Varieties of protective relays and relay protection
A relay is a device in which a sudden change (switching) of the output signal is carried out under the influence of a control (input) signal that changes continuously within certain limits.
Relay elements (relays) are widely used in automation systems because they can be used to control large output powers with low power input signals; performing logical operations; creation of multifunctional relay devices; to carry out switching of electrical circuits; to fix deviations of the controlled parameter from the set level; performs the functions of a memory element, etc. Relays are most widely used in the field of relay protection and automation.
Relay classification
Relays are classified according to different criteria: according to the type of input physical quantities to which they react; by the functions they perform in management systems; by design, etc. According to the type of physical quantities, electrical, mechanical, thermal, optical, magnetic, acoustic, etc. are distinguished. relay.It should be noted that the relay can respond not only to the value of a certain quantity, but also to the difference in values (differential relays), to a change in the sign of a quantity (polarized relays), or to the rate of change of an input quantity.
Relay device
A relay usually consists of three main functional elements: perceptive, intermediate, and executive. Perception (primary) the element perceives the controlled value and transforms it into another physical quantity. The intermediate element compares the value of this quantity with a given value and, if exceeded, passes the main effect to an executive element. The actuator transfers the impact from the relay to the controlled circuits. All these elements can be expressed explicitly or combined with each other. Sensing element depending on the intended use, the relay and the type of physical quantity to which it reacts can have different implementations, both in principle of action and in terms of device.
By the device of the drive, the relays are divided into contact and non-contact.
Contact relays act on the controlled circuit by means of electrical contacts, the closed or open state of which makes it possible to provide either a complete short circuit or a complete mechanical interruption of the output circuit.
Non-contact relays affect the controlled circuit through a sudden (abrupt) change in parameters of the output electrical circuits (resistance, inductance, capacity) or changes in the voltage level (current). The main characteristics of the relay are determined by the dependencies between the parameters of the output and input quantities.
Relays are divided according to the method of inclusion:
- Primary - relays connected directly to the circuit of the protected element. The advantage of primary relays is that no measuring transformers are required to turn them on, no additional current sources are required and no control cables are required.
- Second — relays switched on by current or voltage measuring transformers.
The most common in relay protection technology are secondary relays, the advantages of which can be attributed: they are isolated from high voltage, located in an easily maintained place, they are standard for a current of 5 (1) A or a voltage of 100 V, regardless from the current and voltage of the primary protected circuit...
By design, relays are classified:
- Electromechanical or induction - with movable elements.
- Static — no moving elements (electronic, microprocessor).
Relays are subdivided according to purpose:
- Measuring relays. Measuring relays are characterized by the presence of supporting elements in the form of calibrated springs, sources of stable voltage, current, etc. Reference (sample) elements are included in the relay and reproduce predetermined values (called setpoints) of any physical quantity to which the controlled (influencing) quantity is compared. Measuring relays are highly sensitive (they perceive even minor changes in the observed parameter) and have a high return factor (the ratio of the effective values of the return and actuation of the relay, for example, for a current relay — Kv = Iv / Iav).
-
Current relays react to the magnitude of the current and can be: — primary, built into the circuit breaker drive (RTM); — secondary, connected by current transformers: electromagnetic — (RT -40), induction — (RT -80), thermal — (TPA), differential — (RNT, DZT), on integrated circuits — (PCT), filter — relay for reverse sequence current — (RTF).
- Voltage relays react to the magnitude of the voltage and can be: — primary — (RNM); — secondary, connected through voltage transformers: electromagnetic — (RN -50), on integrated circuits — (RSN), filter — reverse sequence voltage relay — (RNF).
- Resistance relays respond to the value of the ratio of voltage and current — (KRS, DZ-10);
- Power relays react to the direction of the flow of short-circuit power: induction-(RBM-170, RBM-270), on integrated circuits-(RM-11, RM-12).
- Frequency relay react to a change in the voltage frequency — on electronic elements (RF -1, RSG).
- A digital relay is a multi-functional software device that simultaneously functions as a relay for current, voltage, power, etc.
Relays can be maximum or minimum… Relays that are activated when the value acting on it increases are called maximum relays and relays that are activated when this value decreases are called minimum.
Logic or auxiliary relays are classified into:
- Intermediate relays transmit the action of the measuring relays to open the circuit breaker and serve to establish mutual communication between the relay protection elements.Intermediate relays are designed to multiply signals received from other relays, amplify these signals and transmit commands to other devices: electromagnetic direct current-(RP-23, RP-24), electromagnetic alternating current-(RP-25, RP- 26), electromagnetic direct current with delay on actuation or fall-off-(RP-251, RP-252), electronic on integrated circuits — (RP-18),
- Time relays serve to delay the action of protection: electromagnetic direct current — (RV-100), electromagnetic alternating current — (RV-200), electronic on integrated circuits (RV-01, RV-03 and VL)
- Signal or indicator relays serve to register the action of both the relays themselves and other secondary devices (RU-21, RU-1).
According to the method of impact on the switch, the relays are divided:
- Direct-acting relay, the mobile system of which is mechanically connected to the disconnecting device of the switching device (RTM, RTV)
- Indirect relays that control the tripping electromagnetic circuit of the switching device.
The main types of relay protection:
- Current protection — non-directional or directional (MTZ, TO, MTNZ).
- Low voltage protection (ZMN).
- Gas shielding (GZ).
- Differential protection.
- Distance Defense (DZ).
- Differential phase (high frequency) protection (DFZ).