The purpose of this article is to provide guidance and information pertinent to safe grounding practices in ac substation design. Here will be discussed about safety of conventional and gas insulated substation.
AC Substation Grounding Safety as per IEEE
Main points of this article are
- To maintain safe limits of potential differences between human body and substation.
- Study about substation grounding practices according to safety rules and develop system for safe design.
- Develop procedure for practical grounding system design based on following criteria.
- with help of analytical methods, To understand and provide solution of typical gradient problem for substation.
Here will find some basic terms used in substation technology.
What is Ground Return Circuit?
A circuit in which the earth or an equivalent conducting body is utilized to complete the circuit and allow current circulation from or to its current source.
What is Ground?
A conducting connection, whether intentional or accidental, by which an electric circuit or equipment is connected to the earth or to some conducting body of relatively large extent that serves in place of the earth.
What does it mean Grounded?
A system, circuit, or apparatus referred to is provided with ground for the purposes of establishing a ground return circuit and for maintaining its potential at approximately the potential of earth.
What is Ground current?
A current flowing into or out of the earth or its equivalent serving as a ground.
What is Initial symmetrical ground fault current?
The maximum rms value of symmetrical fault current after the instant of a ground fault initiation. As such, it represents the rms value of the symmetrical component in the first half-cycle of a current wave that develops after the instant of fault at time zero. Generally,
What is Decrement factor?
An adjustment factor used in conjunction with the initial symmetrical ground fault current parameter in safety oriented grounding calculations. It allows us to obtain an rms equivalent of the asymmetrical current wave for a given fault duration, accounting for the effect of initial de offset and its attenuation during the fault.
What is Effective asymmetrical fault current?
The rms value of asymmetrical current wave, integrated over the entire interval of fault duration. (See Fig 1.)
NOTE: In terms of this guide, it can be expressed as
Figure 1. Relationship Between Actual Values of Fault Current and Values of If, IF and Df for Fault Duration tf.
To understand more about this topic IEEE Guide for Safety in AC Substation Grounding please check following document.IEEE Guide for Safety in AC Substation Grounding IEEE Std80