What’s the difference between brownout and blackout?
CEBU CITY, Philippines — With parts of the Visayas experiencing rotational brownouts amid tight electricity supply, terms such as “brownout” and “blackout” tend to be used interchangeably in everyday conversations.
But technically, they do not always mean the same thing.
The distinction is particularly important as the Visayas grid faces insufficient supply reserves, prompting utilities to implement controlled rotational interruptions to keep the system from becoming overloaded and potentially triggering a wider failure.
READ: EXPLAINER: Why are rotational brownouts needed in Cebu?
What is a brownout?
According to the National Grid Corporation of the Philippines (NGCP), a brownout is technically not a total absence of power.
It refers to low voltage, meaning electricity remains available but at a reduced voltage level. This can cause lights to become dim or flicker.
READ: Aumentado calls power stakeholders’ meeting over Bohol brownouts
The National Transmission Corporation (TransCo), meanwhile, uses the term differently. It describes a brownout as a deliberate power outage implemented by a utility when electricity demand is much higher than the amount of power being supplied to an area.
That distinction is important in the current Visayas situation.
READ: Cebu faces longer brownouts as Visayas power shortage worsens
Visayan Electric uses the term “rotational brownouts” for the controlled outages being implemented during periods of insufficient power supply.
Under this setup, utilities temporarily cut electricity in selected areas, then rotate the affected areas so that limited available supply can continue reaching other communities.
In other words, the current rotational brownouts are controlled interruptions intended to manage the shortage, rather than an uncontrolled collapse of the power system.
What is a blackout?
A blackout, on the other hand, involves a complete loss of electricity.
NGCP describes a blackout as a grid power outage generally involving a much larger area, usually more than three provinces.
TransCo similarly defines a blackout as a situation in which electrical service in a certain area stops entirely, typically because of an unplanned service interruption.
The key distinction in the current situation is therefore control.
A rotational brownout is deliberately implemented to reduce the load on the system.
A blackout represents a complete loss of electricity that utilities are trying to prevent.
What is power interruption?
Another term that can cause confusion is “power interruption.”
NGCP says that when electricity supply is lost in a specific area or locality, “power interruption” is the more appropriate technical term. TransCo also uses the term for scheduled power losses carried out for maintenance, repairs or improvements.
Why are rotational brownouts happening?
The current rotational brownouts are being implemented as the Visayas Grid faces insufficient supply reserves.
NGCP placed the Visayas Grid under red and yellow alert statuses because of the shortage in available reserves.
Visayan Electric said electricity consumption across the Visayas has continued to rise, particularly during evening peak periods, when households and businesses simultaneously use cooling systems and other high-load appliances.
At the same time, several power plants remain offline or are operating below full capacity because of forced outages and maintenance activities.
That combination reduces the amount of electricity available while demand remains high.
Visayan Electric said rotational interruptions are being used to prevent the entire grid from collapsing.
Rather than allowing the system to reach a point where demand overwhelms available supply, utilities temporarily remove portions of the electrical load and distribute the available supply among different areas.
Why deliberately turn power off?
The purpose of the controlled outages is to prevent a much larger failure.
Engr. Neil Modena, NGCP assistant vice president and head of System Operations–Visayas, said NGCP has to maintain the balance between available power supply and demand.
When supply is insufficient, portions of the load have to be removed from the grid.
Allowing the system to become overloaded could trigger what Modena described as a cascading effect, potentially leading to a wider blackout.
The purpose of the controlled outages, Modena explained, is to prevent an uncontrolled system failure.
Visayan Electric similarly said rotational interruptions prevent the entire grid from experiencing a prolonged blackout that could take significantly longer to restore.
The company said controlled outages allow limited electricity supply to be distributed across more areas instead of allowing a complete system-wide shutdown.
Why don’t the same areas lose power all the time?
Because the amount of load that needs to be removed from the system can change.
CEBECO 3 General Manager Virgilio Fortich Jr. said the duration and extent of rotational brownouts depend on the amount of load reduction required by NGCP.
That requirement can change from hour to hour, depending on the condition of the grid and electricity demand.
As a result, both the areas affected and the duration of interruptions can vary.
When the required load reduction is relatively small, CEBECO may reduce power from smaller portions of its network.
When the required reduction becomes larger, however, the utility may have to turn off entire feeders rather than smaller sections.
Fortich said CEBECO distributes the required load reduction across different areas to comply with NGCP’s instructions.
The utility distributes the required reduction across different cities and areas until it meets the amount of load NGCP has directed it to remove.
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