HP DL360 Power basics for IT professionals - Page 14

Power factor correction, HP ProLiant server power supplies all have peak efficiencies of 85 percent or

Get HP DL360 - ProLiant - G3 PDF manuals and user guides
UPC - 613326948835
View all HP DL360 manuals
Add to My Manuals
Save this manual to your list of manuals

Page 14 highlights

Power factor correction Before computing and storage devices can use electrical power, the AC provided from the source must be transformed to direct current (DC) by a power supply. The term power indicates the rate at which the electricity does work, such as running a central processing unit (CPU) or turning a cooling fan. The power that the electricity provides (apparent power) is simply the voltage times the current, measured in volt-amperes (VA). There is a difference between the power supplied to a device and the power actually used by the device because the capacitive and inductive nature of AC circuits will change the phase relationship of current and voltage as shown in Figure 12. The true power, measured in watts rather than VA, can only be delivered when the current and voltage overlap. Figure 12. Aligned current and voltage for power delivery The power factor (PF) of a device is a number between zero and one that represents the ratio between the real power in watts and the apparent power in VA. A power supply that has a PF of 1.0 indicates that the voltage and current peak together (the voltage and current sine waves are always the same polarity), which means that the VA and watt values are the same. A device with a Power Factor of 0.5 would have a watt value that is half the VA value; for example, a 400VA device with a Power Factor of 0.5 would be a 200W device. A common misconception is that the power factor and the power supply efficiency are related, but this is not the true. Power supply efficiency is the ratio of output power in watts to input power in watts at peak efficiency. For example, a typical white box power supply with a peak efficiency of 75 percent would waste at least 25 percent of the incoming energy by converting it to heat that must then be dissipated. HP ProLiant server power supplies all have peak efficiencies of 85 percent or greater, which increases the amount of power that performs useful work. Devices with a low power factor, on the other hand, do not waste energy. Unused energy is simply returned to the utility and is not paid for by the customer. Utilities charge for true power used as measured in kWhours, not in VA. The main costs associated with a low power factor are for higher amperage circuits to deliver the same amount of true power as a device with a power factor closer to one. Power supplies for servers usually contain circuitry to correct the power factor (that is, to bring input current and voltage into phase). Power-factor correction allows the input current to continuously flow, reduces the peak input current, and reduces energy loss in the power supply, thus improving its operational efficiency. Power-factor-corrected (PFC) power supplies have a power factor near 14

  • 1
  • 2
  • 3
  • 4
  • 5
  • 6
  • 7
  • 8
  • 9
  • 10
  • 11
  • 12
  • 13
  • 14
  • 15
  • 16
  • 17
  • 18
  • 19
  • 20
  • 21
  • 22
  • 23
  • 24
  • 25
  • 26
  • 27
  • 28
  • 29
  • 30
  • 31
  • 32
  • 33
  • 34
  • 35
  • 36
  • 37
  • 38
  • 39
  • 40
  • 41
  • 42
  • 43
  • 44
Power factor correction
Before computing and storage devices can use electrical power, the AC provided from the source
must be transformed to direct current (DC) by a power supply. The term
power
indicates the rate at
which the electricity does work, such as running a central processing unit (CPU) or turning a cooling
fan. The power that the electricity provides (apparent power) is simply the voltage times the current,
measured in volt-amperes (VA).
There is a difference between the power supplied to a device and the power actually used by the
device because the capacitive and inductive nature of AC circuits will change the phase relationship
of current and voltage as shown in Figure 12. The true power, measured in watts rather than VA, can
only be delivered when the current and voltage overlap.
Figure 12.
Aligned current and voltage for power delivery
The power factor (PF) of a device is a number between zero and one that represents the ratio
between the real power in watts and the apparent power in VA.
A power supply that has a PF of
1.0 indicates that the voltage and current peak together (the voltage and current sine waves are
always the same polarity), which means that the VA and watt values are the same.
A device with a
Power Factor of 0.5 would have a watt value that is half the VA value; for example, a 400VA device
with a Power Factor of 0.5 would be a 200W device.
A common misconception is that the power factor and the power supply efficiency are related, but
this is not the true. Power supply efficiency is the ratio of output power in watts to input power in watts
at peak efficiency. For example, a typical white box power supply with a peak efficiency of
75 percent would waste at least 25 percent of the incoming energy by converting it to heat that must
then be dissipated.
HP ProLiant server power supplies all have peak efficiencies of 85 percent or
greater, which increases the amount of power that performs useful work.
Devices with a low power factor, on the other hand, do not waste energy. Unused energy is simply
returned to the utility and is not paid for by the customer.
Utilities charge for true power used as
measured in kWhours, not in VA.
The main costs associated with a low power factor are for higher
amperage circuits to deliver the same amount of true power as a device with a power factor closer to
one.
Power supplies for servers usually contain circuitry to correct the power factor (that is, to bring input
current and voltage into phase). Power-factor correction allows the input current to continuously flow,
reduces the peak input current, and reduces energy loss in the power supply, thus improving its
operational efficiency. Power-factor-corrected (PFC) power supplies have a power factor near
14