×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Reference voltage and MCOV

Reference voltage and MCOV

Reference voltage and MCOV

(OP)
Hello,
About surge arrester, how should the rms. reference voltage relate with MCOV?  

RE: Reference voltage and MCOV

The maximum continuous operating voltage (MCOV) should be higher than the maximum expected operating voltage.  

For solidly-grounded system, use the nominal phase-to-neutral voltage and add 10%.  Make sure MCOV is at least this much.  For ungrounded or impedance-grounded systems, use phase-to-phase voltage.  

RE: Reference voltage and MCOV

Assuming that the reference voltage is the maximum rms system voltage Line-to-Line (ex Enom/Emax: 115/121kV, 230/242, 345/362, 500/550, etc).

For Metal Oxide Surge Arresters (MOSA) the Maximum Continuous Operating Voltage (MCOV) is the maximum designated root-mean-square (rms) value of power-frequency voltage that may be applied continuously between the terminals of the surge arrester (SA).

Maximum System Voltage: Is the highest voltage at which a system is operated.
Note: This is generally considered to be the maximum system voltage as prescribed in ANSI C84.1-1995. Typically varies between 5% to 10% of the nominal system voltage.


1- Grounded Systems: The minimum MCOV could be equal or greater than the maximum Phase-to-Neutral Voltage.
MCOVmin=k.ErmsLL/1.73      (5%<k<10%)


2-Ungrounded systems or grounded through impedance: The minimum recommended MCOV would result in larger value than grounded system. The MCOV is selected basis on the corresponding duty cycle supplied by the SA manufacturer as follow:
Duty-Cycle=k.max(ErmsLL) --> MCOV on  SA Table


Several factors will such as Temporary overvoltage (TOV), COG, FOW, BIL, SWL, Energy Discharge Capability, etc. should be considered in the selection of the SA rating.  Please consider review procedure for SA selection and insulation coordination on in references such as IEEE Std C62.22.

An empiric method could be use as a rule of thumb to estimate the MCOV given the Line-to-Line maximum voltage and the SA duty severity.

a- Normal Duty (<30 min) :   
1.4 <(MCOV/max ErmsLL)< 2.0

MCOV=0.835.ErmsLL – 0.077  

b- Severe Duty (<2000 hrs):    
1.5 <(MCOV/max ErmsLL)< 2.5

MCOV=0.901.ErmsLL  + 2.175.










Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources