Recently, imported electrical equipment has been widely used, which is affected by poor-quality electrical supply of the mains and its correct connection. Faults such as phase failure, current and voltage imbalance negatively affect expensive equipment or completely disable it.
Content
- Purpose of the device
- Emergency situations
- Types of phase failure monitoring devices
- Connection diagram
When working with three-phase asynchronous electric motors, it is necessary to observe the correct connection, since if the phasing will rotate in the opposite direction, which is fraught with consequences and failure of mechanical elements systems. To eliminate such situations, it is necessary to introduce additional protection in the form of a phase control relay unit. When used in systems of such a device, the safety of electrical installations is significantly increased, which prevents the failure of electrical equipment.
Purpose of the device
The main application of the relay is in automated control systems.
. Its main purpose is to monitor the presence of voltage symmetries in each of the phases, the order of their alternation in a three-phase network, protection against breakage of one of the phases and prevention of phase asymmetry stress.It can play the role of protecting electrical equipment in an emergency.
The device has an automatic self-return mode in case of restoration of the electrical network after an emergency shutdown of electrical equipment. An internal electronic circuit monitors the parameters of the power grid.
With normal power supply parameters, a built-in electromagnetic relay is turned on, which connects the voltage to electrical consumers. In the event of a deviation of electrical parameters from the norm, the internal control circuit gives a signal to disconnecting the device, and when the parameters are restored to normal, the power is restored to loads.
Emergency situations
If two or three phases are broken at the same time, the monitoring device turns off instantly. The device constantly monitors the voltage in the mains and provides for the following emergency situations:
- Break of one of the phases;
- In case of imbalance, in the case of an asymmetrical or symmetrical voltage at the output of the permissible parameters;
- Wrong order of connection.
Types of phase failure monitoring devices
A domestic manufacturer produces many different types of protection devices for both three-phase and single-phase networks. The most common relays are from the EL-11E, EL-12E, EL-13E series. Such devices are designed to work in our power grids, where each type of device finds its own purpose and scope.
The EL-11E device monitors the voltage value and performs the function of protecting generators and power supplies. EL-12E performs the functions of tracking the phase sequence and voltage asymmetry between phases. It is used to protect electric motors with power no more than 100kW, and rotation in one direction. EL-13E is used to protect against phase imbalance of asynchronous motors with a power not exceeding 75 kW.
The response time of such devices from the EL series is 0.1 s, 0.15 s, 0.5 s and the ability to adjust the delay from 0.1 s to 10 seconds. The delay makes it possible to avoid false alarms caused by noise in the mains.
All types of protection devices have an indication of the normal and emergency mode of the network on the front side of the case. Functionally it consists of a control unit, which is used as a measuring device, and an executive (power) one.
The control unit monitors the state of the electrical network and has adjustments:
- Setting the lower and upper voltage thresholds;
- Setting the response delay.
The power section consists of an electromagnetic relay, the contacts of which are used as switching the loads of the electrical network.
Connection diagram
The device has terminals (L1, L2, L3) that are connected to three-phase voltage. The neutral wire in such models is usually not output. About six working terminals are used for control circuits. Two pairs of contacts are used, one of which is the switching circuit of the magnetic starter, and the other is used in the control circuits of electrical equipment.
Different relay models may have their own design features of the connection, therefore it is recommended to use the documentation. When setting up the device, you may encounter different options for adjustment and settings..
The simpler models use one or two potentiometers, while the top range models have advanced setting items.
Block microswitches are commonlocated on the printed circuit board in a separate niche. Setting the switches to a certain position creates the given configuration. The required parameters are set using potentiometers or microswitches for the protection setpoints.
