TECHNICAL FIELD OF THE INVENTION
This invention relates generally to a test bench system for motors. More particularly, the present
invention relates to an induction motor test bench system for testing of induction motors. This
system provides a stabilized three phase variable power supply to the AC induction motor for
smooth starting, stopping and functionality testing so that the complete testing of AC induction
motor can be carried out.
BACKGROUND AND THE PRIOR ART
This invention finds its application in the AC induction motor testing. Complete testing of
induction motors is a must before its actual implementation in the field. Motor testing has its
own specialized requirement. Conventional controls like soft starter or an autotransformer based
control is not suited to the application due to lack of full control which is a must for the testing
purposes.
Generally the testing system tests either HT or LT motors. The arrangement of two separate
systems occupies large space. Therefore there is a need to provide a single set up that may be
used for testing both the HT and LT motors. In an industry a number of induction motors are
used. Repair and maintenance is a routine process. After repair it is very important to test the
motor and its different parts can be tested by running the motor at different speed.
Simultaneously the starting and stopping shall not impact the supply system of the testing
section.
Most of the soft starters used in the plant does not meet the above criteria and also are having
very high failure rate. The ramp time and current limits are not variable completely as per user
requirement.
Thus there is a need of the following features in a system for testing the motors:
• Smooth starting and stopping
• Testing at any intermediate voltage
• Testing at any intermediate speed
• Fully auto control with provision of manual intervention
• Variable ramp time for start and stop
The present inventors have developed a test bench system that provides a 3 phase variable power
supply at fixed frequency with full control features for AC induction motor testing (both HT &
LT).
OBJECTS OF THE INVENTION
A basic object of the present invention is to overcome the disadvantages/drawbacks of the known
art.
Another object of the present invention is to provide an induction motor test bench system for
testing of induction motors.
Another object of the present invention is to provide a single test bench system for testing both
the LT and HT induction motors.
Another object of the present invention is to provide variable three phase voltage with fixed
frequency.
Another object of the present invention is to provide for running of motors at different speeds for
complete testing of different parts.
Another object of the present invention is to provide for variable ramp time for start and stop.
Yet another object of the present invention is to provide for full auto control with provision of
manual intervention.
These and other advantages of the present invention will become readily apparent from the
following detailed description read in conjunction with the accompanying drawings.
SUMMARY OF THE INVENTION
There is provided a system of
According to one embodiment of the present invention, there is provided
Other embodiment of the present invention provides
Yet other embodiment of the present invention provides
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The following drawings are illustrative of particular examples for enabling methods of the
present invention, are descriptive of some of the methods, and are not intended to limit the scope
of the invention. The drawings are not to scale (unless so stated) and are intended for use in
conjunction with the explanations in the following detailed description.
In the appended drawing:
Figure 1 illustrates circuits for AC voltage control.
Figure 2A & 2B illustrates principle of operation of AC voltage control.
Figure 3A & 3B illustrates power supply for test bench of AC induction motors.
Figure 4 illustrates block diagram of a test bench system.
DETAILED DESCRIPTION OF THE INVENTION
Accordingly in the present invention there is provided a test bench system where any LT motor
upto 500 KW at 415 V can be tested and any HT motor of 6.6 KV and upto 500 KW can be
tested. However any capacity of motors can be tested by suitably installing higher capacity
components.
Suitable controller and thyristor converter were designed, fabricated and assembled. At present
an analog control system with discrete components has been used. However this can be extended
to any digital control system also. To get a variable 3 phase voltage with fixed frequency the
controller has been used.
The LT supply to the motor is fed through an 415/415 V isolation transformer for reducing the
harmonics. For getting HT supply and feeding to HT motor and 415V / 6.6 KV transformers is
used. Suitable feedback system was developed for proper functioning of the test bench. The
controls has been developed in such a way that both HT and LT motors can be tested at any point
of time but one motor at a time. The total equipment was tested for full functionality test as
required by the test bench.
The system is designed keeping in mind the basic requirement and cost effectiveness. The
control of AC motors requires a drive system. A drive system essentially consists of PI regulators
to control either speed or current. PI regulators are used to control the three phase AC voltage by
suitable electrical circuits.
The system comprises varieties of modular cards sitting in a rack to meet the particular
application of an AC motor. Due to usage of large quantities of such modular card, the spares
availability has become difficult due to obsoleteness; hence asked for replacement to
microprocessor version of the industry standard for its reliability.
However after replacement of the installed systems, the discarded systems were unused and
called for such systems to be used elsewhere. As reliability of the product in sophisticated
application had called for replacement, but due to its simplicity and reparability, the system
could find its place for such application where the importance of up-time is not there. After all
due to changing of components, the system could find its place for next few decades. The present
test bench set up has been designed with such analog system. However in place of analog control
system we can use microprocessor based digital controllers also.
To design a universal system for getting a variable AC voltage with fixed frequency for above
purpose with full PI control and suitable feedbacks and protection circuits was thought upon. The
idea of variable reference, variable ramp time as per user requirement and suitable PI control in
association with automatic control could be achieved using a drive controller. This controller can
be operated in auto mode depending on the motor characteristics, based on the load change with
manual intervention if required.
As manual intervention is a must for motor test after repair, the system has to incorporate
suitable referencing and ramping circuits. All the system must have suitable feed back for
voltage and current. The output voltage is taken and converted to the controller acceptance level
for feedback and current feedback was taken through CT and converted to controller acceptance
level.
After obtaining the variable supply from the drive controller the task was to utilize for both HT
and LT motors. For LT motor supply an isolation transformer 415 V / 415 V was used after
thyristor converter for reducing the switching harmonics.
For HT motor supply one step up transformer 415 V / 6.6 KV was used. Suitable control system
was developed in such a way that in any case either LT supply or HT supply will be available for
testing. In no case both the supplies will be available simultaneously. This will ensure testing of
any one motor at a time.
Advantages:
1. Smooth starting and stopping
2. Testing at any intermediate voltage
3. Testing at any intermediate speed
4. Fully auto control with provision of manual intervention
5. Variable ramp time for start and stop
Application:
Technical: The methodology used based on analog drive system which is simple and easy to
troubleshoot. Future modifications can be carried out at ease. This kind of thyristor based test
bench is not available in steel industry. This is user friendly towards operator and maintenance
personnel. This can be suitably converted to digital control system also.
Economic: The components used in this system are very cost effective
Impact in Industry: This kind of thyristor based AC induction motor test bench will be very
much useful in other industries where the repair of motors are being taken up through own
resources.
Advancement of knowledge: The system gives an idea for operation and maintenance of a drive
system. The system imparts knowledge on motor, transformer, drive controller and harmonics.
The acquaintance in this drive system will help to maintain other drive system elsewhere in the
plant.
Additionally in the present system human safety has been improved and occurrences of hazards
are significantly reduced. The variable AC voltage is achieved through phase control by firing
the thyristors at particular instant. The pulse pattern required is to fire the six thyristors in a
particular fashion to get a chopped voltage output at supply frequency. Therefore by varying the
reference, the firing angle can be shifted to get more or less power depending on requirement.
The other requirements of ramping up and ramping down, Proportional-integral control for
voltage and current and protections are derived from the existing drive control system. Similarly
the feedback circuits were also designed to get the proper feedback keeping in mind the
characteristics of AC motor. Suitable protection features like over voltage and over current
including short circuit have been provided.
Figure 3 illustrates the entire system. The system is built up with following components:
l.MCCB
2. Drive Control System
3. Pulse transformers
4. Feed back modules for voltage and current
5. Thyristor circuit with RC network (thyristor stack)
6. Contactors
7. Isolation transformer (415 V / 415 V)
8. HT transformer (415 V/ 6.6 KV)
9. Breaker (6.6 KV)
10. Cables
11. Terminal blocks for motor connection
Principle of operation:
The power to the thyristor converter is given from of 415 V, 50 Hz system. Same supply is taken
to the power supply module for obtaining the synchronizing supply and control supplies for
operation of the deferent cards in drive system.
Normally the reference is generated through a potentiometer in the range of 0 to 10 V. However
in this case for soft starter application to start an induction motor a fixed initial reference is
applied so that motor can pick up speed. Subsequently the reference is applied in steps. If
required manual operation can be provided through potentiometer or ramping with current limit
to full speed as per ramp time. For other applications, the potentiometer control will be useful
without any fixed initial reference.
The scaled reference is processed through a voltage controller with suitable feed back. The drive
control system is the voltage controller which is also called voltage regulator. The voltage feed
back is obtained from 3 phase output voltage converted to DC and processed through a voltage
transducer to get a signal from 0 to 10 V. The PI control provides a steady state performance.
The output is processed through a current regulator as an inner loop function. Limits are
provided so that motor does not start with excessive initial starting current.
The current regulator has PI function and the output is utilized for getting firing pulse pattern for
a more precise control. The current feed back is obtained from CT converted through a
transducer to obtain 0 to 10 V signal. The firing pulses are sequenced displaced by 60 degree.
The pulse pattern is obtained with reference to the supply voltage which is otherwise termed as
synchronizing supply.
The pulses are passed through pulse transformers for isolation and thyristors are triggered. The
symmetric output waveform but chopped is obtained as output which is variable in nature
because shifted pulse pattern.
The variable output voltage so obtained in applied into LT motors and HT motors through two
different routes.
(i) For LT motor supply one isolation transformer 415 / 415 V is used. The use of transformer
has reduced the harmonics in the system and ensures smooth starting of motor without any jerk.
(ii) For HT motor supply the variable 6.6 KV supply is obtained from step up transformer 415 /
6.6 KV. One HT breaker is used at 6.6 KV side for isolation of HT system.
Suitable interlocking system has been introduced so that at any point of time either LT or HT
supply will be available for testing.
Voltage Feedback module is made of an transformer for step down the voltage from 415V to 12
V, an AC-DC rectifier for converting 12V AC to DC and an s attenuator circuit consist of
resistors for providing 10V DC to the system.
The current feedback module consists of Current transformer in two phase from where the output
current are passed in to a rectifier for converting into DC current and subsequently through a
burden resistance for getting control voltage for feedback. The block diagram is given below.
A thyristor circuit means/stack comprises plurality of thyristor means to get chopped voltages;
The exact arrangement (anti-parallel construction) is shown at Figure-1. The innovative feature
lies with the total test bench system not only thyristor stack alone. Thyristor Stack and thyristor
circuit are same.
Although the embodiments herein are described with various specific embodiments, it will be
obvious for a person skilled in the art to practice the embodiments herein with modifications.
However, all such modifications are deemed to be within the scope of the claims.
It is also to be understood that the following claims are intended to cover all of the generic and
specific features of the embodiments described herein and all the statements of the scope of the
embodiments which as a matter of language might be said to fall there between.
WE CLAIM:
1. A test bench system for complete testing of induction motors, said system comprising:
a moulded case circuit breaker for protection of the said system;
a drive control system for controlling said motors, said drive system comprising a voltage
regulator, said voltage regulator connected to a current regulator and further connected to
a firing circuit;
a pulse transformer receiving input from drive control system;
a thyristor circuit comprising a plurality of thyristors providing chopped voltage output at
supply frequency on receiving input from said pulse transformer;
an isolation transformer for giving supply to a LT induction motor;
a transformer for giving supply to a HT induction motor;
a plurality of cables for making connections in said system;
a voltage feedback module connected to a voltage regulator;
a feedback module comprising current transformer, output from said current transformer
passed to a rectifier and further passed through an attenuator providing control voltage
for feedback;
a power supply module for providing three phase output voltage, said output voltage
converted to DC and further processed through a voltage transducer;
a referencing circuit together with a ramping circuit to facilitate human intervention;
an interlocking means actuating a plurality of contactors; and
a pair of terminal box for connecting motor for testing;
wherein said system adapted to provide substantially stabilized three phase power supply
to an induction motor for testing under variable speed.
2. System as claimed in claim 1 wherein said power supply is substantially variable power
supply at fixed frequency.
3. System as claimed in claim 1 wherein said induction motors comprises both the HT and
LT motors.
4. System as claimed in claim 1 and 3 wherein said isolation transformer giving supply to
LT induction motor adapted to reduce switching harmonics.
5. System as claimed in claim 1 wherein said interlocking means adapted to selectively
provide LT or HT supply at a time thereby ensuring testing of one motor at a time.
6. A test bench system for complete testing of induction motors as herein described and
illustrated with reference to accompanying drawings.

ABSTRACT

This invention relates generally to a test bench system for motors. More particularly, the present
invention relates to an induction motor test bench system for testing of induction motors. This
system provides a stabilized three phase variable power supply to the AC induction motor for
smooth starting, stopping and functionality testing so that the complete testing of AC induction
motor can be carried out. It provides for testing of both the HT as well as LT motors.