ELECTRIC MACHINES

Most of the induction motors that we use are Squirrel Cage Induction (SCI) Motor. This name comes from the shape of the rotor. Some motors copper bars / round conductors are inserted in to the slots and they are short at both ends with end ring. Some other motor rotors are aluminium die-cast type. In both cases the shape of the rotor looks likes that of a Squirrel’s cage. One of the common complaints that we receive on SCI Rotor is broken copper bars or open die-casting. The main indication of a defective SCI Rotor is that motor does not take load. Most often the no-load current drawn by the motor will be same as that by a good motor. But in Some cases fluctuating current is also seen. There will magnetic noise & excessive vibration while running the rotor. The above figure is of a defective SCI Rotor. This rotor is aluminium die-cast type. The above picture shows a more clear view of the defective part of rotor. We can see open aluminium casting on slot. Melted aluminium has ...

Trident Powercraft Pvt Limited (TPPL) is a Bangalore based company manufacturing AC Generators (Alternators), DC Motors and Wind Generators. They have two manufacturing units one at Bangalore and the second at Hubly both in Karnataka. Main customer of TPPL is Kirloskar Oil Engines Limited (KOEL). Most of the Kirloskar Green DG sets available are manufactured with KOEL engines and TPPL Alternators. TPPL also do business with Ashok Leyland Limited and Mahindra Powerol In 2009 Emerson acquired TPPL for Leroy Somer Power Generation . Here I am sharing some informations regarding TAVR 20 used in alternators under 125kVA manufactured by TPPL. TAVR 20 has 6 terminals. This AVR can be used in both single phase and three phase alternators. When used in a single phase alternator short the terminals  N & N1 of AVR. Then connect output phase to U and output neutral to N of AVR. Also connect F1 and F2 leads from the exciter field to the respective terminals of AVR. There will be no con...

Commutator is an essential part of a DC Motor. DC Supply to the Armature of a DC Motor is fed through Carbon Brushes and Commutator. The most common fault observed in DC Motor is sparking of Commutator. The below video shows sparking from a commutator. The common reason for spark from commutator is improper brush contact. This can be due to  Defective brush holder,  Worn out carbon brushes,  Uneven condition of commutator.  Defective armature winding The sparking create pitting of commutator and as we operate the motor spark will increase and will seriously damage commutator.  Spark will make carbon brush burn and it will worn out very fast. The below picture shown damage to the commutator of above motor. Here the segments are worn out at particular (at the place of carbon brushes) part of commutator.  That create sparking. It can be rectified by polishing the commutator. Every time after polishing the commutator it should be ensured that proper unde...

Elgi Electric & Industries Ltd manufactures alternators in technical collaboration with Guinault France. There was 20kVA to 380kVA Alternators available. Now Elgi Electric has stopped production of Alternators and they are more concentrating in AC Motors and DC Motors. Sara Elgi is a group of companies from Textiles, Software, Building etc. The following figure shows a schematic diagram of Elgi Electric make Alternator. There are five windings in Elgi alternators. Exciter Field, Exciter Armature, Main Field, Main Armature, Auxiliary Winding. The Auxiliary Winding is wound over the Main Armature (Stator). This winding gives 40V, 6A AC supply for AVR. Exciter Field is also fitted with Permanent Magnets. This will avoid break down of alternator due to loss of residual magnetism. Due to the permanent magnets there will be around 100V output between phase without AVR. If alternator does not produce 80 to 100V at rated speed with out AVR we can suspect any internal fault with the alte...

  The above diagram shown connection of Kirloskar AVR model KAVR-1. This type of AVR is used in some brush-less alternators manufactured by Kirloskar Electric Company Ltd . This is a single phase sensing AVR. Sensing voltage and working voltage are taken from the main armature (output supply) of the alternator. This is not recommended for unbalanced load. As the AVR is is sensing only the voltage of one phase regulation will not be proper for unbalanced load. Most of the AVR are two phase sensing were as there are some three phase sensing AVR also available. This AVR was used in smaller alternators. Now it is replaced with KAVR-2 which is two phase sensing. This AVR has 3 multy tern potentiometers that are used to adjust the output voltage (P1) Under frequency cut-off (frequency roll off) (P2) and Voltage Stability (P3) By Adjusting P1 clockwise we can increase the output voltage and counterclockwise adjustment of P1 will decrease the output voltage.  AVR is supposed to main...

Many of you may have heard about rewinding a motor. It is necessary to rewind a motor when its winding get defective. It happen in many ways. But the common fault is burning of winding due to insulation failure or overload. Here I am trying to explain the rewinding process of a slip-ring induction motor. This is a 435kW induction motor rotor. This is the rotor that we are going to rewind. All the coils are removed from the slots and it is cleaned. After that two coats of red varnish is applied. This is to improve the insulation resistance value and to protect core from corrosion. After all the above process the rotor looks as above. Now it has a pleasing look. Now the next part start. The above picture shows the winding overhang support. It is insulated using Fibre Glass tape. This has to be before starting rewinding. Now we are going to make the coils. Here we are using annealed copper strips of electrical grade for making rotor coils. These strips in various size comes in spools and...

Here is a 3 phase alternator stator winding. This winding was burnt due to overload in one phase. We can clearly see all coils of a phase winding is overheated and blackened. Normally this type of winding failure do not get warranty repair.