14
(i) the iron core of the electromagnet is damaged by a strong shock, and the fatigue of molded parts and pressed
parts becomes greater, with the result that the mechanical endurance of t he contactor is shor tened by
approximately 50%.
(ii) the contact increasingly jumps due to the strong shock and there is a possibility of abnormal wear and
contact welding due to making and breaking of starting current of the motor.
(2) Where the power source voltage is lower than the rated voltage
When the power source voltage is low, it nears the closing voltage (lower than 85% of the rated voltage) of the con-
tactor. As a result, a case occurs wherein the electromagnet is not attracted to the fullest extent because of variation
of voltage, voltage drop due to rush current of coil, and the like, so that the contact flutters and troubles may be
caused including abnormal contact wear and contact welding, or burning of coil (because the rush current of coil
flows for a long time).
Moreover, the motor may incur failures such as burning caused by continuous flow of starting current.
The starting current of the motor causes voltage drop if the wire of the main circuit is long or fine, so the voltage of
coil becomes lower than 85% of the rated voltage, and the same phenomenon as above may take place ; attention
should be paid to this point. The causes of voltage drop of power source at closing are shown in Table 11 , so that
they should be investigated and measures against them taken.
Table 11. Causes of voltage drop of coil power source
Class Causes
Main circuit ･ The wire of main circuit is fine, so the voltage is dropped by the starting current
of the motor.
･ The wire of main circuit is long, so the voltage is dropped by the starting current
of the motor.
Operating circuit ･ The wire of operating circuit is fine, so the voltage is dropped by the rush current
of the coil.
･ The wire of operating circuit is long, so the voltage is dropped by the rush current
of the coil.
･ The capacity of power source transformer for operating circuit is short, so the
voltage is dropped by the rush current of the coil.
Power source ･ The voltage regulation of power source is large.
2-3-2 Operating Time
Cited below are the items to which attention should be paid when handling the closing and releasing times of the
contactor.
(1) Closing and releasing time
The closing and releasing times of the contactor vary from 10 to 50 ms as shown in the catalog. This is due to the
phase and value of voltage applied to the coil and the friction of the mechanical section. Examples of these variations
are as shown in Fig. 14.
Where it is not desired that two electrical signals are sequentially lapped, the contactor is placed in the other circuit
to create a time lag. However, this time lag is not a strict time difference, but one which is used as appropriate when
an approximate time lag is wanted.
While, if this closing or releasing time is used in place of a timer to get the accurate time lag, no degree of accuracy
can be expected because of the above-mentioned variation from 10 to 50 ms. Attention, therefore, should be paid
to this point.
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