Grounding is clearly one of the most important aspect of the electrical design, but it continues unabated, misinterpreted and misunderstood. Multi-million dollar loss and liability due to the arc of the earth, so that issues relating to land in the top lists, checking electrical contractor.
Grounding Transformers
In other words, the grounding transformer is used, a dirt road that is a baseless "Y" or delta system. Groundingtransformers are generally used:
Enter a relatively low impedance path to ground, thereby maintaining the system neutral or near ground potential Limit the size of ground faults surge restart Provide a source of fault current during line-to-ground faults Allows the connection of the neutral section you want to load
If a line-to-ground fault occurs on a grounded or isolated, there is no reverseshort-circuit current, so no current flows. The system still works, but the other two fault lines do not enhance tensions in the square root of 3, causing an overload of isolation transformers and other related Components, the system is 173%. MOV arrester is particularly sensitive to heat damage caused by leaking through the blocks, although growth is not enough voltage to flash over. Transformer grounding provides the path to the ground to avoidthis.
Large wind farms provide many examples of the use of the transformer grounded to protect against errors in the lines is not well founded. A lot of wind the transformer is the source of the post only because of the distribution system. When an earth leakage circuit breaker will cause the collector to a cable in the cable channel is open, the wind becomes isolated from the supply chain from source to ground.
The wind does not always detect that error, or a stringisolated and grounded, and the generator to continue to energize the cable collector, and tensions between the non-cable failure, and the rising ground above the normal amount of stress, as described above. Transformer grounding placed on-line turbine provides a dirt road, where the chain is isolated from system ground.
Construction:
grounding transformers are generally built up
Liquidation Z (Zn) with or without relatedauxiliary winding or The Wye (YND) related to the delta winding side, that may or may not be used for auxiliary power
The geometry of the Zig-Zag beneficial relationship by limiting the movement of the third harmonic and can be used without being connected to the winding-up or Delta 4 - or 5-leg base design is usually for the purpose of distribution and power transformers. Eliminating the need for a secondary coil, that this option is cheaper and smaller thansimilar to the two transformer windings to the ground. In addition, the use of Zig-Zag transformer provides the earth with a minor in a two winding transformer is Wye-Delta is the same zero impedance.
Grounded Wye transformer, on the other hand, need or a delta connected secondary or application of the basic 4 or 5 feet building to a flow path back to the unbalanced load with the primary relationship. Since it is often desirableAuxiliary transformer secondary and the earth, this advantage may affect the user enters the transformer is grounded in a relationship instead of two rolls of Zig-Zag. The current trend in the design of the wind farm is connected to the Wye primary and secondary, in the delta.
It is important to understand that two and two Zig-zag grounding transformer winding can be seen that the additional power connector, and it could be either a star or delta connectedthe load.
The transformer is an entrenched system of land offers a number of security enhancements to the system is grounded. However, the soil is not only the transformer capacity limitation of the current system, the grounding resistance. For this reason, the neutral ground resistor is often used in conjunction with limiting the powers of the transformer grounded neutral ground fault current. Ohm value should be that the ground fault current large enough to function reliablyequipment protection relays, but low enough to minimize thermal damage.
Determines how the transformer is grounded
The basic parameters of a transformer, the land must be borne in mind:
Primary voltage - the voltage of the grounding system must be connected to liquidation. Do not forget to add the LIB as well. In some Cases, BIL will be dictated by considerations of equipment, such as the 150-kV BIL ratings windfarms 34500 Sun due to the limitation of deathfirst contact. Rated KVA - Because of the transformer and the ground is a tool, usually of short duration, size and cost is lower than a continuous duty transformer of equal kVA. For this reason, the size of the transformers are often not grounded "but the continuous power handling and a short time during the current assessment. No matter how you rate, the land of the transformer must be sized to carry the rated continuous current without exceeding primary phase in the temperature limit. This awardincludes the core magnetization current, the capacitive charging current of the cables, and any additional charges if applicable. More than this value, the transformer will be larger and more expensive. Typical constant current values can be as low as 5 amps to as high as several hundred. Do not forget to claim any additional loads. Continued neutral current - DC three times the current definition of a neutral phase, or in other words, the sequence of zerocurrent. This is generally considered invalid if the system is in balance. However, the design of a transformer is grounded, it is a value that is expected to flow through the neutral circuit without a protection circuit tripping (which will force the current to zero) or the earth leakage current, which is not a symmetric function. Again, this value is necessary for the design of the heat capacity of the transformer grounded. Short-circuit current duration - This value is requiredcalculate the heating time results in less error in the system and must be determined from a study of the construction system. Typical values from a few hundred amperes to several thousand amperes of seconds, not cycles. For example, typical value of 400 amperes for 10 seconds. The duration of the loss of a critical parameter for the design of the transformer. When the protection systems of the earth to the transformer tripping functionality in a relatively short period of timespecified duration (5 -10 seconds). On the other hand, because of the continuous or sustained period of neutral current would be needed if the transformer is used to earth ground fault alarm. Impedance - The impedance can be expressed as a percentage value, or ohms per phase. In both Cases must be chosen so that the phase voltages do not blame him when the earth is temporary capacity-voltage equipment and associated processing, such asarrester and the terminal connectors. Since this description, the range of values, only 8% to almost 100%. This value must come from the system designer. Primary connection - Specify the type of primary contact or zig-zag grounded Wye. Secondary connection - Specify the secondary voltage and a good connection. Specify the size of the additional load must be connected to either Zn-or Wye connected primary windings. If the possibility that twotransformer secondary winding is vacuum condition in the delta winding can be "buried" (not shown), or a jack to raise the ground or the shell of the investigation.
· Services basic general construction - note the following features that apply to each processor
· Transformer built-in tamper-proof compartment stand compartmentalized design position
· Outdoors or inside
° Fluid type of mineral oil,Silicone Envirotemp FR3
· Connectivity pre-outs, live clips, location of terminals - and covers the flanks, exposed, or closed, etc.
• Temperature growth is assumed to 65'C
Site · rise, or environmental concerns
Painting requires special ·
· Resistance neutral ground - the nominal voltage of the NGR should be equal to the line and the earth grounding transformer. The current rating and the duration should becorrespond to the dimensions of the transformer grounded. Do not forget the current rating high enough to exceed the charging cable and a grounding transformer magnetizing current.
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