Elevator Mainline Power – Is it “Dirty”
Why You Should Analyze Elevator Mainline Power—and Act on Harmonics
I have been consulting in the elevator industry since 2007. In the past 7 years, I decided to begin tracking the number of elevator issues I have worked on that were found to have “dirty power” as the root-cause of the issues. In my personal studies, 32% of issues with modern elevator controllers have been traced back to the building’s power being “dirty” and substandard in some way. The term dirty power is extremely vague and will not be addressed in this blog. However, excessive harmonics are a type of dirty power, and they are quite common these days. Let’s expand on this topic…
Elevator drives have evolved from simple contactors to sophisticated variable-frequency drives (VFDs) that deliver ultra-smooth rides. The downside is that a standard 6-pulse rectifier inside the drive pulls jagged, high-peak current instead of a clean sine wave. Those peaks translate—via Fourier analysis—into 5th, 7th, 11th, and other harmonic components that ride on top of the 60 Hz fundamental. If you never measure or mitigate them, expect shorter equipment life, nuisance shutdowns, and potential violations of utility power-quality tariffs.
1 Elevators Are Harmonic Hot-Spots
A typical 6-pulse elevator VFD produces 35 – 55 % total harmonic distortion in current (THD-I) at rated load. Because harmonic currents flowing through feeder and transformer impedance create matching voltage distortion, IEEE 519-2022 limits both current and voltage distortion at the point of common coupling (PCC).
2 Why Harmonics Matter in Real Life
- Controller reliability – DC-bus ripple stresses electrolytic capacitors and IGBTs, while 5th/7th torque pulsations raise motor temperature and can trigger overspeed or overcurrent trips.
- Electrical infrastructure – Harmonic currents add extra I²R heating to feeders and, in the case of 3rd-order “triplen” currents, can push neutral conductors to 170 % of phase current.
- Neighboring loads & safety systems – Distorted bus voltages make LED lighting flicker, reset PLCs, and cause false ground-fault trips.
- Compliance & cost – Utilities may impose penalties or require corrective work when PCC voltage distortion exceeds the 5 % ceiling in IEEE 519.
3 Why You Need a Mainline Power Survey
- Baseline commissioning – Prove every new or modernized elevator meets the spec on day one and establish a benchmark for future troubleshooting.
- Early warning – Trending THD-I/THD-V exposes weakening DC-link capacitors, failed rectifier diodes, or loose neutrals long before a shutdown.
- System-wide insight – Elevators often share risers with HVAC drives, UPSs, and LED lighting. A week-long survey shows which loads create—which merely suffer from—harmonics.
Recommended setup: three-phase power quality analyzer with one-second logging; probes on all phases and neutral; test at the service entrance, the elevator disconnect, and the VFD input.
4 What To Do If Harmonics Are High
- Install a 5 % line reactor. Cheapest first step; typically trims THD-I into the 25 – 40 % range.
- Add a tuned passive filter (usually 5th-order). Drops THD-I to roughly 10 – 18 %; be mindful of power-factor shift at light load.
- Specify a 12- or 18-pulse drive. Uses a phase-shift transformer to cancel key harmonics; expect 10 – 15 % THD-I.
- Upgrade to an Active Front End (AFE) drive. Near-sinusoidal (≤ 5 % THD-I) plus full regenerative braking—best performance but highest up-front cost.
- Retrofit a parallel active harmonic filter. Good when multiple drives share a bus; can hold THD-I/THD-V within IEEE 519 limits.
- Use a delta-wye harmonic-mitigating transformer if the neutral is the weak link—it diverts 3rd-order currents and cools the neutral by 40 – 80 %.
6 Key Take-Away
Analyzing elevator mainline power isn’t optional housekeeping—it’s critical insurance for rider safety, equipment longevity, and regulatory peace of mind. When a survey flags harmonics above spec, act decisively: upgrade the drive, add the right filters or transformers, then document the results. Your elevators will run cooler and smoother, and the rest of the building’s electrical system will thank you.
Need help testing or specifying harmonic mitigation? Argon Elevator Consulting can install the data loggers, read the data, and deliver a plan that keeps your elevators—and your building—running smooth.
