The selection of contactors shall be conducted according to meet the requirements of the controlled equipment. Except that the rated working voltage shall be the same as the rated voltage of the charged equipment, the load rate, use category, operation frequency, working life, installation mode, size and economy of the charged equipment are the basis for selection.
Contactors are used in series and parallel
There are many electrical devices that are single-phase loads and, therefore, several poles of the multipole contactors can be used in parallel.Such as resistance furnace, welding transformer, etc.When used in parallel, a smaller capacity contactor can be selected.However, it must be noted that the agreed heating current of the contactor after parallel is not completely proportional to the number of poles in parallel.This is because the resistance values of the active, static contact loop may not necessarily be completely equal, so that the current flowing through the positive is not equally distributed.Therefore, the current can only increase to 1.8 times in parallel, and after the three poles are in parallel, the current can only be increased to 2 to 2.4 times.
In addition, it should be pointed out that because the pole contacts cannot be connected and disconnected at the same time after parallel, the connected and separation ability cannot be improved.
Sometimes, several poles of the contactor can be used in series, due to the increase of contact breaks can divide the arc into many segments, improving the arc extinguishing ability, and accelerating the quenching of the arc.Therefore, several poles can be increased in series, but can not exceed the rated insulation voltage of the contactor.The agreed heating current and rated working current of the contactor in series will not change.
Effects of the power supply frequency
For the main circuit, the change of frequency affects the skin effect, and the skin effect increases at high frequency. For most products, 50 and 60 Hz have a great effect on the temperature rise of the conductive circuit.However, for the attraction coil, attention should be paid. The 50 H design will reduce the magnetic flux of the electromagnetic line at 60 Hz, and the suction will be reduced. Whether the use depends on the margin of its design.In general, the user is best to use it according to its calibration value and order according to the operating power frequency.
Effects of the operating frequency
The number of hourly operating cycles of the contactors has a great impact on the burn loss of the contacts, so attention should be paid to the selection. The applicable operation frequency is given in the technical parameters of the contactors.When the actual operation frequency of electrical equipment is higher than the given value, the contactor must reduce reduced value.
Selection of AC contactors for controlling electric thermal equipment
This kind of equipment has resistance furnace, temperature regulating heater, etc. The current fluctuation range of such load is very small, which belongs to AC-1 according to the category of use. The contactor can control such load easily, and the operation is not frequent.Therefore, when selecting the contactor, as long as the agreed heating current Ith of the contactor is equal to or greater than 1.2 times the working current of the electrical thermal equipment.Example 1: A contactor is selected to control the 380V and 15KW three-phase Y-shaped HW.Solution: first calculate the rated operating current Ie of each phase.The Ith=1.2Ie=1.2×22.7=27.2A thus selects any type of contactor with the agreed heat current Ith≥27.2A.For example: CJ20-25, CJX2-18, CJX1-22, CJX5-22 and other models.
Control the selection of contactors for lighting equipment
There are many types of lighting equipment, different types of lighting equipment, starting current and starting time is also different.Such loads use category AC-5a or AC-5b.If the starting time is very short, the agreed heating current Ith is equal to 1.1 times of the working current of the lighting equipment Ie. If the starting time is slightly longer and the rate factor is low, the agreed heating current is greater than the working current of the lighting equipment, refer to Table 1. Table 1 Selection principle of contactor for control lighting equipment No. Lighting equipment name starting power supply COS start time min contactor selection principle
Post time: Mar-01-2022
