Millions of surge protection units in the field are not providing adequate protection for today’s microprocessor-based equipment. As John Mitchell at CP Automation explains, surge protection devices (SPDs) must be brought up to speed.
SPDs are designed to prevent excess voltage appearing at the terminals of sensitive equipment. A voltage spike typically lasts one to 30 microseconds and may reach over 1,000 volts. A longer-term voltage surge can last for seconds, minutes or hours and is caused by power transformer failures such as lost neutral or other power company errors.
High voltage surges are normally covered by surge protectors. However, traditional SPDs do not account for low level transient surges. Don’t let the name fool you — these transient surges in the sine wave are very damaging to electrical equipment, as the additional peaks and troughs in the sine wave cause confusion to sensitive devices and machines.
Transient surges can lead to false zero crossings of the sine wave — the instantaneous point at which there is no voltage present. In a sine wave, this normally occurs twice during each cycle. Devices can be falsely triggered because of fast changing signals caused by transients. They detect that the zero point has been crossed, even if it is caused by a transient disturbance in the voltage rather than the normal waveform.
Typical surge protection devices are unable to prevent this confusion, because they are voltage triggered only and therefore unable to detect rapid changes in frequency. Their clamping will only occur at a set point above or below the amplitude of the sine wave and will therefore not act upon low level switching transient events.
The role of variable frequency drives
Part of the issue surrounds the increased use of variable frequency drives (VFDs), which control the frequency and voltage supplied to an electric motor. By implementing VFDs, many businesses reduce energy costs. However, VFDs are very susceptible to changes in power quality.
Power quality issues could be caused by an anomalous event such as a lightning strike to the grid, or by the aforementioned lower level transient surges. If transients are not accounted for, they can lead to confusion in VFDs, such as false zero crossings, false triggering of diodes and timing issues.
A basic SPD may be used alongside a VFD to mitigate the damaging impact of high-power surges, yet many users are still faced with unexplainable lockups, downtime and even some failures in surge protection caused by low level switching transient events.
Why CNC machines are vulnerable
Modern computer numerical control (CNC) machines are often marketed as requiring much less maintenance than their predecessors. With further development from three axis to five axis models, the increased complexity of processes has not been without its pains. As with VFDs, these machines are also at the mercy of power quality.
To operate effectively, it is imperative that CNC machines are equipped with the right tools, settings and programming. The wrong choices can spell disaster for both the product and the CNC machine. One of the most important considerations relates to ensuring good power quality.
A poor power signal can cause issues with random lockups, loss of synchronisation and other ‘no trouble found’ service calls. Partially, this is due to the computer processors of CNC machining centres becoming more complex. Transient surges can lead to loss of synchronisation and unexplained reboots or resets in CNC machines — a huge headache for factory managers.
To eliminate the effects of low-level switching transient events, transient protection systems such as SineTamer offer a new opportunity to protect valuable assets from the transient events that occur millions of times each day. Its frequency attenuation network monitors the frequency, not just the voltage.
The engineered transient disturbance filter is designed to monitor all 360 degrees of the sine wave, making it capable of detecting rapid changes in frequency. This vigilance in turn prevents issues caused by false zero crossings of the sine wave.
Improving surge protection may not require an entire overhaul of existing protective equipment. Today, the industry has access to add-on transient dissipation filters (TDFs), which enhance the capabilities of existing surge arrestors.
The new range of devices give existing surge arrestors the ability to track the frequency of electrical current waveforms, and in turn react to transient surges. With this improved insight, low-level transient surges in the electrical system can be detected and filtered before they harm sensitive equipment, all while using old surge protection equipment.
Whether facility managers choose to completely update their surge protection devices, or take the TDF approach by enhancing what they already have, the bottom line will benefit greatly. Effective power quality filtering results in less downtime, re-boots and general headaches for workers, which enables higher productivity overall.