In manufacturing plants and other institutions, strict requirements are imposed on the uninterrupted operation of the electrical network. The main means of its provision are automatic reserve input, used in single-phase power grids, and a phase switch, which differs from the classic ATS by using additional lines from an inactive phase of a three-phase network.
Device and principle of operation
The input terminals of the device are powered from three phases, and only one comes out of it, which has a voltage indicator that is as close to the optimal as possible. When the main line power is cut off or there is a sudden voltage surge, the three-phase switch will activate another phase - where the indicator is closest to normal. For the most part, the device is used in networks with three phases, but it is also used for a generator - in this case, it is necessary to think over the shape of the triggering pulse.
Mechanical and automatic devices are available. The automatic three-phase phase switch works with support on a microcontroller. Switching the design of several relays, the automatic switch searches among the power lines that are closest to suitable indicators. Positional 3-phase manual switches are available in different numbers of positions (from two to four). The digital order of switching can be different for them. One example: 0-1-0-2-0-3: here zero means all lines are turned off, and the rest of the numbers correspond to phases. High power mechanical devices are often used for reversing motors.
How to choose a phase switch
When choosing a voltage switch, first of all, you need to pay attention to the current parameters for which the device is designed. It is they who determine whether the device is suitable for use in a particular network. It is not recommended to purchase a switch, the current of which is higher than the rated value for the input circuit breaker.
Other important parameters when purchasing a manual or automatic phase finder are:
- flexibility and variability of settings: at a minimum, the setting of the boundaries of the normal voltage and the main phase should be provided;
- indication type: preferred - liquid crystal display; cheap models use LEDs;
- additional features - for example, touch control.
If it is found that the phase distributor does not have enough power to service the network, a switching device can be installed. In this case, the winding of the contactor or starter must be connected to the output terminals of the device.
Scope, purpose and parameters
The scope of application of phase selection devices is extensive: devices are installed at manufacturing enterprises - in automation systems, control, ventilation and others; in hospitals and pharmacies - life support devices, storage of medicines. They are also used in residential buildings: to provide alarm systems, gas boilers.
The use of a 3-phase switch is practiced to transfer power from an active line to another.This option is advisable in situations where interruptions, sudden surges occur in the main line, the voltage becomes too high or ceases to be supplied at all. To ensure uninterrupted supply of the network and prevent emergency incidents, it is necessary to correctly set the values of the key parameters.
Minimum voltage limit
It shows the limit below which you cannot go down, otherwise the network will work intermittently. Set the border in accordance with the documents attached to the device.
Return time
This is the interval after which an attempt is made to redirect contacts to the main source when using the backup core. When this period has passed, the device checks the parameters of the leading phase. If they correspond to normal indicators, the power goes to it, but if not, a second check is carried out later after the same period of time. The use of such a mechanism makes it possible to save resources - for example, leaving a room supplied with a generator, you can turn off the engine for a certain interval (an hour or two). Turning it off for a long time is fraught with a strong drop in temperature in the cold season and the breakdown of electrical appliances, and using the indicated option would be a rational solution.
Switch-on time
It characterizes the time after which the device will try to turn on the power in a situation of its absence on all current-carrying wires. A signal can be generated by means of a relay.
Connection diagram and operating procedure
It is recommended to independently connect the automatic phase changeover only if you have sufficient experience in working with power grids, since you will have to deal with high voltage. Incorrect operations can cause phase-to-phase faults. The apparatus is placed on a din rail inside the shield. Usually, the installation diagram of the device is described in the technical documents attached to it. First, the primary circuits are connected, then the secondary ones.
When the master connects the switch of the power lines to the network, he may prefer any of the three phase conductors as the supply wire. To prevent jamming of the output relay contacts, the device has a special interlock. Also, the introduction of the device into the circuit prevents the occurrence of overloads. Automatic devices are equipped with the option of monitoring the contacts of the starters of the external electrical circuit.
To prevent the contacts of the output relays built into the device from sticking, the device is equipped with an internal interlock. In addition, it monitors the state of the contacts of the starters, which are available in the external electrical circuit. The use of this device allows you to prevent phase overload.
ACE installation parameters
In the technical documentation for the device and on its case, two parameters are indicated - the minimum and maximum voltage, at which the correct operation of the network is possible. The second is especially important - if it is exceeded, the wiring burns out, which can initiate a fire. If the voltage drops too low, the device will trip all the time.
Time parameters are also of great importance - the periods of inclusion and return. In addition, the fitter must select the main phase. It is used by default, and if power surges occur on it, a reserve core is used. During its operation, the device continues to monitor the state of the leading conductor and, when it returns to normal, switches to it.
Features of connection and operation of the device
The main types of ACE
In Russian power grids, two types of devices are most often used - PF 451 and PF 431. To select the desired model, the user must understand the differences between them.
PF 431
Protects household appliances from voltage surges. Suitable for home use, including owners of refrigerators that consume more than 1.5 kW per day, video surveillance systems and other equipment that operates daily for a long time and consumes a lot of power. The device monitors the potential difference at the output. A three-phase voltage is put at the input, at the output - one phase at 220 V with a frequency of 50 Hz.
PF 451
Provides uninterrupted operation of a single-phase line. It differs from the previous one by the absence of an option for setting the leading phase. Connects the one whose voltage parameters are close to optimal.
Connecting a phase changeover device is a good way to ensure a stable power supply for industrial or household equipment. It also increases the degree of electrical safety, preventing the circuit from burning out the wiring.
