SURGE ARRESTER SELECTION GUIDE

Thursday, May 26, 2011

In this Surge Arrester Selection Guide, an overview of the processes and criteria are given. This post is not intended to be an all encompassing reference but only as a review of the basic steps necessary to choose the appropriate surge arrester for a particular application.  In addition, a detailed input from other sources such as the manufacturer should be obtained.

The main objectives of this surge arrester guide are:

Ø    To select the lowest rated surge arrester that will give sufficient equipment insulation protection
Ø   To determine the ratings of the surge arrester such that it will have an acceptable service life when connected to the electric power system.

An arrester of the minimum practical rating is preferred since it provides the highest margin of protection for the equipment insulation system. It should be noted that there is a thin line between service life and protection of a surge arrester. Higher ratings tend to increase its capability to survive on a certain power system. However, this reduces the protective margin it provides for a specific insulation level. Thus, the engineer should properly consider both surge arrester survival and equipment protection in the specification and selection process.

The appropriate selection and application of surge arresters in a system involve the following decisions: Arrester Type and Ratings, Physical Location and Insulation Coordination.

Arrester Types and Ratings

Arrester Class and Types

The surge arrester types are basically based on the main conductive elements:

  • Expulsion Type
  • Silicon Carbide (SiC)
  • Metal Oxide Varistors (MOV)

According to IEEE, there are four classes of surge arresters. In order of protection, capability and cost, the classes are:

  • Station
  • Intermediate
  • Distribution
  • Secondary
Station Class Surge Arrester
Station Class Surge Arrester
Arrester Ratings

  • Duty Cycle
  • Maximum Continuous Operating Voltage (MCOV)
  • Temporary Overvoltage (TOV)
  • Maximum Discharge (ANSI) or Residual (IEC) Voltage
  • Pressure Relief / Short-Circuit Capability
  • Energy Absorption

Arrester Location

NEC Article 280 mentioned that the conductors for the surge arresters should not be longer than necessary, and unnecessary bends should be avoided. In connection, there is a need to assess the physical location of the surge arrester, which affects its lead length, as well as the voltage increase due to separation distance effect.

Insulation Coordination

The degree of insulation coordination is determined by the magnitude of three protective margins. The protective ratios must be met or exceeded if satisfactory insulation coordination is to be achieved, according to the minimum recommendations given in ANSI C62.22.

Ø  Equipment Front-of-Wave Protective Margin
Ø  Impulse Margin of Protection
Ø  Switching Surge Protective Design

References:

Hernandez, J. Lightning Arresters: A Guide to Selection and Application
IEEE Tutorial on Surge Protection in Power Systems
Pryor, L. The Application and Selection of Lightning Arresters

No comments:

Post a Comment

PQWorld

free counters

About Me

My photo
I am an Electrical Engineer with a Masters Degree in Business Administration. My interest is in Power Quality, Diagnostic Testing and Protective Relaying. I have been working in an electric distribution utility for more than a decade. I handle PQ studies, power system analysis, diagnostic testing, protective relaying and capital budgeting for company projects.