Electrical Noise in a Boiler Room

-Tom O’Marra, Electronic Engineering Tech., Danbury CT

This article will give a general insight into electrical noise’s effect on electrical equipment and instrumentation in a boiler room setting as well as some troubleshooting/prevention tips. Noise spectrum analysis, theory and categories will not be discussed.

               Electrical noise is prevalent throughout boiler rooms in the industrial and process control industry. Any seasoned service technician knows the wacky symptoms electrical noise presents and the headaches in troubleshooting to a route cause.

               Electrical noise can be defined as undesirable electrical signals, which interfere or distort the original signal and its intended purpose. Noise can be a constant nuisance, or it can be a temporary, un-repeatable, issue. An electrical system may operate fine for years and seemingly out of nowhere, be struck by the effects of electrical noise leading to perceived poor product performance and unhappy end users. The source of the noise can be system inherent due to design flaws, but mostly, it is an external source which is causing the interference. Noise can enter through almost any I/O point as well as through a systems power source connection.

               In boiler rooms, the most common source of electrical noise comes from high voltage AC wiring running too close to lower voltage DC. Any type of analog input or output can be adversely affected by high voltage AC wiring’s coupling noise wire to wire (known as capacitive coupling). Even high voltage AC I/O can be susceptible to noise interference from higher frequency AC such as motors, variable speed drives (VSD/VFD), or super high voltage ignition transformers.

Below shows a waveform of noise “ripple” and then the same waveform interacting with a typical AC sinewave. You can see how the noise distorts the AC signal.

The same would be true when it comes to electrical noise’s effect on low voltage DC square wave signals.

               The best way to reduce (and hopefully eliminate) the effects of electrical noise on industrial controls is to implement and maintain good equipment wiring practice. At all times high voltage AC wiring should be run separately from any low voltage DC wiring. For extended runs, dedicated conduit for low voltage and high voltage is required. Particular attention should be paid when running any type of three-phase AC.

               Where applicable, utilize shielded cable (especially for three-phase motor and VSD connections) and ground accordingly. Most low voltage DC transmitters and other instrumentation come with a shielded conductor. Consult the manufacturer’s user manual for proper grounding techniques. If the instrument’s body is metal and making a connection to Earth ground, it could be potentially detrimental to ground the shield. For high voltage power supply transformers in electrical cabinets, assure that the incoming neutral is a grounded connection to avoid ground loops.

               Other components such as resistor-caps on ignition transformers and ferrite beads on HMI cabling can counteract electrical noise.

Works Cited: Electrical noise and mitigation: G Vijayaraghavan, Mark Brown, Malcolm Barnes. www.eetimes.com