POWER QUALITY
The problems caused by poor power quality are extremely serious and can make life very difficult for electrical energy consumers, often even causing substantial financial losses for them. The most important power quality issues include:
Voltage and current distortion in the mains is caused mainly by non-linear receivers which take non-sinusoidal current. The most frequently found non-linear receivers include:
Higher harmonics in the mains
All equipments listed above take current in a non-linear way, causing the harmonics and number of such devices is growing. In practice, the harmonics higher that the 20th are very rare and usually have very low values, hence the standard for harmonics analyzers is minimum 25 harmonics, albeit there are devices which can record 50 harmonics or more.
Higher harmonics can cause various unfavorable effects in the mains system:
Fig 1. Current waveform distorted by a compact fluorescent lamp
Voltage dips and interruptions
Voltage dip is a short decrease of voltage value in the 90% - 1% declared voltage range. Duration of such event is conventionally set in the 10 ms - 1 min range. The reason of voltage dips is mainly connecting large loads to the mains, on the side of both, power supplier and power consumer. This phenomenon is more frequent when the line impedance is high (i.e. in rural areas which have small cross section LV overhead lines when consumers increase power consumption). Less frequent cause of voltage dips is short circuits in distribution systems and also in consumer electrical wiring.
Flicker
In terms of power quality, flicker means periodical changes of the luminous intensity as a result of fluctuations of voltage supplied to light bulbs. This phenomenon causes a deteriorated well-being, annoyance, sometimes headache, that is arduousness for people. The tests have proved that maximum arduousness occurs at the frequency of about 9 changes per second. The most sensitive light sources are traditional incandescent bulbs with tungsten filament. Fluorescent lamps have the best flicker "resistance". The flicker is caused by the voltage drop as a result of connecting and disconnecting large loads and some level of flicker is present in the majority of mains systems.
Unbalance
Unbalance is a term connected with three-phase systems and can refer to:
In three-phase systems, the voltage (current) unbalance occurs when values of three component voltages (currents) are different and/or the angles between individual phases are not equal to 120°.
These phenomena are particularly dangerous for three-phase motors, in which even a slight voltage unbalance can cause current unbalance that is many times larger. In such situation, the motor torque is reduced, heat losses in windings increase, and mechanical wear is faster. The unbalance also has an unfavorable effect on power supply transformers.
The most frequent reason of unbalance is uneven load on individual phases. A good example is connecting to three-phase systems of large one-phase loads, such as railway traction motors. In normal conditions, such as LV lines in the rural areas mentioned above, the unbalance can aggravate voltage dips and flicker.
PQM-701 ANALYZER
Fig. 2. Power Quality Analyzer PQM-701
The events described above constitute a part of problems related to power quality. In order to eliminate hazards to the mains systems and equipments which receive power from them, we need to discover the phenomena which happen in the mains and we must be able to interpret them correctly. To do this, we need to have an analyzing tool. The PQM-701 analyzer is such a tool.The analyzer is intended for a wide spectrum of users who need to control the power quality with a portable device. It can be used in practically all types of mains from 110V to 690V, directly or indirectly through transducers. It can be operated in one-phase systems, split-phase systems, 3- and 4-wire three-phase wye systems, or three-phase delta systems. Therefore, the PQM-701 is an instrument which can be used in professional power engineering, by maintenance departments in industrial plants, or by people who provide mains analysis services.
The analyzer is placed in a simple, robust casing with IP65 ingress protection rating. Due to the casing design, the analyzer can be installed practically anywhere, outdoors and indoors. The analyzer has an built-in heater which is activated automatically when the temperature inside the casing drops below 0°C. This ensures optimum operating conditions for the analyzer electronic circuits. With special bands included in the kit, the analyzer can be installed, for instance, on an electric pole.
The analyzer has five voltage input terminals, marked L1/A, L2/B, L3/C, N and PE, and the N terminal (neutral conductor) is shared. The range of voltages measured by four measuring channels is ±1150V maximum. Current is measured by means of four current inputs to which several types of current clamps can be connected, such as flexible clamps F-1, F-2, F-3 with the 3000A nominal range (the only difference between them is the coil size) and the C-4 clamp (range 1000A AC), C-5 clamp (range 1000A AC/DC) and C-6 clamp (range 10A AC).
The instrument is equipped with a high-capacity removable SD memory card (Secure Digital). When the recording is completed, the card can be removed from the analyzer and the data can be transferred quickly to the computer by means of an external card reader and the software which is included in the kit. The data can also be read by two communication links: USB or wireless transmission.
Power quality analyzer PQM-701 is an advanced product
for comprehensive measurements, analysis and recording of the parameters of the
50/60 Hz mains systems and of the power quality according to the
EN 50160.
The PQM-701 records current and voltage crest factors, frequency values in the 40Hz - 70Hz range, active power, apparent power, distortion power, reactive power with determination of its type (capacitive or inductive). Two methods can be used for power measurements: Budeanu or IEEE 1459. Such parameters as active energy, reactive energy, apparent energy, power factor, cosφ and tanφ are of course recorded as well. The next values which we can analyze are transformer overload level caused by harmonic distortion (K-factor), current and voltage harmonics up to the 50th, current and voltage THD, short-term and long-term flicker, voltage and current unbalance. Recorded also are all events, such as voltage dips, swells and interruptions with waveforms (also for currents). After each averaging period, the analyzer can record snapshot waveforms for current and voltage.
All these functions allow a comprehensive analysis of phenomena in the tested electrical mains system.
The PQM-701 is supplied with all necessary connection and power supply leads (power supply from the L1 phase) and 4 pieces of flexible clamps F-3 (dia 12cm; up to 3000A AC). The kit includes crocodile clips, data transmission cable, SD card, USB cable, transport case and of course software. The analyzer features an built-in battery to maintain the device operation in case of loss of voltage in the L1 phase.
Fig. 3. PQM-701 kit with standard
accessories
Due to very wide range, the clamps are optional equipment
to be chosen by the users according to their particular needs. The user has a
choice of current transformer clamps C-4
up to 1000A AC, C-6 up to 10A AC, Hall-sensor clamp C-5 up to 1000A AC/DC and
other flexible clamps: F-1 (dia 40cm), F-2 (dia 25cm), up to 3kA AC. Optional
equipment includes also the OR-1 adapter for wireless transmission.
Sonel Analysis software
A key component which determines the device usefulness in the analyses is the Sonel Analysis software without which the instrument will not work. The software allows configuring individual measuring functions, analysis of data collected during the recording process, and observation of instantaneous mains parameters and it is available in english.
The software allows full configuring of the analyzer in terms of recorded parameters, protections, measurement points preferences (due to four different configurations, the analyzer enables recording in four different points). From the software level, the user can set the recording trigger mode, set the recording time schedule, or configure the memory allocation to individual measurement points.
The function of viewing the parameters measured by the PQM-701 in real time is totally independent of the recording function. The following can be viewed:
Fig. 4. Analyzer configuration
The main software function is reading the data from the meters and data analysis. The user can view the measured data in tables, view the events with their oscillograms, create reports and various diagrams.
The event screen gives the user extensive analysis options for all selected events. With the software, the user can print reports and diagrams. If hundreds of events have been recorded during a recording period, it is possible to mark those which for some reasons are more important for us than the others.
Fig. 5. Current voltage waveforms
Fig. 6. Measured data
Fig. 7. Event waveforms
SUMMARY
The PQM-701 with the software is an exceptionally useful power quality analyzer which can be used in all areas of power engineering, both in professional power engineering and at industrial plants. The instrument is resistant to ambient conditions, easy to operate, and features user-friendly software. The PQM-701 is an excellent alternative to existing analyzers, particularly in terms of price-to-performance ratio.
