DC distribution unit
The principle of high-ohmic distribution implies an augmented increase in resistance of power supply conduits between rectifier (batteries) and load.
At the same time, the supply conduits are sized in a manner so that the voltage drop does not exceed 1V at a nominal current. In that way, the transients (under-voltage and over-voltage), which are present in the case of breaker switch-off or blown a fuse, are diminished.
In case of short-circuit in one of the distribution circuits, in brief, time which is needed for a breaker to switch off, or for a fuse to blow (in practice, about 10ms) the electric circuit which is consisted of supply battery, supply conduits, distribution conduits and power conduits of the device which shorted-out is under short-circuit current. That current is determined by inner resistance of supply battery and a sum of stated conduits resistance. From the point of transient limiting, it is preferred for the short-circuit current to be as low as possible. The short-circuit current accumulates energy in supply conduit inductivity, which is proportional to conduit inductivity and square of the current. In the moment of short-circuit current breaking, that energy is dissipated on other parts of the same distribution board in the form of over-voltage, which can cause damage to other circuits connected to the same distribution board.
The transient current limiting (or high-ohmic) distribution board consists of resistors in addition to protective elements (breakers). The purpose of resistors is to increase the resistance of supply conduits to load, thus decreasing short-circuit current.
Transient current limiting distribution unit, also known as “high-ohmic distribution,” is used for the power supply of sensitive electronic circuits in telecommunication equipment.
- Nominal supply voltage = 48 VDC
- Maximum supply cable = 70 mm2
- Maximum output cable = 16 mm2
- Maximum number of circuits connected = 20
- Allowed current per circuit = 32 A max
- Resistor value per circuit = 30 mΩ
- Protective element type = automatic breaker (2 – 32A, 1p) breaking capacity 10 kA
- Mechanical construction = device fits 19“ rack unit cabinets, height = 3 U
- Maximum inner dissipation = 650 W
- Cooling method = natural vertical air circulation