Surge Protection Devices(SPD) for Solar PV plant

Why SPD is required in Solar PV plant

• The  outdoor installation  location  of solar PV makes them directly exposed to harsh conditions like rain, wind and dust. Among the weather conditions lightning strikes require specific attention as they can severely affect the safety and performance of a PV plant 
  
• Then lightning strike hits the ground, it discharges energy, affecting the electrical field on the ground. For the solar PV plant this poses two risks:

1. A direct impact which can physically destroy the solar equipment on a rooftop
2. Transitory over voltages passing through cables by magnetic coupling, which can lead to the damage of sensitive components such as printed circuit boards (PCB).

• The potential impact of lightning events increases with PV system size. At locations with frequent lightning, unprotected PV systems will suffer repeated and significant damages. This results in substantial repair and replacement costs, system downtime and loss of revenue.
  
• The lightning arrester provides the  protection against direct impact of lightning as per IEC62305.
• For transitory over voltages(due to lightning surges that are produced or propagated by the building’s electrical system )SPD in parallel with the circuit to be protected is required to deliver the energy to the ground and limit the overvoltages.
  

• Surge Protective Devices (SPDs) provide protection against electrical surges and spikes, including those caused directly and indirectly by lightning.
• Properly installed surge protective devices (SPDs) will minimize the potential impact of lightning events.
• Sensitive electrical equipment's of PV system like AC/DC Inverter, monitoring devices and PV array must be protected by surge protective devices (SPD).

Location of SPD in solar PV plant

1. DC Protection at the Input to the Inverter

•     The inverter is one of the most expensive and fragile components of a PV system, and it must be protected from electrical surges originating at the solar panels or from within the feeder cables.

•  If the combiner box and inverter are more then 30 feet apart than an SPD is recommended at both ends of the run.
• In case of string inverter,The DC SPD is provided inside the inverter.In that case there is no need to install DC SPD at inverter Incoming side.

         2. DC Protection at the Combiner Box

• The combiner box is the ideal location for the first tier of protection. A correctly sized SPD can divert surges before they impact the switching function of the combiner box and prevent the surge from propagating down stream.

     3. AC Protection at the Output of the Inverter

• To protect the inverter from surges originating in the facility, an SPD is highly recommended on the output or AC side of the inverter.

     4. A high percentage of surges originate from utility power

• To protect the entire facility and the PV system, a service entrance SPD is essential as Per UL1449 3rd Edition, this SPD should be a UL Type 1 listed device installed on the line side of the main disconnect.
  

Selection of SPD ratings

• The Size, performance and specification of SPD depend on following characteristics

Current characteristic of SPD

• I:Surge Current Rating (KA),
• In: Nominal Discharge Current (In),
• Imax: Maximum discharge Current (Imax)

Voltage characteristic of SPD

• Uc: Maximum Continuous Operating Voltage (MCOV),
• Up: Voltage Protection Rating (VPR) or surge voltage rating (SVR) or Clamping Voltage
  

Types of SPD

Type 1 SPD

• Protection against transient overvoltages due to direct lightning strokes.
  
• If there is LA installed in the vicinity of Solar PV plant,installation of Type-I SPD is must.
  
•  It can discharge the voltage from lightning spreading from the earth conductor to the network conductors.
  

Type 1 SPD is characterized by a 10/350µs current wave.

Type 2 SPD

• Protection against transient overvoltages due to switching and indirect lightning strokes.
  
• The Type 2 SPD is the main protection system for all low voltage electrical installations.
  
• To protect the inverter from surges originating in the facility, Type-II SPD is highly recommended on the output or AC side of the inverter.

Type 2 SPD is characterized by an 8/20µs current wave.

Type 3 SPD

• Type3 SPD is used for local protection for sensitive loads and these SPDs have a low discharge capacity.
  
• The sensitive SCADA and monitoring system circuits  in Solar PV plant should be protected by Type-III SPD. 

Type 2 SPD is characterized by an 1.2/50µs current wave.