EMC analysis to determine the causes of compensating currents in industrial plants
Introduction
In modern industrial plants, undesirable transient currents are increasingly occurring, which not only cause EMC problems but can also lead to production disruptions, equipment wear, or electronic failures. Energy-intensive companies with complex grid structures, decentralized power supplies, and sensitive automation technology are particularly affected.
This white paper shows how a targeted EMC analysis can help to systematically identify the causes of these compensating currents and to eliminate them sustainably.
What are compensating currents?
Equalizing currents are unwanted return flows in the equipotential bonding or earthing system, which are typically caused by
- Grid asymmetries
- Harmonics
- Interference voltages (EMC effects)
- Multiple grounding points
- capacitive couplings between cables and equipment
These currents flow, for example, via PE conductors, earthing systems, or metallic structures – often far from their intended path.
Risks and impacts
The consequences of compensating currents are manifold:
- Corrosion of pipes and earthing
- False tripping of RCDs and protective devices
- Disruptions in communication and measurement data
- Bearing currents in motors, damage to rolling bearings
- Increased EMC load in IT and automation networks
PQE EMC analysis – systematic root cause analysis
A professional EMC analysis combines measurement technology, system expertise, and network analysis. The typical process is divided into the following phases:
1. Inventory
- Plant structure, earthing concept, equipotential bonding system
- Documentation of faults (when, where, how often)
- Visual inspection of critical operating areas
- Measurements
- Current measurement on PE conductors, cable shields and earth connections
- Residual current measurement (e.g. in TN-S vs. TN-C sections)
- Earth resistance measurement at transformer stations, foundation earth electrodes…
- Frequency analysis (FFT) to identify harmonics
- Waveforms of voltages and currents
- Evaluation and documentation
- Classification of interference (galvanic, inductive, capacitive)
- Detecting multiple grounds, loops or poor shielding
- Documentation of faulty system design with regard to EMC
- Reporting with action matrix
EMC analysis potential equalization
EMC analysis transient DC voltage 24 V
EMC Analysis Central Earthing Point ZEP
EMC analysis earthing measurement
Typical causes – practical examples
| Caused | Description | Example |
| Multi-point earthing | Unwanted current paths between multiple grounding points | Data lines cause return currents via PE |
| Frequency converter | Injection of harmonics and supraharmonics (clock frequencies) | PE currents > 1 A when several FIs are operated simultaneously |
| Loop formation | Induced currents caused by cable laying in loops | EMC interference at PLC inputs |
| Poor shield connection | Capacitive coupling in control lines | False triggering of proximity sensors |
Measures to reduce compensating currents
- Conversion from TN-C to TN-S network system
- Optimize potential equalization (e.g. avoid loops)
- Use of isolation transformers or decoupling filters
- Improvement of shielding technology (360° contacting)
- Use of EMC filters
Conclusion
Transient currents are an often underestimated risk to the safe operation of industrial plants. A thorough EMC analysis offers the key to determining the cause and finding sustainable solutions. It's important to remember that every plant is unique, and standard solutions rarely help. This requires experienced specialists, measurement technology, and a deep understanding of the physical relationships in the industrial power grid.
Contact us for a EMC analysis for industry & infrastructure by PQ ENGINEERING – practical, on-site worldwide and solution-oriented.
