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Home > Customers
Power Quality Disturbance Definitions, Classifications and Applicable
Standards
All disturbances relate to voltage unless otherwise stated.
Steady State Disturbances
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Incident Type
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Definition
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Graphic representation
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Applicable standards
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Magnitude (regulation)
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Long term level of voltage established through transformer taps and dynamically controlled by regulators. Measurement of voltage magnitude over the long term serves the basis for the capture and characterization of other power quality disturbances. |
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Presently specified in TSC Appendix 2:and the IESO Market Rules
Appendix 4.1:Voltages below 50kV are maintained in accordance with
CAN/CSA C235
Essentially, systems below 50kV, voltage levels must be regulated
to within +/-6% of nominal voltage.
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Unbalance
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Condition of the 3 phase power system where the rms magnitude or phase angle of the line voltages are not equal. This is usually determined as a percent of the ratio of negative sequence component to positive sequence component. |
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Presently specified in TSC Appendix 2,
Transmission system unbalances are limited to 2% (CAN/CSA E 1000 2-2-97).
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Harmonics
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Components of electricity with frequencies which are an integral multiple of the fundamental frequency (60Hz). This is usually expressed in Total Harmonic Distortion or as individual harmonic order (frequency) components. |
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Presently specified in TSC Appendix 2as
respecting the limitations in Table 11.1 Voltage Distortion Limits
Std. IEEE 519-1992.
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Flicker
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Periodic fluctuation of voltage that results in flicker of lighting, particularly incandescent lighting. This is typically causes by fluctuating loads such as hoists, reciprocating pumps, arc furnaces, etc. |
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Presently specified in TSC
Appendix 2 Ref 5.: Magnitude/limit points-on-a-curve.
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Event-based (Transient) Disturbances
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Incident Type
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Definition
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Graphic representation
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Applicable standards
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Dip (Sag)
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A momentary reduction of voltage magnitude relative to nominal
or pre-event voltage magnitude. This can occur in any combination
of phases.
Voltage dip is characterized by minimum voltage magnitude and duration
of dip event.
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Currently, there are no applicable standards
referenced in the TSC. |
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Swell
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A momentary increase of voltage magnitude relative to nominal or
pre-event voltage magnitude. This can occur in any combination of
phases.
Voltage swell is characterized by maximum swell voltage magnitude
and duration of swell event.
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Currently, there are no applicable standards
referenced in the TSC. |
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Transient
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A very brief (<0.5 cycle) fluctuation in the magnitude of voltage.
The primary causes of transients are switching events and lightning,
either direct strike or induced current. Depending on their severity
(magnitude and/or energy), these events may cause equipment damage.
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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 and 10% for line switching events."
At present, there is no single universal method for the measurement
and characterization of voltage transients.
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