Power System Harmonics, True Power Factor & DPF Measure

Displacement Power Factor (DPF) is the power factor as we know at fundamental system frequency (50Hz in UK). However, True Power Factor (PF) or just Power Factor is the product of the distortion power factor and DPF. Check out the Wikipedia article on this  topic. The following equation related components:

Where,  is the total current harmonic distortion at the point of measurement, and are fundamental and total harmonic RMS currents, and  is the distortion power factor (in other words distortion factor associated with power factor).

The above equation leads to the following conclusions:

• PF≤DPF, True Power Factor is always less than or equal to Displacement Power Factor.
• PF = DPF, True Power Factor equals Displacement Power Factor when there are current harmonics at the point of measurement;
• PF<DPF, suggests presence of harmonics, take it easy: awareness is good.
• PF<<DPF, means its time to take action.

The above observations, comparing DPF and PF will give you a quick assessment of harmonic severity, however if detail assessment is required then you will need to monitor both and .

As I understand, most meters or monitoring equipment that display PF and DFC also may have the ability to calculate both current and voltage total harmonic distortion factors: and , sometimes including individual harmonics levels as numbers and/or as a harmonic spectrum bar chart. Now if have measured these values, i.e. both THD for current and voltage, and individual harmonics levels in %, then compare them against the harmonics standards that govern your electric network, and you will know the severity of the harmonic problem.

In UK, DNOs are required to comply with EN50160 Std. and consumers with G5/4-1 Std.

Power Quality Working Groups

Power systems research and application engineers, depending on their ‘point-of-view’, are broadly divided into four categories:

• Those that take a utility’s point of view;
• Those that take end-user’s point of view;
• Equipment manufacturer’s and third party solutions and services (consultants, experts etc.) provider’s point of view;
• And finally those (e.g. PQ related standards, working groups, regulators, university PQ projects that are funded by independent bodies or institutes etc.) who see the big picture and bring equilibrium among the above three perspectives.

Each of first three groups, i.e. utility (Group 1), customer (Group 2) and equipment manufacturer/consultant (Group 3), have valuable insight, expertise, and know how in their respective representing group. These three representing groups usually have biased view on various PQ issues. Some of these include: ‘who is responsible for PQ problems?’ and ‘who should and how much each should contribute towards problem solution?’ However, it is this biased view that makes them a vital constituent in maintaining a fair share of involved party’s (utility, end-user etc.) PQ improvement responsibility. The final or the fourth group, although seeks to see the big picture, taking a collective view of all three groups preceding it, may lack in depth knowledge of particular PQ problems each of other groups are handling.

When PQ standards are written, a working group is set up, which at best tries to include at least one delegate or more, representing each of these groups to review and to push forward a new standard that is fairly acceptable for all concerned parties.

A comprehensive study, nevertheless, should aim to develop a methodology that includes tools/modules to bring customized voltage disturbance assessment for both utilities and industrial customers, such that results obtained from the tool could be well beneficial for equipment manufacturers to access PQ market potential and to establish specification range of their equipment to meet a specific customer’s or utility’s voltage disturbance immunity criteria. The objective should be to present a tool that brings interaction and integration of data consensus from utilities, customers and equipment manufacturers, thus enabling faster optimization of PQ improvement through iterative interactions of these parties (utilities, customers and equipment manufacturers).

UK Electricity DNOs and TNOs

Here is a list of eight electricity Distribution Network Operators (DNOs) and three electrical Transmission Network Operators (TNOs) in United Kingdom.

Electrical Distribution Companies:

1. CE Electric UK (NEDL & YEDL)
2. EDF Energy
3. E.On (Central Networks)
4. Northern Ireland Electric
5. United Utilities
6. Western Power Distribution
7. Scottish Power (SP)
8. Scottish & Southern Energy (SPD)

Electrical Transmission Companies:

1. National Gird
2. Scottish Power Transmission Ltd (SPT)
3. Scottish Hydro Electric Transmission Ltd (SHETL)