November/December 2019

Contact us to discuss your requirements today: 01744 757070 enquiries@cleveland-electrical.co.uk | www.cleveland-electrical.co.uk The North West’s Premier Electric Motor Rewind Specialists Electric Motor Rewinds Electric Motor Repairs and Refurbishment Electric Motor Maintenance Plans Electric Motor Suppliers including the new B56 Motors 24 Hour Emergency Service TEC Electric Motor Stockists Established 1936, with over 80 years experience, St Helens-based Cleveland Electrical is an expert motor repairs and rewinds company specialising in cost effective armature and stator rewinds. 20,000+ Happy Clients 82 Years in Business 73,000+ Motors Repaired 24 Hour Service CONTROLGEAR AND ENCLOSURES n alternative system, the air circulates freely, unlike in cabinets with conventional mounting plates. Measurements were taken for six hours at a time in each cabinet. The measurements were carried out over two days, with ten sensors recording ambient and internal temperatures. The power consumption of the two systems was not examined because it was assumed that the clocking was identical. Temperatures were measured at critical points in the cabinets – for example, on components with high heat losses. After the air-conditioning systemwas started in the cabinet using the mounting plate (about 40 minutes after the production start-up), the temperatures fluctuated between 29°C and 43°C (as shown in Fig. 2). The temperature measured between a contactor and the trunking was 38.5–42.5°C, indicating an air blockage, while the temperature between a Siemens Simatic ET200S I/O system and a cable duct was 36.5– 38.5°C. At the air intake of the air-conditioning system, the temperature was 33.5°C. The trunking hotspot remained just within the tolerances because the system is designed for an external temperature of 38°C and a maximum internal temperature of 42°C. In the cabinet with the new wiring frame, temperatures were measured after the heat exchanger had started to operate (a maximum of 37 minutes after the production start-up). The temperatures fluctuated between 30°C and 34°C (as shown in Fig 3). The temperature between a contactor and the ET200S in this cabinet was measured as 31–33.5°C, while between the ET200S and the terminals it was 32–33.5°C. At the air intake of the heat exchanger, the temperature was 29.5°C. If the temperature of the air at the outlet of the heat exchanger was identical to the temperature of the air-conditioner, the curves would rise linearly. Despite this, the air is not layered as happens when a mounting plate is used. Hotspots in the new wiring frame systemwere barely detectable. When the cabinet incorporating the wiring frame was tested, the ambient temperature was 23.9°C – some 1.9°C higher than when the cabinet with the mounting plate was tested. If the external temperature had been the same, the cabinet with the wiring frame would have been 1.9K cooler and the curves would have been even lower. The tests demonstrated that using a wiring frame can achieve noticeable cooling and a consistent climate inside control cabinets. This not only protects installed components from the heat, but also increases their life expectancies. Further improvements could be achieved by routing the cooling air to minimise hotspots around components with particularly high heat losses. Further analysis using Lütze’s online AirTemp application reveals that no air-conditioning would be needed in the cabinet using the wiring frame. Assuming an ambient temperature of 25°C and that 70% of the components would be operating at the same time, fan-based cooling would be sufficient. n Fig 2: Heat stress for the components. The thermal diagram for a six-hour operating period shows clear temperature layering inside the control cabinet with a mounting plate. Fig 3: The thermal diagram for the cabinet with the wiring frame reveals a much more even temperature distribution, with lower peaks.