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Technical terms related to SPD

 

Protective devices, lightning arresters, surge protectors, etc.

 
Term Explanation
SPD

Surge protective device.

Device which suppresses excess voltage and current on electrical circuits.

Also known as protective device, lightning arrester, surge protector, etc.
Nominal line voltage (V) Nominal voltage on lines, fixed by JEC, etc. For example, AC 100V, etc.
Maximum line voltage (V) Maximum voltage that can be applied to protective device terminals without triggering the protective device.
Protection level (V) Refers to irregular voltage protection performance. When a protective device is triggered by irregular voltage, this is the maximum voltage remaining across terminals T1 – T2, and the higher voltage between the specified spark-over voltage in response to irregular voltage, and the clamping voltage in response to the specified current.
There is an “AC protection level” and an “Impulse protection level”. Also, levels are displayed separately for line and ground.
Clamping voltage (V) Residual voltage across equipment terminals or across equipment terminals and ground terminals, when overvoltage is limited by the action of an SP diode or similar, while a protective device is operating. This is determined after specifying the overcurrent.
Impulse discharge current (A) The ability of a protective device 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.
AC discharge current (A) The ability of a protective device to maintain its specified performance when 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.
Current capacity (ampacity) (A) This term is used when speaking about lightning-proof transformers, etc., and refers to the current that may flow, either continuously or for a short duration, within the specified temperature rise tolerance.
Withstand voltage (V) Refers to the upper limit of voltage that can be applied to a components for a specified time without destroying its insulation.  There is an AC withstand voltage and an impulse withstand voltage.
Series resistance (Ω) The resistance between the line terminals of the protective device and the equipment terminals (L1 – T1, L2 – T2).
Working attenuation (dB) Refers to the attenuation of electrical signals resulting from the addition of a protective device. Specified in IEC C5301, item 2.1, and its measurement is specified in IEC C6435 – 5.12.
Crosstalk attenuation (dB) This is the value of the effect that a signal carrying line has on other lines.
Return loss (dB) Refers to the level of rebound wave (echo) generated at the characteristic impedance mismatch point at telecommunication cable contacts, etc. Allows the level of characteristic impedance mismatch within cables and at cable connections to be viewed. 
Impedance (Ω) Refers to the impedance of transmission characteristics measurement. Telecommunications transformers read “Line side xxΩ, Device side xxΩ”.
Impedance ratio (Ω) Used in telecommunications transformers. Expressed as “Line side xxΩ, Device side xxΩ”.
Leakage current (A) Current that flows when maximum line voltage is applied to a protective device.
Life Number of times a protective device or lightning protection element should be able to be energized and still perform satisfactorily, after having been energized with the specified impulse current, and AC current for the specified number of times and at a specified time interval.
DC spark over voltage (V) See Lightning protection elements.
Impulse spark over voltage (V) See Lightning protection elements.
Earth-free system A system wherein earthing is not considered necessary because the lightning current flows from the telecommunication lines to the power supply lines, or in reverse.
Frequency bandwidth (Hz) The frequency bandwidth that a protective device can use.
V.S.W.R

When travelling waves are reflected at a contact with different impedances, the travelling waves are affected by the returning waves and a composite wave is generated on the line. This is called a standing wave. The ratio of the standing wave maximum voltage (Vmax) to minimum voltage (Vmin) is called the Voltage Standing Wave Ratio (VSWR). In the case of no reflection, VSWR is 1, and the smaller this value becomes, the less reflection there is.

Insertion loss (dB) Degree of electrical signal loss when a product is inserted.
Contact resistance (Ω) Resistance generated at the connectors and other contacts of a protected device.
Line voltage (V) This is voltage that is generated across T1 – T2 due to operating differences among protective elements when protective devices begin to operate due to irregular voltage against the ground.
Permissible power (W) Maximum permissible power that can be passed through co-axial lightning arresters.
Thermister Self-recovery type circuit opening device used for the same purpose as a heat coil.
Thermister non-operating characteristics (A) Maximum current before there is any current conversion, even when the specified voltage is applied under the specified heat conditions continuously.
Thermister operating characteristics (A) Minimum current before there is any current conversion, even when the specified voltage is applied under the specified heat conditions continuously.
Insulation coordination Refers to selecting the appropriate protective device for the withstand voltage of the equipment to be protected.  Installing a high performance protective device on a piece of equipment that has high withstand voltage is a needless waste of money. Conversely, installing a protective device with a protection level that is poorer than the withstand voltage of the equipment.
Isolation Refers to leakage. This is the amount of signal leakage to other ports (terminals). The larger the value, the smaller the leakage.
IM noise (dB) Level of noise caused by internal modulation and inter-modulation.
Deviation between outputs Differences in the frequency characteristics (insertion loss, phases) among different output terminals.
 
 
 
 
 

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