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(a) State the type of motor starter circuit shown in FIGURE 2(a) (see attached file).
(b) The ends of the motor stator coils are shown as U1 and U2, V1and V2 and W1 and W2
Referring to FIGURE 2(b) (see attached file), sketch the connections of the windings between the contactors C1 and C3 for starting and C1 and C2 for running. Briefly describe the purpose of the contactors C2 and C3.
(HINT: Refer to FIGURE 2(a) and trace the connections from the contactors to the motor windings. Connections to the contactors must be shown.)
(c) Describe briefly the operation of the control circuit of FIGURE 2(c) (see attached file) when the fused isolator is closed and the start button is pressed.
(d) State:
(i) The effect of contactor C2 energising before contact C3 deenergises
(ii) A simple method of ensuring contactor C3 de-energises before contactor C2 is energised
(iii) How contact C3 - 1 affects the operation time between the star point contactor C3 and the main contactor C1.
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Solution Summary
The expert states the types of motor starter circuits shown. The operation of the control circuits are determined.
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Please refer to the attachment.
(a) State the type of motor starter circuit shown in FIGURE 2(a).
(b) The ends of the motor stator coils are shown as U1and U2, V1 and V2 and W1 and W2. Referring to FIGURE 2(b), sketch the connections of the windings between the contactors C1
and C3 for starting and C1 and C2 for running. Briefly describe the purpose of the contactors C2
and C3.
(HINT: refer to FIGURE 2(a) and trace the connections from the contactors to the motor windings. Connections to the contactors must be shown.)
(c) Describe briefly the operation of the control circuit of FIGURE 2(c) when the fused isolator is closed and the start button is pressed.
(d) State: (i) the effect of contactor C2 energising before contact C3 de-energises.
(ii) A simple method of ensuring contactor C3 de-energises before contactor C2 is energised.
(iii) How contact C3 - 1 affects the operation time between the star point contactor C3 and the main contactor C1.
Solution: a) This is known as the star-delta (or Wye - Delta) starter. This is one of the direct on line (DOL), reduced voltage starting methods. In this type of starting, the three stator windings are initially connected in star configuration and then connected directly to the mains, resulting in a phase voltage of line voltage VL/√3. As the motor speeds up, at some stage the connection is changed to delta, resulting ...
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