Current (Magnetic) Relay
Current relays are usually low torque, less horsepower motors. The current (magnetic) relay uses the electrical characteristics of the electric motor work.
As the rotor is gaining speed, magnetic fields, build and turn to the motor. This creates a counter electromotive force (cemf), or the voltage at the start winding. Running winding draws more current when the rotor is not working, or turning slowly than at full speed. Current switches are operated relay is used to close and open the starting winding. They are working on changes in the current thread is running winding. This is done as a winding runs from the beginning.
Magnetic relay is an electromagnet like a solenoid. Either the weight or spring holds the starting winding contact points open when the system is in standby mode. Fig. 8-55 is a circuit weight-operated units. When the motor control (thermostat or pressurestat) close contacts, high current flows in the run winding. Magnetic coil current relay that strongly magnetized. She raises weight or overcomes the spring pressure and closes the contacts.
This action closes the starting winding circuit.
The engine will quickly accelerate (acceleration) by two-thirds or three-quarters of nominal speed. As it does so, the current draw of the running motor winding is reduced. This reduces the magnetic strength of the magnetic current relay. Reduction enough to weight or spring to open the points. Fig. 8-56 shows magnetic current relay in a closed (starting) provisions, as well as in the open (running) position.
Current relays sometimes called the current relay. This is the most rely on a scheme that controls the relay. One type of magnetic current control is used a rotary solenoid. This type can be mounted in any position. Type weight should be set.
One type of weight-operated magnetic current relay is shown in Fig. 8-57. Spring drive type shown in Fig. 8-58. Method of mounting the current starting relays are shown in Figure 8-59.
These relays are available in a number of capacities. The difference between closing the current and the opening of the current settings small. This small difference in the current flow will close the start-up scheme. Then open circuit when the engine reaches about three quarters of the speed. Fig. 8-60 is a circuit with overcurrent relay.
Utilities sometimes reduce the voltage to save the current. The current type the starting relay gives some protection of the engine under these conditions. However, there is still some danger of burnout engine,