1. SC A1 ROTATING ELECTRICAL MACHINES PS2 LIFE MANAGEMENT OF GENERATORS
Refurbishment, Replacement, Power up-rating and Improvements
TREND FOR STATIC EXCITATION SYSTEMS IN LARGE THERMAL GENERATORS
D. K.CHATURVEDI
NTPC LIMITED, INDIA
Background
This paper summarizes problems with the reliability of brushless excitation system based on operating
experience in Indian power plants
Its focus is on the huge Generation loss to address any repair on exciter rotor.
Dependency of user on OEM for arranging spares during emergency.
TG deck extension cost is more than complete excitation system cost.
Performance advantages of Static Excitation System
Absence of rotating exciter - High Initial response
Improved performance during transients & load throw-offs
Great impact of PSS to the transient stability
Elimination of rotating parts -reduced operating cost
High reliability & availability
Hardware with Power Electronic can be subjected to high mechanical stress
BRUSHLESS NEEDS LONG TG DECK
SC A SESSION
Attribute
Static excitation system
Brushless excitation system
Remarks 01
Response
Very fast acting -
Response Ratio 3-5
Slower response
Response Ratio ~2
Critical for System Stability 02
Components
on rotor
Very few
large number of components on rotor: diodes, fuses, flexible CONNECTION, PMG, exciter
component failures in Brushless causes long outages 03
TG Deck
SMALL
LONG
deck cost is higher in Brushless 04
Transfer of current through brushes
brush-gear slip-ring assembly
No such requirement
Available brush-gear are now reliable 05
Machine rating
large Generators and Hydro generators
Generally for small Generators
brushless is not recommended for remote hydro Generators 06
Energy Saving
Lower losses
Higher Losses
Estimated difference 230kW for a 500MW machine 07
Field discharge
Fast
slow As Exciter is Involved
Fault is fed for longer time in BLE. 08
Outage & Failure experience
Very few failures
Large number of failures
Equipment down time is very high in BLE
BRUSHLESS EXCITER FAILURES
BRUSHLESS EXCITER ROTOR