Electronic motor protection relays are available for general-purpose applications. They protect against problems such as overcurrent, phase loss and voltage unbalance. However, some problems that are unique to pumps make considering a protective relay designed specifically for pumping applications worthwhile (see Image 1). These units have different designations—pump protection relays, electronic overload relays, electronic motor protective relays and others—but in general, they tend to have certain characteristics in common. One way that units suitable for pump protection differ from general motor protection relays is their ability to sense underload conditions. This article explores the functions of electronic pump protection relays and provides some pointers on how they are best applied.
A complete understanding of these devices can help users detect problems before equipment is damaged.
02/22/2015
Image 1. A pump protection relay provides valuable information about motor conditions. (Images and graphics courtesy of Littelfuse, Inc.)
Figure 1. An increase in motor amperes may indicate either an undervoltage or an overvoltage condition.
Table 1. The likely causes of relay indications and possible corrections. Click here to view a larger version of this table.