三相摩打起動變壓噐（馬達用開車火牛）

三相摩打火牛開車起動變壓器其實要學習不難，我先比個簡單圖你研究，如果唔明白再問我，下面就係


圖片參考：http://img165.imageshack.us/img165/3701/atstarterzm2.jpg








開始啓動時間如下：
按下“啓動”時，K3M先入，跟住就K2M入，當摩打既速度有75% ~ 80% 時，K3M退出，K1M再入，就完成佐。


Auto transformer Starter.

An Auto transformer starter uses an auto transformer to reduce the voltage applied to a motor during start. The auto transformer may have a number of output taps and be set-up to provide a single stage starter, or a multistage starter. Typically, the auto transformer would have taps at 50%, 65% and 80% voltage, enabling the motor to be started at one or more of these settings.



There are two ways of connecting an auto transformer starter, the most obvious way is to apply full voltage to the transformer via a contactor, and connect the motor to the tap by means of a contactor. When the motor has accelerated to full speed, or has run out of acceleration torque, the tap contactor opens, disconnecting the motor from the transformer and another contactor closes connecting the motor to the supply. The transformer can now be disconnected from the supply. This format is known as an open transition starter and is less than ideal due to the fact that the motor is disconnected for a short period of time during the start period. While the motor is connected and accelerating, there is a rotating magnetic field in the stator which causes flux in the rotor and thus a rotor current to flow. At the instant the motor is disconnected, there is a magnetic field in the rotor which is spinning with-in the stator winding. The motor acts as a generator until the rotor field decays. The voltage generated by the motor is not synchronised to the supply, and so on reconnection to the supply, the voltage across the contactor at closure can be as much as twice the supply voltage resulting in a very high current and torque transient. This open transition switching is often known as the auto-reclose effect as it yields similar characteristics to opening and closing a breaker on a supply to one or more motors. The consequences of open transition switching can be as bad as broken shafts and stripped gears.





2007-09-29 16:44:07 補充：
By a rearrangement of the power circuit, it is possible, at no extra cost, to build a closed transition starter and thereby eliminate the current and torque transients. The closed transition auto transformer starter is known as the Korndorffer starter.

2007-09-29 16:45:19 補充：
The open transition switching is achieved by reconnecting the tap contactor between the transformer and motor, to the star connection of the transformer, hard wiring the motor to the tap, and altering the sequence of contactor control.

2007-09-29 16:47:31 補充：
To start the machine, the main contactor and the star contactors are closed applying reduced voltage to the motor.

2007-09-29 16:48:16 補充：
When the motor has reached full speed, (or run out of acceleration torque) the star contactor is opened effectively converting the auto transformer starter into a primary reactance starter.

2007-09-29 16:48:56 補充：
Next the primary reactance is bridged by a contactor applying full voltage to the motor. At no time does the motor become disconnected from the supply.

以上原理只是包括兩種不同的基本原理
星角起動 在星形接法時,每組線圈承受電壓比角形接法時低,由此降低起動時的碗流量
你所說的開車牛,其實是三個獨立的自偶變壓器,中心抽頭可以由55%-70%不等(也有其他比例),三隻自偶變壓器會跟馬達一樣接駁為星形,100%位置接駁來氣,70%位置供馬達,由於供電位置是自偶變壓器的70%位置,所以電壓只有原本的70%,起動電流便會降低
這種起動方式,通常只有大形電動機才需要,大古坊冷氣機房便有幾台,而且是萬一伏特的
而學習這個專門方面,好像在香港未有,但理論也是由基本而來
除了用自偶變壓器之外,海洋中心地庫也有兩台電阻式起動(如果還未拆除的話)原理也是把起動時電壓降低來壓制起動電流

星角起動器的原理是把起動電流減至電動機的滿載電流的1/3來起動。
課程簡章可以在理工大學、VTC(電機學系)、工聯會、電器工會索取