6.2Surge protective devices technical terms and parameters#
Table 6.2(a) – Surge protective devices technical terms and parameters
| Abbreviation | Full title |
|---|---|
| I L | Rated load current |
| I max | Maximum surge current |
| I n | Nominal surge current |
| U c | Maximum continuous operating voltage |
| U p | Voltage protection level |
| U W | Equipment withstand voltage |
The following terms and definitions are adapted from AS/NZS 1768 and IEC 61643.
Table 6.2(b) – Terms and definitions
| Term | Definition |
|---|---|
| Earth potential rise | The increase in earth potential of an earthing electrode, body of soil or earthed structure, with respect to distant earth, caused by the discharge of current to the general body of earth through the impedance of that earthing electrode or structure. |
| Incoming service | A service entering a structure (for example, electricity supply service lines, telecommunications service lines or other services). |
| Indirect lightning flash | A lightning discharge, composed of one or more strikes that strikes the incoming services or the ground near the structure or near the incoming services. |
| Lightning strike | A term used to describe the lightning flash when the attention is centred on the effects of the flash at the lightning strike attachment point, rather than on the complete lightning discharge. |
| Maximum continuous operating voltage (U ) c | This is the maximum voltage that can be continuously applied to the SPD and should be at least 275 V ac for active to neutral connection. This clamping voltage indicates how well the device will be able to handle the normal overvoltages expected in a power system. |
| Maximum surge current (I ) max | This is the peak value of an 8 / 20 µs waveshape current impulse that the SPD can handle. This is the ‘per mode’ rating (A-N, A-E or N-E) and the device is required to handle this current only once. |
| Mode of protection of an SPD | An intended current path, between terminals that contains protective components, for example, line-to-line, line-to-earth, line-to-neutral, neutral-to-earth. |
| Nominal surge current (In) | This is the peak value of an 8 / 20 µs waveshape current impulse that the SPD can handle for a minimum of 15 impulses. It is an indication of the life of the device. |
| One-port SPD | SPD having no intended series impedance. Note: A one-port SPD may have separate input and output connections. |
| Protection measures | Protection measures taken to reduce the probability of damage. These may include a lightning protection system on the building, isolation transformers and/or surge protection on incoming services (primary protection) and internal equipment (secondary protection). |
| Rated load current (I ) L | This is the maximum continuous rated rms or dc current that can be supplied to a load connected to the SPD. |
| SPD filter dv / dt | This is the average dv / dt that occurs at the output of the surge filter when it is subjected to a standard 6 kV 1.2 / 50 µs, 3 kA 8 / 20 µs waveform. |
| Surge protective device (SPD) | Device that contains at least one non-linear component that is intended to limit surge voltages and divert surge currents. The device is typically non-conductive until a voltage or current exceeds a predetermined value; then the SPD operates to reduce the current or voltage to prevent damage to equipment. |
| Two-port SPD | SPD having a specific series impedance connected between separate input and output connections. |
| Voltage switching type SPD | SPD that has a high impedance when no surge is present, but can have a sudden change in impedance to a low value in response to a voltage surge. |
| Voltage limiting type SPD | SPD that has a high impedance when no surge is present, but will reduce it continuously with increased surge current and voltage. |
| Voltage protection level (U ) p | This is the peak voltage that the SPD lets through after diverting the bulk of the surge to earth and is generally measured at I . It is a gauge of how well n the device clamps an applied voltage surge. |