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Generators / Stamford Generator with low voltage
« on: March 03, 2013, 12:13:16 PM »
I have a Lister TR2 with a Stamford BC164 Generator. It is wired in zigzag for 240 Volt single phase. Trouble is it will not put out anywhere near the correct voltage. I bought this cheap secondhand knowing the generator is faulty but I have no history on it as the guy I got off was selling for a friend who bought it at an auction.
So far I have found the main field to be burnt out and the SX460 AVR was putting out 160 volts continuously into the exciter field. The field has been rewound and I have a new AVR but still not getting correct output. I have been through all the checks in the Stamford service manual. I bought a Megger Meter and checked insulation following the manual. As per the manual with a 12 Volt battery connected to the exciter field I am only getting around 120 volts with no load it should be within 10% of 240 volts. Voltage is = across all windings, I set it up as 3 phase and get 123 volts from neutral to each of the 3 phases. This being consistent and all resistances are correct the stator should not be faulty. Exciter field is 19 ohms as it should be and I measured the resistance of the exciter rotor and it also has equal and within range resistances. I have tested the diodes and they all measure correctly with a multimeter.
I have followed the manual to the letter and still getting low voltage. The only thing I can think is there is a problem with the diodes under load. The field components of the generator have obviously been stressed as the field was burnt put and the AVR putting out 160 volts when it is supposed to have a range up to 90 volts. I tested this by connecting 240 volts mains to the AVR input and measured the output.
Checks that I have done are
Engine speed is correct I can measure 53 HZ at the generator with no load and the under speed LED on the AVR is going off.
Stator is good according to the tests in the manual
Exciter Field " "
Exciter Rotor " "
Diodes " "
Main field has been rewound and measure correctly
I have checked and rechecked the wiring of the Stator terminals and it is correct, also I rewired it to 3 phase and had the same low voltage issue. In Zigzag wiring I am using terminals U and W and getting around 120 Volts.
Is there anybody that has had a similar problem that can shed some light on this before I take it to a rewinder to diagnose that it !
So far I have found the main field to be burnt out and the SX460 AVR was putting out 160 volts continuously into the exciter field. The field has been rewound and I have a new AVR but still not getting correct output. I have been through all the checks in the Stamford service manual. I bought a Megger Meter and checked insulation following the manual. As per the manual with a 12 Volt battery connected to the exciter field I am only getting around 120 volts with no load it should be within 10% of 240 volts. Voltage is = across all windings, I set it up as 3 phase and get 123 volts from neutral to each of the 3 phases. This being consistent and all resistances are correct the stator should not be faulty. Exciter field is 19 ohms as it should be and I measured the resistance of the exciter rotor and it also has equal and within range resistances. I have tested the diodes and they all measure correctly with a multimeter.
I have followed the manual to the letter and still getting low voltage. The only thing I can think is there is a problem with the diodes under load. The field components of the generator have obviously been stressed as the field was burnt put and the AVR putting out 160 volts when it is supposed to have a range up to 90 volts. I tested this by connecting 240 volts mains to the AVR input and measured the output.
Checks that I have done are
Engine speed is correct I can measure 53 HZ at the generator with no load and the under speed LED on the AVR is going off.
Stator is good according to the tests in the manual
Exciter Field " "
Exciter Rotor " "
Diodes " "
Main field has been rewound and measure correctly
I have checked and rechecked the wiring of the Stator terminals and it is correct, also I rewired it to 3 phase and had the same low voltage issue. In Zigzag wiring I am using terminals U and W and getting around 120 Volts.
Is there anybody that has had a similar problem that can shed some light on this before I take it to a rewinder to diagnose that it !