Issues and Solutions in Setting a Quadrilateral Distance Characteristic

The MHO characteristic is used very extensively in North America over the last decades in distance relaying. They are simple to design with electro mechanical components and simple to set. With the introduction of static and numerical relays other characteristics have been developed to overcome certain limitations of the MHO circle. More and more quadrilateral characteristics are used here in North America for ground faults on short lines in particular. The advantage is that the resistive reach can be selected via a setting and is not anymore limited by the characteristic of the MHO circle which particularly is a problem on short lines. This advantage of MHO circle becomes a challenge in quadrilateral characteristic for the setting engineer because he has to select an appropriate setting. This paper will discuss some of the guidelines to set the resistive reach on a quadrilateral characteristic. This paper also discusses the requirements for zone 3 settings from NERC. On the other side the advantage of the MHO circle, to be insensitive for arc faults in combination with heavy load, is a challenge for the quadrilateral characteristic and requires special attention for a secure functionality. The paper will discuss the source of the problem caused by load current in combination with arc faults and introduce some solutions. Guidelines will be outlined to set the quadrilateral characteristic accordingly to prevent an insecure operation.