Electricity is the unseen backbone of modern-day society and often is taken for granted by its users until the proverbial lights go out. An electricity outage can hamper or cripple the operation or critical infrastructure and endanger public safety, even if it is in effect for a brief period of time.
Take for example the power outage that occurred at the New Orleans Superdome during the Super Bowl XLVII game between the Baltimore Ravens and the San Francisco 49ers. The 35-minute outage was later traced to the improper operation of an electrical protective relay device, which signaled the main electrical switchgear, and disconnected power to a wide swathe of the stadium’s lighting and other electrical loads. According to the manufacturer, the culprit of the inoperable relay was an incorrect setting of the device.
Generally speaking, a protective relay’s job is to initiate a “disconnection” under abnormal electrical conditions. A relay requires specific settings that are applied to ensure that a circuit breaker will open in order to isolate an electrical problem or potential problem. The protective relays are connected at key locations within the electrical system to detect abnormal conditions and electrical failures that can be caused by a variety of factors including: insulation breakdown, equipment malfunction, or human error that would otherwise threaten any type of building or facility:
- Facility Operation (e.g., electrical outage, infrastructure damage, or fire);
- Electrical Distribution Equipment (e.g., electrical panels, cables, etc.);
- Customer Loads (e.g., lighting, HVAC equipment, computers, etc.); and
- Personnel Safety (e.g., electric shock, burns, physical trauma, or death).
Settings are evaluated, determined and applied based on the installation of new electrical equipment, or when changes to the electrical system have incurred. The sensing devices, connected to the relay, sense the electrical conditions such as voltage and current. If the sensed input condition, of the current or voltage, is greater than the relay setting then the relay reacts and creates an output condition which typically opens the breaker and circuit. The abnormal condition is present thereby isolating the electrical problem. An incorrect relay setting or applied relay, could potentially result in a power outage of an entire electrical system, as was the case of the Superdome.
Protective relays are effective when engineered and implemented to correctly sense only abnormal conditions of concern and initiate bare minimum disconnection of the electrical system under such conditions. In other words, protective relays directly impact the reliability and safety of an electrical system.
Returning to the case of the Superdome outage, the above background begs the questions:
- Were the relay settings correct or did it malfunction?
- Can any of the other protective relays of the electrical system be inoperable?
- Can the effectiveness of the existing protective relays be improved?
The consequences of not addressing such questions can be substantial. For example, the City of New Orleans was in contention to host the 2018 Super Bowl but lost the bid to Minneapolis. Certainly, a myriad of important factors weighed into the final decision, most notably the $1 billion state-of-the-art stadium that the Minnesota Vikings are scheduled to move into by the start of the 2016 season. However, one wonders whether the infamous 35-minute Super Bowl XLVII power outage somehow played into this decision.
Facilities can prepare by:
- Reviewing their facilities electrical protection and relay settings.
- Comparing the internal relay settings to utility company requirements.
- Reviewing the facility relay protection objectives with the utility company.
- Examining and determining the internal areas of vulnerability.
About Current Solutions, Professional Electrical Engineering and Consulting P.C.
The Current Solutions, P.C. power system engineering team has over 25 years of combined specialized experience working with every type of facility power distribution system, and industries across the U.S. Our consulting services, assist our clients to navigate their power distribution systems complexity, for systems ranging in size from low voltage through medium voltage.
By Mark B. Cavallaro, P.E.
Current Solutions, Professional Engineering and Consulting P.C.
Copyright CSPC © June 2014