UPS System and Inverter: Working Principle

Power Backup Solutions: Understanding UPS Systems and Inverters for Reliable Energy Support

Ensure Uninterrupted Power Supply with a Reliable UPS System

What is the working Principle of UPS? What is the working Principle of Inverter?

Working Principle of UPS – Working Principle of Inverter

UPS System 1 KVA / 3 KVA Inverter

UPS System

UPS System means Uninterrupted Power Supply. As the name indicates, this system supplies uninterrupted A.C. supply.
Necessity:- Un-interrupted power supply is very much necessary in BSNL for the operation of computers, peripherals in O.M.C and for the other telecom equipments.
Capacity: The Capacity of an UPS is the output power it can deliver and is expressed in terms of kilo volt-amperes (KVA). Different capacities of UPS systems are available readily in the market right from 1 KVA onwards.

Principle of UPS System

The Block diagram of UPS is given above single phase AC. supply is first rectified to 120V D.C. supply. Across this 2 sets of 40 AH, 120 volts battery sets are floated. The combined D.C is then fed to the inverter, which converts into A.C of 220 volts.

Block-diagram-of-UPS System

During the available period of input AC mains, the battery sets will be trickle charged and the load will be taken by rectifier only. During the absence of input A.C. mains, the battery set will be taking the load. Working Principle of UPS

Another type of UPS system used in B.S.N.L is designed to work on -48 V D.C supply fed from the exchange power plant.

Specifications of UPS systems

a) Input230V, 1 f, A.C. supply
b) Input BTY120V, 40 AH, two sets of Batteries.
c) Output220 volts, A.C
d) Output currentFor 5 KVA it is 21.5 Amps.

Alarms in UPS system

1) Low Battery– If the battery voltage falls below a specific voltage.
2) Over load– If the load on UPS is more than its capacity UPS will be tripped and overload alarm comes
3) Output High– When output voltage becomes high UPS will be tripped and this alarm comes.
4) Output low:- When output voltage becomes low UPS will be tripped and this alarm comes.
5) Trip– This LED glows once if the inverter trips.

Inverters of 1KVA/3KVA Capacities

Inverter is an alternating current (A.C) generating equipment using D.C voltage source of -48v as its input.


Inverters are very widely used in D.O.T network for the operation of peripherals in CDOT and E-10B exchanges.

Technical Specifications

1) Input

a) Voltage = 44 to57 volts D.C

b) Current = 32A, 96A, 192Amps for 1 KVA, 3KVA, 6KVA inverters respectively.

c) Power drawn = 5KVA/4.5KVA/9KVA for 1 KVA, 3KVA,6KVA inverters respectively.

d) Source = Battery /Float rectifier

e) Source Ripple = Less than 2 %

2) Output

a) Voltage = 220 ± 2% V.A.C

b) Rated KVA = 1, 3, 6 KVAs

c) Rated Current = 4.3A, 12.9A. 25.8 A for 1 KVA                3KVA, 6KVA inverters respectively.

d) Wave form = Sinusoidal

e) Total Harmonic distortion = 5% Max

f) Frequency = 50 ±1 Hertz

g) Voltage adjustment = 220 to 250 volts

h) Over current trip = 120%

i) Efficiency = 70 % minimum

Inverters (Capacity wise) used in DOT are listed below:

Exchange Make and CapacityCapacity and No. of Inverters used
CDOT up to 1400 lines1 KVA x 2 Nos
CDOT above 1400 lines1 KVA x 3 Nos
E10B6 KVA x 3 Nos

Principle of Operation

Low capacity inverters are designed using integrated circuits, transistors, etc whereas higher capacity inverters are designed using thyristors.

The diagram of 1 KVA Inverter is given above. In this Q1 to Q4 are four power transistors arranged in full bridge configuration. This combination acts as a push-pull amplifier gives AC O/P.

Uninterruptible Power Supply (UPS) Systems and Inverters

Main transformer T1 provides input output isolation. Radio frequencies are filtered at the output with the help of RF I suppresser. Regulation and frequency stabilization is done by the control circuit.

Method of Connection of Inverters in CDOT Exchanges

In C-DOT exchanges all the peripherals are divided into two or three groups and connected across the output of individual inverters separately. But in case of failure of any inverter there is a provision for the connection of the group of peripherals connected to the faulty inverter to another inverter.

Method of Connection of Inverters in E10B exchanges

In E10B exchanges, the main computer works on the output supply of the inverter. The inverter system comprises of two 6KVA inverter units and a control cubicle. Normally the total load is shared equally by both the inverters (each operating at half the full load capacity). In case of failure of any inverter unit, the total load will be supplied by the other unit.

This inverter system is most unique in nature because of the following.

  1. sharing the system load equally.
  2. having ability to be in phase synchronization even in the event of failure of master oscillator, which normally synchronizes them.
  3. able to lower overall distortion.
  4. well protected against different fault conditions.

with minimum inter cubicle circulary currents over a wide range of input voltage.

Working Principle of UPS, Working Principle of UPS, Working Principle of UPS

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