Understanding the available data is a necessary step in the process of selecting an arrester of sufficient quality. A provider of high-quality goods and services will reveal all of the pertinent information in a format that is easy to understand and simple to use. This article is intended primarily as an overview for comprehending the arrester datasheet & the information that is behind it.
The rated voltage is a rating that dates back to the time when Non-linear resistor of metal oxide arresters were used, and it has evolved into a value that is common to us. As a result of this, it was incorporated into the MOV arrester. Despite having been proven that the actual operating voltage of a modern MOV arrester has nothing to do with the rated voltage of the arrester, the term “rated voltage” is still frequently used when describing arresters.
8/20μs Maximum Discharge Voltage
The discharge voltages and impulse current amplitudes shown in this data all have the same 8/20μs wave form.
Since the amplitude of lightning can range from just a few kA (1 kA is equal to 1000 amps) to sometimes more than 100 kA.
The information that is located in the 10kA column is utilized the majority of the time when comparing one arrester to another arrester.
It is additionally known to as the voltage at the arrester classification current, but the term “lightning protective level” is more common.
The 10kA, 8/20μs discharge voltage can be utilized for assessing similar ratings when contrasting two arresters; the lower level is seen as providing superior protection.
0.5μs 10kA Maximum Resistance Current (IR)
- The shape of the wave has a quicker rising time than the 8/20μs that is utilized for maximum discharge voltage. It also symbolizes the second following surges that occur during a multi-stroke lightning flash.
- According to IEEE C62.11-2012, the shape of the current wave at this protection level is 1μs to the crest, however there is no description on the tail of the waveform.
- This term is utilized by a number of the vendors.
Switching Surge Maximum Resistance Current (IR)
Surge in switching the protected level is the 3rd type of discharge voltage measured & published for arresters.
Peak current levels might range from 125A to 2000A depending on the arrester class.
This discharge voltage shows an arrester’s response to a slow-rising surge developed within the electrical system during breaker (or) switch operations.
Selection of Arrester Ratings
The arrester rating selection table is probably the most commonly used table in arrester datasheets.
- The system voltage and
- The setting of the source transformer’s neutral grounding
are the two most essential standards in selecting an arrester rating.
This datasheet presumes that the worst-case overvoltage duration and amplitude following a line-to-ground fault are undetermined.
When two ratings are provided, the lower rating is the lowest possible, & the higher rating is for the worst-case condition where no information regarding probable overvoltage events is available.
What are the requirements when selecting surge arrester?
- Continuous voltage (Uc)
- Rated voltage (Ur)
- Nominal discharge current (In)
- Specific energy.
- Line discharge class.
- Pressure relief class (porcelain housing only)
- External insulation level.
- Pollution performance.
|Name of the Manufacturer||To be specified|
|Country of manufacture||To be specified|
|Type||Non-linear resistor of metal oxide|
|Maximum voltage of the system||KV||36|
|Ur (rated operating voltage)||KV||33|
|Uc (rated continuous operating voltage)||KV||33|
|Nominal discharge current||kA||10|
|Residual voltage for:|
|8/20μs of lightning current||KV||110|
|Maximum impulse for steep current in 1/20μs||KVpeak||120|
|500 A/1000 A switching current (30/60μs impulse)||KV||100|
|4/10μs impulse withstand value for high current||KA||100|
|Class for line discharge||Minimum 1|
|Capability of arrester rating to absorb energy in kJ/kV, measured while maintaining thermal stability||kJ/kV||to be particularly specified|
|Class of pressure relief||Class||to be particularly specified|
|Maximum power frequency of one minute of voltage withstand, wet minimum||KV||70|
|The maximum RIV that could be measured at 1000 kHz was done so at 1.05 times the peak voltage of the system.||μV||to be particularly specified|
|Impulse voltage resistance of the arrester’s external assembly insulation||KV crest||170|
|Maximum rating for a short circuit||KA||25|
|Measurement of the overall height of the arrester||mm||to be particularly specified|
|Creepage range of distance||Mm/KV||25|
|Measurement of the weight of the arrester||kg|