No. |
Main structures and performances |
Scheme 1: speed regulating by internal feedback chopped wave made by SCR |
Scheme 2: speed regulating by internal feedback chopped wave made by IGBT |
| 1 |
Startup and bypass performance |
Start the frequency sensitive rheostat and the starting current is 4-5IN. When the speeding regulating device is in sudden malfunction, quickly make the motor bypassed to full-speed operation, which may easily causes the damage to slip ring of motor. Since the input air fluctuates in vast scale instantly, the blowing out of boiler and production halt are caused. |
Hydraulic resistance soft-startup and the starting current is less than 1.5IN. When the speeding regulating device is in sudden malfunction, the motor can be automatically bypassed and gradually raised from the original state of speed regulating operation to full-speed operation, with a transition time of about 30 seconds, which has no influence to slip ring of motor and guarantees the response of air door regulator, and the blowing out of boiler and production halt will not be caused. |
| 2 |
Exterior structure and mode of cooling |
The high-power SCR is in plate type, with a double-side radiator. Both sides of the radiator are respectively in ground insulation. The radiator is electrified and the element is installed inside the air passage. |
The IGBT is in full modular structure, with an insulating base and a single-side radiator. The radiator is earthed but is not electrified and the element is installed outside the air passage. |
| 3 |
Comparison of grades of flow and voltage |
The current of single element of SCR is only 500-2,000A, and the voltage is only 1,200V-5,000V. |
The current of single element of IGBT is only 400-2,400A, and the voltage is only 1,200V-6,500V. |
| 4 |
Working principle in brief |
SCR is a switch element conducted by pulse triggering, without self switching off. |
IGBT is a transistor conducted by voltage control switch, an element with self switching off. |
| 5 |
Mode of conduction and switching off |
It requires a triggering pulse larger than 100 microseconds to conduct SCR and the switching off can only be achieved after the current falls to 0 through the external auxiliary circuit or through the current itself. |
IGBT is conducted by DC voltage of 15V and is switched off by a voltage of 0V. |
| 6 |
Time of conduction and switching off |
The fast switching SCR is conducted by 100 microseconds and is switched off by 150 microseconds. |
The IGBT is conducted by 1-2 microseconds and is switched off by 1-2 microseconds. |
| 7 |
Comparison of working frequency |
Since the time for switching off SCR is about 100 microseconds, the working frequency shall not be high. In the use of inverter, the working frequency can not exceed 300HZ, or the inverter will be in inverted overturning failure. |
Since the time for switching off IGBT is about 1-2 microseconds, the working frequency shall be higher. In the use of chopper and inverter, the working frequency can be 8-10KHZ, and the chopper has no failure of direct conduction and the inverter will never in inverted overturning failure. |
| 8 |
Mode of speed regulating as well as comparison of harmonic and power factor |
The chopped wave speed regulating is achieved by changing the duty ratio of the chopper. Since the SCR inverting angle of the inverter is a variable varying from 30-150 degrees, the larger the inverting angle is, the higher the harmonic current is, and the lower the power factor is, the narrower the scope of speed regulating is. |
The chopped wave speed regulating is achieved by changing the duty ratio of the chopper. Since the IGBT inverting angle of the inverter is invariable as 0 degree, the smaller the inverting angle is, the lower the current of harmonic distortion is, and the higher the power factor is, the wider the scope of speed regulating is. The more stable the inverter works, there will be no inverting overturns. |
| 9 |
Scope and efficiency of speed regulating |
The scope of speed regulating is 50 -95% and 40-85%. Since the minimum SCR inverting angle can only be fixed as 35 degrees or so, the scope of speed regulating is determined. If the rotor voltage and feedback winding voltage are the same, e.g.: U2/E20=0.5 and the minimum rotating speed is 0.5No; then the maximum rotating speed can not achieve the rated rotating speed. Since the SCR system of the inverter is vast, the failures will be frequently occurred with poorer maintenance, and the highest efficiency is 92%. |
The scope of speed regulating is 0-100% and 50-100%. Since the IGBT inverting angle is invariable - 0 degree, the scope of speed regulating is the same as that of high-voltage frequency transformator. If the rotor voltage and feedback winding voltage are the same, e.g.: U2/E20=0.5 and the minimum rotating speed is 0.5No, then the maximum rotating speed can achieve the rated rotating speed. Since the IGBT system in modular structure is simple without inverting overturns. The maintenance is convenient and the efficiency is 98%. Since the inverting angle is 0 degree, the harmonic current is small and the power factor is high, which is good for the effective capacitance compensation. |
| 10 |
Comparison of performance of chopper and inverter in use |
SCR generally is the element made in China with lower cost performance. It is conducted by controlling the pole triggering, and can not be self switched off after being conducted. The switching off can only be realized after the current passing the anode-cathode is 0 and lasts for about 100 microseconds, or it can not be switched off, which will then lower the capacity of resisting disturbance of thyristor without self-protective capacity and self-recovery. When it is lost due to the pulse interference of 5-10us, it can not be self switched off, so the failure signal of interference can not be removed, which will result in the direct connection failure of the chopper. Since the working frequency of SCR is lower, the pulsating movement of rotor current will be greatly increased, the harmonic content of motor current will achieve 10% above, and the power factor of motor will be lowered at the same time, thus bringing inverting overturns in inverter and externally short circuiting on feedback winding of motor. Since the triggering sensitivity of SCR is variable, when the equipment is operated in high temperature, especially in summer, the triggering will be more sensitive with the variation of environmental temperature, some interfering signals will make it conducted by triggering by mistake. Especially when the network fluctuates, or the current is suddenly changed when the motor is in instant blocked operation, the failure of burning out the rapid fuse and SCR will be frequently occurred. |
IGBT is a high-voltage and high-power power electronic element manufactured by ABB and Siemens, which is a high-power insulated gate transistor provided with function of self switching off with the time of 1-2 microseconds for switching off. When the grid is added with DC voltage of 15V, the collector – emitter is conducted, while if the gird voltage is 0, the collector – emitter all will be quickly switched off within 1-2 microseconds. When it is lost due to the pulse interference of 5-10us, it can be self switched off at the same time and the failure current can be effectively cut off within 2 microseconds, so the protective capacity can be reliably achieved with strong capacity of resisting disturbance caused by pulse.
IGBT has no failure of direction connection. Since the speed of IGBT conduction and switching off is high, the working frequency of chopper made by IGBT can be up to 8-10KHZ, which will make the pulsation of current of rotor greatly reduced, the harmonic content of motor current will be less than 4% and the power factor will also be greatly improved. In use of inverter, there is no inverter overturns. Since the speed of IGBT switching off is high, the failure current can be removed effectively with extremely high self-protective capacity.
|
