Dec 8, 2019
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Miscellaneous

The 10 most important types of faults in the three-phase networks

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elcome dear friends of protection and control engineering. What are the 10 typical types of faults in three-phase networks? In today's article we dedicate ourselves to these elementary basics and show you at the end of the article still some exotics. Here we go:

Starpoint Treatment

There is no chance to avoid this important topic. The star point treatment has a significant influence on insulation faults in the three-phase network. With regard to the types of faults that arise, we must always differentiate between two differently grounded network variants. The same question is:

Is this network effectively grounded or not?

The ineffective grounding of a network starts from an earth fault factor δ> 1.4 upwards (more precisely from 1.39). Everything below 1.4 is referred to as an effectively grounded network. In our article "Neutral point treatment | The solidly grounded network" we had already described this connection.

The low-impedance-grounded-network can also have a δ > 1.4 (up to 1.9 in the resistively earthed network) in case of unfavorable short-circuit current conditions. So let's take a look at the first 5 types of faults in the effectively grounded network:

Effectively grounded network (δ <1.4)

Fault 1: The single-pole-to-ground short circuit

Regardless of the selected network form: The most common error is always the ground fault. The following figure shows a single-pole to ground fault.

Fault 5: The three-pole-to-ground short circuit

Let us now turn to the non-effective grounded network.

Non-effective grounded network (δ> 1.4)

Fault 7: The two-pole short circuit

This fault is identical in all network types. There are positive- and negative sequence system available, but not the zero system component.

Fault 9: The three-pole short circuit

The three-pole short circuit is also independent of the present network form, only the positive sequence system is involved.

Are there other types of faults?

There are many more types of errors, we show you 3 exciting guys.

The double ground fault

The common consequence of insufficient isolation coordination. Starting from a single-pole ground fault to a double ground fault, due to the excessive voltage stress (stationary and transient) in non-effective grounded networks.

The multi fault

A rather rare, but very sophisticated state of fault. Here a longitudinal and a transverse error mixes into a multiple error. The broken line hangs on the supply side in the air and on the consumer side it lies against earth. If the relay is located on the supply side (left) to locate the ground fault, the earth fault will be difficult to detect. The measurement must be made backwards via a wrong phase and also via the connected load impedance of the following transformer (> 10 kΩ are very probable).

Bauch's paradox

The Bauch's paradox rarely appears in practice. The prerequisite is that there is a large feed-in capacity on one side and only consumers are connected to the grounded opposite end. With this special constellation, short-circuit currents also occur in the faultless conductors in the case of a single-pole earth short circuit. In the worst case, the amplitudes in all three conductors are the same size and the single-pole earth fault appears as a three-pole short circuit (right in the picture).