Even though a power surge with minor fluctuations lasting a few microseconds may seem like a very brief event, it can easily damage many of the electronic devices we use daily.
What is a Power Surge?
A power surge is an abnormally high voltage that lasts for a short period.
A power surge is a transient voltage, current, or power wave in an electrical circuit. It typically lasts less than half a cycle of the normal voltage waveform and can have additive or subtractive polarity, either positive or negative.
What Causes Power Surges?
Power surges usually originate from a source such as the grid supply or a generator, and this abnormally high voltage lasts for a few microseconds. A typical surge can last up to 50 microseconds. Although this is an extremely short duration, the voltage can reach up to 6,000 volts and 3,000 amps when it reaches equipment or circuits.
Surges can be generated by various events, including:
- Equipment failures
- Lightning strikes
- Capacitor bank switching
- Load changes
The ability of equipment to withstand these events greatly affects its reliability.
Depending on the source and voltage level, there are different types of power surges. A surge can range from 5 to 10 volts when a hair dryer is turned on to several thousand volts when lightning strikes a transformer.
Internal Power Surges
Internal power surges mostly occur in homes, industrial facilities, and other commercial buildings. They are usually caused by the switching on and off of inductive loads, such as motors. This leads to high current flows, redirecting some of the electricity to other components in the circuit.
Major household appliances like air conditioners and refrigerators are the primary culprits behind these surges. Smaller devices like hair dryers and other electric appliances can also cause surges.
External Power Surges
These types of surges originate outside the building’s electrical system. They can be caused by:
- Lightning strikes
- Tree branches touching power lines
- Animals causing short circuits in transformers
- Power returning after an outage
- Interference from TV or telephone lines
Transient Waveforms
Transient overvoltage waveforms vary depending on their shape and duration. Most last between a few microseconds to a few milliseconds. The waveform can be oscillatory or non-oscillatory for impulsive transients. The surge oscillation smooths out and diminishes over time due to capacitive load switching.
Impulsive surges are non-oscillatory transient events that increase current or voltage levels in either a positive or negative direction. They are classified based on the time it takes for the wave to reach its peak value.
Transient waveforms can be caused by:
- Poor grounding
- Incorrect grid interference
- Switching inductive loads
These can lead to physical damage to equipment, data loss, or data corruption.
Effects of Power Surges on Electronic Components
Short-term overvoltages can disrupt, damage, or destroy electronic equipment in factories, homes, or any other location. These surges are common causes of failures in electronic and computer equipment.
- Low-level surges do not blow fuses or melt electronic components but gradually degrade them, leading to eventual malfunction.
- High-level surges cause immediate damage, such as blown fuses, exploding semiconductors, resistors, and capacitors.
How to Protect Equipment from Power Surges?
These electrical surges can be diverted to the ground before reaching the equipment. Depending on the expected surge magnitude and the equipment being powered, different methods can be used. The most common solution is using Surge Protective Devices (SPDs).
SPDs limit the instantaneous overvoltage reaching the equipment and prevent damage by diverting the surge to an alternative path, such as the ground.
Most Common Surge Protection Devices
- Metal Oxide Varistor (MOV)
- Silicon Avalanche Diode (SAD)
- Gas Discharge Tube (GDT)
Factors to Consider When Choosing Surge Protection Devices
- Efficiency
- Reliability
- Availability
- Energy Capacity
- Cost
SPD Operating Modes
Surge protection devices have two main operating modes:
- Standby Mode: Operates under normal power conditions with minimal function and almost no power consumption.
- Diversion Mode: Activated when a surge is detected. Diverts harmful current away from the load and reduces the resulting voltage to a safe level.
SPDs do not stop or suppress surges—they redirect them to the ground.
Installation Methods
Surge protection devices can be integrated into power supply designs in different ways:
- Surge-protected plugs or automatic voltage protection can be used in power outlets.
- Another approach is installing a surge protector at the service line entry, protecting the home or building from most external surges.