Technical characteristics of SPD

• The important technical characteristics of SPD

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Maximum continuous operating voltage UC

The maximum continuous operating voltage (old: rated voltage) is the maximum root mean square value (rms) of the allowable voltage applied to both ends of the surge protector under working conditions. This value is the maximum voltage when the surge protector is in the defined non-conducting state. After the surge protector responds and discharges the lightning current, it should be able to restore this state.

UC value should be selected according to the nominal voltage of the protected system and the requirements of the corresponding installation specifications (IEC 60364-5-53/A2 (IEC 64/1168/CDV:2001)). For TN and TT systems, 10% voltage fluctuations should be considered, that is, the maximum continuous voltage UC of the 230/400V system cannot be lower than 253V.

Lightning impulse current limp

　　The waveform is an impulse test current of 10/350μs. Its various parameters (peak value, electric quantity, specific energy) all simulate the load current generated by lightning strikes in nature.

　　 Lightning impulse current (10/350μs) is used for the level 1 SPD test. Such SPD must be able to discharge lightning impulse current many times without damage.

Nominal discharge current In

　　 The nominal discharge current In is the peak value of the current flowing through the SPD with a waveform of 8/20μs. It is used for the SPD classification of level 2 test and the pretreatment test of SPD of level 1 and 2 tests.

Voltage protection level UP

The maximum voltage peak is measured at the SPD terminal, which characterizes the SPD's ability to suppress surges.

According to the type of SPD, the voltage protection level can be determined by the following tests:

　　→ Lightning impulse flashover voltage at 1.2/50μs (100%)

　　→ The residual voltage of the nominal discharge current (according to EN 61643-11: Ures)

According to the overvoltage category described in IEC 60664-1 (EN 60664-1), select a surge protector suitable for the on-site environment; Note: The minimum required in a 230/400V three phase spd system is 2.5KV and only applies to fixed electrical equipment; The voltage protection level of the surge protector used for terminal power protection is much less than 2.5KV.

IEC 60364-5-53/A2 (IEC 64/1168/CDV:2001) also stipulates that the minimum voltage protection level of SPD is used to protect 230/400V low-voltage electrical equipment must be less than 2.5KV; the minimum voltage protection level can pass level 1. It can be realized by coordinating with the energy of level 2 SPD or directly using a composite lightning current/surge protector.

Short circuit withstand capability(Isccr)

　　 When the backup protection fuse is installed upstream of the surge protector, the value of the expected power frequency short-circuit current that the surge protector can control.

Freewheeling interruption capability at UC (Ifi)

Freewheeling interruption capability is also called arc extinguishing capability. When UC is applied, the surge protector can automatically interrupt the root mean square value (rms) of the expected continuous current.

According to IEC 62305-3 (EN 62305-3) and IEC 60364-5-53/A2 (IEC 64/1168/CDV:2001), the SPD's freewheeling suppression capability should correspond to the maximum expected short-circuit current value at the SPD installation site; For the power distribution system with very large short-circuit current, in order to protect the equipment, the corresponding backup fuse must be selected to cut off the power frequency continuous current flowing through the protection equipment.

According to IEC 60364-5-53/A2 (IEC 64/1168/CDV:2001) and EN 61643-11, when the SPD connected between the neutral line and the PE line operates, power frequency freewheeling may occur (such as : Spark gap), its freewheeling interruption capability must meet Ifi≥100Arms.

Freewheeling suppression capability (based on "level 1" spark gap)

Freewheeling suppression is an important performance index of SPD based on spark gap. It can greatly limit the power frequency freewheeling, so that the actual current flowing through the equipment is significantly reduced than the short-circuit current that may occur at the installation site.

High freewheeling suppression capability can prevent upstream protective components (such as fuses) from tripping due to excessive power frequency freewheeling current.

The ability to suppress power frequency freewheeling is one of the very important parameters in the reliability of electrical equipment, especially the spark gap type surge protector with low voltage protection level.

Energy coordination

In order to ensure the selectivity of various types of SPD, the energy coordination between all levels of SPD is very important. The characteristics of the basic principle of energy coordination are as follows: each protection level can only discharge a certain amount of interference energy, and the energy cannot exceed the specified value during SPD design. If there is a higher interference energy, the higher-level SPD (such as the "level 1" SPD) must be able to quickly discharge the lightning current to reduce the burden of the subsequent SPD, thereby avoiding its overload damage. This coordination must take into account all possible interferences, such as surges generated by switches, partial lightning currents, etc. According to IEC 62305-4 (EN 62305-4) manufacturers must verify the energy coordination performance of their SPD.

Red/Line series products are energy-coordinated with each other, which has been verified by experiments.

Transient overvoltage (TOV)

　　 TOV (Temporary Over Voltage) is a term used to describe surges caused by faults in medium and low voltage power grids.

　　 For the L-N circuit in the TN and TT system, when the measurement time is 5 seconds: UTOV=1.45×U0, (U0 represents the rated AC voltage of the phase line to the ground).

　　 For the 230/400V system, the TOV to be considered for the SPD between L and N is UTOV=333.5V.

　　 For the TOV generated in the high-voltage system due to a ground fault, in the N-PE circuit of the TT system, the transient overvoltage value that needs to be considered within 200ms is: UTOV=1200V. According to IEC 60364-5-53/A2 (IEC 64/1168/CDV:2001), SPDs installed in low-voltage electrical equipment must have TOV tolerance.

　　 According to the TOV value calibrated by EN 61643-11, the Red/Line series products fully meet this requirement, and at the same time meet the requirements of IEC 60364-5-53/A2 (IEC 64/1168/CDV:2001).