Entering Outdoor Substations, Part 8 of 8
Dave Smith has been an Industrial Maintenance Electrician since 1975. He has taught maintenance, troubleshooting and safety courses to thousands of electricians in mines, mills, refineries, factories, plants, power stations and offshore platforms throughout North America and the Middle East. Dave is a hands-on guy and teache...
(At the end of Part 7 “Entering indoor substations” in January 2012, Dave explained the importance of getting in and out of a substation as quickly as possible, and always knowing where you are in relation to any machine.)
In previous columns, I’ve written about my belief that you don’t want to be in a situation where an exploding door – whether it’s being blown open or blown off its hinges – can hit any part of your body. When dealing with a substation, you’re facing thousands of horsepower worth of energy and explosive action.
You do not want to be in a situation where any part of the metal containment system hits your body, so follow the safe work practices I’ve preached in previous columns.
The task of racking equipment in or out is a much higher risk; you need to be very capable of following switching orders and reading a single-line diagram. Find the single-line diagram for the substation, look at it, then look at the equipment to correlate the two so you know how the substation operates, and triple-check to make sure you are at the right gear.
Look at the front of the switchgear to see whether an arc flash hazard study has been done on the substation; you want to know the IE, minimum required PPE and the flash boundary.
It is important to understand that ATPV (Arc Thermal Performance Value) or EBT (Energy Break-open Threshold) ratings of your clothing are based on 50% probability. Were we playing Texas hold ‘em, 50% probability means “All in” but in electrical safety, 50% is a coin toss and definitely not worth the risk.
So understand that, while personal protective equipment (PPE) manufacturers try to make their gear as protective as possible, CSA Z462 wants you to realize that arc flash calculations are not an exact science and to understand there is inherent risk in everything we do.
When you are the person racking something in or out, one of the most critical things to ensure is that you have personal (local) control over the system. I tell the story of an operator who was closing a starter while someone else was hitting a remote switch. The switch closed just as the starter was racking to the bus bar. This starter design has a mesh grill on the front of it, and the unfortunate operator was subjected to an arc flash blowing out through the metal grill. Luckily, his Category 2 coveralls protected him; had he been in street clothes with a combination of polyester and cotton, it is highly likely he would have been blown straight to the burn ward… perhaps the morgue.
You must know how to put an individual piece of equipment into local control; if you don’t know how, then you simply are not qualified to operate the equipment. A great deal of equipment now is PLC-controlled, and even when Off, it may be energized.
You must understand the starting process for the equipment you’re operating. Be they low- or high-voltage, you must know whether the disconnect switches you’re operating are load-break or non-load-break switches. There have been hundreds of horror stories in our electrical history where unwitting, unknowing or untrained people have tried to operate non-load-break switches under load conditions.
You cannot bring the blades out of the jaws fast enough to extinguish an arc with this equipment; it was never designed to do this. Opening non-load break switches under load merely draws an arc that can go phase-to-phase and phase-to-ground, causing an immediate explosion.
Make sure you know the equipment, that you are following safe work practices, and that you’re wearing the correct PPE.
Until next time, be ready, be careful and be safe.©
