The Hot Spot 3 relay accepts up to three inputs from resistance temperature detectors (RTD) and provides up to three user adjustable trip points which can be used to initiate alarms, cooling systems or shutdown. The relay is ideally suited for the protection of electric motor windings, transformers, generator windings and bearing temperature. The analogue output can be used for remote monitoring of high temperatures.

Operation
RTD temperature sensors are often fitted inside electric motors to detect hot spots in the windings or the bearings. RTD sensors are popular because they offer a good accuracy for a reasonable price. The same sensors can be used inside transformers, generator sets, gas turbines or as part of a process control system. Hot spots can be caused by many conditions such as overloads, over voltage, unbalanced supply, worn bearings, ineffective cooling, poor ventilation, shorted turns, insulation breakdown, single phasing etc.

The Hot Spot 3 protector continuously monitors the three RTD temperature sensors and offers up to three user adjustable set points and relay contacts. These can be used to raise alarms, switch on cooling systems or shut down the affected equipment. The highest temperature is indicated with a yellow LED and can be accurately measured or remotely displayed using the 0/1mA analogue output signal.

The temperature is compared with the user adjustable set points. When the measured temperature exceeds the set point, the relay will de-energise and a red LED will illuminate to indicate the trip condition. When the temperature drops below the set point, the relay will reset to the energised condition and the LED will extinguish. The range consists of three product models which offers one, two or three adjustable set points.