- Phase shift
- Sinusoidal waveform distortion (switching power supplies)
TPF (TruePF) is the ratio of the active power to the apparent power at the power outlet. TPF shows what portion of apparent power is converted by the load to active power. TPF can be viewed as the sum of useful power and losses.
- For a sine waveform, the TPF (TruePF) is the cosine of the phase shift between the current and the voltage in the electrical circuit (Cos Phi).
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When TPF = 1, all power is active (the phase shift is zero).
This would be the case with a purely resistive load, such as an electric heater. - When TPF = 0, all power is reactive – the load is either purely capacitive (phase shift -90° = the voltage lags behind the current) or purely inductive (phase shift +90° = the current lags behind the voltage).
- In general, TPF < 1 (non-zero phase shift between the current and the voltage), and this causes undesired losses in power lines, in the power supply as well as in the appliance.
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TPF in practical terms:
In general, with TPF = 0.65, a 1000 VA UPS can supply 650 Wh to a computer power supply. For switching power supplies in computers, 0.7 is a typical TPF value.
Why measure TPF (True Power Factor)?
The TPF value can uncover a faulty load / change in the load type.
For example, TPF measurement can be used to detect a clogged filter of a pump because the TPF changes in time as the filter gradually gets clogged.
Difference between TPF a PF
PF (Power Factor or Cos Phi) expresses the ratio of the active energy to the apparent energy as well as the ratio of resistance to impedance in a given electrical circuit. TPF, unlike PF, also takes into account non-sinusoidal waveforms. Such distortions of the sinusoidal waveform are caused e.g. by switching power supplies.
In the context of NETIO products
Some NETIO products can measure TPF (True Power Factor / TruePF) for the whole device (one value). Other products measure TPF per power output (electrical socket) separately and then calculate the overall TPF for the whole device. The TPF differs at each output depending on the nature of the connected appliance.
Measurement accuracy may fluctuate at low currents (less than 0.1 A), or when the nature of the load changes quickly.