Electricity and Control November 2020

DRIVES, MOTORS + SWITCHGEAR

The drive as a sensor for condition monitoring Norbert Hanigovszki, Jörg Dannehl, Sanjeet Kumar Dwivedi - Danfoss Engineering

Variable speed drives have been used for over half a century, with the main advantage being the reduced use of electrical energy they enable.With the advance of Industry 4.0, the drive moves from being purely a power processor to being an intelligent element of the automation system.The ability of the drive to act as a smart sensor makes it a natural choice when implementing condition monitoring. Here we look at how this capability can be used in water and wastewater applications.

T oday more than 20% of all electric motors are driven by variable speed drives. In water and wastewater applications, drives are used for the reduced energy use they enable, as well as for other reasons – such as in process control (keeping water pressure constant and thus avoiding leakage caused by high pressure), preventing water hammer, or optimising well exploitation. The introduction of microprocessors to control drives brought with it additional functionality – that of a power pro- cessor. For example, drives can perform pump de-ragging in wastewater applications, they can control several pumps in a cascade system in water pumping applications, or can bypass certain frequencies to avoid resonances. The advance of Industry 4.0 has given an additional boost to these functions. As Industry 4.0 deals with infor- mation and networking, we start using drives as smart and networked sensors. Motor and drive systems in Industry 4.0 Industry 4.0, or the fourth industrial revolution (following the first industrial revolution – mechanisation, the second – electrification and the third – automation), can be char- acterised by networking. It could be defined as follows: ‘In- dustry 4.0 describes the intelligent networking of people,

things and systems by using all the possibilities of digitali- sation across the entire value chain’. The impact of this trend on motor systems is a migra- tion from what is known as the ‘automation pyramid’, to networked systems. This means the various elements of the system, such as motors, drives, sensors and controls, are interconnected and are also connected to a cloud – where data is stored, processed, analysed and decisions are made. The drive as a sensor In variable speed drive applications, the availability of mi- croprocessors in the drive and bus communication options, combined with current and voltage sensors, opens new op- portunities. Moreover, additional sensors (such as vibration and pressure sensors) can be connected to the drive at almost no cost. This allows the drive to be used as a smart sensor for condition monitoring. The available information offers various use cases, for example in: system optimisa- tion, energy efficiency optimisation, and condition-based maintenance.

Embedded condition-based monitoring Condition monitoring is a technique used to monitor the

health of equipment in service. For this purpose, key parameters need to be selected as indica- tors of developing faults. Equipment condition typically degrades over time. Figure 2 shows a typical degradation pattern, also known as the PF-curve. The point of functional failure is when the equipment fails to provide the intended function. The idea of condition-based mainte- nance is to detect the potential failure before the actual failure occurs. In this way, maintenance actions can be planned before functional fail- ure, with the advantages of reduced downtime, elimination of unexpected production stops, maintenance optimisation, reduced spare parts’ stock, and others.

Figure 1: Industry 4.0 sees the transition from the automation pyramid (left) to networked systems (right).

10 Electricity + Control NOVEMBER 2020