Case application

on 14 Sep 2020 17:27

Generally speaking, the frequency of industrial AC power is usually 50 Hz (Europe, Asia, Africa) or 60 Hz, such as North America. However, some electrical applications use different frequencies.

For example, 400 Hz is used for civil and military aviation, communications industry, etc. Transformers and motors designed for 400Hz application are more compact and lighter than equivalent equipment at 50 or 60 Hz.

At such frequencies, current cannot be transmitted over long distances at low cost, so the use of 400 Hz power supplies is usually limited to airplanes or specific buildings for economic reasons.

The main advantages of 400 Hz equipment are small size and light weight, which is why they are used in the aviation sector. In addition, 400 Hz applications typically have a power of several hundred kW, with relatively low short-circuit current, which rarely reaches 4 times the rated voltage.

But even at 400Hz, there are still harmonics...

The current waveform consumed by the load connected to the distribution network is usually no longer a pure sine wave. This current distortion causes voltage distortion, which also depends on the source impedance.

These interferences, called harmonics, are caused by the use of non-linear loads on the grid, such as equipment including power electronic equipment, switching power supplies, variable speed drives, etc. They may have a direct impact on some electrical appliances: functional problems (synchronization, switching), untimely trips, measurement errors on energy meters, etc. What's more serious and more expensive is that the extra heat may shorten the life of rotating machinery, capacitors, transformers, and neutral conductors. To avoid these problems, regular preventive maintenance is required.

At 400Hz, some interference will be amplified.
For example, when the aircraft is parked on the bridge, it can be charged through the aircraft bridge or a mobile generator set. When power is supplied to the aircraft through a 400 Hz gallery bridge channel, new interference introduced by grounding may appear. On a power supply with a frequency of 400 Hz, harmonics can cause high leakage currents due to the stray capacitance between the device or conductor and the ground. They provide a possible path for leakage currents, the effects of which may include untimely tripping of the RCD.

In all parts of the device, cables carrying harmonic currents overheat faster than other parts. Since 400 Hz sources are usually low power, the harmonic values are higher.

Although specific cables can be used for these applications, harmonic filtering solutions must be implemented after making the necessary measurements. The size of these filters will depend on the harmonic frequencies encountered and their amplitudes.

How to measure it?
Compere KPM53, KPM73 multi-function smart power meter, KPM75 power quality analyzer can be used to monitor 400HZ ac equipment and system current, voltage, power, power factor, 4-quadrant electrical energy, harmonics, and other parameters.

Please contact us if u need.