Power limiter OM-110. Connection diagram, setup and principle of operation

The technical conditions for connecting to general power supply networks were not invented in vain. Each power line is allocated a certain amount of power. It is limited by the capabilities of the last transformer substation. If you connect consumers with a larger load, the transformer substation will overheat and may fail. If everything goes according to plan (or rather according to the project), there will be no problems. Engineers limit the input power of each facility using a circuit breaker: it will trip if the current exceeds what is allowed by technical conditions. However, in reality the following situations may arise:

• short-term overloads for several subscribers at once, associated either with an emergency or with power surges;
• unauthorized connections to the general line (without taking into account design capacities), which are carried out by careless electricians for a fee;
• illegal replacement of input circuit breakers with a higher current (either independently or with the help of the same electricians);
• banal theft of electricity through temporary unauthorized switching on, bypassing metering devices and input machines.

What happens in such cases?

• The circuit breaker at the output of the transformer substation is constantly triggered (if not, the transformer will simply burn out). In this case, all consumers on this line suffer.
• So-called “drawdowns” occur on the line. The power supply system is self-regulating: to maintain power (without exceeding), and increased current consumption, the voltage is reduced. Many residents of the private sector (especially in garden cooperatives) often observe a value of 160–180 volts instead of 220 on the network.

To combat such phenomena, power limiters are installed. This is an automatic switching device that allows you to disconnect the consumer when deviating from the specified parameters.

What is the purpose of a power limiter?

Many people are familiar with network voltage limiters. This is a protective device that controls the amount of input voltage along a predetermined “corridor”. Such devices can be found in many apartments or households.

The voltage relay really protects electrical appliances from power surges, but that’s where its functions end.

A power consumption limiter (single-phase or three-phase) works on a different principle. More precisely, it has wider functionality:

1. Just like a voltage relay, the device monitors the input parameters of electricity. If the value is outside the set parameters, the power to the object is turned off. At the same time, electrical appliances are preserved. After returning to normal, power supply is restored.
2. Control functions during operation of electrical installations. The power limiter can maintain parameters to prevent emergency situations.
3. Protection against unauthorized connections to your electrical network. You can set strict limits on power consumption on the line, and control your network with an accuracy of 10 W. If an illegal power take-off occurs, the device will turn off the power grid.

Principle of operation

The device constantly monitors the network status, especially when the load increases. If the set limit for electricity consumption is sharply exceeded, the device automatically turns off one of the lines in the circuit. At the end of a time period specified by the owner, the device also automatically resumes power to the line and, after the power level is lower than the set one, the line is reconnected.

The measuring unit of the device determines data on consumed electricity using current and voltage sensors. Based on this information, the logical block determines the exact amount of power in real time and compares it with critical parameters. If the power at a certain moment approaches the maximum permissible values, a command is sent to the actuator and contactor to immediately turn off the excessive load.

After the device has been triggered, the owner should turn off excessively loading devices. After a certain time has passed, the device will turn on and continue functioning normally.

Adjustment of the response threshold, shutdown period and resumption period is carried out using potentiometers. There are two groups of contacts on the pins:

• to regulate the switching on and off of the device;
• to connect power.

Some models have the function of monitoring the connection of only priority loads. Non-priority connections are not enabled.

How does a power limiter work?

Structurally, the device consists of three independent parts, each of which performs its own function.

The first block records the parameters of the power supply line. Unlike a voltage relay, data is taken for both voltage and current. For this purpose, two transformers are installed in the measuring module. They are galvanically isolated from the power line and do not affect the power network after the device.

The next module is intelligent. He has three tasks:

• Fixing parameters and calculating the instantaneous power value on the line. The program is built on Ohm's laws; engineers have not yet invented anything new. The same module allows you to monitor parameters in real time (the more complex the device, the more indicators can be seen on the display).
• Receiving operator commands: setting operating modes, protection, power limits. Again, depending on complexity (and therefore cost). There is practically no limit to the functionality: the technology is limited only by the common sense of the developer. Three-phase limiters analyze the parameters of each phase. Depending on the specified program, an emergency shutdown can be performed when problems occur in one or several phases.

The actuator performs only one task: upon command from the intelligent module, shutdown. When the control unit “decides” that the parameters are normal: a command to turn on will be received.

The power limiter connection diagram implies two options:

1. Installation at the electricity supplier, in which case the device performs a supervisory function. The main task is to control unauthorized power take-off.
2. Connection at the consumer after the metering device. The tasks are broader: from monitoring the “theft” of energy to broad protection of your electrical equipment from collisions on the power supply line.

Design

The design of devices can be based on several bases:

• electromechanical inertial relays;
• semiconductor relays;
• microprocessor controllers.

Due to the presence of customizable chips, the devices have increased variability of settings and are easy to use. The module is quite easy to program; some models display the adjustable parameters on the display.

Main design elements of a programmable single-phase power relay model OM-110

How to connect the device correctly

Three-phase and single-phase power limiters differ in the way they are switched on. In addition, different models of the same group have their own characteristics. We will look at several popular models that can be used both at large corporate facilities and at home.

Advice:

Despite the fact that purchasing such a device is associated with additional costs, its installation is definitely useful. You will not only get rid of problems with variations in power supply parameters (and this means protecting your electrical appliances and the safety of information on personal computers). Unauthorized connection is a direct loss that can exceed the price of the limiter many times over. In addition, power limiters perform the same tasks as circuit breakers and voltage relays. So you will also save money by not buying several switches instead of one.

Each model is supplied with a data sheet and installation diagrams. To use the device correctly, it is advisable to understand the general connection principle.

Price overview

You can buy a power limiter at any special electrical store; the price depends on the type of device and its brand.

Sales are also carried out at branded dealer centers, these are Novatek, ABB, Scan and others. Before purchasing, be sure to check all quality certificates, device passport and warranty conditions. In most cases, warranty service is valid for 1 year from the date of installation.

Single-phase power limiter OM-1

This device is quite compact and can be easily installed in a panel on a DIN rail. The main purpose is to control the excess power of the line. Additional features: circuit protection against short circuits and neutral wire breakage. Of course, you can set a voltage limit.

OM-1 can work independently, that is, it can switch off with its own contact group. The user only selects the installation scheme according to consumer priority: with normally closed or open contacts (see illustration).

If the consumer current exceeds the parameters of the contact group, additional contactors and magnetic latches can be installed. In this case, the limiter acts as a control switch, and the power lines are opened by third-party devices.

Three-phase power limiter OM-630

This device operates independently only when performing protective functions. That is, voltage and current limitations. In this case, the installation diagram looks like this:

Your object is completely protected from collisions on the line; the restart time is set on the control panel. Regardless of the use of three-phase input (consumers can be either 220 or 380 volts), shutdown is carried out if there is a discrepancy between the parameters for any connection method.

If you need power control (the main purpose), the load is connected via a contactor. Shutdown parameters are programmed using a personal computer: a special port is provided for this.

As in the previous case, connection is possible for consumers of different priorities. The circuit provides switching into groups with normally closed and open contacts.

If the power consumption of the entire group is exceeded, those consumers that have a lower priority are switched off first. Essential facilities will remain open.

The shutdown time is programmable: when the timer counts down, the consumers will be powered again.

Despite the pronounced industrial purpose of the OM-630, it can be used in facilities with low power consumption: up to 5 kW. In this case, the connection diagram provides a little trick:

There are vertical through holes in the device body. Cables are passed through them and the load is applied to them. There are as many cables as there are phases in the load.

If the power is below 5 kW, the number of turns is determined by the formula: 5/power consumption. The number is always rounded to a plus. For example, if the power is 2 kW, we get a coefficient of 2.5. This means there will be 3 turns.

This model does not have a digital segment indication of operating modes and emerging problems. Instead, there are indicator LEDs on the front panel. The documentation contains a table from which you can decipher the indicator readings.

Application area

The use of limiters is effective and rational in individual houses, apartments, and administrative and public buildings.

Using the devices it is possible:

• monitor incoming electricity and stop its supply during power surges, thereby preventing overload of electrical appliances;
• protect the network from third-party connections;
• control the operation of various mechanisms - car engines, machine tools, microwave ovens.

Three-phase power limiter OM-310

This device has the widest functionality among its analogues.

• Traditional protection against voltage surges. The limiter can replace the digital voltage control relay.
• Overload protection based on the maximum current value, while the parameters can be adjusted linearly or differentially.
• Full RCD functions with finely customizable parameters. Essentially, this is a differential automatic machine in one housing with a power limiter.
• Since the limiter is three-phase, it can be used to control line voltage imbalances and even the phase rotation order. If the shift is incorrect, the protection is also triggered.

The connection diagram is quite complex and varies greatly depending on the use case. We will consider a typical inclusion with different consumer priorities. Of course, external magnetic contactors are used for the load power lines.

Like any other professional device, OM-310 is programmed using a computer using the “COM port” interface format. At the same time, such power limiters can be combined into a network of their own format. In this case, one operator controls the entire system of objects.

For ease of understanding, let’s look at an illustration with a breakdown of the main controls and terminal groups of the OM-310 power limiter:

Despite the apparent complexity of the design, even a novice electrician can easily understand the circuit.

Choice

Power limiters are available in various types. When choosing a specific model, you must first determine the number of phases, operating voltage and the range in which the power is regulated.

The remaining parameters are optional and do not fundamentally affect performance. Equipment for them is selected at will from existing equipment.

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You need to choose a specific model of power limiter after the energy supply project has been approved based on all the technical requirements and wishes of the consumer.