Chopped Graphite/Graphite Electrode in different materials have different definition of graphite pieces, some data and literature is not very big graphite particles are called graphite pieces (such as Graphite Powder) some is graphite products have a certain size, for Graphite Broken into patches, we here say of graphite for a second, usually called graphite blocks. Graphite is produced from graphitization and machining process of graphite products. It is used as additive and conductive material in the manufacture of graphite waste in steel and foundry industries, and can also be processed according to customer's requirements. They are also widely used in electric arc furnaces (steelmaking) and electrochemical furnaces (metallurgical and chemical industries).
Main use of graphite
Graphite pieces due to its low ash content, conductive and heat conduction performance is good, so there are a wide range of USES, can be added to the formula of less ash or dust products, graphite broken broken into small particles commonly use. Ingredients to add a certain amount of graphite, the plastic paste after kneading, especially during extrusion can reduce the friction resistance paste to squeeze the mouthpiece, to improve the coefficient of pressure type. Graphite pieces of coal adsorption properties of asphalt is better, to join the carbon block can rise to reduce the "short" waste (i.e., the product after roasting top produce honeycomb structure), and can improve the thermal conductivity of the carbon block and alkali corrosion resistance. The electrode paste used in hermetically-sealed thermal furnace is added to a certain amount of graphite to increase the conductivity and thermal conductivity of the electrode paste and accelerate the sintering speed of electrode paste. When the graphite is ground into small particles or fine powder, it is also used as raw material for the production of graphite chemical equipment (such as graphite-resin tubes). The graphite can also be used as a carbon addition agent for the electric furnace.
Graphite classification
1. Raw and broken. It is a raw blank that is not qualified after molding.
2. Roasting is the cutting debris that is recovered after the roasting of raw billet and after inspection of unqualified waste and the processing of calcined products.
3. The graphite is broken, and it is inspected by the graphite-producing waste and the cutting debris produced by graphite products in the process of processing.
Graphite Broken Graphite Broken,Broken Graphite Electrode,Graphitized Anode Broken,Graphite Tablets Fengcheng Ruixing Carbon Products Co., Ltd , http://www.lnfcrxts.com
2. Method of preventing inrush current caused by misoperation The relay protection tester has a distinct characteristic of magnetizing inrush current, that is, it contains a large number of second harmonics. This characteristic is used in the main transformer main protection to prevent the protection from malfunction caused by the excitation inrush current. However, if it is used in 10kV line protection, the protection device must be reconstructed, which will greatly increase the complexity of the device, so its practicality is very poor. Another characteristic of magnetizing inrush current is that its magnitude decays with time. The initial inrush current is very large. After a certain period of time, the inrush current decays to zero. The current flowing through the protection device is the line load current. The current surge protection feature is used to use the inrush current characteristics. A short time delay can prevent malfunction caused by magnetizing inrush current. The biggest advantage of this method is that the protective device (or only a simple modification) is not modified. Although it will increase the fault time, it is stable to the system like 10kV. The smaller impact still applies. In order to ensure reliable escape of magnetizing inrush current, the accelerating circuit in the protection device is also added with delay. Through years of exploration, a time limit of 0.15 to 0.2 s has been added to the 10 kV line current quick-break protection and acceleration circuit. In recent years, operation has been performed safely, and the protection device has been mistakenly avoided due to magnetizing inrush current in the line. action.
3, TA saturation issues 3.1 SA saturation impact on protection Relay protection tester 10kV line at the exit short circuit currents are generally small, especially in rural power grids, often away from the power supply, the system impedance. For the same line, the size of the short-circuit current at the outlet will vary with the size of the system and the mode of operation. With the continuous expansion of the system scale, the short-circuit current of the 10kV system will become larger, which can reach hundreds of times the rated current of TA. Some existing TAs with small transformation ratios in the system may be saturated; on the other hand, Short circuit fault is a transient process. Short circuit current contains a large number of non-periodic components, which further accelerates TA saturation. In the short circuit of 10kV line, due to TA saturation, the current on the secondary side will be very small or close to zero, so that the protection device will refuse to move and the fault will be cut off by the bus tie breaker or main transformer backup protection, not only prolonging the fault time, This will increase the scope of faults, affect the reliability of power supply, and seriously threaten the safety of operating equipment.
3.2 Methods to Avoid TA Saturation TA saturation is in fact magnetic flux saturation in the TA core, and the magnetic flux density is proportional to the induced potential. Therefore, if the TA secondary load impedance is large, the secondary loop induced potential under the same current conditions. If it is large, or under the same load impedance, the larger the secondary current, the greater the induced potential. Both of these conditions will make the magnetic flux density in the core large. When the magnetic flux density reaches a certain value, the TA is saturated. When TA is severely saturated, the primary current becomes the excitation current, the secondary-side induction current is zero, and the current flowing through the current relay is zero, and the protection device will refuse to operate. Avoiding TA saturation mainly starts from two aspects. First, when selecting a TA, the ratio cannot be selected too small. Consider the problem of TA saturation when the line is short-circuited. Generally, the TA ratio of the 10kV line protection is better than 300/5. On the other hand, TA secondary load impedance should be minimized, TA should be avoided as much as possible for protection and measurement, and the secondary cable length and secondary cable cross-section should be shortened. For integrated automation substations, 10kV lines should be selected for protection, measurement and control as much as possible. A product, and installed on the control panel in place, this can effectively reduce the secondary loop impedance and prevent TA saturation.
4, the use of transformer protection 4.1 the use of transformer protection problems The transformer used is a more special equipment, the capacity is small but the reliability requirements are very high, and the installation location is very special, generally connected to the 10kV bus, the high-voltage side short circuit The current is equal to the short-circuit current of the system, which can reach several ten thousand amps, and the short-circuit current at the low-voltage side is also large. There has been insufficient attention to the reliability of the transformer protection used, which will pose a great threat to the safe operation of the transformer used up to the entire 10 kV system. Traditional transformer protection uses fuse protection, and its safety and reliability are still relatively high. However, as the system's short-circuit capacity increases and the requirements for comprehensive automation increase, this approach has gradually failed to meet the requirements. Now substations newly built or transformed, especially integrated automation institutes, are equipped with transformer cabinets that are used in most cases. The protection configuration is similar to the 10kV line, and TA saturation problems for protection are often overlooked. Because of the small transformer capacity used, the primary rated current is very small and the protection measurement shares TA. To ensure the accuracy of the measurement, the design time TA is very small, and some places even choose 10/5. In this way, when the transformer used fails, TA will be severely saturated, and the current in the secondary circuit is almost zero, so that the transformer protection device used will refuse to move. If the fault is on the high-voltage side, the short-circuit current is enough to make the bus-bar protection or main transformer backup protection act to open the fault. If the fault is on the low-voltage side, the short-circuit current may not reach the start value of the bus-tie protection or main transformer backup protection, causing the fault. Can not be removed in time, eventually burning the transformer used, seriously affecting the safe operation of the transformer.
4.2 Solution To solve the problem of protection against transformers used in transformer protection, start with a reasonable allocation of protection. The selection of the TA must take into account the saturation of the transformer when it is used. At the same time, the TA used for measurement must be separated from the TA for protection and the TA used for protection. On the high voltage side, in order to ensure the protection of the transformer used, the measuring TA is installed on the low voltage side of the transformer used to improve the measurement accuracy. In setting value setting, the current quick-break protection can be set according to the short circuit of the low voltage outlet of the transformer used, and the overload protection can be set according to the capacity of the transformer used.
5, distribution transformer protection 5.110kV distribution transformer protection problems exist 10kV distribution transformer protection configuration are mainly circuit breakers, load switches or load switches plus fuses. The load switch is less expensive than investment, but it cannot be used to cut off the short-circuit current and it is rarely used. The circuit breaker has good technical performance, but the equipment investment is high, the use of the equipment is complex and the application is not widely used. The protection configuration of the load switch plus fuse combination can be avoided. The use of circuit breakers that are complicated to operate and expensive, to make up for the shortcomings of the load switch that cannot open and close the short-circuit current, and to meet the needs of the actual operation, this configuration can be used as a protection method for distribution transformers. However, for large-capacity distribution transformers equipped with gas relays, circuit breakers can be used in conjunction with the gas relays to effectively protect the transformers and, if necessary, zero-sequence protection. These problems are worth noting. .
5.2 Solution Regardless of whether the 10kV ring power supply unit or the end-user high-voltage power distribution unit uses the load switch to increase the cut-off capacity, the backup current-limiting fuse combination protection configuration can provide both the rated load current and the disconnection. Short-circuit current, and the ability to open and close no-load transformers, can effectively protect the distribution transformer. For this reason, it is recommended to use the load switch to increase the configuration of the backup current-limiting fuse combination with the cut-off capacity as a protection method for the distribution transformer protection. The standard GB14285 "Technical Regulations for Relay Protection and Safety Automatic Devices" stipulates that when selecting protection equipment for distribution transformers, when the capacity is equal to or greater than 800 kVA, a circuit breaker with relay protection device shall be used. For this provision, it can be understood as based on the following two needs.
When the distribution transformer capacity reached 800kVA and above, most of the past used oil-immersed transformers and were equipped with gas relays. The use of circuit breakers can be matched with the gas relays to effectively protect the transformers. 
Detailed discussion on the five major safety issues in relay protection tester operation
1, line problems 1.1 inrush current inrush current line <br> <br> impact protection tester of inrush current protection means is put into operation, the magnetic flux in the core of the transformer can not be mutated load, The non-periodic component magnetic flux appears, which causes the transformer core to saturate and the excitation current increases rapidly. Transformer excitation inrush current, secondary load tester provides current transformer and voltage transformer secondary load measurement. In the actual operation of the voltage transformer, the total admittance of the secondary measuring device and the secondary cable connected to it and the capacitance between them and the earth line. Can reach the transformer rated current 6 ~ 8 times, and with the size of the transformer capacity, the smaller the transformer capacity, the larger the magnetizing inrush multiple. Exciting inrush current has a large non-periodic component and decays with a certain time coefficient. The decay time constant is also related to the size of the transformer. The larger the capacity, the larger the time constant and the longer the inrush current exists. The 10kV line is equipped with a large number of distribution transformers. When the line is put in, these distribution transformers are connected to the line. At the instant of closing, the excitation inrush currents generated by the transformers are superposed on each other and reflected back and forth, resulting in a complex In the electromagnetic transient process, when the system impedance is small, a large inrush current occurs and the time constant is also large. In the current protection of two-stage current protection, the operating current value tends to be small because of the need to balance the sensitivity, especially when the long line or system impedance is large. The magnetizing inrush current value may be greater than the setting value of the device, which will cause the protection to malfunction. This situation is not prominent when the number of line transformers is small, the capacity is small, and the impedance of the system is large. Therefore, it is easily overlooked, but it may appear when the number of line transformers and the capacity increase.