91 The Bourns® Model SM91527L can meet the above requirements. A separate series of mandatory tests are necessary to check the quality of the insulation material itself. Reinforced insulation is tested by applying a DC or AC voltage between the primary and secondary side and measuring the amount of leakage current between the two sides. This is also known as a dielectric test as the permittivity of the insulation material will accumulate charge, which translates into a leakage current. Another name for this test is Hi-POT. Another required procedure for systems with working voltages higher than 750 VDC is to put the transformer through an ageing process using high temperature and humidity. The ageing test consists of ramping up the DC voltage from zero to a value dependent on the working voltage while at the same time measuring the amount of charge in coulombs gathered in the insulation. This test is also known as partial discharge. Additional Transformer Requirements Transformers with reinforced insulation (color red) are now also required at the point of entry into networks, especially if the battery management board could be exposed to enable testing and diagnostics by a technician. One exception is for racks that hold battery modules that are shielded by plastic walls and use transformers for communications in a daisy chain configuration. This part of the application does not require reinforced insulation. For communications in a daisy chain configuration, an ideal solution is Bourns® Model SM91501ALO signal transformer with functional insulation for 1500 V, and this product is also UL listed. This device has two channels instead of one and is well-suited for placement in the middle of a daisy chain. This Bourns model will still require Hi-POT and impulse tests, but the procedure is less severe (4.3 kV DC Hi-POT and 8 kV Impulse). In a 1500 V BESS, Figure 2 highlights where a reinforced single channel transformer and a functional two-channel transformer would be located. The BESS is divided into strings of 50 V battery modules where each is monitored and each has a two-channel functional insulation transformer in the isoSPI™ bus. This configuration enables the string to be protected with the reinforced single-channel magnetics component such as the Bourns® Model SM91501ALO transformer. Figure 2: Reinforced Transformer and Signal Transformer Placements in a High Voltage Battery System Achieving Higher Battery Storage Efficiency This article has presented an established reinforced insulation solution for isoSPI™ buses in 1500 V renewable energy systems. Using the example of Bourns® Model SM91527L was shown to help meet higher battery energy storage efficiency needs. This UL listed single-channel signal transformer with common mode choke is designed for entry points into strings of battery modules. The signal performance of the Model SM91527L has been tested to meet recommendations by IC manufacturers for operation with their drivers, and is shown to meet energy storage system specifications in terms of surge voltage and other tests for insulation. Bourns www.bourns.com Bourns Magnetic Products https://t1p.de/hzwkd Bourns Magnetic Capabilities https://t1p.de/kavq Share In addition, the Bourns® Model SM91501ALO has UL recognition and is a two-channel transformer rated to 1500 VDC (functional insulation), which is suitable for battery module enclosures inaccessible to human contact. To meet the requirements of the rapidly expanding renewable energy system market, Bourns is committed to continued innovation in the development of magnetics components for 1500 V and beyond to help keep these applications safe and maximize efficiencies. Bourns’ high-voltage BMS signal transformers have been designed to work with selected ICs as indicated in the datasheets for Model SM91501ALO (https:// t1p.de/2jpf0 ) and Model SM91527L (https://t1p.de/g6pk ). Bourns® Model SM91501ALO is developed for use with Analog Device’s Model LTC6804/681X, NXP’s Model MC33771/33772 and Texas Instruments’ Model BQ79616. Bourns® Model SM91527L is developed for use with NXP’s Model MC33771C series and Analog Device’s Model LTC6804/681x series. *“isoSPI” is a trademark of Linear Technology Corp. Figure 2: Reinforced Transformer and Signal Transformer Placements in a High Voltage Battery System
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