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Transformer protection methods used

In Electronic Infomation Category: T | on April 14,2011

Transformer protection method commonly used transformer are not normal working overload, external short circuit caused by over-current, short circuit caused by an external grounding the neutral point voltage, fuel tank leak caused by lower oil surface or cooling system failure caused by temperature and SJA1000N datasheet and so on. In addition, large-capacity transformers, magnetic flux density due to its higher rated working voltage and SJA1000N price and frequency than the flux density is proportional to the over-voltage or low frequency operation, the transformer over-excitation may cause disturbances. For the above, a large transformer protection methods generally use the following: gas protection (protection of the transformer internal short circuit fault and SJA1000N suppliers and the oil level lower), differential protection trip current protection (protection of the transformer winding or lead wire of each phase of the phase short circuit, large ground ground short-circuit current systems and Winding), over current protection (protection of the external phase short circuit, and as gas protection and differential protection or Current Protection of backup protection), the zero sequence current protection (protection of large earth current system of external single-phase ground short circuit), overload protection (overload protection of symmetry, only act on the signal), over-excitation protection (protection of transformer over-excitation does not exceed allowable limits)

Transformer tank of gas protection responses within the various fault and the transformer oil level reduced. 0.8MVA oil-immersed transformers and over and over and 0.4MVA workshop Transformer, gas protection should be installed. Slightly when the fuel tank of gas or oil fault plane decreases, the signal should be instantaneous; when a large amount of gas should move on each side of the transformer circuit breaker disconnect. Load regulating oil-immersed transformer voltage regulating equipment, gas protection should be installed.

Transformer protection method commonly used two: longitudinal differential protection or Current Protection

Reaction transformer lead wire, casing and internal short-circuit fault of the longitudinal differential protection or Current Protection. Protection of instantaneous action at each side of the transformer circuit breaker disconnect.

1. On 6.3MVA the following auxiliary transformer and parallel operation of transformers, and the 10MVA transformer and the following stand alone auxiliary transformer operation, when the backup protection for longer than 0.5s, Current Protection should be installed.

2. 6.3MVA or more of the work of auxiliary transformer and parallel operation of transformer, 10MVA or more auxiliary power transformer and separate transformer operation and 2MVA circuit protection and over power flow sensitivity does not meet the requirements of the transformer, should be installation of longitudinal differential protection.

3. On the high side voltage of 330kV and above transformers can be equipped with a double longitudinal differential protection.

4. For the generator transformer, when the circuit breaker between the generator and transformer, the generator installation of a separate longitudinal differential protection. When there is no circuit breaker between the generator and transformer when, 100MVA and below the generator and transformer common longitudinal differential protection; 100MVA or more generators. In addition to common longitudinal generator transformer differential protection, the generator should be a separate installation of longitudinal differential protection. Generator of 200 ~ 300MVA transformer transformer can also add a separate longitudinal differential protection, that is, double fast protection. External phase transformer short-circuit

reaction and for gas conservation and longitudinal differential protection (or the Current Protection) backup overcurrent protection, low voltage starting over current protection, composite Overcurrent protection of voltage, negative sequence current protection and impedance protection, protection action should be brought after the time limit for action on the trip.

1, over-current protection should be used for step-down transformer.

2, starting compound voltage over current protection, should be used to step-up transformer, the system connect the transformer and overcurrent protection does not meet the sensitivity requirements of step-down transformer.

3, negative sequence current and single-phase overcurrent protection of low voltage starting can be used to step-up transformers 63MVA and above.

4, when using the 2,3-protection can not meet the requirements of sensitivity and selectivity, can be used impedance protection.

Transformer protection method used four: zero sequence current protection

Reactions earth current system of external ground short-circuit the transformer zero-sequence current protection. 110kV and above a large ground current system may be grounded if the transformer neutral point run, for both sides or three sides of the power of the step-up transformer or step-down transformer zero sequence current protection should be installed for the primary protection of transformer backup protection, and backup protection of the adjacent components.

What is the zero sequence current protection

Use of ground zero sequence current generated when the protective action of the device, called the zero sequence current protection. Cable lines are used in a special zero-sequence current transformer to achieve grounding protection. Sets the zero sequence current transformer to the three core cable, the current relay connected to the transformer secondary coil, in normal operation with or without ground fault, because the cable and three-phase current vector of zero, zero sequence transformer secondary coil current is zero (only a small imbalance current), so the current relay action. When a ground fault, zero-sequence transformer secondary winding to a larger current, the current relay to send a signal or the removal of fault.

Transformer protection method used Five: overload protection Symmetrical transformer overload

response overload protection.

Transformer for 400kVA and above, when the number of units running in parallel operation or separately, and for other load standby power should be based on the situation may overload overload protection installed. On the auto-transformer and multi-winding transformers, protective devices should be able to respond Ceguo common winding and the load conditions. Over the transformer load current, in most cases, are three-phase symmetrical, so the overload protection as long as access to a phase current, current relay to achieve, and thus a definite role in the signal delay. Choose which side of protection when installed, it can reflect the need to consider all the windings of the transformer overload situation. In the absence of regular duty of the substation, if necessary, action overload protection can be part of the trip or disconnect the load.

Six transformer protection method: overexcitation protection

Reaction transformer overexcitation of over-excitation protection.

Current large transformer design, in order to save materials, reduce cost, reduce transport weight of the rated core flux density are designed to be high, about 1.7 ~ 1.8 T, close to the saturation flux density (1.9 ~ 2 T ), so the over-voltage situations, it is prone to over-excitation. Magnetization curves for the other "hard" in the over-excitation, due to core saturation, excitation impedance decreases, the excitation current increases rapidly, when it reached the normal magnetic flux density of 1.3 ~ 1.4 times the density, the excitation current up to rated current level. Second, because of non-sinusoidal excitation current, containing many high-order harmonic component, while the core and other metal components of the eddy current losses proportional to the square of frequency, can cause core, metal components, insulation materials, serious overheating, if the over-excitation times more high, duration is too long, may damage the transformer. Therefore, the high side should be installed for the 500kV transformer overexcitation protection.

Installation of transformer overexcitation protection is designed to detect the transformer overexcitation conditions, timely signal or action on the trip, so that the transformer over-excitation does not exceed allowable limits, to prevent transformer damage due to excessive excitation.

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