Power Equipment

Power Equipment used in quality power systems include:

Rectifiers	Inverters	Batteries
Generators	Transfer Switches	UPS Systems

UPS Systems

Under Voltage Protection utilising an Uninterruptible Power Supply. A UPS consists of:

• A Rectifier to convert incoming raw AC to DC
• A Battery to store DC power and supply when raw AC fails
• An Inverter to convert the DC back to AC
• A redundant internal Static Bypass Switch to improve system reliability
• An external Transfer Switch either Static or Mechanical

UPS systems are generally specified to have a 10 minute battery. This allows for:

• Degradation of life of the battery
• A fail to start of the generator

Not all UPS systems have generator support. In those cases 20 minute or longer batteries are suggested. Alternatively the risk is acceptable using a standard 10 minute battery.

Transfer Switch

UPS Bypass Transfer Switches are either:

• Mechanical operation
• Static Electronic operation

Generators

Generator = Diesel Engine with Alternator

An engine should be sized on the amount of power it will supply. Yes this sounds a simple statement. Unfortunately due to complications with non linear loads and transient loads the engine needs to have some oversizing. Too much oversizing means the engine will run lightly loaded.

If an engine runs less than 30% load then damage can develop over time, as fuel is burnt at too low a temperature to boil off fuel residues. Residues form on the cylinders that are abrasive. This is known as glazing the bores.

Alternators need to be sized to both carry the current and for the amount of distortion that is acceptable to the site equipment. Again, this sounds a simple statement. The complication here is that normal loads do not draw a clean current. As such the alternator needs to be oversized to combat non linearity.

The next major issue with selection is whether to have a redundant engine. This raises many complex control issues and must be addressed on a by project basis.