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Show all categories Where has all the power gone?
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  6. Where has all the power gone?
  1. Measuring harmonics accurately
  2. Current Sensors and Power Analyzer - Engineered Together
  3. Identify Your Losses Accurately - Across All Frequencies
  4. Tracing Power Losses: Power Analyzer and Current Sensors from a Single Source

Where has all the power gone?

Kai Scharrmann, Roy Hali, Ryuji Nishizawa · 03.06.2025
Power Electronics · 4 min. reading duration

Energy efficiency is essential for creating a low-emission or even carbon-neutral future. It plays a crucial role in the transition from combustion engines to electric vehicles and minimizing the impact of power-hungry AI applications on data center energy consumption. Understanding where power is lost – whether in converters, motors, or data centers – is key to unlocking significant efficiency gains and addressing the growing demand for energy in a sustainable way.

Where has all the power gone?
Kai Scharrmann, Roy Hali, Ryuji Nishizawa
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Active power is the portion of power consumed by a system to perform useful work, such as driving motors, powering machines, or running devices. However, only the main power component directly contributes to this work; the rest, known as harmonic power, is lost as vibration, noise, and heat.

Reducing harmonics is therefore crucial for engineers to minimize energy losses.

Measuring harmonics accurately

A power analyzer calculates the efficiency of an electrical system like a motor or transformer by measuring both the fundamental and harmonic components of power. At high frequencies and high currents, this becomes challenging: accurate measurement requires high-quality current sensors. These sensors must not only maintain accuracy across the entire frequency range, but their phase shift also needs to be known in order to calculate power correctly. To make matters worse, the phase shift of a current sensor is typically frequency dependent. Unless a sensor has a consistent time delay across all frequencies, accurate power measurements are difficult – regardless of the analyzer used.

Figure 1: Active power and harmonics over the frequency band

Current Sensors and Power Analyzer - Engineered Together

What happens if your power analyzer and current sensor combination doesn’t meet high-frequency measurement requirements? When measuring the efficiency of an inverter using SiC semiconductors with a carrier frequency of 50 kHz or higher, your setup might yield efficiency values that exceed reality – sometimes even suggesting efficiencies over 100%. While such an extreme result is an obvious red flag, a more concerning scenario is when the analyzer shows 96% efficiency instead of the true 94% – or 96% instead of the true 98% – due to limitations of the current sensors. This is the real issue: how would you know? The key is to not only rely on the power analyzer's specified accuracies but also consider the current sensors' impact.

As an example, consider the power losses in a motor system. In such systems, harmonics of the main frequency are converted into noise and vibration, which can be identified without direct power measurements. However, high-frequency harmonic power is primarily converted into heat within the motor. Measuring this high-frequency power is challenging due to the motor’s inductive nature: at higher frequencies, the phase angle between voltage and current approaches 90°. Since active AC power is calculated as Voltage × Current × cos(θ), any phase error pushing this phase angle beyond 90° results in a negative measured power loss – appearing as a false gain!

The reason for this inaccurate measurement is an uncompensated phase error of the current sensor. Such phase errors distort the measurement and can lead to incorrect conclusions about a system's energy losses. There is a solution to this: With the right combination of power analyzer and current sensors made for power measurement, phase errors can be corrected ensuring accurate power measurements even for high currents and high frequencies. This lets you know precisely how much power is lost in your system. However, the next crucial question is: where exactly these losses occur – and how to trace them?

Identify Your Losses Accurately - Across All Frequencies

Power analyzers offer various features to determine at which frequencies power losses occur. A traditional method is harmonics analysis, which uses the motor’s main frequency as a base. Since motor main frequencies are typically low, harmonics analysis is generally limited to frequencies below 100 kHz. As an example, with a 50 Hz fundamental frequency, the 2000th harmonic corresponds to 100 kHz – which already marks the practical upper limit for harmonic power analysis in most instruments.

For a comprehensive view of power losses across the entire frequency range, an advanced feature like Power Spectrum Analysis (PSA) is required. PSA uses FFT but isn’t restricted to the main motor frequency; instead, it covers the full frequency range of the power analyzer – up to 6 MHz in the case of HIOKI’s PW8001. As a result, PSA opens up new possibilities for identifying losses that may remain undetected with conventional methods.

Figure 2: Visualize power loss over the frequency band with Power Spectrum Analysis (PSA)

To use the PSA (Power Spectrum Analysis) function effectively, two key conditions must be met:

1. Any phase shift introduced by the current sensors must be accurately compensated by the analyzer.

2. The current sensors must provide a flat amplitude response across the entire frequency range.

When both conditions are met, power losses can be accurately identified across all relevant frequencies.

Figure 3: HIOKI power analyzer and current sensors – engineered from a single source

Tracing Power Losses: Power Analyzer and Current Sensors from a Single Source

Since HIOKI designs, engineers, and manufactures both the power analyzer and current sensors in-house, these components are optimized for high-frequency power measurements. This high level of accuracy provides confidence in precise determination of power loss and pinpointing where power has gone. This is a critical step toward improving energy efficiency in motors, inverters and other power electronics applications.

Find out more about precise power measurement tools

PW8001 - High Precision Power Analyzer PW8001 - High Precision Power Analyzer
PW8001
PW8001 - High Precision Power Analyzer
High precision power analyzer for power converter and inverter efficiency analysis, ±0.03% basic accuracy, 15 MHz sampling rate, 18-bit conversion, automatic phase shift correction for HIOKI current sensors, 1 ms data update rate and excellent noise resistivity of 110 dB @ 100 kHz.Technical details:Basic power accuracy ±0.03%8 power channels combined with motor analysisExcellent noise resistivity of 110 dB @ 100 kHz5 MHz frequency measurement band for powerStable and accurate measurement at 1 ms data update rateFunctions:8 power channels in combination with motor analysis for dual drivetrain analysisUnique power range with 2 A to 2 kA high accuracy HIOKI current sensorsPlug & Play connectivity with HIOKI current sensorsAutomatic Phase Shift Correction secures accurate high-frequency power measurementVisualize high-frequency loss with Power Spectrum Analysis measurementApplications:R&D and production line testing of high efficiency power converters and invertersLoss measurement of transformers and other inductive components under loadMotor efficiency measurementDetailed Description:The HIOKI PW8001 Power Analyzer is a state-of-the-art measurement instrument designed for the most demanding power analysis tasks, providing precise measurement results when evaluating efficiency of latest high accuracy electrical devices and systems. The PW8001 has 8 slots for power input units, which all can be used in combination with the motor analysis function.For the configuration of the PW8001, two types of input units are available that can freely be combined in one instrument according to the application requirements.The U7005 High Bandwidth input unit offers ultimate precision with ±0.03% basic accuracy, a sampling frequency of 15 MHz, 18-bit A/D conversion and a maximum input voltage of 1000 VAC. It is suitable for applications such as efficiency measurements of SiC and GaN based inverters motor drives, and accurate inductor loss measurement of inductors under load. Excellent resistivity for external noise of 110 dB at 100 kHz, ensure accurate and stable results even in the proximity to high frequency power switching semiconductors. For high-voltage applications, the U7001 input unit provides ±0.07% basic accuracy, a maximum input voltage of 1500 VDC, a sampling frequency of 2.5 MHz, 16-bit A/D conversion and a maximum voltage to ground of 1500 VDC CAT II. It is a suitable unit for applications which need less bandwidth, such as testing of the efficiency of industrial motor drives using IGBTs, or wind turbines and PV power converters. Combined with HIOKI’s extensive lineup of high-accuracy and high-bandwidth current sensors, probes and direct connection current boxes, the PW8001 offers a unique and comprehensive solution for reliably measuring applications from small electronic devices to large-scale power systems. The PW8001 power analyzer and the current sensors are developed and produced by HIOKI, making the advanced automatic phase shift correction function possible. This ensures accurate phase angle measurement between the voltage and current, even at high frequencies and low power factors. The PW8001 offers the unique Power Spectrum Analysis function. While the traditional FFT function determines the harmonics based on the fundamental frequency, limiting the frequency range, this new function covers the entire frequency spectrum of the analyzer. The Power Spectrum Analysis function delivers quick visibility into the high frequency power, providing developers with valuable data for further system efficiency improvements. Other advanced functions like wideband harmonic analysis, and motor analysis, ensure precise and reliable power analysis results for a wide range of applications in the power electronics industry, such as the development of high efficiency power converters, electrical drivetrains and electrical motors. The 1 ms update rate enables high-speed data refresh, allowing precise detection and analysis of rapid power fluctuations, such as those occurring during battery charging or discharging in EVs. This feature ensures unprecedented updates without compromising on measurement accuracy. The optical link function allows the connection of two PW8001 power analyzers to increase the maximum number of measurement channels to 16. It enables synchronized power measurements and efficiency calculation from multiple inputs, optimizing measurement setup and eliminating timing differences in data collection because the sampling of all inputs is synchronized.
CT6877A - AC/DC-Current sensor CT6877A - AC/DC-Current sensor
CT6877A
CT6877A - AC/DC-Current sensor
Hioki's pass-through AC/DC current sensors are premium devices for use with power meters, memory HiCorders and high performance oscilloscopes.
CT6875A - AC/DC Current sensor CT6875A - AC/DC Current sensor
CT6875A
CT6875A - AC/DC Current sensor
The CT6875 AC/DC Current Sensor is designed for accurate current measurements across a broad frequency range, from DC to 2 MHz (Model CT6875-01: DC to 1.5 MHz). With a rated current of 500 A, it is ideal for R&D, quality evaluation, manufacturing, and maintenance in industries such as wireless charging systems, inverter motors, PV power conditioners, and EV quick charging facilities. In combination with the Power Analyzer PW8001, the sensor allows for precise high-frequency and low power factor measurements. Technical Details: Rated Current: 500 A Frequency Bandwidth: CT6875: DC to 2 MHzBasic Accuracy: Amplitude: ±0.04 % rdg. ±0.008 % f.s., Phase: ±0.08° Maximum Conductor Diameter: 36 mm Maximum Rated Voltage to Ground: 1000 V CAT III Operating Temperature: -40°C to 85°C Input Impedance Requirement: 1 MΩ or higher Output Terminal: ME15W Cable length: 3m

€1,698.00*
CT6904A - High-precision AC/DC current sensor, 500 A / 4 MHz CT6904A - High-precision AC/DC current sensor, 500 A / 4 MHz
CT6904A
CT6904A - High-precision AC/DC current sensor, 500 A / 4 MHz
High-accuracy pass-through AC/DC current sensor, zero-flux detection with flux gate technology, currents up to 500 A, bandwidth from DC to 4 MHz, CMRR of 120 dB at 100 kHz, linearity ±5 ppm, 3 m cable length with ME15W connector
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