Operation with an engine generator set

User’s Manual

See figure 11 below.

If a stand-by generator is included in the installation, it is generally started automati- cally in the event of a normal AC source failure and connected to the main low volt- age switchboard. It is disconnected when

output voltage quality and continuity

The output voltage is stable in amplitude and frequency and is free of interruptions or transients outside specified tolerances, irre- spective of normal AC source or load distur- bances (outages, load step changes, etc.).

When the bypass AC source frequency returns to within the specified tolerances, the inverter is gradually re-synchronized to the bypass line at a rate of 0.5 Hz to 2 Hz/s (as per the value personalized by the after-sales support department), thus avoiding exposing the load to sudden fre- quency variations.

normal AC source power is restored. With such a system, the required battery time may be reduced to the time neces- sary for starting and bringing on line the stand-by generator. The battery (D) sup- plies power to the inverter (B) during the transfers:

■normal AC source to the generator;

■generator to the normal AC source. The transfer sequences described above (normal AC source ➜ battery, battery ➜ generator, generator ➜ battery, and bat- tery ➜ normal AC source) are fully auto- matic. They in no way affect the load and require no manual operation by the user.

NOTE

To avoid load surges on the generator, the rectifi- er/charger is started with a 10 second maximum current consumption walk-in (lasting 3 to 10 seconds, depending on the percent load).

To avoid overloading an undersized engine gener- ator set, it is possible to set a maximum power level drawn by the nor- mal AC input. Any addi- tional power required is supplied by the battery. This modification can be made on site by an MGE UPS SYSTEMS field engineer.

steady state voltage regulation

For stable or slowly varying load condi- tions, the inverter output voltage is regu- lated to within ±0.5% in amplitude.

The frequency of the output voltage can theoretically be regulated to within 0.1% of the rated value, however the output fre- quency range may be intentionally extend- ed to a maximum of ±2 Hz so that the inverter can remain synchronized with the bypass AC source and its inherent fre- quency fluctuations, thus enabling transfer of the load to the bypass line at any time.

NOTE

The output frequency range can be personalized and if necessary modified on the customer site by a qualified MGE UPS SYS- TEMS support technician from ±0.25 Hz to ±2 Hz in

0.25HZ steps. When the bypass AC source voltage moves out- side this frequency range, the inverter is desynchro- nised and operates in "free running" mode, with the output frequency regu- lated to a high level of accuracy by a quartz oscillator.

transient voltage regulation

The inverter output voltage is not notably affected by instantaneous major variations in load characteristics.

This is made possible by the PWM (Pulse Width Modulation) chopping technique and the microprocessor-based regulation system that instantly compensates for any variation. In particular, the inverter output voltage remains within +/- 2% of the rated voltage for load step changes of 0 to 100% or of 100 to 0%.

Example of an installation with an engine generator set

		Galaxy PW
generator	main LV switchboard		C
G		Mains 2
G
		A	B
HV system		Mains 1
			D

Fig. 11

Introduction