Transformer upgrades are changes made to increase or improve a site’s transformer capability so it can support additional electrical load—such as expanding EV charging. An upgrade can involve replacing the transformer with a higher kVA unit, adding a second transformer, changing voltage levels (LV/MV interface), improving cooling, or upgrading associated switchgear and protection.
In EV charging projects, transformer upgrades are often required when charger rollout exceeds the capacity of the existing electrical infrastructure.
Why Transformer Upgrades Matter in EV Charging
Transformer upgrades can be a critical dependency for scaling charging:
– Enable more chargers or higher simultaneous charging power
– Reduce voltage drop issues and nuisance trips during peak charging periods
– Improve reliability for fleet depots and high-utilization public hubs
– Avoid constant power limiting that harms throughput and driver experience
– Support future-proofing so expansions don’t require repeated major works
However, transformer upgrades can also be among the highest-cost and longest-lead-time elements of a deployment.
Common Triggers for Transformer Upgrades
Transformer upgrades are typically triggered when:
– Calculated peak demand exceeds transformer rating under realistic scenarios
– Existing transformers are already near capacity due to building loads
– Voltage regulation limits are exceeded (chargers fail to start or derate frequently)
– Thermal limits are reached (overheating, protective operations)
– The network operator (DSO) imposes capacity constraints at the connection point
– New DC fast chargers or depot-scale loads are added
Types of Transformer Upgrade Approaches
Typical upgrade pathways include:
Replace with a Higher-Rated Transformer
– Swap the existing transformer for a larger kVA unit
– Often requires physical space checks, foundation upgrades, and switchgear rework
– May increase short-circuit levels, requiring protection coordination updates
Add a Second Transformer (Parallel or Split Load)
– Add capacity while keeping the existing transformer
– Can split loads by zone (building vs chargers) or operate in parallel (design-dependent)
– Requires careful protection and load sharing design
Upgrade the Connection or Voltage Level
– Move from LV-only arrangements to an MV-fed transformer station (site-dependent)
– Often associated with broader substation upgrades and new switchgear
– Can improve capacity and voltage stability for large hubs
Improve Cooling / Thermal Performance
– Enhance ventilation, fans, or oil cooling arrangements (where applicable)
– Can increase usable capacity margin, but is not a substitute for true undersizing
Upgrade Associated Infrastructure
Transformer upgrades often require supporting changes:
– Main LV panels and busbars
– Sub-distribution boards (SDBs) and feeder cabling
– Protection devices and settings coordination
– Metering arrangements and capacity monitoring
– Civil works (ducts, pits, access, surface reinstatement)
– Earthing and bonding checks (touch voltage risk management)
Operational Alternatives to Full Transformer Upgrades
Sometimes upgrades can be deferred or reduced by:
– Implementing load management with a maximum site demand limit
– Using time-of-use optimization to shift charging off-peak
– Staggering fleet charging schedules (charge-by-departure)
– Adding stationary storage for peak shaving (site economics dependent)
– Phased rollout planning (install EV-ready infrastructure, add chargers gradually)
These options can be cost-effective, but they may not fully remove the need for upgrades at high-growth sites.
Common Pitfalls
– Underestimating lead times and permitting requirements for transformer works
– Not assessing short-circuit level changes after upsizing (protection mismatch)
– Ignoring space, access, and maintenance clearance requirements
– Upgrading the transformer but leaving downstream bottlenecks (SDB capacity, feeder size)
– Overbuilding capacity without a clear expansion roadmap and utilization forecast
– Weak coordination with the DSO, causing delays and redesign
Best Practices
– Start with a measured or modeled load profile and realistic diversity assumptions
– Confirm DSO connection constraints early and document upgrade responsibilities
– Design upgrades with modular expansion (spare ways, spare ducts, staged feeder sizing)
– Combine infrastructure upgrades with managed charging to control peaks
– Validate protection coordination and earthing/bonding after any upgrade
– Monitor performance post-upgrade and adjust site caps based on real data
Related Glossary Terms
Transformer Sizing
Substation Capacity
Substation Upgrades
Grid Connection Strategy
Maximum Site Demand Limit
Load Management
Managed Charging
Stationary Storage
Three-phase Power
Power Derating