Knowledge Base > Technology > Inverter


The static inverters are intended for supplying AC power to operate different type of equipments associated with Electronic Exchanges, Transmission equipments such as computer based interface equipments etc., used in the Indian telecom network for full safety of highly sophisticated equipment as well.

  • 100% Pure, reliable and regulated Power.
  • Low running cost.
  • Extended power backup time.
  • Easy maintenance.
  • No humming noise from any load.
  • Great power saving.

Performance requirements

The DC input voltage to the inverter may be of any value in the range of 42 to 57 V. The DC supply is floating battery power plant.
In case of DC supply variations beyond 43-57 V and in the range of 40 to 65 V the equipment should not be damaged and the components should be able to withstand without overheating or damage.
Since the battery is common to other equipment in the stations, the inverter should not give rise to ripple voltage across the Dc input exceeding the normally permissible psophometric noise of 2 mV with battery floated and 4 mV without battery on float.
The positive terminal of the battery shall be taken as earthed.
If the input exceeds the limit 40 - 60 V DC, the inverter is isolated. The restoration is to be possible by the manual operation of a RESET push – button switch provided on the face panel.

The inverter shall be required to deliver a continuous uninterrupted single phase single wave output at 230 V/50 Hz AC as required. It shall be capable of delivering 6 KVA at any power factor from unity to 0.8 lagging. On energizing the output shall build up gradually within 5 seconds.

The output of the inverter shall be possible to set at any value between 225 to235 V. It shall be maintained within +/- 2 % of the set value for:

  1. Input voltage from 42 to 57 V DC
  2. Load current variations from zero to 100 % (full load)
  3. Load power factor variations from unity to 0.8 lagging.

The output voltage shall be free of modulation and hunting.

The frequency of the output voltage shall be 50 +/- 0.5 Hz under various input and output/load condition.

The inverter shall be capable of taking 150 % of its full rated load for 5 minutes without any damage or over heating of the components. When taking 150 % of overload, the output voltage may vary by 10 % of the rated voltage. In case excessive overload or short circuit at the output the inverter shall be isolated for DC.
The inverter should automatically get switched off or disconnected in the event of the output voltage exceeding 250 volts for more than 1 second with an inverse characteristic between load voltage and switch off time. The inverter shall be possibility to operate remotely

Efficiency and power factor:

The full load efficiency of the inverter shall be NOT LESS THAN 80 % for input voltage of 230 V AC at unity power factor.

Power factor:
Power factor with resistive load and at nominal input shall be better than 0.9 lagging without the use of power factor improvement capacitors.

Adequate protection shall be incorporated for
1. Reverse of polarity at input Inverter shall trip
2. Input under voltage (below 40 V for 1 sec)  Inverter shall be isolated
3. Input over voltage (beyond 60 V for 1 sec)  Inverter shall be isolated
4. Output over voltage (beyond 250 V for 1 sec) Inverter shall be switched off
Automatically with an inverse
Characteristic between load
Voltage & switch-off time
With audio and visual alarm Warning
5. Output frequency below 45 Hz Input contactor shall trip.
6. RC snubbers for surge & transient protection

The protective arrangement shall also include:
a) Contactors, MCBs at the input of the inverter and with HRC fuses back-up.
b) HRC fuses in the DC input lead.


The following supervisory indications shall be provided front on the panel of the cubicle. Wide angle LEDs to give positive visual indication for the following:
1. INVERTER ON LOAD                                                   Green LED
2. LOAD ON COMMERCIAL MAINS                                  Amber LED
3. INVERTER FAIL                                                             Red LED
The following alarm conditions shall be displayed visually by lamps on the front panel of the cubicle together with the sounding of audible alarm.

1. Inverter output
a) Fail
b) Exceeds 250 V for 1 sec.
c) Fail below 250 V for 1 sec.
d) Fails below 210 V for 1 sec.
2. DC over voltage (DC voltage exceeds 60 V for 1 sec.)
3. DC under voltage (DC voltage fails below 40 V for more than 1 second)



  • The design will incorporate inverter circuits using transistorized/MOSFET/IGBT technology based on the load capacity.
  • The efficiency is > 85 %(typically)
  • Compact size
  • Static by pass switch for automatic transfer to raw AC mains.
  • Reverse polarity protection with low power loss.
  • De-Sat sensing to reduce the MOSFET/IGBT failures.

Product Features:

The important features of units are:

  1. Possibility of remote control ON/OFF.
  2. Power supply fault detection, isolation of the inverter and generating a signal.
  3. Protective arrangement if the power supply bias is reversed.
  4. On-load switch/circuit breaker.
  5. Fuses and protection against overload and short circuit.
  6. Circuits like pilot generator, regulator power stage, gating pulse generator, input filter control, alarm and supervisory circuits.
  7. In the event of inverter failure it shall be possible to transfer the load to AC commercial/SB mains and back to inverter on its restoration by means of transfer switch manually.

These functions and facilities have to be met by the various circuit blocks incorporating MOSFET/IGBT inverter suitably interconnected with other control and regulatory as well as auxiliary circuits as may be necessary to achieve the performance limits specified here in.

Salient Features:

There are many different power circuit topologies and control strategies used in inverter designs. Different design approaches address various issues that may be more or less important depending on the way that the inverter is intended to be used.
This Power Inverter is configured with the latest Soft Start Technology (SST) and supplies continuous power and peak watts in the form of 230 volt AC outlets to run most house hold or telecom appliances. Before introduction of SST, high start-up currents from large inductive loads could shut down an inverter.

SST improves inverter operation by:

• Gradual voltage ramp-up during inverter start-up, eliminating failed cold starts under load.
• Output that momentarily dips in voltage and quickly recovers to allow large. Motorized loads to start, eliminating most shutdowns from momentary overloads.
• A new technology that cools the power transistors more efficiently, and, combined.  With Soft Start, dramatically increases reliability and life of the product.




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