IEC 61000-4-24-2015 pdf download.Electromagnetic compatibility (EMC) – Part 4-24: Testing and measurement techniques – Test methods for protective devices for HEMP conducted disturbance.
4 Test methods for protective devices (excluding filter) for conducted disturbance
4.1 General The actual behaviour of a protective device under HEMP conditions depends very much on how it is integrated into its place of use and other attendant circumstances (e.g. quality of shielding between the protected and unprotected side of a protection element). The following test methods take this into account. They are defined so that the results obtained are as far as possible related to the qualities of the device under test (DUT), and the test arrangement does not differ too much from practical protection arrangements. NOTE Clause 4 is intended to apply for a protective device such as gas discharge tubes, varistors and two-port SPDs, excluding the HEMP combination filter. For a HEMP combination filter, Clause 5 applies.
4.2 Test setup The test setup consists of a pulse generator (G), a launching line, a test fixture for the DUT, and a termination with a connecting line and oscilloscope (see Figure 1). Various source impedances may be used, but the example shown in Figure 1 uses 50 Ω. Other values could be specified.
To prevent parasitic coupling between the pulse generator and the oscilloscope, both the unprotected and protected side of the setup shall be entirely shielded. It is recommended to use cables with multiple braided wire shields or solid shields. The cable and connectors shall be capable of withstanding the high voltage pulse without a breakdown. Grounding loops shall be avoided.
4.3 Pulse generator
The pulse generator shall produce a normally rectangular voltage pulse into a matched termination. The output voltage (into a matched termination) shall be adjustable to a value 2 times higher than the expected limiting voltage of the DUT. Both polarities shall be available. The characteristics of a pulse generator are as follows:
– characteristic impedance: 50 Ω or an alternative value
– pulse wavefront , du/dt: at least 1 kV/ns
– pulse duration: at least 20 ns
4.4 Launching line The launching line consists of a coaxial cable with a characteristic impedance of 50 Ω or the value specified. The cable between the pulse generator and the DUT shall be long enough so that reflections from the DUT do not arrive at the pulse generator during the pulse front. To achieve this condition, the one-way propagation time along the cable shall be greater than half the front time of the pulse. Due to the frequency-dependent attenuation of the cable, the steepness of the pulse front may be lowered and thus adjusted to the desired value, by further extending the launching line.IEC 61000-4-24 pdf download.