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Overspeed Protection
for Turbines
CTo
A reliable overspeed protection system is indispensible
for turbomachinery. For gas and steam turbines, this
means reliable detection of over-speed and immediate
closing of the trip valve in response.
The Voith CTo overspeed protection system provides both
functions in a single device. An electronic monitoring unit
detects overspeed and an electrohydraulic assembly ac-
tuates the trip valve immediately.
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All the world‘s our home
We are a reliable partner to manufacturers and operators
of turbomachinery in all international markets. Voith control
technology has proven its value in tens of thousands of
applications in power plants around the world and ensures
economical, reliable operation of gas turbines, steam
turbines and compressors.
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Benefits
• Compact design
• Direct mounting onto the actuating mechanism of the trip
valve on the turbine
• No space required in the control cabinet
• Short signal paths; on-site detection,
evaluation and actuation
• Device insensitive to malfunctions
• Especially well-suited for turbines operating in a lower
power range (retrofits and new systems)
• Partial stroke test during operation
• Speed sensor optional, triply redundant
• Explosion-proof designs optional
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Design and functionDesign
The CTo consists of a 3/2-way hydraulic unit, a current-cont-
rolled electromagnet (solenoid) and the evaluation and control
electronics.
Functionality
If no trip criteria are satisfied, the solenoid generates the force
FMag
. This magnetic force presses the control piston of the
hydraulic unit against a restoring spring. In this position, the
hydraulic unit connects the pressure supply to the actuator of
the trip valve, causing it to open.
If a trip criterion is satisfied (e.g. overspeed), the solenoid ex-
citer current is interrupted immediately. The restoring spring
shifts the con trol piston back to its original position by means
of the spring force FF, draining the actuator of the trip valve
and causing it to close.
Partial stroke test
The partial stroke test (“Trip-Sim”) permits testing of the trip
valve during turbine operation. During a pulse with an adjust-
able length, the CTo drains the oil from the trip actuator. The
trip valve moves briefly towards the closed position and re-
opens immediately.
1 Voith CTo, attached directly to the actuator
of the trip valve on a steam turbine
2 Controlled-extraction condensing turbine
SST-110 (TWIN AFA 46)
Manufacturer: Siemens Turbomachinery
Equipment GmbH
Power: 2 400 kW; speed: 14 953 rpm
Trip speed: 15 850 rpm
3 Controlled-extraction condensing turbine
SST-110 (TWIN CA 56)
Manufacturer: Siemens Turbomachinery
Equipment GmbH
Power: 4 730 kW; speed: 14 786 rpm
Trip speed: 15 820 rpm
4 Steam turbine KT 600-5(9) E2
Manufacturer: M+M Turbinentechnik GmbH
Power: 9 000 kW; speed: 7 673 rpm
Trip speed: 8 426 rpm
3 4
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CTo technical data
Hydraulic data
Maximum input pressure 25 bar (362 psi)
Flow rate
330 l / min at p = 4 bar
(87 U.S.gal / min at p = 58 psi)
Operating medium Hydraulic oil or turbine oil
Temperature of the operating medium + 10 °C to + 70 °C (+ 50 °F to + 158 °F)
Electrical data
Supply voltage 24 VDC
Current consumption 0.5 A, briefly 3 A
Trip speed 4 000 to 10 000 Hz, adjustable
Remote display of actual speed 4 – 20 mA
Ambient conditions
Ambient temperature - 20 °C to + 80 °C (- 4 °F to + 176 °F)
Protection class IP 65 to EN 60529
Explosion protection Optional EEx d IIC T4, others upon request
Mechanical data Dimensions H x W x D
265 x 105 x 155 mm
(10.4 x 4.1 x 6.1 inch)
Weight Approx. 14 kg (31 lbs)
Example of incorporating the Voith CTo into a turbine control system
Speed controller
(e.g. Voith TurCon D)
Solenoid,
evaluation/
control
electronics
Reset
+ 24 VDC
K
K
CTo
A
T
0 V
T r i p c i r c u i t
T r i p - S i m
S p e e d
FMag F
F
Hydraulic
cylinder with
spring return
Medium Control valve
Trip valve
Turbine
P
mA
Illustration: turbine in operation
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Voith Turbo GmbH & Co. KG
Electronic Drive Systems
Voithstr. 1
74564 Crailsheim, Germany
Tel. +49 7951 32 - 470
Fax +49 7951 32 - 605
voith.com