This paper is the second of three articles outlining the actual cause of most arc-flash events. The first outlines some of the dangers and causes of arc flash events and explains how they can be prevented.
In my previous article, I explained that commonly proposed solutions for arc flash include special clothing and “fast-acting” relays whose purpose is to de-energize the circuit breaker, which ideally would mitigate the arc flash event damage. These methods take effect only AFTER the event has begun.
In consideration of employee safety, this “fast-acting” approach is not fast enough and is allowed to continue too long to guarantee results. Arc flash events must be prevented or instantly suppressed. This requires a device that will prevent or correct power quality problems without any delay. In many cases it is this delay which allows the arcing to continue which causes even more severe unrepairable damage to the power system.
Arc flash events can now be addressed using voltage control.
Here are the facts:
- Most arc flash events begin as single line-to-ground faults.
- Most grounds start as arcing ground faults.
- Ground faults are caused by insulation breakdown in the power system.
- Most arcing ground faults are not caused by worker error.
- Insulation breakdown can be caused by age, moisture, dirt, conductive dust, over-voltage or simply a lift truck driving over an extension cord
- Arc flash events cannot be prevented with the normal or traditional approaches of FR clothing, face shields or shoe spats.
- Most arc flash events which injure or kill people have a liability cost of over a million dollars.
- Employee injury starts a long investigation which generally interrupts production in your facility.
- Companies go out of business due to the costs associated with these events.
- As an arc fault continues for several milliseconds it transitions from melting metal to a burning unquenchable plasma fire which causes the air to expand 67,000 times in volume causing a concussive wave which can crush the chest, stop the heart and stop breathing.
- Arc flash is preventable for far less than the event would cost you.
Voltage Control: Why it Matters
In order to adequately resolve power quality problems such as arc flash events, the solution must operate fast enough to engage simultaneously with the cause and effect of the problem. Otherwise, the power system is forever a step behind, and true event prevention is not achieved. Some power quality protection devices have a delay while the voltage is rising and after it reached some predetermined threshold there is a reaction time, delay, so even if the total delay is only 17 thousandths of a second that is enough time for a voltage spike to travel from Alaska to Texas. No, using current to try to protect sensitive equipment is not a long term solution.
Electrical engineers are familiar with conventional transient voltage surge suppression (TVSS) devices. These devices attempt to control high voltage spikes by redirecting the associated surge of current to ground, which results in a delayed drop in voltage. This surge of noisy current can cause other problems: current flows through the path of least resistance, which could be the ground connection of variable speed drives, operator terminals, or control systems such as PLCs. Fast-acting relays, mentioned earlier, operate on the same basis as TVSS: they attempt to diminish the consequences of a problem after it’s already happened.
While current-driven devices encounter a voltage imbalance with a separate and disproportionate current imbalance, the Phaseback VSGR corrects phase voltage imbalances using the energy caused by the voltage imbalance, also known as event energy.
The Bottom Line
Preventing phase-to-ground voltage imbalance is the key to good power quality and efficient operation of all electrical loads and devices within your facility. Everything must operate within its specifications, and the middle of the CBEMA curve shows the limitations and tolerance of equipment. When voltages are held within the CBEMA curve, equipment operates normally. The VSGR provides a voltage correction to hold the voltages in the center of the CBEMA curve. With this magnitude of protection, even the most sensitive equipment can operate efficiently and reliably within most any power system at the lowest possible cost.
Now that you know that you can make your electrical system safer, more reliable and efficient you can use this voltage control solution or continue doing the same things over and over hoping for different results.
William Hinton is Director of Engineering for Applied Energy. Learn more about arc flash events in the arc flash test lab report.
