IEN: What are the major power quality and availability problems facing industry? Their solutions?
Kenyon: Line-current harmonics that are injected to the electrical network by non-linear loads connected to the network, and are multiples of 60 Hz, are a growing concern.
Common examples of such devices found in industrial environments include variable-frequency drives (VFD), welders, switch-mode power supplies, battery chargers, UPS systems, computers, electronic lighting, etc. These can generate current harmonics that cause additional losses in the supply system and degrade the active-power-handling capacity of the system. The harmonics also affect the voltage waveform -- and that can cause malfunction in other sensitive devices that are connected to the same transformer as those producing harmonics.
IEN: What innovations are in store for industrial users of power equipment, systems, components, software, and services?
Kenyon: Harmonic mitigation at the device level reduces heat losses in transformer and network. Because the current harmonics from all devices connected to the supply system sum up in the network, a small reduction of the harmonics generated in every device could lead to remarkably big savings in transformer heat losses. The heat losses in a transformer are directly related to the loading of the transformer, and the copper losses of the transformer are related to the square of the current. If the converter feeds the motor with a certain power, it requires the same fundamental current component Is1 regardless of the choke. The additional losses are caused by the unwanted harmonics generated by the device.
So we are seeing new technology in motor drives, such as the Swing Choke in ABB''s line ACS550 industrial drives. How does the technology work? In rectifiers with conventional LC-filters, the harmonic content increases rapidly as the load decreases. The amplitude of the harmonic currents also decreases, but their part of the rms current increases. By reducing the harmonics at partial load, the harmonics in the whole supply system decrease. This is the basis for the idea of a swinging choke device, able to decrease the THD at partial loads; create a choke whose inductance increases when the load decreases. The size and weight of the swinging choke is the same as for a conventional choke. The only way it differs from a conventional choke is that its inductance changes according to the current through it.
The Choke design, built into the ABB drive, is uniquely able to reduce harmonics at both full and partial loads, for a total harmonic reduction of up to 30%, compared to traditional reactor designs; and up to 64%, compared to drives with no reactors (estimates are based on a power system impedance of 1%).