16-02-2013, 03:19 PM
Surge protector
[attachment=51213]
INTRODUCTION
A surge protector (or surge suppressor) is an appliance designed to protect electrical devices from voltage spikes. A surge protector attempts to limit the voltage supplied to an electric device by either blocking or by shorting to ground any unwanted voltages above a safe threshold. This article primarily discusses specifications and components relevant to the type of protector that diverts (shorts) a voltage spike to ground; however, there is some coverage of other methods.
The terms surge protection device (SPD), or the obsolescent term transient voltage surge suppressor (TVSS), are used to describe electrical devices typically installed in power distribution panels, process control systems, communications systems, and other heavy-duty industrial systems, for the purpose of protecting against electrical surges and spikes, including those caused by lightning. Scaled-down versions of these devices are sometimes installed in residential service entrance electrical panels, to protect equipment in a household from similar hazards.[1]
Clamping voltage
Also known as the let-through voltage. This specifies what spike voltage will cause the protective components inside a surge protector to divert unwanted energy from the protected line.[2] A lower clamping voltage indicates better protection, but can sometimes result in a shorter life expectancy for the overall protective system. The lowest three levels of protection defined in the UL rating are 330 V, 400 V and 500 V. The standard let-through voltage for 120 V AC devices is 330 volts.[3]
Underwriters Laboratories (UL),[4] a global independent safety science company, defines how a protector may be used safely. UL 1449, 3rd edition became compliance mandatory in September 2009 to increase safety compared to products conforming to 2nd edition. A Measured Limiting Voltage test, using six times higher current (and energy), defines a Voltage Protection Rating (VPR). For a specific protector, this voltage may be higher compared to a Suppressed Voltage Ratings (SVR) in previous editions that measured let-through voltage with less current. Due to non-linear characteristics of protectors, let-through voltages defined by 2nd edition and 3rd edition testing are not comparable.
A protector may be larger to obtain a same let-through voltage during 3rd edition testing. Therefore, a 3rd edition protector should provide superior safety with increased life expectancy.
Joules rating
This number defines how much energy an MOV-based surge protector can theoretically absorb in a single event, without failure. Counter-intuitively, a lower number may indicate longer life expectancy if the device can divert more energy elsewhere and thus absorb less energy. In other words, a protective device offering a lower clamping voltage while diverting the same surge current will cause more of the surge energy to be dissipated elsewhere in that current's path. Better protectors exceed peak ratings of 1000 joules and 40,000 amperes.
It is often claimed[by whom?] that a lower joule rating is undersized protection, since the total energy in harmful spikes can be significantly larger than this. However, if properly installed, for every joule absorbed by a protector, another 4 to 30 joules may be dissipated harmlessly into ground. A MOV-based protector (described below) with a higher let-through voltage can receive a higher joule rating, even though it lets more surge energy through to the device to be protected.
The joule rating is a commonly quoted but very misleading parameter for comparing MOV-based surge protectors. A surge of any arbitrary ampere and voltage combination can occur in time, but surges commonly last only for nanoseconds to microseconds, and experimentally modeled surge energy has been far under 100 joules.[7] Well-designed surge protectors should not rely on MOVs to absorb surge energy, but instead to survive the process of harmlessly redirecting it to ground.
Transient voltage suppression (TVS) diode
A TVS diode is a type of Zener diode, also called an avalanche diode or silicon avalanche diode (SAD), which can limit voltage spikes. These components provide the fastest limiting action of protective components (theoretically in picoseconds), but have a relatively low energy absorbing capability. Voltages can be clamped to less than twice the normal operation voltage. If current impulses remain within the device ratings, life expectancy is exceptionally long. If component ratings are exceeded, the diode may fail as a permanent short circuit; in such cases, protection may remain but normal circuit operation is terminated in the case of low-power signal lines. Due to their relatively limited current capacity, TVS diodes are often restricted to circuits with smaller current spikes. TVS diodes are also used where spikes occur significantly more often than once a year, since this component will not degrade when used within its ratings. A unique type of TVS diode (trade names Transzorb or Transil) contains reversed paired series avalanche diodes for bi-polar operation.
TVS diodes are often used in high-speed but low-power circuits, such as occur in data communications. These devices can be paired inseries with another diode to provide low capacitance[26] as required in communication circuits.
Quarter-wave coaxial surge arrestor
Used in RF signal transmission paths, this technology features a tuned quarter-wavelength short-circuit stub that allows it to pass a bandwidth of frequencies, but presents a short to any other signals, especially down towards DC. The passbands can be narrowband (about ±5% to ±10% bandwidth) or wideband (above ±25% to ±50% bandwidth). Quarter-wave coax surge arrestors have coaxial terminals, compatible with common coax cable connectors (especially N or 7-16 types). They provide the most rugged available protection for RF signals above 400 MHz; at these frequencies they can perform much better than the gas discharge cells typically used in the universal/broadband coax surge arrestors. Quarter-wave arrestors are useful fortelecommunications applications, such as Wi-Fi at 2.4 or 5 GHz but less useful for TV/CATV frequencies. Since a quarter-wave arrestor shorts out the line for low frequencies, it is not compatible with systems which send DC power for a LNB up the coaxial downlink.
[attachment=51213]
INTRODUCTION
A surge protector (or surge suppressor) is an appliance designed to protect electrical devices from voltage spikes. A surge protector attempts to limit the voltage supplied to an electric device by either blocking or by shorting to ground any unwanted voltages above a safe threshold. This article primarily discusses specifications and components relevant to the type of protector that diverts (shorts) a voltage spike to ground; however, there is some coverage of other methods.
The terms surge protection device (SPD), or the obsolescent term transient voltage surge suppressor (TVSS), are used to describe electrical devices typically installed in power distribution panels, process control systems, communications systems, and other heavy-duty industrial systems, for the purpose of protecting against electrical surges and spikes, including those caused by lightning. Scaled-down versions of these devices are sometimes installed in residential service entrance electrical panels, to protect equipment in a household from similar hazards.[1]
Clamping voltage
Also known as the let-through voltage. This specifies what spike voltage will cause the protective components inside a surge protector to divert unwanted energy from the protected line.[2] A lower clamping voltage indicates better protection, but can sometimes result in a shorter life expectancy for the overall protective system. The lowest three levels of protection defined in the UL rating are 330 V, 400 V and 500 V. The standard let-through voltage for 120 V AC devices is 330 volts.[3]
Underwriters Laboratories (UL),[4] a global independent safety science company, defines how a protector may be used safely. UL 1449, 3rd edition became compliance mandatory in September 2009 to increase safety compared to products conforming to 2nd edition. A Measured Limiting Voltage test, using six times higher current (and energy), defines a Voltage Protection Rating (VPR). For a specific protector, this voltage may be higher compared to a Suppressed Voltage Ratings (SVR) in previous editions that measured let-through voltage with less current. Due to non-linear characteristics of protectors, let-through voltages defined by 2nd edition and 3rd edition testing are not comparable.
A protector may be larger to obtain a same let-through voltage during 3rd edition testing. Therefore, a 3rd edition protector should provide superior safety with increased life expectancy.
Joules rating
This number defines how much energy an MOV-based surge protector can theoretically absorb in a single event, without failure. Counter-intuitively, a lower number may indicate longer life expectancy if the device can divert more energy elsewhere and thus absorb less energy. In other words, a protective device offering a lower clamping voltage while diverting the same surge current will cause more of the surge energy to be dissipated elsewhere in that current's path. Better protectors exceed peak ratings of 1000 joules and 40,000 amperes.
It is often claimed[by whom?] that a lower joule rating is undersized protection, since the total energy in harmful spikes can be significantly larger than this. However, if properly installed, for every joule absorbed by a protector, another 4 to 30 joules may be dissipated harmlessly into ground. A MOV-based protector (described below) with a higher let-through voltage can receive a higher joule rating, even though it lets more surge energy through to the device to be protected.
The joule rating is a commonly quoted but very misleading parameter for comparing MOV-based surge protectors. A surge of any arbitrary ampere and voltage combination can occur in time, but surges commonly last only for nanoseconds to microseconds, and experimentally modeled surge energy has been far under 100 joules.[7] Well-designed surge protectors should not rely on MOVs to absorb surge energy, but instead to survive the process of harmlessly redirecting it to ground.
Transient voltage suppression (TVS) diode
A TVS diode is a type of Zener diode, also called an avalanche diode or silicon avalanche diode (SAD), which can limit voltage spikes. These components provide the fastest limiting action of protective components (theoretically in picoseconds), but have a relatively low energy absorbing capability. Voltages can be clamped to less than twice the normal operation voltage. If current impulses remain within the device ratings, life expectancy is exceptionally long. If component ratings are exceeded, the diode may fail as a permanent short circuit; in such cases, protection may remain but normal circuit operation is terminated in the case of low-power signal lines. Due to their relatively limited current capacity, TVS diodes are often restricted to circuits with smaller current spikes. TVS diodes are also used where spikes occur significantly more often than once a year, since this component will not degrade when used within its ratings. A unique type of TVS diode (trade names Transzorb or Transil) contains reversed paired series avalanche diodes for bi-polar operation.
TVS diodes are often used in high-speed but low-power circuits, such as occur in data communications. These devices can be paired inseries with another diode to provide low capacitance[26] as required in communication circuits.
Quarter-wave coaxial surge arrestor
Used in RF signal transmission paths, this technology features a tuned quarter-wavelength short-circuit stub that allows it to pass a bandwidth of frequencies, but presents a short to any other signals, especially down towards DC. The passbands can be narrowband (about ±5% to ±10% bandwidth) or wideband (above ±25% to ±50% bandwidth). Quarter-wave coax surge arrestors have coaxial terminals, compatible with common coax cable connectors (especially N or 7-16 types). They provide the most rugged available protection for RF signals above 400 MHz; at these frequencies they can perform much better than the gas discharge cells typically used in the universal/broadband coax surge arrestors. Quarter-wave arrestors are useful fortelecommunications applications, such as Wi-Fi at 2.4 or 5 GHz but less useful for TV/CATV frequencies. Since a quarter-wave arrestor shorts out the line for low frequencies, it is not compatible with systems which send DC power for a LNB up the coaxial downlink.