Filters take active approach to power quality

Edited by the Engineeringtalk editorial team Jun 4, 2004

Advanced microprocessor controlled power quality filters solve the growing problem of harmonics in electrical power networks.

ABB has upgraded its PQF range of microprocessor controlled active power quality filters designed to solve the growing problem of harmonics in low voltage electrical networks.

Two new models are now available, the PQFM for small to medium three-phase industrial loads and the PQFK, a three-phase, four-wire unit for industrial and commercial networks having high triplen (third and its odd multiple) harmonics.

The increasing use of nonlinear loads in all types of industrial and commercial applications has resulted in the introduction of potentially harmful harmonics into the power network that can lead to overheating of cables, motors and transformers, damage to sensitive equipment, tripping of circuit breakers and blowing of fuses as well as premature ageing of the installation.

ABB PQF active filters provide a reliable and cost-effective solution to this problem by continuously monitoring the current in real time to determine what harmonics are present and then injecting harmonic currents in the network with exactly the opposite phase to the components that are to be filtered.

The two harmonics effectively cancel each other out so that the feeding transformer sees a clean sinewave.

ABB PQF active filters are factory assembled and tested, ready to install and use at site.

They have a modular construction, which allows easy extension to cater for future load growth.

There is also no need to apply a derating factor when PQF units are coupled in parallel, which makes it feasible to achieve a high rating within a small footprint.

Since the PQF does not operate according to the conventional low harmonic impedance principle employed by passive filters it remains unaffected by changes in network parameters and cannot be overloaded.

The PQF range offers a number of new features such as: event logging with real time stamp, programmable load balancing, isolation between control and power units by optical fibre link, digital I/O and Modbus communication.

The filters are fully programmable and can either be pre-programmed by ABB or programmed on site using PQF-Manager, a simple, user-friendly front panel module that offers direct control, programming and monitoring capability.

The PQF can also be controlled by a standard PC via its RS232 port and the optional PQF-Link software.

PQF units can also adopt the secondary roles of reactive power compensation and load balancing.

The PQFM is ideal for small to medium three-phase industrial loads and can comprise of one master and up to seven slave units.

It is suitable for direct connection up to 690V and is offered in two voltage groups: 208-480 and 480-690V.

In recent years, many industrial and commercial three-phase networks have had to cope with growing single-phase loads from computer equipment, fluorescent lighting, switch mode power supplies and so on.

These loads generate third harmonics, which tend to collect in the neutral conductor of the low voltage network.

It is not uncommon for the neutral current to exceed that in any of the phases giving rise to a possibility of overload in the neutral conductor.

As well as the danger of cables and transformers overheating the third harmonic can reduce energy efficiency and cause damage to sensitive control and other electronic equipment.

Most conventional passive filters are ineffective in dealing with this problem due to the low reactive power demand of the loads.

ABB's PQFK is a three-phase, four wire active filter designed specifically to eliminate harmonics including zero-sequence current in the neutral ie the triplen (third or its odd multiples) harmonic.

It is ideally suited for loads consisting of multiple single-phase loads such as commercial offices and buildings and computer centres as well as UPS, HVAC, lighting and lift applications.

The PQFK is suitable for direct connection up to 415V and comprises three ranges to suit various applications - 40, 70 and 100A RMS current at 50/60Hz.

Modular construction enables up to three slave units to be added to a master PQFK.