Download Steam turbine anti-motoring (reverse power) Rotor damage risk

TechC@RE machinery breakdown
EXPERIENCE FEEDBACK
Steam turbine anti-motoring (reverse power)
Rotor damage risk
Return of power
Mechanical repair
of steam turbine
Start of
acceptance test
Black out
on public network
Turbine running
as a synchronous
motor
15 days
5 days
2 hours
20 minutes
Mechanical
damage to turbine
Breakdown duration: 1 month
Steam turbine are used to drive synchronous alternators for electricity production.
TURBINE
DAMAGE TO TURBINE
GENERATOR
GENERATOR
ELECTRICAL CURRENT
ELECTRICAL CURRENT
Motoring can happen when a turbine’s steam supply is lost whilst the generator is still coupled to a
network (or operated in parallel with another generator). The generator will then become a synchronous
motor and will actually drive the steam turbine with the potential for significant mechanical damage.
A reverse power protection device should be inserted within the generator protection scheme, in
compliance with Institute of Electrical and Electronics Engineers standard IEEE C37.102-2006 – Guide
for AC Generator Protection (Section 4.5.5).
This document is © AXA Matrix RC – March 2015Version
For further information or specific questions contact: [email protected]
Steam turbine anti-motoring
EXPERIENCE
FEEDBACK
Facts
1. A large paper mill has a steam turbo-generator connected to the public network
or can be operated in island mode.
2. In order to increase its power output, the steam turbo-generator was refurbished/
upgraded in 2012.
3. T he upgrade focused on mechanical components, as the electrical components
were overhauled/ upgraded some years earlier by another contractor.
4. During re-commissioning; the sequence of power disconnection and power
reconnection to the public network induced motoring of the steam turbine.
Total loss amount: several millions euros (shaft, bearings, blades, packing seals)
Main causes
Lack of bearings lubrication causing
significant wear/vibration to rotor
shaft and thermal stresses
Generator running as
synchronous motor
Client agreement
on testing without
environment analysis
Lack of formalized procedures
for testing protection systems on
re-start up/commissioning.
Aggravating factors
Operator waited more than 15 minutes before calling an electrical technician
to open the main generator breaker.
Lack of a dedicated electrical technician during the commissioning/test
procedures.
Suggested recommendations
Annual testing of reverse power (anti-motoring) protection.
It should provide backup for sequential tripping schemes.
Control the presence of safety chains, test safety valves, surge
valves on steam supply, pressure/ level devices on lubrication
system, bearing temperature, over speed protection, vibration
monitoring, earth fault, loss of field, over voltage/current
instrumentation, including anti-motoring. Annual testing and
calibration is recommended.
Operators should be trained on identifying generator motoring
conditions and on subsequent shutdown/isolation procedures.
This document is © AXA Matrix RC – March 2015Version
For further information or specific questions contact: [email protected]
oxygenemultimedia.fr - Photos : Shutterstock, © 2000 Geothermal Education Office, NRC
Failure of protection
relay on anti-motoring
chain (partially wired)