Continuous measurement of power quality with Class A sub metering.

The Sonel PQM-750 analyser is the answer to the growing demands of the power quality market. The meter has been developed for precise, and continuous monitoring of network parameter in a compact design with modular structure and advanced functionality.

Evolution of power quality analysers

Sonel has been developing its own range of power quality analysers for many years. Starting with the pioneering Sonel PQM-701, through to the next generations of Class S analysers such as the Sonel PQM-700 / PQM-707 meters, and more recently with the advanced Sonel PQM-711 Class A model. All of these instruments are portable and well suited for measurements and diagnostics at various measurement locations, wherever there was a power quality problem to be solved.

However, as technology has developed along with a transformation of the power industry and the changing pattern of electricity consumption, the need for continuous monitoring of network parameters has emerged with a simultaneously requirement to monitor at multiple points in the power system. Variability of loads, distributed generation, supra-harmonic, uncontrolled power dissipation, asymmetrical loads and many other phenomena, cause serious threats to stable system operation. So parameter monitoring, data aggregation and alerting at critical moments are crucial today. The Sonel PQM-750 fixed power quality analyser was developed for these type of tasks.

The Sonel PQM-750 analyser

Class A precision – the highest measurement standard

Analysers can be divided according to various criteria, but one of the most relevant is the measurement class of the analyser or logger. The IEC 61000-4-30 standard defines two classes: Class A (from Advanced) and Class S (from Survey). Class S meters have slightly lower measurement accuracy and these measurements may give different results at the same measuring point for different meters from different manufacturers. On the other hand, Class A meters should record the same results when connected at the same measurement point.

The Sonel PQM-750 is a certified Class A analyser.

The Sonel PQM-750 is confirmed as a Class A analyser by documents produced from an accredited testing laboratory. This means that multiple units of this device at different points in the network will measure its parameters with the highest precision according to the IEC 61000-4-30 standard. The Sonel analyser is built with high quality components and a 24-bit analogue-to-digital converter takes care of the data processing quality. The sampling frequency of the signals can reach up to 80 kHz meaning that harmonic measurements of up to the 256th order and a frequency band monitoring up to 150 kHz for super-harmonics can be made. All these parameters mean the meter can record more than 15,000 parameters at once.

Compact design and easy installation

It is not only precise measurements that are give an advantage to the analyser. The unit has a small enclosure, which is extremely important for installation in switch cabinets. Often there is not much room for expansion and adding a larger device is not possible. The compact Sonel PQM-750 is suitable for mounting on a DIN-TH35 rail. By not taking up much space, the analyser can be installed without problems in many areas where there is already a working infrastructure. However, if needed, a wall-mounting kit can be provided with the analyser.

Mounting the Sonel PQM-750 analyser on a DIN-TH35 rail

Even though the meter is small, there is no reduction in the functions that are important for energy suppliers, namely the ability to seal voltage and current inputs. In this way, any interference with the connection system can be clearly diagnosed.

Sonel PQM-750 analyser with current and voltage input protection

Adaptable to different requirements thanks to modularity

The Sonel PQM-750 features great flexibility due to its modular design. As standard, the analyser is offered as a main unit which contains the necessary components for operation:

5 inputs for measuring voltages up to 1000 V
5 built-in current transformers with a rated range of 5 A
2 digital inputs and a 1-wire temperature measurement interface
2 controllable relay outputs
a relay with a watchdog function
built-in power supply with a voltage range of 85…264 V AC / 120…300 V DC
built-in Li-Ion rechargeable battery to power the meter in the event of a power failure on the main power supply or PoE supply
Li-Ion battery to support the internal clock
2 built-in Ethernet ports for communication with servers; one of the ports allows the meter to be powered from the LAN in the PoE standard
synchronisation with an NTP time server is possible via the LAN port
two built-in RS-485 ports, one for communication and the other as a receiver of IRIG-B signals for precise time synchronisation of the analyser
built-in USB host port for analyser operation
built-in memory and a microSD card slot for data storage
a 2.4″ colour touchscreen for basic on-site operation of the analyser
built-in protocols for data exchange: IEC 61850, Modbus RTU, Modbus TCP/IP, proprietary SonelFrame.

Sonel PQM-750 – built-in screen for on-site operation of the analyser

Sonel PQM-750 expansion capabilities and optional extensions

The modular design allows the analyser to be adapted to different requirements. The analyser is equipped with an edge connector located on the right side, which is used to connect external expansion modules. From the available extensions, you can choose:

optional power supply for voltage range 18…60 V DC
optional built-in current transformers with a rated range of 1 A
internal module for measuring voltage transients up to 6 kV with a sampling frequency of up to 10 MHz.
Expected options in the near future will include:
- optional current inputs for the connection of external current transformers
- solid-state relays (SSRs) instead of mechanical relays
- external GPS module for super-precise time synchronisation
- external GSM module for communication
- external I/O module
- external operator panel for full on-site operation of the analyser
- additional communication protocols

Sonel PQM-750 analyser with external GPS module

Webserver – convenient operation and remote configuration

The functionality of the analyser is complemented by a built-in web server (webserver). It allows for the remote configuration and reading of current data or viewing of recorded events from any web browser. Operation is simple and intuitive as the server functionalities are not permanently built in and future updates to the meter will expand its capabilities. The ability to both locally and remotely update the analyser is another key value to make the meter “future proof”. This makes it quick and easy to update the meter without leaving the office nd is crucial as the market requirement change meaning the unit is poised to keep up with any future needs and standards.

Webserver in Sonel PQM-750 – analyser summary screen

Webserver – Phase diagram

Webserver – example screens of current readings

Webserver – information screen of recorded events

Webserver – graphs of an example of recorded voltage collapse

The built-in web server allows extensive configuration of the analyser, which is very important in order to properly adapt its operation to the actual needs of the individual user.

Webserver – example configuration screen

From the web server, settings can also be made to integrate the meter with the users IT systems (e.g. SCADA system). The standard IEC 61850 or Modbus protocols can be used for this purpose as well. Further full integration using SonelFrame proprietary protocol is also possible once a suitable driver has been written for the customers system. Thanks to the built-in FTP client, the accumulated data in the internal memory can be automatically sent once a day to a designated FTP server as PQDIF files. The PQDIF format is one of the most widely used data exchange formats in the world. Interoperability with virtually any software that uses standard communication protocols ensures the analyser’s versatility.

Cyber security – a sign of the times

The Sonel PQM-750 analyser has a number of features designed to make cyber tampering difficult. Built-in firewall, encrypted in-house software, PIN code to operate the embedded screen, login system to operate the embedded webserver, encrypted data transmission from the webserver are all examples of security solutions.

24-hour recording and analysis of energy network parameters

All this makes the Sonel PQM-750 analyser a powerful tool for 24/7 recording and analysis of power network parameters. Its reduced dimensions, modular design, precise measurements, advanced technology, ability to interface with database and SCADA systems are undoubted advantages that provide the power sector (generation and distribution), industry and service companies with a high-end power quality monitoring meter.

Learn more about our products and services by visiting our Power Quality Expert product catalogue, Sonel product catalogue , Electrex product catalogue or Elspec product catalogue or you can contact us to discuss your measurement requirements further.

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Continuous measurement of power quality with the Sonel PQM-750 power quality sub meter