⚡ Article summary in 45 seconds
- Power quality disturbances – voltage dips, surges, higher harmonics and unbalance – account for 15–40% of unplanned production line stoppages in Polish industrial plants, according to EAB Solutions power quality audits.
- BESS improves power quality, but not equally effectively in all scenarios. Systems with fast PCS (Power Conditioning System) respond to dips and surges in under 20 ms. For harmonic distortion and phase unbalance BESS without an active power filter will not help at all.
- Plants that did not perform a power quality (PQ) analysis before BESS deployment often buy a system that solves only part of the problem (EAB Solutions estimate based on pre-project documentation review from over 60 deployments). Full diagnosis costs PLN 5,000–12,000 and is a prerequisite for correct technology selection.
- EN 50160 describes power quality parameters at the grid connection point – but does not guarantee quality deep inside the plant installation. Disturbances often come from the plant's own equipment: VFD drives, induction furnaces, rectifiers, welders.
- EAB Solutions combines PQ analysis with BESS and active filter design – one deployment can simultaneously eliminate contracted-power penalties and disturbances that reset controls and shorten drive lifetime.
Table of contents:
- What is power quality (PQ) and why is it not just electricians' business?
- PQ threat map in an industrial plant – what generates disturbances and where
- What does poor power quality cost? Figures from audits
- When BESS improves power quality – and when it does not
- Case study #1: Automotive plant – voltage dips and robot resets
- Case study #2: Plastics producer – VFD harmonics and drive damage
- Case study #3: Industrial cold store – phase unbalance and motor overheating
- What does a power quality audit look like and what comes after?
- FAQ – frequently asked questions
What is power quality (PQ) and why is it not just electricians' business?
Power quality (PQ) is the set of parameters describing how closely voltage and current at a point in the installation match nominal values – in terms of amplitude, frequency, waveform shape and phase symmetry. In simple terms: good power quality means production equipment receives exactly the energy it needs to operate to specification.
The problem is that no power network – public or in-plant – delivers ideal energy. Voltage fluctuates, brief dips and surges occur, current contains harmonics from electronic equipment, phases are unbalanced. EN 50160 defines acceptable disturbance levels at the point of connection to the public grid. It does not regulate what happens inside the plant installation.
That is why PQ is not a topic only for maintenance electricians. It is a financial problem affecting the production director (downtime), chief technologist (scrap), maintenance manager (shorter drive life) and CFO (costs). A plant where PLC controllers reset every few weeks, a welder cannot hold arc parameters, or VFD drives trip on protection faults – probably has a power quality problem. And probably does not know it yet, because nobody measured grid parameters with a Class A analyzer for long enough.
PQ threat map in an industrial plant – what generates disturbances and where
Power quality disturbances have two sources: external (DSO grid) and internal (the plant's own equipment). In industrial practice internal sources dominate – and are harder to control because the plant is both their creator and victim.
| Disturbance type | Standard / parameter | Typical sources in plant | Production impact | Mitigation method |
|---|---|---|---|---|
| Voltage dip duration: 10 ms – 1 min amplitude: >10% Un |
EN 50160 IEC 61000-4-11 |
Large motor start-ups, grid faults, ATS switching | PLC reset, VFD trip, robot stop, loss of process parameters | BESS with PCS <20 ms, industrial UPS, ATS with BESS as switching buffer |
| Momentary surges (transients) duration: <1 ms amplitude: up to several times Un |
EN 61000-4-5 | Lightning, capacitor switching, switching operations in switchgear | Drive insulation damage, controller errors, shorter converter life | SPD surge protectors in 3-level cascade: Class I (infeed, before/after transformer – lightning protection), Class II (main switchboard – switching surges), Class III (end equipment – drives and PLC protection). Omitting any level reduces effectiveness of the others. BESS does not protect against transients. |
| Higher harmonics voltage THD >8% |
EN 50160 IEC 61000-3-2 |
VFD drives, 6- and 12-pulse rectifiers, UPS, chargers, induction furnaces | Motor and transformer overheating, false protection trips, energy metering errors | Active power filter (APF), passive LC filter, 12/18-pulse drives or drives with input filter |
| Voltage unbalance >2% per EN 50160 |
EN 50160 IEC 61000-2-2 |
Uneven phase loading, large single-phase loads, grid faults | 3-phase motor overheating (10–25°C rise), shorter life, vibration | Phase load balancing, static var compensator (SVC), BESS with phase balancing function |
| Voltage flicker Pst >1.0 |
EN 50160 IEC 61000-4-15 |
Arc welders, EAF arc furnaces, rolling mills, cyclic presses | Lighting flicker, vision sensor errors, measurement system interference | BESS with fast PCS (FFR mode), StatCom, synchronous var compensator |
| Supply interruptions duration: >1 min |
EN 50160 / SAIDI | DSO grid faults, own transformer station faults, protection trips | Production stop, batch loss, restart required | BESS as support until generator start or ATS; covered in more detail in articles on production continuity |
Key observation:
BESS with fast PCS effectively eliminates voltage dips, flicker and brief outages. For higher harmonics and momentary surges BESS will not help – active power filters or SPD protectors are needed. Technology choice must be preceded by measurement – otherwise the plant invests in a tool for a problem it does not have and lacks a tool for the problem that generates cost.
What does poor power quality cost? Figures from audits
The cost of poor power quality is usually spread across several lines in the plant's accounts and visible in none of them as a separate item. That keeps it unidentified – and unaddressed – for years.
| Cost category | Mechanism | Typical annual cost (plant 1–5 GWh) | Identifiability without PQ measurement |
|---|---|---|---|
| Unplanned downtime from controller resets and drive trips | Voltage dip or disturbance impulse causes PLC reset or VFD protection fault; line restart takes 20–120 minutes | PLN 15,000–90,000 | Low – events logged as 'equipment failure', not 'grid problem' |
| Accelerated wear and VFD replacement | Current THD above 15–20% shortens DC-link capacitor and IGBT lifetime by 30–50% | PLN 20,000–80,000 | Very low – costs visible in maintenance as 'normal repairs' |
| Motor overheating and shortened life | 3–5% voltage unbalance increases rotor losses and winding temperature by 10–25°C; insulation life drops 30–50% | PLN 10,000–50,000 | Low – visible only when motor replaced before end of life |
| Scrap and rejects in energy-sensitive processes | Voltage variation during welding, powder coating, injection moulding – process parameter change without setpoint adjustment | PLN 30,000–200,000 | Very low – cost included in 'normal' scrap level |
| Faulty energy metering and reactive power overpayment | Harmonics cause meter errors and false reactive power reading; plant pays for reactive power it does not produce | PLN 5,000–25,000 | Low – requires energy balance analysis |
| Penalties for emitting disturbances to DSO grid | Plants exceeding THD and unbalance limits per EN 61000-3-12 may receive orders to eliminate disturbances or face contractual penalties | PLN 0–60,000 | Low – appears only after DSO intervention |
Total potential cost of poor power quality: in plants where EAB Solutions performed a full PQ audit, identifiable costs related to power quality totalled PLN 40,000–450,000 per year – with over 70% of those costs not previously attributed to grid problems.
When BESS improves power quality – and when it does not
This is the question that should precede every BESS deployment decision in a PQ context. Energy storage is not a universal disturbance filter – its effectiveness depends on disturbance type, system parameters and technical configuration.
| PQ problem | Does BESS help? | Conditions for effectiveness | Alternative or complement |
|---|---|---|---|
| Voltage dips (10 ms – 1 min) | YES – effective | PCS with response time <20 ms (FFR mode); capacity sized for support time until ATS or generator | Industrial UPS for individual critical devices |
| Short supply outages (<1 min) | YES – effective | As above; BESS takes over supply before generator start | ATS with reserve transformer |
| Voltage flicker from arc furnaces | YES – with FFR | Dedicated PCS in fast reactive power regulation mode; BESS must support StatCom (Q-compensation) operation | StatCom, synchronous compensator; consultation with furnace manufacturer |
| Higher harmonics (THD >8%) | NO – alone | BESS without active filter does not eliminate harmonics; may slightly damp them in island mode | Active power filter (APF) – up to 50th harmonic; passive LC filter for specific harmonics |
| Momentary surges (transients <1 ms) | NO | BESS response time (even FFR) is too slow for sub-millisecond impulses | SPD cascade: Class I (infeed – lightning), Class II (main switchboard – switching surges), Class III (end equipment – drives, PLC). Each level protects different equipment and does not replace the others. |
| Phase voltage unbalance | PARTIALLY | BESS with advanced PCS and phase management algorithm can actively correct unbalance – requires dedicated configuration and specification at order | Static var compensator (SVC/StatCom) with separate phase control |
| Frequency variation | YES – off-grid | In island mode BESS with V/f inverter maintains stable frequency; in grid-connected mode frequency is set by the TSO | Not applicable to standard plants connected to the public grid |
Practical selection rule: if the main problem is voltage dips and brief outages – BESS with FFR is the optimal choice. If harmonics or surges dominate – BESS will not help without an active filter or SPD. If the plant has a combination of problems (the rule, not the exception) – the project must include several technologies. A PQ audit determines which.
Case study #1: Automotive plant – voltage dips and robot resets
| Industry | Automotive components (stamping, welding, assembly) |
|---|---|
| Location | Lower Silesia voivodeship |
| Contracted power | 1,800 kW |
| Annual consumption | 8.2 GWh |
| Tariff | B23 (supply from 15 kV MV grid) |
| PQ problem | Voltage dips to 65–80% Un, duration 80–400 ms, frequency: 3–5 events per month |
| Solution deployed | BESS 800 kWh / 600 kW with PCS in FFR mode (<15 ms response) |
Problem
The robotic welding line (12 robots, Fanuc control) entered alarm state three to five times a month after a brief voltage dip on the MV grid. Line reset, robot recalibration and weld inspection after stop took 90–150 minutes total. With three shifts and downtime cost PLN 2,200/h, one event cost PLN 3,300–5,500. Annually: PLN 120,000–275,000 – on that line alone.
Previous approach: replace robots with a newer model more resistant to dips (solution: PLN 1.4 million), buy UPS at each station (solution: PLN 320,000, ineffective for the whole line), accept costs as permanent operational risk. None of these options was implemented.
Deployment
A 30-day Class A PQ audit identified dip sources: compressor start-ups in the adjacent hall (plant's own equipment) and switching on the distributor's MV line. BESS 800 kWh with FFR-mode PCS was designed: the system detects a dip within 5 ms and within the next 10 ms delivers full discharge power, maintaining voltage on plant busbars until the grid stabilizes or ATS takes over.
Rationale for 800 kWh / 600 kW sizing: for dip protection alone marginal capacity would suffice – the longest dip lasted 400 ms, which at 600 kW is approx. 0.07 kWh of energy. 800 kWh capacity was chosen considering peak-shaving function (peaks lasting 10–30 minutes) and reserve for planned plant expansion. A 400 kWh system with the same FFR PCS would be equally effective for PQ protection – but insufficient for peak shaving. Both functions in one system justify the larger capacity.
Results after 12 months
| Indicator | Result |
|---|---|
| Welding line reset count | 38 → 0 (complete elimination) |
| Downtime savings | PLN 130,000–195,000/year |
| Additional effect: peak shaving | Elimination of 6 contracted power exceedance penalties: PLN 72,000/year |
| Total annual savings | PLN 202,000–267,000/year |
| BESS system CAPEX | PLN 1,150,000 |
| Simple payback | 4.3–5.7 years (without subsidy); 2.6–3.4 years with 40% subsidy |
Lesson from deployment: for two years the plant considered replacing robots as the solution – costing PLN 1.4 million without eliminating the cause. A PQ audit for PLN 8,500 showed grid dips were the source and BESS with FFR eliminates the problem definitively at lower CAPEX with added peak-shaving benefit. The order should always be: diagnosis → design → equipment.
Case study #2: Plastics producer – VFD harmonics and drive damage
| Industry | Plastics production (extrusion, injection moulding) |
|---|---|
| Location | Silesia voivodeship |
| Contracted power | 900 kW |
| Annual consumption | 4.1 GWh |
| Tariff | B23 |
| PQ problem | Voltage THD: 9.8–13.2% (EN 50160 limit: max 8%); current THD: 22–31% |
| Solution deployed | Active power filter (APF) 400 A + EMS with PQ monitoring |
Problem
The plant operated 24 injection moulding machines and 8 extruders, each with a VFD drive. As production scale grew, harmonics from drives exceeded the internal grid's ability to absorb them. Voltage THD at the main switchboard reached 13.2% – 65% above the EN 50160 limit.
Effects: three VFD drives in 18 months required input transformer or IGBT module replacement (cost: PLN 35,000–65,000 each); two distribution transformers showed winding temperature 18–22°C above nominal near alarm threshold; main meter readings showed capacitive reactive power for which the plant paid penalties.
Important design note: the plant considered buying BESS as the solution. Preliminary analysis showed BESS without active power filter would not eliminate harmonics – and their level was the main problem. BESS would have been investment solving a different problem (peak shaving), not the one generating cost.
Deployment
A 400 A active power filter (APF) with correction up to the 50th harmonic was installed, integrated with an EMS monitoring THD in real time. In the second phase – after power quality stabilized – BESS 400 kWh was installed for peak shaving.
Why APF, not 12/18-pulse drives? Multi-pulse drives or drives with LCL input filter eliminate harmonics at source – optimal when buying a new machine park. The plant operated 32 machines bought in different years; replacing all with 12-pulse versions would cost PLN 2.4–3.8 million with months of line downtime. APF as a single switchboard device cost PLN 280,000 and worked from commissioning day without production intervention. For new investments or planned drive replacement we recommend considering 12/18-pulse versions as source-level elimination.
Results after 12 months
| Indicator | Result |
|---|---|
| Voltage THD after APF | 13.2% → 4.1% (below EN 50160) |
| VFD failure rate | 3 replacements/18 months → 0 in first year after deployment |
| Drive repair savings | PLN 70,000–130,000/year |
| Reactive power penalty elimination | PLN 18,000/year |
| Peak-shaving savings (BESS) | PLN 55,000/year |
| Total savings | PLN 143,000–203,000/year |
| CAPEX (APF + BESS + EMS) | PLN 720,000 |
| Simple payback | 3.5–5.0 years |
Lesson from deployment: BESS without APF was not the solution to harmonics – it would have been spending on a tool for a different task. Correct order: PQ audit → identify dominant problem → select technology. Here harmonics dominated, so APF was the first investment. BESS added in phase two and added value but did not replace the filter.
Case study #3: Industrial cold store – phase unbalance and motor overheating
| Industry | Refrigeration and cold logistics |
|---|---|
| Location | Mazovia voivodeship |
| Contracted power | 1,100 kW |
| Annual consumption | 5.3 GWh |
| Tariff | B23 |
| PQ problem | Voltage unbalance: 2.8–4.1% (EN 50160 limit: max 2%); compressor motor winding temperature +18–24°C above nominal |
| Solution deployed | Phase load balancing + EMS with unbalance monitoring + BESS 500 kWh for peak shaving |
Problem
The cold store operated 31 screw compressors powered by 15–75 kW 3-phase motors. Maintenance reported repeated winding overheating, premature bearing replacement and two winding burnouts in 24 months. In-house diagnosis pointed to 'poor motor quality' – without measuring grid parameters.
PQ audit showed voltage unbalance of 2.8–4.1% – exceeding EN 50160. At 3% unbalance a 3-phase motor generates negative-sequence current causing extra rotor losses equivalent to 10–25°C winding temperature rise (depending on load). A 10°C temperature rise cuts insulation life by approx. 50% (Arrhenius rule – for Class F insulation, 155°C rating, at rated load; Class H insulation has 180°C rating and somewhat less impact from the same temperature delta). The plant replaced motors without knowing it was putting them in an environment that destroys them faster.
Deployment
The first step was redesigning phase load distribution – moving some compressors to other circuits and balancing phase draw to unbalance below 1.5%. This step was investment-free (design work and electrician labour) and reduced unbalance from 4.1% to 1.8%. In the second phase EMS with continuous PQ monitoring on the main switchboard and BESS 500 kWh for peak shaving on compressor start-ups was installed.
Results after 18 months
| Indicator | Result |
|---|---|
| Voltage unbalance after phase balancing | 4.1% → 1.8% (below EN 50160) |
| Compressor winding temperature | Reduction of 14–20°C; all within nominal range |
| Motor failures (18 months before / after) | 3 winding burnouts → 0; bearing replacements: 8 → 2 |
| Service and replacement savings | PLN 45,000–85,000/year |
| Peak-shaving savings (BESS) | PLN 78,000/year (contracted power renegotiation 1100 → 920 kW) |
| Total savings | PLN 123,000–163,000/year |
| Deployment cost (design + EMS + BESS) | PLN 580,000 |
| Simple payback | 3.6–4.7 years |
Lesson from deployment: the first step – phase load balancing – cost a few thousand zloty for design and electrician work and brought immediate unbalance reduction. It was only possible because PQ audit identified the problem. Without measurement the plant would have kept replacing motors for years, blaming the manufacturer. BESS in this case was a complement – valuable, but not the first tool.
What does a power quality audit look like and what comes after?
A power quality (PQ) audit is measurement of the plant's electrical grid parameters using a Class A analyzer (per IEC 61000-4-30 Class A) for long enough to capture a representative set of events. Minimum measurement period is 7 days (full production week); for plants with seasonal production profile or repeating cycles – 30 days.
| PQ audit stage | Scope | Time |
|---|---|---|
| 1. Installation inventory and UR interview | Identify disturbance-generating equipment (VFD, furnaces, welders), failure and report history, main switchboard layout | 1 day |
| 2. Class A analyzer installation | Analyzer on main switchboard; optional sub-meters on key circuits (production lines, compressor rooms) | 0.5 day |
| 3. Measurement campaign | Continuous recording of 10-minute EN 50160 aggregates + events (voltage dips, transients, harmonics); data export every 7 days | 7–30 days |
| 4. Analysis and report | EN 50160 parameter summary, exceedance identification, correlation of PQ events with maintenance downtime logs, technology recommendation and economic justification | 3–5 days |
| 5. Presentation and design | Results review with management and maintenance; solution design (APF, BESS, SPD, phase balancing) with CAPEX and estimated ROI | 1 day |
| Parameter | Value |
|---|---|
| PQ audit cost (plant 0.5–10 GWh) | PLN 5,000–12,000 net for one measurement point (Class A analyzer, 7–30 day campaign, report). Multi-hall plants or those with several switchboards / own GPZ substation need several analyzers in parallel – individual quote, typically PLN 12,000–25,000. |
| Time from order to final report | 3–5 weeks |
| Measurement standard | IEC 61000-4-30 Class A; reporting per EN 50160 |
| Is PQ audit required for subsidies? | Not a formal KPO/NFOŚiGW document (EN ISO 50002 audit is required), but forms part of the energy audit measurement campaign and can run in parallel |
| What if results are within limits? | Plant receives confirmation that power quality is not the problem source; attention shifts to other areas (production schedule, equipment maintenance) |
PQ audit as a tool in relations with the DSO
PQ audit serves not only internal diagnosis – it can be an instrument in relations with the distribution system operator. If measurement shows disturbances (dips, unbalance, surges) originate in the DSO grid, the plant has grounds to file a formal non-compliance complaint under EN 50160 and connection agreement terms.
Possible actions: quality complaint to the DSO with Class A analyzer documentation (only Class A is accepted as contractual evidence); demand parameter improvement within a set deadline; in extreme cases – claim compensation for damaged equipment and downtime. A PQ audit costing around PLN 8,000 can be a prerequisite for recovering tens of thousands of zloty from the distributor – worth knowing before deciding that investment in APF or BESS lies entirely on the plant side.
Is your plant losing money on poor power quality – without knowing it?
Free preliminary PQ risk assessment in 48h – based on failure history and energy bills.
- PQ audit with Class A analyzer – identify the problem before deciding on BESS or APF.
- Integrated design: BESS + APF + EMS in one project process, with subsidy analysis.
→ info@eabsolutions.com.pl | ul. Domaniewska 44, 02-672 Warsaw
FAQ – frequently asked questions
Not automatically – it depends on technical specification and system configuration. A standard container LFP system with a conventional PCS (response time 100–500 ms) is effective for peak shaving but too slow to eliminate voltage dips lasting 80–400 ms. BESS with a dedicated PCS module in FFR mode (Fast Frequency Response, response <20 ms) works as both a peak-shaver and protection against dips. When ordering a system you must specify PQ requirements – and require written confirmation of response-time parameters from the supplier.
Warning signs that should prompt a PQ measurement: PLC controller resets or VFD trips without an obvious mechanical cause; VFD drives requiring replacement more often than every 5–7 years; transformers running at elevated temperature; motors wearing bearings or overheating; flickering lighting in the hall; reactive power penalties on the bill despite installed capacitor banks; quality variations in energy-sensitive processes (welding, powder coating, injection moulding). Each symptom alone may have other causes – but a combination of two or more almost always points to a PQ problem.
No – and that is a key misunderstanding. EN 50160 regulates power parameters at the point of connection to the public DSO grid – the boundary between the distributor and the plant. It says nothing about what happens inside the plant installation. The plant's own equipment (VFD drives, induction furnaces, welders) is often the main source of disturbances while the DSO grid may deliver acceptable power that the plant then degrades itself. EN 50160 compliance at the plant boundary and a 'good result' do not rule out serious PQ problems inside the installation.
Yes – and it is the recommended configuration for plants with a combination of harmonics and dips/power exceedances. APF runs continuously, eliminating harmonics from VFD drives and rectifiers. BESS runs cyclically (charge/discharge), handling peak shaving and support during dips. Both systems can be managed by a common EMS that optimizes their cooperation. The key is proper specification of the point of common coupling (PCC) and coordination of control algorithms – a task for the system designer, not separate APF and BESS suppliers.
Important technical note: APF changes the current waveform shape at the PCC, which can affect BESS control algorithms – especially in FFR mode, which relies on continuous current and voltage measurement. Poor coordination can lead to mutual regulator oscillation or false protection trips. This risk is eliminated by a common regulation bandwidth specification for both systems and one designer responsible for the whole – not two separate orders glued together with integration at the end.
A PQ audit with a Class A analyzer, 7–30 day measurement campaign and EN 50160 report costs PLN 5,000–12,000 net for plants with consumption of 0.5–10 GWh. A reliable audit requires a Class A analyzer (not Class B or S) – only Class A records sub-millisecond events and meets IEC 61000-4-30 requirements for contractual and claims purposes. EAB Solutions delivers PQ audit as part of a comprehensive energy analysis – results feed both EMS/BESS design and the EN ISO 50002 audit required for subsidies.
Yes – and this question comes up often. UDT acceptance and acceptance tests (ATB) confirm compliance of the installation with the design and regulations: correct connections, earthing protection, protection operation. They do not measure power quality under real production conditions. A new installation can be accepted without technical objections and still generate 11% THD from day one when all VFD drives start together. UDT acceptance and PQ audit answer different questions – and both are needed for a full picture.
Yes – although in Poland the enforcement mechanism is still relatively rarely applied in practice. EN 61000-3-12 (for equipment >16 A/phase) and individual DSO connection conditions set maximum harmonic and unbalance emission levels. If limits are exceeded the DSO may require the plant to eliminate disturbances within a set deadline, and if not – impose additional charges or limit connection capacity. For plants with large arc furnaces, welders or electrolysis lines the risk is higher and worth assessing proactively before distributor intervention.
See also
Why Monitoring Is Not Enough – How Intelligent Energy Management (EMS) Differs from Classic Measurement Systems
Visualizing energy consumption alone won't lower bills. Classic monitoring shows how much and when you consume energy. Intelligent Energy Management System (EMS) goes a step further: it forecasts, decides and controls devices in real-time.
Why energy monitoring is no longer enough in a production plant
Monitoring consumption is a good starting point, but in the reality of industry it is far from sufficient. An intelligent EMS will stop costs that a consumption chart alone will not.
Energy Prediction in Industry – How Algorithms Predict Peaks and Energy Prices
Rising energy costs, tariff sensitivity, and the growing role of renewables mean industrial plants must act faster, more precisely, and more consciously. Energy prediction enables cost reduction, production stabilization, and limiting the impact of price fluctuations.