Medium voltage (3 ~ 10KV) method of motor starting analysis and comparison of late Pan G Link Road just 1 2 Mukai 1 Abstract: This paper on the traditional medium voltage motors start method and the recent soft launch of several commonly used methods are theoretical analysis, in the comprehensive index of these startup methods on the basis of comparison, that the swit
ching technology in medium voltage transformer motor soft start is the start method the preferred method.
Keywords: medium voltage motor, full voltage directly to start, soft start, the switch transformer
1, Introduction to AC motor starting has been a subject of concern, especially in high-voltage large-capacity AC motor with its usage the dramatic increase in soft-start problem becomes more prominent.
is well known, ordinary squirrel-cage motor full-load pressure directly at the start, starting current may reach 5-7 times the rated current. When the motor capacity is relatively large, the starting current will cause a sharp decline in the grid voltage, voltage and frequency will also change, which will destroy the grid with the normal operation of other devices, and even cause power loss of stability, resulting in more accidents.
motor full voltage startup-current in the stator windings and rotor cage bar have a great impact, will destroy the bar cage winding insulation and cause fracture, causing motor failure, high current will produce large amounts of Joule heat, damage winding insulation and reduce motor life.
motor direct full-voltage starting torque when starting approximately 2 times the rated torque, the gear transmission equipment, it will impact greatly accelerated gear wear or broken; for the belt drive devices, plus wear a big belt and even pulled off the belt.
class load for the pump, the motor starts the whole pressure, water flow will be in a very short period of time to reach full speed, in the face of pipe bend, the speed of the current rush to the wall, and have a great impact to form a water hammer effect, will destroy the pipeline. If a long line in front of the pump, when the pump motor suddenly stopped, the water flow will impact the high-speed water pump impeller, have a great impact, will deform or damage the impeller.
the above points will cause the device to increase suspension units, the impact of normal production, increased maintenance costs.
medium pressure (3-10KV) larger than the capacity of the motor,
puma orange, generally in the 200KW or more. In recent years, many industries increasing production capacity, the drive motor of its production equipment is also growing, such as steel, chemical industry, 10000KW above has been more and more use of the motor, these problems have become more and more serious, people are getting their high degree of concern.
2, the traditional way of starting a direct full pressure start
2.1 motor direct full pressure starts, too much on the line starting current will have a greater pressure drop, so that large voltage fluctuations, in the power of Parallel line the normal operation of other devices, the general requirement is often caused by motor starting grid voltage is not more than 10%, occasionally causing the motor to start the grid voltage is not more than 15%. You can also press the power situation to decide whether to allow the motor started directly, as shown in Table 1:
Table 1: Press the power capacity to determine when the motor started directly
allow direct power supply situation of maximum power to start the motor (KW )
1KVA small-capacity power plant generating capacity of each
0.1 ~ 0.12KW
substation
often starts, the transformer capacity of not more than 20%
occasional starts, do not transformer capacity is greater than the 30%
high voltage lines connecting lines do not exceed the motor short-circuit capacity of 3%
Transformer - Motor Group
motor capacity of the transformer capacity of not more than 80%
will produce short-term motor starting inrush current, if the current impact of this short break by a periodic function, it will contain a short period of harmonic current, harmonic current, or as short-term rapid changes in harmonic current.
We know that the electricity load in the largest proportion of the motor, the electrical driving force behind the 90%, electricity accounts for 60% or more, such a huge number of motor starts, will have a short period of harmonic currents, so that a significant increase in the harmonic power. Harmonic content increases, will result in reduced life of electrical equipment, net loss increased, the system increase the likelihood of occurrence of harmonic resonance. At the same time, it may cause malfunction of relay protection and automatic device, instrument instruction and electricity metering and communications are not allowed to interfere with a range of issues.
will direct full pressure start off in the timely generation high-voltage switching operation over a large steepness of the voltage, the stator voltage distribution around the ancestors uneven, causing great damage to its insulation. Number of motor failures are due to self-harm caused by insulation.
into account in the economic conditions permit, should be avoided under the direct activation of the motor way, we supply to ensure power quality. In China, the current in the low-voltage motor soft start method has been very common, but in terms of medium voltage motor starter equipment and technical reasons as soft start approach is still relatively small.
2.2 Stator loop vacuum string reactor start
the stator loop vacuum string reactor start shown in Figure 1, starts K2 closed reactor in series with the motor M connected to the grid, to be close to the rated motor speed After speed, K1 closed, K2 off, the removal of the reactor L, the motor accelerates to rated speed.
based motor in series reactor is started, it's terminal voltage UL and added directly to start the ratio of rated voltage UN K (K
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Linear Mode
