Three-phase symmetrical load. Device for determining phase rotation - homemade phase indicator

To calculate currents, the circuit diagram, the value and type of resistance, and the voltage of the energy source must be specified. Calculations are usually carried out for complex values.

A symmetrical load in a star-star circuit with a neutral wire is shown in Fig. 4.8.

If the neutral wire in the circuit of a symmetrical receiver (
) has a very low resistance (Z 0 = 0), then the potential of point O / is almost equal to the potential of point O, and the points merge into one. Three separate circuits are formed in the circuit, the complex values ​​of the currents in each of which are determined as in a single-phase circuit
;
;

Where Ė A, Ė IN, Ė WITH– phase voltages at the generator terminals.

According to Kirchhoff's first law, the current in the neutral wire of a 4-wire system is equal to the geometric sum of the phase currents
.

In general, the complex voltage between zero points 0 – 0` in the presence of a neutral wire

.

With a uniform symmetrical load, the current I 0 =0, and the neutral wire can be removed from the circuit without changing its operating mode. For a 3-wire system, i.e. not containing a neutral wire (Z N = ∞), the term 1/ Z N will be absent in the denominator.

When determining the phase voltage of the receiver, if you do not take into account the source resistance, then
can be replaced by

Moving on to the actual values ​​of quantities in the case when the loads in all phases are equal and are of an active nature ,

Where
− the value of the line voltage, the currents accordingly take values
,
,
.

The total power of a three-phase circuit with an active load is equal to

.

4.4. Unbalanced load with star connection

With an asymmetrical load and the absence of a neutral wire, voltage appears between the zero points of the O generator and the O receiver , as a result of which the phase voltages of the receiver are different. Calculated ratio
between phase and line voltages is disrupted. To determine the voltage between zero points, as well as the phase voltages of the receiver, we assume that in electrical circuit there is a neutral (neutral) wire whose resistance
. Then the voltage between the zero points of the source and receiver

,

Where g A , g B , g C , g N – conductivity of phase and neutral wires,

T

Rice. 3. 9. 3.10.

.e. for an asymmetric system when determining the denominator takes into account the conductivity of the neutral wire g N ..

In Fig. 4.9. shows a vector diagram without a neutral wire, in which ,
,− vectors of phase voltages of the source, and
,
,
− vectors of linear voltages of the source, as well as linear voltages of the receiver. To construct the voltage vector and receiver phase voltage vectors
,
,we use their values ​​obtained above.

Relationship between phase and linear vectors
,
,And
,
,
, we define by expressions
,
,
.

The vector diagram is constructed for active asymmetric phase load (
).

When the value of phase active resistances changes, the voltage
may vary within wide limits. In accordance with this, point N on the diagram can occupy different positions, and the phase voltages of the receiver can differ from each other quite significantly.

Let's consider a special case of an asymmetric load, when
. Because the
, then
, we get
,
And
. Dot N on the diagram will move to point C, the voltage will increase to the phase voltage of the source, and the voltage
,
− up to linear voltages.

When phase voltages change, phase currents and powers change - “phase imbalance”.

If, under an asymmetrical load, the zero points of the source and receiver are connected with a neutral wire, then since the resistance of the neutral wire is small, (
And
), then the phase voltages of the receiver are identical and shifted in phase relative to each other by an angle . Turning on the neutral wire leads to corresponding changes in the vector diagram of the electrical circuit. So, if an electrical circuit without a neutral wire corresponds to the vector diagram shown in Fig. 3.9. solid line, then the same circuit when the neutral wire is turned on corresponds to the diagram shown in the same figure with a dotted line.

Vector constructed in accordance with the expression.
.

In the presence of a neutral wire in circuits with an asymmetrical load, as well as in the case of a symmetrical load, the relation remains in force

.

Based on the foregoing, we can conclude that the neutral wire is necessary in order to equalize the phase voltages of the receiver during an asymmetrical load, i.e. receive the same voltages in all phases of the receiver, equal .

Phase currents, phase angles between phase voltages and currents, as well as phase powers with an asymmetric load in a circuit with a neutral wire will generally be different. They can be determined using the following formulas:
,
,
.

The phase shift angles between phase currents and voltages depend on the magnitude and nature of the receiver phase resistances and are equal

,
,
.

The powers for phase “A” are equal

Active and reactive power of a three-phase receiver when connected by a star
,
.

If, in addition to phase currents, it is necessary to find the current in the neutral wire, then the problem should be solved in a complex form. In this case, it is necessary first of all to express in complex form that
,
,

The current in the neutral wire can also be determined from a vector diagram without resorting to solving the problem in complex form.

A phase meter or, in other words, a phase indicator will help you phase a generator or electric motor. However, it is not easy to find in stores or there is simply no point in buying it for one-time use. For cable wires, it is imperative to know the input phases, otherwise short circuit. If the definition is correct, it will be much more convenient to calculate the voltage. What is phasing, and how to determine the phases, how to use a multimeter and make such a device at home - about all the nuances below.

Why do phases alternate?

Phasing or phasing is a clarification of the similarity of the phases under current of each of the 3 lines. The phased windings are coordinated, which ensures correct work various electrical appliances.

Currently, you can do this yourself.

Checking phase rotation is mandatory when using three-phase electric motors using alternating current.

Nuances:

1. Phasing affects the direction of rotation of the motor, which is a very important condition, especially if several mechanisms use motors of the same order.
2. Another case where you definitely need to pay attention to phase rotation is when using an induction-type electric meter. In the reverse order, spontaneous rotation of the disk located on the counter often occurs. These meters are currently less demanding in terms of phasing, but the corresponding data also appears on the indicator.
3. In some cases, monitoring the phase arrangement can be performed without the use of special instruments. For example, if a three-phase power supply is connected when connecting power cables. If the cores inside this cable are different in color, then the continuity occurs many times faster. In some cases, you just need to peel off the outer insulation of the cable to find out which phase is which. Wires of the same color indicate that the phases are the same.

However, color coding not always a guarantee correct location phases, because not all manufacturers adhere to such standards. Sometimes you can find different colors at different ends of the cable, so the ideal and most reliable way to determine which phase is which is to use core continuity tests.

The versatility of the phase detector

The mechanism for calculating the phasing sequence, that is, the determinant, is best suited for this. It is designed to detect phasing, in which the voltage lags behind the value in phase. The point of this lag taken as a starting point is needed to correctly connect to the network devices that require compliance with the phase sequence. One example of such a device could be a three-phase four-wire electric meter.

The design of such a device is simple:

1. The base is an electrical insulating material, for example, textolite.
2. It contains 2 wall-mounted electric sockets, inside of which there are ordinary incandescent lamps, covered with translucent casings.
3. On their basis, the capacitor and the terminal block for connecting the wires are strengthened.

Often such determinants are made independently at home. When such a detector is connected to a 3-phase network, due to the inserted capacitor in each phase, the voltage changes, so incandescent lamps glow differently. Based on the glow intensity of the lamps, one can judge whether the remaining two wires belong to the remaining phases.

When connected of this element to calculate the phasing rotation when the three-phase network is de-energized, line B is selected as the average.

In relation to this phase, 1 of the unconnected wires, for example, A, will be leading. That is, the voltage in it will lead the value in phase B. And the last phase C will be lagging, the voltage in it will lag behind B. The diagram of such a connection is as follows. When voltage is applied to the detector, one of the light sources will burn brighter and the other worse. The line where the diode burns brighter is the lagging line. The phase where the lamp is half lit is advanced. In this way it can be determined whether the phase sequence is correct.

In some cases, it is not necessary to determine the phases in a three-phase circuit. For example, if the same motor is connected to a three-phase network, it can rotate in both directions. To change direction, you need to swap any 2 phases. You can also distribute the load evenly across all phases to avoid distortion.

If we conditionally designate different lines in any 3-phase network, like the letters A, B, C, then the following options for their alternation can be distinguished:

• Reverse (CBA, BAC, ACB).
• Direct (ABC, BCA, CAB);

If the equipment is connected to a 3-phase line with a power wire, the order of the phases can be checked without using special instruments. In this case, look at the multi-colored or digital markings of the wire insulation.

It should also be noted that in practice, insulation marking may not be the most accurate criterion. After all, not all manufacturers guarantee the same insulation color at the beginning and end of the cable.

Achieve the most correct readings Maybe a cable testing method. For example, using 2 tele-tubes. In this case, 1 of them is active, that is, it has a battery, the other is passive and has no current. There are also paired headsets, which are equipped with headphones, as well as clips, or specifically designed for the use of phasing. You can also use a megger. At the same time, it is imperative to strictly observe safety measures.

Principles of checking phasing

This operation is performed before connecting 2 or more lines that operate independently in parallel operation. Also from an updated generator, after a major overhaul, during which the scheme for connecting the stator to the network could have changed. It is imperative to check the identity or color of the phase conductors. After all, they will need to be connected later.

This operation:

1. Aimed at preventing errors when connecting installation lines in parallel.
2. It allows you to correctly check all contacts.
3. The correct connection of current-carrying cables connected to the device is checked.

The coincidence of identical currents along the line is checked, namely the absence of an angular shift. Only upon receipt positive results During phasing, generators or transformers operate in parallel and are connected for simultaneous operation.

Features of direct phase sequence

This is also called the asymmetric component method. More details, asymmetrical definition element electronic components. It is based on the decomposition of an asymmetric system into 3 symmetric ones: direct, inverse, zero.

Where direct phase sequence is used:

1. The method is used to determine asymmetric orders of action of electrical power components.
2. This method is used by some elements of relay protection and automation. For example, the principle of operation of a voltage transformer with a sequence to zero is based on this. The principle is based on the summation of voltage values ​​in all phases.
3. For 3-phase transport power lines, the result is a matrix of exact eigendirections.

This determination method is successfully used to calculate asymmetrical modes of a 3-phase line, or the occurrence of a circuit short circuit. A phase indicator helps determine the direct sequence of phases, which is necessary for the operation of some devices. If necessary, the phase sequence can be easily changed.

Our gardening partnership installed a three-phase electric meter with a current transformer. The meter was new with all seals. However, when the load is completely switched off, the meter disk rotates slowly, that is, the meter is “self-propelled”. It is clear that the partnership did not want to pay for the energy recorded by the meter, which it did not actually use.

At first they decided that the meter was faulty. The meters were replaced several times, but the self-propelled gun remained. As a result, we came to a different conclusion - the meter is not to blame. We began to think what causes such a “self-propelled movement”? The factory instructions attached to the three-phase meter state: it is necessary to connect the meter to the network, observing the phase rotation sequence, so that phase A of the network is connected to the first terminal of the meter, phase B to the second, and phase C to the third terminal of the meter.

.

The phase sequence can be easily established using a phase indicator. There is always one at power plants, in electrical facilities of large factories, but where would it be in gardening societies? Our attempt to rent a phase indicator for a couple of days from a large institution was unsuccessful. We had to make our own “Device for determining the phase sequence”, with the help of which it was possible to determine this correct sequence. As a result, after eliminating the violation of the sequence of phase alternation, the “self-propelled” meter disappeared. Therefore, there was no longer any need to pay for energy unused by gardeners.

Device for determining the phase sequence in a three-phase network

So, the above-mentioned “Device for determining the phase sequence” is designed to determine the phase in which the voltage lags behind the voltage in the phase arbitrarily taken as the starting point. Knowing this lag is necessary for correct connection to a network of devices in which it is necessary to maintain the phase sequence, for example, three-phase four-wire (with zero) electricity meters.

The design of the device is quite simple (Fig. 1). On a base made of electrical insulating material, such as textolite, there are two wall-mounted electric sockets with conventional incandescent lighting lamps screwed into them, covered with transparent casings made from plastic containers for juices, water, etc. A capacitor and terminals for connecting wires are also fixed on the base.

Some terminals from the lamps and the capacitor are soldered (point O), the other ends of the wires are connected to terminals A, B and C (Fig. 2).

The principle of operation of the “Device for determining the phase sequence” is as follows. When connecting the “Device...” to a three-phase network, due to the presence of a capacitor in each phase, the voltage changes, which leads to different incandescence of the lamps. (In our case, phase B is connected to the capacitor.) By the amount of incandescence (brightness of the lamps) it is judged whether the remaining phases (wires) belong to phase A or phase C.

9.1. General concepts and definitions

Phasing consists of checking the phase coincidence of the voltage of each of the three phases of the electrical installation being switched on with the corresponding phases of the network voltage, and includes the following operations:

checking and comparing the phase order of the switched-on electrical installation and network;

checking the phase coincidence of voltages of the same name, the absence of angular shift between them;

checking the identity (color) of the phases that are supposed to be connected. The purpose of this operation is to check the correct connection of all elements of the electrical installation, that is, the correct supply of conductive parts to the switching device.

Phase - a conductor, bundle of wires, input, winding or other element of a multiphase alternating current system that is current-carrying when normal mode work (GOST 24291-90).

A three-phase system is a combination of three symmetrical voltages, the amplitudes of which are equal in value and shifted in phase by the same angle.

The phase of a three-phase system is also understood as a separate section of a three-phase circuit through which the same current passes, shifted relative to the other two in phase. Based on this, a phase is called the winding of a generator, transformer, electric motor, or the wire of a three-phase line, in order to emphasize that they belong to a specific section of the three-phase circuit.

Elements of equipment belonging to phase A are painted in yellow, phase B - in green and phase C - in red.

Three-phase voltage and current systems may differ from each other in the order of the phases.

If the phases follow each other in the order A, B, C, this is called direct phase order. If the phases follow each other in the order A, C, B, it is called reverse phase order.

In cases where the phase order or the phase order of the electrical installation and the network do not match, a short circuit occurs when the switch is turned on.

There is only one option possible in which the occurrence of a short circuit is excluded: when both coincide.

By coinciding phases during phasing, we mean precisely this option, when the same voltages are applied to the switch inputs, which in pairs belong to the same phase, and the designations (colors) of the switch inputs are consistent with the designation of the voltage phases.

Phasing can be preliminary, performed during the installation and repair of equipment, and when putting it into operation, performed immediately before the first start-up of new or repaired equipment, if the phases could have been swapped during the repair.

Preliminary phasing checks the phase sequence of interconnected equipment elements. Arbitrary connection current-carrying conductors may disrupt the order of phase rotation, which will lead to the need to swap conductors at the end couplings or change the installation of busbars in the switchgear cell. Such operations are not only undesirable, but also often impracticable. Therefore, before connecting the cores, their phasing is first checked.

Preliminary phasing is carried out on equipment that is not under voltage. The main types of equipment are phased visually, by “diagnosis”, using a megohmmeter or pulse finder.

Regardless of the preliminary phasing, it must be carried out when putting electrical equipment into operation. Moreover, phasing when commissioning electrical equipment is carried out only by electrical methods.

9.2. Methods and procedure for performing phasing

There are direct and indirect methods for phasing equipment when putting it into operation.

Direct phasing methods are those in which it is performed at the inputs of equipment that is directly under operating voltage. Such methods are widely used in installations with voltages up to 110 kV.

Indirect phasing methods are those in which it is performed not at the operating voltage of the installation, but at the secondary voltage of the voltage transformers connected to the phased parts of the installation. Such phasing methods are less visual than direct ones, but their use is not limited to the voltage class of the installation.

Of the direct phasing methods, the methods of phasing transformers and power lines are of greatest practical interest.

In practice, the direct method of phasing a transformer with LV windings up to 380 V is widely used without installing a jumper between the terminals.

This method is used to phase power transformers, the secondary windings of which are connected in a star with an output zero point, as well as measuring transformers with secondary windings with a grounded neutral.

Phasing is carried out with a voltmeter on the side of the LV winding, which must be designed for double phase voltage, since such a voltage may appear between the terminals of the phased transformers.

Before starting phasing you should check:

whether the neutral points of the secondary windings are grounded or connected to a common neutral wire;

transformer voltage symmetry;

If the measured voltages differ significantly from each other, the position of the tap switches of both transformers is checked. By switching branches, the voltage difference is reduced to permissible value 10 %.

The essence of phasing is to find terminals between which the voltage difference is close to zero. To do this, the wire from the voltmeter is connected to one terminal of the first transformer, and the other terminal alternately touches the three terminals of the second transformer. Further actions depend on the results obtained. If during one measurement, for example, between terminals a1 - a2, the voltmeter reading is close to zero, then these terminals are marked and the voltmeter is connected to the second terminal, for example, b1 of the first transformer and the voltage is measured between terminals b1 - b2; b1 - c2. If one of the voltmeter readings, for example, between terminals b1 - b2 is again close to zero, then the phasing is completed. There is no need to measure the voltage between terminals c1 - c2, since with the two previous zero voltmeter readings, the voltage between the third pair of phases should also be close to zero.

If after measuring voltages a1 - a2; a1 - b2; a1 - c2; b1 - a2; b1 - b2; b1 - c2 none of the voltmeter readings were close to zero, then the phased transformers belong to different groups of connections and their inclusion in parallel operation is unacceptable.

When phasing cable lines and overhead lines of 6-10 kV, indicators are used. In Fig. Figure 9.1 shows the sequence of operations when phasing 10 kV lines with an UVNF type indicator.

To check the serviceability of the indicator, the probe of the tube containing the resistor is touched to ground, and the probe of the other tube is brought to one of the terminals of the device under voltage (Fig. 9.1, a); the neon lamp should light up. Then the probes of both tubes touch one conductive part (Fig. 9.1, b). In this case, the indicator lamp should not light up. The voltage is checked at all six terminals of the switching device (Fig. 9.1, c). This check is carried out in order to eliminate errors in the phasing of a line that has a break. Absolute values the voltages between phase and ground do not play a role, since during phasing the indicator will be connected either to line voltage (phase mismatch) or to a small voltage difference between phases of the same name (phase coincidence). Therefore, the presence of voltage in each phase is judged by the glow of the indicator lamp.

The process of phasing itself consists in the fact that the probe of one indicator tube touches any extreme terminal of the device, for example, phase C, and the probe of the other tube touches alternately three terminals from the side of the phasing line (Fig. 9.1, d). In two cases of touch (C - A1 and C - B1), the lamp lights up brightly, but in the third (C - C1) it will not light, which will indicate the same phases.

After identifying the first pair of pins of the same name, the probes alternately touch other pairs, for example, A - A1 and A - B1. The absence of light from the indicator lamp in one touch will indicate that the next pair of pins is the same. The phase coincidence of the third pair of terminals B - B1 is checked only for control - the phases must match.

Phases of the same name are connected for parallel operation. If the same pairs of disconnectors or switches are not opposite each other, the installation is turned off and the buses are reconnected in the order necessary for phase matching.

Before you begin phasing, you should make sure that the safety requirements for preparing the workplace are met and that special requirements for working with measuring rods on live equipment are observed.

Work with the voltage indicator must be done only with dielectric gloves. When phasing, do not bring the connecting wire close to grounded parts. Phasing cannot be done during rain, snow and fog, since the insulating parts of the voltage indicator may become wet and will be blocked.

The indirect method is usually used to phase transformers and lines of all voltage classes, most often with a double bus system.

In a switchgear, where both bus systems are in operation, one bus system is released to perform phasing, placing it in reserve.

When the bus coupling switch is turned on, use a voltmeter to check the phase coincidence of the secondary voltages of the VT of the working and backup bus systems. Then the bus coupling switch is turned off and the operating current is removed from its drive. On backup system buses include a circuit for which phasing should be done. Voltage is applied through the phased circuit from the opposite end and phasing is performed at the terminals of the secondary VT circuits of the working and backup bus systems.

For three-winding transformers, phasing is performed in two steps: from the LV winding side and from the MV side.

First, the transformer is switched on to the backup LV bus system and voltage is supplied to it from the HV side. Phasing is performed at the VT terminals belonging to the LV busbars. If the phases coincide, the transformer is disconnected from the LV side, switched on to the backup MV bus system and phasing is performed at this voltage.

After receiving positive results in both cases of phasing, the transformer is considered to be in phase and is put into operation.

When phasing bus transformers, it is necessary to take into account the grounding circuit of the secondary windings of the voltage transformer, since both the neutral and one phase can be grounded.

In the first case, for phasing you can use a voltmeter with a scale for double phase voltage, in the second - for double line voltage. In addition, the phasing of voltage transformers, in which the phase of the secondary windings is grounded, is performed using a phase indicator, which is permissible, since the phases of the phasing voltages are rigidly connected and it is only necessary to establish the coincidence of the voltage of the same phases, as well as any other phase. If they do not match, the phase indicator disk will rotate in one direction when voltage is applied to its terminals from the first VT, and in the other when voltage is applied from the second VT.

In practice, there are cases when phased electrical installations have different phase orders.

For example, it is necessary to carry out phasing and switch on two electrical installations for parallel operation, one of which has a direct phase order, and the other has a reverse phase order. They are connected by power lines. To enable two electrical installations for parallel operation, it is necessary that one of them in relation to the other has the same phase order - only in this case is their synchronization possible.

In order for the phase orders of electrical installations to coincide, that is, so that the reverse order of the phases of one electrical installation in relation to another becomes direct, the order of phase alternation on power lines is changed. This can be done by moving the phase wires on the same support along the line, that is, changing their alternation in space.

Thus, by changing the order of phase alternation on the line, the order of the phases of the voltage vectors of one electrical installation in relation to another changes, although the absolute orders of the phases of the voltage vectors of the electrical installations remain the same. This is the interdependence of the concepts of sequence order and phase alternation.

8.1.Basic concepts and definitions

Electrical equipment of three-phase current (synchronous compensators, transformers, power transmission lines) is subject to mandatory phasing before the first connection to the network, as well as after repairs, during which the order and rotation of phases could be violated.

In general, phasing consists of checking the phase coincidence of the voltage of each of the three phases of the switched-on electrical installation with the corresponding phases of the network voltage.

Phasing involves three significantly different operations. The first of them consists of checking and comparing the order of the phases of the switched-on electrical installation and network. The second operation consists of checking the phase coincidence of voltages of the same name, i.e., the absence of an angular shift between them. Finally, the third operation consists of checking the identity (color) of the phases whose connection is supposed to be performed. The purpose of this operation is to check the correct connection between all elements of the electrical installation, i.e., ultimately, the correct supply of conductive parts to the switching device.

Phase. A three-phase voltage system is understood as a set of three symmetrical voltages, the amplitudes of which are equal in value and shifted (the amplitude of a sinusoid of one voltage relative to the preceding amplitude of a sinusoid of another voltage) by the same phase angle (Fig. 8.1, a).

Thus, the angle that characterizes a certain stage of a periodically changing parameter (in this case, voltage) is called the phase angle or simply phase. When considering two (or more) sinusoidally varying voltages of the same frequency together, if their zero (or amplitude) values ​​do not occur simultaneously, they are said to be out of phase. The shift is always determined between identical phases. The phases indicate in capital letters A, B, C. Three-phase systems are also represented by rotating vectors (Fig. 8.1, b).

In practice, a phase of a three-phase system is also understood as a separate section of a three-phase circuit through which the same current passes, shifted relative to the other two in phase. Based on this, the winding of a generator, transformer, motor, or three-phase line wire is called a phase in order to emphasize that they belong to a specific section of the three-phase circuit. To recognize equipment phases, colored marks in the form of circles, stripes, etc. are applied to equipment casings, busbars, supports and structures. Elements of equipment belonging to a phase A, painted yellow, phases V-v green and phase S-to red. Accordingly, the phases are often called yellow, green and red: g, h, k.

Thus, depending on the issue under consideration, a phase is either an angle characterizing the state of a sinusoidally varying quantity at each moment of time, or a section of a three-phase circuit, i.e., a single-phase circuit that is part of a three-phase circuit.

The order of the phases. Three-phase voltage and current systems may differ from each other in the order of the phases. If the phases (eg mains) follow each other in order A, B, C - this is the so-called direct phase order (see § 7.3). If the phases follow each other in order A, C, B - This is the reverse order of the phases.

The order of the phases is checked with an induction phase indicator of type I-517 or a phase indicator of the FU-2 type with a similar design. The phase indicator is connected to the voltage system being tested. The terminals of the device are marked, i.e. indicated by letters A,V, S. If the phases of the network coincide with the markings of the device, the phase indicator disk will rotate in the direction indicated by the arrow on the device casing. This rotation of the disk corresponds to the direct order of the network phases. Rotating the disk in the opposite direction indicates the reverse order of the phases. Obtaining the direct order of phases from the reverse is done by changing the positions of any two phases of the electrical installation.

Sometimes instead of the term “phase sequence” they say “phase sequence”. To avoid confusion, we agree to use the term “phase rotation” only when it is related to the concept of a phase as a section of a three-phase circuit.

Phase rotation. So, by phase alternation we should understand the order in which the phases of a three-phase circuit (windings and terminals of electrical machines, line wires, etc.) are located in space, if you start bypassing them each time from the same point (point) and carry out in the same direction, for example, from top to bottom, clockwise, etc. Based on this definition, they talk about alternating designations for the terminals of electrical machines and transformers, the colors of wires and busbars.

Phase coincidence. When phasing three-phase circuits, there are various options for alternating the designations of inputs on the switching device and supplying voltages of different phases to these inputs (Fig. 8.2, a, b). Options in which the order of phases does not match, or the order of alternation of phases of the electrical installation and the network, when the switch is turned on, leads to a short circuit.

At the same time, the only possible option is when both coincide. A short circuit between the connected parts (electrical installation and network) is excluded here.

By phase coincidence during phasing, this is precisely the option understood, when the same voltages are supplied to the switch inputs, belonging in pairs to the same phase, and the designations (colors) of the switch inputs are consistent with the designation of the voltage phases (Fig. 8.2, c).