Understanding SPDs in Modern Power Systems
Introduction
Across New Zealand, Australia and the Pacific Islands, critical infrastructure is being pushed further into exposed terrain of mountain ranges, rural catchments, coastal treatment plants and remote energy sites. These environments are highly susceptible to lightning and transient overvoltage events. At the same time, modern power electronics have become more compact, more efficient, and far more sensitive.
This is where a dangerous gap often appears: power systems are more vulnerable than ever, but surge protection for power systems is still treated as a secondary add-on instead of a core design philosophy.
In utilities, water and wastewater, renewable energy, and industrial facilities, surge protection is not about ticking a compliance box. It’s about maintaining operational continuity, asset lifespan, and safety in environments where downtime is measured in lost production, lost water supply, or significant financial penalties.
This article explores why surge protection is essential for modern power systems, focusing on MOV degradation, lightning zones, transient studies, and proper SPD placement, with real-world relevance to New Zealand, Australia, and the Pacific.
The Problem: Sensitive Electronics in Harsh Environments
Power electronics now underpin almost every critical operation:
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DC power systems
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Remote telemetry and SCADA
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PLC and I/O modules
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Variable speed drives
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Communication networks
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Battery-backed UPS and DC systems
These components operate with much lower voltage tolerance than legacy equipment. In rural New Zealand and across remote Pacific locations, infrastructure is often located on elevated sites, ridgelines, or near exposed water catchments.
Add to this the increasing intensity of storms across Australia and the Pacific due to climate variability, and you have an environment where surge risk is not hypothetical, it is guaranteed over the operational life of the asset.
Yet many sites still rely on incomplete or poorly coordinated surge protection, often focused only on the incoming AC supply.
MOV Degradation: The Hidden Failure Mode
One of the most misunderstood elements of surge protection is MOV degradation.
Metal Oxide Varistors are the core component of most Surge Protection Devices (SPDs). They clamp transient overvoltages by absorbing excess energy. Under normal voltage, the MOV remains high resistance but then during a surge, it becomes low resistance and shunts energy to earth.
However, MOVs do not last forever as over time they degrade with every surge event, even minor ones.
The clamping voltage increases
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Response time decreases
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Leakage current may increase
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Failure becomes more likely
The problem is that this degradation is usually invisible. From the outside, the SPD still “looks” installed and functional but internally, it may already be compromised.
In harsh environments like exposed water catchment sites or wind-prone hilltop installations common across New Zealand, MOV degradation happens faster due to:
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Repeated micro-surges
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Higher lightning activity
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Poor earth conditions
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Elevated ambient temperatures
Without proper monitoring or replacement programs, many systems are relying on surge protection that simply no longer exists in any meaningful sense.
Lightning Zones and Energy Pathways
Modern lightning protection design follows the concept of Lightning Protection Zones (LPZ), as defined by IEC 62305.
In practice, though, many projects only apply this concept to the incoming AC supply.
This is a critical mistake.
Transient energy doesn’t just travel along power conductors. It couples into systems through:
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Communication and data lines
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Sensor and instrumentation loops
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DC power distribution
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Antenna and radio mast systems
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Ground and bonding networks
A real example from a remote water catchment site in the ranges:
The site had surge protection installed on the incoming AC supply and the outgoing DC power distribution. On paper, it seemed well protected.
However, a lightning strike on a nearby communications mast introduced transient energy directly into the system via the connected I/O and data lines. Control modules, PLC I/O and communication equipment failed almost instantly. The main AC and DC SPDs survived but the system still went down.
The missing link was coordinated protection on the signal and data infrastructure, and no transient pathway analysis had been conducted across zones.
Surge protection must cover every entry and exit point, not just power.
Why Transient Studies Are Often Overlooked
Transient studies are still underutilised in many infrastructure projects, particularly in smaller utilities or budget-constrained regional sites.
A proper transient study considers:
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Likely lightning strike points
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Electromagnetic coupling into nearby conductors
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Induced surges from switching events
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Earthing and bonding performance
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Cable routing and segregation
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Equipment withstand voltage
Without this, surge protection becomes guesswork.
In rural New Zealand, where sites may rely on long cable runs, overhead lines, or isolated grounding systems, transient energy behaviour is significantly different from urban environments.
Similarly, in Australia and tropical Pacific regions, where storm intensity and soil resistivity differ, surge propagation behaves differently again.
A study doesn’t need to be overly complex, but it must exist. Otherwise, SPDs are just being placed where space allows, rather than where physics demands.
Proper SPD Placement: Beyond the Switchboard
Another major failure point is poor SPD placement.
Placing a surge protection device at a main switchboard is not enough. SPDs must be coordinated across protection zones:
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At building or site entry points
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At distribution panels
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Near critical equipment or sensitive electronics
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On data and communication ingress points
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On field device interfaces in exposed areas
Each layer should be designed with coordinated energy handling, so that large surges are dealt with at entry points and smaller residual surges are suppressed near sensitive equipment.
At remote infrastructure sites, such as pump stations, treatment plants, or telemetry outstations, this layered protection is often the difference between nuisance faults and complete system outages.
Conditions Unique to NZ, Australia and the Pacific
Surge protection design is not universal.
New Zealand, Australia and the Pacific Islands present some unique challenges:
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High lightning exposure in elevated rural areas
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Long copper cable runs between infrastructure elements
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Coastal salt and humidity corrosion
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Remote installations with limited maintenance access
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Tropical storm intensity in the Pacific
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High soil resistivity in some regions impacting earthing effectiveness
These conditions accelerate degradation of components and increase coupling pathways for transient energy.
Designing surge protection without considering these environmental factors is short-sighted.
This is why locally experienced power system specialists, such as those working within Zyntec Energy’s projects across critical infrastructure, approach surge protection as part of system resilience, not just compliance.
The Role of Surge Protection in DC Systems and Backup Power
DC systems, especially those supporting backup power infrastructure, are increasingly critical.
When a surge event takes out DC supply systems, it doesn’t just take out a measurement point, it can disable entire control and protection schemes.
This is particularly dangerous in water and wastewater facilities, where restored power without functioning control systems can lead to operational instability, or even safety risks.
Surge protection must therefore be integrated into:
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DC distribution architectures
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Battery monitoring systems
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Control system interfaces
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Communications between PLCs and remote assets
At Zyntec Energy, surge resilience is increasingly being treated as a fundamental design layer in customised DC power and backup power solutions, not as an optional bolt-on after installation.
Why “Compliance Only” Design Falls Short
Many projects still aim for “minimum compliance” rather than operational resilience.
The reality is:
Compliance does not guarantee survivability.
Standards define minimum acceptable performance, not what is needed for high-reliability environments like utilities, water, mining, or distributed energy.
True surge protection requires:
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Understanding equipment sensitivity
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Understanding site exposure
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Modelling energy pathways
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Coordinating protection devices
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Planning maintenance and replacement
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Integrating monitoring
Without this, surge protection becomes a theoretical exercise rather than practical engineering.
Final Thoughts
Surge protection for modern power systems is no longer a “nice-to-have.” It is an essential part of system engineering, particularly in exposed environments across New Zealand, Australia and the Pacific.
MOV degradation, poor zone design, lack of transient studies and incorrect SPD placement are not just technical oversights, they are recurring root causes of system failures.
As power systems continue to get smarter and more interconnected, the risk from transients increases, not decreases.
Designing for surge resilience means designing for real-world conditions, not just the drawing board.
This is an area where Zyntec Energy continues to support infrastructure operators and engineering teams by helping review existing systems, integrate smarter protection into new designs, and strengthen resilience across critical power and control environments.
If you’re responsible for critical power infrastructure, it may be time to reassess whether your surge protection strategy is genuinely protecting your system or simply creating a false sense of security.
Visit Zyntec Energy’s website to learn more about resilient power system design or contact our team for a surge protection and transient assessment tailored to your site conditions and risk profile.
Because in critical infrastructure, protection only works when it’s systematic, not selective.
