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:
- Input voltage from 42 to 57 V DC
- Load current variations from zero to 100 % (full load)
- 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 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.