LIGHTNING PROTECTION 3: SURGE ARRESTER

In the last article we talked about the advantages of grounding your panels and equipment in protecting from lightning; electrical surges and shocks from electrical faults. However grounding DOES NOT protect your solar equipment from the major cause of failure in the event of a lightning strike: induced high voltages. A current carrying conductor generates a magnetic field around it; and a change in this field generates a voltage (basics of electricity generation). This same principle can be applied to a lightning strike; as it can be likened to a cable carrying very high current with a magnetic field around it which can induce voltage to metals; equipment or any current carrying object in its vicinity. Table below illustrates how even at a distance of 100m away from a lightning strike; a voltage of 2000V can be induced into your equipment; more than enough to damage your solar equipment; esp the inverter.

Source: Surgetek- “Surge Arresters: Are they the solution?” [1]

These “surge” voltages occur in a very short period of time; a fraction of a second.. but the damage caused can be huge. This is the cause of damage to most “inverter boards” or “processor” as they are commonly called. But how do you protect against this induced voltage?? Surge Arrester is the answer!! Surge arresters are also called Surge Protector Devices (SPD) or Transient Voltage Surge Suppressor (TVSS).

How it works?? When lightning strikes in the vicinity of a conductor, surge incidents and transients occur on a conductor …these are bypassed to the ground by the arrester instead of passing through the equipment/appliances, the arrester itself is connected to grounding. Excess energy is also dissipated inside the SPD box as heat energy; when the surge occurs. The varistors (fancy word for variable resistor) in the arrestor only conduct at extremely high surge voltages thus isolating conductor from equipment. Surge arrestors do NOT protect against a DIRECT lightning strike/electrification to conductor but only from induced transients that result from a lightning strike (from indirect lightning strike).

Surge Arresters have classes according to the way they work. At minimum; you should have Class 2 (sometimes referred to as Class A) Surge Arresters in the Main Electrical Board. These can withstand a nominal surge current of 5kA and a peak surge current of 10kA [2].. Some European Standards require higher peak current of 25kA [3]. Class 2 arrestors divert lower surge current in the electrical board BUT exclude inverters as they are connected direct to rooftop panels.

For protection of appliances/equipment further down the Class 2 Surge Arrester; inside the building; one needs to install Class 1 (sometimes referred to as Class B) Surge Arresters. These are used to divert strong lightning charge and induced voltages in the event of a lighting strike. These have a typical surge handling capacity of 12.5kA (10/350) per phase… the (10/350) means that intensity reaches peak in 10µs then after 350µs it diminishes to half then flattens.

To avoid the nuisance or inconvenience of coupling and coordinating Class1 and Class 2 surge arresters; manufacturers have developed what are called “combination arresters”.. these have a pre-triggering technology that combines Class 1 and Class 2 surge arresters in the same packaging [1].

Class 3 (Also called Class D) surge arresters are required for protection in dissipating any charges that may be induced between the electrical distribution board (DB) and the equipment/Appliances [1]. These type of arresters are used for protection of “sensitive equipment”. Class 3 Arresters typically have a rating of 5kA (8/20)

Surge Arrester between panels and inverter/charge controller?: an appropriately sized surge arrester is connected to the live and neutral lines from the solar panels; with the arrester connected to earth grounding

All classes of surge arrestors have different recommended spacing from the mains breaker; and ways of installing the wiring.. thus to ensure that the surge protection device installed in your system works in the event of a lightning strike it’s imperative that you get qualified personnel to size; classify and install these vital protection devices in your system.. especially in the coming rainy season.

Source:

1. Surgetek- “Surge Arresters: Are they the solution?”

2. SANS 10142-1:2008

3. IEC 2020

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About Author:

Lovewell Chitiyo is a Mechanical Engineer with 15 years experience in the building services Engineering consultancy, renewable energy systems and sustainable design fields. He is currently studying Masters in Renewable Energy at Stellenbosch University in South Africa

Lovewell is an Accredited Professional with the Green Building Council of South Africa for Existing Buildings Performance and New Buildings; Interiors, holding several qualifications and certification in Renewable Energy and Sustainability.

Lovewell also has vast experience in design, supervision, installation and commissioning of several projects locally and regionally in the last 15 years.