Application note for the Dranetz automatic characterizer in HDPQ portable instruments.
The RMS variation characterizer analyzes cyclic records saved in the database and determines which of those records constitute an event based on a selected criterion. The result is a database record that contains the description of the event, detail of the event, and indices to the cyclic records in the database.
IEEE 1159 characterizer
RMS variations are characterized based on the IEEE 1159 Categories and Typical Characteristics of Power System Electromagnetic Phenomena. The table below summarizes the relationships between categories, duration, and magnitude:
|Category||Typical duration||Typical Voltage Magnitude|
|Short Duration Variations|
|Sag||0.5 – 30 cycles||0.1 – 0.9 pu|
|Swell||0.5 – 30 cycles||1.1 – 1.8 pu|
|Interruption||0.5 cycles – 3 sec||< 0.1 pu|
|Sag||30 cycles – 3 sec||0.1 – 0.9 pu|
|Swell||30 cycles – 3 sec||1.1 – 1.4 pu|
|Interruption||3 sec – 1 min||< 0.1 pu|
|Sag||3 sec – 1 min||0.1 – 0.9 pu|
|Swell||3 sec – 1 min||1.1 – 1.2 pu|
|Long Duration Variations|
|Interruption, Sustained||> 1 minute||0.0 pu|
|Undervoltages||> 1 minute||0.8 – 0.9 pu|
|Overvoltages||> 1 minute||1.1 – 1.2 pu|
IEC 61000-4-30 characterizer
RMS variations are characterized based on the IEC 61000-4-30 standard. Unlike the IEEE 1159 standard, the requirement does not consider the relationship between the magnitude and duration. The table below summarizes the requirement of the standard.
|Category||Typical duration||Typical Voltage Magnitude|
|Interruption||>=1 cycle||0.01 pu|
|Dip||>=1 cycle||0.9 pu|
|Swell||>=1 cycle||1.1 pu|
Contiguous cycles recorded in the database are grouped together and called a data aggregate. Min and max values are calculated through the group and saved with the record. This mode is used when the selected preset is inrush or fault recorder.
The RMS variation characterizer goes through the database periodically to analyze newly acquired data for events. It runs in the background routine where the other housekeeping routines are located. Whenever the instrument is idle, the 5-second ISR sets a flag to signal the characterizer to run. Once the flag is set, the characterizer will start from the last database index from the previous run up to the last index in the database.
The characterizer was intuitively designed to allow data characterization in groups. Aggregating channels in an event illustrates a fault as a system instead of independently treating each phase in a multi-phase system as a separate entity.
Channels are grouped according to the selected circuit type. In a three-phase circuit for instance, channels Va, Vb, and Vc are grouped together. A fault on more than one phase will result an aggregate event. For example, a sag occurred on phases A and B. The sag on phase A lasted for 30 cycles, 50 cycles for phase B. The result will be an aggregated event that has a total duration of 50 cycles.
An event starts when any channels in the group is out of limit and ends until all channels in the group are in limit. The group mask simply indicates which phases are grouped together. Split phase for example has two groups. Volts A and B (0x0003), and Amps A and B (0x0030).
When an event is in progress, the state of any channels in the group might change that will alter the category where the event should fall in. A sag for example might become an interruption. When this occurs, the characterizer will save the sag event, reset the start indices and counters, and wait for the interruption to come back in limit.
There are priorities when determining the state of an aggregated event based on severity. The highest is interruption, next is sag, then swell. Take for example an event on three-phase system that has a swell on derived channels A and B, and a sag on channel C. The aggregator will characterize the event as sag because of its priority, and the phenomena that the sag caused an unbalance to the system pulling the neutral that caused a swell on the other phases. Another example is an interruption on one phase and sag on the other phases. The characterizer will characterize the aggregated event as interruption because of priority through severity.
After finding an event, the characterizer will pass the search result to the categorizer. From the raw result, the categorizer will populate the necessary details of the event.
The IEEE and IEC characterizer use the same categorizer. Parameters that are not required by the IEC standard are still populated. The display screen decides whether the extra information is displayed based on the selected characterizer mode.
Brief Overview of the transient characterizer
Type – type of transient. Can be one of the following:
- Unipolar Transient – One impulse in any direction.
- Bipolar Transient – Two impulses in opposite directions.
- Oscillatory Transient – at least three cycles of “visual” oscillation.
- Arcing – Like oscillatory, but random. It follows a general envelope of the sine wave, that is, the values do not go to zero.
- Multiple Zero Crossing – Impulse goes through the zero crossing.
- Notching – Impulses are negative and regularly spaced.
- Dropout – Starts with a sharp edge but goes to zero.
- Switch On – Start at zero and then has a sharp edge.
- Switch off – Starts at normal, has a sharp edge and goes to zero.
- Phase shift – Change in phase of fundamental frequency.
- DC – If DC (unipolar) is present for more than one full cycle.
- Cap Switch – A special case of oscillation with initial negative direction followed by positive impulse reaching from 1.2 to 1.8 times the normal peak. Oscillation frequency is 400 to 2kHz.
- Flat top – Flattened Top.
- Peak Limit – Set if peak exceeds the user threshold.
- Amplitude Change – Smooth changes in amplitude.
- Miscellaneous – Set if any of the transient does not fall to any of the above categories.
Duration – In case of multiple hits, the width of the disturbance is measured from the start of the first to the end of the last. The reported notch width is the worst case. Duration can be any of the following:
- Multiple notch
- Eight cycle
- Multiple eight cycle
- Quarter cycle
- Multiple quarter cycle
- Half cycle (+/- 10%)
- Full cycle (+/- 10%)
Severity – Describes the severity of the transient based on the amplitude of the peak. Severity can be mild, moderate or severe.
Input – The input where the transient was detected.
Summary DB Record – Points to the related summary record in the database.
First Impulse Direction – Describes the direction of the transient, either positive or negative. Positive direction adds energy to the wave, that is, it heads away from the zero crossing. Negative on the other hand, subtracts energy from the wave. It heads towards the zero crossing.
Start Offset – Offset to be added to the timestamp for location of the start of the transient.
Point on Wave in Degrees – Phase degrees that corresponds to the main timestamp – the start of the wave sample set.
Microseconds per degree – Period in microseconds per degree in the waveform.
Width – Width of the entire transient in microseconds.
Offset to 50% – Offset to start of impulse at 50% width.
Width at 50% – Width of impulse at 50% width.
Amplitude at 50% – Actual signed amplitude at 50% width.
Offset to 10% – Offset to start of impulse where it exceeds 10%.
Rise time from 10% to 90% – Rise time in microseconds.
Amplitude at 10% – Actual signed amplitude at 10%.
Amplitude at 90% – Actual signed amplitude at 90%.
Offset to max peak – offset in microseconds.
Peak Value – Signed peak value in the whole run.
Peak Value Adjacent – uses adjacent peaks.
Worst peak-to-peak Value – worst peak-to-peak deviation in the whole run.
Zero Crossing Oscillating frequency – measured oscillating frequency in hertz.
Peak Oscillating Frequency – highest measured oscillating frequency in hertz.
The transient characterizer produces a record that contains the above information. High frequency and low frequency transients use the same database record. Some parameters are not populated for the low frequency, depending on the classification of the event.