System Studies and Switchgear Specification

Overview

Power Testing Ltd (PTL) has been engaged by a large secure industrial facility to provide support as part of an investigation to upgrade their 11 kV distribution system.  System studies such as load flow analysis and fault level study are required for the existing system and the planned future combined heat and power (CHP) generator.

Challenge

System studies are necessary to determine whether the site operates within its design capability and the planned future upgrades to maintain safe operation. The industrial site consists of various 11 kV switchboards, step up transformers, cables, static and dynamic load that need to be correctly modelled during steady state and fault conditions. Detailed sensitivity analysis and outage conditions are crucial to validate the safe operation for the extreme operating scenarios.

Solution

PSC developed system models for the existing and future systems taking into consideration the new CHP generation and range of operating scenarios. Investigation into the fault level for the future system showed that the fault level of the main incoming switchboard is higher than the manufacturers rated break and make short circuit rating leading to a potentially unsafe operating arrangement. PSC recommended replacement of the 11 kV switchgear and provided a technical specification for the updated switchboard, including:

  • Circuit breaker operating parameters and ratings
  • Single line diagrams and protection key line diagrams for the new switchboard
  • Protection relay functional requirements
  • Voltage transformer and current transformer requirements.

Results 

The studies concluded in a detailed presentation of the steady state and short circuit results identifying potentially unsafe operating conditions.  PSC provided a detailed technical specification for the replacement of the 11 kV switchgear and followed up with the supplier to review the offer and compliance with the requirements.