Switched mode power supply (SMPS): Working Principle of SMPS  ITI’s 50V – 2000A Power Plant?

 ITI’s 50V – 2000A POWER PLANT (Multi Rack Type) Suitable for VRLA Batteries with 100A Switched mode power supply (SMPS) Rectifier Modules


The power system is intended primarily to provide uninterrupted DC power to Telecom equipment and current for charging the batteries in the presence of AC Mains. The system works from commercial AC mains which is rectified and regulated to –50V DC and is fed to the equipment (exchange). The system has provision to connect three sets of VRLA batteries and a facility to charge them simultaneously to ensure that an uninterrupted DC power supply is always available to the exchange.

The power system –50V, 2000A has the following features :

  • Multi-rack configuration.
  • Facility to parallel a maximum of 21 nos. (or 22 nos.) of 100A (5600W) Rectifier modules operation from three-phase, 400V, 50Hz AC input.
  • Termination for three sets of VRLA batteries and exchange.
  • System input: Three-phase, 4-wire, 50 Hz supply.

The power system has a single DC bus called the auto float/charge bus. Depending upon the status of the batteries, the output DC voltage is maintained at 54.0 + 0.5 V under auto float conditions. During auto-charge, the maximum DC voltage reached across the bus is 55.2 volts. The exchange battery and rectifier modules are connected in parallel.

The system employs natural convection cooling and has AC input distribution, DC output distribution, protection, and alarm circuitry for rectifiers, battery, and equipment.

Technical Specification

For Module

(1) Input Voltage :

  • 320V to 480V r m s three-phase (Nominal Voltage – 400V).
  • Frequency: 45 Hz …. 65 Hz.

(2) Output Voltage :

Float mode:

Nominal voltage:  -54.0 + 0.5V,

Adjustment range:  -48.0 to –56.0 V

Charge mode Voltage :  -55.2 + 0.5 V

(3) Rated current: 100 Amps.

(4) Psophometric noise:

Less than 4 mV without battery floated.

Less than 2 mV with battery floated.

(5)  Input power factor: Greater than 0.95 lag with 25% to 100% load at nominal input.

(6) Efficiency: Greater than 90% at full load and nominal input.

(7) Protection:

  • Short circuit protection.
  • Input over/under voltage protection.
  • Output over-voltage protection.
  • Constant current features settable from 80 Amps. to 110 Amps. In auto float/charge mode.

(8) Alarms and indicating lamps:

  • FR/BC on Auto Float/Charge: Green LED
  • Rectifier module overvoltage :  Red LED
  • DC output fail/Under voltage: Red LED
  • FR/BC Over Load (Voltage Drop): Amber/Yellow LED
  • Mains Available: Green LED

For System

(1) Input Voltage :

  • 3 Phase, 4 Wire, 50 Hz (Range – 320V to 480V RMS)
  • Frequency:           45 Hz …. 65 Hz.

(2) Output Voltage:

Float mode Voltage:  -54.0 + 0.5V

Charge mode Voltage: -55.2 + 0.5V

(3) Rated Current:

Equipment:  1100 Amps.

Batteries: 300 Amps. Each.

(4) Protection

  • Short circuit/Overload protection.
  • Input over/under voltage protection.
  • Battery/Equipment over-voltage protection.

(5) Alarms and indicating lamps :

(a) Load Voltage High – Red LED

(b)  Load Voltage Low – Red LED

(c) Fuse Fail – Red LED

(d) FR/BC Fail – Red LED

(FR/BC No Output MCB Trip)

(e) Mains available – Green LED

(f) Mains out of range  – Red LED

(g) Mains Fail –  Red LED

(h) System (Exchange) Overload –  Red LED

  • FR/BC Float/Charge Mode – Green LED

(j) Mains “ON”/Battery Discharge – Red LED

Functional description of power system

This Power System is of multi-rack type and comprises:

  • Eight racks – One main, one auxiliary, and six extension racks.
  • AC Distribution module in each rack.
  • Rectifier modules (A maximum of three modules in the extension rack and two each in the main rack and auxiliary rack).
  • DC distribution module in each rack.
  • Metering in each rack.
  • Power system controller in the main rack.

(a) Rack:

The rack is made of mild steel profiles with hinged front door. The door accommodates display and alarm enunciator. The rack is convection cooled and has ventilator slots in the front and sides. The rear panel is screw type and can be dismantled. The cabinet accommodates 19” subsystems. Air baffles are provided for better heat transfer. Depending upon the load requirement (Equipment and Batteries), additional modules can be added. The bottom and top also have ventilator features. The DC power termination and distribution is done at the top. The AC power termination and distribution is done at the bottom.

(b)  AC Distribution Panel :

The AC input to the rack is terminated at the bottom of the rack on screw-type terminals. Individual AC circuit breakers are provided for each module. The line, neutral, and earth are terminated on the molded plug which is fixed to the respective sockets on the rectifier module. To monitor AC input current, 3 nos. of single-phase AC current transformers are mounted on the panel of the main rack. A small signal transformer is mounted on the PSC panel to provide AC input to the power system controller card.

(c) Rectifier module:

The SMPS rectifier module – 50V, 5600 watts works on 400V AC input and provides – 50V DC for the system. The input is through a 9 pin AC socket and the DC output is through terminals. The module has a front panel to indicate the status and faults in the module. The control signal is taken through an 8 pin telephone jack and is terminated onto the power system controller card.

The rectifier modules are convection cooled and can be jacked in and out of the cabinet easily. The DC output from each module is terminated on the respective DC bus bar mounted on the DC distribution panel.

(d) DC Distribution Panel:

This panel is mounted at the top of the cabinet. The panel incorporates the following :

  • Input from individual rectifier modules terminated on the cabinet.
  • DC shunts to monitor current in various paths.
  • Termination of batteries 1, 2, and 3.
  • Termination of equipment positive and negative.
  • Fuses for batteries 1, 2, and 3.

(e) Metering:

The front panel of the main rack consists of two AC meters to monitor individual line-to-line voltage and current. The selector switch selects the relevant phases. The DC meters monitor both voltage and current of batteries and exchange.

(f)  Power system controller:

The Power system controller card consists of an electronic circuit which monitors the state of each rectifier module and display their status. It also controls the operation of the module so as to make it work in auto float or auto charge mode. The current signals are monitored continuously to ensure equal sharing of current. In case of faults, the same is displayed and for faults like input voltage beyond limits, DC output over-voltage, overload, etc. it shuts off the module. The various alarms as per the following details are displayed on the front panel with an audible alarm.

(1) Mains out of range: Red

(2) Load voltage high (above 57V) : Red

(3)  Load Voltage low (below 42V) : Red

(4)  Mains fail: Red

(5) System overload: Red

(6) Mains available: Green

(7) System overload : Red

(8) Mains on battery discharge: Red

(9) FR/BC in Float-charge mode : Green

(10) FR/BC Fail: Red

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