Published By Terry Chandler Director of Engineering, Power Quality Thailand LTD/Power Quality Inc., USA.
Emails: terryc@powerquality.org, terryc@powerquality.co.th
1. A new revision of the IEC standard for PQ monitors 61000-4-30 Class Edition 3 2015 has been released.
Why?
It includes new parameters and new requirements for accuracy over the entire operating temperature range.
2. The PQ Instrument must have 4 each differential voltage and 4 differential current channels.
(Differential means two connections per channel high and low. ) Some power monitor instruments are equipped with a single ended (non-differential input). A differential input channel is not referenced to ground, but both sides of the input are “floating”.
Where the voltage or current that is measured with this single ended inputs is always measured between that specific point and ground.
Why?
Without differential voltage channels, ALL voltage measurements are made relative to ground. This means measurements in an AC Delta circuit require a ground connection. But a power transformer delta output is not referenced to ground! So the measurement results will have unknown errors because of ground potential rise. For example during a fault or during a lightning strike. The result is invalid data.
3. All parameters, on all channels must be recorded synchronized and simultaneously in all modes all the time. This means the instrument records all the parameters and the user chooses which parameters to view after the recording period.
Why?
If the user has to select the parameters to be recorded before starting the recording, he is forced to guess what parameters are required for this site. If he guesses wrong, then the recording time is wasted and he’ll have to do it again.
4. All parameters must be sampled at the same frequency regardless of the monitor mode, setup or duration of monitoring period.
Why?
This is required to provide consistent data for analysis and comparison between voltage levels or different points on the network. It’s also required in the event a dispute between the utility and the user. Because different sample frequencies mean different resolution on time of event and possible gaps in the data when the instrument is “blind”. (not sampling). How can user decide which is needed for each site to be surveyed.
5. The instrument must have an enunciator type displaying the QOS (Quality of supply) while monitoring. This display must show the current state of the Quality of Supply real time of voltage, current, frequency, imbalance, swells, sag events, transients, flicker, THD without disrupting monitoring.
Why?
So the user ( or even none experienced user) can determine very quickly at any time during the monitoring the status of the Quality of Supply without transfering data to a computer or even touching the instrument.
6. The instrument must be capable of automatically testing the wiring connections for errors and alerting the user to the situation automatically.
Why?
To correct any connection errors before monitoring
7. The instrument must be have built-in software to analyze voltage events and catagorize them per the IEC or IEEE International standards.
Why?
So the report generated identifies the PQ incidents compared to the IEEE or IEC standard automatically.
8. Software must include the capability for the user to correct connection errors, time of day errors and align the time stamps of data taken by separate monitors.
Why?
So user can correct the data and prepare the report without having to repeat the monitoring, using the existing data file.
9. Software must include the capability to post process the periodic waveform event data and determine the individual voltage, current , power harmonics and interharmonics to the 125th harmonic.
Why?
This is advanced capability to provide additional data analysis from waveforms recorded during the monitoring period
10. Software must provide the capability to calculate TDD (Total Demand Distortion) and Even/ODD THD.
Why?
In the case where the instrument does not have these calculations built in.
11. Software must include the capability automatically generate reports to International standards and allow the user to define their own standard.
Why?
Reduce the engineering time to generate reports that are complete and easily understood.
12. Software must include the capability to calculate additional parameters for the recorded data , such as a virtual neutral current.
Why?
It gives the user the option of using the 4th current channel to monitor ground current
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