Smart motor controls are needed that can maximize resilience and uptime of machinery in the next generation of Industry 4.0 manufacturing, metals and basic materials processing, mineral extraction and mining, and critical infrastructure like drinking water and wastewater plants. The motor controls in these applications must be able to control and protect motors between 75 horsepower (HP) and 700 HP. Comprehensive protection, including overload protection, ground fault protection, and phase imbalance protection, is needed to support resilient operation. They should also include self- diagnostics for contact wear and coil over/under voltage detection with visible indicators to support predictive maintenance and have modular designs for faster servicing to maximize uptime. Compliance with National Electrical Code (NEC), UL, and International Electrotechnical Commission (IEC) short circuit current rating (SCCR) is needed to ensure electrical equipment can withstand high currents without damage and that it’s safe. These motor controls must also comply with IEC 60947- 4-1, which covers the safety of electromechanical contactors and starters, including motor protective switching devices (MPSD), instantaneous-only motor protective switching devices (IMPSD), and actuators of contactor relays.
Figure 1: SCCR calculations begin with individual component ratings (yellow boxes), move up to determine the SCCR of branch circuits (red dashed box), and then consider the SCCR needs of the completed control panel (grey rectangle). (Image source: Schneider Electric)
This article begins with an overview of SCCR requirements. It then takes a deep dive into a recently developed family of smart motor controls from Schneider Electric, including modular contactors and overload relays detailing the operation of the protective functions and how self- diagnostics is implemented. It looks at how those overload relays meet the requirements of IEC 60947-4-1 and presents how the modular design speeds preventative maintenance. It closes by looking at how two contactors
can be used to assemble a reversing assembly, enabling bidirectional control of AC motors. The SCCR is an essential characteristic when specifying a control panel that contributes to overall dependability. It’s used when sizing power components like contractors and conductors. IEC 60947-4-1 details three phases for calculating the SCCR (Figure 1):
1. Identify the SCCR of each protection and/or control
component and each block and element in the distribution system.
we get technical
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