Safety electrical drawings

Electrical drawings include symbols and diagrams that depict an electrical process system. Electrical drawings show unit electricians where power transmission lines run and places where it is stepped down or up for operational purposes. A complex P ID is designed to be used by a variety of crafts. The primary users of the document after plant start-up are process technicians, instrument and electrical, mechanical, safety, and engineering. 

A process technician typically traces power to the unit from a motor control center (MCC). The primary components of an electrical system are the MCC, motors, transformers, breakers, fuses, switch gears, starters, and switches. Specific safety rules apply to the operation of electrical systems. The primary safety system is the isolation of hazardous energy through lock-out/tag-out measures. Process technicians are required to have training in this area. Figure 7-22 shows the basic symbols and flow path associated with an electrical drawing. Electrical lines are typically run in cable trays to switches, motors, ammeters, substations, and control rooms. 

The accident resulted from a routine safety test of some electrical control equipment at the start of a normal reactor shutdown for routine maintenance. The test was to determine the ability to continue to draw electrical power from a turbine generator during the first minute of coast-down following a station blackout. In a blackout, the reactor automatically scrams and diesel generators start to assume load (about 1 minute required). 

Handover documentation (e.g., as-built drawings, electrical safety checks)... 

The case study of the United Kingdom electricity supply industry draws heavily from the masters thesis of James Joosten (Department of Engineering Physics, University of Wisconsin-Madison), titled The Impacts of Restructuring the Electricity Market on Nuclear Safety Lessons Learned from the United Kingdom. Finally, the authors acknowledge Lesley Klein for her help and patience in typing and formatting this manuscript... 

Air filtration, the real heart of the system, was a major concern for the safety community. It was necessary to build in redundancy with every major component to ensure a fail-safe system. This consisted of dual High Efficiency Particulate Air (HEPA) and carbon filters, dual vacuum gauges, dual air pressure alarms, dual motor blowers to draw air through the glovebox, dual sources of electricity and a Hame Photometric Detector (FPD) to monitor between the carbon beds for possible breakthrough of chemical compounds. This was necessary because the effluent air from the filter beds was being released into the working environment of the operators. Army... 

After consideration of these questions, detailed mechanical design drawings will be made of all of the BOP items that need to be sourced or fabricated. A basic electrical line diagram will be drawn up that shows how the various electrical and control items link together, with safety features included. A hazard identification (hazid) and/or hazard and operability study (hazop) or similar safety analysis will also be carried out. These considerations are outside the scope of this book but it is hoped that the reader would have gained enough understanding of the systems to be able to inquire further. 

Ill-103. Reactivity control system, reactor shutdown system The function of the mechanical and electrical design shall be described. The description shall include the materials and dimensions and shall be supported by drawings. The reactivity control mechanisms and their instrumentation, such as their position or status (coupled/decoupled), should be presented, together with their insertion time and interlocks. The effects of corrosion, fatigue, neutron doses, etc., on the lifetime of the mechanical and electrical components shall also be discussed. The safety related design parameters should be presented, such as ... 

The Central Electricity Generating Board lay emphasis on safety requirements by including a special clause 33A in their Contract Conditions and drawing attention to it in their standard acceptance letter. The Clause reads... 

For very many of these features it was possible to draw up performance criteria for their design which, if incorporated in future models, may have the effect of reducing the hazards associated with them. Many of the criteria which were drawn up, although desirable, may have only a small impact upon the safety of lawnmowers for example, one such recommendation was that to make the cable on electric mowers easier to control, its free end should be routed and... 

WSRC committed to issue system drawings (both P IDs and electrical one-line diagrams) to the control room.based on a verified system configuration and identified 13 safety system P IDs that will be established in the control room prior to restart. 

---