Voltage control relay: principle of operation, diagram, connection nuances

Voltage drops are far from uncommon in domestic homes.They occur due to wear and tear of electrical networks, short circuits and uneven load distribution across individual phases.

As a result, household appliances either do not receive enough electricity or burn out from its excess. To avoid these problems, it is recommended to install a voltage control relay (VCR).

We propose to understand what advantages the use of such a device provides, what are the differences between an RLV and a stabilizer, how to choose a suitable relay and connect it.

Why do you need a voltage regulating relay?

The proper name for the device in question is “voltage control relay.” But the middle word in conversations between electricians often falls out of this term.

In principle, this is one and the same electrical safety device. Plus, this equipment is often called “zero break protection”. Why will become clear below.

Don't be confused RCD machines and RKN. The former protect the line from overload and short circuit, and the latter from power surges. These are devices with different functional purposes.

The main task of the RKN is to disconnect electrical appliances from the network when the voltages in it are too high or too low, so that the equipment connected to the power supply does not fail

The inscription “~220 V” is familiar to all Russians. Household appliances connected to sockets operate at this alternating voltage in the house.However, in fact, the maximum voltage in the home electrical network only fluctuates around this mark with a spread of +/-10%.

In some cases, the differences reach large values. The voltmeter may well show drops of up to 70 and surges of up to 380 W.

For electrical engineering, both excessively low and high voltages are dangerous. If the refrigerator compressor does not receive enough electricity, it simply will not start. As a result, the equipment will inevitably overheat and break down.

At low voltage, the average person in most cases is not even able to outwardly determine whether the equipment is working properly or not in such a situation. Visually, you can only see dimly glowing incandescent light bulbs, the voltage to which is supplied less than it should be.

With high bursts everything is much simpler. If you apply 300-350 W to the power input of a TV, computer or microwave, then at best the fuse in them will blow. And most often they will “burn out” themselves. And it’s also good if there is no real ignition of the equipment and no fire.

Apartment buildings are usually powered from a three-phase 380 V network, and the apartment already has single-phase 220 V wiring from the electrical panel on the floor

The main problems with voltage drops in high-rise buildings arise due to a break in the working zero. This wire is damaged due to carelessness by electricians during repairs, or it itself simply burns out from old age.

If the house on the access line has a set of the necessary protection of a modern level, then as a result of such a break, the automatic RCD is triggered. Everything ends relatively normally.

However, in old housing stock, where there are no circuit breakers, the loss of zero leads to phase imbalance.And then in some apartments the voltage becomes low (50–100 V), and in others sharply high (300–350 V).

Who will end up with what comes out of the outlet depends on the load connected to the power grid at that particular moment. It is impossible to accurately calculate and predict this in advance.

As a result, for some, all equipment stops working, while for others it burns out from overvoltage. This is where you need a voltage control relay. If problems arise, it will turn off the network, preventing damage to TVs, refrigerators, etc.

In the private sector, the problem with voltage surges is somewhat different. If the cottage is located at a great distance from the street transformer, then with increased electricity consumption in houses before it, at this extreme point the voltage may drop to critically low levels.

As a result, due to a prolonged lack of “volts”, electric motors in household electrical appliances will inevitably begin to burn and fail.

Types of ILV devices

All relay models that perform the functions of a voltage regulator are divided into single-phase and three-phase.

Single phase relay. Usually installed in cottages and apartments - nothing more is required in house panels.

In electrical panels of private and apartment buildings, single-phase relays are usually used in a compact design on a DIN rail (+)

Three phase relay. Such RNAs are intended for industrial use. They are often used in protection circuits for three-phase machine tools. Moreover, if such a three-phase switch is required at the input of such complex equipment, then it is often chosen in a combined version with control not only of voltage, but also of phase synchronization.

The main disadvantage and at the same time advantage of a three-phase relay is the complete shutdown of power at the output when the voltage jumps even in one of the phase lines at the input. In industry this is only beneficial. But in everyday life, voltage fluctuations in one phase are often not critical, and the RKN takes over and turns off the protected network.

In some cases, such highly reliable reinsurance is needed. However, in the vast majority of situations it is unnecessary.

By type and dimensions

The entire range of voltage relays is divided into three types:

• plug-socket adapters;
• extension cords with 1-6 sockets;
• compact “bags” for DIN rail.

The first two options are used to protect one specific electrical appliance or a group. They plug into a regular indoor outlet.

The third option is for installation in an electrical panel as part of the protective system of the electrical network of an apartment or cottage.

The adapters and extensions of the regulators in question are quite large.Manufacturers try to make them as small as possible so that they do not spoil the interior with their appearance.

But the internal components of the voltage relay have their own rigid dimensions, and they also need to be arranged in one housing with a socket and plug. In terms of design, you can't turn around here.

Relays on a DIN rail for installation in a distribution panel have more compact dimensions, there is nothing superfluous in them. They are connected to the network using connections of wires and terminals.

By base and additional functions

The internal logic and operation of the relay for voltage control are built on the basis of a microprocessor or a simpler comparator. The first option is more expensive, but involves more accurate and smooth adjustment of the ILV response thresholds. Most of the protective devices sold are now microprocessor-based.

The upper (Umax) and lower (Umin) thresholds are the two main adjustable parameters of the RKN - if the input voltage is outside the set range, the relay disconnects the output line from the electric current (+)

At a minimum, there is a pair of LEDs on the relay body, which can be used to determine the presence of voltage at the input and output. More advanced devices are equipped with displays showing the set permissible limits and the voltage available in the line.

Threshold values ​​are adjusted using a potentiometer with a graduated scale or buttons with parameters displayed on the display.

The relay itself responsible for switching inside the RKN is made according to a bistable circuit. This coil has two stable states. Energy is expended only in switching the latch. No electricity is required to hold the contacts in the closed or open position.

On the one hand, this minimizes energy consumption, and on the other, it ensures that the coil does not heat up when the regulator is operating.

When choosing a voltage relay in the parameters, you need to look at:

• operating range in Volts;
• possibility of setting upper and lower response thresholds;
• presence/absence of voltage level indicators;
• shutdown time when the ILV is triggered;
• delay time for resumption of electricity supply;
• maximum switched power in kW or transmitted current in Amperes.

According to the last parameter, the relay should be taken with a margin of 20–25%. If there is no RV switch suitable for the high loads existing in the line, then a low-power model is taken, and a magnetic starter is connected at its output.

The situation with setting thresholds is as follows. If they are set too strictly, the relay operation frequency will be high. There will have to be a compromise here.

These parameters must be adjusted so that they provide the proper level of protection, but do not allow the ILV to be switched too frequently. Constant switching on and off will not benefit both the equipment connected to the network and the voltage regulator itself.

Moreover, some relays do not have the ability to independently adjust thresholds at all. They are set “rigidly”. For example, the factory set the lower limit to 170 V, and the upper limit to 265 V.

Such ILVs are cheaper, but they must be selected more carefully. Then it will not be possible to reconfigure these devices; if there are errors in the calculations, you will have to purchase new ones to replace the ones that are not suitable.

The choice of time parameters for disconnecting and resuming power to the output line depends on the connected load and the characteristics of a particular network (+)

If short-term (fractions of a second) slight voltage drops constantly occur in the electrical network, then it is better to set the shutdown time at the lower threshold to the maximum. This way there will be fewer alarms, and the threat to the powered equipment will be minimal.

The turn-on delay should be selected depending on the type of electrical appliances plugged into the outlet. If the connected equipment has a compressor or electric motor, then the voltage supply time should be increased to 1–2 minutes.

This will avoid sudden surges in voltage and current when power is restored to the network, which will protect refrigerators and air conditioners from breakdowns.

And for computers and TVs, this parameter can be reduced to 10–20 seconds.

Which is better: stabilizer vs relay

Often, instead of connecting control relays in the panel, electricians recommend installing them in the house Voltage regulator. In some cases this may be justified. However, there are a number of nuances that must be remembered when choosing one or another option for protecting electrical appliances.

In terms of functionality, the stabilizer not only equalizes the voltage, but also turns off when the voltage is too high. A voltage relay is an exclusively protective automatic device. It seems that the first includes the functions of the second.

But compared to the RKN stabilizer:

• more expensive and noisy;
• more inert during sudden changes;
• does not have the ability to adjust parameters;
• takes up much more space.

When the input voltage is reduced so that the output of the stabilizer has the required indicators, it begins to “draw” more current from the network. And this is a direct path to wiring burnout if it was not originally designed for this.

The second main disadvantage of the stabilizer in comparison with the control relay is its inability to intercept a sharp voltage surge when the zero is broken.

Literally half a second with 350-380 W in the outlet is enough for all the equipment in the house to burn out. But most stabilizers are not able to adapt to such changes and pass high voltage, turning off only 1-2 seconds after the start of the surge.

In addition to stabilizers and relays, overvoltage and undervoltage releases can also be used to protect the line from voltage surges in the network. But they have a longer response time compared to the RLV. Plus, they do not turn the power back on automatically; their operation is more like an RCD.

After a power outage, these releases will have to be reset manually.

ILV connection diagrams

In the panel, the voltage relay is always installed after the meter in the break of the phase wire. He must control and, if necessary, cut off the “phase”. There is no other way to connect it.

Most often, for single-phase consumers, a standard circuit with direct load through a relay (+) is used.

There are two main circuits for connecting single-phase relays of the mains voltage regulator:

• with direct load through the RLV;
• with load connection via contactor - with connecting a magnetic starter.

When installing an electrical panel in a house, the first option is almost always used. There are plenty of various ILV models with the required power on sale. Plus, if necessary, these relays can be installed in a parallel circuit and several by connecting a separate group of electrical appliances to each of them.

Installation is extremely simple.On the body of a standard single-phase relay there are three terminals - “zero” plus phase “input” and “output”. Just make sure not to mix up the connected wires.

Conclusions and useful video on the topic

To make it easier for you to navigate connection diagrams and choosing a suitable voltage regulator relay, we have made a selection of videos describing all the nuances of the operation of this device.

How to protect equipment from power surges using RKN:

Voltage relay setting:

The mains voltage control relay is an excellent protection against “zero break” and sudden changes in voltage. It's easy to connect. You just need to insert the corresponding wires into the terminals and tighten them. In almost all cases, a standard circuit with direct load through the ILV is used.

Share with readers your experience of connecting and using voltage relays. Please leave comments, ask questions about the topic of the article and participate in discussions - the feedback form is located below.