17.0 lightning protection ms 1 hingga 18

Chapter 17

Lightning Protection, Surge Protection and Earthing System

1.0 Lightning Protection

Lightning protection system needs to give direct strike protection by arresting the lightning discharge current and minimizing the possible generation of induce voltage by proper grounding and bonding. Early Streamer Emission (ESE) Type shall not be used.

Before installing the lightning protection system, some assessment needs to consider such as:

Quantify the risk of a lightning strike to your business premises Identify vital equipment which could be damaged in the event of such a

strike However buildings and structures required to be protected due to security

reason or safety reason or locations on high ground or environmental requirements shall be provided with lightning systems regardless of the heights.

Assess building material used and structure design Accurately estimate the impact in terms of both cost and image that

downtime due to a lightning strike could have on your business Develop and implement a strategy to limit the impact of such a strike Schedule a future reassessment to ensure that your strategy keeps pace

with the growth of your company and maintenance is not neglected

The above consideration should be advisory to the client or actual confirmation of the client.

Lightning protection systems shall be the integrated type complying to latest version of BS 6651 “Code of Practice for Protection of Structures Against Lightning”.

Panduan Teknik Edisi Ke-4 2008 Cawangan Kejuruteraan Elektrik Pg 1 of 23

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2.0 Faraday Cage / Structural Bonding Concept

The Faraday cage concept together with the earthed reinforcements of the building structure and foundations shall form the basis of the lightning protection system for the office building. An air termination networks and the bonding of all external metallic fixtures/structures to the reinforcements and down conductors, together with the earth electrodes shall be an integral component of the lightning protection scheme.

Reason to using this system is because of:

Mechanical and electrically bonded in concrete structure and permanent in nature

Routing of the conductor using building structure Achieving good earthing Create equal potential and minimized the chance of surge generated Intended to last the life of the structure Blend with the style and the materials of a structure Aesthetic of the building Prevent theft & vandalism

The bonding between the reinforcement and the external connections shall be exothermic welding type or as per details in Appendix 1.


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1.0 Surge Protection Devices

Surge protection devices (SPDs) shall be provided for the main electrical distribution system including sub-switch boards and distribution boards, computers, electronic equipment, fire alarm panel, PABX equipment, UPS equipment, CCTV equipment, MATV equipment, card access equipment, etc. which are susceptible to lightning and switching surges. They shall be installed in various locations of low voltage and equipment installation.

The SPDs shall be one-port type compatible with the 240/415 V, 3 phase, 4 wire, 50 Hz with solidly earthed neutral supply system it is protecting. The SPDs modes of protection shall be each phase-to-neutral, each phase-to-earth and neutral-to-earth for either single phase or three phase supply system. However, for cases where the incoming feeder circuit breaker in the main switchboard is rated 600A or less, SPDs with modes of protection at each phase-to-neutral and neutral-to-earth may be allowed to be installed in the whole electrical installation. SPDs for three phase supply system installation shall be of mono block or modular type. Unless otherwise specified, SPDs shall be of the type complying with MS IEC 61643-1 and MS IEC 61643-12 and in accordance with recommendations of IEC 62305 and the relevant parts and sections of MS IEC 60364.

The SPDs shall be of voltage limiting type with metal oxide varistors (MOVs) or combination type with MOVs and gas discharge tube (GDT)/spark gap. MOVs and GDT/spark gap shall comply with MS IEC 61643-331 and MS IEC 61643-311 respectively. The normal operating voltage shall be 240V and the maximum continuous operating voltage (Uc) of SPDs shall be minimum 275V (phase-to-neutral, phase-to-earth and neutral-to-earth). The continuous operating current (Ic) for each mode of protection shall not exceed 3 mA. In the case where the MOVs are used, the SPDs shall be provided with integrated thermal protection function to avoid thermal runaway due to degradation.

The impulse current (Iimp), nominal discharge current (In), maximum discharge current (Imax) and open-circuit voltage (Uoc) rating per mode of protection of SPD and the respective voltage protection level (Up) shall be as indicated in Table 1. Unless otherwise specified, the class of SPDs to be installed with respect to the location of switchboard and/or distribution board shall be as in Table 1.


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Table 1 – Classification of SPDs

Location of Switchboard / Distribution Board

Switchboard Receiving Energy from the Licensee or Other Building

Sub-Switchboard and/or Distribution Board Receiving Energy from Switchboard Located in the Same Building

Final Distribution Board Receiving Energy from Sub-Switchboard or Distribution Board Located in the Same Building

Impulse Test Classification (MS IEC 61643-1)

Class I Class II Class II Class III

Impulse Current, Iimp (10/350 μs) per mode

≥ 10 kA

Nominal Discharge Current, In (8/20 μs) per mode

≥ 20 kA ≥ 10 kA

Maximum Discharge Current, Imax (8/20 μs) per mode

≥ 65 kA ≥ 40 kA

Open-Circuit Voltage, Uoc

(1.2/50 μs) per mode

≥ 6 kV

Voltage Protection Level, Up (L-N, L-E, N-E) at Iimp or In or Uoc

≤ 2500 V ≤ 2000 V ≤ 1500 V ≤ 1000 V

The size of connecting leads shall be as recommended by the SPD manufacturer. The connecting leads shall be as short as possible and shall be tightly bound together throughout the whole length with cable-ties or other approved means. Either a four-pole moulded case circuit breaker (MCCB) or a fuse of rating as recommended by the SPD manufacturer shall be provided for disconnecting the SPDs from the system in the event of SPDs failure or for maintenance. In the case where an MCCB is used, the breaking capacity of the MCCB shall comply with the a.c. interrupting capacity of the switchboard or distribution board.


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The SPDs shall be equipped with visual indicator showing the protection status of the SPDs. Unless otherwise specified, SPDs shall be provided with auxiliary contact for connection to remote monitoring of SPDs protection status. A durable label with red lettering on a white background with words as stated below shall be fastened externally on the front cover of the SPDs compartment.

Equipment susceptible to voltage variations shall be provided with suitable surge protection and automatic voltage regulating systems.

2.0 SPD kA Rating

The following will discuss on the rating of SPD.

Refer to Diagram 1

a) SPD kA rating should be based on the weakest link in the design

e.g. if the SPD is using 40kA varistor for L-N while N-E is using 80kA varistor the SPD should be rated at 40kA not 80kA

b) SPD should not use multiple varistor for rating

e.g. if the SPD rating is 80kA it has to be a single varistor at 80kA and not 4 nos of 20kA varistors in parallel (Please refer diagram 2)

- theoretically it is correct in normal operation however it will not apply in transient condition or surges since the waveform is exponential non linear in nature and not sinusoidal steady state. This micro second phenomenon may result in varistor does not operate at the exact response time and one may operates earlier to bare the maximum burden of the surge current. - the impedance of the MOV of the same rating may not be exactly the same. The difference in the impedance during the occurrence of surge may result in unequal distribution of surge current


AMARAN

1. Pemasangan ini dilindungi oleh Surge Protective Device, SPD 2. SPD tidak lagi berfungsi apabila “petunjuk” bertukar warna.3. Sila buat pemeriksaan pada SPD secara bulanan dan setiap

kali selepas berlaku kejadian kilat/petir.4. Sila hubungi ‘orang kompeten’ untuk penggantian SPD.5. Pastikan juga ‘circuit breaker’ ke SPD sentiasa berada dalam

keadaan ON (I).

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c) There are some SPD that has 3 performance indicators - the degradation indication SPD (yellow) usually design using multiple parallel MOV. This is not proper as explain in item (b).


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Diagram 1: Basic Circuit of SPD


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Diagram 2: Single Varistor Vs Multiple Varistor


During transient, I1≠I2≠I3≠I4

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d) For Cat C – Why high kA rating per phase (L-N) is required?

Using 80kA per phase (L-N) as an example. Malaysia’s highest lightning discharge current recorded is around *40kA. The induced surge current into electrical system is assume highest at 50% of the lightning discharge current i.e. 20kA surge.

With 80kA per phase (L-N) surge protector it can withstand the frequency of lightning surges in Malaysia’s condition which is about *200-300 days per year.

Whereas for Cat B chances only 20% surge current induced and Cat A is only about 10% because of the reduce size of cable in the electrical system.

3.0 Let Through Voltage

Declared SPD let through voltage shall be accompanied with the test value/type of waveform in kV/kA. The waveform used are the Combination Wave 1.2/50µs, Open Circuit Voltage and 8/20µs, Short Circuit Current as per Fig 1 & Fig 2 if test to MS IEC 61643 – 1:2004 Class III as per table 1.

Fig 1 : Combination Wave, Open Circuit Voltage


0 20 40 60 80 TIME, µs 100

1.0

V(t)/Vp

0.8

0.6

0.4

0.2

0.0

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* Source: Malaysian Meteorological Department

Fig 3 : Combination Wave, Short-Circuit Current

Fig 2: Combination Wave, Short Circuit Current

Table 1: Test Value as Per Compliance Standard of MS IEC 61643 – 1:2004

Cat A Cat B Cat C

1.2/50µs 2kV 6kV 20kV

8/20µs 1kA 3kA 10kA

Let Through Voltage

<350V <1kV <3kV

For Cat C the let through voltage does not necessary be too low since generally all the equipment in Category C could withstand up to 3kV of surge current. Moreover there are few stages of surge protective device that should be installed at Category B and at Category A before the current supply reach to the electronic equipment in order to be safe.


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Cat C the let through voltage shall not necessary be too low. The Cat C †voltage limiting device is expensive for very low let through voltage comparing to the total cost of SPD installed in stages before the electronic equipment.

†voltage limiting device i.e. varistor and suppressor diode

4.0 Location Category

Diagram and tables below illustrates the application of three location categories to the wiring of a power system.

Cat A Cat B Cat C

0.5µs/100kHz 6kV 6kV None

0.5µs/100kHz 200A 500A None

1.2/50µs 2kV 6kV 20kV

8/20µs 1kA 3kA 10kA

Cat A Cat B Cat C


Area 1 Cat A Area 2 Cat B Area 3 Cat C

Long final sub-circuits and power outlets

Major sub mains < short final sub-circuits & load centers

External services, overhead lines /underground cable to detached buildings

Diagram 3: The Application of Three Location Categories To The Wiring of A Power System

Table 2: Applicable Standard Waveforms for Location Categories A, B and C

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Recommended kA rating per phase

<10kA 20kA-40kA 40kA-80kA

Recommended let-through voltage at

6Kv/3kA<700V <1kV <2kV

5.0 SPD Design Requirement

The following is the requirement on SPD design.

Module Vs 3+1 Module

7 Module SPD shall be used instead of 3 + 1 ModulePlease refer to Diagram 4

7 Modules 3 + 1 Modules

1) Protection between Live - Neutral, Live – Earth & Neutral – Earth

1) Protection only between Live – Neutral & Neutral – Earth Only

2) All MOV operates on its own rating 2) The neutral to earth protection have more burden as all current will pass through this MOV irrespective of surge entrance and may damage faster

3) Longer life cycle since more path for surge to travel to earth

3) Less path for discharge current and weakest point at Neutral to Earth makes it life cycle shorter

Monoblock Type Vs Modular Type

Monoblock type SPD shall be used instead of modular type SPD.

Monoblock Type Modular type

1) Lower Impedance since most contact are soldered & permanent

1) Higher Impedance since there are many mechanical contact


Table 4: Physical & Technical Comparison Between 7 Module Vs 3+1 Module

Table 3: Recommended Rating & Let-through Voltage for Location Categories A, B and C

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2) Low risk of sparking 2) Mechanical contact can result in sparking. When one module is being replace, the contact become loose and may cause more sparking.

3) There is only one unit and the indicator shows the exact status i.e. good or damaged

3) When one module is damaged the whole unit has to be replaces as well to avoid more sparking.


Table 5: Technical Comparison Between Monoblock Type Vs Modular Type

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Diagram 4: 3+1 Module Vs 7 Module


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6.0 SPD Installation

The following is the method on how to install the SPD:

The SPD should not be more than 25 cm from the incoming power supply. If space constraint and should the SPD located more than 25 cm from the incoming power supply an MCCB should be installed and bigger cable should be used to connect the supply to MCCB before connecting to the SPD. This is to take into account the impedance of the cable.

16mm cable should be used to connect the incoming power supply to the SPD. No strand should be cut in order to make sure that full strength of the cable is being used.

MCCB is used in normal circumstances to ensure that the SPD is being isolated from the main electrical system for easy maintenance to avoid power supply interruption.


E

N

ELCB

L1 L2 L3 PSP

Not more than 250 mm

Main Switch (incoming isolator)

From circuit breaker on main switchboard

Diagram 5: Wiring For Single Phase and Three Phase Installation

16mm cable

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Typical Design for Surge Protection System

Surge protection System for Power System

Diagram 6: Typical Surge Protection for Power System


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Surge Protection System for Fire Alarm System

Diagram 7: Typical Surge Protection for Fire Alarm System

Surge Protection System for PABX System


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Diagram 8: Typical Surge Protection for PABX System

Surge Protection System for CCTV System


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Diagram 9: Typical Surge Protection for CCTV System

Surge Protection System for ICT Networking System


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Diagram 10: Typical Surge Protection for ICT Networking System


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17.0 lightning protection ms 1 hingga 18

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