Table of Contents
1/. What is a Surge Protection Device (SPD)?
According to the IEC 61643-1 standard "Surge protective devices connected to low-voltage power distribution systems—Part 1", the term Surge protection device (SPD – Surge protection device or TVSS – Transient voltage surge suppressor) is often used to refer to a device for limiting overvoltage and diverting surge current, such as lightning impulse current.
2/. Lightning arresters and filter benefits.
a. Types of lightning protection devices.
There are three types of surge protection devices on the market today:
- Surge arresters without filters (also called shunts connected in parallel).
- Surge arresters with RFI/EMI filters are capacitors (also known as shunts in parallel).
- Surge arrester with low-pass filter LC consisting of an inductor and capacitor (also known as a series-connected arrester)
b. Lightning arrester characteristics and filter benefits
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Lightning arresters are connected in parallel
Surge arresters without filters, installed in parallel with the electrical network or equipment to be protected
o It reduces the voltage amplitude produced by the lightning impulse.
o Do not reduce the rate of variation dv/dt and di/dt of the lightning impulse.
o Do not reduce interference (RFI/EMI interference) on the transmission line (radio frequency/electromagnetic interference, harmonic noise, etc.)..
o The residual voltage (1) after cutting the lightning current to ground is still very high.
Surge arresters in parallel are often used to protect common electrical and electronic equipment.
Figure 1: Waveform of a shunt circuit breaker
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Lightning arrester in parallel
The parallel lightning arrester has a filter that is made of capacitors installed in parallel with the arrester, this type of equipment is installed in parallel with the electrical network or equipment to be protected.
o It reduces the voltage amplitude produced by the lightning impulse.
o The parallel lightning arrester can only filter out a portion of RFI/EMI noise (radio frequency interference and electromagnetic interference), not lightning impulses at typical lightning frequencies (see figure 4).
o Do not reduce the rate of variation dv/dt, di/dt of the lightning impulse.
o The residual voltage (1) after cutting the lightning current to ground is still very high.
Parallel-connected lightning arresters, as well as parallel-connected lightning arresters, are often used to protect common electrical and electronic equipment.
Figure 2: Waveform of a parallel-connected surge arrester
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Lightning protection devices connected in series
Lightning protection device connected in series with the device to be protected: this device completely overcomes the disadvantages of the above two types of equipment, thanks to the addition of an LC filter connected in series with the load to be protected.
o Significantly reduces the rate of variation of voltage dv/dt and current dv/dt of the lightning current, resulting in a low, suitable voltage amplitude at the arrester's output with an operating voltage at a low-voltage 220/380V network.
o Capable of filtering lightning, filtering power, filtering RFI/EMI noise very well, even in frequency bands that RFI/EMI filter cannot filter.
o Low residual voltage (1) after the lightning current is disconnected from the ground
Figure 3: Waveform of a series-connected surge arrester
The series-connected lightning protection device is used to protect common electrical and electronic equipment and sensitive electrical and electronic equipment. This is a highly effective lightning protection device and the optimal technical solution for important, sensitive electrical and electronic equipment.
Lightning arrester (TSG-SRF, TDF) of ERICO (http://www.erico.com) uses a low-pass filter that can filter out lightning, and noise at frequencies that RFI / EMI filters (radio frequency interference / electromagnetic interference) cannot do. (see filter cutoff histogram)
Figure 4: Cut-off frequency of filters
(1): Residual voltage – Up: Voltage protection level, Let through voltage
