Scope
- Existing system: current measurement of capacitor steps, reactive power controller settings, condition of contactors and fuses.
- Measurement: reactive power, power factor and harmonic profile; step requirements, rate of load change and resonance risk.
- Design: step arrangement (kVAr), detuned compensation, static (thyristor-switched) compensation for fast-changing loads, shunt reactors against capacitive excess.
- Commissioning: controller settings and verification measurement; checks of inductive and capacitive ratios.
- Daily tracking: in the Energy Monitoring Portal, inductive and capacitive ratios are updated every day from OSOS data; exceeding or approaching a limit appears as an alert in the portal.
Method and instruments
A Kyoritsu KEW 6315 recording covering a typical working week gives the reactive power, power factor and harmonic profile; step sizes are chosen from the smallest and largest reactive demand of the load.
The need for filtering is determined from the measured voltage and current harmonics and a resonance frequency calculation. If capacitors resonate with the network inductance at a harmonic frequency, harmonic currents and voltages are amplified and the capacitors fail quickly; detuned steps prevent this.
Hourly OSOS data shows the reactive behaviour in the months outside the measurement week; night-time and weekend capacitive excess is found with this data.
Regulations and standards
- TS EN 60831-1, -2Shunt power capacitors of the self-healing type for LV systems
- TS EN 61921Low-voltage power factor correction banks
- TS EN 61439-1, -2Low-voltage switchgear assemblies
- IEEE 519Recommended harmonic limits
- EPDK tariff rulesReactive energy limits and charges
Deliverables
- Measurement and compensation calculation report: reactive demand, step arrangement, filter selection, resonance check
- Board single-line diagram and bill of materials
- Verification measurement after commissioning: cosφ, inductive and capacitive ratios, THD
- Daily reactive ratio tracking and alerts for Energy Monitoring Portal users
Frequently asked questions
Why do reactive energy charges occur?
When the ratio of inductive or capacitive reactive energy to active energy exceeds the limit. The most common causes are faulty or insufficient steps, wrong controller settings, capacitors left connected at low load at night and at weekends (capacitive excess) and capacitors degraded by harmonics.
How is capacitive excess prevented?
Fixed capacitors that stay connected at low load and long cables generate capacitive energy. The step arrangement and controller settings are adjusted for low load and, if needed, a shunt reactor is added. Hourly reactive OSOS data shows the hours in which the excess occurs.
Do we need a harmonic filter?
If loads such as variable speed drives, UPS, LED lighting and charging units have a high share and the measured voltage THD is rising, capacitors are selected with detuning reactors. The decision is based on the measured harmonic spectrum and a resonance calculation.