FIELD OF INVENTION
The present invention relates to a method of mounting Forced Ventilation (FV) unit at non driving end (NDE) side of Totally enclosed fan cooled (TEFC) motor for variable speed application at constant torque.
BACKGROUND OF INVENTION
BHEL Bhopal is pioneer in design & manufacturing of large and medium range rotating electrical machines, for safe as well as hazardous area of applications. Motors are designed with different with different types of method of cooling having IC codes as per standard IEC 60034-6.
TEFC motor with cooling code IC411 has one internal fan and one external fan at NDE side of motor, both of which are shaft mounted. The internal fan circulates air in internal air circuit, and takes away the heat from hot active parts (winding and core) and distributes the heat inside the internal surface of motor. The shaft mounted external fan draws air from ambient and blow it over outer cooling ribs of the motor.
As per the latest constant torque applications, IC 411 motors are not suitable for complete speed domain. During low speed operation, motor shaft speed reduces, resulting in considerable reduction in amount of air delivered by external fan. However, as the torque requirement remains same the reduced airflow

becomes insufficient to maintain thermal equilibrium resulting in over heating of motor.
As described above, TEFC IC411 motor has limitation for operation in constant torque applications. The only available option in such specific cases was CACA motors having IC666 cooling. These motors are lesser efficient, and have more noise, vibration, weight and size as compared to TEFC motors. Therefore, basic design modification was required for TEFC motor, to make it suitable for constant torque and variable speed of operation thus fulfilling all the customer’s requirements. This led to the design development of highly energy efficient, compact sized, optimally designed, forced ventilated TEFC motor with IC416 cooling.
OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose a method of mounting Forced Ventilation (FV) unit at non driving end (NDE) side of TEFC motor for variable speed application at constant torque that eliminates the disadvantage of using shaft mounted external fan of prior art.
Another object of the invention is to propose a method of mounting Forced Ventilation (FV) unit at non driving end (NDE) side of TEFC motor for variable

speed application at constant torque which is capable of providing a more efficient Fan Cooling system in a totally enclosed fan cooled motor.
A still another object of the invention is to propose a method of mounting Forced Ventilation (FV) unit at non driving end (NDE) side of TEFC motor for variable speed application at constant torque which provides outer cooling air generated from a separately driven fan that guarantee constant torque which provides outer cooling air generated from a separately driven fan that guarantee constant torque at every operating state/speed.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1 - Shows cooling air circuit with IC411 motor according to prior art.
Fig. 2 - Shows cooling air circuit with IC416 motor according to the invention.
Fig. 3 - Shows forced ventilation (FV) unit assembly along with bracket.
Fig. 4 - Shows the special bracket used for mounting the auxiliary motor in
the FV unit assembly.

Fig. 5 - 3D model of the special bracket.
Fig. 6 - Shows a photograph of Fan motor unit.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
METHODS OF COOLING WITH IC 411 (Prior Art)
FIG-1 shows a typical cooling circuit of self-ventilated rib cooled TEFCMotor. In this arrangement, a shaft mounted external fan and internal fan. Provided at non-drive end side of motor as can be seen in the diagram.
The heat losses from laminated stator (8) and rotor (9) core and stator winding (7) is transmitted through internal cooling circuit. The internal fan at the non-drive end draws air through ventilation holes in the rotor.The internal ribs of the frame and end shield plays a significant role in cooling of the motor. This internal cooling circuit is harmonized to the condition of totally enclosed fan cooled motor.
The shaft mounted external fan (12) draws air from outside and blows it over the outer cooling ribs from non drive end to drive. The stator frame acts as a heat exchanger between internal and external cooling air circuit and provide a uniform cooling throughout the motor.

COOLING AIR CIRCUIT OF MOTOR WITH IC 416 COOLING ACCORDING TO INVENTION
Fig -2 shows a typical Cross-sectional arrangement of Motor with method of cooling IC416. Non Driving end side is responsible for providing cooling air circuit of Motor.
This FV unit (F) mounted on special bracket having motor and optimised axial fan draws the air axially from the outside and blows it over the outer cooling ribs. The internal fan (6) extracts heat from Stator Winding (7), Stator Core (8) and Rotor Core (9) and throws out air radially at the top of the machine. Heat is exchanged with inner cooling ckt at this location and thus provide an efficient and uniform cooling. Furthermore, provision of cut-out (10) with an optimaly designed Bracket shown in fig-4 provide a unique ventilation (11) for bearing and end-shield.
By optimizing the design of the bracket (2) with cut out (10) on periphery and providing additional ventilation hole (11) at the back of the bracket leads to the uniform cooling of bearing and end shield at non-drive side of motor (3).
The non-drive end shield is designed for mounting this special bracket without obstructing the cooling of the motor.
Furthermore, with the optimized electrical and mechanical design of motor and fan of FV unit apparatus, results in optimized quantity of air flow.

This type of motor has been manufactured in BHEL first time. Also it has been established that the results of temperature rise of this type of motor according to invented method is far better then the previous arrangement.
As shown in Fig. 3 an optimally designed FV unit assembly (F) comprises the following:
(i) a modified end shield (1) having increased boss height in order to mount new and optimized bracket (2).
(ii) a new cylindrical bracket (2) with optimized design for uniform cooling.
(iii) an auxiliary motor (3).
(iv) a cooling fan (5).
(v) a robust fan casing (4) to accommodate complete system.

WE CLAIM
1. A method of mounting Forced ventilation (FV) unit at non driving end (NDE)
side of TEFC motor for variable speed application at constant torque comprising
the steps of;
eliminating shaft mounting external Fan (12);
designing and developing a highly energy efficient compact sized force ventilated TEFC motor for IC416 cooling;
manufacturing a robust cylindrical shaped bracket (2) to hold a fan and motor unit (3);
disposing a long and optimized fan casing (4) to cover whole FV unit assembly; wherein,
the fan and motor unit (3) is disposed in the FV unit assembly to deliver required quantity of air at required pressure for uniform and efficient cooling of motor irrespective of rotor speed.
2. The method as claimed in claim 1, wherein a cut out (10) is configured on the
periphery of the bracket (2) with additional ventilation holes (11) being provided
at back of bracket (2) for ventilation of bearing and end shield.