation

Documentation shall be retained and archived by the Supplier in a systematic manner to ensure traceability between components and their associated documentation.

Such documentation shall be made available to BN upon request.

4.7.1 Basis for technical assessment

The Supplier shall provide, as part of the tender submission, all documentation necessary to enable a technical evaluation of the surge arrester.

4.7.2 Document format

A 3d model of the surge arresters shall be part of the delivery. The file format shall be STEP or STEP-XML in accordance with ISO 10303. The model shall as a minimum include the outer physical dimensions and weight of the device.

Type test certificates and data sheets shall be available on request.  

4.7.3 Language

Documents intended for use in connection with BN’s work activities (installation and maintenance) shall be provided in Norwegian.

4.7.4 Documents to be retained by the supplier

The following documents shall be retained by the Supplier and made available upon request by BN:

• Sampling test reports
•  Traceability documentation

4.7.5 Documents to accompany each delivery

The following documents shall be included with each delivery:

• Routine test and final inspection report
• Maintenance manual
• Installation manual

4.7.6 Documents to be included in the tender

The following documents shall be included in the tender submission for technical verification:

• Copy of the type test certificate(s)
• Proposed procedures for routine testing and a template for the test report
•  Copy of the Supplier’s Quality Manual and Quality Plan
• Copy of the Supplier’s assessments referred to in Sections 4.1.3, 4.2.1, and 4.2.3
• Draft installation and maintenance manuals
• General arrangement, sectional, and assembly drawings
• Datasheet/catalogue including the TOV curve

5 Reference documents

6 Appendix

Check-list: Section 7 must be filled out and delivered by the Supplier as a part of documentation and shall be included in the tender submission for technical verification.

7 Check-list

The Supplier shall complete all items in the checklist below and provide references to the relevant supporting documentation.

Any deviations from the specified requirements shall be clearly identified, and the non-compliant items shall be described in the comments field.

8 Change log

 

Change log for Surge arresters 15 kV low and medium voltage