ELECTRIC MACHINES

Automatic Voltage Regulator (AVR) is one of the main component of an Alternator. Main functions of AVR is to built-up the rated voltage and maintain the output voltage within the limit at no-load and on-load conditions. There will not be any output or abnormal output when an AVR fails. What are to be checked before replacing an AVR Disconnect the  AVR. Then check all windings of alternator for continuity and insulation resistance. If any defect is found then rectify it. Never replace the AVR if any winding is having a very low IR value or winding is defective. Connect the AVR after rectifying the defect and then start the machine. If there is no output voltage go to step 2. Check the condition of diodes in RRA. If found defective then replace the defective diode of Rotating Rectifier Assembly (RRA). Start the DG Set. If alternator does not develop  voltage go to step 3. Then run the alternator at idle speed without connecting AVR and note the output voltage. The output volta...

Kerala Electrical & Allied Engineering Company Ltd (KEL) is a Public Sector Undertaken company fully owned by government of Kerala. Their main products are Alternators and Transformers. All alternators manufactured by KEL (in collaboration with Leroy Somer, France) are of Brush Less Excitation type. In lower rantings (<100kVA) no electronic regulator (AVR) is required to regulate the output voltage. In this type of alternator the voltage is build up and regulated with compound excitation system. In higher rating compound excitation & electronic voltage regulators are used to regulate the output voltage. This dual regulation gives high reliability. In this type of alternator one advantage is that we can operate the machine even after an AVR failure. With AVR we will get a 2% voltage regulation and in the second mode it will be 5%. The alternator manufacturing division of KEL is situated in Kasaragod district of Kerala. The above picture shows the regulating part of a KEL ...

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...