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Abstract 

    In the electrical power industry, equipment such as RTU*, DTU*, FTU* and TTU* are switch monitoring devices installed in the substation close to the feed breakers (a disconnector which is located in series at the end of a feeder , within a substation bay, in order to isolate the system) , which is widely suitable for use in automation engineering applications, urban, rural or enterprise power distribution networks. These can be used for automated functions such as monitoring, protection and communications in a ring network cabinet in the distribution substation and master station with the implementation of monitoring and fault identification, isolation and power recovery of the fault in the distribution network. The internal structure and design is very similar to power supplies. 

    [1] RTU：Remote terminal unit 

    [2] FTU：Feeder terminal unit 

    [3] TTU：Distribution Transformer supervisory Terminal Unit 

    [4] DTU：Data Transfer unit Typical FTU* system structure

    The chart above shows that FTU monitors three phase current, voltage and binary signal by way of datta analysis. 

The power supply requirement is as follows: 

● Employing a UPS (uninterruptable power supply) by inserting a dual power supply for switched power and automatic battery switching. 

● DC-DC converter with the ability to work within a wide input voltage range caused by the charge and discharge from battery banks. 

● DC –DC converter must be compatible with both 24V and 48V battery voltage input. 

● High 3KV isolation voltage of the power supply can isolate the interference away from the AC end of the primary power source. 

● System power break time remains more than 500 ms when the power supply and the battery power supply disconnects. 

Recommended Power supply solutions 

To satisfy the above requirement for a power supply , Mornsun has recently released their URF_LP-20WR3 series which is a 20W 3000VAC high isolation range of DC/DC converters. 

Featuring 

● High efficiency 

● Wide Operating temperature between -40℃ to 85 . 

● Wide 4:1 (18-75V) input which suits both 24V and 48V battery input voltages. 

● Isolation voltage up to 3000VAC can isolate interference introduced from the battery charging side. 

● Design meets EMC - CISPR22 / EN55022 CLASS A 

Recommended product 

● URF2405LP – 20WR3 

Design reference 

● Power-off-delay: The extension of power-off time is necessary for the system to save data during a ppower outage of the main power supply and battery. The most common method to do this is to add some high value capacitors (could be as high as several thousand μF). Capacitors with a higher capacitance will be needed for the input, especially in situations where the input voltage drops away , so the power off time delay will also be greatly reduced. 

● For a higher level of EMC requirement, please kindly refer to the datasheet.