Posted in Construction on November 24th, 2020
Technical Query – Raise Only When You Know What You Are Doing
A technical query (TQ) is a document containing a question or questions which is raised by the contractor to their client. It is a contractual document which requires a formal response from the client. A TQ is a method to clarify and resolve ambiguities in the contract or scope of work. In most cases, the parties will be able...
Posted in Design on September 15th, 2020
Determining the required sizes of earthing conductors and earth electrodes
The sizes of earth conductors and earth electrodes are almost always chosen from typical sizes as provided by a particular project standard. If using non-typical sizes can extensively impact the cost of the project, it would be best for the Electrical Engineer to calculate the required sizes of earth conductors and earth electrodes.
IEC 60949:1988 - Calculation of thermally permissible...
Posted in Design / Protection on September 14th, 2020
The Purpose of Maximum and Minimum Short-circuit Currents
The calculation of maximum and minimum short circuit currents has been discussed in IEC 60909 - Calculation of Maximum and Minimum Short-circuit Currents. What are the significance of these values?
The maximum calculated short-circuit current values are used for
- Selecting interrupting devices of adequate short-circuit interrupting and peak rating,
- Checking the ability of components of the...
Posted in Design / Protection on September 8th, 2020
Circuit Breaker Ratings – A Primer for Protection Engineers
This paper prepared by Bogdan Kasztenny, Schweitzer Engineering Laboratories, Inc. and Joe Rostron, Southern States, LLC which was presented at the 71st Annual Conference for Protective Relay Engineers and can be accessed at here.
This paper "Circuit Breaker Ratings – A Primer for Protection Engineers" deals primarily on high voltage circuit breakers:
- Explains the asymmetrical short-circuit interrupting current rating ...
Tolerable Risk – IEC 62305-2
In performing risk assessment as an essential step in the application of IEC 62305, the calculated risk of loss due to lightning shall be below the tolerable level.
Tolerable risk (RT) as defined in IEC 62305-2 is
- tolerable risk RT
- maximum value of the risk which can be tolerated for the structure to be protected
- Also referred to...