Joined: 19 October 2002
I am seeking expertise review to identify the reason(s) for repeated alternator failure on an 11kV power plant rated for 16MVA using 12x 415V generators arranged as per the following, installed/ commissioned in two phases and operating all in parallel with necessary protection and load management system:
1) The first phase commissioned in 2010 is having 3x 3,000kVA power sources and each source consists of 2x 1,500kVA generators supplying 11kV through 1x Synchronizing panel, 1x 3,000kVA, 415V/ 11,000V (D/Y) transformer, 1x neutral grounding resistor (NGR) and 1x Ring Main Unit (RMU)
2) The second phase commissioned in 2012 is having 2x 3,000kVA power sources and each source consists of 3x 1,250kVA generators supplying 11kV through 1x Synchronizing panel, 1x 3,000kVA, 415V/ 11,000V (D/Y) transformer, 1x neutral grounding resistor (NGR) and 1x Ring Main Unit (RMU)
3) All 5x power sources are connected for parallel operation through the RMU with MICOM protection relay for over current, short circuit and ground fault
4) All 12x generators are provided with synchronizing and load sharing controllers (DEEPSEA 7510) for automatic load management (start/ stop based on power demand) with protection for over current (110%), short circuit current (300%) and reverse power (5%).
The first phase (3x 3,000kVA) installed 3years ago and operated over 8,000 hours is working without any problem, but second phase source (2x 3,000kVA) installed two years ago is having repeated alternator failures (different brand from the first source)
- The generators # 2 & 6 subjected heavy flash over in the generator terminal box after 4months from commissioning (Jul/2012) without any apparent reasons. Manufacturer/ dealer is informed, but couldn't identify the reason and repaired suspecting less clearance between the bus bar though it is same on all sets.
- Generator # 6 is failed again after 10 months of operation (May/2013) due to main rotor (low insulation resistance), exciter stator (brunt), droop transformer (burnt) and AVR (faulty). Manufacturer/ dealer is been informed, but couldn't identify the reason and supplied replacement components after suspecting/ blaming overload, unbalanced load, maintenance, tropical weather etc. though there is no chance for overload, unbalance load and maintenance and weather conditions are common for all sets.
- Generator # 5 is failed after 17 months of operation (Aug/2013) due to low insulation resistance of main rotor and defective AVR. It became okay, as we dried the rotor and replaced the AVR
- The generator # 2 is failed again after 13months of operation (Aug/ 2013) due to main rotor (low insulation). As usual, the manufacturer is suspecting the overload, unbalanced load, maintenance and weather conditions, though it is noticed that there are trace of melting insulation (silicon like material), brittle of rubber tape insulation (common on other sets which are still working) and one of the coil is open circuited as the strip type winding wire for about 20cm is missing (It seems one end is cracked and the other end is tear off)