Device for sequential switching of consumers. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Protection of equipment from emergency operation of the network, uninterruptible power supplies
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It is known that after a short power outage or when switching to backup power, many domestic and industrial air conditioners require a three-minute restart delay. In addition, in air conditioning systems containing a large number of electric motors, the simultaneous start-up of the latter is undesirable, since their total starting current, which is many times higher than the rated current, can cause network overload. The proposed device - a three-channel timer - provides automatic exposure and alternate connection to the network of three groups of electricity consumers.
The timer is simple, assembled from available parts and does not require adjustment. Its scheme is shown in the figure.
(click to enlarge)
Clock pulses generated from a voltage of 6,3 V 50 Hz using the limiter R1VD1 and the Schmitt trigger on the elements DD2.2, DD2.3 are fed to the input of the frequency divider (counters DD1, DD3, DD4). The total division ratio is 1000, the pulse repetition period at pin 11 of the counter DD4 is 20 s. The R2C2 circuit and the DD2.1 element are used to set the counter to its initial state when turned on. An alternating voltage of 6,3 V is obtained from the mains using a low-power step-down transformer not shown in the diagram or from a separate winding of the power transformer.
The output of the divider is connected to the clock input (pin 13) of the DD5 register, which is included in a scheme that provides a log shift in each cycle. 0 from high to low order. There are 12 bits in total, therefore, at the output of the third (pin 6 of DD5), a low level will appear after (12-3) -20 = 180 s after power is applied to the timer, after 20 s - at pin 5 and after another 20 s - at pin 4 .
The switching device connected to pin 6 of the DD5 register consists of an optocoupler U1, a diode myTaVD2-VD5 and a triac VS1. At the first operation of the timer, the triac closes the power circuit of the winding of the three-phase contactor KM1 PMA-3/02, which connects the consumer (air conditioner compressor motor) to the network. The high load capacity of the DD5 register output allows you to control the optocoupler U1 LED without an additional power amplifier. With the help of a specially provided group of contacts, the triggered contactor is self-blocking, so the further behavior of the timer does not affect the operation of the engine.
With pins 5 and 4 of register DD5, switching nodes are connected, which operate with a delay of 20 and 40 s relative to the first one. Depending on the nature and power of the load, the nodes can be made according to various schemes, but self-blocking must be provided for in them.
Author: D. Pankratiev, Tashkent, Uzbekistan
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