Comparison Zubr CV2-40 red vs DigiTOP PS-40A

— Voltage relay. Protective devices that automatically turn off the protected area when the mains voltage goes beyond the specified parameters. Usually, such devices are able to respond to both a significant increase and a significant decrease in voltage. A voltage relay will be a useful addition to traditional protection such as plugs or a circuit breaker, since such protection only reacts to excess current and does not monitor voltage. And in three-phase networks, protective relays can also provide monitoring of phase synchronization, triggering in case of skew, breakage, sticking or phase sequence violation.

— Current relay. Protective devices that automatically turn off the protected area when the consumed current exceeds the specified parameters. It is similar in purpose to circuit breakers, however, firstly, the current relays can also respond to a decrease in current, and secondly, such a device may not work instantly, but after a certain time. It makes sense to install a current relay where short-term operation at high currents is allowed, however, the time of this operation must be limited, and also where long-term idle operation at low currents is undesirable. A classic example is connecting a power-controlled motor: the current at maximum power can be set as an upper limit, and the lower limit can be set just above the no-load current. The shutdown time in such devices, usually, can be set within a few minutes.
...> — Power relay. Protective devices that automatically turn off the protected section of the circuit when the power consumption is exceeded. Such a device monitors both the current strength and the voltage at the same time — we recall that the power is calculated by the formula "current strength multiplied by voltage." The need for a power relay is due to the fact that in some situations it is not an excess of current or voltage that gives an overload, but a combination of them — moreover, both volts and amperes can remain within acceptable values.

— Multifunctional relay. Models that combine the capabilities of several protective devices. A multifunctional device usually has the function of a voltage relay (with upper and lower trip limits) and a power relay or current relay (both with only an upper limit). See above for details of each variety; here we note that their multifunctional relay allows you to get by with one device instead of two.

— Phase selection relay. Protective devices used when supplying a single-phase load through a three-phase network. As the name suggests, such a relay provides automatic selection of the most favorable phase; in other words, if a failure occurs on the current phase, the device switches the load to another phase, with more stable voltage indicators. Such devices are mainly intended for connecting especially important and sensitive devices that have increased requirements for voltage stability.

— Impulse relay. Control devices that close or open the circuit when a short-term voltage pulse is applied to the control input. Also, such devices are called bistable, since each of the switch positions (both “on” and “off”) is stable and changes only when a control pulse is received. One of the options for using such relays is to control lighting from several places at the same time, for example, from two switches installed at different ends of a long corridor. By connecting both of these switches to an impulse relay, one can turn on the light at the entrance to the corridor, and the second one can turn it off at the exit, regardless of the direction of movement. Theoretically, even on one relay, you can tie up as many switches as you like; there are more complex schemes for the use of bistable control devices.

The number of phases for which the relay is designed.

— 1. Single-phase power is known to everyone from classic 230 V household sockets. Actually, some relays for this voltage are even made in the form of socket adapters (see "Installation"). However, models are also produced for other values of alternating voltages — for example, 110 V.

— 3. Three-phase 400 V power supply is used mainly for high consumption devices for which 230 V networks do not provide enough power. Also note that switchboards in private houses are often connected to a three-phase electrical network, with further power distribution for individual phases. However, in such cases, it is more reasonable to use three separate relays for each of the phases, and not one three-phase device: in the first case, only part of the home network will lose power in the event of a power failure, in the second, the entire network.

— 1/3. A specific variant used exclusively in the phase selection relay. Such models take three phases as input, and only one is fed to the load; see "Device" for details.

Width expressed in unit units. This unit is used to measure the width of rack-mounted devices and makes it easy to estimate how much space you need. Width in unit is always expressed as whole numbers, 1 unit is approximately equal to 17.5 mm. There are models 1U, 2U, 3U and more

The rated power of the relay in kilovolt-amperes, in other words, the maximum apparent load power with which the device can normally operate.

From a physical point of view, kilovolt-amperes and kilowatts mean the same thing, but in kW it is customary to indicate only the active power of the load (see below), and in kVA — full. In AC networks, these powers can vary because active power (the power consumed by resistive-type devices such as heaters) is added to reactive power (the power consumed by capacitors and inductors). The apparent power is calculated from these two quantities.

When selecting control relays for AC networks, it is best to take into account the full power, especially if you plan to connect equipment with electric motors to the device. However, for many modern household appliances, only active power is given in the characteristics — in kilowatts. There are calculation methods that allow converting active power into total power, depending on the type and characteristics of the load; such techniques can be found in special sources.

Voltage measurement range supported by the device.

Many modern control relays are equipped with digital displays, which can display, including current voltage; this parameter specifies the operating range of the built-in voltmeter. In this case, the voltage measurement range can be noticeably wider than the difference between the smallest minimum and the largest maximum shutdown threshold (see below). This allows you to use the relay also for online diagnostics of the network status.

For a current relay (see "Device") in this case, the range of operating voltages can be given directly — the voltage at which the device can normally perform its functions.

Measurement accuracy provided by the device. In this case, different types of measurements may be implied, depending on the purpose of the relay (see "Device"). Note that in power relays and multifunctional devices, the measurement accuracy for voltage and current is usually the same, and a common parameter is given in the characteristics for them.

Accuracy is indicated by the maximum measurement error provided by the device. First of all, the operation accuracy depends on this parameter: the lower the error, the smaller the actual deviations from the specified operation parameters. For modern control relays, an indicator of 3 – 5% is considered acceptable, 1.5 – 3% is not bad, 1 – 1.5% is good, less than 1% is excellent. However, in fact, it is also worth choosing according to this parameter, taking into account how sensitive the connected load is to the accuracy of the specified operation parameters.

Also note that many modern relays are equipped with digital displays that can display various parameters. In such models, the measurement accuracy also determines the accuracy of the readings of such a built-in "tester".

Time to turn off the device on the lower limit of voltage or current. This is a kind of "reaction time" of the relay: the period of time between reaching the lower limit and turning off the protected network segment.

The lower this value, the more advanced the protection will be, the lower the probability of failure of sensitive devices due to untimely operation of the relay. On the other hand, a high response rate for the lower limit is not as critical as for the upper one, and the shutdown time can be quite long — 1 s or more.

Also note that for some devices, this paragraph gives the minimum turn-off time (fastest response time), while in certain modes this time may be longer. For example, a voltage relay with a lower limit of 160 V may provide tripping after less than 0.05 s when the voltage drops below 120 V and tripping after 1 s when the voltage is in the range of 120 – 160 V, but above 120 V. This avoids unnecessary shutdowns with relatively weak and short-term voltage deviations. In the characteristics of such a device, 0.05 s will be indicated.

The device shutdown time on the upper limit of voltage or current. This is a kind of "reaction time" of the relay: the period of time between reaching the upper limit and turning off the protected network segment.

The lower this value, the more advanced the protection will be, the lower the probability of failure of sensitive devices due to untimely operation of the relay. Note that a short reaction time in this case is especially important, because too high a voltage or current is a serious danger to any device.

The reclosing delay is the time after a safety shutdown after which the device turns on the mains power again. Usually, in modern control relays this time can be adjusted, so the characteristics indicate the range from the minimum to the maximum value.

Adjustment of the delay allows you to adjust the format of the relay to the characteristics of the network. So, if voltage failures do not mean critical problems, you can set the minimum re-closing time, and if jumps occur only with serious problems that need to be fixed, it is better to turn on the maximum delay. Note that triggered relays usually allow manual reclosing, and in most models it is possible to completely disable the automatic reclosing function.