what is a relay
A relay is an electrical switch that uses electromagnetic force to control the operation of one or more electrical circuits. Relays usually consist of components such as electromagnets, contacts, and springs. When an electromagnet is activated, it creates a magnetic field that attracts or releases contacts, opening or closing a circuit.
Classification of relays
Relays are divided into DC relays and AC relays.
DC relays are powered by a DC power supply. According to the polarity of the current passed, they can be divided into non-polar, biased and polarized relays. DC relays are all electromagnetic relays, which use the magnetic field generated by the electrification of the coil to attract the armature and drive the on-off or conversion of the contact system.
AC relays are powered by AC power. According to the principle of action, there are electromagnetic relays and induction relays. Electromagnetic relays are similar to DC relays, except that a degaussing sheet or degaussing ring is added to the coil to prevent oscillation. The induction relay uses the alternating magnetic field generated by the coil to interact with the current induced in the flap by another alternating magnetic field to generate electromagnetic force to make the flap rotate and act.
Application of Relays in Railway
Relays are also widely used in railway signaling systems, the main types are: DC non-polar relays, polarized relays, polarity maintaining relays, etc.
DC non-polar relay is a kind of DC electromagnetic relay, its coil is not divided into positive and negative poles, and it can be connected to DC power supply of any polarity.
Bipolar relay is a kind of DC polarized relay. Its coil is divided into positive and negative poles, and it can only be connected to a certain polarity of DC power supply. When the forward current is passed to the coil, the front contact and the middle contact are closed; when the reverse current is passed to the coil, the rear contact and the middle contact are closed; when the coil is de-energized, the relay does not act.
Polarity maintaining relays are a special type of polarized relay with polarity and maintaining functions. When the polarity maintaining relay is energized, the contacts will be closed according to the polarity of the coil, and the contacts will maintain the original state after the power is released.
AC relay: A relay powered by an AC power source. According to its operating principle, there are electromagnetic relays and induction relays. Such as signal machine filament conversion relay, FD type electric code generator, JRJC type binary two-position relay, rectifier relay, etc.
Rectifier relay: It is made on the basis of a non-polar relay. A rectifier and voltage regulator is added before the coil input, so that the AC becomes DC, and finally it is passed into the coil. The DJ (filament relay) on the signal machine uses a rectifier relay.
Two-element two-position relay: It is an induction relay that uses the interaction of an alternating magnetic field and another alternating magnetic field to generate eddy currents in the flaps of the movable part of the relay. The GJ (track relay) of the 25HZ phase-sensitive track circuit uses a binary two-position relay.
Time relay: When the input signal is added or removed, the output part needs to be delayed or limited to the specified time before closing or disconnecting the relay of the controlled circuit. A time relay is used in the starting circuit of the turnout.
Relay Naming Rules
For example: JWXC-1700
J: Relay
W: Promise
X: signal
C: insert
1700 is the resistance value of the coil. When the coil is fed with direct current, the current I flowing through the coil = voltage/coil resistance.
Commonly used models of non-polar relays: JWXC-1700
Commonly used models of polarity relays: JPXC-1000
Common models of polarity maintaining relays: JYXC-660, JYJXC-135/220
Common models of rectifier relays: JZXC-480, JZXC-H18
Graphical symbols for railway signaling relays
Reasons for using relays in railway signaling systems
Reliability: The relay is a reliable switching device that can work stably under harsh environmental conditions. In railway signaling systems, relays are ideal for critical components such as signal machines, switches and track circuits that require highly reliable switching control.
High precision: The operation precision of the relay is very high, and the switching state can be accurately controlled. In the railway signal system, accurate switch control is very important to ensure the safety and normal operation of trains.
Safety: The relay can withstand high voltage and current, and can complete the switching operation in a short time. In the railway signal system, since the signal control involves the safety of the train, the relay is required to have a high degree of safety and fast response speed.
Flexibility: Relays can be combined and configured according to actual needs to meet different signal control requirements. In the railway signal system, different train operation modes and station line characteristics require different signal control configurations, and the flexibility of relays can well meet these needs.