1. What is the difference between a grading ring and a corona ring?
A grading ring is used to ensure a uniform voltage distribution along the length of an electrical device. This is important for surge arresters so each MOV block in the arrester is energized at the appropriate voltage.
A corona ring is traditionally used to electrically shield external hardware to prevent corona from developing. This corona could lead to degradation of insulating materials or create interference to electronic communication.Surge arresters below 500 kV system voltage do not typically need corona rings.
2. How do I know if I need a grading ring or corona ring for my arrester?
The REGA Surge Protection Brass Engineers have performed all necessary electric field calculations to make this decision. Therefore, all of our surge arrester part numbers already include rings if required, and you need not specify rings. They will automatically ship with your arrester, stacked on a separate pallet.
3. What does MCOV rating of a surge arrester mean?
MCOV stands for the Maximum Continuous Operating Voltage. It represents the power frequency voltage that may be continuously applied to a surge arrester. The MCOV selected for a given system voltage is a function of the maximum line-to-line voltage as well as the system grounding parameters. REGA Surge Protection Arresters Systems application engineers can assist with the proper MCOV selection for your specific requirement.
4. How does MCOV rating differ from Duty Cycle rating?
The Duty Cycle rating of a surge arrester is the power frequency voltage at which the arrester can successfully withstand the duty cycle test per IEEE Standard C62.11. The Duty Cycle rating is a short-term TOV (Temporary Over-Voltage) rating.
5. What is the difference between a station class and an intermediate arrester?
Generally, station class arresters have the lowest protective characteristics and most durability, while intermediate arresters perform at levels slightly less robust than station class arresters. Both of these arresters have traditionally been used in sub-station applications. The arrester IEEE/ANSI Standard C62.11 defines the performance levels of each of these designs.
6. Why is the system grounding type important to consider when selecting the MCOV rating?
The type of grounding determines the amount of neutral shift during a fault on the power system. The resulting TOV on the arrester could cause damage unless the
arrester is sized properly.Your REGA Surge Protection Arresters Systems sales representative can help with the selection of the proper size arrester for your application.
7. How do I use the pressure relief rating value in making my arrester selection?
When a surge arrester fails, it will become shorted. It then will conduct the available short circuit current in the substation.To minimize the possibility of a catastrophic failure, you should select an arrester with a pressure relief rating that is greater than the available short-circuit current in your substation.
8. What routine maintenance and testing does REGA Surge Protection Arresters Systems recommend for station class surge arresters?
REGA Surge Protection Arresters Systems arresters are designed to provide years of successful service without any recommended maintenance. Arresters do not require field testing;however, if testing must be performed we recommend that REGA Surge Protection Arresters Systems be contacted prior to beginning a testing.
9. I have a question that is not covered in this section.
We’ll be happy to answer any of your arrester questions. Just contact your local REGA Surge Protection Arresters Systems sales representative or call our main customer service line at +86 573 83998019.
A Glossary of Terms Used in This Catalog
BIL (Basic Lightning Impulse Insulation Level): The electrical strength of insulation in terms of the crest value of a standard lightning impulse under standard atmospheric conditions.
Crest Value: The maximum value that a wave, surge or impulse attains.
Design Tests: Tests made on each design to establish performance characteristics and to demonstrate compliance with the appropriate standards of the industry.Once made, they need not be repeated unless the design is changed so as to modify performance.
Discharge Counter: A device for recording the number of arrester discharge
Discharge Voltage: The voltage that appears across the terminals of an arrester
during passage of discharge current. Sometimes referred to as IR.
Discharge Withstand Current: The specified magnitude and wave shape of a discharge current that can be applied to an arrester a specified number of times without causing damage to it.
Duty Cycle Voltage: The designated maximum permissible voltage between its terminals at which an arrester is designed to perform its duty cycle.
Fault Current: The current from the connected power system that flows in a short circuit.
Front-of-Wave Impulse Sparkover Voltage: The impulse sparkover voltagewith a wave front that rises at a uniform rate and causes sparkover on the
Grading Ring: A metal ring mounted to electrostatically modify the voltage
gradient or distribution.
Ground Terminal: The conducting part provided for connecting the arrester
Impulse Protective Level: The discharge-voltage value for a defined wave shape.
Impulse Withstand Voltage: The crest value of an impulse that, under specified conditions, can be applied without causing a disruptive discharge.
Line Terminal: The conducting part of an arrester provided for connecting the arrester to the circuit conductor.
Maximum Design Cantilever Load-Static (MDCL-Static): The maximum cantilever load the surge arrester is designed to continuously carry.
Metal-Oxide Surge Arrester (MOSA): A surge arrester utilizing valve elements fabricated from nonlinear resistance metal-oxide materials.
MOV (Metal Oxide Varistor): The power semi-conductor that limits the surge voltage allowing the arrester to perform its protection function. This is the
electrically active component of the surge arrester.
MCOV (Maximum Continuous Operating Voltage): The maximum designated root-mean-square (rms) value of power-frequency voltage that may be applied continuously between the terminals of the arrester.
Partial Discharge (PD): A localized electric discharge resulting from ionization in an insulation system when the voltage stress exceeds critical value. The discharge partially bridges the insulation between electrodes.
Reference Current (Iref): The peak value of the resistive component of a power-frequency current high enough to make the effects of stray capacitance of the arrester negligible.
Reference Voltage (Vref): The lowest peak value independent of polarity of power-frequency voltage, divided by the square root of 2, required to produce a resistive component of current equal to the reference current of the arrester.
Routine Tests: Tests made by the manufacturer on every device to verify that the product meets the design specifications.
Surge Arrester: A protective device for limiting surge voltages on equipment by diverting surge current and returning the device to its original status. It is
capable of repeating these functions multiple times.
TOV (Temporary Over-Voltage): A power frequency voltage in excess of normal line-to-ground voltage. A TOV is typically system-generated. The magnitude and duration are a function of the power system parameters.
Arrester Routine Factory Testing: After assembly, the arresters are 100 percent tested as follows:
Discharge Voltage: Determined by the sum of the resistor elements, each arrester is tested to be within a manufacturer specified range that aligns with the arrester’s published ratings.
Reference Voltage: The voltage at which the arrester conducts the reference current per the table below. This test verifies the proper MOV blocks were used in the assembly.
Partial Discharge (PD): Power-frequency voltage is raised to the duty cycle voltage rating of the arrester or unit, held for not less than 2s, and then lowered to 1.05 times the MCOV of the arrester or unit. The measured PD shall not exceed 10 pC.
Seal Test: The helium-mass spectrometer test is performed on arresters with >10% internal gas volume to verify the environmental seal of the arrester or unit.
Power Frequency (PF): A minimum voltage of 1.20 times the MCOV of the arrester or unit is applied to verify the measured values of watts loss does not exceed the arrester or unit’s specified limits.
The above testing procedure indicates our diligence in producing high quality metaloxide arresters.