MAAMBA COLLIERIES LIMITED
300 MW COAL FIRED POWER PROJECT
NAVA BHARATH
BY
SK SHAKDAR

DIGITIAL ELECTRO-HYDRAULIC SYSTEM
NAVA BHARATH
Preface: -
The control & Protection system of the steam turbine can be divided into LP
Protection System, HP/LP interface device, HP fire-resistant Oil system and turbine safety
monitoring protection system.
Overview :-
The control and protection system is an actuating mechanism of HP fire-resistant
oil comprising Digital electro-Hydraulic Control system (DEH), which accepts orders from
DEH and accomplishes task such as latching-on turbine, actuating Valves and tripping the
unit etc.

DIGITIAL ELECTRO-HYDRAULIC SYSTEM
NAVA BHARATH
 Main function of DEH system are as follows:
I. Turbine auto latching
II. Over speed protection
a) Over speed limiting (OPC @ 103% of RPM)
b) Over speed Tripping (110% of )
III. On-line test
a) Spray oil test
b) Electrical test, mechanical test
 DEH Electric Over Speed Test:
 Mechanical Over Speed Test:
c) Valve leak test
d) HP Trip Device Solenoid valve test
IV. Manual Trip
V. Mechanical Trip Solenoid (3 YV)

DIGITIAL ELECTRO HYDRAULIC SYSTEM
I. Turbine auto latching:
Turbine latching is the process of making steam turbine enter into security
mode. The emergency governor gear is of fly loop structure, HP safety oil and return oil to
oil tank are controlled with the levers of emergency tripping device.
When steam turbine is latched to reset all levers of emergency tripping device,
HP safety oil and oil return port to oil tank will be shut off in turn pressurizing the
pressure switches PS1, PS2, and PS3 to send out signals to DEH, by this the pressure of
HP safety oil is built up. –
Allowable conditions for turbine latching:
a)Steam turbine in tripped condition;
b)All main steam valves are full closed.
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DIGITIAL ELECTRO HYDRAULIC SYSTEM
LOW PRESSURE (LP)PROTECTIONDEVICE
NAVA BHARATH

DIGITIAL ELECTRO HYDRAULIC SYSTEM
After DEH receives the order of turbine LATCH, then resetting solenoid valve
1 YV of reset & test group valve is energized; letting turbine lube oil to enter into
cavity chamber of emergency governing device, this pushes the lever of tripping
mechanism which is connected to trip & isolation valve to isolate HP fire-resistant oil
to get drained in turn generating the HP SAFETY OIL (Trip Oil) Line. LATCH condition is
monitored by ZS1 (latching in Progress) signal and ZS2 (Turbine Latched) signal in DEH.
When HP safety oil to the EH oil tank is blocked by trip & isolation valve ,
PS1, PS2, and PS3 will send out signals to ETS, and the pressure (14 Mpa) of HP safety
oil is built up. At the same time, HP tripping solenoid valve HPT1 (5 YV), HPT2 (6YV),
HPT3 (7YV) and HPT4 (8YV) are energized by blocking the HP SAFETY OIL.
Supply for all the solenoid valves is 220 V DC which is supplied from DEH.
NAVA BHARATH

DIGITIAL ELECTRO HYDRAULIC SYSTEM
II. Over speed protection
a) Over Speed limiting (103%):
Over speed limiting mainly composed of 2 solenoid valves mounted on the High
Pressure (HP) Protection system.
Under normal condition, the 2 over speed limit solenoid valves (23 YV and 24 YV)
are both de-energized, to build up the over speed limit oil pressure when the HP safety oil
has been created, and the release valves (Trip Solenoid Valves) of all governing valve
actuators (Stop Valves and Control valves) are in the closed status.
When OPC i.e. 103% of rated Turbine speed protection is acted/required, the 2
solenoid valves (23 YV and 24 YV) are energized, to discharge the over speed limit oil
pressure and quickly close all the governing valves (GCV & ICV) therefore controlling the
turbine at rated speed. As soon as the OPC condition is restored both the solenoid valves
(23 YV and 24 YV) are de-energized and remain in normal state.
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DIGITIAL ELECTRO HYDRAULIC SYSTEM
b) Over speed protection: (OST-Over Speed Trip)
When turbine speed reaches 110% ~111% of the rated speed (3300 ~ 330r/min),
the 2 over speed limit solenoid valves (23 YV and 24 YV) are energized by letting out the
over speed limit oil pressure, there by quickly closing all governing valve actuators (GCV &
ICV).
Simultaneously the mechanical trip valve of trip & isolated group valve is
actuated through Electrical trip mechanism to the drain HP safety oil, so as to quickly close
the main steam stop valves and governing valves. This Electrical Trip Mechanism is
triggered from DEH by sending out the trip signal to 3YV Solenoid Valve.
Note: Present condition of Over Speed Protection is modified to 107% of rated speed i.e.
3210 r/min. This modification is considered keeping in view for ease of operation.
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DIGITIAL ELECTRO HYDRAULIC SYSTEM
HIGH PRESSURE (HP)
PROTECTION DEVICE
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DIGITIAL ELECTRO HYDRAULIC SYSTEM
III. On-line test
a) Spray oil test:
In order to guarantee that the fly ring of Emergency Over Speed Governor to
quickly fly out once the over speed of units occurs to trip the steam turbine, the fly-ring
should be tested for free movement. During the fly ring movement test oil is sprayed on the
fly ring to increase centrifugal force, so that it can fly out. The fly-out of fly-ring due to oil
injection test shall not result in tripping. In order to improve the reliability, test isolation valve
is added (2YV solenoid valve).
 Allowable conditions for oil injection test:
The speed within (2985~3015) r/min & HP expansion differential < 3mm.
During the test, 4YV is energized, after detecting that isolation valve is isolated, 2YV
energized, oil is sprayed into emergency tripper, fly ring strikes out, and ZS2 sends signals,
then de-energize 2YV, after a period of time, 1YV latched automatically, de-energize isolation
valve, test finished.
NAVA BHARATH

DIGITIAL ELECTRO HYDRAULIC SYSTEM
b) Electrical test and Mechanical test
 DEH electric over speed test : {Note: Modified set valve to 3210 r/min}
When it is detected that the unit speed is up to 110% of the rated speed
(3330r/min), an electrical shutdown signal is sent out to enable the solenoid valve (3YV)
and the mechanical shutdown electromagnet in the HP trip module, to discharge the HP
safety oil and to trip steam admission into the unit. The test can be carried out by setting
target value as 3310r/min and the appropriate rate in the DEH- GE OC-4000 system.
 Mechanical over speed test : {Note: Tripping Observed at 3240 r/min}
When speed is up to 110% ~ 111% of the rated speed (3300 ~ 3330 r/min), the
fly ring of emergency governor will strike the stay hook of emergency trip device to trip the
hook, so that mechanical trip valve of trip & isolated group valve is actuated to open HP
safety oil the outlet and to discharge the HP safety oil. Closes all the main steam stop
valves and governing valves quickly, to break steam admission into the unit.
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DIGITIAL ELECTRO HYDRAULIC SYSTEM
Before the test, DEH electric over speed value should be adjusted to a
higher value. When the test is processing, set the higher target and setting speed to rises
the actual speed. While the actual speed near upon 110% rated speed, flying ring strikes
out, leak safety oil and the turbine will be tripped.
c) Valve leak test
 The conditions of leak test to inspect the valve leakage
a) The turbine in LATCHED
b) Speed > 2990r/min
c) Grid disconnected.
 Valve leakage test is carried on
o Stop Valve Leak Test.
o Governing Vale Leak Test.
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DIGITIAL ELECTRO HYDRAULIC SYSTEM
o Stop Valve Leak Test:
At unit constant speed of 3000 r/min close down the 4 Main steam stop vales,
there speed should be lower than (P/Po x 1000) r/min after a certain while.
Where P- Measure d steam inlet Pressure, Po-Rated Steam Pressure.
When the required rotational speed is achieved, DEH sends out a signal and the
test is termed to be passed. If the required rotational speed is not achieved leak test is fail.
o Governing Valve Leak Test:
At unit constant speed of 3000 r/min close down the 6 Governing control vales,
there speed should be lower than (P/Po x 1000) r/min after a certain while.
Where P- Measure d steam inlet Pressure, Po-Rated Steam Pressure.
When the required rotational speed is achieved, DEH sends out a signal and the
test is termed to be passed. If the required rotational speed is not achieved leak test is fail.
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DIGITIAL ELECTRO HYDRAULIC SYSTEM
d) HP tripping Solenoid valve test :
In order to improve reliability, HP trip over speed limit valve adopts redundant
design. HP tripping solenoid valves can be tested on DEH system. Under normal conditions,
HPT1 (5YV), HPT2 (6YV), HPT3 (7YV) and HPT4 (8 YV) solenoid valves are energized, and
pressure switches PS4 & PS5 are in normal positions.
During test, HPT1 or HPT3 is de-energized, and then PS5 will act; if Pressure Switch
(PS) signal is not changed after SOV acted in 15 seconds, then consider this test as failed.
HPT1, HPT3 solenoid test finished, make HPT1, HPT3 back to energized state, PS5 reset.
And then do test for HPT2, HPT4. HPT2 or HPT4 is de-energized, and then PS4 will
act; if Pressure Switch (PS) signal is not changed after SOV acted in 15 seconds, then
consider this test as failed. HPT2, HPT4 solenoid test finished, make HPT2, HPT4 back to
energized state, PS4 reset.
At any time during test any one HP Trip Solenoid Valve can be tested.
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DIGITIAL ELECTRO HYDRAULIC SYSTEM
HIGH PRESSURE
PROTECTION DEVICE
NAVA BHARATH

DIGITIAL ELECTRO HYDRAULIC SYSTEM
NAVA BHARATH
III. Manual Trip:
Manual shutdown mechanism is provided as an artificial way to intercept the unit at
emergency. Under an emergency condition of the unit, operator may manually pull the
manual shutdown mechanism, to trip the stay hook of the emergency governor through link
lever and to actuate the mechanical trip valves of trip and isolated valve block, so as to
discharge the HP SAFETY OIL and rapidly close all the steam inlet valves, breaking the unit
from steam admission. ZS3 gives out a signal to DEH,
IV. Mechanical Trip Solenoid (3 YV)
After receiving various electrical shutdown signal, the mechanical trip solenoid is
activated to drive the link lever of mechanical trip mechanism, and trip the stay hook of the
emergency trip governor device. This in turn leads to discharge the HP SAFETY OIL and rapidly
close all the steam inlet valves, breaking the unit for steam admission.
For both the Manual trip and Mechanical Trip Solenoid indication to DEH is done through ZS3.

DIGITIAL ELECTRO HYDRAULIC SYSTEM
HP trip Device Pressure switch set value
PS-1 HP fire Resistant oil Pressure 7.8 Mpa
PS-2 HP fire Resistant oil Pressure 7.8 Mpa
PS-3 HP fire Resistant oil Pressure 7.8 Mpa
PS-4 HP fire Resistant oil Test Pressure 9.6 Mpa (Raising)
PS-5 HP fire Resistant oil Test Pressure 4.8 Mpa (Falling)
Lube Oil Pressure Set values:
PSA1 Lube Oil Low Alarm 0.115 Mpa
PSA2 Starts AC lube oil pump 0.115 Mpa
PSA3 Starts DC lube oil pump 0.105 Mpa
PSA4 Lube Oil low trip to Emergency Trip system 0.07 Mpa
PSA5 Lube Oil low trip to Emergency Trip system 0.07 Mpa
PSA6 Lube Oil low trip to Emergency Trip system 0.07 Mpa
PSA7 Turning gear enables 0.07 Mpa
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DIGITIAL ELECTRO HYDRAULIC SYSTEM
NAVA BHARATH
Low-condensed vacuum tripper:
PSB1 Low vacuum alarm -0.8 Mpa (vacuum)
PSB2 Low vacuum trip to Emergency Trip system -0.7 Mpa (vacuum)
PSB3 Low vacuum trip to Emergency Trip system -0.7 Mpa (vacuum)
PSB4 Low vacuum trip to Emergency Trip system -0.7 Mpa (vacuum)