One of the essential tools of an electrician is a phase indicator, with which you can quickly determine the correct phase sequence. In everyday life, this device is very rarely useful for home craftsmen, and if 220 V is supplied to the house, then in general there is no need for it. But in production and with frequent work with a three-phase power network, it is still better to acquire this device. Next, we will tell you how to use the phase indicator and how this device works.
Content:
- The need for application
- User manual
The need for application
There are situations during which the connection of a three-phase network must be carried out in phase sequence. The fact is that the direction in which the rotor rotates when the asynchronous motor is connected to the network is not guaranteed to be accurately indicated if we do not strictly follow the phasing procedure.
For example, when it comes to operating a fan for a specific system or a drive to operate a pump, the direction of rotation must be clearly known. This ensures the execution of the technological cycle. Therefore, it is important to observe the connections in series in this case. In order to solve this problem, you should resort to using a special device called a phase indicator. This allows you to understand what it is for. The scope of the phase indicator is quite wide and is constantly growing.
If the phasing is set correctly, then the order of the phases goes from A further to B and ends with C. The direction of rotation of the motor is determined in the same order. For example, if the wires that power the windings are connected in the correct order, then the motor rotor is conventionally operated in a clockwise direction. However, in a situation where two of these phases are reversed, the direction of rotation of the rotor will be violated. Then the technological process in which the engine is involved will simply be disrupted. This will cause the equipment used in the drive to be disturbed and damaged. After that, if you perform the reverse procedure with the phases, then the order of the engine will return to normal and the process will be correct.
User manual
As you know, there are several types of phase indicators. The simplest version of this device, which is typical for most situations, is the I517M device. It is essentially a small size asynchronous motor with three phases. It is very sensitive in terms of phase rotation. You can easily understand how the I517M phase indicator works and how it works by looking into its design.
The instructions describing how to use the device are simple. As terminals for such a phase indicator, conclusions from the windings of a conventional stator are used. Proceeding from this, the rotation of the indicator-type disk, where the mark is additionally applied, can indicate what the order of the phase sequence is. This will be clear from the direction in which the phase indicator disc rotates. In a situation where all phases are connected in the correct way, the disc will rotate in the direction of the arrow on the clock. Otherwise, its direction of rotation will be reversed.
The markup on the disc is of a contrasting nature. This makes it possible to independently determine the direction in which it will rotate without much difficulty. Accordingly, if at least one phase is not connected, the disk will not rotate.
How to use the old-style phase indicator is shown in the video (using the example of the FU-2 device):
In addition to the presented phase indicator, there is another device, which is quite simple in its design. It is based on incandescent lamps. Neon lamps, or the most common LEDs, can also be used in the design of the device. The main factor that determines the effectiveness of such a phase indicator is the resistance of complex circuits. This feature is due to the type of light bulb connection. They are connected directly via capacitors and act as signaling devices.
In a situation where, for example, the first of the bulbs is powered through a capacitor, its brighter glow occurs. The light bulb that follows it will carry out its power supply through the resistor. Therefore, the intensity of its glow will be noticeably less. Also, it may not glow at all. From this it follows that it is possible to determine the order with which the phases on the motor will alternate. It is only necessary to understand in which branch the resistor is located, and where the capacitor is connected.
The described principle of operation is fundamental in the design of phase indicator circuits, which operate on neon-type lamps or LEDs. The purpose of such lamps is clear. There are devices of a more complex design. They are created on the electronic principle of work. In this case, phase-type voltages are analyzed using a graphical technique.
It is necessary to consider the simplest example of such a phase indicator. This is a simple device that anyone can assemble if they wish. The structure includes three branches of nonsemetric type. Each of these branches has its own components installed. Oddly enough, a simple phase indicator circuit creates good conditions in order to determine the order with which the phases will alternate in a three-phase type network. In this case, it is not necessary to carry out an additional connection to the zero-type wire.
This is a very simple principle, which is the occurrence of unbalanced phase currents when there is an unbalanced load. Therefore, the voltage drops across the components of reactive and active type circuits will also be completely different.
There is a capacitive load in one of the phases. The rest of the phases have an active load. During the coupling of such a circuit to a three-phase network, if the condition of the proximity of the ratings to it is met, the voltages on the phases will have the following indicators: branch B will give data 1.49 * Uph, branch designation C - 0.4 * Uph. In this case, Uph is the phase voltage of the usual type for a symmetrical three-phase network (for example, 220 V).
It follows that in a situation where the connection is carried out correctly, as well as all phases are arranged in the order of A, B and C, then the branch marked B will have a voltage that is three times higher than C. In this case, the voltage across the resistor will be 60 volts. Then a neon-type light bulb will probably emit light during operation. This will be a light indication of the correctness of the phasing.
In the future, if at least a couple of phases are reversed, then the voltage across the resistor will drop. However, this drop will not be enough to power a neon-type light bulb. Then it will not emit light. This is direct evidence that the wrong phasing was performed. Thus, a reverse procedure will be carried out in the engine, which provides for a change in the direction of rotation of its shaft.
Typically, an instrument includes a body and three probes. Each of them has its own color coding. In some situations, a letter designation is additionally used. Usually green, red and yellow are used. The same sequence can be - red, yellow and green.
Next, we install the probes on the phase-type conductors and press the button. There are devices where such a button is present. However, some devices do not have it. Then the probes are simply installed, and the device produces a light alarm. Additionally, there may be an audible alarm. The sound is intermittent when the phasing is correct and continuous in another situation.
The video below clearly shows how to use the phase indicator:
Important to rememberthat the mains voltage is dangerous to humans. Therefore, you need to be careful when using a phase indicator!
That's all we wanted to tell you about what a phase indicator is, how it works and what it is used for. We hope the provided instruction was useful and interesting for you!
You probably don't know:
- Why is phase imbalance in a three-phase network dangerous?
- How to use a clamp meter
- What is a phase monitoring relay
