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When powering the electrical installation from a 3-phase network, a decrease or increase in voltage, a break in one of the phases or the “0th” conductor, as well as asymmetry of I and U is possible. To protect the equipment from these situations, a phase control relay is installed.
Below we will consider what are the features of this device, what it is intended for, and what are the subtleties of connecting the product. In addition, we give tips on choosing and describe the best models that are worthy of attention.
What is it for
The phase and voltage monitoring relay is a device that is necessary when connecting equipment to a three-phase system, as well as in situations where it is important to observe the correct alternation.
In practice, the product is used when equipment is frequently moved, when changing the phasing may damage it or cause incorrect operation.
A vivid example is a screw-type compressor, the incorrect connection of which and the inclusion for a period of more than five seconds leads to a breakdown of an expensive product.
The phase and voltage monitoring relay allows you to identify the following problems:
- Breakage of any of the phases;
- Increase or decrease in voltage above (below) a given level;
- Violation of phasing (order of connection of phases);
- Break “zero”;
- Asymmetry of I and U (here we are talking about phase imbalance, when the angle between the vectors is much more or less than 120 degrees).
The schematic diagram of the device is shown below.
Some relays provide the ability to change the settings for the upper and lower limit U, as well as T (time) of operation.
As a rule, the output contact group of the relay is “dry”. In this case, there are two options available – normally closed and open. Some models have elements that work on the induction principle.
The device and the principle of operation
Despite the variety of voltage phase monitoring relays, the design features are almost unchanged. The device is based on microprocessors with a program embedded in them and the possibility of user settings. This design ensures reliable operation and unpretentious maintenance.
The design of the product also includes a circuit that calculates the order (sequence) of phases, as well as controls the compliance of the current situation with the program that is embedded in the relay.
On the simplest models, three phases and a neutral conductor are suitable for the input, and a relay with a changing contact is provided at the output terminals.
Voltage for the internal circuit is usually supplied from the first phase (L1). For clarity, a pair or more indicators are installed (much depends on the product model) and the manufacturer.
In more expensive relays, a regulator is provided that allows you to change the setpoint over time (see photo above). Thanks to this option, it is possible to increase or decrease the time the relay operates during the execution of a certain program.
In addition, many devices have a circuit that responds to a decrease or increase in voltage.
The operation of the phase control relay U is based on the selection of negative sequence harmonics (from 2 and above). In this case, only multiples of the “two” harmonics are used, that is, the “fourth”, “sixth”, “eighth” and other harmonic components. It is they who appear in the event of a break in any of the supply phases.
To select such U, special filters (also inverse sequence) are used, the role of which is played by analog type filters. They include active and reactive nodes (resistors and capacitors, respectively).
See also:
Types
The most popular types of relays designed to control phases include EL models of the following series – 11, 12, 13, 11MT and 12MT.
It is important to consider that the scope of the product depends on their types of voltage phase monitoring relay (EL):
- 11 and 11 MT – protection of power supplies, participation in the ATS system, power supply to converters and generator sets.
- 12 and 12MT – to protect cranes with a power not exceeding 100 kW.
- 13 – are used when connecting electric motors of a reversible type with a power of up to 75 kW.
Devices are fixed on a special DIN rail or only with screws (depending on the situation).
Features
Modern phase monitoring relays are selected taking into account the following characteristics:
- VOLTAGE. Working U directly depends on the specification of the equipment. For example, EL series 11 can operate on voltages from 100 to 415 V (including 110 V, 220 V, 380 V and 400 V). As for EL 13, they operate on voltages of 220 and 380 V.
- OPERATION LIMIT. This parameter also depends on the type of relay and the situation. So, with a symmetrical decrease in voltage, EL devices of series 11, 12 and 13 have a minimum limit of 0,7; 0,5 and 0,5 Ufn, respectively. If one or more phases fail, all relays will trip. If the alternation is broken, then the models EL11 and 12 recognize the problem and close the contact group, but EL13 does not.
- DELAY TIME. This indicator reflects how much the operation of the voltage phase monitoring relay is delayed when the required setting (set threshold) is reached. For models EL11 and 12, this indicator is from 0,1 to 10 seconds (depending on the adjustment), and for EL13 – up to 0,15 s.
- WORKING TEMPERATURE. As in the cases discussed above, here the situation depends on the type of relay. EL types 11 and 12 operate from 40 degrees of frost to 40 degrees of heat. As for EL13, these relays have a smaller range – from -10 to +45 degrees Celsius.
- Storage temperature – from -60 to +50 degrees Celsius.
- Product weight – 300 grams (EL 11 and 13) and 250 grams (EL 12).
The subtleties of choice
When choosing a voltage phase control relay, you need to focus on the technical parameters of the device that is connected to the circuit.
For example, consider the situation when you need to choose a model for connecting ATS.
The algorithm of actions is as follows:
- WE DETERMINE THE METHOD OF CONNECTION – with or without “zero”.
- WE DETERMINE THE PARAMETERS. For the ATS circuit, it is important that the device controls the fact of phase failure and the phase sequence. The delay time must be between 10 and 15 seconds. It is required to have control of fluctuations U more or less than the setpoint. To switch a relay with a 0-wire, a visual inspection is required for each of the phases.
After analyzing the considered requirements, EL11E can be preferred.
In addition, when choosing, you need to take into account the modification of the relay. For example, domestically produced devices are designated as EL.
As for foreign products, their marking is somewhat different. For example, RANA B380 A A 3 C. Here “RANA” is the name of the series, B380 is the voltage of 380V. The next two letters A are regulation using a potentiometer and the type of mounting (under the DIN rail). The number “3” indicates the size of the case 3,5 cm, and C is the last digit of the marking.
Phase control relay EL-11E (380 V, 50 Hz), RKF, IEC
These models of phase control relays are produced by the Meander company, which has been operating on the market since 1992. The company is located in the city of St. Petersburg.
The company’s activities are based on the development and manufacture of industrial automation devices. During the existence of the company, it was possible to take a leading position in the manufacture of electronic devices in the Russian market. The number of manufactured goods exceeds 500 units.
The company’s clients are such giants as Gazprom, Russian Railways, Aurora Concern, Lenenergo and others. The company’s products are in high demand due to their quality and wide range of products.
Customers receive electronic time relays, voltage control devices, overcurrent relays, lighting control devices and much more.
Description and technical characteristics of the relay EL-11E (380 Volt, 50 Hz)
Relay EL-11E has one normally closed, normally open and changeover contact.
The device is designed to control the phases in a 3-phase network, it operates on an alternating voltage of 380 Volts. In practice, it is used to control the presence of U and the correct symmetry.
See also:
In addition, relays can be used to check the correct phase rotation in 3-phase voltage systems and in other cases.
Technical characteristics of EL-11E and other modifications of the series.
Additional pluses include control of the minimum and maximum U, hysteresis function for 3-phase current.
The circuit diagram is shown below.
Description and technical characteristics of RKF-M05-1-15 / RKF-M05-2-15
Relays RKF-M05-1-15 / RKF-M05-2-15 are used to control 3-phase U in 3-wire networks (where “neutral” is not provided).
With the help of the device, it is possible to control the breakage, the correct alternation and the fact of “sticking” of the phases. The voltage response threshold is in the range from 105 to 130% of the nominal U.
The lower threshold U can be adjusted from 70 to 95%. The time setting can also be changed from 0,1 to 10 s, depending on the task.
The relay is produced in a plastic housing and mounted on a DIN rail with a width of 35 mm. The maximum voltage is 400 V.
Description and technical characteristics IEC EL-11M-15
Relay EL-11M-15 is a device designed for use in automatic control circuits. It is used to control U in 3-phase networks without a 0-th conductor. With the help of the device, it is possible to control and determine in time the order of alternation, the fact of breakage and “sticking together” of different phases.
See also:
In addition, EL-11M-15 responds to the fact of an increase or decrease in U above (below) the set parameter.
It is applied to protection of converters of the electric power and other power supplies. This model cannot be used in ATS circuits where there is a neutral.
This is due to the fact that in the event of a break in the “0” wire, a voltage imbalance occurs and a breakdown of consumers operating on one phase is possible.
The model consumes less than 2 VA. Shutdown occurs when the nominal U is exceeded by more than 30 percent of the set value. Shutdown occurs when U decreases below 0,8 U nom. When there is an asymmetry between the phases of more than 30%, a shutdown occurs.
Phase control relay Schneider
Schneider is considered one of the best manufacturers of devices in the power industry. The products of this enterprise are actively used both at civilian facilities and in large industrial organizations.
The advantages of the company’s products are in a flexible pricing policy, high quality and special conditions for customers.
The company manufactures circuit breakers, fuses, load break switches and switchboard equipment.
In addition, relays, circuit breakers, sockets, contactors and many other devices are produced at the Schneider plant.
Popular models include relays:
- 1-phase voltage control (from 65 to 260 V and time delay from 0,1 to 10 s – RM17UBE
- 3-phase voltage monitoring (208 to 480 V) – RM17TE
- 1-phase voltage control (160 to 280 V, 30 second delay) – EZ9C
- 3-phase voltage control (from 208 to 480 V) – RM17TT00 and others.
Phase monitoring relay ABB
ABB has been operating since 1883, which is another confirmation of the reliability and demand for Swiss brand products.
Initially, the manufacturer manufactured generators and lighting devices, but since 1891, the production of electrical machines began.
At the present stage, the manufacturer’s offices operate in numerous countries of the world, and their number has exceeded 100.
The company manufactures and markets products for the automation of production, generation and transmission of electricity, protection and automation of various facilities in the energy sector.
The most popular models include the following voltage monitoring relays – CM-PVE, CM-MPS.21S, CM-MPS.41S, CM-PFS and others.
All of them differ in voltage level, type of fastening, exposure time and other parameters.
How to connect the device? Scheme
We note right away that if a frequency converter is used in the equipment connection diagram, the installation of a voltage monitoring relay is not required.
When connecting the product, it is important to focus on the instructions supplied by the manufacturer. In most cases, the diagram is indicated directly on the product body, which simplifies installation and connection.
Connection to the product contacts at the input and output is carried out using wires, and they are fastened under special clamps.
As a conductor, wires of 2,5 “square” or twin wires of 1,5 “square” are used. When connecting, it is important to observe the correct alternation of the three phases.
The connection scheme can be different, both with a “zero” wire and without it. The first option, as a rule, is found in private houses and apartments. In this case, the load is evenly connected to each of the phases. If there is a deviation from the norm, the relay is activated.
Scheme and video connection EL-11M-15
Wiring diagram RFK-M05-1-15, RFK-M05-2-15
To avoid extinguishing the light in the entire apartment or house, three different products are installed (individually for each of the phases). If problems occur in one of the phases, the responsible relay is activated, and the load continues to flow in the remaining phases.
See also:
The importance of the phase control relay is difficult to overestimate. With its help, it is possible to determine in time a break in any of the phases, an increase or decrease in U above (below) a given parameter, problems in phasing or a break in the “zero” conductor.
But this is only part of the product’s ability to prevent a more serious accident and protect expensive equipment from damage.