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Electrical Machine Repair Plant Mumbai

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1. INTRODUCTION

2.  ACTIVITY PROFILE

3. CAPABILITIES  OF  SERVICING & RENOVATION

4.SPECIAL FACILITIES AVAILABLE

5. MAJOR JOBS CARRIED OUT

 

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Repair / Reconditioning Of Electrical Machines

1.  INTRODUCTION

BHEL is the largest manufacturer of rotating electrical machines in the country, and has established itself as an industry leader. There are approximately about 30,000 BHEL make HT machines all across the country in various industries and power plants. Since nineties, BHEL has been adding about 1000 HT machines per year to this population of machines.

Rotating electrical machines of various types and ratings are required for the operation of any industrial plant or power plant. Failure or breakdown of a rotating electrical machine can occur for various reasons at any time during the life of the machine. For any plant, the cost of downtime as a result of failure or breakdown of an electrical machine would be enormous. The costs of replacement of these machines often used for very critical operations, are quite exorbitant and the process of procurement very cumbersome. So, most of the times, the industry/power plant goes in for repair/reconditioning of their old machines.

At this critical juncture, BHEL, Electrical Machines Repair Plant (EMRP) steps in to cater to this need of the industry. The technological expertise of BHEL as the premier manufacturer of electrical machines in India is available to the industry through EMRP.

Phase I of this unit of BHEL was set up in 1978 to cater to repair and maintenance of traction machines for the Indian Railways. With time, Railways developed in-house facilities for repair of traction machines. Consequently, Phase II of EMRP’s operations was launched.

During Phase II, EMRP developed facilities for industrial machines, from coil manufacturing to total service of industrial rotating machines, and the product profile expanded to include large and medium range industrial machines, mini/midi hydro generators. EMRP has successfully revamped many machines. Over the years, EMRP has evolved into a Unit that is capable of offering total service to various industries for all types of rotating electrical machines.

In India, when any industrial plant or power plant is set up, the rotating electrical machines required for the operation of the plant are procured from various companies from all over the world. EMRP has developed the capability to repair rotating electrical machines of both BHEL and non-BHEL make having technology of the sixties or technology of the nineties. In short, EMRP uses “Tomorrow's technology in Yesterday's equipment”. In most cases of imported, non-BHEL or very old machines, technical details / drawings are often not available.  Moreover, the technology and the insulating material used in very old machines have by now become obsolete. BHEL’s EMRP has developed the technical expertise in using Reverse Engineering techniques for designing and manufacturing windings and components of these old and not-so-old non-BHEL machines.

 

2. ACTIVITY PROFILE

 A. Assessment of Fault - When a machine is received at EMRP, a series of tests and measurements,as follows, are carried out to assess the nature of fault and the extent of damage to the machine:

Visual inspection of machine: Electric motors are normally received in assembled form. Sometimes only the damaged stator or rotor or armature is received. So, as a first step in the process of repair a record of the condition of the stator, rotor and assembly components of the machine is made.

Electrical Test on stator/rotor like IR & PI measurement, winding resistance, impedance measurement and core flux test. Drop test and if required bar to bar test on DC armature/commutator

Mechanical tests on rotor like run-out check of the shaft, dye penetration test and ultrasound test

B. Determination the method of Repair/Reconditioning
After assessment of fault that has occurred in the machine, it can be designated as either mechanical or electrical. Most of the times, mechanical faults would result in an electrical failure of the machine. Sometimes electrical faults also cause mechanical damage to the machine.

The next step after the assessment of the fault and the extent of ensuing damage on the various parts of the machine is to decide about the modus operandi to be followed for refurbishing the machine.  The method of repair to be done depends on the type of fault that has occurred on the machine.

The repair/reconditioning of electric machines done at EMRP can be broadly categorised as presented in Table-I.

 TABLE-I

TYPES OF MECHANICAL & ELECTRCIAL REPAIR JOB CARRIED OUT

Type of Fault

Type of Repair

Mechanical

Breaking of shaft

Bearing seizure

 

Breaking of  rotor bar

Hot spots of core

Breaking or wearing out of assembly components

Reshafting

Change of bearing and repair/replacement of bearing housing components

Recaging

Restaggering of core / Electro-chemical cleaning

Repair / replacement of the damaged component

Electrical

Insulation flash-over

Inter-turn fault

Cable flash-over

Commutator

Inter-turn short in field coils

Change / repair of winding

Change of winding

Cable replacement

Commutator rebuilding using old parts

Replacement/Re-insulation of the field coils depending upon the fault

 

 

C.Designing of Winding/Shaft/Assembly Components using REVERSE ENGINEERING TECHNIQUES for non-BHEL Machines

Reverse Engineering Technique is the process of generating detailed    manufacturing drawings/details of a sub-assembly from the final equipment/ component.

The standard engineering practices of designing an equipment is by first designing all the sub-assemblies of the component and then integrating all the sub-assemblies to form the final equipment/component. The dimensions and the mechanical and electrical properties of every component that forms the part of the sub-assembly of the equipment determine the dimensions and properties of the subsequent major assembly.

Reverse engineering is required when we have to work backwards from the complete machine. Any damaged component or winding has to be designed to suit the original machine frame. The liberties available to a designer of new machines are not available while trying to retrofit an old or damaged machine. Often the techniques and material used in the old machines are now obsolete. So the components have to be designed within the constraints of the old machine for the present-day techniques and materials.

The method of reverse engineering can be elaborated as

(a) Detailed dimensioning of the machine
(b) Cross-checking the dimension by suitable means
(c) Detailed dimensioning of the component to be redesigned
     (in case the item is broken or sheared, as many
     dimensions as possible)
(d) Conducting tests to evaluate the material characteristics of
     the component
(e) Design and preparation of drawings for the new component
(f)  Checking the fitting of the new component  with its
     matching components
(g) Deciding on the technology and system to be used for
     manufacturing the component

The design details/drawings required for the repair of the non-BHEL machine are developed using Reverse Engineering Techniques.

D.   Quality Control During Various Stages Of Repair/Manufacture of Winding/Damaged Components

EMRP has firmly established quality management system that ensures that quality control checks are done during various stages of repair. After completing the repairs, the machines are subjected to proof testing and routine testing to prove the soundness of the repaired/reconditioned machine.

The quality checks are based on International/National/BHEL standards. BHEL standards are generally based on International/National standards. But in crucial areas, the internal standards followed by BHEL are more stringent than the corresponding International/National standards. A computerised databank of the results of quality checks are maintained for records and future references.

Some of the checks done as per Quality Assurance Plan during different stages of repair are:

arrow.gif (123 bytes) During coil manufacture and coil assembly

 (a) Dimensional and specified checks of incoming raw material
     such as copper conductor, insulating materials & tooling
     etc.
(b) Dimensional and configuration check of coil stacks.
(c) Inter-turn testing of coil stacks.
(d)Corona resistance measurements (above 5 kV rated
     machines).
(e) Tan-d measurements of coils.
(f) High voltage proof test on 100% of all coils for slot
    insulation and overhang insulation.
(g)Inter-turn testing on 100 % of finished coils.
(h)During rewinding, AC HV test on the coils after wedging as
    they are being assembled.
(i) Inter-turn test on all coils after assembly but before making
    series connections.

arrow.gif (123 bytes) After completion of rewinding/repairs/ reconditioning of High voltage 3-phase
    Induction motors
(a)                IR / PI measurements by motorized megger.
(b)               Inter-turn test on stator windings.
(c)                AC HV test on windings to earth as per relevant
         standards.
(d)               Winding resistance of stator (& rotor wherever
         applicable).
(e)                Checking of RTD / BTD / Heaters resistance & IR
          values.
(f)                 No load run of the machine.
(g)                Vibration measurements on the motor during no load
          run.
(h)                Bearing / winding temperature measurements during no
         load run.
(i)                  Tan delta test on wound stator  (Optional).
(j)                 Turns ratio test (for wound rotor only).

arrow.gif (123 bytes)After completion of repairs/reconditioning of DC machines
(a)                IR measurements of armature, main pole and inter-pole
         coils.
(b)               Winding resistance / impedance tests main pole and
         inter-pole coils.
(c)                Milli-volt drop test on armature.
(d)               Neutral axis checking / setting.
(e)               AC HV test on armature, main pole and inter-pole coils.
(f)                 No load run of the machine.
(g)               Vibration measurements on the motor during no load
         run.
(h)                Bearing temperature measurements during no load run.

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3.        Capabilities For Servicing And Renovation Of Rotating Electrical Machines

 

BHEL’s EMRP has full-fledged capabilities for servicing, repairing and renovation of rotating electrical machines of all capacities and voltage ratings.  Brief details of the same are given in Table-II.

TABLE-II

SERVICING AND RENOVATION CAPABILITY

S.No

Description

AC Machines

DC Motor/ Generator

SCIM

SRIM

Sync. Motor/ Generator

1.     

Overhauling of motor

b

b

b

b

2.     

Diagnostic testing of motor

b

b

b

b

3.     

Manufacture of stator coils

b

b

b

 

4.     

Rewinding of stator

b