Reactive power and power factor: why it shows up on the bill and how to compensate it correctly in Moldova and Romania

What reactive energy is

Induction motors, transformers, chokes and ballasts need a magnetic field in order to work. The energy of this field flows back and forth between the grid and the equipment 100 times a second without being converted into mechanical work or useful heat — this is reactive energy (kvarh). The power that does useful work is active power P (kW); the power that actually loads cables and transformers is apparent power S (kVA):

The lower cos φ is, the higher the current for the same useful power. Losses in cables and in the transformer grow with the square of the current, and the voltage drop grows in proportion to it. In the example above, raising the power factor from 0.75 to 0.95 cuts the current by 21% and the Joule losses by 38% — with no change in production.

The opposite, capacitive regime appears with overcompensation, with long medium-voltage cables running unloaded or with many electronic power supplies, and in Romania it is charged in the same way as the inductive regime.

How reactive energy is billed in Romania

The rules are set by the Methodology approved by ANRE Order No. 33/2014, as amended by ANRE Order No. 76/2016:

• the limit power factor is 0.9, for both the inductive and the capacitive regime (Art. 9);
• only the reactive energy above the value corresponding to this limit is paid for, calculated separately for each settlement interval and delimitation point;
• if the average power factor is between 0.65 and 0.9, the regulated price applies; below 0.65 — three times the regulated price (Art. 11);
• the regulated price is approved by ANRE for each distribution operator's concession area;
• household customers with approved power of up to 30 kW do not pay for reactive energy (Art. 8).

Example: in one month a factory draws 200 MWh of active energy and 176 Mvarh of inductive reactive energy from the grid — the power factor is 0.75. The free allowance is 200 × 0.484 = 96.9 Mvarh; 79.1 Mvarh is billed at the regulated price. If the power factor fell to 0.6, 169.8 Mvarh would be billed, and at triple the price.

How it is billed in the Republic of Moldova

In Moldova, a low power factor is billed not in kvarh but as additional active energy — the technological consumption (losses) in the network caused by reactive energy flow. The Regulation on electricity supply (ANRE Decision No. 169/2019) provides that:

• the technological consumption caused by the power factor of a non-household consumer's installations is calculated according to the Instruction approved by ANRE Decision No. 89/2003 (point 83);
• it is billed only if cos φ, calculated at the delimitation point, is below 0.92 for installations connected at 0.4 kV and below 0.87 at 10(6) kV (the mandatory clauses of the supply contract, points 3.5 and 10.5);
• the regime for capacitive reactive energy and for compensation equipment — its power and the hours when overcompensation is allowed or forbidden — is set by the system operator in the annex to the contract;
• if the meter is not installed at the delimitation point, the losses in the consumer's transformers and lines are added (ANRE Decision No. 246/2007).

How large the compensation should be

For 400 kW and a rise from 0.75 to 0.95: Q_C = 400 × (0.882 − 0.329) ≈ 221 kvar. The target is usually set slightly above the limit on the bill — 0.95 instead of 0.9 or 0.92 — because the load varies over time.

Which type of compensation

• Fixed, at the motor or at the transformer — for constant loads. On motors, the capacitor rating must not exceed the motor's no-load reactive power, so that the motor does not self-excite when it is disconnected.
• Automatic, in steps, at the main switchboard — the controller switches steps in and out according to the load. This is the usual solution for industrial sites.
• Detuned, with blocking reactors — when there are harmonics in the network.
• Active filters or static var generators (SVG) — for loads that change very quickly (welding, cranes, furnaces) or with high harmonics; they regulate continuously, without steps.

Harmonics and the danger of resonance

Variable-frequency drives, rectifiers, UPS units and LED drivers draw non-sinusoidal currents, with 5th, 7th, 11th and 13th harmonics (250, 350, 550, 650 Hz). A capacitor's impedance is inversely proportional to frequency, so it “attracts” these currents. Together with the transformer's inductance it forms a circuit that resonates at a frequency close to:

Example: a 1,000 kVA transformer with u_k = 6% gives a short-circuit power of about 16.7 MVA at the 0.4 kV busbars. With a 400 kvar capacitor bank, f_r ≈ 50 × √(16,700 / 400) ≈ 323 Hz — between the 5th and the 7th harmonic, exactly where drives produce the most. The result: high currents through the capacitors, overheating, blown fuses and voltage distortion.

The classic solution is a reactor in series with each step. With a 7% detuning factor, the tuning frequency is 50 / √0.07 ≈ 189 Hz: above it the step behaves inductively and can no longer resonate with the 5th, 7th and higher harmonics. When harmonics also have to be reduced, not just avoided, active filters are used.

Voltage quality limits are set by the EN 50160 standard (for example, total harmonic distortion of the voltage of at most 8% in low- and medium-voltage networks), and measurement is done with class A analysers according to IEC 61000-4-30.

Why reactive energy rises after solar panels are installed

A solar PV system for self-consumption reduces the active energy drawn from the grid, but the motors still need the same reactive energy, and inverters usually run at a power factor close to 1. At the connection point, the ratio of reactive to active energy rises.

Example: before the panels, a factory draws 200 MWh and 96 Mvarh from the grid — a power factor of 0.90, right at the limit, nothing to pay in Romania. After the panels cover 80 MWh, 120 MWh comes from the grid along with the same 96 Mvarh: the power factor falls to 0.78, and 37.9 Mvarh of reactive energy appears on the bill.

The solutions: resizing and reprogramming the compensation, using the inverters' ability to produce reactive power (if the connection permit allows it) or a static var generator. That is why, in our solar PV projects for businesses, checking the power factor is part of the study.

The steps of a compensation project

1. A class A measurement at the main switchboard, usually for a week: powers, power factor, current and voltage harmonics, unbalance, events.
2. Analysis of the bills for at least 12 months and of the contract rules.
3. Sizing: total power, the number and size of steps, the type (standard, detuned, active), the installation point.
4. Installation and commissioning, with the controller settings and the capacitor discharge times adjusted.
5. A verification measurement after installation and maintenance: capacitors gradually lose capacitance, contactors wear out, and thermography reveals overheated connections early.

We carry out power quality measurements with a class A analyser, size compensation and harmonic filtering and provide maintenance and thermography for the installations.

Frequently asked questions

Sources and references

1. ANRE Romania — Methodology for setting payment obligations for reactive electricity (Order No. 33/2014, consolidated) — in Romanian
2. Despre-energie.ro — ANRE Order No. 76/2016 on payment for reactive energy — in Romanian
3. ANRE Moldova — Regulation on electricity supply, Decision No. 169/2019 — in Romanian
4. Legis.md — ANRE Decision No. 89/2003, Instruction on calculating technological electricity consumption — in Romanian
5. Premier Energy — Instruction on calculating technological electricity consumption in distribution networks — in Romanian