Challenge: There are many industrial applications where monitoring electrical heating elements for leakage to earth is needed. Insulation of electrical apparatus may degrade over time contributing to leakage. When a heating process should not be interrupted until the process is completed, disconnecting power through a ground fault circuit interrupter is not an ideal approach. For example, if the heating process is stopped before annealing parts are brought to the target temperature, they will not be properly hardened and must be scrapped. While letting the process complete is not as safe as disconnecting the offending circuit supply source power, it is certainly better and more cost effective than scrapping the parts.
Solution: NK Technologies provides a smart way to control premature process interruptions utilizing the AGT-FD series ground fault relay. Producing an output signal proportional to this current to earth is a way to monitor deteriorating insulation or direct shorts to ground. The sensor produces a signal which can be read with a panel meter or a programmable logic controller. If the fault current exceeds an allowable level, a limit alarm contact or an output from the PLC can be used to control a signal (audible or visual) letting the equipment operator know a problem is imminent or a hard fault to earth has occurred. The operator can then initiate procedures preventing shutdown of the entire system. With an analog sensor output, there can be multiple alarm points. For example, one alarm would trip if fault current exceeds 10 or 20 mA, while another alarm can trigger when the fault exceeds 50 mA. This allows more extensive action if a higher fault current is detected.
This solution is also ideal for enhancing a preventative maintenance program. Using the same monitoring approach, leakage levels can be established at the point at which preventative maintenance occurs, allowing the offending element to be removed and replaced or another corrective action taken in a cost-effective manner. Additional applications that benefit from this approach include monitoring electric heating processes, semiconductor wafer fabrication, AC motor loads, plastic molding processes, heat trace cable systems, and snow melt protection.