Power Distribution
Overview - Power Distribution Units (PDUs)
Power Distribution for IT systems encompasses the whole critical power system. However, in this instance we are addressing the specific power distribution from the load side of the UPS to the power cabling delivering quality, uninterrupted power to the cabinet level or power cable level. This distribution is done by traditional power distribution units. Cabinet level power distibution often is referred to as PDUs however the term CPDU for cabinet power distribtion units is more appropriate.
PDUs come in two styles.
Transformer Based PDUs - Transformer based PDUs typically step down 480 volt power to 120/208 volt computer voltages. Various types of transformers may be involved from standard to harmonic isolation transformers. Types available are:
- K1 standard type transformer
- designed for general building use require derating for non-linear load use
- generally not properly applied to IT loads
- K13 light grade K factor transformers
- designed for lighter non-linear IT load use
- designed to survive full harmonic loads up to K13
- requires derating for load profiles above K13
- K20 robust grade K factor transformers
- designed for robust non-linear IT loads
- designed to survive full harmonic loads up to K20
- requires derating for load profiles above K20
- Dual Secondary Harmonic Cancellation Transformers
- cancels harmonic current
- Triple Secondary Harmonic Cancellation Transformers
- cancels additional harmonic current
- Quad Secondary Harmonic Cancellation Transformers
- cancels the most harmonic current
PDUs provide a simple pacakge of a main input breaker or switch, a transformer when required or desired andone or more panelboards. Typical kVA ranges are from 15 to 750 kVA and including one to six panelboards of output or to incorporate output subfeed breakers which in turn feed remote power distribution such as RPP units.
Transformerless PDUs - These are similar to the above but lack a transformer. Incoming power is already useable 120/208 volt power. These units are smaller in footprint, often 2' x 2', and provide 1 to 4 panelboards for up to 168 breakers feeding IT loads. Cables can be top or bottom entry.
Increasingly common is to include Branch Current Monitoring Systems (BCMS) as part of PDUs. This allows the reading of current on each circuit out of a PDU. Alarms thresholds can be set to alert when current goes too high (circuit overload) or too low (likely equipment shutdown). Advanced systems allow reading of voltage, kVA, kW on each circuit which is especially beneficial in co-location and managed IT centers. Branch Current Monoitoring was invented and patented by Power Distribution, Inc.