Characteristics of Surge Protective Devices

International standard IEC 61643-11 defines the characteristics and tests for SPD connected to low-voltage distribution systems.

Preferred values means values which are often used in practice. Depending on real conditions lower and in some cases higher values may be needed.

Frequency range is from 47 Hz to 63 Hz AC.

Impulse discharge current for class I test (I_imp) is a crest value of a discharge current through the surge protection device with specified charge transfer Q and specified energy W/R in the specified time.

Preferred values of impulse discharge current I_imp for class I tests:

• I_imp — 1; 2; 5; 10; 12,5; 20 and 25 kA;
• Q — 0,5; 1; 2,5; 5; 6,25; 10 and 12,5 As;
• W/R — 0,25; 1,0; 6,25; 25; 39; 100 and 156 kJ/Ω.

NOTE. Specific energy for class I test (W/R) is energy dissipated by a unit resistance of 1 Ώ with the impulse discharge current I_imp. This is equal to the time integral of the square of the current (W/ R = ∫ i²d t ).

Nominal discharge current for class II test (I_n) is a crest value of the current through the SPD having a current waveshape of 8/20.

NOTE. 8/20 current impulse is a current impulse with a nominal virtual front time of 8 μs and a nominal time to half-value of 20 μs.

Preferred values of nominal discharge current for class II tests I_n: 0,05; 0,1; 0,25; 0,5; 1,0; 1,5; 2,0; 2,5; 3,0; 5,0; 10; 15 and 20 kA.

Open circuit voltage (U_oc) is an open circuit voltage of the combination wave generator at the point of connection of the device under test.

Preferred values of open-circuit voltage for class III tests U_oc: 0,1; 0,2; 0,5; 1; 2; 3; 4; 5; 6; 10 and 20 kV.

Voltage protection level (U_p) is the maximum voltage to be expected at the SPD terminals due to an impulse stress with defined voltage steepness and an impulse stress with a discharge current with given amplitude and waveshape.

The voltage protection level is given by the manufacturer and may not be exceeded by:

• the measured limiting voltage, determined for front-of-wave sparkover (if applicable) and the measured limiting voltage, determined from the residual voltage measurements at amplitudes corresponding to In and/or Iimp respectively for test classes II and/or I;
• the measured limiting voltage at U_oc, determined for the combination wave for test class III.

Preferred values of voltage protection level U_p: 0,08; 0,09; 0,10; 0,12; 0,15; 0,22; 0,33; 0,4; 0,5; 0,6; 0,7; 0,8; 0,9; 1,0; 1,2; 1,5; 1,8; 2,0; 2,5; 3,0; 4,0; 5,0; 6,0; 8,0 and 10 kV.

Maximum continuous operating voltage (U_c) is the maximum r.m.s. voltage, which may be continuously applied to the SPD’s mode of protection.

The U_C value covered by this standard may exceed 1 000 V.

The voltage applied continuously between the terminals of the surge protective device (SPD) must not exceed its maximum continuous operating voltage U_C.

Preferred values of r.m.s. maximum continuous operating voltage U_c: 45; 52; 63; 75; 85, 95; 110; 130; 150; 175; 220; 230; 240; 255: 260; 275; 280; 320; 335; 350; 385; 400; 420; 440; 460; 510; 530; 600; 635; 660; 690; 800; 900; 1 000; 1 500; 1 800 and 2 000 V.