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Analogue Protection for Machines
Published in Helmut Ungrad, Wilibald Winkler, Andrzej Wiszniewski, Peter G. Harrison, Protection Techniques in Electrical Energy Systems, 2020
Helmut Ungrad, Wilibald Winkler, Andrzej Wiszniewski, Peter G. Harrison
Generators which are directly connected to the busbars are typically of low power and the stator ground fault protection is based on supervising either the amplitude [8.5] or the direction [8.15, 8.16] of the neutral current. The neutral current is measured using either a core-balance c.t. or three single-phase c.t’s in a Holmgren arrangement. Monitoring the amplitude is applicable in ungrounded systems where the current IES flowing from the system to a ground fault in the generator is much larger than the current IEG flowing from the generator to a ground fault on the external system, i.e. the condition IES » IEG is fulfilled. The zone of protection extending from the generator terminals towards the star-point for a scheme of this kind is limited to approximately 70 % of the stator winding.
4 Harmonics
Published in C. Sankaran, Power Quality, 2017
The ANSI/IEEE derating method is very useful when it is necessary to calculate the allowable maximum currents when the harmonic makeup of the load is known. For example, the load harmonic conditions might change on an existing transformer depending on the characteristics of new or replacement equipment. In such cases, the transformer may require derating. Also, transformers that supply large third harmonic generating loads should have the neutrals oversized. This is because, as we saw earlier, the third harmonic currents of the three phases are in phase and therefore tend to add in the neutral circuit. In theory, the neutral current can be as high as 173% of the phase currents. Transformers for such applications should have a neutral bus that is twice as large as the phase bus.
Review of Control Topologies for Shunt Active Filters
Published in L. Ashok Kumar, S. Albert Alexander, Computational Paradigm Techniques for Enhancing Electric Power Quality, 2018
L. Ashok Kumar, S. Albert Alexander
Non-sinusoidal loads, such as office equipment, draw highly distorted phase currents. When the load is nonlinear, significant neutral current flow into the system that can be as high as 1.7 times the phase current. The triplen harmonic currents (third, sixth, ninth, etc.) add in phase in, the neutral conductor of a three-phase system. The main problem associated with excessive neutral currents is the overheating of the neutral wire. This can be hazardous in an office building that has computers and other nonlinear loads and where the neutral conductor is designed to hand only allow levels of neutral currents arising mainly from small phase imbalances. In building wiring systems, the first indication of high neutral current is often a fire or a failed transformer.
Experimental Validation of ADALINE Least Mean Square Algorithm in a Three-Phase Four-Wire DSTATCOM to Enhance Power Quality
Published in Electric Power Components and Systems, 2020
Trilochan Penthia, Anup Kumar Panda, Mrutyunjaya Mangaraj
In addition, the importance of a three-phase four-wire (3P4W) DSTATCOM and the consequences of the excessive neutral current presence in a distribution system have already been discussed in the literatures [16, 20, 21]. In short, extensive use of non-linear as well as unbalanced loads in a three-phase distribution system is the major source of excessive neutral current. In a United States electricity grid, approximately 22.6% of the sites had a neutral current in excess of 100% of the grid phase current, as reported in [16]. Moreover, inclusion of single-phase non-linear loads in a 3P4W DSTATCOM produce critical zero-sequence fundamental component which may adversely affect the neutral conductor and sensitive loads of the system. Mostly, presence of unbalanced phase currents, the 3rd harmonic due to supply voltage 3rd harmonic, and 3rd harmonic produced by a single-phase non-linear load are responsible for the production of neutral current in a 3P4W distribution system [22].