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Technical terms related to lightning protection elements

 

Arresters, SSPD, SP diodes, etc.

 
Term Explanation
Ceramic arrester

Single or multiple gaps designed to protect equipment, human beings, or both, from high excess voltage by discharging into a sealed envelope, rather than into airgaps. The ceramic envelopes are filled with gas and their performance against lightning surges is excellent.

(Also known as gas discharge tubes (GDT), lightning arrester tubes, surge arresters.)
DC spark over voltage (V) Voltage which starts the discharge when a gradually rising DC voltage (100V/s to 2kV/s) is applied across the terminals of an element.
AC spark over voltage (V) Voltage (rms) discharged when gradually rising AC voltage (15Hz to 62Hz) is applied across the terminals of an element.
Impulse spark over voltage (V) When impulse voltage is applied across the terminals of an element, this is the maximum voltage that appears across the terminals until current begins to flow.
AC discharge current (A) The ability of a protective device to maintain its specified performance when the terminals of an element are energized at short durations and a low number of repetitions with AC current , and at a specific time interval. For example, the ability to maintain performance at 5A – 1 sec., 10 times – 3 minute intervals, or 65A – 0.1 sec., 1 time, etc.
Impulse discharge current (A) The ability of an element to maintain its specified performance when energized with a comparatively large current and a low number of repetitions, and at a specific time interval.  For example, the ability to maintain performance at 8/20μs – 5kA – 10 times – 3 minute intervals, or 8/20μs – 20kA - 1 time, etc.
Impulse life The ability of an element to maintain its specified performance when energized with a comparatively small impulse current and a high number of repetitions, and at a specific time interval.  For example, the ability to maintain performance at 10/20μs – 500A – 50 times – 2 minute intervals, etc.
Insulation resistance (Ω) The resistance value when a specified DC voltage is applied across the terminals of an element.
Capacitance (F) The Capacitance when a specified frequency signal voltage is applied across the terminals of an element.
Follow current When single arresters are used on power supply circuits, if the arrester begins to work upon detecting an irregular voltage, after the irregular voltage has been cleared there is sometimes a phenomenon known as follow current, where the connected supply voltage continues to discharge.
Holdover voltage (V) AC applied voltage across the terminals which can be cut off within a semi-cycle or less by the DC voltage discharge, when impulse current is energized across the terminals of an arrester, with DC voltage applied with the specified conditions.
AC follow current (cutoff current) DC applied voltage across the terminals which can be cut off within the specified time by the DC voltage discharge, when impulse current is energized across the terminals of an arrester, with AC voltage applied with the specified conditions.
Response time Time taken until element begins to operate after test voltage, such as 1kV/s, etc., is applied.
dV/ dt characteristics When spark-over voltage is tested at 1kV/ μs, 10kV/ μs, 10V/ μs, etc., the voltage tends to get higher as the test voltage increase becomes steeper.
Failsafe function A short circuit is forced across terminals before an element can suffer heat damage due to discharge current. This function combines high reliability as a protective function with fire and accident prevention functionality.
UL standards US safety standards. Approved products carry the UL mark.
Breakdown voltage (V) Voltage that appears across terminals when a test current It (usually 1mA) is applied.
Standoff voltage (V)

Voltage that appears across terminals when specified current (very small when compared with test current It) is applied.

For example, this is the voltage when 5μA is applied, and is used as a target value when selecting appropriate elements for protective devices.
Breakover voltage (V) Voltage at which discharge starts when a comparatively fast rising test voltage (100V/ μs) is applied across terminals.
Leakage current (A) Current that flows when standoff voltage is applied to a protective device.
Holding current (A)

Current required to guarantee OFF, after a surge has been cleared.

(Maximum current of a circuit that can use an SSPD.)
Varistor voltage (V) The voltage across varistor terminals when a specified DC current is applied. For ZnO varistors, usually 1mA is used.
 
 
 
 
 

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