10
Fig. 13 Operating circuit
(Explanation)
(1) When BSa is closed, current flows as (＋) → BSS → BSa
→ 52b → (CC) → (－) and is excited only at (CC) coil and
picked up.
(2) When picked up, the changeover 52b contact opens, current flows
as (＋)→ BSS → 52a → (HC) → (CC) → (－) and is excited at
both coils HC and CC. After pick-up, the internal resistance of
(HC) is large in comparison to that of (CC) so current decreases
and heat loss of the coil is reduced.
Remarks : CC : Closing coil
HC : Holding coil
2-2 PERFORMANCE
The performance of the contactor is guaranteed by carrying out a test under the testing conditions set forth according
to the standard and satisfying the value specified therein. The testing conditions vary with the types of loads, which
are classified into categories from AC1 to AC4 as given in Table 5.
Table 5. Utilization categories (IEC 60947-4-1)
Category Typical applications
AC1
AC2
AC3
AC4
Non-inductive or slightly inductive loads, resistance furnaces.
Slip-ring motors: Starting, plugging
1)
.
Squirrel-cage motors: Starting, switching off motors during running.
Squirrel-cage motors: Starting, plugging
1)
, inching
2)
.
1) By plugging, is understood stopping or reversing the motor rapidly by reversing motor primary
connections while the motor is running.
2) By inching (jogging), is understood energizing a motor once or repeatedly for short periods to
obtain small movements of the driven mechanism.
The major test items to determine the performance of the contactor are as follows.
・ Temperature rise test
・ Making and breaking capacities test
・ Mechanical endurance test
・ Electrical endurance test
(1) Temperature rise test
When the temperature rise becomes constant after the rated operational current or rated thermal current has flowed
to the main circuit and auxiliary circuit, the temperature rise of each section should be measured. The temperature
rise mentioned above must not exceed the specified limits given in Table 6 and Table 7.
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