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Power Quality Requirements at a

Point of Connection

(project ‘KTI’)

Power Quality and Energy Saving Symposium

Presented by: Sharmistha Bhattacharyya

TU/Eindhoven, 27th January 2011

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Motivation

Increasing use of sensitive apparatus and industrial processes

Growth of decentralized generations and their increased influences

Economic pressure on network operator due to deregulation

Power quality (PQ) related arguments among the involved parties at

the point of connection (POC).

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Themes of project ‘KTI’

Characteristics and

interactions of the

apparatus and the

installations (ECN)

Development of new power

electronic devices delivering

a good power quality (TU/e-

EPE)

Research on new boundary conditions for

power quality; societal importance; and

various consequences

(TU/e- EPS, Laborelec, ECN)

Theme -1

Theme -2 Theme -3

consequences of poor PQ?

optimal PQ requirements

at a POC?

responsibilities of different parties at a POC?

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Mutual responsibilities on PQ in the system

Regulators

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Research Approach

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Main deliverables - I

• Overview of various consequences of poor PQ

• Present PQ performance of the Dutch networks

• Flicker study: define emission limits at LV customer’s

POC, proposal for compatibility levels

• Harmonics study: analyze harmonic interactions in the

network, and propose harmonic current limits at a POC

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• Voltage dip: propose limiting numbers of voltage dips in

a MV network

• Guidelines on optimal PQ criteria at a point of

connection (POC)

• Define PQ responsibilities of involved parties (namely:

the network operator, the customer and the device

manufacturer) at a POC

Main deliverables - II

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Overview of PQ consequences

Network operators also suffer extra losses; and in

extreme situation device’s early aging and failure

Source: European power

quality survey report, 2008

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Financial impacts of poor PQ

LPQI survey (2003-2004) in EU-25 countries estimated PQ related

financial losses as 151.7 thousand million Euros

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Some Plt values in MV

grid exceed the limit

(0.05% cases)

Comparison of Plt trends

PQ Performance in the Dutch Network

(as per

EN50160)

(as per Dutch

Grid Code)

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Harmonics in the Dutch network

Total harmonics distortion (THDv)

Voltage variations are generally found to be

within the standard limits

Local incidents are

reported for some

specific order harmonic

voltages that exceeded

the standard limits

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Voltage dips in HV network (2008)

Residual

voltage

(p.u)

Duration of dips (s)

0.01-0.02 0.02-0.1 0.1-0.5 0.5-2.5 2.5-5

0.8-0.9 0.05 2.05 0.95 0.1 0.1

0.7-0.8 0.05 2.05 0.95 0 0

0.6-0.7 0 0.17 0.07 0 0

0.5-0.6 0 0.17 0.07 0 0

0.4-0.5 0 0.17 0.07 0 0

0.3-0.4 0 0.125 0.08 0 0

0.2-0.3 0 0.125 0.08 0 0

0.1-0.2 0 0.125 0.08 0 0

<0.1 0 0.13 0.09 0 0

10s

0.2s

SEMI

graph

Total 7.8 dips per year

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Main Research Contributions

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Flicker Problem in the Network

• Many complaints about flicker problem

• Lack of a global standard on flicker planning level

• Customers not aware of flicker emission at POC

Three

cases are

analysed

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Flicker Severity in the Network

Emission limit at LV customer’s POC is estimated

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Proposed planning and compatibility limits on

flicker severity

• Compatibility level should be specified for 95%, (99%) and 100% of the time and also for 95% and 100% locations

• In future, EN50160 standard can be extended for 100% sites and 100% times.

note: proposed limits are shown for 95% time and 95% sites

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Typical household model used in

harmonic simulation

Individual

spectrum

measurement

+

Combined

measurement

at POC

Harmonic fingerprint database are made for

each device and at the POC

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House models for case studies

• House with high load

(average load demand of 7.5A)

• House with average load

(average load demand of 5.6A)

• House with average load and solar inverter

(average net load demand of 3.5A)

• House with low load

(average load demand of 2.2A)

2 PC, 1 TV, 1

Refrigerator, 6 CFL, 1

vacuum cleaner (at low

power stand) and linear

load (125W)

2 PC, 1 TV, 1 Refrigerator,

10 CFL, 1 vacuum cleaner

(at high power stand), and

linear load (125W)

1 PC, 1 TV, 1

Refrigerator, 2 CFL and

linear load (125W)

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Harmonics simulation

Two background pollutions: high (6%), average (3.2%)

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Harmonic current spectrums of devices

(house with average load demand)

High emission from Vacuum cleaner at low

power stand

CFL PC

TV

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Lab Measurements

TV PC

THD (%) 6.6 6.6 9.4 9.4 2.5 2.5 4.5 4.5

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Harmonic simulation results

• Some orders of

harmonic voltages

exceeded EN50160

standard limits

•Harmonic currents at

household’s terminal

decay exponentially

with high orders

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Field survey at a household’s POC

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Observations on Harmonics Simulations

• Harmonic voltages between 9th to 25th orders are of comparable magnitude

• Harmonic currents decreases exponentially with increasing harmonic orders

• Summation component ‘alpha (α)’ for 3rd harmonic is proposed 1.2 as sufficient diversity exists in the network

• New planning level values for ‘triple n’ harmonics are proposed

• Small installations (such as households) should fulfil maximum impedance (or short circuit ratio) criterion

• No separate harmonic current emission limit is proposed for households (should be as IEC/TR 61000-3-14, stage 1)

• For large LV installations, harmonic emission limits are proposed

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Proposed Limits on Harmonics

Current emission limits at a

LV installation

Harmonic voltage planning levels

for ‘triple n’ harmonics

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Example of Responsibility Sharing on

Harmonics and Flicker

Network operator should be responsible to provide a network

impedance at a customer’s POC that is smaller than maximum limit

Customer should follow the suggested limits on flicker and harmonic

current emissions at his POC

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Historical Average Voltage dips events

recorded in the Dutch HV Network

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Expected Number of Voltage Dips in the

Dutch MV Network

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Average voltage dips in the Dutch MV network

(in EN50160 format)

Residual

voltage U

(in % of

Un)

Duration (ms)

10<t≤20 20<t≤100 100<t≤ 500 500<t≤ 5000

90>U≥80 0.075 1.85 0.75 1.64

80>U≥70 0.075 1.85 0.74 0.49

70>U≥60 0.025 0.26 0.18 0.31

60>U≥50 0.025 0.26 0.13 0.23

50>U≥40 0.025 0.26 0.11 0.11

40>U≥30 0 0.21 0.14 0.04

30>U≥20 0 0.21 0.13 0.04

20>U≥10 0 0.21 0.12 0.04

U<10 0 0.21 0.13 0.04

Total 0.23 5.30 2.43 2.92

Total number around 10.8 dips in a year;

out of which 2.8 dips can cause process interruptions.

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Example of Responsibility Sharing Borders

on Voltage Dips

Can not be avoided, responsible for information!

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Conclusions

• Flicker emission limits at LV installations are estimated

• Planning and compatibility level limits for flicker are proposed

• Proposal for modifications of harmonic voltage planning levels for ‘triple n’ orders are proposed

• Harmonic current emission limits are suggested

• Expected number of voltage dip events in the Dutch network is estimated

• PQ responsibilities for different parties are defined