Phase shift is the change in the relative timing (phase angle) between two AC waveforms—most commonly voltage and current, or between two voltages in different parts of a network. It is measured in degrees (°) or radians and represents how much one waveform leads or lags another.
In EV charging contexts, phase shift is most often discussed in relation to power factor, transformers, and power quality.
Why Phase Shift Matters in EV Charging
Phase shift affects how effectively power is delivered and how electrical equipment is sized and operated. In EV charging sites, it can influence:
– Power factor and reactive power flow (kvar)
– Apparent power (kVA) demand on transformers and switchgear
– Cable and transformer heating due to higher current for the same kW
– Power quality measurements and compliance reporting
– Behavior of systems using capacitors, filters, or certain transformer configurations
Common Causes of Phase Shift
– Inductive loads (current lags voltage): motors, transformers, inductors
– Capacitive loads (current leads voltage): capacitor banks, some filter networks
– Power electronics and control strategies (non-linear loads can distort waveforms and affect measured phase relationships)
– Transformers with vector groups that introduce a fixed phase displacement between primary and secondary
– Long feeders and network impedance effects under heavy load (small shifts)
Phase Shift and Power Factor
For sinusoidal waveforms, phase shift (φ) is directly related to power factor:
– PF = cos(φ)
A larger phase shift increases reactive power and raises kVA for the same real power (kW), which can reduce the usable capacity of the electrical supply for EV chargers.
Phase Shift in Three-Phase Systems
In three-phase systems, “phase shift” can also describe:
– The 120° separation between phases (normal by design)
– A transformer phase displacement between two three-phase systems (vector group-dependent)
This is important when interconnecting systems or measuring across transformer boundaries.
How Phase Shift Is Measured
Phase shift is typically measured using:
– Power quality analyzers
– Smart meters reporting PF, kvar, kVA, and phase angle
– LV panel monitoring modules with per-phase voltage/current measurements
Accurate measurement requires stable waveforms; heavy harmonics can affect readings.
Practical Impacts at Charging Sites
Phase shift issues can show up as:
– Lower-than-expected power factor and higher kVA demand
– Increased heating in cables/transformers at high utilization
– Utility penalties where reactive power is billed or PF is regulated
– Misleading measurements if harmonics are significant and instruments are not suited to distorted waveforms
Related Glossary Terms
Phase Angle
Power Factor (PF)
Reactive Power
Apparent Power (kVA)
Power Quality
Harmonic Distortion
K-rated Transformers
Transformer Vector Group
Load Measurement