Published on July 9, 2026 at 2:11 PM
Industrial electricity bills consist of at least two line items. The first, active energy in kWh, is something every plant manager understands. The second, reactive energy in kVArh, is often ignored until the utility’s invoice shows a reactive power penalty for the first time and the amount exceeds 20-30% of the total bill. Only then does the need for a power analyzer like the Extech PQ3450 arise: not to measure more electricity, but to understand WHAT KIND of current the plant is drawing, how it is split into active, apparent and reactive power, and where compensation measures (reactive power capacitors, active filters) make economic sense.
Active, Reactive and Apparent Power: The Three Types of Power
With purely resistive loads (incandescent lamps, heating), current and voltage are in phase. The power consumed is called active power (P, measured in watts): P = U × I × cos(φ), where φ = 0° and cos(φ) = 1.
With inductive loads (motors, transformers, fluorescent lamp ballasts), the current lags behind the voltage. The phase angle φ is no longer 0. The apparent power S (in VA) supplied by the grid is greater than the active power P actually consumed. The difference is called reactive power Q (in VAr): Q = U × I × sin(φ).
The mathematical relationship: S² = P² + Q², the „power triangle.“ The power factor cos(φ) = P/S indicates how efficiently the grid is working for the load.
Why Utilities Charge for Reactive Power
Reactive current also flows through the transmission lines. It causes losses (copper losses due to resistance) and takes up capacity that other customers could use. To give industrial customers an incentive to minimize their reactive current draw, German utilities typically charge as follows:
- Active energy (kWh): Price per unit.
- Reactive energy (kVArh): An additional charge applies once the ratio of reactive to active energy exceeds 0.5 (corresponding to cos φ = 0.89).
Consumers with a cos(φ) below 0.89 therefore pay TWICE: once for active energy and once for the „excess“ reactive energy. A motor-heavy plant with a cos(φ) of 0.72 typically sees reactive power costs of 30-40% on top of the active power bill.
What the PQ3450 Measures
The Extech PQ3450 is a 3-phase power analyzer that measures up to 35 parameters simultaneously:
- Voltages: Phase-to-phase (400 V nominal), phase-to-ground (230 V).
- Currents: Phase-to-ground for all three phases.
- Active power P: Per phase (P1, P2, P3) and for the total system.
- Apparent power S: Per phase and for the system.
- Reactive power Q: Per phase and for the system.
- Power factor PF = cos(φ): Per phase and for the system.
- Energy counters: kWh, kVAh, kVArh, cumulative over the measurement period.
- Phase angle: For each phase separately.
- Harmonics: Up to the 50th order (2nd to 50th harmonic).
- Unbalance: Between the three phases.
Flexible Current Probes: The 1200 A Clamp
The PQ3450 comes with flexible Rogowski current probes (selectable 200 A, 1200 A or 3000 A). Rogowski probes are flexible cables that are wrapped around the conductor being measured. Unlike rigid clamp-on jaws, they have no fixed opening and can also encircle thick busbars.
For industrial customers with a 100-800 A main supply line, the 1200 A version is standard. Larger facilities (aluminum electrolysis, steel mills) use the 3000 A version.
Adjustable Ratios for High-Voltage Systems
For measurements on medium-voltage systems (10-30 kV) directly at the grid connection point, external current transformers (CT) and voltage transformers (PT) are used to step the signals down. The PQ3450 has adjustable CT ratios (1 to 600) and PT ratios (1 to 1000), so the display shows the actual grid voltage and current rather than the transformed values.
Practical example: a 20 kV grid connection with a PT ratio of 100:1 and a CT ratio of 400:5. Once configured in the PQ3450, the display shows 20 kV rather than 200 V, along with the actual system current in amperes.
Datalogger: 30,000 Readings on an SD Card
For reactive power compensation studies, a spot measurement is not enough. You need to record the load profile over 24-48 hours to determine the average and maximum reactive current. The PQ3450 logs to an SD card in Excel format with timestamps.
The sampling rate is selectable from 2 seconds to 2 hours. At a 1-minute sampling interval, 30,000 readings are enough for 21 days of continuous recording. When the recording is finished, the SD card is inserted into a PC, and the Excel file can be copied directly into evaluation spreadsheets.
Compensation Calculation
For reactive power compensation, it is not enough to assume that „measured reactive current = required compensation capacitance.“ A calculation is needed:
- Current state: cos(φ_1) = 0.72, active power P = 100 kW → S = 138 kVA, Q = 96 kVAr.
- Target state: cos(φ_2) = 0.95, same active power → new Q₂ = 32.9 kVAr.
- Required compensation power: Q₁ – Q₂ = 96 – 32.9 = 63.1 kVAr.
This calculation is carried out in the Excel file from the logger. An electrical engineer or grid consultant then prepares the order for a reactive power compensator (capacitor bank) rated at 63 kVAr or more.
Where the PQ3450 Delivers the Most Value
Industrial plants with reactive power charges: Initial analysis for compensation planning.
After compensation installation: Verification that the new cos(φ) is actually >0.95 and that no unwanted overcompensation occurs.
Motor-heavy plants: Metal, paper and cement industries with many large induction motors.
Solar photovoltaic systems: Verification that inverters comply with the required grid parameters.
Central UPS systems: Server rooms and data centers.
Harmonics investigations: With electronic loads (frequency converters, switch-mode power supplies), harmonics are the second cost item on the bill.
Wind power plants: Inverter characteristics and grid compliance.
What You Get for Your Money
Extech PQ3450 3-phase power analyzer with datalogger, measures up to 35 simultaneous electrical parameters (voltages, currents, active/apparent/reactive power, power factor, harmonics up to the 50th order, phase angles, unbalance), 1200 A flexible Rogowski current probes, adjustable CT/PT ratios for high-voltage measurements, SD card for recording 30,000 readings in Excel format, selectable sampling rate from 2 s to 2 h, large backlit dot-matrix display, built-in clock and calendar. 3,244 EUR.
Compared with permanently installed power quality analysis systems (Fluke 1748, Chauvin Arnoux CA8336: 8,000-25,000 EUR), the PQ3450 is a portable alternative for occasional measurements and compensation studies. For maintenance teams responsible for optimizing electricity costs, the instrument usually pays for itself within a few months after the first compensation measure is identified.
Learn more: Extech PQ3450 3-Phase Power Analyzer in the Shop →
