Power Quality measurements in the MV distribution grid

In the majority of cases, the installation of regenerative power generation systems in the distribution grid is connected with the use of frequency converters. In general, converters are to be regarded as disturbance emitters, since high-frequency components are generated by the steep current rises and transient phenomena. Higher interference levels can be caused by defective modules or if systems are only operated in the partial load range. Transients and harmonics can generally be transferred to higher voltage levels by the transformer and cause interference to neighboring installations. At the same time, equipment is exposed to a higher load and thus its service life is adversely affected. However, new types of consumer equipment, such as charging stations for e-cars, also often produce grid disturbances of up to 150 kHz. For this reason, among others, all technical guidelines from low to extra-high voltage in Germany (VDE-AR-N 4100 to 4130) have been extended with current harmonic measurement up to 9 kHz. This set of guidelines enables distribution network operators to protect their networks, equipment and customers from grid disturbances. If the instrument transformers and the power quality analyzers are specified in the technical connection conditions, all costs from medium voltage onwards can be passed on to the plant operator. Adjustable access rights in the PQ-SCADA system allow the network operator as well as the plant operator to access the measurement data and initiate countermeasures in sufficient time in the event of impermissible disturbance levels.

While the power quality analyzer can measure the line voltage directly in the low voltage range, instrument transformers or sensors are required in the medium voltage range. Ritz Instrument Transformers offers a wide portfolio of optimized transformers and sensors.

In contrast to the usual voltage transformers, the voltage sensors have a small signal output that reaches a maximum peak value of 10 volts. Usual power analyzers cannot process these small signals. Neo Messtechnik offers the mobile device PQA 8000 H with switchable voltage inputs for this application. Here the customer can set the measuring range (600 or 20 volts peak value). Thus, measurements up to 500 kHz in medium and low voltage can be realized. Frequency-optimized voltage transformers with the usual 100/√3 volts can also be connected with the 600 volt range. All stationary and mobile analyzers are thus perfectly matched to the Ritz PQ sensors.

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