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Even harmonics cancel out due to the symmetry The Point of Common Coupling (PCC) with the

between the positive and negative halves of a consumer/utility interface is the closest point on the

periodic wave & majority of non-linear loads produce utility side of the customer’s service where another

odd harmonics. utility customer is or could be supplied. For the

CESC LT distribution system, the Feeder Pillar Box

➤ Uneven current draw between the positive & (bus-bar) may be considered as the PCC.

negative halves of one cycle of operation can

generate even harmonics, but the presence of LIMITS ON SYSTEM HARMONICS

even harmonics in a power system can normally be

neglected for all intents and purposes. IEEE std 519-2014 gives us the allowable Voltage and

current harmonics limits in a power system. Voltage

➤ The major point of interest is the odd Triplen harmonic limits are based on the THD values whereas the

harmonics i.e. with frequencies in odd multiples of current harmonic limits vary based on the short circuit

3 (h = 3,9,15,…). Other harmonics are either positive strength of the system they are being injected into.

or negative sequenced, thus the eﬀective current

in Neutral is zero under balanced condition but for Table 1: IEEE std 519-2014 voltage harmonic limits

triplen harmonics, the currents in three phases add

up in the neutral increasing the neutral current. Voltage Distortion Limits

MEASUREMENT OF HARMONICS Bus Voltage Individual Total Voltage

at PCC Voltage Distortion

Harmonics in the system need to be quantiﬁed before THD (%)

further analysis. Two factors are deﬁned for this purpose: Distortion (%)

1. THD (Total Harmonic Distortion):TheTotal Harmonic Below 69 kV 3.0 5.0

Distortion (THD) is an indicator of the distortion of a

signal. For a signal y, the THD is deﬁned as: 69 kV to161 kV 1.5 2.5

Thus, THD is the ratio of the r.m.s. value of all the 161 kV and above 1.0 1.5

harmonic components of the signal y, to the

fundamental Y1. Note: High-voltage systems can have up to 2.0% THD where the cause

2. TDD (Total Demand Distortion): TDD is the per is an HVDC terminal that will attenuate by the lime it is tapped for a user.

phase harmonic current distortion against full load

demand of the system. It may be expressed as: Table 2: IEEE std 519-2014 Current harmonic limits

IL is deﬁned as the maximum demand load current Currant Distortion Limits for General Distribution Systems

(fundamental frequency component) at PCC (Point (120 VThrough 69000 V)

of Common Coupling). This would be the maximum

current averaged over a demand interval for a given Maximum Harmonic Current Distortion in Percent of IL

customer. TDD = THD at full load.

Individual Harmonic Order (Odd Harmonics)

ISC / IL <11 11≤h< 17 17≤h<23 23≤h<35 35≤h TDD

<20* 4.0 2.0 1.5 0.6 0.3 5.0

20<50 7.0 3.5 2.5 1.0 0.5 8.0

50<100 10.0 4.5 4.0 1.5 0.7 12.0

100<1000 12.0 5.5 5.0 2.0 1.0 15.0

>1000 15.0 7.0 6.0 2.5 1,4 20.0

Even harmonics are limited to 25% of the odd harmonic limits above.

Current distortions that result in a dc oﬀset, e.g. half-wave converters,

are not allowed.

* All power generation equipment is limited to these values of current

distortion, regardless of actual ISC / IL.

Where

ISC = maximum short-circuit current at PCC.

IL = maximum demand load current (fundamental frequency

component) at PCC.

TDD = Total demand distortion (RSS), harmonic current distortion

in % of maximum demand load current (15 or 30 min

demand).

PCC = Point of common coupling.

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between the positive and negative halves of a consumer/utility interface is the closest point on the

periodic wave & majority of non-linear loads produce utility side of the customer’s service where another

odd harmonics. utility customer is or could be supplied. For the

CESC LT distribution system, the Feeder Pillar Box

➤ Uneven current draw between the positive & (bus-bar) may be considered as the PCC.

negative halves of one cycle of operation can

generate even harmonics, but the presence of LIMITS ON SYSTEM HARMONICS

even harmonics in a power system can normally be

neglected for all intents and purposes. IEEE std 519-2014 gives us the allowable Voltage and

current harmonics limits in a power system. Voltage

➤ The major point of interest is the odd Triplen harmonic limits are based on the THD values whereas the

harmonics i.e. with frequencies in odd multiples of current harmonic limits vary based on the short circuit

3 (h = 3,9,15,…). Other harmonics are either positive strength of the system they are being injected into.

or negative sequenced, thus the eﬀective current

in Neutral is zero under balanced condition but for Table 1: IEEE std 519-2014 voltage harmonic limits

triplen harmonics, the currents in three phases add

up in the neutral increasing the neutral current. Voltage Distortion Limits

MEASUREMENT OF HARMONICS Bus Voltage Individual Total Voltage

at PCC Voltage Distortion

Harmonics in the system need to be quantiﬁed before THD (%)

further analysis. Two factors are deﬁned for this purpose: Distortion (%)

1. THD (Total Harmonic Distortion):TheTotal Harmonic Below 69 kV 3.0 5.0

Distortion (THD) is an indicator of the distortion of a

signal. For a signal y, the THD is deﬁned as: 69 kV to161 kV 1.5 2.5

Thus, THD is the ratio of the r.m.s. value of all the 161 kV and above 1.0 1.5

harmonic components of the signal y, to the

fundamental Y1. Note: High-voltage systems can have up to 2.0% THD where the cause

2. TDD (Total Demand Distortion): TDD is the per is an HVDC terminal that will attenuate by the lime it is tapped for a user.

phase harmonic current distortion against full load

demand of the system. It may be expressed as: Table 2: IEEE std 519-2014 Current harmonic limits

IL is deﬁned as the maximum demand load current Currant Distortion Limits for General Distribution Systems

(fundamental frequency component) at PCC (Point (120 VThrough 69000 V)

of Common Coupling). This would be the maximum

current averaged over a demand interval for a given Maximum Harmonic Current Distortion in Percent of IL

customer. TDD = THD at full load.

Individual Harmonic Order (Odd Harmonics)

ISC / IL <11 11≤h< 17 17≤h<23 23≤h<35 35≤h TDD

<20* 4.0 2.0 1.5 0.6 0.3 5.0

20<50 7.0 3.5 2.5 1.0 0.5 8.0

50<100 10.0 4.5 4.0 1.5 0.7 12.0

100<1000 12.0 5.5 5.0 2.0 1.0 15.0

>1000 15.0 7.0 6.0 2.5 1,4 20.0

Even harmonics are limited to 25% of the odd harmonic limits above.

Current distortions that result in a dc oﬀset, e.g. half-wave converters,

are not allowed.

* All power generation equipment is limited to these values of current

distortion, regardless of actual ISC / IL.

Where

ISC = maximum short-circuit current at PCC.

IL = maximum demand load current (fundamental frequency

component) at PCC.

TDD = Total demand distortion (RSS), harmonic current distortion

in % of maximum demand load current (15 or 30 min

demand).

PCC = Point of common coupling.

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