PQ Parameter

Definition

Planning / Compliance Target(s)

Reference Regulation / Industry Standard(s)

Power Frequency Variation

Frequency range of supplied voltage waveform, quantified as the mean value over 10 s intervals

< +/ 0.5 Hz

NPCC Directory 12

Steadystate long duration (> 1 min) voltage variation

Range of rms value of supplied voltage, quantified as the mean value over a prescribed time interval and expressed as a percentage of nominal

Tx TSC Appendix 2: In accordance with IESO Market Rules Appendix 4.1
Dx +/6% of nominal voltage (for voltage levels < 50 kV)
Table 2 below (for voltage levels < 1 kV)

TSC Appendix 2
IESO market rules Appendix 4.1
CSA Standard CAN3C23583 (reaffirmed in 2015).

Voltage Unbalance

A condition in a 3phase system in which the rms values of the linetoline voltages (fundamental frequency component), or the phase angles between consecutive line voltages, are not all equal. The degree of inequality is usually expressed as the ratio of the negative sequence components to the positive sequence component.
Voltage unbalance is considered in relation to long term effects, i.e. for durations of 10 min or longer

TxTSC Appendix 2:
Up to 2%  95% of the time over minimum 1 week interval
According to CAN/CSA E 1000 2297
DxUp to 3% (per IEC for LV and MV networks)

NOP32 (internal HONI policy) CAN/CSAC61000122:04 (for 135 kV Systems)
CAN/CSAC6100022:04 (for voltage levels < 1 kV)

Voltage Harmonics

A measure of the distortion present in the normally 60 Hz sinusoidal nature of the waveform. This is usually expressed in terms of the relative magnitude of individual harmonic orders (frequency components) or as Total Harmonic Distortion (THD) reflecting aggregated contribution of multiple harmonic components.

Tx Table 4 below
Dx  Long term effects (arise from harmonics levels that are sustained for 10 min or more):
Table 3 below for compatibility levels Long term THD limit = 8%
 Short term effects
Table 3 below multiplied by a scale factor K (given in CAN/CSAC6100022:04) for compatibility levels
Short term THD limit = 11%

IEEE 519 2014
IEEE 519 2014
CAN/CSAC6100022:04 (reaffirmed 2014)

Voltage Flicker

Repetitive or sudden fluctuations of voltage magnitude that results in variations in light intensity from electric luminaires, particularly incandescent lighting, perceptible to the human eye as “flicker”. These fluctuations may be produced by fluctuating loads, operation of transformer tap changers and other operational adjustments of the supply system or equipment connected to it.
In normal circumstances the value of rapid voltage changes is limited to 3% of nominal supply voltage. However step voltage changes up to 4% can occur infrequently (for example due to capacitor switching operations in the supplying network)
Voltage fluctuations occurring in low voltage networks are termed “flicker”. Flicker severity is calculated with respect to both short term (< 3 s) and long term (> 10 min) effects.

Planning Level:
Shortterm flicker Index (Pst):
HV: <= 0.8 MV: <= 0.9
Longterm flicker Index (Plt)HV: <= 0.7 MV: <= 0.6
Compatibility Level for LV
Pst <= 1.0 Plt <= 0.8

CAN/CSAC6100037
CAN/CSA  C6100022 Flicker severity is measured in accordance with CAN/CSA 61000415.

Voltage Sag

A momentary reduction of voltage magnitude relative to nominal or preevent voltage magnitude, characterized in terms of magnitude and duration. This can occur in any combination of phases.

0.1 pu  0.9 pu for ≤ 1min

IEEE 11592009
IEC 6100028

Voltage Swell

A momentary increase of voltage magnitude relative to the nominal or preevent voltage magnitude, characterized in terms of magnitude and duration. This can occur in any combination of phases.

>1.1pu for ≤ 1min

IEEE 11592009
IEC 6100028

Undervoltage

A longduration reduction of voltage magnitude relative to nominal or preevent voltage, characterized in terms of magnitude and duration.
This can occur in any combination of phases.

0.1 pu  0.9 pu for > 1min

IEEE 11592009
IEC 6100028

Overvoltage

A longduration rise of voltage magnitude relative to nominal or preevent voltage, characterized in terms of magnitude and duration.
This can occur in any combination of phases.

> 1.1pu for > 1min

IEEE 11592009
IEC 6100028

Voltage Transient

A very brief (< 1 cycle) fluctuation in the magnitude of voltage. The primary causes are switching events and lightning, either direct strike or induced current. Depending on their severity (magnitude and associated energy discharge), such events may cause equipment damage.

TSC Appendix 2 specifies that “All Equipment shall be able to withstand capacitor switching surges that transiently increase voltage to twice normal levels. Sustained voltage changes shall be limited to 4% for capacitor switching events”.

At present there is no agreed Standard on characterization of voltage transients.

Voltage Interruption

A sudden and sustained reduction of the voltage on all phases at a particular point on an electricity supply system below a threshold.

Short term: ≤ 10% of nominal for ≤ 1min
Long term: 0% for > 1min

IEEE 11592009
IEC 6100028
