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Brake Motors

Brake Motors are offered for various applications requiring almost instantaneous stopping of driven load. These motors are offered in frame sizes 71 to 132M. Their operation is of 'fall safe' type, i.e., the brake is applied when, power to the motor is switched off, or, if power failure occurs.

Construction

A Brake Motor is an integral combination of an A.C. induction motor and a disc type, fail safe, electromagnetic brake unit. It consist of following:

A. C. Induction motor.
Encapsulated brake coil housed in the non-driving end End-shield.
Brake liner attached to the armature disc at its interface with the cooling fan.
Cooling fan.
The rectifier unit is provided inside the Terminal Box. It converts A.C. supply into D.C. supply for the Brake coil.

Operation

Under no power condition Brake springs keep the Brake Liner pressed against the cooling fan. This prevents rotor shaft rotation, because, the fan is keyed to it. When power is switched on, the Brake coil gets energized through the Rectifier unit. It instantly attracts the armature disc by overcoming the spring force. This action results in releasing of the fan allowing the rotor to rotate freely.

When power fails or when it is switched off, the brake coil gets de-energised. This results in the springs pressing the brake liner against cooling fan, i.e. returning armature disc to its original position. This causes almost instantaneous braking of rotor. Fail safe condition is thus ensured.

For applications, where total load stopping time is not very critical, A. C. side interruption can be used.

However, for applications, where faster braking is required, D.C side interruption should be used. An additional contactor interlocked with main contactor should be used.

Special Features

Being simple and rugged-in construction, these motors need very little maintenance.
No separate DC supply is necessary, because a rectifier unit is provided. The rectifier is open type and fixed between the two terminals inside the terminal box. Being open type, it ensures good heat dissipation and is very easy to replace. Varistor is provided across the DC terminals to protect the brake coil and rectifier against line and switching surges. The rectifier assembly is tested for 10,000 cycles at the rate of 6,000 cycles per hour.
Special brake liner is used, which ensures that, the braking torque value remains quite stable throughout the use. Compensation for liner wear is easily done by advancing the position of the fan by tightening the castle nut at the non-drive end. The design of Brake motor facilitates a very easy replacement or armature disc and brake liner assembly
Since the fan serves as a braking surface (unlike some other designs), it also serves to cool the Brake coil and the motor. These Brake coil and the motor. These Brake Motors being fan-cooled, are available in smaller frame sizes than other brake motors which are surface cooled. Therefore, these motors are more compact and economical for a given application.
For crane and hoist duty application Brake Motors are offered with special motors. These rotors are specially suited for S3 and S4 duty normally encountered in hoist and crane applications.
Mechanical manual release of the brake as an optional feature is available from 90S to 132M frames. In case of power failure, the brake can be released manually with a lever by turning it through 90.
The working of the rectifier unit has been successfully type tested for one million operations.

Applications

Brake Motors are used for numerous applications. A few of them are listed below :

Textile Machinery
Machine Tools
Printing Machines
Cranes and Hoists
Material Handling Equipments.

Leather Processing Machines.
Geared Motors
Cable Reeling Drums.
Rolling Mills

Enquiry Details :

When placing an enquiry kindly furnish the following information :

Application details
Output and speed.
Duty cycle with number of starts stops per hour.
Ambient temperature and special environmental factors likely to affect the motor, if any.

Method of mounting
Load GD referred to motor shaft
Braking torque required
Maximum permissible stopping time.

Any other special features required.

* These are inter-related parameters and related by following formula

Total Stopping time Ts = GD² X N
                                    --------------- + tapp
                                       375 T
Where T = braking torque in kgm
          GD² = load GD2 + rotor GD2
          N = speed of rotation in r.p.m.
          t = brake application time ( to be obtained from Table 1 )

Specifications of Brake Motors (3 phase, 415 + 10% volts, 50 + 5% Hz)S

Frame Size	Outputs (KW)				Brake release time (millisecs)	Brake application time (millisecs)		Braking torque (kgm)
Frame Size	2P	4P	6P	8P	Brake release time (millisecs)	AC side interruption	DC side interruption	Braking torque (kgm)
71	0.37 0.55	0.25 0.37	0.25	-	50 50	135 135	25 25	0.5 0.5
80	.0.75 1.10	0.55 0.75	0.37 0.55	-	55 55	225 225	45 45	1.0 1.0
90 S	1.50	1.10	0.75	0.37	100	260	50	2.0
90 L	2.20	1.50	1.10	0.55	100	260	50	2.0
100 L	3.70	2.20	1.50	0.75 1.10	135 135	270 270	50 50	4.0 4.0
112 M	-	3.70	2.20	1.50	145	290	60	5.0
132 S	5.50, 7.5	5.50	3.70	2.20	145	270	60	5.0
132 M	9.3	7.50	5.50	-	145	270	60	5.0

Other braking torque values upto 40% higher can be given for special applications.

Other outputs can be offered on request where feasible.

Brake release time : The time interval between the instant supply to the brake coil is interrupted to the instant the brake is applied. The value depends on whether the circuit is interrupted on AC side or DC side. For performance details, please refer standard Motor Catalogue.