Slip ring | Advantages | Disadvantages | Application | MCB

Slip ring | Advantages | Disadvantages | Application

Hi guys here we learn about Slip ring and their advantage, disadvantages, and application of Slip ring. Also information about working and construction.

Slip ring rotor

— Fig a shows the construction of slip ring rotor.

— The rotor winding is connected in the star connection like a normal three phase star connected transformer.

— Fig. 7.4.1 (a) shows that alongwith the rotor drum, the motor shaft also carries three sliprings which are circular in shape and rotate at the same speed as that of the rotor.

— The rotor winding terminals are permanently connected to these sliprings.

The sliprings are continuously in contact with three brushes which are pressed against the sliprings using springs.

— Many a times an external resistance is necessary to be connected in the rotor resistance. So a variable resistance is connected in the rotor winding.

— Such an external resistance is essential to develop a high starting torque.

— Thus external resistance can be added through the combination of sliprings and brushes.

— In other words the rotor is accessible to the user due to the use of slip rings and brushes.

Disadvantages of slip ring rotor:

1. More wear and tear so frequent maintenance is required.

2. Increased loss in rotor so efficiency is reduced.

3. Poor power factor at full load.

4. Needs a rotor resistance starter.

5. It has a low pull out torque.

Advantages of slip ring rotor:

1. External resistance can be connected to rotor. So it is possible to adjust the starting torque.

2. High starting torque can be obtained.

3. Speed control using rotor resistance control is possible to achieve.

Applications of Slip ring :

Slip ring rotors are preferred for applications such as carinas, elevators, lifts, compressors etc. which need high starting torque.

MCB ( Miniature Circuit Breaker) :

~ The miniature circuit breakers (MCB) have become an integral part of domestic, commercial and industrial applications.

~ It is basically a tripping device which acts as a switch. Under the normal operating conditions, it acts as a closed switch

whereas when the current goes above a predetermined level, it acts as an open switch, to break the circuit.

~ The MCB is available in the moulded case which contains the tripping and switching mechanism.

~ The switching mechanism is based on the thermal and magnetic sensing devices. Such sensing mechanism is present inside the MCB.

~ We can connect an MCB in series with each line of the ac supply going to the load just the way we connect fuse links in series with each supply line.

~ If the load currents flowing through the MCBs are at safe levels, then the MCBs act as closed switches and connect the ac supply to the load.

~ But if the load current goes above a certain value, then the corresponding rise in temperature is sensed by the temperature sensor inside the MCB, the MCB will trip and

will act as an open switch to disconnect the load from the supply.

~ The MCB can replace the thermal overload relay and contactor successfully. So we don't have to use two separate devices for protection.

Specifications :

Miniature circuit breakers are available in following ratings :

Current rating: 5, 10, 15, 20, 30, 40, 50, 60 Amps

As well as 0.5, 1, 2, 2.5, 3, 3.5, 6, 7.5, 8, 10, 12, 35, 45,

55 Amp.