Surge Protection Device Working Principle
Surge protection device, also known as lightning protector, is an electronic device that provides safety protection for various electronic equipment, instruments and meters, and communication lines. When sudden peak current or voltage is generated in an electrical circuit or communication circuit due to external interference, surge protection device can conduct shunting within a very short time to avoid damage to other equipment in the circuit.
- Class-I protection
The aim is to prevent the surge voltage from passing directly from LPZ0 to LPZ1, limiting the surge voltage within a range of tens to hundreds of thousands to 2,500-3000 V.The power lightning arrester installed on the low-voltage side of incoming power transformer as the class-I protection shall be the three-phase voltage switch type power lightning arrester, whose lightning flux shall not be lower than 60KA. The power supply lightning arrester at this level shall be a large-capacity power lightning arrester between each phase connected to entrance of the user power supply system and the earth. Generally, it is required to have the maximum impact capacity of over 100KA per phase for the power lightning arrester at this level, and the required limit voltage is less than 1500V, which is called as class-I power lightning arrester. These electromagnetic lightning arresters are specially designed to withstand high currents of lightning and induced lightning, so as to attract high energy surges which divert large amounts of surge current to the earth. They only provide limited voltage (the maximum voltage appearing on the circuit when the shock current flows through the power lightning arrester is called limited voltage) for medium class protection, because class-I protectors mainly absorb the large surge current, they cannot fully protect the sensitive electrical equipment inside the power supply system.
The class-I power lightning arrester is designed to protect against the 10/350μs, 100KA lightning stroke, meeting the maximum protection standard specified by the IEC. The technical reference is that the lightning flux is 100KA (10/350μs) or more; the residual pressure value is not greater than 2.5 KV; response time is less than or equal to 100ns.
- Class-II protection
The aim is to further limit the value of the residual surge voltage through the first stage lightning arrester to 1500-2000v.
The potential connection is performed according to LPZ1 - LPZ2.As the secondary protection, the power lightning arrester for distribution cabinet line output should be the pressure-limited power supply type lightning arrester, whose lightning current capacity should not be lower than 20KA, and should be installed at the sub-distribution place where power is supplied to important or sensitive power equipment. These power supply lightning arresters can absorb the residual surge energy of surge discharger at the entrance of user power supply, and have an excellent inhibitory effect on transient overvoltage. The maximum impact capacity required by power lightning protection device used at this place is more than 45kA per phase, and the required limit voltage should be less than 1200V, which is called class- II power lightning protection device. The general user power supply system can meet the requirements of power equipment operation with the second level protection.
The secondary power supply lightning arrester adopts class C protector for full-mode protection of phase -- medium, phase -- ground and medium -- ground. The main technical parameters are: Residual pressure peak value is not greater than 1000V; Response time is not greater than 25ns.
- Class-III protection
The final aim is to protect the device, reducing the residual surge voltage to below 1000V which can protect the equipment from damage.
The power lightning arrester installed at the input end of electronic information equipment AC power supply shall be a series voltage limiting type power lightning arrester when it is used as the class III protection. The lightning current capacity should not be lower than 10KA.
A built-in power lightning protection device should be used in the internal power supply of the electrical equipment which functions as the final line of defense, so as to completely eliminate the tiny transient overvoltage. The power lightning arrester used at this level requires a maximum impact capacity of 20KA per phase or less, and the required limit voltage should be less than 1000V. It is necessary to provide class-III protection for some particularly important or sensitive electronic devices, as well as to protect the electrical equipment from transient overvoltage produced within the system.
For the rectifier power supply used in microwave communication equipment, mobile station communication equipment and radar equipment, it is advisable to select the DC power lightning arrester which is suitable for working voltage protection as the final protection.