Disturbances due to high frequency signals (above 2 kHz) Martin Lundmark EMC on Site

OUTLINE 1.BACKGROUND 2.CONDUCTIVE AND RADIATED EMISSION IN A THREE-PHASE GRID 3.ORIGIN OF CONDUCTIVE HIGH-FREQUENCY LEAKAGE CURRENT 4.MEASUREMENTS 5.CONCLUSION

BACKGROUND Sign of HF-harmonics PWM motor drives-motor bearing currents TV and audio studios- disturbances Power Line Communication-signal interference Distribution transformers-damage Power supply units-damage Cable and cable termination- damage Electronic office equipment-malfunction Fluorescent lights-league currents

BACKGROUND CHANGING CIRCUMSTANCES IN POWER LOADS… The use of power electronics Faster changes in loads than in the power grid …AND IN COMMUNICATION The changes from analogue to digital communications technique The radiated emission of electronic equipment is limited with respect to analog radio communications services

BACKGROUND The changes from analogue to digital communications technique

CONDUCTIVE AND RADIATED EMISSION IN A THREE-PHASE GRID

CONDUCTIVE EMISSION IN A THREE-PHASE GRID

ORIGIN OF CONDUCTIVE HF LEAKAGE CURRENT Symmetrical load current in a three phase system

ORIGIN OF CONDUCTIVE HF LEAKAGE CURRENT Symmetrical load current, including harmonics, in a three phase system

ORIGIN OF CONDUCTIVE HF LEAKAGE CURRENT Symmetrical load current, including HF- harmonics, in a three phase system

A detail of the left graph shows the damped peak having about a 156 microsecond period time, a frequency close to 6.4 kHz. A 2 kHz high-pass filter used on the simulated neutral current from HF fluorescent lamps in three-phase connection Symmetrical load current, including HF- harmonics, in a three phase system ORIGIN OF CONDUCTIVE HF LEAKAGE CURRENT 1 1 1

Neutral current (RMS) when increasing the numbers of three-phase connected HF- fluorescent lamps, unfiltered upper left, 2 kHz high-pass filter down left. To the right- the neutral current shown on the left is divided by the number of three-phase connected groups of HF-fluorescent lamps. Symmetrical load current, including HF- harmonics, in a three phase system <2 kHz >2 kHz

1 Highest peak value in neutral current above 2 kHz when increasing the numbers of three- phase connected HF fluorescent lamps, to the left. To the right, the peak value is divided by the number of three-phase connected groups of HF fluorescent lamps. Symmetrical load current, including HF- harmonics, in a three phase system

The impedance for 2.5 mm 2 Cu wire with a length of 100 m upper line, 30 m middle line and 1 m lower line. Z = R + jX Z 100 m 1 m 30 m

Calculations on the neutral peak voltage with increasing numbers of HF- fluorescent lamps with (upper line) and with only the wire resistance (lower line). Z = R + jX, for 2.5 mm 2 Cu wire with a length of 30 m ORIGIN OF CONDUCTIVE HF LEAKAGE CURRENT Symmetrical load current, including HF- harmonics, in a three phase system

ORIGIN OF CONDUCTIVE HF LEAKAGE CURRENT

MEASUREMENTS

Communications failures on a specific communication line in a server room powered by a 50 kVA uninterruptible power supply P-N P-PE N-PE

MEASUREMENTS A- building, in the office part of the LTU Skellefteå Campus.

MEASUREMENTS D-building, first floor, adjacent to room 3045.

MEASUREMENTS A- building D-building, first floor

CONCLUSION It is possible to find HF- harmonics, almost everywhere in power grids. The origin to the HF- harmonics is finding in power electronics in domestic, commercial and industrial equipment. The number of emitting devices is growing significantly. Literature describes interference on electronic office equipment, in TV and audio studios and in power grid using power line communication due to HF- harmonics, to give some examples. Literature also describes damage in distribution transformers, cable and cable termination and in motor bearings due to HF- harmonics. While the symmetrical fundamental frequency current is cancelled and the zero- sequence harmonics is summarized in the neutral wire the HF- harmonic current increased when the number of loads symmetrically increased in the three phases, and there was almost no cancellation. Adding the effect of increasing impedance in wires resulting from increasing frequency, one origin of conductive high-frequency leakage current in the grid is shown.

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