Improving power quality by Active Harmonic Filters (AHF)

Home / Portfolio

Project description

OMV Petrom is the largest energy company in South-East Europe, being active on the entire energy value chain, from wells that extract oil and natural gas, to refining and distribution of oil products and electricity production. In Romania, the company currently operates 193 onshore and offshore oil and gas fields, including some fields with a very long history, as well as recently discovered deposits. In this context, regular modernization and revamping activities of existing facilities are carried out. Projects that improve energy efficiency are of special importance for OMV Petrom.

One of the recent revamping programs took place in OMV Petrom’s South Moldova production sector. The main objective of this project was the modernization of electrical panels to increase productivity and improve energy efficiency. In order to meet this target, the electrical equipment for the oil extraction wells and the actuators had been updated to the state of the art variable speed drive technology.


Beneficiary: OMV Petrom

Industry: Oil & Gas

Project type: Improving power quality by Active Harmonic Filters

Finantare: Beneficiary sources

The customer’s challenge

At the end of the revamping program, all the approximately 500 pumps in this site were equipped with frequency converters. While this helped to bring production to the next level and significantly improve energy efficiency, at the same time a new problem was introduced with this technology.

One side effect of the extensive installation of frequency converters is a remarkable increase in harmonic distortion. Harmonics are caused by the non-linear characteristics of power electronic devices, such as frequency converters, which draw non-sinusoidal current from the grid. This leads to higher-frequency components that are superimposed to the fundamental sine wave.

Due to the grid topology, in this site, the distortion was not only limited to the low voltage (LV) network but migrated also to medium voltage (MV) level. Measurements revealed that the THD-I (Total Harmonic Distortion) in the MV grid exceeded 30% at times.

High THD levels have a negative impact on power quality (PQ) and can lead to various problems. In the OMV Petrom site, the high distortion level was the root cause for several issues that also affected productivity:


Unwanted random triggering of the circuit breakers in the 110/20/6kV substation which supplies the OMV Petrom production site as well as other consumers


Overheating of power transformers, power cables (incl. neutral conductor) due to excessive harmonic currents


Malfunction of sensitive electronic components due to disturbed supply voltage as a consequence of the current harmonics in the system


Increased active power loss


Measurement errors in the four quadrants systems of active and reactive power

The proposed solution

The technical solution that was designed by Servelect and approved by the regional distribution system operator (DSO) is based on harmonic mitigation by means of active harmonic filters (AHF). An AHF is a power conditioning device that continuously measures the harmonics and dynamically injects a compensation current that cancels the harmonics. For this project, Servelect used standard AHF units from TDK Electronic’s PQSine series and designed a customized turnkey solution.

Based on measurements and comprehensive simulations Servelect identified the optimal locations for the installation of the filter units. As selection criteria, the harmonic distortion level as well as the installed load were considered. Amongst the 50 transformer stations, the ideal locations for the AHF installation were selected with the target to bring down the THD level in the MV grid.

Some of the particular challenges of this project were the environmental conditions in the area. Usually AHF is installed indoor in an industrial environment. In an oil production site that is situated in a remote location, the conditions are obviously much more tough. The AHF cabinets had to be installed outdoor close to the oil pumps. For this purpose, a special enclosure had to be designed to protect the units from external influences such as rain, snow, and dust. The climatic conditions with low temperatures in the winters below 0 °C and warm summers also required the installation of a heat exchanger for temperature control.

In order to minimize the impact on the running production, all involved partners had to agree on a tight timeline for the commissioning. The main task of the commission team was the electrical connection of the AHF cabinets and the verification of the main control parameters in the HMI.

The results

For the system setup, the CT parameters had to be entered and the operating mode selected. Apart from harmonic compensation, the AHF can also be used for power factor correction and load balancing.

In the first instance, the AHF performance was already checked during commissioning. The integrated power quality monitor of the AHF shows various parameters that allow the operator to check the system performance. In the LV grid where the AHF units were installed, the THD-I values could be reduced from values as high as 50% to values in the range of 4-10%. This significant power quality improvement in the LV grid also helped to subsequently reduce the harmonic distortion in the MV and maintain the specified limits. Moreover the negative effects that go along with poor power quality could be diminished to a large extend or eliminated completely.

The use of active harmonic filters is not only limited to this particular application but can be applied for any installation with power quality issues caused by non-linear loads. Typical applications include wastewater plants, HVAC systems, electric smelters, oil and gas industry, petrochemical plants, ports, mining, pharmaceutical industry, pulp and paper mills, large ships and renewables such as wind power or large photovoltaic parks.