Classification of the relay by the method of influence on the switch Prepared by: Adilkhan Bexultan Checked by: Utesh Margulan

Outline: Basic information regarding relay Types of relays by method of influence to the switch Direct relays Indirect relays

Basic information regarding relay A relay is classified into many types, a standard and generally used relay is made up of electromagnets which in general used as a switch. Dictionary says that relay means the act of passing something from one thing to another, the same meaning can be applied to this device because the signal received from one side of the device controls the switching operation on the other side. So relay is a switch which controls (open and close) circuits electromechanically. The main operation of this device is to make or break contact with the help of a signal without any human involvement in order to switch it ON or OFF. It is mainly used to control a high powered circuit using a low power signal.

Basic information regarding relay Here is simple animation illustrating how relays use one circuit to switch on a second circuit. When power flows through the first circuit (1), it activates the electromagnet (brown), generating a magnetic field (blue) that attracts a contact (red) and activates the second circuit (2). When the power is switched off, a spring pulls the contact back up to its original position, switching the second circuit off again. This is an example of a "normally open" (NO) relay: the contacts in the second circuit are not connected by default, and switch on only when a current flows through the magnet. Other relays are "normally closed" (NC; the contacts are connected so a current flows through them by default) and switch off only when the magnet is activated, pulling or pushing the contacts apart. Normally open relays are the most common.

Types of relays by method of influence to the switch Depending on the method of inclusion in the protected circuit relays are divided into primary and secondary. Primary direct-acting relays are connected directly to the main electrical circuit, and secondary through current transformers and voltage transformers. According to the method of influence on the switch of the protected object are different: direct relay; indirect relay.

Direct relays Relay of direct action act directly on the tripping of the circuit breaker. The direct relay controls the circuit of the switch-off electromagnet. The primary relay of direct action. the relay is connected directly to the main electrical circuit. the relay acts directly on the mechanical actuator of the switch. In power supply systems, primary direct-acting relays are used relatively rarely. For example, in DC traction networks of electrified transport. In AC systems, such relays are used in circuit breakers. They're called uncouplers. Secondary current and direct-acting voltage relays. the relay can act directly on the switch drive or through a device; relays are activated via CT or VT, but operate directly on the switch mechanism. The inclusion of windings via CT or VT allows you to expand the use of the relay; with the help of secondary direct-acting relays can perform protection in installations up to 35 kV.

Indirect relays Primary indirect action relays: the relay is connected directly to the main electrical circuit. the relay acts on the switch-off electromagnet. Secondary current and indirect-acting voltage relays. They are widely used due to the following advantages: their parameters do not depend on the parameters of the protected element, as relays are connected via CT or VT; have a sufficiently high sensitivity with minor errors and relatively low power consumption; their adjustment is made without switching off the element of the power supply system; the relay can be installed anywhere convenient for operation; Disadvantages: significant power consumption; large size; lack of reliability due to the presence of the contact system; require a source of operating current.