SMART MAINTANENCE OF ELECTRICAL MACHINES

SMART MAINTANENCE OF ELECTRICAL MACHINES

ABSTRACT

  Maintenance of the electrical machines is one of the most important aspects in the power sector. As the technology is growing correspondingly the demand for the power is also growing which results in the increased number of generating stations, distribution stations etc...

Conventional methods of protection and maintenance are not certain, moreover they takes long operating time. If faults are undetected, it can lead to overheating along with catastrophic electrical failure. These events typically require extensive repairs with an extended shutdown of the machine. It is highly desirable to detect such faults at an early or incipient stage so that remedial action can be taken before a complete failure occurs. With the advancement in the power electronic, embedded controllers and sensor technology there is tremendous revolution in the field of electrical maintenance. This paper brings to fore the various methods of electric machine maintenance and various ways of protection of machines against overloads and fault condition in a smart way.

Introduction

 The maintenance of the electric machine is of top most priority in the electrical power sector. The electrical power sector can be broadly classified into generation & transmission sector and distribution sector. The large machines used in the generation sector are “alternators”, transformers and various kinds of induction motors are in many of the industries. If these machines are not properly monitored it may lead to the poor performance of the machines which is highly undesirable. Electrical machines are used in every industry in one or the other way like “Boilers” , “air handlers” , “pumps” , and “cooling towers” etc…  

The care taken to ensure the proper working of these of the electrical machine is referred as “Electrical Machine Maintenance”. our main objective in this paper is bring out smart maintenance technique for electrical machineries which reduces the errors and maximize the performance of the machine. We are introducing an automatic fault detection and semi-automatic fault correction system. This system uses GSM technology for intimating the faulty condition to the operator via SMS. By adopting this system we can achieve better maintenance and best productivity.

 Large electrical machine 

Electrical machines are majorly classified as follows:

The large electrical machines which are used in the power generation sector and industrial sector are alternator and induction motors.

 

Large Alternators

Turbo – generator of 250 MVA

Need for maintenance:

 The care and precautions what we take in order to make sure the optimal working of the machine is basically refer as   maintenance.

In the electrical machines the major faults are:

•         Overheating of machine winding.
•         Large vibration of the machine.
•         Misalignment of shafts.
•        Storage of large machines.

For the better operation of the electrical machine, we need to reduce these faults to a maximum extent which will improve the performance of the machine. Optimally maintenance of electrical machines will reduces the losses and hence the over process of production will be economical.

Types of maintenance:

Pre- operative maintenance:

This type of maintenance is done when the machine is brought the customer site. Some of the activities of pre-operative maintenance are:

•         Visual inspection.
•         Cleaning and blowing dry air.
•         Checking air gap, bearing.
•         Measurement of insulation resistance.

Preventive maintenance or operative maintenance:

This type of maintenance is done when the machine is operating condition. Some of the activities of preventive maintenance are:

•           Maintenance of cooling system.
•        Measuring vibrations.
•           Misalignment of the shafts.
•           Checking for the unbalance voltage.

1.                   Maintenance of cooling system:

Overheating of the electrical machine windings is one of the serious issue in maintenance. the various causes for the generation of heat in the windings are:

•        Over loading the machine.
•        Short circuit.
•        Running the machine for the long time.

Cooling system can be broadly classified into two categories

 a) Natural cooling.                 b) Forced cooling.

Usually for the large machines the cooling system preferred is “forced cooling” which consist of the air cooling or water cooling or any liquid as coolant medium, which will be  passed through the cooling ducts manually whenever necessary.

       i.            2.               Measuring of vibrations:

     Whenever the machine is installed on the working site it should be properly bolted to minimize the vibrations. Usually due to aging or some wear and tear the nuts and bolts of the machine may become loose which may lead to huge vibration and cause inconvenience sometime it may also cause disaster.  In the preventive maintenance schedule vibration check is done half yearly once.

                     3.           Checking the unbalance voltage:

         Almost all large electric machines are polyphase machines, when there is unbalance voltage or single phase operation of polyphase machine may cause excessive overheating. It requires only a slight unbalance voltage applied to polyphase machine to cause large unbalance currents and results in overheating and ultimately failure of the machine. In such case the power supply should be checked and corrected even if there is slight unbalance is found.

 

 Smart maintenance of electrical machines:

 In the previous section we have seen the different maintenance schedule and their operations. We are introducing a semi-automated maintenance system. This uses the following components and equipment:

•      Sensors.
•      Embedded controllers.
•      GSM module.
•      Unbalance detection circuit.  

Sensors:

The sensors which are used in this system are:

         1.      Temperature sensor  ( sensitive thermo-couple):

          A thermocouple consists of two dissimilar conductors in contact, which produces a voltage when heated. The size of the voltage is dependent on the difference of temperature of the junction to other parts of the circuit.   

                                  Highly sensitive Thermocouple

          2.       Vibration sensor:

The vibration sensor is an electro-mechanical transducer works on principle of piezoelectric effect, which converts the vibrational energy into corresponding electric voltage.

Embedded controller:  (AT mega16 microcontroller)

Microcontrollers can sever as brain to electro-mechanical system. It can be programmed interact with the hardware of the system and also with user. The AT mega16 microcontrollers used here has 40 pin DIP package, Analog to Digital converters, high speed timers and counters, and serial communication ports etc…  The pin out diagram of AT mega16 is as shown below.

    3.     GSM modem:

GSM modem is a wireless modem that works with the gsm wireless network. Sim 300 GSM modem is used for this system which is designed with power saving technique. The sim300 is integrated with the TCP/IP protocols, AT commands are developed to use these protocols which are very helpful for data transfer.

                       GSM  modem

Various AT (attention) commands are:

·         AT+CMGW                // write a message to memory.

·         AT+CMGS                 // send a message.

·         AT+CMSS                  // send a message from memory.

·         AT+CMGF =1                        // set the message mode to normal testing mode.

Unbalance detection circuit:

The transformer steps down the 230v ac voltage to corresponding 5-0-5  v  compatible with the TTL circuits corresponding to each phase. These low power sinusoidal signals are then half wave rectified to obtain only positive peak of cycle. Now in order to convert sinusoidal to square pulses, analog comparator LM324 is used with the negative threshold is set using 10k pot such that the output duty cycle is 33% of each phase. The purpose of conversion of 33% duty cycle for each phase because of the fact that each Phase in 3 phase supply differs with a phase difference of 120º.

Balanced voltage supply:

The typical logic of XOR gate is such that the output is logic high whenever the three inputs are exactly 33% duty cycle indicating the high average value in turn means all three phases are exactly differed by 120º.

Unbalanced voltage supply:

Considering the phase error with  overlapping and non-overlapping pulses,  the output will be a pulsed waveform  indicating the lesser  average value. The principle behind obtaining the pulsed waveform is that whenever any of the two inputs are logic high or logic low at same instant, then output will be logic low. Thus the error in phase is detected.

Block diagram:

Working principle:

The block diagram of the smart maintenance system is as shown. The temperature sensor is mounted on the machine outer body such that it form a part of the machine winding and the vibration sensor is mounted on the foot of the machine basement. All the output of the sensors is interfaced to the microcontroller. The microcontroller is connected to the gsm module. When the machine is powered up the unbalanced voltage detector circuit detects any unbalance in the voltage or phase error. If any phase error exists then the microcontroller operates the relay and disconnects the machine from the main supply. Whenever the temperature raise of the machine windings is beyond the permissible limits then the temperature sensor send a signal to the microcontroller, in turn the microcontroller activates the cooling system available for the machine when the machine attains the ambient temperature then the cooling system is automatically deactivated. Due to any negative sequence or any mechanical imbalance the vibration in the machine increased to a high value then a signal is recorded at the microcontroller. The microcontroller buzzes an alarm and intimates the operator.

All the imbalance or fault conditions are automatically monitored and controlled. With the help of the GSM modem the faulty condition is intimated to the operator via an SMS and the operator has the flexibility to operate the maintenance unit form the remote place.

Advantages:

          ·         The system modernizes the maintenance of electrical machines.

          ·         Early detection of faults

          ·         Performances of the machine will be improved.

          ·         Reliable.

Load Specifications:

3phase, 415-440v, 8-11A, 50hz, 3.7kw, 1-5HP, 1440rpm

Limitations:

       ·         Initial cost of installation is quite high.

Conclusion:

Maintenance is very essential for any electrical machine. By adopting the automation will yield in better result and the performance and efficiency of the machine is improved. This system enables us to detect the fault at the earliest and hence better protection and maintenance can be achieved.