10 December 2010

Elgi Electric Alternator & AVR Circuit

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 alternator.

The AVR has SIX connections. One pair (X1 & X2) gives input supply to the AVR from the Auxiliary winding. There is a 6.3A, 240V Fast blow 20mm glass fuse in the input section of the AVR. The DC out put from the AVR to the exciter field coils are available at (E+) & (E-) terminals of the AVR. There 3 voltage selection in sensing side of AVR. 0-110V, 0-220V, 0-415V. The normal selection is 0-415V. These terminals are connected to the V & W (Y & B) phase output terminals of alternator. The following figure shows the wiring diagram on Elgi Electric make Alternator and AVR. Earlier there was SIX lead out alternators but the last alternators were of 4 leads. The stator winding was internally STAR connected and common neutral was taken out.
There are Potentiometers for adjusting Output Voltage (P1), Voltage Stability (P2), Under Frequency cut-off (P3), Voltage Droop for parallel operation (with out Current Transformer) (P4), Quadrature Droop for parallel operation (with current transformer) (P5), Excitation Current Limit (P6). All these POT other than P1 and Droop setting are factory set. We can also connect an external potentiometer (470 Ohms, 3Watts) at LINK1 for adjusting the output voltage. AVR used in all type of Elgi Alternators (20kVA to 380kVA Brush-less) are the same. 

If we are not getting normal output from the alternator then it is very easy to check whether there is any fault with the alternator winding. Check all winding for any grounding and continuity. For this first remove the outgoing cable from the alternator. Check each winding including auxiliary winding and exciter field winding. If it shows healthy then   remove the F6.3A glass fuse from the AVR. Start DG. Check voltages at output terminals of Alternator and X1X2 terminals at AVR. For a good alternator we should get a balance output of  around 100V at alternator terminals between phase and 10V at X1X2 leads. If it is OK then the fault will be with AVR. If we are not getting balance output at alternator terminals then the there can be a winding failure. If we are getting very low output (2V or less than 10V) then the fault will be with exciter armature, RRA or main field.

09 December 2010

Kirloskar AVR KAVR-1 Circuit Diagram

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 maintain the output voltage with in the limit (for brush-less alternators it is 1% from full load to no-load) at 3% variation in frequency. If engine speed goes bellow 1440rpm (i.e. 48Hz) AVR will stop functioning and will reduce the output voltage. This is done to protect the exciter field, exciter armature and main field windings. At low speed the magnetic flux required to maintain the output voltage will be more and for that more current is required to flow through these windings. It will also reduce the alternator efficiency. Normally FRO (P2) is set at factory and need not be to disturbed.

Voltage Stability Pot (P3) is used to stabilize the output voltage in case there  is a fluctuation of voltage at no-load. On-load fluctuation can be of many reasons like fluctuating prime mover, fluctuating load, high percentage of non-linear load. STAB (P3) is also factory set and need not be disturbed at site.