Info Letters

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Basics & General

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Info Letter No. 21: The influence of the contact resistance at the earth-fault location on the zero sequence voltage UEN in compensated networks
The earth fault in compensated networks is usually presented without a contact resistance at the fault…
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Info Letter No. 20: Capacitance of conductors
In the conductors of electrical power supplies, a distinction is made between the operating capacitance…
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Info Letter No. 18: Transient relay for high resistance, intermittent and recurrent earth faults (Part 2)
Figure 3 can also be used for the determination of static earth faults. In an isolated network the entire…
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Info Letter No. 17: Transient relay for high resistance, intermittent and recurrent earth faults (Part 1)
The statistics show that earth faults constitute a large proportion of network faults. Conventional relays…
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Info Letter No. 8: Apparent power and reactive power in three-phase networks
The range of electromechanical and electronic measuring devices in analog – and digital technology…
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Info Letter No. 5: Zero sequence voltage in three-phase networks
With balanced network operation and inequality of the impedances in the consumer circuit, the phase…
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Info Letter No. 4: Summation of Alternating Currents
For the parallel connection of power sources, the principle of superposition applies, when all resources…
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Info Letter No. 2: Measurement Transformers in three-phase networks (Part 2)
In a symmetrically loaded three-wire three-phase network, a two-pole insulated voltage transformer…
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Info Letter No. 1: Measurement Transformers in three-phase networks (Part 1)
The direct connection of measuring devices into the network is limited for safety reasons to values…

Power Quality

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Info Letter No. 23: Direction of harmonics Sources of harmonics in the power system
The direction of the power flow of harmonics is determined by the sign of the active power. The figure…
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Info Letter No. 22: Definition of power measurements according to the standards DIN 40110-2 and IEEE 1459
There is a wide range of electronic measuring devices for the digital measurement of power…
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Info Letter No. 19: The evaluation of power quality and detection of interference in medium voltage network
For various reasons, interest in the continuous monitoring of network quality in medium-voltage…

Voltage Regulation

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Info Letter No. 16: Hot-spot temperature and service life of transformers
The failure of a transformer not only has major economic consequences for the energy supplier, it can…
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Info Letter No. 13: Parallel operation of step transformers
The rule of thumb that with parallel operation of transformers the ratio of the rated outputs should not…
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Info Letter No. 11: Voltage regulation with step transformers in parallel to busbars (Part 3)
Direct measurement of the circulating current is not possible with the usual measurement…
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Info Letter No. 10: Voltage regulation with step transformers parallel to busbars (Part 2)
The following considerations apply to a symmetrical operation of a three-phase network, so that the…
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Info Letter No. 9: Voltage regulation with step transformers in parallel to busbars (Part 1)
Within a station, the transformers are in close proximity. Therefore, the line impedances between the…
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Info Letter No. 7: Load-dependent voltage change
For the regulation of the voltage ULoad at a predetermined value at the specified load point (e.g. the…

Short-Circuit and Earth Fault Indicators

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Info Letter No. 15: Earth fault location using the harmonic procedure (Part 2)
For the study of the behaviour of the harmonic currents and voltages in the compensated network, at…
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Info Letter No. 14: Earth fault location using the harmonic procedure (Part 1)
For the following considerations a network with three outputs and an earth fault in line 1 in output…
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Info Letter No. 6: Detection of transient earth faults
When there is an earth fault in a conductor, at the start of the earth fault three events occur at the…
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